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papers from the latest issue:
The thermopile: An anisotropic temperature sensor
10 October 2012,
08:12:15
Publication year:
2012
Source:Sensors and Actuators A: Physical, Volume 187
Suvhashis Thapa, Siva Mahesh Tangutooru, Eric J. Guilbeau, Niel D. Crews
This article discusses the operation of thermopiles when used under non-isothermal baseline conditions. Although isothermal baselines are the common thread among existing thermopile applications, this article demonstrates that these sensors can also be used to detect subtle thermal events that are superimposed over much larger steady-state or transient temperature gradients. The larger temperature variation will not contribute to the transduced voltage as long as specific thermal symmetry conditions are matched with a specific thermopile design. This article discusses this sensing anisotropy that corresponds to certain thermopile designs, and experimental results are presented which demonstrate the relative performance under several thermal conditions. Thermopile performance characteristics of baseline voltage, baseline drift and noise, and signal sensitivity have been compared experimentally for isothermal and high gradient conditions. When symmetry conditions were met, certain thermopile geometries exhibited a sensing anisotropy of more than 1000:1.
Source:Sensors and Actuators A: Physical, Volume 187
Suvhashis Thapa, Siva Mahesh Tangutooru, Eric J. Guilbeau, Niel D. Crews
This article discusses the operation of thermopiles when used under non-isothermal baseline conditions. Although isothermal baselines are the common thread among existing thermopile applications, this article demonstrates that these sensors can also be used to detect subtle thermal events that are superimposed over much larger steady-state or transient temperature gradients. The larger temperature variation will not contribute to the transduced voltage as long as specific thermal symmetry conditions are matched with a specific thermopile design. This article discusses this sensing anisotropy that corresponds to certain thermopile designs, and experimental results are presented which demonstrate the relative performance under several thermal conditions. Thermopile performance characteristics of baseline voltage, baseline drift and noise, and signal sensitivity have been compared experimentally for isothermal and high gradient conditions. When symmetry conditions were met, certain thermopile geometries exhibited a sensing anisotropy of more than 1000:1.
A micromechanical bandpass filter with adjustable bandwidth and bidirectional control of centre frequency
10 October 2012,
08:12:15
Publication year:
2012
Source:Sensors and Actuators A: Physical, Volume 187
M.S. Hajhashemi, Alborz Amini, Behraad Bahreyni
This paper introduces a tunable, narrow-band, micromechanical filter whose bandwidth and centre frequency can be adjusted independently. The filter is made of two micro-resonators that are electrostatically coupled using a middle electrode. A low coupling strength results in nearly constant bandwidth while one tunes the centre frequency bi-directionally by applying a DC voltage to the coupling electrode. On the other hand, the bandwidth of the filter is independently modified by applying axial stress to one of the resonators, without affecting the signal attenuation through the filter. Analytic and numerical models for the behaviour of the filter are also presented. Test devices with a centre frequency of about 300kHz were fabricated in a standard micromachining process. Experimental results support the design principle and validity of the proposed models.
Source:Sensors and Actuators A: Physical, Volume 187
M.S. Hajhashemi, Alborz Amini, Behraad Bahreyni
This paper introduces a tunable, narrow-band, micromechanical filter whose bandwidth and centre frequency can be adjusted independently. The filter is made of two micro-resonators that are electrostatically coupled using a middle electrode. A low coupling strength results in nearly constant bandwidth while one tunes the centre frequency bi-directionally by applying a DC voltage to the coupling electrode. On the other hand, the bandwidth of the filter is independently modified by applying axial stress to one of the resonators, without affecting the signal attenuation through the filter. Analytic and numerical models for the behaviour of the filter are also presented. Test devices with a centre frequency of about 300kHz were fabricated in a standard micromachining process. Experimental results support the design principle and validity of the proposed models.
Study of the subthreshold swing of a pMOSFET as a dosimetric parameter
10 October 2012,
08:12:15
Publication year:
2012
Source:Sensors and Actuators A: Physical, Volume 187
J. Banqueri, M.A. Carvajal, M.S. Martínez-García, D.P. Morales, A.J. Palma
A study of the degradation of the subthreshold swing in a general-purpose pMOSFET is carried out to evaluate its use as a dosimetric parameter. Its reliability in terms of sensitivity, linearity, and reproducibility is experimentally tested and compared with the threshold voltage shift under gamma rays from a 60Co source up to 56Gy, typical in radiotherapy treatments. The dependence of the subthreshold swing as a function of temperature is characterized and modelled as a mean for thermal compensation when used for dose measurement. Very promising results have been obtained for the subthreshold swing as a complementary dosimetric parameter to the threshold voltage for enhancing the confidence of dose verification systems based on MOSFETs.
Source:Sensors and Actuators A: Physical, Volume 187
J. Banqueri, M.A. Carvajal, M.S. Martínez-García, D.P. Morales, A.J. Palma
A study of the degradation of the subthreshold swing in a general-purpose pMOSFET is carried out to evaluate its use as a dosimetric parameter. Its reliability in terms of sensitivity, linearity, and reproducibility is experimentally tested and compared with the threshold voltage shift under gamma rays from a 60Co source up to 56Gy, typical in radiotherapy treatments. The dependence of the subthreshold swing as a function of temperature is characterized and modelled as a mean for thermal compensation when used for dose measurement. Very promising results have been obtained for the subthreshold swing as a complementary dosimetric parameter to the threshold voltage for enhancing the confidence of dose verification systems based on MOSFETs.
Highlights
► pMOS Subthreshold swing analysed as dosimetric parameter. ► Sensitivity, linearity and reproducibility of the response to the radiation. ► Subthreshold swing response comparable to threshold voltage. ► Enhanced reliability for the dose verification of radiotherapy treatments.Active density-based separation using standing surface acoustic waves
10 October 2012,
08:12:15
Publication year:
2012
Source:Sensors and Actuators A: Physical, Volume 187
Myeong Chan Jo, Rasim Guldiken
In this paper, we demonstrate active, sheathless density-based particle separation using standing surface acoustic waves. Density-based separation is critical for many biological applications, such as white blood cell classification, stem cell isolation, fetal cell collection from maternal blood, and specific bacterium sorting. Current gold standard separation techniques are only capable of separation based on particle size; hence, separation cannot be achieved for same-size particles with different densities. Here, the separation is accomplished with an acoustic force field (active technique) without using sheath flow. We demonstrate the separation of two 10μm diameter, different-density particle streams (polystyrene: 1.05g/cm3, melamine: 1.71g/cm3) with 98.8% separation efficiency.
Source:Sensors and Actuators A: Physical, Volume 187
Myeong Chan Jo, Rasim Guldiken
In this paper, we demonstrate active, sheathless density-based particle separation using standing surface acoustic waves. Density-based separation is critical for many biological applications, such as white blood cell classification, stem cell isolation, fetal cell collection from maternal blood, and specific bacterium sorting. Current gold standard separation techniques are only capable of separation based on particle size; hence, separation cannot be achieved for same-size particles with different densities. Here, the separation is accomplished with an acoustic force field (active technique) without using sheath flow. We demonstrate the separation of two 10μm diameter, different-density particle streams (polystyrene: 1.05g/cm3, melamine: 1.71g/cm3) with 98.8% separation efficiency.
Morphology-dependent humidity adsorption kinetics of ZnO nanostructures
10 October 2012,
08:12:15
Publication year:
2012
Source:Sensors and Actuators A: Physical, Volume 187
N. Asar, A. Erol, S. Okur, M.C. Arikan
The humidity-sensing characteristics of ZnO nanostructures are investigated using a quartz crystal microbalance (QCM) measurement. ZnO nanostructures are synthesized via sol–gel route in nanoparticle (ZnO-NP) and nanowire (ZnO-NW) morphologies with diameter about 20–30nm. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) methods are used to determine the morphology and crystal structure of ZnO nanostructures. Humidity sensing capabilities are discussed in terms of the different morphologies. The results show that ZnO-NP is more sensitive to humidity changes than ZnO-NW. QCM results are analyzed using Langmuir adsorption model to determine adsorption rates, Gibbs free energy of adsorption (ΔG), and adsorbed mass amount by the synthesized ZnO nanostructures. Negative value of ΔG for humidity adsorption on ZnO nanostructures indicates that the process is spontaneous and adsorption capacity increases with size reduction. Gibbs free energy of the ZnO-NP is found to be more negative, indicating that the ZnO-NP has more favorable adsorption sites compared to the ZnO-NW. Experimental and theoretical results exhibit that humidity-sensing properties of ZnO nanostructures are morphology-dependent.
Source:Sensors and Actuators A: Physical, Volume 187
N. Asar, A. Erol, S. Okur, M.C. Arikan
The humidity-sensing characteristics of ZnO nanostructures are investigated using a quartz crystal microbalance (QCM) measurement. ZnO nanostructures are synthesized via sol–gel route in nanoparticle (ZnO-NP) and nanowire (ZnO-NW) morphologies with diameter about 20–30nm. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) methods are used to determine the morphology and crystal structure of ZnO nanostructures. Humidity sensing capabilities are discussed in terms of the different morphologies. The results show that ZnO-NP is more sensitive to humidity changes than ZnO-NW. QCM results are analyzed using Langmuir adsorption model to determine adsorption rates, Gibbs free energy of adsorption (ΔG), and adsorbed mass amount by the synthesized ZnO nanostructures. Negative value of ΔG for humidity adsorption on ZnO nanostructures indicates that the process is spontaneous and adsorption capacity increases with size reduction. Gibbs free energy of the ZnO-NP is found to be more negative, indicating that the ZnO-NP has more favorable adsorption sites compared to the ZnO-NW. Experimental and theoretical results exhibit that humidity-sensing properties of ZnO nanostructures are morphology-dependent.
A leaf-mounted thermal sensor for the measurement of water content
10 October 2012,
08:12:15
Publication year:
2012
Source:Sensors and Actuators A: Physical, Volume 187
Joseph J. Atherton, Mark C. Rosamond, Dagou A. Zeze
We present a microfabricated thermal sensor for the real-time measurement of the water content of plant leaves. The device consists of a thin-film micro-heater which induces a temperature gradient within a leaf to which it is attached. Temperature differences (ΔT) between two thin-film thermocouples spaced 50μm and 160μm from the heater can be related to the thermal properties of the sample under inspection which, in turn, are dependent on the leaf water content. The sensor is fabricated on a flexible polyimide substrate to ensure that it is robust enough to operate reliably without causing visible damage to the leaves. To demonstrate the device's operation, it was clamped to abscised leaves which were allowed to dry over a period of around 6h. The device's output was then compared to the relative water content of the leaf which was directly measured by weighing the leaf. For the range considered, a linear dependence was observed between ΔT and the water content of the leaf. It is suggested that the changes in ΔT are dominated by the thermal contact resistance between the device and the leaf. The device was subsequently used to monitor the real-time water content of leaves in situ on plants subjected to water stress conditions.
Source:Sensors and Actuators A: Physical, Volume 187
Joseph J. Atherton, Mark C. Rosamond, Dagou A. Zeze
We present a microfabricated thermal sensor for the real-time measurement of the water content of plant leaves. The device consists of a thin-film micro-heater which induces a temperature gradient within a leaf to which it is attached. Temperature differences (ΔT) between two thin-film thermocouples spaced 50μm and 160μm from the heater can be related to the thermal properties of the sample under inspection which, in turn, are dependent on the leaf water content. The sensor is fabricated on a flexible polyimide substrate to ensure that it is robust enough to operate reliably without causing visible damage to the leaves. To demonstrate the device's operation, it was clamped to abscised leaves which were allowed to dry over a period of around 6h. The device's output was then compared to the relative water content of the leaf which was directly measured by weighing the leaf. For the range considered, a linear dependence was observed between ΔT and the water content of the leaf. It is suggested that the changes in ΔT are dominated by the thermal contact resistance between the device and the leaf. The device was subsequently used to monitor the real-time water content of leaves in situ on plants subjected to water stress conditions.
Highlights
► We present a micro-thermal sensor for the real-time detection of the water content of plant leaves. ► Temperature differences (ΔT) induced within leaf can be related to the water content. ► A flexible polyimide substrate ensures it is robust enough to operate on leaves. ► A comparison of device output against leaf weight demonstrated operation. ► The device can monitor the real-time water content of leaves in situ on plants subjected to water stress conditions.Synthesis of multiwalled carbon nanotube-based infrared radiation detector
10 October 2012,
08:12:15
Publication year:
2012
Source:Sensors and Actuators A: Physical, Volume 187
Rahat Afrin, Jibran Khaliq, Mohammad Islam, Iftikhar Hussain Gul, Arshad Saleem Bhatti, Umair Manzoor
Different morphologies (worm-like, straight and twisted) of multiwalled carbon nanotubes (MWCNT) are synthesized by carefully controlling the C2H2 flow rate. Unique mixed ferrite nanoparticles were synthesized and characterized as the appropriate catalyst for the growth of MWCNT. Scanning electron microscope and transmission electron microscope was extensively used to explore the morphological and structural properties. Electrical properties of MWCNT suggest semiconducting behavior. Infrared (IR) radiation detection is demonstrated using MWCNT and prototypes of room temperature and low temperature. IR radiation detectors have been made using different morphologies of MWCNT as the active sensor material.
Source:Sensors and Actuators A: Physical, Volume 187
Rahat Afrin, Jibran Khaliq, Mohammad Islam, Iftikhar Hussain Gul, Arshad Saleem Bhatti, Umair Manzoor
Different morphologies (worm-like, straight and twisted) of multiwalled carbon nanotubes (MWCNT) are synthesized by carefully controlling the C2H2 flow rate. Unique mixed ferrite nanoparticles were synthesized and characterized as the appropriate catalyst for the growth of MWCNT. Scanning electron microscope and transmission electron microscope was extensively used to explore the morphological and structural properties. Electrical properties of MWCNT suggest semiconducting behavior. Infrared (IR) radiation detection is demonstrated using MWCNT and prototypes of room temperature and low temperature. IR radiation detectors have been made using different morphologies of MWCNT as the active sensor material.
Highlights
► Morphology of MWCNTs can be controlled by carefully controlling flow rates of hydrocarbon. Randomly oriented, rigid and coiled MWCNT were successfully synthesized. ► The effect of catalyst on formation mechanism of the developed prototype sensors have good response towards IR radiations is important. ► The developed prototype sensors have good response towards IR radiations.Hollow-core photonic crystal fiber based modal interferometer for strain measurement
10 October 2012,
08:12:15
Publication year:
2012
Source:Sensors and Actuators A: Physical, Volume 187
Huaping Gong, Xiaorui Li, Yongxing Jin, Xinyong Dong
A modal interferometer based on a 1.2mm hollow-core photonic crystal fiber (HC-PCF) for strain measurement is presented. The modal interferometer is fabricated by splicing the two ends of the HC-PCF to single-mode fibers (SMF). The air-holes in the core and cladding of the HC-PCF are fully collapsed in the splicing process, and the length of each collapsed region is about 300μm. The transmission spectra with different strain levels are measured. The sensitivity of 1.83pm/μɛ is achieved in the range of 0–1260μɛ, and the resolution for strain measurement was about 11μɛ for wavelength demodulation.
Source:Sensors and Actuators A: Physical, Volume 187
Huaping Gong, Xiaorui Li, Yongxing Jin, Xinyong Dong
A modal interferometer based on a 1.2mm hollow-core photonic crystal fiber (HC-PCF) for strain measurement is presented. The modal interferometer is fabricated by splicing the two ends of the HC-PCF to single-mode fibers (SMF). The air-holes in the core and cladding of the HC-PCF are fully collapsed in the splicing process, and the length of each collapsed region is about 300μm. The transmission spectra with different strain levels are measured. The sensitivity of 1.83pm/μɛ is achieved in the range of 0–1260μɛ, and the resolution for strain measurement was about 11μɛ for wavelength demodulation.
A high-sensitivity pressure sensor based on surface transverse wave
10 October 2012,
08:12:15
Publication year:
2012
Source:Sensors and Actuators A: Physical, Volume 187
Along Kang, Jinqiu Lin, Xiaojun Ji, Weibiao Wang, Hongyun Li, Chenrui Zhang, Tao Han
A new scheme for STW-based pressure sensors with high performance has been proposed. Different from the conventional analytical procedure using the perturbation theory, the pressure-induced frequency shifts for STW on quartz is obtained utilizing a Green's function simulator and the effective material constants dependent on pressure biasing have been calculated by the finite element method (FEM). The normalized pressure sensitivity (NPS) of STW on quartz as a function of the cut orientation in vicinity of BT-cut quartz has also been calculated, and the calculated results demonstrate that all the NPS on the given cut-orientation are 3 times higher than the commonly used ST-cut quartz of Rayleigh mode. To further improve the whole performance of the sensor, an optimized sensor configuration with an equi-intensity cantilever is proposed, whose geometry has been determined by using FEM software. The experimental results demonstrate that the pressure sensitivity of the proposed STW-based pressure sensors is sufficiently high and the relative frequency shift varies linearly with pressure loading.
Source:Sensors and Actuators A: Physical, Volume 187
Along Kang, Jinqiu Lin, Xiaojun Ji, Weibiao Wang, Hongyun Li, Chenrui Zhang, Tao Han
A new scheme for STW-based pressure sensors with high performance has been proposed. Different from the conventional analytical procedure using the perturbation theory, the pressure-induced frequency shifts for STW on quartz is obtained utilizing a Green's function simulator and the effective material constants dependent on pressure biasing have been calculated by the finite element method (FEM). The normalized pressure sensitivity (NPS) of STW on quartz as a function of the cut orientation in vicinity of BT-cut quartz has also been calculated, and the calculated results demonstrate that all the NPS on the given cut-orientation are 3 times higher than the commonly used ST-cut quartz of Rayleigh mode. To further improve the whole performance of the sensor, an optimized sensor configuration with an equi-intensity cantilever is proposed, whose geometry has been determined by using FEM software. The experimental results demonstrate that the pressure sensitivity of the proposed STW-based pressure sensors is sufficiently high and the relative frequency shift varies linearly with pressure loading.
A LAPS array with low cross-talk for non-invasive measurement of cellular metabolism
10 October 2012,
08:12:15
Publication year:
2012
Source:Sensors and Actuators A: Physical, Volume 187
Ning Hu, Da Ha, Chengxiong Wu, Jie Zhou, Dmitry Kirsanov, Andrey Legin, Ping Wang
Cellular metabolism is ubiquitous biological mechanism involved in many significant physiological processes, and most of the biological cascade reactions are tightly coupled. Non-invasive measurement of cellular metabolism is important to study the metabolism mechanism and drug effect in a long-term detection. In this study, the two processes of heavy doping and thick oxidation fabricated a new light-addressable potentiometric sensor array, which was applied to detect the cellular metabolism induced pH change. The performance of the LAPS was tested by the basic characteristic experiments and renal cell experiments. The result showed that the stability and pH resolution of LAPS array were greatly improved. With the development of the sensor design and fabrication, the LAPS will be a utility tool in the field of biological metabolism.
Source:Sensors and Actuators A: Physical, Volume 187
Ning Hu, Da Ha, Chengxiong Wu, Jie Zhou, Dmitry Kirsanov, Andrey Legin, Ping Wang
Cellular metabolism is ubiquitous biological mechanism involved in many significant physiological processes, and most of the biological cascade reactions are tightly coupled. Non-invasive measurement of cellular metabolism is important to study the metabolism mechanism and drug effect in a long-term detection. In this study, the two processes of heavy doping and thick oxidation fabricated a new light-addressable potentiometric sensor array, which was applied to detect the cellular metabolism induced pH change. The performance of the LAPS was tested by the basic characteristic experiments and renal cell experiments. The result showed that the stability and pH resolution of LAPS array were greatly improved. With the development of the sensor design and fabrication, the LAPS will be a utility tool in the field of biological metabolism.
Preparation of electromagnetic reflective wool using nano-ZrO2/citric acid as inorganic/organic hybrid coating
10 October 2012,
08:12:15
Publication year:
2012
Source:Sensors and Actuators A: Physical, Volume 187
Mazeyar Parvinzadeh Gashti, Arash Almasian, Mahyar Parvinzadeh Gashti
Nano-ZrO2 particles were stabilized on wool surface using citric acid (CA) as a crosslinking agent and sodium hypophosphite (SHP) as a catalyst under UV irradiation. The influence of the amount of nano-ZrO2 on the performance of wool fiber was investigated by the use of Fourier transform infrared spectrophotometer (FTIR), horizontal flammability apparatus (HFA), scanning electron microscope (SEM), water contact angle tester (WCA), reflectance spectrophotometer (RS) and electromagnetic transition instrument (ETI). The possible interactions between nano-zirconia particles, cross-linking agent and wool free radicals were elucidated by the FTIR spectroscopy. Results indicated that the stabilized nano-zirconia enhances the flame retardancy and electromagnetic reflection of wool.
Source:Sensors and Actuators A: Physical, Volume 187
Mazeyar Parvinzadeh Gashti, Arash Almasian, Mahyar Parvinzadeh Gashti
Nano-ZrO2 particles were stabilized on wool surface using citric acid (CA) as a crosslinking agent and sodium hypophosphite (SHP) as a catalyst under UV irradiation. The influence of the amount of nano-ZrO2 on the performance of wool fiber was investigated by the use of Fourier transform infrared spectrophotometer (FTIR), horizontal flammability apparatus (HFA), scanning electron microscope (SEM), water contact angle tester (WCA), reflectance spectrophotometer (RS) and electromagnetic transition instrument (ETI). The possible interactions between nano-zirconia particles, cross-linking agent and wool free radicals were elucidated by the FTIR spectroscopy. Results indicated that the stabilized nano-zirconia enhances the flame retardancy and electromagnetic reflection of wool.
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