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Electronics, Volume 3, Issue 2 (June 2014), Pages 205-397

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Research

Jump to: Review

Open AccessArticle Use of a Wireless Network of Accelerometers for Improved Measurement of Human Energy Expenditure
Electronics 2014, 3(2), 205-220; doi:10.3390/electronics3020205
Received: 8 February 2014 / Revised: 12 March 2014 / Accepted: 19 March 2014 / Published: 3 April 2014
Cited by 8 | PDF Full-text (888 KB) | HTML Full-text | XML Full-text
Abstract
Single, hip-mounted accelerometers can provide accurate measurements of energy expenditure (EE) in some settings, but are unable to accurately estimate the energy cost of many non-ambulatory activities. A multi-sensor network may be able to overcome the limitations of a single accelerometer. Thus, the
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Single, hip-mounted accelerometers can provide accurate measurements of energy expenditure (EE) in some settings, but are unable to accurately estimate the energy cost of many non-ambulatory activities. A multi-sensor network may be able to overcome the limitations of a single accelerometer. Thus, the purpose of our study was to compare the abilities of a wireless network of accelerometers and a hip-mounted accelerometer for the prediction of EE. Thirty adult participants engaged in 14 different sedentary, ambulatory, lifestyle and exercise activities for five minutes each while wearing a portable metabolic analyzer, a hip-mounted accelerometer (AG) and a wireless network of three accelerometers (WN) worn on the right wrist, thigh and ankle. Artificial neural networks (ANNs) were created separately for the AG and WN for the EE prediction. Pearson correlations (r) and the root mean square error (RMSE) were calculated to compare criterion-measured EE to predicted EE from the ANNs. Overall, correlations were higher (r = 0.95 vs. r = 0.88, p < 0.0001) and RMSE was lower (1.34 vs. 1.97 metabolic equivalents (METs), p < 0.0001) for the WN than the AG. In conclusion, the WN outperformed the AG for measuring EE, providing evidence that the WN can provide highly accurate estimates of EE in adults participating in a wide range of activities. Full article
(This article belongs to the Special Issue Wearable Electronics)
Open AccessArticle End-Fire Antenna for BAN at 60 GHz: Impact of Bending, On-Body Performances, and Study of an On to Off-Body Scenario
Electronics 2014, 3(2), 221-233; doi:10.3390/electronics3020221
Received: 28 February 2014 / Revised: 27 March 2014 / Accepted: 31 March 2014 / Published: 8 April 2014
Cited by 1 | PDF Full-text (1787 KB) | HTML Full-text | XML Full-text
Abstract
A compact end-fire wearable Yagi-Uda antenna covering the entire 57–64 GHz frequency band is characterized in free space, in the presence of a skin-equivalent phantom and under bending conditions. The results demonstrate that, when placed on the body and/or bended, the antenna preserves
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A compact end-fire wearable Yagi-Uda antenna covering the entire 57–64 GHz frequency band is characterized in free space, in the presence of a skin-equivalent phantom and under bending conditions. The results demonstrate that, when placed on the body and/or bended, the antenna preserves satisfactory performances. The possibility of its use for an on/off-body communications at 60 GHz is investigated numerically and experimentally in a representative scenario in terms of E-field and power flow distributions, as well as in terms of path gain. It is shown that this antenna is a suitable candidate for high-data-rate short-range on/off-body transmissions. Full article
(This article belongs to the Special Issue Wearable Electronics)
Open AccessArticle Optical and Surface Characterization of Radio Frequency Plasma Polymerized 1-Isopropyl-4-Methyl-1,4-Cyclohexadiene Thin Films
Electronics 2014, 3(2), 266-281; doi:10.3390/electronics3020266
Received: 21 February 2014 / Accepted: 14 April 2014 / Published: 23 April 2014
Cited by 7 | PDF Full-text (986 KB) | HTML Full-text | XML Full-text
Abstract
Low pressure radio frequency plasma-assisted deposition of 1-isopropyl-4-methyl-1,4-cyclohexadiene thin films was investigated for different polymerization conditions. Transparent, environmentally stable and flexible, these organic films are promising candidates for organic photovoltaics (OPV) and flexible electronics applications, where they can be used as encapsulating coatings
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Low pressure radio frequency plasma-assisted deposition of 1-isopropyl-4-methyl-1,4-cyclohexadiene thin films was investigated for different polymerization conditions. Transparent, environmentally stable and flexible, these organic films are promising candidates for organic photovoltaics (OPV) and flexible electronics applications, where they can be used as encapsulating coatings and insulating interlayers. The effect of deposition RF power on optical properties of the films was limited, with all films being optically transparent, with refractive indices in a range of 1.57–1.58 at 500 nm. The optical band gap (Eg) of ~3 eV fell into the insulating Eg region, decreasing for films fabricated at higher RF power. Independent of deposition conditions, the surfaces were smooth and defect-free, with uniformly distributed morphological features and average roughness between 0.30 nm (at 10 W) and 0.21 nm (at 75 W). Films fabricated at higher deposition power displayed enhanced resistance to delamination and wear, and improved hardness, from 0.40 GPa for 10 W to 0.58 GPa for 75 W at a load of 700 μN. From an application perspective, it is therefore possible to tune the mechanical and morphological properties of these films without compromising their optical transparency or insulating property. Full article
(This article belongs to the Special Issue Organic Semiconductors) Print Edition available
Open AccessArticle Strong Coupling between Plasmons and Organic Semiconductors
Electronics 2014, 3(2), 303-313; doi:10.3390/electronics3020303
Received: 17 February 2014 / Revised: 10 April 2014 / Accepted: 16 April 2014 / Published: 6 May 2014
Cited by 3 | PDF Full-text (947 KB) | HTML Full-text | XML Full-text
Abstract
In this paper we describe the properties of organic material in strong coupling with plasmon, mainly based on our work in this field of research. The strong coupling modifies the optical transitions of the structure, and occurs when the interaction between molecules and
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In this paper we describe the properties of organic material in strong coupling with plasmon, mainly based on our work in this field of research. The strong coupling modifies the optical transitions of the structure, and occurs when the interaction between molecules and plasmon prevails on the damping of the system. We describe the dispersion relation of different plasmonic systems, delocalized and localized plasmon, coupled to aggregated dyes and the typical properties of these systems in strong coupling. The modification of the dye emission is also studied. In the second part, the effect of the microscopic structure of the organics, which can be seen as a disordered film, is described. As the different molecules couple to the same plasmon mode, an extended coherent state on several microns is observed. Full article
(This article belongs to the Special Issue Organic Semiconductors) Print Edition available
Open AccessArticle Footwear and Wrist Communication Links using 2.4 GHz and UWB Antennas
Electronics 2014, 3(2), 339-350; doi:10.3390/electronics3020339
Received: 19 February 2014 / Revised: 21 May 2014 / Accepted: 26 May 2014 / Published: 4 June 2014
Cited by 1 | PDF Full-text (1148 KB) | HTML Full-text | XML Full-text
Abstract
It is reported that wearable electronic devices are to be used extensively in the next generation of sensors for sports and health monitoring. The information obtained from sensors on the human body depends on the biological parameters, the measurement rate and the number
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It is reported that wearable electronic devices are to be used extensively in the next generation of sensors for sports and health monitoring. The information obtained from sensors on the human body depends on the biological parameters, the measurement rate and the number of sensors. The choice of the wireless protocol depends on the required data rates and on system configurations. The communication link quality is achieved with narrowband technologies such as Bluetooth or Zigbee, provided that the number of sensors is small and data rates are low. However, real-time measurements using wideband channels may also be necessary. This paper reports narrowband link performance at 2.45 GHz for comparison with two UWB channels centered at 3.95 GHz and 7.25 GHz. A monopole antenna covering 2.45 GHz and UWB is optimized for an on-body communication link between the footwear and the wrist. The cumulative distribution function of several path loss measurements is reported and compared for a subject standing and walking. Results show that the larger bandwidth in the UWB channel reduces fading and stabilizes the channel predictability. Full article
(This article belongs to the Special Issue Wearable Electronics)
Open AccessArticle SmartStep: A Fully Integrated, Low-Power Insole Monitor
Electronics 2014, 3(2), 381-397; doi:10.3390/electronics3020381
Received: 15 March 2014 / Revised: 3 June 2014 / Accepted: 9 June 2014 / Published: 18 June 2014
Cited by 7 | PDF Full-text (686 KB) | HTML Full-text | XML Full-text
Abstract
Shoe-mounted wearable sensors can be used in applications, such as activity monitoring, gait analysis, post-stroke rehabilitation, body weight measurements and energy expenditure studies. Such wearable sensors typically require the modification or alteration of the shoe, which is not typically feasible for large populations
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Shoe-mounted wearable sensors can be used in applications, such as activity monitoring, gait analysis, post-stroke rehabilitation, body weight measurements and energy expenditure studies. Such wearable sensors typically require the modification or alteration of the shoe, which is not typically feasible for large populations without the direct involvement of shoe manufacturers. This article presents an insole-based wearable sensor (SmartStep) that has its electronics fully embedded into a generic insole, which is usable with a large variety of shoes and, thus, resolves the need for shoe modification. The SmartStep is an always-on electronic device that comprises a 3D accelerometer, a 3D gyroscope and resistive pressure sensors implemented around a CC2540 system-on-chip with an 8051 processor core, Bluetooth low energy (BLE) connectivity and flash memory buffer. The SmartStep is wirelessly interfaced to an Android smart phone application with data logging and visualization capabilities. This article focuses on low-power implementation methods and on the method developed for reliable data buffering, alleviating intermittent connectivity resulting from the user leaving the vicinity of the smart phone. The conducted tests illustrate the power consumption for several possible usage scenarios and the reliability of the data retention method. The trade-off between the power consumption and supported functionality is discussed, demonstrating that SmartStep can be worn for more than two days between battery recharges. The results of the mechanical reliability test on the SmartStep indicate that the pressure sensors in the SmartStep tolerated prolonged human wear. The SmartStep system collected more than 98.5% of the sensor data, in real usage scenarios, having intermittent connectivity with the smart phone. Full article
(This article belongs to the Special Issue Wearable Electronics)
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Review

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Open AccessReview Organic Thin-Film Transistor (OTFT)-Based Sensors
Electronics 2014, 3(2), 234-254; doi:10.3390/electronics3020234
Received: 23 January 2014 / Revised: 25 March 2014 / Accepted: 27 March 2014 / Published: 8 April 2014
Cited by 18 | PDF Full-text (827 KB) | HTML Full-text | XML Full-text
Abstract
Organic thin film transistors have been a popular research topic in recent decades and have found applications from flexible displays to disposable sensors. In this review, we present an overview of some notable articles reporting sensing applications for organic transistors with a focus
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Organic thin film transistors have been a popular research topic in recent decades and have found applications from flexible displays to disposable sensors. In this review, we present an overview of some notable articles reporting sensing applications for organic transistors with a focus on the most recent publications. In particular, we concentrate on three main types of organic transistor-based sensors: biosensors, pressure sensors and “e-nose”/vapour sensors. Full article
(This article belongs to the Special Issue Organic Semiconductors) Print Edition available
Open AccessReview Anomalous Response in Heteroacene-Based Organic Field Effect Transistors under High Pressure
Electronics 2014, 3(2), 255-265; doi:10.3390/electronics3020255
Received: 15 February 2014 / Revised: 28 March 2014 / Accepted: 31 March 2014 / Published: 10 April 2014
Cited by 2 | PDF Full-text (693 KB) | HTML Full-text | XML Full-text
Abstract
Carrier transport properties of organic field effect transistors in dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene single crystals have been investigated under high pressure. In contrast to the typical pressure effect of monotonic increase in charge transfer rates according to the application of
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Carrier transport properties of organic field effect transistors in dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene single crystals have been investigated under high pressure. In contrast to the typical pressure effect of monotonic increase in charge transfer rates according to the application of external hydrostatic pressure, it is clarified that the present organic semiconductor devices exhibit nonmonotonic pressure response, such as negative pressure effect. X-ray diffraction analysis under high pressure reveals that on-site molecular orientation and displacement in the heteroacene molecule is assumed to be the origin for the anomalous pressure effects. Full article
(This article belongs to the Special Issue Organic Semiconductors) Print Edition available
Open AccessReview Wearable Photoplethysmographic Sensors—Past and Present
Electronics 2014, 3(2), 282-302; doi:10.3390/electronics3020282
Received: 25 February 2014 / Revised: 15 April 2014 / Accepted: 18 April 2014 / Published: 23 April 2014
Cited by 58 | PDF Full-text (422 KB) | HTML Full-text | XML Full-text
Abstract
Photoplethysmography (PPG) technology has been used to develop small, wearable, pulse rate sensors. These devices, consisting of infrared light-emitting diodes (LEDs) and photodetectors, offer a simple, reliable, low-cost means of monitoring the pulse rate noninvasively. Recent advances in optical technology have facilitated the
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Photoplethysmography (PPG) technology has been used to develop small, wearable, pulse rate sensors. These devices, consisting of infrared light-emitting diodes (LEDs) and photodetectors, offer a simple, reliable, low-cost means of monitoring the pulse rate noninvasively. Recent advances in optical technology have facilitated the use of high-intensity green LEDs for PPG, increasing the adoption of this measurement technique. In this review, we briefly present the history of PPG and recent developments in wearable pulse rate sensors with green LEDs. The application of wearable pulse rate monitors is discussed. Full article
(This article belongs to the Special Issue Wearable Electronics)
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Open AccessReview Embroidery and Related Manufacturing Techniques for Wearable Antennas: Challenges and Opportunities
Electronics 2014, 3(2), 314-338; doi:10.3390/electronics3020314
Received: 27 February 2014 / Revised: 17 May 2014 / Accepted: 21 May 2014 / Published: 30 May 2014
Cited by 30 | PDF Full-text (1692 KB) | HTML Full-text | XML Full-text
Abstract
This paper will review the evolution of wearable textile antennas over the last couple of decades. Particular emphasis will be given to the process of embroidery. This technique is advantageous for the following reasons: (i) bespoke or mass produced designs can be manufactured
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This paper will review the evolution of wearable textile antennas over the last couple of decades. Particular emphasis will be given to the process of embroidery. This technique is advantageous for the following reasons: (i) bespoke or mass produced designs can be manufactured using digitized embroidery machines; (ii) glue is not required and (iii) the designs are aesthetic and are integrated into clothing rather than being attached to it. The embroidery technique will be compared to alternative manufacturing processes. The challenges facing the industrial and public acceptance of this technology will be assessed. Hence, the key opportunities will be highlighted. Full article
(This article belongs to the Special Issue Wearable Electronics)
Open AccessReview Bandgap Science for Organic Solar Cells
Electronics 2014, 3(2), 351-380; doi:10.3390/electronics3020351
Received: 18 February 2014 / Revised: 28 April 2014 / Accepted: 26 May 2014 / Published: 11 June 2014
Cited by 8 | PDF Full-text (966 KB) | HTML Full-text | XML Full-text
Abstract
The concept of bandgap science of organic semiconductor films for use in photovoltaic cells, namely, high-purification, pn-control by doping, and design of the built-in potential based on precisely-evaluated doping parameters, is summarized. The principle characteristics of organic solar cells, namely, the exciton,
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The concept of bandgap science of organic semiconductor films for use in photovoltaic cells, namely, high-purification, pn-control by doping, and design of the built-in potential based on precisely-evaluated doping parameters, is summarized. The principle characteristics of organic solar cells, namely, the exciton, donor (D)/acceptor (A) sensitization, and p-i-n cells containing co-deposited and D/A molecular blended i-interlayers, are explained. ‘Seven-nines’ (7N) purification, together with phase-separation/cystallization induced by co-evaporant 3rd molecules allowed us to fabricate 5.3% efficient cells based on 1 µm-thick fullerene:phthalocyanine (C60:H2Pc) co-deposited films. pn-control techniques enabled by impurity doping for both single and co-deposited films were established. The carrier concentrations created by doping were determined by the Kelvin band mapping technique. The relatively high ionization efficiency of 10% for doped organic semiconductors can be explained by the formation of charge transfer (CT)-complexes between the dopants and the organic semiconductor molecules. A series of fundamental junctions, such as Schottky junctions, pn-homojunctions, p+, n+-organic/metal ohmic junctions, and n+-organic/ p+-organic ohmic homojunctions, were fabricated in both single and co-deposited organic semiconductor films by impurity doping alone. A tandem cell showing 2.4% efficiency was fabricated in which the built-in electric field was designed by manipulating the doping. Full article
(This article belongs to the Special Issue Organic Semiconductors) Print Edition available

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