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papers from the latest issue:
Development of polyaniline/Cu2ZnSnS4 (CZTS) thin film based heterostructure as room temperature LPG sensor
13 February 2013,
08:57:08
15 April 2013
Publication year: 2013
Source:Sensors and Actuators A: Physical, Volume 193
In this study, we report simple fabrication and room temperature liquefied petroleum gas (LPG) sensing performance of polyaniline/Cu2ZnSnS4 (CZTS) heterojunction. Synthesis of polyaniline/CZTS heterojunction was carried out by layer-by-layer deposition of CZTS followed by electrodeposition of polyaniline. The CZTS and polyaniline films were characterized using X-ray diffraction (XRD), FT-Raman, thermoemf and scanning electron microscopic (SEM) techniques. The CZTS thin film was found to be nanocrystalline with densely compact microstructure while polyaniline were amorphous with interconnected fuzzy nanofibrous architecture. The maximum gas response of 44% was observed at 0.06vol% of LPG for polyaniline/CZTS heterojunction based sensor. The LPG response of heterojunction was decreased from 44 to 12% at the relative humidity of 90%. Good stability and fast response and recovery time periods of the present heterojunction suggest that the polyaniline/CZTS heterojunction is a potential candidate for room temperature LPG sensor.
Publication year: 2013
Source:Sensors and Actuators A: Physical, Volume 193
In this study, we report simple fabrication and room temperature liquefied petroleum gas (LPG) sensing performance of polyaniline/Cu2ZnSnS4 (CZTS) heterojunction. Synthesis of polyaniline/CZTS heterojunction was carried out by layer-by-layer deposition of CZTS followed by electrodeposition of polyaniline. The CZTS and polyaniline films were characterized using X-ray diffraction (XRD), FT-Raman, thermoemf and scanning electron microscopic (SEM) techniques. The CZTS thin film was found to be nanocrystalline with densely compact microstructure while polyaniline were amorphous with interconnected fuzzy nanofibrous architecture. The maximum gas response of 44% was observed at 0.06vol% of LPG for polyaniline/CZTS heterojunction based sensor. The LPG response of heterojunction was decreased from 44 to 12% at the relative humidity of 90%. Good stability and fast response and recovery time periods of the present heterojunction suggest that the polyaniline/CZTS heterojunction is a potential candidate for room temperature LPG sensor.
Photofield effect and photoresponse properties of the transparent oxide-based BaInZnO thin-film transistors
13 February 2013,
08:57:08
15 April 2013
Publication year: 2013
Source:Sensors and Actuators A: Physical, Volume 193
The photoresponse properties of the BaInZnO (BIZO) thin film transistors were investigated by the output and transfer characteristics. The drain current of the BIZO (10% Ba) and BIZO (20% Ba) transistors in turn-on and turn-off states is significantly increased with light illumination. The photoresponse values of the BIZO (10% Ba) and BIZO (20% Ba) transistors in turn-off and turn-on states were found to be 4.56 and 6.27, respectively, while the photoresponse values of the BIZO (10% Ba) and BIZO (20% Ba) transistors in turn-off and turn-on states were found to be 6.14 and 11.714, respectively. The photoresponse values of the transistors in turn-off state are lower than that of turn-on state. This indicates that the dominant photocurrent mechanism of the BIZO transistors is based on photovoltaic effects. The photoresponse properties of the BIZO transistors were improved with the increasing doping ratio of Ba. The obtained results indicate that BIZO transistors could be used as a photosensor for optoelectronic applications.
Publication year: 2013
Source:Sensors and Actuators A: Physical, Volume 193
The photoresponse properties of the BaInZnO (BIZO) thin film transistors were investigated by the output and transfer characteristics. The drain current of the BIZO (10% Ba) and BIZO (20% Ba) transistors in turn-on and turn-off states is significantly increased with light illumination. The photoresponse values of the BIZO (10% Ba) and BIZO (20% Ba) transistors in turn-off and turn-on states were found to be 4.56 and 6.27, respectively, while the photoresponse values of the BIZO (10% Ba) and BIZO (20% Ba) transistors in turn-off and turn-on states were found to be 6.14 and 11.714, respectively. The photoresponse values of the transistors in turn-off state are lower than that of turn-on state. This indicates that the dominant photocurrent mechanism of the BIZO transistors is based on photovoltaic effects. The photoresponse properties of the BIZO transistors were improved with the increasing doping ratio of Ba. The obtained results indicate that BIZO transistors could be used as a photosensor for optoelectronic applications.
Fabrication and characterization of a double-heater based MEMS thermal flow sensor
13 February 2013,
08:57:08
15 April 2013
Publication year: 2013
Source:Sensors and Actuators A: Physical, Volume 193
This paper presents a micro flow sensor based on two heaters acting also as temperature sensors. The two heating/sensing elements of the sensor are arranged in the diagonal arms of the Wheatstone bridge and suspended in an airflow channel by solid beams. The length of the heater and the distance between the heaters were optimized by numerical modeling. The solid beams were fabricated by a heavily doped p-type silicon layer and a silicon nitride layer, which was immune to airflow disturbances and thermal noises. The experimental results indicated that the micro flow sensor with a high sensitivity of 0.30mV/(ml/min) exhibited an excellent linear response within the range of 0.5–6sccm. This micro sensor demonstrated great potentials in biological applications, micro gas chromatography systems, medical instrumentation and process control.
Publication year: 2013
Source:Sensors and Actuators A: Physical, Volume 193
This paper presents a micro flow sensor based on two heaters acting also as temperature sensors. The two heating/sensing elements of the sensor are arranged in the diagonal arms of the Wheatstone bridge and suspended in an airflow channel by solid beams. The length of the heater and the distance between the heaters were optimized by numerical modeling. The solid beams were fabricated by a heavily doped p-type silicon layer and a silicon nitride layer, which was immune to airflow disturbances and thermal noises. The experimental results indicated that the micro flow sensor with a high sensitivity of 0.30mV/(ml/min) exhibited an excellent linear response within the range of 0.5–6sccm. This micro sensor demonstrated great potentials in biological applications, micro gas chromatography systems, medical instrumentation and process control.
Highlights
► The device with two heaters working as temperature sensing elements is proposed for the first time. ► The fabrication process of the MEMS based gas flow sensor with optimum heater length and the heaters distance was presented. ► The micro gas flow sensor was applied to flow rate measurement with characterization results described and discussed.Love mode surface acoustic wave ultraviolet sensor using ZnO films deposited on 36° Y-cut LiTaO3
13 February 2013,
08:57:08
15 April 2013
Publication year: 2013
Source:Sensors and Actuators A: Physical, Volume 193
Love mode surface acoustic wave (SAW) ultraviolet (UV) sensors were fabricated through sputtering ZnO films on 36° Y-cut LiTaO3 substrate. Crystalline structure, morphology and photoluminescence (PL) of the sputtered ZnO films were characterized using X-ray diffraction, atomic force microscopy and fluorescence spectrometer. The PL spectra revealed that different defects in the ZnO films were dependent on the oxygen partial pressure during deposition. UV sensing measurements showed that at a power density of 350μWcm−2, the amplitude of the Love mode SAW UV sensor decreased up to −6.4dB with a frequency shift of ∼150kHz under a 254nm illumination. When this device was illuminated with 365nm UV light at 570μWcm−2, the amplitude of the transmission signal decreased only −2.5dB without any significant frequency shift. A frequency hopping effect during the downshift and recovery periods was identified due to the simultaneous interplays between the variations of the acoustic velocity and attenuation during the acoustic-electric interaction.
Publication year: 2013
Source:Sensors and Actuators A: Physical, Volume 193
Love mode surface acoustic wave (SAW) ultraviolet (UV) sensors were fabricated through sputtering ZnO films on 36° Y-cut LiTaO3 substrate. Crystalline structure, morphology and photoluminescence (PL) of the sputtered ZnO films were characterized using X-ray diffraction, atomic force microscopy and fluorescence spectrometer. The PL spectra revealed that different defects in the ZnO films were dependent on the oxygen partial pressure during deposition. UV sensing measurements showed that at a power density of 350μWcm−2, the amplitude of the Love mode SAW UV sensor decreased up to −6.4dB with a frequency shift of ∼150kHz under a 254nm illumination. When this device was illuminated with 365nm UV light at 570μWcm−2, the amplitude of the transmission signal decreased only −2.5dB without any significant frequency shift. A frequency hopping effect during the downshift and recovery periods was identified due to the simultaneous interplays between the variations of the acoustic velocity and attenuation during the acoustic-electric interaction.
MOEMS uniaxial accelerometer based on EpoClad/EpoCore photoresists with built-in fiber clamp
13 February 2013,
08:57:08
15 April 2013
Publication year: 2013
Source:Sensors and Actuators A: Physical, Volume 193
In this paper, a novel polymer MOEMS (micro-opto-electro-mechanical systems) accelerometer is reported. Low cost, photopatternable epoxies, EpoClad and EpoCore, are lithographically patterned through a 2 masks process to form this accelerometer in a simple and robust fabrication process. EpoClad is used for the cladding layer and EpoCore for the waveguides, fiber optic clamps and the seismic mass. Fiber optic clamping structures are presented that can be fabricated without extra process steps, and still assure both in-plane and out-of-plane clamping. The acceleration sensing principle is based on light intensity modulation by the seismic mass's position. A laser diode light source and a photodiode, connected to the sensor core through optical fibers, are used to extract the intensity variation as a function of acceleration. A vibration test was conducted to evaluate the performance of this MOEMS accelerometer.
Publication year: 2013
Source:Sensors and Actuators A: Physical, Volume 193
In this paper, a novel polymer MOEMS (micro-opto-electro-mechanical systems) accelerometer is reported. Low cost, photopatternable epoxies, EpoClad and EpoCore, are lithographically patterned through a 2 masks process to form this accelerometer in a simple and robust fabrication process. EpoClad is used for the cladding layer and EpoCore for the waveguides, fiber optic clamps and the seismic mass. Fiber optic clamping structures are presented that can be fabricated without extra process steps, and still assure both in-plane and out-of-plane clamping. The acceleration sensing principle is based on light intensity modulation by the seismic mass's position. A laser diode light source and a photodiode, connected to the sensor core through optical fibers, are used to extract the intensity variation as a function of acceleration. A vibration test was conducted to evaluate the performance of this MOEMS accelerometer.
Sensitivity enhancement of a surface plasmon resonance based fibre optic refractive index sensor utilizing an additional layer of oxides
13 February 2013,
08:57:08
15 April 2013
Publication year: 2013
Source:Sensors and Actuators A: Physical, Volume 193
We have experimentally demonstrated the capability of metal and different oxide combinations to be used in surface plasmon resonance (SPR) based fibre-optic refractive index sensor by using wavelength interrogation technique. The analysis of the sensor response is carried out using multilayered structure and geometrical optics. The configuration contains copper as a SPR active metallic layer covered by one of the three oxide layers TiO2, SiO2, and SnO2. The thickness of the copper layer is optimized to achieve the most pronounced dip at the resonance condition. The maximum sensitivity is obtained for TiO2 film. Further, increase in the thickness of the TiO2 layer increases the sensitivity of the sensor. The trend of sensitivity obtained by experimental results match qualitatively with the theoretical results obtained using the N-layer model and the ray approach. The additional advantages of oxide layer, apart from sensitivity enhancement, are protection of metallic layer from oxidation, tunability of the resonance wavelength region, biocompatibility and capability of gas sensing.
Publication year: 2013
Source:Sensors and Actuators A: Physical, Volume 193
We have experimentally demonstrated the capability of metal and different oxide combinations to be used in surface plasmon resonance (SPR) based fibre-optic refractive index sensor by using wavelength interrogation technique. The analysis of the sensor response is carried out using multilayered structure and geometrical optics. The configuration contains copper as a SPR active metallic layer covered by one of the three oxide layers TiO2, SiO2, and SnO2. The thickness of the copper layer is optimized to achieve the most pronounced dip at the resonance condition. The maximum sensitivity is obtained for TiO2 film. Further, increase in the thickness of the TiO2 layer increases the sensitivity of the sensor. The trend of sensitivity obtained by experimental results match qualitatively with the theoretical results obtained using the N-layer model and the ray approach. The additional advantages of oxide layer, apart from sensitivity enhancement, are protection of metallic layer from oxidation, tunability of the resonance wavelength region, biocompatibility and capability of gas sensing.
Pressure sensitivity of piezoresistive nickel–carbon Ni:a-C:H thin films
13 February 2013,
08:57:08
15 April 2013
Publication year: 2013
Source:Sensors and Actuators A: Physical, Volume 193
The piezoresistive effects of nickel–carbon thin films, i.e., the sensitivity to hydrostatic pressure and uniform strain, are investigated in this study. Thin films, which were obtained by reactive sputtering processes with thicknesses up to 1200nm, exhibit pressure sensitivity coefficients (PCR) about −20ppm/bar and gauge factors up to 30 on Si/SiO2 substrates. A linear change of the thin film's resistance in respect to the applied hydrostatic pressure was observed. Additionally, the temperature coefficients of resistance were determined in the range of −300 to 0ppm/K, while the temperature coefficient of the PCRs was obtained as good as 0ppm/K.
Publication year: 2013
Source:Sensors and Actuators A: Physical, Volume 193
The piezoresistive effects of nickel–carbon thin films, i.e., the sensitivity to hydrostatic pressure and uniform strain, are investigated in this study. Thin films, which were obtained by reactive sputtering processes with thicknesses up to 1200nm, exhibit pressure sensitivity coefficients (PCR) about −20ppm/bar and gauge factors up to 30 on Si/SiO2 substrates. A linear change of the thin film's resistance in respect to the applied hydrostatic pressure was observed. Additionally, the temperature coefficients of resistance were determined in the range of −300 to 0ppm/K, while the temperature coefficient of the PCRs was obtained as good as 0ppm/K.
Piezoelectric properties of PVDF/MWCNT nanofiber using near-field electrospinning
13 February 2013,
08:57:08
15 April 2013
Publication year: 2013
Source:Sensors and Actuators A: Physical, Volume 193
This study reports the use of near-field electrospinning to fabricate polyvinylidene fluoride (PVDF) piezoelectric nanofibers mixed with multiwalled-carbon nanotubes (MWCNT). This study also investigates the mechanical strength and piezoelectric characteristics of a single PVDF/MWCNT nanofiber. The morphology and polarization intensity of piezoelectric fiber can be controlled by adjusting the traveling velocity of the X–Y stage, the DC voltage, and the gap between the needle and collection plate. The optimal parameters of the PVDF solution, such as the PVDF powder weight percentage and MWCNT content, were also determined. X-ray diffraction (XRD) analysis shows a high diffraction peak at 2θ =20.8° in the piezoelectric crystal β-phase structure. ANSYS finite element analysis (FEA) software with coupled field analysis was used to realize piezoelectric actuation behavior of the PVDF fibers. A nano-indentation test (NanoIndenter XP System, MTS co.) was used to investigate Young's modulus of the PVDF fiber. Finally, the fixed–fixed beam structures of PVDF composite fibers were tested using a DC voltage supply. Comparing the polarized fiber with non-polarized fibers, the measurement of the center displacements as a function of electric field was conducted and characterized.
Publication year: 2013
Source:Sensors and Actuators A: Physical, Volume 193
This study reports the use of near-field electrospinning to fabricate polyvinylidene fluoride (PVDF) piezoelectric nanofibers mixed with multiwalled-carbon nanotubes (MWCNT). This study also investigates the mechanical strength and piezoelectric characteristics of a single PVDF/MWCNT nanofiber. The morphology and polarization intensity of piezoelectric fiber can be controlled by adjusting the traveling velocity of the X–Y stage, the DC voltage, and the gap between the needle and collection plate. The optimal parameters of the PVDF solution, such as the PVDF powder weight percentage and MWCNT content, were also determined. X-ray diffraction (XRD) analysis shows a high diffraction peak at 2θ =20.8° in the piezoelectric crystal β-phase structure. ANSYS finite element analysis (FEA) software with coupled field analysis was used to realize piezoelectric actuation behavior of the PVDF fibers. A nano-indentation test (NanoIndenter XP System, MTS co.) was used to investigate Young's modulus of the PVDF fiber. Finally, the fixed–fixed beam structures of PVDF composite fibers were tested using a DC voltage supply. Comparing the polarized fiber with non-polarized fibers, the measurement of the center displacements as a function of electric field was conducted and characterized.
Comparative displacement study of bilayer actuators comprising of conducting polymers, fabricated from polypyrrole, poly(3,4-ethylenedioxythiophene) or poly(3,4-propylenedioxythiophene)
13 February 2013,
08:57:08
15 April 2013
Publication year: 2013
Source:Sensors and Actuators A: Physical, Volume 193
The stress gradient generated due to electrochemical oxidation/reduction of a conducting polymer in a bilayer actuator causes a bending movement. Here we report a comparative study of the displacement of bilayer actuators prepared using different conducting polymers. The effects of conducting polymers obtained from electrochemical or chemical synthesis route: different polymers (polypyrrole (PPy), poly(3,4-ethylenedioxythiophene) PEDOT and poly(3,3-dihexyl-3-4-dihydro-2H-thieno[3,4b][1,4]-dioxepine [PProDOT(Hx)2]); and different electrolytes (0.1M lithium trifluromethanesulfonate/propylenecarbonate (LiTFSI/PC) and 1-ethyl-3-methyl imidazolium trifluromethanesulfonate (EMITFSI)) on the displacement amplitude and displacement patterns of these actuators were investigated and compared. The results indicate that the bilayer actuator consisting of an electrochemically synthesized conducting polymer exhibits far greater displacements compared to chemically synthesized polymers at the same stimulating voltage. Similarly, amongst the three conducting polymers considered, the PPY actuator showed greater displacement followed by PProDOT and PEDOT. Furthermore, the use of different electrolyte solution during polymerization as well as during actuation was found to affect not only displacement distance but also its pattern.
Publication year: 2013
Source:Sensors and Actuators A: Physical, Volume 193
The stress gradient generated due to electrochemical oxidation/reduction of a conducting polymer in a bilayer actuator causes a bending movement. Here we report a comparative study of the displacement of bilayer actuators prepared using different conducting polymers. The effects of conducting polymers obtained from electrochemical or chemical synthesis route: different polymers (polypyrrole (PPy), poly(3,4-ethylenedioxythiophene) PEDOT and poly(3,3-dihexyl-3-4-dihydro-2H-thieno[3,4b][1,4]-dioxepine [PProDOT(Hx)2]); and different electrolytes (0.1M lithium trifluromethanesulfonate/propylenecarbonate (LiTFSI/PC) and 1-ethyl-3-methyl imidazolium trifluromethanesulfonate (EMITFSI)) on the displacement amplitude and displacement patterns of these actuators were investigated and compared. The results indicate that the bilayer actuator consisting of an electrochemically synthesized conducting polymer exhibits far greater displacements compared to chemically synthesized polymers at the same stimulating voltage. Similarly, amongst the three conducting polymers considered, the PPY actuator showed greater displacement followed by PProDOT and PEDOT. Furthermore, the use of different electrolyte solution during polymerization as well as during actuation was found to affect not only displacement distance but also its pattern.
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