查看更多>>摘要：A multipoint space-domain active fiber cavity ringdown (FCRD) sensing technique based on frequency-shifted interferometry (FSI) is proposed and investigated for quasi-distributed magnetic field measurements. Multiple FSI-based fiber ringdown cavities (RDCs) are cascaded together to constitute a sensor array, share one continuous-wave optical source and one slow balanced detector, and thus the system is economical and highly sensitive. In each RDC a bidirectional erbium-doped fiber amplifier (Bi-EDFA) is inserted to compensate the inherent cavity loss for achieving higher sensitivity. Compared to the time-domain active FCRD techniques, the amplifier has lower gain fluctuation because the continuous light (instead of pulse light) coupled into the cavity enables more stable optical power, and has lower amplified spontaneous emission noise due to the use of two narrow bandpass filters and differential detection. Magnetic fields in different locations are synchronously resolved in the space domain by measuring the ringdown distances of continuous light, rather than measuring the ringdown times of pulse light in the time domain as in conventional multipoint FCRD techniques. A dual-point active FSI-FCRD magnetic field sensor was experimentally built, and two side-polished fibers coated with magnetic fluid were incorporated inside the fiber cavities as the sensing probes. By applying the external magnetic field from 0 to 230 Gs, the sensitivities of 6.68 x 10(-3) and 4.45 x 10(-3)/(km Gs) were respectively achieved, which are at least one order of magnitude higher than the conventional passive FCRD techniques. After repeated measurements, the obtained ringdown baseline stabilities of the two units were 0.91% and 2.00%, which were much higher than those of time-domain active FCRD sensing systems. Using power budget analysis, the maximum number of identical sensing units can be expected to be 48 over a 25.89-km distance under the nearly same experimental conditions. The proposed multipoint active FCRD sensing scheme has the merits of low cost, high sensitivity, good stability, and strong multiplexing ability, which would find good application pros-pects at electric grids, national defense, biology, and medicine for monitoring quasi-distributed magnetic field.
Lu, Yen-WenKarmakar, Rajat SubhraChu, Chia-PeiLiao, Ying-Chih...
12页
查看更多>>摘要：A tactile-sensing device, made of biodegradable Polyvinyl alcohol (PVA) material, has been developed. The device has a composite PVA film, with conductive fillers of Iron (Fe) particle or multi-walled carbon nanotube (MWCNT), sandwiched in between top and bottom PVA substrates. The filler allows conducting paths to be formed when the contact areas between the substrates increases with an external applied force, resulting in the reduction of Electrical Contact Resistance (ECR). Our sensors employ a much simpler structure and fabrication method compared to other previously reported biodegradable tactile sensors. The devices are optimized with their filler weight percentage and device structure, showing excellent sensitivity (1.998 kPa-1) in the subtle pressure range (0~0.5 kPa). These tactile sensors are tested for air flow and vibration detections, showing the potential for future low-cost biodegradable wearable health monitoring applications.
查看更多>>摘要：The ability to monitor toxic gases under room-temperature conditions, with enhanced response and selectivity present in the atmosphere, is still considered as a technical challenge. In this context, we have fabricated AlGaN/ GaN high electron mobility transistors (HEMTs) based sensors incorporating molybdenum disulphide (MoS2) functionalization for very sensitive, selective, and quick measurement of even trace amounts of hazardous NO2 gas in the ambient under room-temperature conditions. MoS2 structures with vertically aligned flower-like structure were synthesised using a simple hydrothermal technique and applied to the gate region of AlGaN/ GaN HEMTs. The electrical characterisations of MoS2 functionalized AlGaN/GaN HEMTs are then used to detect the presence of NO2 gas. The fabricated sensor showed an enhanced relative sensing response in the range of 40.5-56.7% for 1-100 ppm NO2 gas with complete recovery to 1 ppm NO2 concentration under roomtemperature conditions (25 ᵒC) without applying any external thermal or optical stimuli. Furthermore, the cyclic and selectivity tests were performed and we found our sensor to be highly selective towards NO2 gas among various other gases. The experimental results showed that MoS2 had excellent properties for NO2 gas detection when used on such GaN-based sensing platform. These findings may be attributed to the exposed edge sites of MoS2 which compliment with configurations with sulphur and the chemisorption phenomenon on its surface that results in altering the drain to source current (IDS) of the HEMT at a constant drain to source voltage (VDS) of 0.5 V. These findings suggest that gas sensors based on the AlGaN/GaN HEMT structure appear to be a promising candidate for the advancement of application potentials of nitride-based integrated electronics.
查看更多>>摘要：Ultrasonic peening (UP) systems have recently attracted much attentions as a flexible dieless plastic deformation manner with merits of deep stress penetration and efficient shaping capability. Compared with conventional shot peening techniques, UP systems are promising for special processing in vacuum conditions but rarely explored before. In this paper, an ultrasonic peening system is designed, fabricated and finally characterized in vacuum conditions. The transducer can amplify the vibration amplitude and then trigger rod pin arrays to accelerate simultaneously towards the workpiece. Numerical results reveal that under high-speed impact one compressive residual-stress layer is created and results into the bulk deformation of the workpiece. Measurements on the prototype ultrasonic peening transducer confirm the vibration performance and captured rapid movement of rod pin arrays verifies the proposed impact principle. With the driving voltage of 100 V at resonance, one piece of 5 mm 7055 aluminum alloy specimen could be deformed with 0.61 mm arc height after 10 min peening. At last, the validation for ultrasonic peen forming in vacuum conditions is conducted and variation for the deformation level is obtained and analyzed. The proposed method and tested results open a new way for ultrasonic peen forming to be implemented for special processing in extreme environments.
查看更多>>摘要：In this paper we show an up-to-now unexplained source of offset drift affecting the fundamental mode orthogonal fluxgate. After a sudden change or removal of the magnetic field, we observe an offset transient which lasts units to hundreds of seconds. We exclude the thermal origin of such transient as well as the electric origin in the pickup coil resonance circuit or sensing amplifiers. We prove that this transient has magnetic origin, since it depends on both the amplitude and the duration of the pulse of magnetic field applied to the sensor which can be expressed as magnetic energy. We conclude that operating the fundamental mode orthogonal fluxgate in a closed feedback-loop is useful by suppressing this transient behavior by keeping the core in a (almost) zero field, however when switching the magnetometer sensor on/off, this transient has to be taken into account.
Kim, SoaramYoo, ByungseokMiller, MatthewBowen, David...
9页
查看更多>>摘要：We have developed a highly stretchable and flexible strain sensor based on eutectic gallium indium (EGaIn) and EcoFlex through a simple and low-cost fabrication process. The sensor has two different sensing channels in a single device with novel architecture that can allow fast and effective detections simultaneously from the different joint movements. The sensor is tested with several different angles up to 90 (strain: 250 %) using a 3D printed test setup to imitate joint movements, and it shows superior performance with an exceptional signal-tonoise ratio (69 dB), gauge factor (-3), measurement resolution (0.43 %), and response/recovery times (0.4 s/0.2 s), leveraging the high conductivity of EGaIn and excellent deformability of EcoFlex. Furthermore, the sensor successfully demonstrates the motions of a human finger as a practical application.
查看更多>>摘要：Bimorph-based electrothermal micromirrors can generate large lateral-shift-free (LSF) vertical displacement by employing electrothermal bimorph actuators with multiple segments of bimorphs. The vertical displacement of an LSF bimorph actuator is maximized when all the bimorph segments have equal temperature change. However, due to the distributed heat conduction and convection, the temperature changes on different bimorph segments are different. We report a new LSF bimorph actuator design with non-uniform width bimorph segments to achieve a uniform temperature distribution among multiple bimorph segments. A model is developed to optimize the new LSF bimorph design with three biomorph segments with the widths of 25 mu m, 110 mu m and 75 mu m, which reaches the same average temperature of 316 K on the three bimorphs with incentive current of 5 mA and convection coefficient of 500 W/m(2)K.
查看更多>>摘要：A two-dimensional acoustic horn packaged with a 2-D acoustic particle velocity sensor (APVS) is presented. The particle velocity amplification factor of the 2-D acoustic horn is analyzed theoretically and experimentally. The experimental results show a good agreement with the theoretical expectations. Compared with the previous horn model, this model considers the gain attenuation at low frequency and the influence of chip assembly deviation. As the particle velocity distribution changes greatly in the boundary layer, the assembly deviation of the chip has a great influence on the package gain. Furthermore, a microphone and the 2-D particle velocity sensor was packaged in the acoustic horn to detect the acoustic pressure and 2-D particle velocity at one point. The acoustic horn has an omnidirectional response for acoustic pressure. By using the mode domain beamforming, the direction of the incident wave was estimated with this two-dimensional sound intensity probe.
Braga, Thyago SantosVieira, Nirton C. S.Antonelli, EduardoDonadon, Mauricio Vicente...
10页
查看更多>>摘要：The vertically aligned multi-walled carbon nanotubes (VACNTs) / polydimethylsiloxane (PDMS) nanocompositebased strain sensors presented in this study show different behavior depending on catalyst concentrations for VACNT growth. Under static tensile load, the sensor with lower catalyst concentration shows a high gauge factor (GF-1400), whereupon tunneling effect is the mechanism that dictates the sensitivity. For higher concentrations, the GF decreases (GF-40) and shows an ohmic conduction. Morphological examinations showed VACNTs are homogeneously and randomly distributed as clusters with CNT bridging in the PDMS polymer matrix. Based on dielectric impedance (DI) and direct current (DC) electrical analysis, it was possible to identify that cut-off frequency (fc) increases with VACNTs concentration. Cut-off frequency can also define high sensitivity VACNT sensors with lower VACNT density. When compared with dispersed MWCNT sensors, VACNTs have a reducedfc due to the larger internal resistance variation associated with the high tunneling effect. This effect associated with the high sensitivity of the VACNT/PDMs sensors makes it a key factor to understand the mechanisms responsible for increasing the sensitivity and manufacturing of high GF nanocomposite stretchable sensors.
查看更多>>摘要：Flexible strain sensors have aroused great interest because of their prospective applications in motion detection, healthcare, and wearable electronics. However, the construction of strain sensing materials with both ultra-high sensitivity and excellent stretchability via a facile and scalable strategy remains a challenge. Here, an ultra sensitive and highly stretchable strain sensor with a unique hybrid conductive network was fabricated based on reduced graphene oxide (RGO)/multi-walled carbon nanotubes (MWCNT) hybrid fillers, carbonized woven fabric, and natural rubber (NR). The RGO/MWCNT/carbonized woven fabric (GMWF) composite was obtained by fast reduction of graphene oxide (GO)/acid-treated MWCNT (MWCNT-COOH) hybrid fillers and pyrolysis of woven fabric in an alcohol flame synchronously. The resulting GMWF/NR strain sensor exhibited a laudable trade-off between sensitivity and detection range (gauge factor of 1451, 3587, and 8225 within 0 32%, 32 49%, and 49 67% strain, respectively), fast response (200 ms), low detection limit (0.5%), and outstanding durability (1000 cycles). It could detect full-range (vigorous and subtle) human activities in real time. This integration of synergistic conductive fillers and facile template method to construct the hybrid conductive network demonstrates an effective strategy for fabricating high-performance strain sensors for wearable electronic devices.
NSTL
Elsevier