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Sensors, Volume 9, Issue 10 (October 2009), Pages 7580-8381

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Editorial

Jump to: Research, Review

Open AccessEditorial Guest Editor’s Concluding Remarks―Advances in Usage of ANN, Discussion of an Unsolved Problem, and Some Differences between Papers Written by Engineers and by Physicians
Sensors 2009, 9(10), 8126-8129; doi:10.3390/s91008126
Received: 5 August 2009 / Revised: 18 August 2009 / Accepted: 28 August 2009 / Published: 16 October 2009
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Abstract
I take this opportunity to discuss a few things that I have learned from being Guest Editor of this special issue of Sensors devoted to Neural Networks and Sensors. The advancement in artificial neural network (ANN) technology is very impressive. The wide [...] Read more.
I take this opportunity to discuss a few things that I have learned from being Guest Editor of this special issue of Sensors devoted to Neural Networks and Sensors. The advancement in artificial neural network (ANN) technology is very impressive. The wide variety of fields in which this technology applies in the form of practical applications to clearly identifiable real problems demonstrates that ANNs are being routinely used to solve non-trivial problems. I mention that because A. K. Dewdney wrote in 1997 that while ANNs have been used to solve a few toy problems, he was surprised that anyone takes them seriously as general problem-solving tools [1]. The ANN applications reported by Yu Liu et al. [2], Erkan Beşdok [3], Guillermo Zatorre et al. [4], Amir Jabbari et al. [5], Mohamed Lamine Hafiane et al. [6], Kai-Wei Chiang et al. [7], Raúl Vicen-Bueno et al. [8], Juan L. Pedreño-Molina et al. [9], and P. B. Garcia-Allende et al. [10] are far more than toy applications. The lesson to be learned here is that it is a bad idea to publically bet against technological progress in computer applications. [...] Full article
(This article belongs to the Special Issue Neural Networks and Sensors)

Research

Jump to: Editorial, Review

Open AccessArticle A Community-Based Event Delivery Protocol in Publish/Subscribe Systems for Delay Tolerant Sensor Networks
Sensors 2009, 9(10), 7580-7594; doi:10.3390/s91007580
Received: 6 August 2009 / Revised: 26 August 2009 / Accepted: 3 September 2009 / Published: 28 September 2009
Cited by 7 | PDF Full-text (658 KB) | HTML Full-text | XML Full-text
Abstract
The basic operation of a Delay Tolerant Sensor Network (DTSN) is to finish pervasive data gathering in networks with intermittent connectivity, while the publish/subscribe (Pub/Sub for short) paradigm is used to deliver events from a source to interested clients in an asynchronous [...] Read more.
The basic operation of a Delay Tolerant Sensor Network (DTSN) is to finish pervasive data gathering in networks with intermittent connectivity, while the publish/subscribe (Pub/Sub for short) paradigm is used to deliver events from a source to interested clients in an asynchronous way. Recently, extension of Pub/Sub systems in DTSNs has become a promising research topic. However, due to the unique frequent partitioning characteristic of DTSNs, extension of a Pub/Sub system in a DTSN is a considerably difficult and challenging problem, and there are no good solutions to this problem in published works. To ad apt Pub/Sub systems to DTSNs, we propose CED, a community-based event delivery protocol. In our design, event delivery is based on several unchanged communities, which are formed by sensor nodes in the network according to their connectivity. CED consists of two components: event delivery and queue management. In event delivery, events in a community are delivered to mobile subscribers once a subscriber comes into the community, for improving the data delivery ratio. The queue management employs both the event successful delivery time and the event survival time to decide whether an event should be delivered or dropped for minimizing the transmission overhead. The effectiveness of CED is demonstrated through comprehensive simulation studies. Full article
(This article belongs to the Section Chemical Sensors)
Open AccessArticle A Real-Time Tool Positioning Sensor for Machine-Tools
Sensors 2009, 9(10), 7622-7647; doi:10.3390/s91007622
Received: 4 August 2009 / Revised: 2 September 2009 / Accepted: 3 September 2009 / Published: 28 September 2009
Cited by 8 | PDF Full-text (3201 KB) | HTML Full-text | XML Full-text
Abstract
In machining, natural oscillations, and elastic, gravitational or temperature deformations, are still a problem to guarantee the quality of fabricated parts. In this paper we present an optical measurement system designed to track and localize in 3D a reference retro-reflector close to [...] Read more.
In machining, natural oscillations, and elastic, gravitational or temperature deformations, are still a problem to guarantee the quality of fabricated parts. In this paper we present an optical measurement system designed to track and localize in 3D a reference retro-reflector close to the machine-tool’s drill. The complete system and its components are described in detail. Several tests, some static (including impacts and rotations) and others dynamic (by executing linear and circular trajectories), were performed on two different machine tools. It has been integrated, for the first time, a laser tracking system into the position control loop of a machine-tool. Results indicate that oscillations and deformations close to the tool can be estimated with micrometric resolution and a bandwidth from 0 to more than 100 Hz. Therefore this sensor opens the possibility for on-line compensation of oscillations and deformations. Full article
(This article belongs to the Special Issue State-of-the-Art Sensors Technology in Spain)
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Open AccessArticle Description of a PortableWireless Device for High-Frequency Body Temperature Acquisition and Analysis
Sensors 2009, 9(10), 7648-7663; doi:10.3390/s91007648
Received: 8 August 2009 / Revised: 10 September 2009 / Accepted: 18 September 2009 / Published: 28 September 2009
Cited by 5 | PDF Full-text (726 KB) | HTML Full-text | XML Full-text
Abstract
We describe a device for dual channel body temperature monitoring. The device can operate as a real time monitor or as a data logger, and has Bluetooth capabilities to enable for wireless data download to the computer used for data analysis. The [...] Read more.
We describe a device for dual channel body temperature monitoring. The device can operate as a real time monitor or as a data logger, and has Bluetooth capabilities to enable for wireless data download to the computer used for data analysis. The proposed device is capable of sampling temperature at a rate of 1 sample per minute with a resolution of 0.01 °C. The internal memory allows for stand-alone data logging of up to 10 days. The device has a battery life of 50 hours in continuous real-time mode. In addition to describing the proposed device in detail, we report the results of a statistical analysis conducted to assess its accuracy and reproducibility. Full article
(This article belongs to the Section Chemical Sensors)
Open AccessArticle A Portable Luminometer with a Disposable Electrochemiluminescent Biosensor for Lactate Determination
Sensors 2009, 9(10), 7694-7710; doi:10.3390/s91007694
Received: 16 July 2009 / Revised: 8 September 2009 / Accepted: 17 September 2009 / Published: 28 September 2009
Cited by 13 | PDF Full-text (786 KB) | HTML Full-text | XML Full-text
Abstract
A hand-held luminometer for measuring electrochemiluminescence (ECL) for lactate determination and based on one-shot biosensors fabricated using screen-printed electrodes is described. The lactate recognition system is based on lactate oxidase and the transduction system consists of electro-oxidation of luminol, with all the [...] Read more.
A hand-held luminometer for measuring electrochemiluminescence (ECL) for lactate determination and based on one-shot biosensors fabricated using screen-printed electrodes is described. The lactate recognition system is based on lactate oxidase and the transduction system consists of electro-oxidation of luminol, with all the reagents immobilized in a Methocel membrane. The membrane composition and reaction conditions have been optimized to obtain adequate sensitivity. The luminometer is based on a large silicon photodiode as detector and includes a programmable potentiostat to initialize the chemical reaction and signal processing circuitry, designed to acquire a low level photocurrent with offset cancelation, low pass filtering for noise attenuation and adjustable gain up to 1012 V/A. The one-shot biosensor responds to lactate rapidly, with an acquisition time of 2.5 min, obtaining a linear dependence from 8 × 10−6 to 2 × 10−4 M, a detection limit of 2.4 × 10−6 M and a sensor-to-sensor reproducibility (relative standard deviation, RSD) of around 7–10 % at the medium level of the range. Full article
(This article belongs to the Section Biosensors)
Open AccessArticle Delay QoS and MAC Aware Energy-Efficient Data-Aggregation Routing in Wireless Sensor Networks
Sensors 2009, 9(10), 7711-7732; doi:10.3390/s91007711
Received: 13 August 2009 / Revised: 14 September 2009 / Accepted: 23 September 2009 / Published: 28 September 2009
Cited by 5 | PDF Full-text (698 KB) | HTML Full-text | XML Full-text
Abstract
By eliminating redundant data flows, data aggregation capabilities in wireless sensor networks could transmit less data to reduce the total energy consumption. However, additional data collisions incur extra data retransmissions. These data retransmissions not only increase the system energy consumption, but also [...] Read more.
By eliminating redundant data flows, data aggregation capabilities in wireless sensor networks could transmit less data to reduce the total energy consumption. However, additional data collisions incur extra data retransmissions. These data retransmissions not only increase the system energy consumption, but also increase link transmission delays. The decision of when and where to aggregate data depends on the trade-off between data aggregation and data retransmission. The challenges of this problem need to address the routing (layer 3) and the MAC layer retransmissions (layer 2) at the same time to identify energy-efficient data-aggregation routing assignments, and in the meantime to meet the delay QoS. In this paper, for the first time, we study this cross-layer design problem by using optimization-based heuristics. We first model this problem as a non-convex mathematical programming problem where the objective is to minimize the total energy consumption subject to the data aggregation tree and the delay QoS constraints. The objective function includes the energy in the transmission mode (data transmissions and data retransmissions) and the energy in the idle mode (to wait for data from downstream nodes in the data aggregation tree). The proposed solution approach is based on Lagrangean relaxation in conjunction with a number of optimization-based heuristics. From the computational experiments, it is shown that the proposed algorithm outperforms existing heuristics that do not take MAC layer retransmissions and the energy consumption in the idle mode into account. Full article
(This article belongs to the Special Issue Sensor Configuration and Smart Sensors)
Open AccessArticle Defect Detection in Arc-Welding Processes by Means of the Line-to-Continuum Method and Feature Selection
Sensors 2009, 9(10), 7753-7770; doi:10.3390/s91007753
Received: 8 July 2009 / Revised: 28 August 2009 / Accepted: 24 September 2009 / Published: 29 September 2009
Cited by 9 | PDF Full-text (2338 KB) | HTML Full-text | XML Full-text
Abstract
Plasma optical spectroscopy is widely employed in on-line welding diagnostics. The determination of the plasma electron temperature, which is typically selected as the output monitoring parameter, implies the identification of the atomic emission lines. As a consequence, additional processing stages are required [...] Read more.
Plasma optical spectroscopy is widely employed in on-line welding diagnostics. The determination of the plasma electron temperature, which is typically selected as the output monitoring parameter, implies the identification of the atomic emission lines. As a consequence, additional processing stages are required with a direct impact on the real time performance of the technique. The line-to-continuum method is a feasible alternative spectroscopic approach and it is particularly interesting in terms of its computational efficiency. However, the monitoring signal highly depends on the chosen emission line. In this paper, a feature selection methodology is proposed to solve the uncertainty regarding the selection of the optimum spectral band, which allows the employment of the line-to-continuum method for on-line welding diagnostics. Field test results have been conducted to demonstrate the feasibility of the solution. Full article
(This article belongs to the Section Chemical Sensors)
Open AccessArticle Investigation of SOI Raman Lasers for Mid-Infrared Gas Sensing
Sensors 2009, 9(10), 7814-7836; doi:10.3390/s91007814
Received: 30 July 2009 / Revised: 16 September 2009 / Accepted: 25 September 2009 / Published: 30 September 2009
Cited by 10 | PDF Full-text (827 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, the investigation and detailed modeling of a cascaded Raman laser, operating in the midwave infrared region, is described. The device is based on silicon-on-insulator optical waveguides and a coupled resonant microcavity. Theoretical results are compared with recent experiments, demonstrating [...] Read more.
In this paper, the investigation and detailed modeling of a cascaded Raman laser, operating in the midwave infrared region, is described. The device is based on silicon-on-insulator optical waveguides and a coupled resonant microcavity. Theoretical results are compared with recent experiments, demonstrating a very good agreement. Design criteria are derived for cascaded Raman lasers working as continuous wave light sources to simultaneously sense two types of gases, namely C2H6 and CO2, at a moderate power level of 130 mW. Full article
(This article belongs to the Special Issue Gas Sensors 2009)
Open AccessArticle Optimization of TiO2 and PMAPTAC Concentrations of a Chemical Humidity Sensing Mechanism
Sensors 2009, 9(10), 7837-7848; doi:10.3390/s91007837
Received: 7 August 2009 / Revised: 24 September 2009 / Accepted: 25 September 2009 / Published: 30 September 2009
Cited by 1 | PDF Full-text (624 KB) | HTML Full-text | XML Full-text
Abstract
This work aims to achieve an optimization of the TiO2 and PMAPTAC concentrations in a chemical resistive-type humidity sensing mechanism (RHSM). Our idea is based primarily on the modeling of the sensing mechanism. This model takes into account the parameters of [...] Read more.
This work aims to achieve an optimization of the TiO2 and PMAPTAC concentrations in a chemical resistive-type humidity sensing mechanism (RHSM). Our idea is based primarily on the modeling of the sensing mechanism. This model takes into account the parameters of non-linearity, hysteresis, temperature, frequency, substrate type. Furthermore, we investigated the TiO2 and PMAPTAC effects concentrations on the humidity sensing properties in our model. Secondly, we used the Matlab environment to create a database for an ideal model for the sensing mechanism, where the response of this ideal model is linear for any value of the above parameters. We have done the training to create an analytical model for the sensing mechanism (SM) and the ideal model (IM). After that, the SM and IM models are established on PSPICE simulator, where the output of the first is identical to the output of the RHSM used and the output of the last is the ideal response. Finally a “DIF bloc” was realized to make the difference between the SM output and the IM output, where this difference represents the linearity error, we take the minimum error, to identify the optimal TiO2 and PMAPTAC concentrations. However, a compromise between concentrations, humidity and temperature must be performed. The simulation results show that in low humidity and at temperature more than 25 °C, sample 1 is the best (in alumina substrate). However, the sample 9 represents the best sensor (in PET substrate) predominately for the lowest humidity and temperature. Full article
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Open AccessArticle Integration of an On-Axis General Sun-Tracking Formula in the Algorithm of an Open-Loop Sun-Tracking System
Sensors 2009, 9(10), 7849-7865; doi:10.3390/s91007849
Received: 29 July 2009 / Revised: 19 August 2009 / Accepted: 28 September 2009 / Published: 30 September 2009
Cited by 28 | PDF Full-text (2925 KB) | HTML Full-text | XML Full-text
Abstract
A novel on-axis general sun-tracking formula has been integrated in the algorithm of an open-loop sun-tracking system in order to track the sun accurately and cost effectively. Sun-tracking errors due to installation defects of the 25 m2 prototype solar concentrator have [...] Read more.
A novel on-axis general sun-tracking formula has been integrated in the algorithm of an open-loop sun-tracking system in order to track the sun accurately and cost effectively. Sun-tracking errors due to installation defects of the 25 m2 prototype solar concentrator have been analyzed from recorded solar images with the use of a CCD camera. With the recorded data, misaligned angles from ideal azimuth-elevation axes have been determined and corrected by a straightforward changing of the parameters’ values in the general formula of the tracking algorithm to improve the tracking accuracy to 2.99 mrad, which falls below the encoder resolution limit of 4.13 mrad. Full article
(This article belongs to the Section Chemical Sensors)
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Open AccessArticle Synthesis Methods, Microscopy Characterization and Device Integration of Nanoscale Metal Oxide Semiconductors for Gas Sensing
Sensors 2009, 9(10), 7866-7902; doi:10.3390/s91007866
Received: 28 July 2009 / Revised: 25 September 2009 / Accepted: 29 September 2009 / Published: 30 September 2009
Cited by 15 | PDF Full-text (1455 KB) | HTML Full-text | XML Full-text
Abstract
A comparison is made between SnO2, ZnO, and TiO2 single-crystal nanowires and SnO2 polycrystalline nanofibers for gas sensing. Both nanostructures possess a one-dimensional morphology. Different synthesis methods are used to produce these materials: thermal evaporation-condensation (TEC), controlled oxidation, [...] Read more.
A comparison is made between SnO2, ZnO, and TiO2 single-crystal nanowires and SnO2 polycrystalline nanofibers for gas sensing. Both nanostructures possess a one-dimensional morphology. Different synthesis methods are used to produce these materials: thermal evaporation-condensation (TEC), controlled oxidation, and electrospinning. Advantages and limitations of each technique are listed. Practical issues associated with harvesting, purification, and integration of these materials into sensing devices are detailed. For comparison to the nascent form, these sensing materials are surface coated with Pd and Pt nanoparticles. Gas sensing tests, with respect to H2, are conducted at ambient and elevated temperatures. Comparative normalized responses and time constants for the catalyst and noncatalyst systems provide a basis for identification of the superior metal-oxide nanostructure and catalyst combination. With temperature-dependent data, Arrhenius analyses are made to determine activation energies for the catalyst-assisted systems. Full article
(This article belongs to the Special Issue Gas Sensors 2009)
Open AccessArticle Determination of Diclofenac on a Dysprosium Nanowire- Modified Carbon Paste Electrode Accomplished in a Flow Injection System by Advanced Filtering
Sensors 2009, 9(10), 7903-7918; doi:10.3390/s91007903
Received: 6 June 2009 / Revised: 11 July 2009 / Accepted: 29 July 2009 / Published: 30 September 2009
Cited by 13 | PDF Full-text (355 KB) | HTML Full-text | XML Full-text
Abstract
A new detection technique called Fast Fourier Transform Square-Wave Voltammetry (FFT SWV) is based on measurements of electrode admittance as a function of potential. The response of the detector (microelectrode), which is generated by a redox processes, is fast, which makes the [...] Read more.
A new detection technique called Fast Fourier Transform Square-Wave Voltammetry (FFT SWV) is based on measurements of electrode admittance as a function of potential. The response of the detector (microelectrode), which is generated by a redox processes, is fast, which makes the method suitable for most applications involving flowing electrolytes. The carbon paste electrode was modified by nanostructures to improve sensitivity. Synthesized dysprosium nanowires provide a more effective nanotube-like surface [1-4] so they are good candidates for use as a modifier for electrochemical reactions. The redox properties of diclofenac were used for its determination in human serum and urine samples. The support electrolyte that provided a more defined and intense peak current for diclofenac determination was a 0.05 mol L−1 acetate buffer pH = 4.0. The drug presented an irreversible oxidation peak at 850 mV vs. Ag/AgCl on a modified nanowire carbon paste electrode which produced high current and reduced the oxidation potential by about 100 mV. Furthermore, the signal-to-noise ratio was significantly increased by application of a discrete Fast Fourier Transform (FFT) method, background subtraction and two-dimensional integration of the electrode response over a selected potential range and time window. To obtain the much sensivity the effective parameters such as frequency, amplitude and pH was optimized. As a result, CDL of 2.0 × 10−9 M and an LOQ of 5.0 × 10−9 M were found for the determination for diclofenac. A good recovery was obtained for assay spiked urine samples and a good quantification of diclofenac was achieved in a commercial formulation. Full article
(This article belongs to the Section Chemical Sensors)
Open AccessArticle Vehicle Signal Analysis Using Artificial Neural Networks for a Bridge Weigh-in-Motion System
Sensors 2009, 9(10), 7943-7956; doi:10.3390/s91007943
Received: 31 July 2009 / Revised: 22 September 2009 / Accepted: 24 September 2009 / Published: 12 October 2009
Cited by 4 | PDF Full-text (1559 KB) | HTML Full-text | XML Full-text
Abstract
This paper describes the procedures for development of signal analysis algorithms using artificial neural networks for Bridge Weigh-in-Motion (B-WIM) systems. Through the analysis procedure, the extraction of information concerning heavy traffic vehicles such as weight, speed, and number of axles from the [...] Read more.
This paper describes the procedures for development of signal analysis algorithms using artificial neural networks for Bridge Weigh-in-Motion (B-WIM) systems. Through the analysis procedure, the extraction of information concerning heavy traffic vehicles such as weight, speed, and number of axles from the time domain strain data of the B-WIM system was attempted. As one of the several possible pattern recognition techniques, an Artificial Neural Network (ANN) was employed since it could effectively include dynamic effects and bridge-vehicle interactions. A number of vehicle traveling experiments with sufficient load cases were executed on two different types of bridges, a simply supported pre-stressed concrete girder bridge and a cable-stayed bridge. Different types of WIM systems such as high-speed WIM or low-speed WIM were also utilized during the experiments for cross-checking and to validate the performance of the developed algorithms. Full article
(This article belongs to the Special Issue Neural Networks and Sensors)
Open AccessArticle A Label-Free Electronic Biosensor for Detection of Bone Turnover Markers
Sensors 2009, 9(10), 7957-7969; doi:10.3390/s91007957
Received: 29 July 2009 / Revised: 29 September 2009 / Accepted: 30 September 2009 / Published: 12 October 2009
Cited by 9 | PDF Full-text (522 KB) | HTML Full-text | XML Full-text
Abstract
This paper describes the development of a biosensor based on label-free immunosensing for the detection of the C-terminal telopeptide bone turnover marker from type-1 collagen. A self-assembled monolayer (SAM) of dithiodipropionic acid was deposited on a gold electrode. Then streptavidin and biotinylated [...] Read more.
This paper describes the development of a biosensor based on label-free immunosensing for the detection of the C-terminal telopeptide bone turnover marker from type-1 collagen. A self-assembled monolayer (SAM) of dithiodipropionic acid was deposited on a gold electrode. Then streptavidin and biotinylated anti-human C-terminal telopeptide antibody were successively conjugated on the self-assembled monolayer. Electrochemical impedance measurements were made to characterize each step of the SAM/streptavidin/biotinylated antibody binding. Subsequently, electrochemical impedance was measured with different concentrations of C-teminal telopeptide. A detection limit of 50 ng/mL and a dynamic range up to 3 μg/mL were achieved. To our knowledge, this is the first attempt to develop a label-free immunosensor based on electrochemical impedance with DC bias for detection of bone-related degradation and rebuilding products. The electronic biosensor might eventually be used for quantitative point-of-care screening of bone health. It is hoped that analysis of bone turnover markers can indicate the beginning of bone diseases such as osteoarthritis and osteoporosis so that treatment might start early when it is most effective. Full article
(This article belongs to the Section Biosensors)
Open AccessArticle Micro Sensor Node for Air Pollutant Monitoring: Hardware and Software Issues
Sensors 2009, 9(10), 7970-7987; doi:10.3390/s91007970
Received: 5 August 2009 / Revised: 22 September 2009 / Accepted: 24 September 2009 / Published: 12 October 2009
Cited by 36 | PDF Full-text (1492 KB) | HTML Full-text | XML Full-text
Abstract
Wireless sensor networks equipped with various gas sensors have been actively used for air quality monitoring. Previous studies have typically explored system issues that include middleware or networking performance, but most research has barely considered the details of the hardware and software [...] Read more.
Wireless sensor networks equipped with various gas sensors have been actively used for air quality monitoring. Previous studies have typically explored system issues that include middleware or networking performance, but most research has barely considered the details of the hardware and software of the sensor node itself. In this paper, we focus on the design and implementation of a sensor board for air pollutant monitoring applications. Several hardware and software issues are discussed to explore the possibilities of a practical WSN-based air pollution monitoring system. Through extensive experiments and evaluation, we have determined the various characteristics of the gas sensors and their practical implications for air pollutant monitoring systems. Full article
(This article belongs to the Special Issue Modeling, Testing and Reliability Issues in MEMS Engineering - 2009)
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Open AccessArticle A Coupled Field Multiphysics Modeling Approach to Investigate RF MEMS Switch Failure Modes under Various Operational Conditions
Sensors 2009, 9(10), 7988-8006; doi:10.3390/s91007988
Received: 30 July 2009 / Revised: 15 September 2009 / Accepted: 16 September 2009 / Published: 12 October 2009
Cited by 6 | PDF Full-text (971 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, the reliability of capacitive shunt RF MEMS switches have been investigated using three dimensional (3D) coupled multiphysics finite element (FE) analysis. The coupled field analysis involved three consecutive multiphysics interactions. The first interaction is characterized as a two-way sequential [...] Read more.
In this paper, the reliability of capacitive shunt RF MEMS switches have been investigated using three dimensional (3D) coupled multiphysics finite element (FE) analysis. The coupled field analysis involved three consecutive multiphysics interactions. The first interaction is characterized as a two-way sequential electromagnetic (EM)-thermal field coupling. The second interaction represented a one-way sequential thermal-structural field coupling. The third interaction portrayed a two-way sequential structural-electrostatic field coupling. An automated substructuring algorithm was utilized to reduce the computational cost of the complicated coupled multiphysics FE analysis. The results of the substructured FE model with coupled field analysis is shown to be in good agreement with the outcome of previously published experimental and numerical studies. The current numerical results indicate that the pull-in voltage and the buckling temperature of the RF switch are functions of the microfabrication residual stress state, the switch operational frequency and the surrounding packaging temperature. Furthermore, the current results point out that by introducing proper mechanical approaches such as corrugated switches and through-holes in the switch membrane, it is possible to achieve reliable pull-in voltages, at various operating temperatures. The performed analysis also shows that by controlling the mean and gradient residual stresses, generated during microfabrication, in conjunction with the proposed mechanical approaches, the power handling capability of RF MEMS switches can be increased, at a wide range of operational frequencies. These design features of RF MEMS switches are of particular importance in applications where a high RF power (frequencies above 10 GHz) and large temperature variations are expected, such as in satellites and airplane condition monitoring. Full article
(This article belongs to the Special Issue Modeling, Testing and Reliability Issues in MEMS Engineering - 2009)
Open AccessArticle Collaborative Distributed Scheduling Approaches for Wireless Sensor Network
Sensors 2009, 9(10), 8007-8030; doi:10.3390/s91008007
Received: 4 August 2009 / Revised: 4 September 2009 / Accepted: 29 September 2009 / Published: 13 October 2009
Cited by 3 | PDF Full-text (661 KB) | HTML Full-text | XML Full-text
Abstract
Energy constraints restrict the lifetime of wireless sensor networks (WSNs) with battery-powered nodes, which poses great challenges for their large scale application. In this paper, we propose a family of collaborative distributed scheduling approaches (CDSAs) based on the Markov process to reduce [...] Read more.
Energy constraints restrict the lifetime of wireless sensor networks (WSNs) with battery-powered nodes, which poses great challenges for their large scale application. In this paper, we propose a family of collaborative distributed scheduling approaches (CDSAs) based on the Markov process to reduce the energy consumption of a WSN. The family of CDSAs comprises of two approaches: a one-step collaborative distributed approach and a two-step collaborative distributed approach. The approaches enable nodes to learn the behavior information of its environment collaboratively and integrate sleep scheduling with transmission scheduling to reduce the energy consumption. We analyze the adaptability and practicality features of the CDSAs. The simulation results show that the two proposed approaches can effectively reduce nodes’ energy consumption. Some other characteristics of the CDSAs like buffer occupation and packet delay are also analyzed in this paper. We evaluate CDSAs extensively on a 15-node WSN testbed. The test results show that the CDSAs conserve the energy effectively and are feasible for real WSNs. Full article
(This article belongs to the Special Issue Sensor Algorithms)
Open AccessArticle Fabrication of Poly(p-Phenylene)/Zeolite Composites and Their Responses Towards Ammonia
Sensors 2009, 9(10), 8031-8046; doi:10.3390/s91008031
Received: 8 September 2009 / Revised: 23 September 2009 / Accepted: 9 October 2009 / Published: 13 October 2009
Cited by 10 | PDF Full-text (746 KB) | HTML Full-text | XML Full-text
Abstract
Poly(p-phenylene) (PPP) was chemically synthesized via oxidative polymerization using benzene and doped with FeCl3. The electrical conductivity response of the doped PPP (dPPP) towards CO, H2 and NH3 is investigated. dPPP shows no electrical conductivity response towards the first two gases (CO and H2), but it shows a definite negative response towards NH3. The electrical conductivity sensitivity of dPPP increases linearly with increasing NH3 concentration. To improve the sensitivity of the sensor towards NH3, ZSM-5 zeolite is added into the conductive polymer matrix. The electrical sensitivity of the sensor increases with increasing zeolite content up to 30%. The effect of the type of cation in the zeolite pores is investigated: namely, Na+, K+, NH4+ and H+. The electrical conductivity sensitivity of the composites with different cations in the zeolite can be arranged in this order: K+ < no zeolite < Na+ < NH4+ < H+. The variation in electrical sensitivity with cation type can be described in terms of the acid-base interaction, the zeolite pore size and surface area. The PPP/Zeolite composite with H+ possesses the highest electrical sensitivity of −0.36 since H+ has the highest acidity, the highest pore volume and surface area, which combine to induce a more favorable NH3 adsorption and interaction with the conductive polymer. Full article
(This article belongs to the Section Chemical Sensors)
Open AccessArticle A Radio-Aware Routing Algorithm for Reliable Directed Diffusion in Lossy Wireless Sensor Networks
Sensors 2009, 9(10), 8047-8072; doi:10.3390/s91008047
Received: 21 July 2009 / Revised: 7 September 2009 / Accepted: 30 September 2009 / Published: 13 October 2009
Cited by 4 | PDF Full-text (2061 KB) | HTML Full-text | XML Full-text
Abstract
In Wireless Sensor Networks (WSNs), transmission errors occur frequently due to node failure, battery discharge, contention or interference by objects. Although Directed Diffusion has been considered as a prominent data-centric routing algorithm, it has some weaknesses due to unexpected network errors. In [...] Read more.
In Wireless Sensor Networks (WSNs), transmission errors occur frequently due to node failure, battery discharge, contention or interference by objects. Although Directed Diffusion has been considered as a prominent data-centric routing algorithm, it has some weaknesses due to unexpected network errors. In order to address these problems, we proposed a radio-aware routing algorithm to improve the reliability of Directed Diffusion in lossy WSNs. The proposed algorithm is aware of the network status based on the radio information from MAC and PHY layers using a cross-layer design. The cross-layer design can be used to get detailed information about current status of wireless network such as a link quality or transmission errors of communication links. The radio information indicating variant network conditions and link quality was used to determine an alternative route that provides reliable data transmission under lossy WSNs. According to the simulation result, the radio-aware reliable routing algorithm showed better performance in both grid and random topologies with various error rates. The proposed solution suggested the possibility of providing a reliable transmission method for QoS requests in lossy WSNs based on the radio-awareness. The energy and mobility issues will be addressed in the future work. Full article
(This article belongs to the Special Issue Sensor Algorithms)
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Open AccessArticle Identification of Tea Storage Times by Linear Discrimination Analysis and Back-Propagation Neural Network Techniques Based on the Eigenvalues of Principal Components Analysis of E-Nose Sensor Signals
Sensors 2009, 9(10), 8073-8082; doi:10.3390/s91008073
Received: 2 July 2009 / Revised: 27 July 2009 / Accepted: 29 July 2009 / Published: 14 October 2009
Cited by 11 | PDF Full-text (70 KB) | HTML Full-text | XML Full-text
Abstract
An electronic nose (E-nose) was employed to detect the aroma of green tea after different storage times. Longjing green tea dry leaves, beverages and residues were detected with an E-nose, respectively. In order to decrease the data dimensionality and optimize the feature [...] Read more.
An electronic nose (E-nose) was employed to detect the aroma of green tea after different storage times. Longjing green tea dry leaves, beverages and residues were detected with an E-nose, respectively. In order to decrease the data dimensionality and optimize the feature vector, the E-nose sensor response data were analyzed by principal components analysis (PCA) and the five main principal components values were extracted as the input for the discrimination analysis. The storage time (0, 60, 120, 180 and 240 days) was better discriminated by linear discrimination analysis (LDA) and was predicted by the back-propagation neural network (BPNN) method. The results showed that the discrimination and testing results based on the tea leaves were better than those based on tea beverages and tea residues. The mean errors of the tea leaf data were 9, 2.73, 3.93, 6.33 and 6.8 days, respectively. Full article
(This article belongs to the Section Chemical Sensors)
Open AccessArticle Efficient Aggregation of Multiple Classes of Information in Wireless Sensor Networks
Sensors 2009, 9(10), 8083-8108; doi:10.3390/s91008083
Received: 22 July 2009 / Revised: 8 September 2009 / Accepted: 27 September 2009 / Published: 14 October 2009
Cited by 7 | PDF Full-text (350 KB) | HTML Full-text | XML Full-text
Abstract
Congestion in a Wireless Sensor Network (WSN) can lead to buffer overflow, resource waste and delay or loss of critical information from the sensors. In this paper, we propose the Priority-based Coverage-aware Congestion Control (PCC) algorithm which is distributed, priority-distinct, [...] Read more.
Congestion in a Wireless Sensor Network (WSN) can lead to buffer overflow, resource waste and delay or loss of critical information from the sensors. In this paper, we propose the Priority-based Coverage-aware Congestion Control (PCC) algorithm which is distributed, priority-distinct, and fair. PCC provides higher priority to packets with event information in which the sink is more interested. PCC employs a queue scheduler that can selectively drop any packet in the queue. PCC gives fair chance to all sensors to send packets to the sink, irrespective of their specific locations, and therefore enhances the coverage fidelity of theWSN. Based on a detailed simulation analysis, we show that PCC can efficiently relieve congestion and significantly improve the system performance based on multiple metrics such as event throughput and coverage fidelity. We generalize PCC to address data collection in a WSN in which the sensor nodes have multiple sensing devices and can generate multiple types of information. We propose a Pricing System that can under congestion effectively collect different types of data generated by the sensor nodes according to values that are placed on different information by the sink. Simulation analysis show that our Pricing System can achieve higher event throughput for packets with higher priority and achieve fairness among different categories. Moreover, given a fixed system capacity, our proposed Pricing System can collect more information of the type valued by the sink. Full article
(This article belongs to the Special Issue Wireless Sensor Technologies and Applications)
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Open AccessArticle Neural Network Emulation of the Integral Equation Model with Multiple Scattering
Sensors 2009, 9(10), 8109-8125; doi:10.3390/s91008109
Received: 3 August 2009 / Revised: 29 September 2009 / Accepted: 12 October 2009 / Published: 15 October 2009
Cited by 1 | PDF Full-text (161 KB) | HTML Full-text | XML Full-text
Abstract
The Integral Equation Model with multiple scattering (IEMM) represents a well-established method that provides a theoretical framework for the scattering of electromagnetic waves from rough surfaces. A critical aspect is the long computational time required to run such a complex model. To [...] Read more.
The Integral Equation Model with multiple scattering (IEMM) represents a well-established method that provides a theoretical framework for the scattering of electromagnetic waves from rough surfaces. A critical aspect is the long computational time required to run such a complex model. To deal with this problem, a neural network technique is proposed in this work. In particular, we have adopted neural networks to reproduce the backscattering coefficients predicted by IEMM at L- and C-bands, thus making reference to presently operative satellite radar sensors, i.e., that aboard ERS-2, ASAR on board ENVISAT (C-band), and PALSAR aboard ALOS (L-band). The neural network-based model has been designed for radar observations of both flat and tilted surfaces, in order to make it applicable for hilly terrains too. The assessment of the proposed approach has been carried out by comparing neural network-derived backscattering coefficients with IEMM-derived ones. Different databases with respect to those employed to train the networks have been used for this purpose. The outcomes seem to prove the feasibility of relying on a neural network approach to efficiently and reliably approximate an electromagnetic model of surface scattering. Full article
(This article belongs to the Special Issue Neural Networks and Sensors)
Open AccessArticle Biomimetic Yeast Cell Typing—Application of QCMs
Sensors 2009, 9(10), 8146-8157; doi:10.3390/s91008146
Received: 17 August 2009 / Revised: 22 September 2009 / Accepted: 25 September 2009 / Published: 16 October 2009
Cited by 12 | PDF Full-text (1424 KB) | HTML Full-text | XML Full-text
Abstract
Artificial antibodies represent a key factor in the generation of sensing systems for the selective detection of bioanalytes of variable sizes. With biomimetic surfaces, the important model organism Saccharomyces cerevisiae and several of its growth stages may be detected. Quartz crystal microbalances [...] Read more.
Artificial antibodies represent a key factor in the generation of sensing systems for the selective detection of bioanalytes of variable sizes. With biomimetic surfaces, the important model organism Saccharomyces cerevisiae and several of its growth stages may be detected. Quartz crystal microbalances (QCM) with 10 MHz fundamental frequency and coated with polymers imprinted with synchronized yeast cells are presented, which are able to detect duplex cells with high selectivity. Furthermore, a multichannel quartz crystal microbalance (MQCM) was designed and optimized for the measurement in liquids. This one-chip system based on four-electrode geometry allows the simultaneous detection of four analytes and, thus, provides a monitoring system for biotechnology and process control. For further standardization of the method, synthetic stamps containing plastic yeast cells in different growth stages were produced and utilized for imprinting. Mass-sensitive measurements with such MIPs resulted in the same sensor characteristics as obtained for those imprinted with native yeast cells. Full article
(This article belongs to the Section Chemical Sensors)
Open AccessArticle A Distributed Sensor Network for the Control of a Bioclimatic House in Spain
Sensors 2009, 9(10), 8197-8214; doi:10.3390/s91008197
Received: 11 June 2009 / Revised: 5 October 2009 / Accepted: 12 October 2009 / Published: 19 October 2009
Cited by 6 | PDF Full-text (1408 KB) | HTML Full-text | XML Full-text
Abstract
The XXI century home should be a digital habitat, a connected residence, but at the same time it should be involved in sustainability and the environment. The location of new technologies at home, and its acceptance by the user, requires, among other [...] Read more.
The XXI century home should be a digital habitat, a connected residence, but at the same time it should be involved in sustainability and the environment. The location of new technologies at home, and its acceptance by the user, requires, among other actions, a significant diffusion and activity to be undertaken. This work proposes the development of a Smart House network designed for its integration into a sustainable and bioclimatic solar house. The paper focuses on a specific aspect of the house design, the control system bus, developed for the management of the different parameters, variables, sensors and actuators which coexist at home. Finally, the system has been installed in a laboratory bioclimatic house. Environmental variable experiments based on the control of passive elements, such as phase shift gels, are presented. Experimental results show that the system is able to benefit from the bioclimatic elements in the house by taking into account the user preferences. Full article
(This article belongs to the Special Issue State-of-the-Art Sensors Technology in Spain)
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Open AccessArticle Sensor Calibration Based on Incoherent Optical Fiber Bundles (IOFB) Used For Remote Image Transmission
Sensors 2009, 9(10), 8215-8229; doi:10.3390/s91008215
Received: 26 August 2009 / Revised: 11 September 2009 / Accepted: 25 September 2009 / Published: 19 October 2009
Cited by 6 | PDF Full-text (507 KB) | HTML Full-text | XML Full-text
Abstract
Image transmission using incoherent optical fiber bundles (IOFB) requires prior calibration to obtain the spatial in-out fiber correspondence in order to reconstruct the image captured by the pseudo-sensor. This information is recorded in a Look-Up Table (LUT), used later for reordering the [...] Read more.
Image transmission using incoherent optical fiber bundles (IOFB) requires prior calibration to obtain the spatial in-out fiber correspondence in order to reconstruct the image captured by the pseudo-sensor. This information is recorded in a Look-Up Table (LUT), used later for reordering the fiber positions and reconstructing the original image. This paper presents a method based on line-scan to obtain the in-out correspondence. The results demonstrate that this technique yields a remarkable reduction in processing time and increased image quality by introducing a fiber detection algorithm, an intensity compensation process and finally, a single interpolation algorithm. Full article
(This article belongs to the Special Issue Image Sensors)
Open AccessArticle Major Improvements of Quartz Crystal Pulling Sensitivity and Linearity Using Series Reactance
Sensors 2009, 9(10), 8263-8270; doi:10.3390/s91008263
Received: 16 July 2009 / Revised: 23 September 2009 / Accepted: 23 September 2009 / Published: 19 October 2009
Cited by 6 | PDF Full-text (256 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents a new method of substantially improving frequency pullability and linearity using reactance in series with an AT fundamental crystal operated with a series load capacitance in the range of 3 to 50 pF and frequencies in the range of [...] Read more.
This paper presents a new method of substantially improving frequency pullability and linearity using reactance in series with an AT fundamental crystal operated with a series load capacitance in the range of 3 to 50 pF and frequencies in the range of 3.5 to 21 MHz. The research describes high quartz pullability and linearity by varying the load capacitance. The paper also gives impedance circuits for crystal unit (3.5 MHz) together with load capacitance and compensation reactance. The experimental results show that the new approach using compensation method of quartz crystal connected in series reactance increases the frequency pulling range by ×25 to ×100 depending on the type of oscillator and compensation factor ˝k˝ in the temperature range of 10 to 40 °C. Full article
(This article belongs to the Special Issue Sensor Configuration and Smart Sensors)
Open AccessCommunication Fluorescence Enhancement of Fluorescein Isothiocyanate-Labeled Protein A Caused by Affinity Binding with Immunoglobulin G in Bovine Plasma
Sensors 2009, 9(10), 8271-8277; doi:10.3390/s91008271
Received: 27 August 2009 / Revised: 29 September 2009 / Accepted: 15 October 2009 / Published: 20 October 2009
Cited by 6 | PDF Full-text (198 KB) | HTML Full-text | XML Full-text
Abstract
Fluorescence enhancement of fluorescein isothiocyanate-labeled protein A (FITC-protein A) caused by the binding with immunoglobulin G (IgG) in bovine plasma was studied. FITC-protein A was immobilized onto a glass surface by covalent bonds. An increase in fluorescence intensity was dependent on IgG [...] Read more.
Fluorescence enhancement of fluorescein isothiocyanate-labeled protein A (FITC-protein A) caused by the binding with immunoglobulin G (IgG) in bovine plasma was studied. FITC-protein A was immobilized onto a glass surface by covalent bonds. An increase in fluorescence intensity was dependent on IgG concentration ranging from 20 to 78 μg/mL in both phosphate buffer saline and bovine plasma. This method requires no separation procedure, and the reaction time is less than 15 min. A fluorescence enhancement assay by the affinity binding of fluorescence-labeled reagent is thus available for the rapid determination of biomolecules in plasma. Full article
(This article belongs to the Section Biosensors)
Open AccessArticle Cross-Layer Active Predictive Congestion Control Protocol for Wireless Sensor Networks
Sensors 2009, 9(10), 8278-8310; doi:10.3390/s91008278
Received: 29 July 2009 / Revised: 18 September 2009 / Accepted: 25 September 2009 / Published: 20 October 2009
Cited by 10 | PDF Full-text (1292 KB) | HTML Full-text | XML Full-text
Abstract
In wireless sensor networks (WSNs), there are numerous factors that may cause network congestion problems, such as the many-to-one communication modes, mutual interference of wireless links, dynamic changes of network topology and the memory-restrained characteristics of nodes. All these factors result in [...] Read more.
In wireless sensor networks (WSNs), there are numerous factors that may cause network congestion problems, such as the many-to-one communication modes, mutual interference of wireless links, dynamic changes of network topology and the memory-restrained characteristics of nodes. All these factors result in a network being more vulnerable to congestion. In this paper, a cross-layer active predictive congestion control scheme (CL-APCC) for improving the performance of networks is proposed. Queuing theory is applied in the CL-APCC to analyze data flows of a single-node according to its memory status, combined with the analysis of the average occupied memory size of local networks. It also analyzes the current data change trends of local networks to forecast and actively adjust the sending rate of the node in the next period. In order to ensure the fairness and timeliness of the network, the IEEE 802.11 protocol is revised based on waiting time, the number of the node‟s neighbors and the original priority of data packets, which dynamically adjusts the sending priority of the node. The performance of CL-APCC, which is evaluated by extensive simulation experiments. is more efficient in solving the congestion in WSNs. Furthermore, it is clear that the proposed scheme has an outstanding advantage in terms of improving the fairness and lifetime of networks. Full article
(This article belongs to the Section Chemical Sensors)
Open AccessArticle A CMOS-Compatible, Low-Noise ISFET Based on High Efficiency Ion-Modulated Lateral-Bipolar Conduction
Sensors 2009, 9(10), 8336-8348; doi:10.3390/s91008336
Received: 30 July 2009 / Revised: 25 September 2009 / Accepted: 14 October 2009 / Published: 21 October 2009
Cited by 7 | PDF Full-text (440 KB) | HTML Full-text | XML Full-text
Abstract
Ion-sensitive, field-effect transistors (ISFET) have been useful biosensors in many applications. However, the signal-to-noise ratio of the ISFET is limited by its intrinsic, low-frequency noise. This paper presents an ISFET capable of utilizing lateral-bipolar conduction to reduce low-frequency noise. With a particular [...] Read more.
Ion-sensitive, field-effect transistors (ISFET) have been useful biosensors in many applications. However, the signal-to-noise ratio of the ISFET is limited by its intrinsic, low-frequency noise. This paper presents an ISFET capable of utilizing lateral-bipolar conduction to reduce low-frequency noise. With a particular layout design, the conduction efficiency is further enhanced. Moreover, the ISFET is compatible with the standard CMOS technology. All materials above the gate-oxide are removed by simple, die-level post-CMOS process, allowing ions to modulate the lateral-bipolar current directly. By varying the gate-to-bulk voltage, the operation mode of the ISFET is controlled effectively, so is the noise performance measured and compared. Finally, the biasing conditions preferable for different low-noise applications are identified. Under the identified biasing condition, the signal-to-noise ratio of the ISFET as a pH sensor is proved to be improved by more than five times. Full article
(This article belongs to the Special Issue ISFET Sensors)
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Open AccessArticle Microgyroscope Temperature Effects and Compensation-Control Methods
Sensors 2009, 9(10), 8349-8376; doi:10.3390/s91008349
Received: 29 July 2009 / Revised: 28 August 2009 / Accepted: 21 September 2009 / Published: 21 October 2009
Cited by 28 | PDF Full-text (820 KB) | HTML Full-text | XML Full-text
Abstract
In the analysis of the effects of temperature on the performance of microgyroscopes, it is found that the resonant frequency of the microgyroscope decreases linearly as the temperature increases, and the quality factor changes drastically at low temperatures. Moreover, the zero bias [...] Read more.
In the analysis of the effects of temperature on the performance of microgyroscopes, it is found that the resonant frequency of the microgyroscope decreases linearly as the temperature increases, and the quality factor changes drastically at low temperatures. Moreover, the zero bias changes greatly with temperature variations. To reduce the temperature effects on the microgyroscope, temperature compensation-control methods are proposed. In the first place, a BP (Back Propagation) neural network and polynomial fitting are utilized for building the temperature model of the microgyroscope. Considering the simplicity and real-time requirements, piecewise polynomial fitting is applied in the temperature compensation system. Then, an integral-separated PID (Proportion Integration Differentiation) control algorithm is adopted in the temperature control system, which can stabilize the temperature inside the microgyrocope in pursuing its optimal performance. Experimental results reveal that the combination of microgyroscope temperature compensation and control methods is both realizable and effective in a miniaturized microgyroscope prototype. Full article
(This article belongs to the Special Issue Modeling, Testing and Reliability Issues in MEMS Engineering - 2009)
Open AccessArticle Arrays of Regenerated Fiber Bragg Gratings in Non-Hydrogen-Loaded Photosensitive Fibers for High-Temperature Sensor Networks
Sensors 2009, 9(10), 8377-8381; doi:10.3390/s91008377
Received: 27 August 2009 / Revised: 11 September 2009 / Accepted: 16 October 2009 / Published: 22 October 2009
Cited by 15 | PDF Full-text (219 KB) | HTML Full-text | XML Full-text
Abstract
We report about the possibility of using regenerated fiber Bragg gratings generated in photosensitive fibers without applying hydrogen loading for high temperature sensor networks. We use a thermally induced regenerative process which leads to a secondary increase in grating reflectivity. This refractive [...] Read more.
We report about the possibility of using regenerated fiber Bragg gratings generated in photosensitive fibers without applying hydrogen loading for high temperature sensor networks. We use a thermally induced regenerative process which leads to a secondary increase in grating reflectivity. This refractive index modification has shown to become more stable after the regeneration up to temperatures of 600 °C. With the use of an interferometric writing technique, it is possible also to generate arrays of regenerated fiber Bragg gratings for sensor networks. Full article
(This article belongs to the Section Chemical Sensors)

Review

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Open AccessReview Fiber Loop Ringdown — a Time-Domain Sensing Technique for Multi-Function Fiber Optic Sensor Platforms: Current Status and Design Perspectives
Sensors 2009, 9(10), 7595-7621; doi:10.3390/s91007595
Received: 31 July 2009 / Revised: 9 September 2009 / Accepted: 17 September 2009 / Published: 28 September 2009
Cited by 48 | PDF Full-text (810 KB) | HTML Full-text | XML Full-text
Abstract
Fiber loop ringdown (FLRD) utilizes an inexpensive telecommunications light source, a photodiode, and a section of single-mode fiber to form a uniform fiber optic sensor platform for sensing various quantities, such as pressure, temperature, strain, refractive index, chemical species, biological cells, and [...] Read more.
Fiber loop ringdown (FLRD) utilizes an inexpensive telecommunications light source, a photodiode, and a section of single-mode fiber to form a uniform fiber optic sensor platform for sensing various quantities, such as pressure, temperature, strain, refractive index, chemical species, biological cells, and small volume of fluids. In FLRD, optical losses of a light pulse in a fiber loop induced by changes in a quantity are measured by the light decay time constants. FLRD measures time to detect a quantity; thus, FLRD is referred to as a time-domain sensing technique. FLRD sensors have near real-time response, multi-pass enhanced high-sensitivity, and relatively low cost (i.e., without using an optical spectral analyzer). During the last eight years since the introduction of the original form of fiber ringdown spectroscopy, there has been increasing interest in the FLRD technique in fiber optic sensor developments, and new application potential is being explored. This paper first discusses the challenging issues in development of multi-function, fiber optic sensors or sensor networks using current fiber optic sensor sensing schemes, and then gives a review on current fiber optic sensor development using FLRD technique. Finally, design perspectives on new generation, multi-function, fiber optic sensor platforms using FLRD technique are particularly presented. Full article
(This article belongs to the Special Issue Laser Spectroscopy and Sensing)
Open AccessReview Connectivity, Coverage and Placement in Wireless Sensor Networks
Sensors 2009, 9(10), 7664-7693; doi:10.3390/s91007664
Received: 25 August 2009 / Revised: 25 September 2009 / Accepted: 25 September 2009 / Published: 28 September 2009
Cited by 56 | PDF Full-text (267 KB) | HTML Full-text | XML Full-text
Abstract
Wireless communication between sensors allows the formation of flexible sensor networks, which can be deployed rapidly over wide or inaccessible areas. However, the need to gather data from all sensors in the network imposes constraints on the distances between sensors. This survey [...] Read more.
Wireless communication between sensors allows the formation of flexible sensor networks, which can be deployed rapidly over wide or inaccessible areas. However, the need to gather data from all sensors in the network imposes constraints on the distances between sensors. This survey describes the state of the art in techniques for determining the minimum density and optimal locations of relay nodes and ordinary sensors to ensure connectivity, subject to various degrees of uncertainty in the locations of the nodes. Full article
(This article belongs to the Special Issue Wireless Sensor Technologies and Applications)
Open AccessReview Structure and Sensor Properties of Thin Ordered Solid Films
Sensors 2009, 9(10), 7733-7752; doi:10.3390/s91007733
Received: 28 July 2009 / Revised: 9 September 2009 / Accepted: 9 September 2009 / Published: 28 September 2009
Cited by 11 | PDF Full-text (2310 KB) | HTML Full-text | XML Full-text
Abstract
Miniaturized gas sensors and biosensors based on nanostructured sensing elements have attracted considerable interest because these nanostructured materials can be used to significantly improve sensor sensitivity and the response time. We report here on a generic, reversible sensing platform based on hybrid [...] Read more.
Miniaturized gas sensors and biosensors based on nanostructured sensing elements have attracted considerable interest because these nanostructured materials can be used to significantly improve sensor sensitivity and the response time. We report here on a generic, reversible sensing platform based on hybrid nanofilms. Thin ordered Langmuir-Blodgett (LB) films built of fluorene derivatives were used as effective gas sensors for both oxidative and reductive analytes. A novel immobilization method based on thin LB films as a matrix has been developed for construction of sensing protein layers. Biomolecules can often be incorporated into and immobilized on Langmuir-Blodgett films using adsorption methods or by covalent immobilization of proteins. The sensor sensitisation was achieved by an amphiphilic N-alkyl-bis(thiophene)arylenes admixed into the film. The interlaced derivative was expected to facilitate the electron transfer, thereby enhancing the sensor sensitivity. The results suggest that this may be very promising approach for exploring the interactions between proteins and high throughput detection of phenol derivatives in wastewater. Full article
(This article belongs to the Special Issue Gas Sensors 2009)
Open AccessReview Advances in Multi-Sensor Data Fusion: Algorithms and Applications
Sensors 2009, 9(10), 7771-7784; doi:10.3390/s91007771
Received: 30 June 2009 / Revised: 13 August 2009 / Accepted: 17 September 2009 / Published: 30 September 2009
Cited by 66 | PDF Full-text (626 KB) | HTML Full-text | XML Full-text
Abstract
With the development of satellite and remote sensing techniques, more and more image data from airborne/satellite sensors have become available. Multi-sensor image fusion seeks to combine information from different images to obtain more inferences than can be derived from a single sensor. [...] Read more.
With the development of satellite and remote sensing techniques, more and more image data from airborne/satellite sensors have become available. Multi-sensor image fusion seeks to combine information from different images to obtain more inferences than can be derived from a single sensor. In image-based application fields, image fusion has emerged as a promising research area since the end of the last century. The paper presents an overview of recent advances in multi-sensor satellite image fusion. Firstly, the most popular existing fusion algorithms are introduced, with emphasis on their recent improvements. Advances in main applications fields in remote sensing, including object identification, classification, change detection and maneuvering targets tracking, are described. Both advantages and limitations of those applications are then discussed. Recommendations are addressed, including: (1) Improvements of fusion algorithms; (2) Development of “algorithm fusion” methods; (3) Establishment of an automatic quality assessment scheme. Full article
(This article belongs to the Special Issue Sensor Algorithms)
Open AccessReview Resonant Magnetic Field Sensors Based On MEMS Technology
Sensors 2009, 9(10), 7785-7813; doi:10.3390/s91007785
Received: 27 July 2009 / Revised: 3 September 2009 / Accepted: 16 September 2009 / Published: 30 September 2009
Cited by 45 | PDF Full-text (3194 KB) | HTML Full-text | XML Full-text
Abstract
Microelectromechanical systems (MEMS) technology allows the integration of magnetic field sensors with electronic components, which presents important advantages such as small size, light weight, minimum power consumption, low cost, better sensitivity and high resolution. We present a discussion and review of resonant [...] Read more.
Microelectromechanical systems (MEMS) technology allows the integration of magnetic field sensors with electronic components, which presents important advantages such as small size, light weight, minimum power consumption, low cost, better sensitivity and high resolution. We present a discussion and review of resonant magnetic field sensors based on MEMS technology. In practice, these sensors exploit the Lorentz force in order to detect external magnetic fields through the displacement of resonant structures, which are measured with optical, capacitive, and piezoresistive sensing techniques. From these, the optical sensing presents immunity to electromagnetic interference (EMI) and reduces the read-out electronic complexity. Moreover, piezoresistive sensing requires an easy fabrication process as well as a standard packaging. A description of the operation mechanisms, advantages and drawbacks of each sensor is considered. MEMS magnetic field sensors are a potential alternative for numerous applications, including the automotive industry, military, medical, telecommunications, oceanographic, spatial, and environment science. In addition, future markets will need the development of several sensors on a single chip for measuring different parameters such as the magnetic field, pressure, temperature and acceleration. Full article
(This article belongs to the Special Issue Sensor Configuration and Smart Sensors)
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Open AccessReview Magnetic Field Sensors Based on Giant Magnetoresistance (GMR) Technology: Applications in Electrical Current Sensing
Sensors 2009, 9(10), 7919-7942; doi:10.3390/s91007919
Received: 15 September 2009 / Revised: 25 September 2009 / Accepted: 29 September 2009 / Published: 12 October 2009
Cited by 62 | PDF Full-text (1014 KB) | HTML Full-text | XML Full-text
Abstract
The 2007 Nobel Prize in Physics can be understood as a global recognition to the rapid development of the Giant Magnetoresistance (GMR), from both the physics and engineering points of view. Behind the utilization of GMR structures as read heads for massive [...] Read more.
The 2007 Nobel Prize in Physics can be understood as a global recognition to the rapid development of the Giant Magnetoresistance (GMR), from both the physics and engineering points of view. Behind the utilization of GMR structures as read heads for massive storage magnetic hard disks, important applications as solid state magnetic sensors have emerged. Low cost, compatibility with standard CMOS technologies and high sensitivity are common advantages of these sensors. This way, they have been successfully applied in a lot different environments. In this work, we are trying to collect the Spanish contributions to the progress of the research related to the GMR based sensors covering, among other subjects, the applications, the sensor design, the modelling and the electronic interfaces, focusing on electrical current sensing applications. Full article
(This article belongs to the Special Issue State-of-the-Art Sensors Technology in Spain)
Open AccessReview Magnetic Nanoparticle Sensors
Sensors 2009, 9(10), 8130-8145; doi:10.3390/s91008130
Received: 3 August 2009 / Revised: 29 September 2009 / Accepted: 30 September 2009 / Published: 16 October 2009
Cited by 99 | PDF Full-text (437 KB) | HTML Full-text | XML Full-text
Abstract
Many types of biosensors employ magnetic nanoparticles (diameter = 5–300 nm) or magnetic particles (diameter = 300–5,000 nm) which have been surface functionalized to recognize specific molecular targets. Here we cover three types of biosensors that employ different biosensing principles, magnetic materials, [...] Read more.
Many types of biosensors employ magnetic nanoparticles (diameter = 5–300 nm) or magnetic particles (diameter = 300–5,000 nm) which have been surface functionalized to recognize specific molecular targets. Here we cover three types of biosensors that employ different biosensing principles, magnetic materials, and instrumentation. The first type consists of magnetic relaxation switch assay-sensors, which are based on the effects magnetic particles exert on water proton relaxation rates. The second type consists of magnetic particle relaxation sensors, which determine the relaxation of the magnetic moment within the magnetic particle. The third type is magnetoresistive sensors, which detect the presence of magnetic particles on the surface of electronic devices that are sensitive to changes in magnetic fields on their surface. Recent improvements in the design of magnetic nanoparticles (and magnetic particles), together with improvements in instrumentation, suggest that magnetic material-based biosensors may become widely used in the future. Full article
(This article belongs to the Special Issue Nanotechnological Advances in Biosensors)
Open AccessReview Semiconducting Metal Oxide Based Sensors for Selective Gas Pollutant Detection
Sensors 2009, 9(10), 8158-8196; doi:10.3390/s91008158
Received: 25 August 2009 / Revised: 9 September 2009 / Accepted: 10 September 2009 / Published: 16 October 2009
Cited by 92 | PDF Full-text (832 KB) | HTML Full-text | XML Full-text
Abstract A review of some papers published in the last fifty years that focus on the semiconducting metal oxide (SMO) based sensors for the selective and sensitive detection of various environmental pollutants is presented. Full article
(This article belongs to the Special Issue Metal-Oxide Based Nanosensors)
Open AccessReview Breath Analysis Using Laser Spectroscopic Techniques: Breath Biomarkers, Spectral Fingerprints, and Detection Limits
Sensors 2009, 9(10), 8230-8262; doi:10.3390/s91008230
Received: 1 September 2009 / Revised: 9 October 2009 / Accepted: 10 October 2009 / Published: 19 October 2009
Cited by 154 | PDF Full-text (1532 KB) | HTML Full-text | XML Full-text
Abstract
Breath analysis, a promising new field of medicine and medical instrumentation, potentially offers noninvasive, real-time, and point-of-care (POC) disease diagnostics and metabolic status monitoring. Numerous breath biomarkers have been detected and quantified so far by using the GC-MS technique. Recent advances in [...] Read more.
Breath analysis, a promising new field of medicine and medical instrumentation, potentially offers noninvasive, real-time, and point-of-care (POC) disease diagnostics and metabolic status monitoring. Numerous breath biomarkers have been detected and quantified so far by using the GC-MS technique. Recent advances in laser spectroscopic techniques and laser sources have driven breath analysis to new heights, moving from laboratory research to commercial reality. Laser spectroscopic detection techniques not only have high-sensitivity and high-selectivity, as equivalently offered by the MS-based techniques, but also have the advantageous features of near real-time response, low instrument costs, and POC function. Of the approximately 35 established breath biomarkers, such as acetone, ammonia, carbon dioxide, ethane, methane, and nitric oxide, 14 species in exhaled human breath have been analyzed by high-sensitivity laser spectroscopic techniques, namely, tunable diode laser absorption spectroscopy (TDLAS), cavity ringdown spectroscopy (CRDS), integrated cavity output spectroscopy (ICOS), cavity enhanced absorption spectroscopy (CEAS), cavity leak-out spectroscopy (CALOS), photoacoustic spectroscopy (PAS), quartz-enhanced photoacoustic spectroscopy (QEPAS), and optical frequency comb cavity-enhanced absorption spectroscopy (OFC-CEAS). Spectral fingerprints of the measured biomarkers span from the UV to the mid-IR spectral regions and the detection limits achieved by the laser techniques range from parts per million to parts per billion levels. Sensors using the laser spectroscopic techniques for a few breath biomarkers, e.g., carbon dioxide, nitric oxide, etc. are commercially available. This review presents an update on the latest developments in laser-based breath analysis. Full article
(This article belongs to the Special Issue Gas Sensors 2009)
Open AccessReview Turbidimeter Design and Analysis: A Review on Optical Fiber Sensors for the Measurement of Water Turbidity
Sensors 2009, 9(10), 8311-8335; doi:10.3390/s91008311
Received: 22 July 2009 / Revised: 17 September 2009 / Accepted: 18 September 2009 / Published: 20 October 2009
Cited by 18 | PDF Full-text (453 KB) | HTML Full-text | XML Full-text
Abstract
Turbidimeters operate based on the optical phenomena that occur when incident light through water body is scattered by the existence of foreign particles which are suspended within it. This review paper elaborates on the standards and factors that may influence the measurement [...] Read more.
Turbidimeters operate based on the optical phenomena that occur when incident light through water body is scattered by the existence of foreign particles which are suspended within it. This review paper elaborates on the standards and factors that may influence the measurement of turbidity. The discussion also focuses on the optical fiber sensor technologies that have been applied within the lab and field environment and have been implemented in the measurement of water turbidity and concentration of particles. This paper also discusses and compares results from three different turbidimeter designs that use various optical components. Mohd Zubir and Bashah and Daraigan have introduced a design which has simple configurations. Omar and MatJafri, on the other hand, have established a new turbidimeter design that makes use of optical fiber cable as the light transferring medium. The application of fiber optic cable to the turbidimeter will present a flexible measurement technique, allowing measurements to be made online. Scattered light measurement through optical fiber cable requires a highly sensitive detector to interpret the scattered light signal. This has made the optical fiber system have higher sensitivity in measuring turbidity compared to the other two simple turbidimeters presented in this paper. Fiber optic sensors provide the potential for increased sensitivity over large concentration ranges. However, many challenges must be examined to develop sensors that can collect reliable turbidity measurements in situ. Full article
(This article belongs to the Section Chemical Sensors)

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