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923 KiB

Open AccessArticle

Temperature Grid Sensor for the Measurement of Spatial Temperature Distributions at Object Surfaces

by Thomas Schäfer, Markus Schubert and Uwe Hampel

Sensors 2013, 13(2), 1593-1602; https://doi.org/10.3390/s130201593 - 25 Jan 2013

Cited by 17 | Viewed by 8225

Abstract

This paper presents results of the development and application of a new temperature grid sensor based on the wire-mesh sensor principle. The grid sensor consists of a matrix of 256 Pt1000 platinum chip resistors and an associated electronics that measures the grid resistances [...] Read more.

This paper presents results of the development and application of a new temperature grid sensor based on the wire-mesh sensor principle. The grid sensor consists of a matrix of 256 Pt1000 platinum chip resistors and an associated electronics that measures the grid resistances with a multiplexing scheme at high speed. The individual sensor elements can be spatially distributed on an object surface and measure transient temperature distributions in real time. The advantage compared with other temperature field measurement approaches such as infrared cameras is that the object under investigation can be thermally insulated and the radiation properties of the surface do not affect the measurement accuracy. The sensor principle is therefore suited for various industrial monitoring applications. Its applicability for surface temperature monitoring has been demonstrated through heating and mixing experiments in a vessel. Full article

(This article belongs to the Special Issue State-of-the-Art Sensors Technology in Germany 2012)

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325 KiB

Open AccessArticle

Deposition of Bacteriorhodopsin Protein in a Purple Membrane Form on Nitrocellulose Membranes for Enhanced Photoelectric Response

by Young Jun Kim, Pavel Neuzil, Chang-Hoon Nam and Martin Engelhard

Sensors 2013, 13(1), 455-462; https://doi.org/10.3390/s130100455 - 27 Dec 2012

Cited by 9 | Viewed by 7684

Abstract

Bacteriorhodopsin protein (bR)-based systems are one of the simplest known biological energy converters. The robust chemical, thermal and electrochemical properties of bR have made it an attractive material for photoelectric devices. This study demonstrates the photoelectric response of a dry bR layer deposited [...] Read more.

Bacteriorhodopsin protein (bR)-based systems are one of the simplest known biological energy converters. The robust chemical, thermal and electrochemical properties of bR have made it an attractive material for photoelectric devices. This study demonstrates the photoelectric response of a dry bR layer deposited on a nitrocellulose membrane with indium tin oxide (ITO) electrodes. Light-induced electrical current as well as potential and impedance changes of dried bR film were recorded as the function of illumination. We have also tested bR in solution and found that the electrical properties are strongly dependent on light intensity changing locally proton concentration and thus pH of the solution. Experimental data support the assumption that bR protein on a positively charged nitrocellulose membrane (PNM) can be used as highly sensitive photo- and pH detector. Here the bR layer facilitates proton translocation and acts as an ultrafast optoelectric signal transducer. It is therefore useful in applications related to bioelectronics, biosensors, bio-optics devices and current carrying junction devices. Full article

(This article belongs to the Special Issue State-of-the-Art Sensors Technology in Germany 2012)

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7907 KiB

Open AccessArticle

Probabilistic Evaluation of Three-Dimensional Reconstructions from X-Ray Images Spanning a Limited Angle

by Anja Frost, Eike Renners, Michael Hötter and Jörn Ostermann

Sensors 2013, 13(1), 137-151; https://doi.org/10.3390/s130100137 - 21 Dec 2012

Cited by 6 | Viewed by 6024

Abstract

An important part of computed tomography is the calculation of a three-dimensional reconstruction of an object from series of X-ray images. Unfortunately, some applications do not provide sufficient X-ray images. Then, the reconstructed objects no longer truly represent the original. Inside of the [...] Read more.

An important part of computed tomography is the calculation of a three-dimensional reconstruction of an object from series of X-ray images. Unfortunately, some applications do not provide sufficient X-ray images. Then, the reconstructed objects no longer truly represent the original. Inside of the volumes, the accuracy seems to vary unpredictably. In this paper, we introduce a novel method to evaluate any reconstruction, voxel by voxel. The evaluation is based on a sophisticated probabilistic handling of the measured X-rays, as well as the inclusion of a priori knowledge about the materials that the object receiving the X-ray examination consists of. For each voxel, the proposed method outputs a numerical value that represents the probability of existence of a predefined material at the position of the voxel while doing X-ray. Such a probabilistic quality measure was lacking so far. In our experiment, false reconstructed areas get detected by their low probability. In exact reconstructed areas, a high probability predominates. Receiver Operating Characteristics not only confirm the reliability of our quality measure but also demonstrate that existing methods are less suitable for evaluating a reconstruction. Full article

(This article belongs to the Special Issue State-of-the-Art Sensors Technology in Germany 2012)

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813 KiB

Open AccessArticle

Influence of Cobalt on the Properties of Load-Sensitive Magnesium Alloys

by Christian Klose, Christian Demminger, Gregor Mroz, Wilfried Reimche, Friedrich-Wilhelm Bach, Hans Jürgen Maier and Kai Kerber

Sensors 2013, 13(1), 106-118; https://doi.org/10.3390/s130100106 - 21 Dec 2012

Cited by 12 | Viewed by 7491

Abstract

In this study, magnesium is alloyed with varying amounts of the ferromagnetic alloying element cobalt in order to obtain lightweight load-sensitive materials with sensory properties which allow an online-monitoring of mechanical forces applied to components made from Mg-Co alloys. An optimized casting process [...] Read more.

In this study, magnesium is alloyed with varying amounts of the ferromagnetic alloying element cobalt in order to obtain lightweight load-sensitive materials with sensory properties which allow an online-monitoring of mechanical forces applied to components made from Mg-Co alloys. An optimized casting process with the use of extruded Mg-Co powder rods is utilized which enables the production of magnetic magnesium alloys with a reproducible Co concentration. The efficiency of the casting process is confirmed by SEM analyses. Microstructures and Co-rich precipitations of various Mg-Co alloys are investigated by means of EDS and XRD analyses. The Mg-Co alloys’ mechanical strengths are determined by tensile tests. Magnetic properties of the Mg-Co sensor alloys depending on the cobalt content and the acting mechanical load are measured utilizing the harmonic analysis of eddy-current signals. Within the scope of this work, the influence of the element cobalt on magnesium is investigated in detail and an optimal cobalt concentration is defined based on the performed examinations. Full article

(This article belongs to the Special Issue State-of-the-Art Sensors Technology in Germany 2012)

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616 KiB

Open AccessArticle

Investigation of a Passive Sensor Array for Diagnosis of Loosening of Endoprosthetic Implants

by Cathérine Ruther, Christian Schulze, Andrea Boehme, Hannes Nierath, Hartmut Ewald, Wolfram Mittelmeier, Rainer Bader and Daniel Kluess

Sensors 2013, 13(1), 1-20; https://doi.org/10.3390/s130100001 - 20 Dec 2012

Cited by 10 | Viewed by 8293

Abstract

Currently, imaging methods are used to diagnose loosening of endoprosthetic implants, but fail to achieve 100% accuracy. In this study, a passive sensor array which is based on the interaction between magnetic oscillators inside the implant and an excitation coil outside the patient [...] Read more.

Currently, imaging methods are used to diagnose loosening of endoprosthetic implants, but fail to achieve 100% accuracy. In this study, a passive sensor array which is based on the interaction between magnetic oscillators inside the implant and an excitation coil outside the patient was investigated. The excited oscillators produce sound in the audible range, which varies according to the extent of loosening. By performing several experimental tests, the sensor array was optimized to guarantee reproducible and selective excitation of the sound emission. Variation in the distance between the oscillators demonstrated a definite influence on the quality of the generated sound signal. Furthermore, a numerical design analysis using the boundary element method was generated for consideration of the magnetic field and the selectivity of the oscillators during excitation. The numerical simulation of the coil showed the higher selectivity of a coil with a C-shape compared to a cylindrical coil. Based on these investigations, the passive sensor system reveals the potential for detection of implant loosening. Future aims include the further miniaturization of the oscillators and measurements to determine the sensitivity of the proposed sensor system. Full article

(This article belongs to the Special Issue State-of-the-Art Sensors Technology in Germany 2012)

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535 KiB

Open AccessArticle

Improved Membrane-Based Sensor Network for Reliable Gas Monitoring in the Subsurface

by Detlef Lazik and Sebastian Ebert

Sensors 2012, 12(12), 17058-17073; https://doi.org/10.3390/s121217058 - 12 Dec 2012

Cited by 14 | Viewed by 5380

Abstract

A conceptually improved sensor network to monitor the partial pressure of CO₂ in different soil horizons was designed. Consisting of five membrane-based linear sensors (line-sensors) each with 10 m length, the set-up enables us to integrate over the locally fluctuating CO₂ [...] Read more.

A conceptually improved sensor network to monitor the partial pressure of CO₂ in different soil horizons was designed. Consisting of five membrane-based linear sensors (line-sensors) each with 10 m length, the set-up enables us to integrate over the locally fluctuating CO₂ concentrations (typically lower 5%_vol) up to the meter-scale gaining valuable concentration means with a repetition time of about 1 min. Preparatory tests in the laboratory resulted in a unexpected highly increased accuracy of better than 0.03%_vol with respect to the previously published 0.08%_vol. Thereby, the statistical uncertainties (standard deviations) of the line-sensors and the reference sensor (nondispersive infrared CO₂-sensor) were close to each other. Whereas the uncertainty of the reference increases with the measurement value, the line-sensors show an inverse uncertainty trend resulting in a comparatively enhanced accuracy for concentrations >1%_vol. Furthermore, a method for in situ maintenance was developed, enabling a proof of sensor quality and its effective calibration without demounting the line-sensors from the soil which would disturb the established structures and ongoing processes. Full article

(This article belongs to the Special Issue State-of-the-Art Sensors Technology in Germany 2012)

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1548 KiB

Open AccessArticle

Photonic Crystal Based Sensor for Organic Solvents and for Solvent-Water Mixtures

by Christoph Fenzl, Thomas Hirsch and Otto S. Wolfbeis

Sensors 2012, 12(12), 16954-16963; https://doi.org/10.3390/s121216954 - 12 Dec 2012

Cited by 42 | Viewed by 9414

Abstract

Monodisperse polystyrene nanoparticles with a diameter of 173 nm were incorporated into a polydimethylsiloxane matrix where they display an iridescent color that can be attributed to the photonic crystal effect. The film is of violet color if placed in plain water, but turns [...] Read more.

Monodisperse polystyrene nanoparticles with a diameter of 173 nm were incorporated into a polydimethylsiloxane matrix where they display an iridescent color that can be attributed to the photonic crystal effect. The film is of violet color if placed in plain water, but turns to red in the presence of the non-polar solvent n-hexane. Several solvents were studied in some detail. We show that such films are capable of monitoring the water content of ethanol/water mixtures, where only 1% (v/v) of water leads to a shift of the peak wavelength of reflected light by 5 nm. The method also can be applied to determine, both visually and instrumentally, the fraction of methanol in ethanol/methanol mixtures. Here, a fraction of 1% of methanol (v/v) results in a wavelength shift of 2 nm. The reflected wavelength is not influenced by temperature changes nor impeded by photobleaching. The signal changes are fully reversible and response times are <1 s. Full article

(This article belongs to the Special Issue State-of-the-Art Sensors Technology in Germany 2012)

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797 KiB

Open AccessArticle

Nonlinear Magnetoelectric Response of Planar Ferromagnetic-Piezoelectric Structures to Sub-Millisecond Magnetic Pulses

by Florian Kreitmeier, Dmitry V. Chashin, Yury K. Fetisov, Leonid Y. Fetisov, Irene Schulz, Gareth J. Monkman and Mikhail Shamonin

Sensors 2012, 12(11), 14821-14837; https://doi.org/10.3390/s121114821 - 2 Nov 2012

Cited by 12 | Viewed by 7318

Abstract

The magnetoelectric response of bi- and symmetric trilayer composite structures to pulsed magnetic fields is experimentally investigated in detail. The structures comprise layers of commercially available piezoelectric (lead zirconate titanate) and magnetostrictive (permendur or nickel) materials. The magnetic-field pulses have the form of [...] Read more.

The magnetoelectric response of bi- and symmetric trilayer composite structures to pulsed magnetic fields is experimentally investigated in detail. The structures comprise layers of commercially available piezoelectric (lead zirconate titanate) and magnetostrictive (permendur or nickel) materials. The magnetic-field pulses have the form of a half-wave sine function with duration of 450 µs and amplitudes ranging from 500 Oe to 38 kOe. The time dependence of the resulting voltage is presented and explained by theoretical estimations. Appearance of voltage oscillations with frequencies much larger than the reciprocal pulse length is observed for sufficiently large amplitudes (~1–10 kOe) of the magnetic-field pulse. The origin of these oscillations is the excitation of bending and planar acoustic oscillations in the structures. Dependencies of the magnetoelectric voltage coefficient on the excitation frequency and the applied magnetic field are calculated by digital signal processing and compared with those obtained by the method of harmonic field modulation. The results are of interest for developing magnetoelectric sensors of pulsed magnetic fields as well as for rapid characterization of magnetoelectric composite structures. Full article

(This article belongs to the Special Issue State-of-the-Art Sensors Technology in Germany 2012)

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1141 KiB

Open AccessArticle

Automatic Suppression of Intense Monochromatic Light in Electro-Optical Sensors

by Gunnar Ritt and Bernd Eberle

Sensors 2012, 12(10), 14113-14128; https://doi.org/10.3390/s121014113 - 19 Oct 2012

Cited by 24 | Viewed by 8050

Abstract

Electro-optical imaging sensors are widely distributed and used for many different tasks. Due to technical improvements, their pixel size has been steadily decreasing, resulting in a reduced saturation capacity. As a consequence, this progress makes them susceptible to intense point light sources. Developments [...] Read more.

Electro-optical imaging sensors are widely distributed and used for many different tasks. Due to technical improvements, their pixel size has been steadily decreasing, resulting in a reduced saturation capacity. As a consequence, this progress makes them susceptible to intense point light sources. Developments in laser technology have led to very compact and powerful laser sources of any wavelength in the visible and near infrared spectral region, offered as laser pointers. The manifold of wavelengths makes it difficult to encounter sensor saturation over the complete operating waveband by conventional measures like absorption or interference filters. We present a concept for electro-optical sensors to suppress overexposure in the visible spectral region. The key element of the concept is a spatial light modulator in combination with wavelength multiplexing. This approach allows spectral filtering within a localized area in the field of view of the sensor. The system offers the possibility of automatic reduction of overexposure by monochromatic laser radiation. Full article

(This article belongs to the Special Issue State-of-the-Art Sensors Technology in Germany 2012)

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1335 KiB

Open AccessArticle

Optimization of Passive Low Power Wireless Electromagnetic Energy Harvesters

by Antwi Nimo, Dario Grgić and Leonhard M. Reindl

Sensors 2012, 12(10), 13636-13663; https://doi.org/10.3390/s121013636 - 11 Oct 2012

Cited by 44 | Viewed by 20668

Abstract

This work presents the optimization of antenna captured low power radio frequency (RF) to direct current (DC) power converters using Schottky diodes for powering remote wireless sensors. Linearized models using scattering parameters show that an antenna and a matched diode rectifier can be [...] Read more.

This work presents the optimization of antenna captured low power radio frequency (RF) to direct current (DC) power converters using Schottky diodes for powering remote wireless sensors. Linearized models using scattering parameters show that an antenna and a matched diode rectifier can be described as a form of coupled resonator with different individual resonator properties. The analytical models show that the maximum voltage gain of the coupled resonators is mainly related to the antenna, diode and load (remote sensor) resistances at matched conditions or resonance. The analytical models were verified with experimental results. Different passive wireless RF power harvesters offering high selectivity, broadband response and high voltage sensitivity are presented. Measured results show that with an optimal resistance of antenna and diode, it is possible to achieve high RF to DC voltage sensitivity of 0.5 V and efficiency of 20% at −30 dBm antenna input power. Additionally, a wireless harvester (rectenna) is built and tested for receiving range performance. Full article

(This article belongs to the Special Issue State-of-the-Art Sensors Technology in Germany 2012)

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773 KiB

Open AccessArticle

Numerical Investigations on Electric Field Characteristics with Respect to Capacitive Detection of Free-Flying Droplets

by Andreas Ernst, Klaus Mutschler, Laurent Tanguy, Nils Paust, Roland Zengerle and Peter Koltay

Sensors 2012, 12(8), 10550-10565; https://doi.org/10.3390/s120810550 - 3 Aug 2012

Cited by 3 | Viewed by 6886

Abstract

In this paper a multi-disciplinary simulation of a capacitive droplet sensor based on an open plate capacitor as transducing element is presented. The numerical simulations are based on the finite volume method (FVM), including calculations of an electric field which changes according to [...] Read more.

In this paper a multi-disciplinary simulation of a capacitive droplet sensor based on an open plate capacitor as transducing element is presented. The numerical simulations are based on the finite volume method (FVM), including calculations of an electric field which changes according to the presence of a liquid droplet. The volume of fluid (VOF) method is applied for the simulation of the ejection process of a liquid droplet out of a dispenser nozzle. The simulations were realised using the computational fluid dynamic (CFD) software CFD ACE+. The investigated capacitive sensing principle enables to determine the volume of a micro droplet passing the sensor capacitor due to the induced change in capacity. It could be found that single droplets in the considered volume range of 5 nL < V_drop < 100 nL lead to a linear change of the capacity up to ΔQ < 30 fC. The sensitivity of the focused capacitor geometry was evaluated to be S_i = 0.3 fC/nL. The simulation results are validated by experiments which exhibit good agreement. Full article

(This article belongs to the Special Issue State-of-the-Art Sensors Technology in Germany 2012)

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Review

Jump to: Research

7174 KiB

Open AccessReview

Scanning Ion Conductance Microscopy for Studying Biological Samples

by Patrick Happel, Denis Thatenhorst and Irmgard D. Dietzel

Sensors 2012, 12(11), 14983-15008; https://doi.org/10.3390/s121114983 - 6 Nov 2012

Cited by 59 | Viewed by 11233

Abstract

Scanning ion conductance microscopy (SICM) is a scanning probe technique that utilizes the increase in access resistance that occurs if an electrolyte filled glass micro-pipette is approached towards a poorly conducting surface. Since an increase in resistance can be monitored before the physical [...] Read more.

Scanning ion conductance microscopy (SICM) is a scanning probe technique that utilizes the increase in access resistance that occurs if an electrolyte filled glass micro-pipette is approached towards a poorly conducting surface. Since an increase in resistance can be monitored before the physical contact between scanning probe tip and sample, this technique is particularly useful to investigate the topography of delicate samples such as living cells. SICM has shown its potential in various applications such as high resolution and long-time imaging of living cells or the determination of local changes in cellular volume. Furthermore, SICM has been combined with various techniques such as fluorescence microscopy or patch clamping to reveal localized information about proteins or protein functions. This review details the various advantages and pitfalls of SICM and provides an overview of the recent developments and applications of SICM in biological imaging. Furthermore, we show that in principle, a combination of SICM and ion selective micro-electrodes enables one to monitor the local ion activity surrounding a living cell. Full article

(This article belongs to the Special Issue State-of-the-Art Sensors Technology in Germany 2012)

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