Selected papers from the latest issue:
A computationally efficient numerical model of the offset of CMOS-integrated vertical Hall devices
05 April 2012, 09:29:18
Publication year: 2012
Source:Sensors and Actuators A: Physical, Volume 178
T. Kaufmann, M.C. Vecchi, P. Ruther, O. Paul
This paper describes a computationally efficient numerical model to study effects determining the offset of five-contact vertical Hall sensors (VHS). It applies a two-dimensional finite element model implemented in COMSOL Multiphysics and allows to take into account the junction field effect (JFE) altering the depletion layer width between n-well and p-doped regions as well as resistive asymmetries due to contact shifts. Doping profiles of realistic devices were extracted using SYNOPSYS TCAD simulations based on three sets of process parameters with different doping doses of the n-well and p+-diffusions. The VHS offset was compared with experimental results obtained using complementary metal oxide semiconductor (CMOS)-based VHS and analyzed as a function of the input voltage. It was shown that the linear offset components are modeled adequately by resistive imbalances caused by lateral contact shifts in the nanometer range. The JFE in turn is responsible for the nonlinear effects of dominantly quadratic dependence on the input voltage. Both effects contribute additively to the overall offset. According to the simulations, the nonlinear contribution is strongly reduced at higher n-well doping concentrations.
Source:Sensors and Actuators A: Physical, Volume 178
T. Kaufmann, M.C. Vecchi, P. Ruther, O. Paul
This paper describes a computationally efficient numerical model to study effects determining the offset of five-contact vertical Hall sensors (VHS). It applies a two-dimensional finite element model implemented in COMSOL Multiphysics and allows to take into account the junction field effect (JFE) altering the depletion layer width between n-well and p-doped regions as well as resistive asymmetries due to contact shifts. Doping profiles of realistic devices were extracted using SYNOPSYS TCAD simulations based on three sets of process parameters with different doping doses of the n-well and p+-diffusions. The VHS offset was compared with experimental results obtained using complementary metal oxide semiconductor (CMOS)-based VHS and analyzed as a function of the input voltage. It was shown that the linear offset components are modeled adequately by resistive imbalances caused by lateral contact shifts in the nanometer range. The JFE in turn is responsible for the nonlinear effects of dominantly quadratic dependence on the input voltage. Both effects contribute additively to the overall offset. According to the simulations, the nonlinear contribution is strongly reduced at higher n-well doping concentrations.
Electromechanical performance of poly(vinylidene fluoride)/carbon nanotube composites for strain sensor applications
05 April 2012, 09:29:18
Publication year: 2012
Source:Sensors and Actuators A: Physical, Volume 178
A. Ferrreira, J.G. Rocha, A. Ansón-Casaos, M.T. Martínez, F. Vaz, S. Lanceros-Mendez
This paper reports on the piezoresistive behavior of polymer based nanocomposites, composed of poly(vinylidene fluoride) – PVDF and carbon nanotubes (CNTs). The samples were prepared by hot pressing with CNT sample concentrations up to loadings of 10wt.%. The phase present in the polymer was the α-phase. The correlation between the electrical resistivity and mechanical solicitations is presented in this work for the different composites and for varying mechanical solicitations. The values of the gauge factor, ranging up to 6.2, and the linearity of the response over a wide strain range shows the viability of these materials to be used as piezoresistive sensors. The stability of the signal, the time response and the temperature behavior were also evaluated. The observed electrical and electromechanical behavior can be explained in the framework of the percolation theory.
Source:Sensors and Actuators A: Physical, Volume 178
A. Ferrreira, J.G. Rocha, A. Ansón-Casaos, M.T. Martínez, F. Vaz, S. Lanceros-Mendez
This paper reports on the piezoresistive behavior of polymer based nanocomposites, composed of poly(vinylidene fluoride) – PVDF and carbon nanotubes (CNTs). The samples were prepared by hot pressing with CNT sample concentrations up to loadings of 10wt.%. The phase present in the polymer was the α-phase. The correlation between the electrical resistivity and mechanical solicitations is presented in this work for the different composites and for varying mechanical solicitations. The values of the gauge factor, ranging up to 6.2, and the linearity of the response over a wide strain range shows the viability of these materials to be used as piezoresistive sensors. The stability of the signal, the time response and the temperature behavior were also evaluated. The observed electrical and electromechanical behavior can be explained in the framework of the percolation theory.
Numerical study of a ferrule-top cantilever optical fiber sensor for wind-tunnel applications and comparison with experimental results
05 April 2012, 09:29:18
Publication year: 2012
Source:Sensors and Actuators A: Physical, Volume 178
A. Cipullo, G. Gruca, K. Heeck, F. De Filippis, D. Iannuzzi, A. Minardo, L. Zeni
We present a numerical analysis of an air flow velocity sensor based on a fiber-optic ferrule-top cantilever. The device forms a low-finesse Fabry–Perot interferometer, with one of the two reflecting surfaces constituted by a cantilever beam. Under the effect of the flow pressure, the cantilever bends producing a change in the cavity length of the Fabry–Perot and therefore a modification of its optical response. The numerical analysis, performed by use of finite-element method (FEM), is then compared with a set of experimental results obtained in a small wind-tunnel.
Source:Sensors and Actuators A: Physical, Volume 178
A. Cipullo, G. Gruca, K. Heeck, F. De Filippis, D. Iannuzzi, A. Minardo, L. Zeni
We present a numerical analysis of an air flow velocity sensor based on a fiber-optic ferrule-top cantilever. The device forms a low-finesse Fabry–Perot interferometer, with one of the two reflecting surfaces constituted by a cantilever beam. Under the effect of the flow pressure, the cantilever bends producing a change in the cavity length of the Fabry–Perot and therefore a modification of its optical response. The numerical analysis, performed by use of finite-element method (FEM), is then compared with a set of experimental results obtained in a small wind-tunnel.
ZnO nanorods grown on polymer substrates as UV photodetectors
05 April 2012, 09:29:18
Publication year: 2012
Source:Sensors and Actuators A: Physical, Volume 178
I-Chuan Yao, Tseung-Yuen Tseng, Pang Lin
Vertical well-aligned and uniform ZnO nanorods were successfully prepared on low cost and flexible PET polymer substrate by aqueous solution method under various growth conditions. Current–voltage (I–V) and current–time (I–t) relationships measurements demonstrate that the photocurrent can be increased by more than 25 times upon UV illumination (λ =365nm) with a power density of 70μW/cm2. The photocurrents can be repeatedly and reproducibly switched by modulating UV exposure with power densities of 25–70μW/cm2. The fast response time (100s) and rapid recovery time (120s) are achieved in UV turn-on/off switching measurements. Owing to the good performance including mechanical flexibility, nondestructive properties, high reliability and multilevel photoresponse, the well-aligned ZnO nanorods grown on transparent and flexible PET polymer substrates have high potential for UV photodetector applications.
Source:Sensors and Actuators A: Physical, Volume 178
I-Chuan Yao, Tseung-Yuen Tseng, Pang Lin
Vertical well-aligned and uniform ZnO nanorods were successfully prepared on low cost and flexible PET polymer substrate by aqueous solution method under various growth conditions. Current–voltage (I–V) and current–time (I–t) relationships measurements demonstrate that the photocurrent can be increased by more than 25 times upon UV illumination (λ =365nm) with a power density of 70μW/cm2. The photocurrents can be repeatedly and reproducibly switched by modulating UV exposure with power densities of 25–70μW/cm2. The fast response time (100s) and rapid recovery time (120s) are achieved in UV turn-on/off switching measurements. Owing to the good performance including mechanical flexibility, nondestructive properties, high reliability and multilevel photoresponse, the well-aligned ZnO nanorods grown on transparent and flexible PET polymer substrates have high potential for UV photodetector applications.
Gold nano-particle-based thermal sensors fabricated using microspotting and DEP techniques
05 April 2012, 09:29:18
Publication year: 2012
Source:Sensors and Actuators A: Physical, Volume 178
Siu Ling Leung, Minglin Li, Wen J. Li, John D. Mai
We show that pearl chains of gold nano-particles (Au NPs) are formed consistently between microelectrodes by combining microspotting and dielectrophoretic (DEP) techniques. Experimental results on various sized Au particles and DEP parameters, including voltage and frequency, are reported in this paper to explore the critical parameters in controlling the pearl chain formation (PCF) process between microelectrodes. PCF is observed from 10kHz to 5MHz for 100nm diameter Au NPs, and 100kHz to 10MHz for 10nm Au NPs. Variations in formation rate are detected when the applied voltage and particle size varies. At higher voltages, PCF occurs at a higher rate and the formation time decreases. The optimum frequency for Au NPs PCF shifts to a higher frequency region when the particle size decreases. Theoretical analysis is carried out by calculating the DEP force with AC electrokinetics to explain the observations at DEP frequencies ranging from 10Hz to 10MHz. Finally, Au NP chains formed between the microelectrodes are shown to vary in resistance consistent with predictions for a simplified model of an impinging jet system, indicating that these Au particle sensors could potentially be used to precisely measure localized temperatures and other localized thermal phenomena.
Source:Sensors and Actuators A: Physical, Volume 178
Siu Ling Leung, Minglin Li, Wen J. Li, John D. Mai
We show that pearl chains of gold nano-particles (Au NPs) are formed consistently between microelectrodes by combining microspotting and dielectrophoretic (DEP) techniques. Experimental results on various sized Au particles and DEP parameters, including voltage and frequency, are reported in this paper to explore the critical parameters in controlling the pearl chain formation (PCF) process between microelectrodes. PCF is observed from 10kHz to 5MHz for 100nm diameter Au NPs, and 100kHz to 10MHz for 10nm Au NPs. Variations in formation rate are detected when the applied voltage and particle size varies. At higher voltages, PCF occurs at a higher rate and the formation time decreases. The optimum frequency for Au NPs PCF shifts to a higher frequency region when the particle size decreases. Theoretical analysis is carried out by calculating the DEP force with AC electrokinetics to explain the observations at DEP frequencies ranging from 10Hz to 10MHz. Finally, Au NP chains formed between the microelectrodes are shown to vary in resistance consistent with predictions for a simplified model of an impinging jet system, indicating that these Au particle sensors could potentially be used to precisely measure localized temperatures and other localized thermal phenomena.
Design, fabrication and characterization of high temperature piezoelectric vibration sensor using YCOB crystals
05 April 2012, 09:29:18
Publication year: 2012
Source:Sensors and Actuators A: Physical, Volume 178
Kyungrim Kim, Shujun Zhang, Giovanni Salazar, Xiaoning Jiang
A shear-mode piezoelectric accelerometer using YCa4O(BO3)3 single crystals (YCOB) was designed, fabricated and successfully tested for high temperature vibration sensing applications. Dynamic modeling of the accelerometer was presented first, followed by YCOB single crystal sample preparation, sensor assembly and experimental setup establishment. The prototyped accelerometer was tested at temperatures ranging from room temperature to 1000°C and at frequencies ranging from 50Hz to 350Hz. The sensitivity of the prototype was found to be 5.9±0.06pC/g throughout the tested frequency, temperature and acceleration ranges. In addition, YCOB piezoelectric accelerometers retained the same sensitivity at 1000°C for a dwell time of 9h, exhibiting a high stability and reliability.
Source:Sensors and Actuators A: Physical, Volume 178
Kyungrim Kim, Shujun Zhang, Giovanni Salazar, Xiaoning Jiang
A shear-mode piezoelectric accelerometer using YCa4O(BO3)3 single crystals (YCOB) was designed, fabricated and successfully tested for high temperature vibration sensing applications. Dynamic modeling of the accelerometer was presented first, followed by YCOB single crystal sample preparation, sensor assembly and experimental setup establishment. The prototyped accelerometer was tested at temperatures ranging from room temperature to 1000°C and at frequencies ranging from 50Hz to 350Hz. The sensitivity of the prototype was found to be 5.9±0.06pC/g throughout the tested frequency, temperature and acceleration ranges. In addition, YCOB piezoelectric accelerometers retained the same sensitivity at 1000°C for a dwell time of 9h, exhibiting a high stability and reliability.
Thermal conductivity detector compact Spice model based on experimental measurements and 3D simulations
05 April 2012, 09:29:18
Publication year: 2012
Source:Sensors and Actuators A: Physical, Volume 178
F. Rastrello, P. Placidi, A. Scorzoni, E. Cozzani, M. Messina, I. Elmi, S. Zampolli, G.C. Cardinali
In this paper a novel compact Spice model of a thermal conductivity detector (TCD) is presented and validated against an extensive experimental characterization and 3D simulations. The TCD used is based on the ultra low power (ULP) technology and it has been electrically characterized with different helium and nitrogen gas flow rates, via a microfluidic experimental setup. Extraction of global electro-thermal parameters, exploited for the development of the Spice model, has been performed by using both 3D electro-thermal FEM simulations made with COMSOL Multyphisics® and experimental measurements. The first result we discuss is the good agreement between 3D FEM simulations of the device, made with COMSOL Multiphysics®, and the experiments, with a maximum error of 2.9% for He flow rate of 9sccm and around 1.8% for the N2 carrier gas at each considered flow rate. We have demonstrated that the Spice model can reproduce very well the FEM simulations for all the gas flow rates and the operating power values taken into consideration, using simulation parameters extracted from FEM data itself. Results of the Spice model compare well also with the real behavior of a TCD device for both the used gases, using parameters either extracted from FEM simulations or calibrated with experimental measurements, with a maximum error of 0.9% for the He flow rate of 0.29sccm and a maximum error of 0.8% for the N2 flow rate of 10.3sccm. The novelty of the proposed approach is to provide a useful instrument for the electronic designer who wants to incorporate a Spice electro-thermal model in a simulation environment. The TCD can initially be simulated with an electro-thermal FEM model for a reduced number of operating conditions, then the Spice model can be calibrated and exploited for the electronic design. After device production, the Spice model can eventually be optimized using the experimental results, thus improving the accuracy of the whole electronic circuit simulation.
Source:Sensors and Actuators A: Physical, Volume 178
F. Rastrello, P. Placidi, A. Scorzoni, E. Cozzani, M. Messina, I. Elmi, S. Zampolli, G.C. Cardinali
In this paper a novel compact Spice model of a thermal conductivity detector (TCD) is presented and validated against an extensive experimental characterization and 3D simulations. The TCD used is based on the ultra low power (ULP) technology and it has been electrically characterized with different helium and nitrogen gas flow rates, via a microfluidic experimental setup. Extraction of global electro-thermal parameters, exploited for the development of the Spice model, has been performed by using both 3D electro-thermal FEM simulations made with COMSOL Multyphisics® and experimental measurements. The first result we discuss is the good agreement between 3D FEM simulations of the device, made with COMSOL Multiphysics®, and the experiments, with a maximum error of 2.9% for He flow rate of 9sccm and around 1.8% for the N2 carrier gas at each considered flow rate. We have demonstrated that the Spice model can reproduce very well the FEM simulations for all the gas flow rates and the operating power values taken into consideration, using simulation parameters extracted from FEM data itself. Results of the Spice model compare well also with the real behavior of a TCD device for both the used gases, using parameters either extracted from FEM simulations or calibrated with experimental measurements, with a maximum error of 0.9% for the He flow rate of 0.29sccm and a maximum error of 0.8% for the N2 flow rate of 10.3sccm. The novelty of the proposed approach is to provide a useful instrument for the electronic designer who wants to incorporate a Spice electro-thermal model in a simulation environment. The TCD can initially be simulated with an electro-thermal FEM model for a reduced number of operating conditions, then the Spice model can be calibrated and exploited for the electronic design. After device production, the Spice model can eventually be optimized using the experimental results, thus improving the accuracy of the whole electronic circuit simulation.
Variation in phase transformation paths of NiTi films as a function of film thickness
05 April 2012, 09:29:18
Publication year: 2012
Source:Sensors and Actuators A: Physical, Volume 178
Ashvani Kumar, Devendra Singh, Davinder Kaur
NiTi shape memory alloy thin films of different thickness have been grown on silicon (100) substrates using dc magnetron co-sputtering. Differences in microstructure such as crystallinity, grain size, grain size distribution and surface roughness of these films were studied using X-ray diffractrometer (XRD) and atomic force microscope (AFM). The influence of film thickness on phase transformation behavior was studied using four probe resistivity method. NiTi films exhibited mainly three kinds of transformation behaviors i.e. incomplete, constrained and complete austenite to martensite phase transformation for the films having lower (≤300nm), intermediate (0.6–1.1μm) and higher (2.3μm) thickness, respectively. It is proposed that the constrained or incomplete transformation could be due to the special constraints (resistance force) introduced by the inter-diffusion of film, higher number of grain boundaries and increased level of the intrinsic defects. The level of actuation force can be tuned by choosing the different transformation paths that can have immense technological importance in the fabrication of various types of MEMS devices.
Source:Sensors and Actuators A: Physical, Volume 178
Ashvani Kumar, Devendra Singh, Davinder Kaur
NiTi shape memory alloy thin films of different thickness have been grown on silicon (100) substrates using dc magnetron co-sputtering. Differences in microstructure such as crystallinity, grain size, grain size distribution and surface roughness of these films were studied using X-ray diffractrometer (XRD) and atomic force microscope (AFM). The influence of film thickness on phase transformation behavior was studied using four probe resistivity method. NiTi films exhibited mainly three kinds of transformation behaviors i.e. incomplete, constrained and complete austenite to martensite phase transformation for the films having lower (≤300nm), intermediate (0.6–1.1μm) and higher (2.3μm) thickness, respectively. It is proposed that the constrained or incomplete transformation could be due to the special constraints (resistance force) introduced by the inter-diffusion of film, higher number of grain boundaries and increased level of the intrinsic defects. The level of actuation force can be tuned by choosing the different transformation paths that can have immense technological importance in the fabrication of various types of MEMS devices.
High-speed CMOS magnetic angle sensor based on miniaturized circular vertical Hall devices
05 April 2012, 09:29:18
Publication year: 2012
Source:Sensors and Actuators A: Physical, Volume 178
M. Banjevic, B. Furrer, M. Blagojevic, R.S. Popovic
We present a high-speed CMOS integrated magnetic angle sensor consisting of two 8-contact circular vertical Hall devices (CVHD). The biasing and sensing of the Hall voltage is rotated clockwise for the first device, and counter clockwise for the second one. The output voltages of the two devices are processed separately in two channels and they act as a reference signal one to another. The output of the sensor is a pulse width modulated signal whose width is proportional to twice the angle enclosed between the in-plane magnetic induction vector and the reference axis. The information on the angle is directly present in the pulse width modulated signal without the need for either arctg function implementation or complicated angle detection algorithms. The sensor's concept together with optimized interface and signal conditioning electronics allows for very high bandwidth. The measurement range of the sensor is 0–90°, with possibility for further extension. The sensor achieves tracking the angle of the in-plane magnetic vector oscillating at up to 200kHz (12,000,000rpm), or equivalently, having an angular speed of 628,000rad/s. To our knowledge, this is the highest bandwidth of a completely CMOS integrated magnetic angle sensor. The maximum absolute error for these speeds is ±4° without any calibration, the response time is 1μs, and the angular resolution is 0.5°.
Source:Sensors and Actuators A: Physical, Volume 178
M. Banjevic, B. Furrer, M. Blagojevic, R.S. Popovic
We present a high-speed CMOS integrated magnetic angle sensor consisting of two 8-contact circular vertical Hall devices (CVHD). The biasing and sensing of the Hall voltage is rotated clockwise for the first device, and counter clockwise for the second one. The output voltages of the two devices are processed separately in two channels and they act as a reference signal one to another. The output of the sensor is a pulse width modulated signal whose width is proportional to twice the angle enclosed between the in-plane magnetic induction vector and the reference axis. The information on the angle is directly present in the pulse width modulated signal without the need for either arctg function implementation or complicated angle detection algorithms. The sensor's concept together with optimized interface and signal conditioning electronics allows for very high bandwidth. The measurement range of the sensor is 0–90°, with possibility for further extension. The sensor achieves tracking the angle of the in-plane magnetic vector oscillating at up to 200kHz (12,000,000rpm), or equivalently, having an angular speed of 628,000rad/s. To our knowledge, this is the highest bandwidth of a completely CMOS integrated magnetic angle sensor. The maximum absolute error for these speeds is ±4° without any calibration, the response time is 1μs, and the angular resolution is 0.5°.
Experimental and theoretical studies on MEMS piezoelectric vibrational energy harvesters with mass loading
05 April 2012, 09:29:18
Publication year: 2012
Source:Sensors and Actuators A: Physical, Volume 178
Robert Andosca, T. Gus McDonald, Vincent Genova, Steven Rosenberg, Joseph Keating, Cole Benedixen, Junru Wu
Experimental and theoretical investigations on micro-scale multi-morph cantilever piezoelectric vibrational energy harvesters (PZEHs) of the MicroElectroMechanical Systems (MEMS) are presented. The core body of a PZEH is a “multi-morph” cantilever, where one end is clamped to a base and the other end is free. This “fixed-free” cantilever system including a proof-mass (also called the end-mass) on the free-end that can oscillate with the multi-layer cantilever under continuous sinusoidal excitations of the base motion. A partial differential equation (PDE) describing the flexural wave propagating in the multi-morph cantilever is reviewed. The resonance frequencies of the lowest mode of a multi-morph cantilever PZEH for some ratios of the proof-mass to cantilever mass are calculated by either solving the PDE numerically or using a lumped-element model as a damped simple harmonic oscillator; their results are in good agreement (disparity≤0.5%). Experimentally, MEMS PZEHs were constructed using the standard micro-fabrication technique. Calculated fundamental resonance frequencies, output electric voltage amplitude V and output power amplitude P with an optimum load compared favorably with their corresponding measured values; the differences are all less than 4%. Furthermore, a MEMS PZEH prototype was shown resonating at 58.0±2.0Hz under 0.7 g (g =9.81m/s2) external excitations, corresponding peak power reaches 63μW with an output load impedance Z of 85kΩ. This micro-power generator enabled successfully a wireless sensor node with the integrated sensor, radio frequency (RF) radio, power management electronics, and an advanced thin-film lithium-ion rechargeable battery for power storage at the 2011 Sensors Expo and Conference held in Chicago, IL. In addition, at 58Hz and 0.5, 1.0 g excitations power levels of 32, and 128μW were also obtained, and all these three power levels demonstrated to be proportional to the square of the acceleration amplitude as predicted by the theory. The reported P at the fundamental resonance frequency f 1 and acceleration G-level, reached the highest “Figure of Merit” [power density×(bandwidth/resonant frequency)] achieved amongst those reported in the up-to-date literature for high quality factor Q f MEMS PZEH devices.
Source:Sensors and Actuators A: Physical, Volume 178
Robert Andosca, T. Gus McDonald, Vincent Genova, Steven Rosenberg, Joseph Keating, Cole Benedixen, Junru Wu
Experimental and theoretical investigations on micro-scale multi-morph cantilever piezoelectric vibrational energy harvesters (PZEHs) of the MicroElectroMechanical Systems (MEMS) are presented. The core body of a PZEH is a “multi-morph” cantilever, where one end is clamped to a base and the other end is free. This “fixed-free” cantilever system including a proof-mass (also called the end-mass) on the free-end that can oscillate with the multi-layer cantilever under continuous sinusoidal excitations of the base motion. A partial differential equation (PDE) describing the flexural wave propagating in the multi-morph cantilever is reviewed. The resonance frequencies of the lowest mode of a multi-morph cantilever PZEH for some ratios of the proof-mass to cantilever mass are calculated by either solving the PDE numerically or using a lumped-element model as a damped simple harmonic oscillator; their results are in good agreement (disparity≤0.5%). Experimentally, MEMS PZEHs were constructed using the standard micro-fabrication technique. Calculated fundamental resonance frequencies, output electric voltage amplitude V and output power amplitude P with an optimum load compared favorably with their corresponding measured values; the differences are all less than 4%. Furthermore, a MEMS PZEH prototype was shown resonating at 58.0±2.0Hz under 0.7 g (g =9.81m/s2) external excitations, corresponding peak power reaches 63μW with an output load impedance Z of 85kΩ. This micro-power generator enabled successfully a wireless sensor node with the integrated sensor, radio frequency (RF) radio, power management electronics, and an advanced thin-film lithium-ion rechargeable battery for power storage at the 2011 Sensors Expo and Conference held in Chicago, IL. In addition, at 58Hz and 0.5, 1.0 g excitations power levels of 32, and 128μW were also obtained, and all these three power levels demonstrated to be proportional to the square of the acceleration amplitude as predicted by the theory. The reported P at the fundamental resonance frequency f 1 and acceleration G-level, reached the highest “Figure of Merit” [power density×(bandwidth/resonant frequency)] achieved amongst those reported in the up-to-date literature for high quality factor Q f MEMS PZEH devices.
Capacitive humidity sensors based on the dielectrophoretically manipulated ZnO nanorods
05 April 2012, 09:29:18
Publication year: 2012
Source:Sensors and Actuators A: Physical, Volume 178
Leping Chen, Jian Zhang
In this paper, the capacitive relative humidity sensors based on dielectrophoretically manipulated ZnO nanostructure were constructed and studied. The humidity-sensitive ZnO nanorods were first synthesized by the thermal decomposition technique and deposited among the micromachined electrodes pairs via dielectrophoretic manipulation. The manipulated samples were detected as the capacitive sensors in which the nanostructured ZnO acted as the sensing elements. The capacitive humidity sensors were constructed by detecting the variations of the ZnO dielectric constant changing with the humidity environment. The results showed that the sensor had high humidity sensitivity, good stability, fast response/recovery time and well reproducibility. The dielectrophoresis manipulation can also improve the sensitivity of the sensor efficiently.
Source:Sensors and Actuators A: Physical, Volume 178
Leping Chen, Jian Zhang
In this paper, the capacitive relative humidity sensors based on dielectrophoretically manipulated ZnO nanostructure were constructed and studied. The humidity-sensitive ZnO nanorods were first synthesized by the thermal decomposition technique and deposited among the micromachined electrodes pairs via dielectrophoretic manipulation. The manipulated samples were detected as the capacitive sensors in which the nanostructured ZnO acted as the sensing elements. The capacitive humidity sensors were constructed by detecting the variations of the ZnO dielectric constant changing with the humidity environment. The results showed that the sensor had high humidity sensitivity, good stability, fast response/recovery time and well reproducibility. The dielectrophoresis manipulation can also improve the sensitivity of the sensor efficiently.
A temperature sensor based on a MWCNT/SEBS nanocomposite
05 April 2012, 09:29:18
Publication year: 2012
Source:Sensors and Actuators A: Physical, Volume 178
G. Matzeu, A. Pucci, S. Savi, M. Romanelli, F. Di Francesco
The fabrication of a temperature sensor based on multi-walled carbon nanotubes (MWCNTs)/styrene-b-(ethylene-co-butylene)-b-styrene (SEBS) triblock copolymer composite is reported. The device was realized by drop casting 10μl of a MWCNTs dispersion in a toluene solution of SEBS onto gold electrodes fabricated onto a polyimide support. Thermogravimetric and electrical resistance measurements highlighted a good reproducibility of film composition and sensing properties. A negative temperature coefficient with an absolute value comparable to the highest values in metals was measured when a substantial amount of MWCNTs was incorporated into the nanocomposite (40% by weight), and a five-fold increase was observed close to the percolation threshold. Though such sensitivity seems to be partly lost after the first heating, the results allowed us to be optimistic about the feasibility of realizing nanocomposite films with temperature sensitivities comparable to that of common thermistors in the range 20–60°C.
Source:Sensors and Actuators A: Physical, Volume 178
G. Matzeu, A. Pucci, S. Savi, M. Romanelli, F. Di Francesco
The fabrication of a temperature sensor based on multi-walled carbon nanotubes (MWCNTs)/styrene-b-(ethylene-co-butylene)-b-styrene (SEBS) triblock copolymer composite is reported. The device was realized by drop casting 10μl of a MWCNTs dispersion in a toluene solution of SEBS onto gold electrodes fabricated onto a polyimide support. Thermogravimetric and electrical resistance measurements highlighted a good reproducibility of film composition and sensing properties. A negative temperature coefficient with an absolute value comparable to the highest values in metals was measured when a substantial amount of MWCNTs was incorporated into the nanocomposite (40% by weight), and a five-fold increase was observed close to the percolation threshold. Though such sensitivity seems to be partly lost after the first heating, the results allowed us to be optimistic about the feasibility of realizing nanocomposite films with temperature sensitivities comparable to that of common thermistors in the range 20–60°C.
Torsion sensor based on the coil-less fluxgate effect
05 April 2012, 09:29:18
Publication year: 2012
Source:Sensors and Actuators A: Physical, Volume 178
S. Atalay, N. Bayri, A. Fidan, F.E. Atalay, V. Yagmur
The torsion dependence of the coil-less fluxgate properties of amorphous (Co0.94Fe0.06)72.5Si12.5B15 wire was investigated. The results show that the second harmonic of the output voltage from the wire ends, U wire, varied linearly at the ±30π rad/m torsion range for as-cast wire and ±5π rad/m torsion range for annealed wire. It was also found that if the sample was annealed at higher torsion, the curve shifted negatively or positively depending on the direction of torsion applied during the annealing. Most importantly, the output signal changed its sign as the direction of external torsion reversed, and therefore the proposed torsion sensor could detect whether torsion was in the negative or positive (clockwise or anti-clockwise) direction.
Source:Sensors and Actuators A: Physical, Volume 178
S. Atalay, N. Bayri, A. Fidan, F.E. Atalay, V. Yagmur
The torsion dependence of the coil-less fluxgate properties of amorphous (Co0.94Fe0.06)72.5Si12.5B15 wire was investigated. The results show that the second harmonic of the output voltage from the wire ends, U wire, varied linearly at the ±30π rad/m torsion range for as-cast wire and ±5π rad/m torsion range for annealed wire. It was also found that if the sample was annealed at higher torsion, the curve shifted negatively or positively depending on the direction of torsion applied during the annealing. Most importantly, the output signal changed its sign as the direction of external torsion reversed, and therefore the proposed torsion sensor could detect whether torsion was in the negative or positive (clockwise or anti-clockwise) direction.
Non-contact temperature determination of embedded magnetic phases of hard coatings by exploitation of the magnetic hysteresis
05 April 2012, 09:29:18
Publication year: 2012
Source:Sensors and Actuators A: Physical, Volume 178
Claas Thede, Steffen Chemnitz, Iulian Teliban, Christoph Bechtold, Christian Klever, Michael Stüber, Eckhard Quandt
A non-contact temperature sensor is described which is based on the temperature dependency of the hysteresis of a magnetic phase embedded in a non-magnetic hard coating. For the measurement principle the technique of frequency mixing is used, with extension toward phase sensitivity as indicator for the temperature. The sensor's capabilities such as selectivity and sensitivity are investigated on TiN–FeCo magnetic multilayers. The sensor has been proven for temperatures up to 500°C and shows capabilities for higher temperatures.
Source:Sensors and Actuators A: Physical, Volume 178
Claas Thede, Steffen Chemnitz, Iulian Teliban, Christoph Bechtold, Christian Klever, Michael Stüber, Eckhard Quandt
A non-contact temperature sensor is described which is based on the temperature dependency of the hysteresis of a magnetic phase embedded in a non-magnetic hard coating. For the measurement principle the technique of frequency mixing is used, with extension toward phase sensitivity as indicator for the temperature. The sensor's capabilities such as selectivity and sensitivity are investigated on TiN–FeCo magnetic multilayers. The sensor has been proven for temperatures up to 500°C and shows capabilities for higher temperatures.
Deposition and characterization of thick graded index SixOyFz films with low stress
05 April 2012, 09:29:18
Publication year: 2012
Source:Sensors and Actuators A: Physical, Volume 178
Aron Michael, Abdullah Al Hafiz, Tom Puzzer, Chee Yee Kwok
This paper develops deposition techniques that are suitable for realizing low stress thick and crack free fluorine doped graded index silica (Si x O y F z ) films by the hollow cathode plasma enhanced chemical vapour deposition (HC-PECVD) system from a mixture of SiH4/O2/CF4. Silica films are deposited by varying O2, SiH4, CF4 flow rates, and RF powers. The refractive index, stress, deposition rate, chemical bonding state and chemical composition of such films have been investigated. The results indicate that low stress thick graded index silica film can be deposited by either (i) employing RF power below a certain value, which we shall refer it as ‘threshold RF power’ or (ii) increasing O2/SiH4 flow rate ratios. The threshold RF power is found to be 200W using 50sccm of O2, and 20sccm of SiH4. At RF powers below this threshold value, no oxygen deficiency is observed in the film even at a higher CF4 flow rate. On the other hand, stressed silicon rich film results at CF4 flow rates of 10sccm when the RF power is increased to 300W. By increasing O2 flow rate to 100sccm and decreasing SiH4 flow rate to 15sccm, the plasma at 300W RF power remains not oxygen deficient for up to 50sccm of CF4 flow rates. These deposition parameters are employed to deposit 28μm thick 1-D GRIN lens with a net stress of only 30MPa (compressive), and the graded index profile is optically tested. Moreover, the effect of moisture on such films has been investigated and a simple preventative measure is proposed.
Source:Sensors and Actuators A: Physical, Volume 178
Aron Michael, Abdullah Al Hafiz, Tom Puzzer, Chee Yee Kwok
This paper develops deposition techniques that are suitable for realizing low stress thick and crack free fluorine doped graded index silica (Si x O y F z ) films by the hollow cathode plasma enhanced chemical vapour deposition (HC-PECVD) system from a mixture of SiH4/O2/CF4. Silica films are deposited by varying O2, SiH4, CF4 flow rates, and RF powers. The refractive index, stress, deposition rate, chemical bonding state and chemical composition of such films have been investigated. The results indicate that low stress thick graded index silica film can be deposited by either (i) employing RF power below a certain value, which we shall refer it as ‘threshold RF power’ or (ii) increasing O2/SiH4 flow rate ratios. The threshold RF power is found to be 200W using 50sccm of O2, and 20sccm of SiH4. At RF powers below this threshold value, no oxygen deficiency is observed in the film even at a higher CF4 flow rate. On the other hand, stressed silicon rich film results at CF4 flow rates of 10sccm when the RF power is increased to 300W. By increasing O2 flow rate to 100sccm and decreasing SiH4 flow rate to 15sccm, the plasma at 300W RF power remains not oxygen deficient for up to 50sccm of CF4 flow rates. These deposition parameters are employed to deposit 28μm thick 1-D GRIN lens with a net stress of only 30MPa (compressive), and the graded index profile is optically tested. Moreover, the effect of moisture on such films has been investigated and a simple preventative measure is proposed.
Effects of wire properties on the field-tunable behaviour of continuous-microwire composites
05 April 2012, 09:29:18
Publication year: 2012
Source:Sensors and Actuators A: Physical, Volume 178
F.X. Qin, H.X. Peng, M.H. Phan, L.V. Panina, M. Ipatov, A. Zhukov
The microwire composites consisting of continuous Co-rich amorphous glass-coated ferromagnetic microwires embedded in a E-glass prepreg matrix were fabricated, and the influences of wire periodicity (b), composition and radius on the field-tunable properties have been systematically investigated in a broad microwave frequency range of 0.9–18GHz. It has been found that the field tunability, effective operational frequency and field of the composites are strongly dependent on these factors. With decreasing b from 15 to 7mm, the field tunability of effective permittivity (n ɛ ) increases from 0.77% to 16%m/A by more than 20 times. The detected cups and resonances of the transmission and reflection spectra are identified. Their changes with wire periodicity have been shown to be due to a combination of the dielectric and magnetic response arising from the interactions between microwave and microwires and microwires by themselves. The best possible field tunability occurs below the plasma frequency. The effective magnetic field for realisation of the field-tunable properties has been found to be about 500A/m, which is associated with the anisotropy field. In addition, field tunability is found to be positively correlated with the magnetic softness and GMI properties of the wire fillers, which are determined by the wire composition and geometry. These findings are of practical importance in developing multifunctional microwire composites for a broad range of engineering applications, such as structural health monitoring, NDT and microwave tunable devices.
Source:Sensors and Actuators A: Physical, Volume 178
F.X. Qin, H.X. Peng, M.H. Phan, L.V. Panina, M. Ipatov, A. Zhukov
The microwire composites consisting of continuous Co-rich amorphous glass-coated ferromagnetic microwires embedded in a E-glass prepreg matrix were fabricated, and the influences of wire periodicity (b), composition and radius on the field-tunable properties have been systematically investigated in a broad microwave frequency range of 0.9–18GHz. It has been found that the field tunability, effective operational frequency and field of the composites are strongly dependent on these factors. With decreasing b from 15 to 7mm, the field tunability of effective permittivity (n ɛ ) increases from 0.77% to 16%m/A by more than 20 times. The detected cups and resonances of the transmission and reflection spectra are identified. Their changes with wire periodicity have been shown to be due to a combination of the dielectric and magnetic response arising from the interactions between microwave and microwires and microwires by themselves. The best possible field tunability occurs below the plasma frequency. The effective magnetic field for realisation of the field-tunable properties has been found to be about 500A/m, which is associated with the anisotropy field. In addition, field tunability is found to be positively correlated with the magnetic softness and GMI properties of the wire fillers, which are determined by the wire composition and geometry. These findings are of practical importance in developing multifunctional microwire composites for a broad range of engineering applications, such as structural health monitoring, NDT and microwave tunable devices.
Silicon anisotropic etching in TMAH solutions containing alcohol and surfactant additives
05 April 2012, 09:29:18
Publication year: 2012
Source:Sensors and Actuators A: Physical, Volume 178
Irena Zubel, Małgorzata Kramkowska, Krzysztof Rola
Wet chemical etching of Si(100) and Si(110) wafers in TMAH solutions containing Triton X-100 and alcohol additives was studied in a wide range of alcohol concentrations. TMAH solutions containing butanol-2 and ternary solutions composed of TMAH+Triton+alcohol, used in the experiments, had not been investigated before. The phenomena associated with the presence of surfactant and alcohol additives in etching solutions were analyzed and the mechanism including co-solving of surfactant molecules in alcohol and interplay in the adsorbing mechanism was proposed. The influence of these phenomena on the etching rates and morphologies of Si(100) and Si(110) was discussed. The addition of alcohol, especially butanol-2, to a TMAH solution resulted in significant improvement of the etched surface finish. The roughness of Si(110) surfaces etched in TMAH+butanol solutions was superior to the roughness of the surfaces etched in TMAH+Triton. The best surface roughness parameters of Si(110) (Ra=0.0322μm and RMS=0.0549μm), measured with an optical profilometer on the area of 1.6mm×1.6mm, were achieved after etching in a ternary solution of TMAH+Triton+butanol. This solution appears to be a good candidate in applications where high quality finish of etched surfaces is required on a substantially high area.
Source:Sensors and Actuators A: Physical, Volume 178
Irena Zubel, Małgorzata Kramkowska, Krzysztof Rola
Wet chemical etching of Si(100) and Si(110) wafers in TMAH solutions containing Triton X-100 and alcohol additives was studied in a wide range of alcohol concentrations. TMAH solutions containing butanol-2 and ternary solutions composed of TMAH+Triton+alcohol, used in the experiments, had not been investigated before. The phenomena associated with the presence of surfactant and alcohol additives in etching solutions were analyzed and the mechanism including co-solving of surfactant molecules in alcohol and interplay in the adsorbing mechanism was proposed. The influence of these phenomena on the etching rates and morphologies of Si(100) and Si(110) was discussed. The addition of alcohol, especially butanol-2, to a TMAH solution resulted in significant improvement of the etched surface finish. The roughness of Si(110) surfaces etched in TMAH+butanol solutions was superior to the roughness of the surfaces etched in TMAH+Triton. The best surface roughness parameters of Si(110) (Ra=0.0322μm and RMS=0.0549μm), measured with an optical profilometer on the area of 1.6mm×1.6mm, were achieved after etching in a ternary solution of TMAH+Triton+butanol. This solution appears to be a good candidate in applications where high quality finish of etched surfaces is required on a substantially high area.
Hi,
ReplyDeleteGreat ideas that I have never thought of-thank you!
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