查看更多>>摘要：To satisfy the cooling demands required by the highly integrated electronic devices, a heat exchanger integrated with a ball valve piezoelectric pump and a multi-stage Y-shaped micro-channel heat sink was proposed and demonstrated. The effects among the flow rate, back pressure of the piezoelectric pump, and the driving frequency of the heat exchanger were investigated to assess the driving performance. Subsequently, the piezoelectric heat exchanger was used to cool the CPU of commercial computers, and the performance of the heat exchanger was discussed under different thermal power consumption. The results showed that the temperature of the CPU under extreme thermal load was controlled by the heat exchanger within 55 celcius. The relationship between heat resistance and convection heat transfer coefficient was also analyzed. When the CPU was operating at 30 W, the heat sink owned the smallest thermal resistance and the largest heat transfer coefficient. From the conclusion of the comparative tests, the heat exchange speed and heat exchange effect of the piezoelectric heat exchanger were obviously better than the original air cooling system of the computer. The proposed heat exchanger may contribute in the field of the heat exchange of electronic devices in near future due to its certain performances.
Liu, ZiyiYoshida, ShinyaHorsley, David A.Tanaka, Shuji...
11页
查看更多>>摘要：In this study, we fabricated a row-column addressed 2-dimensional piezoelectric micromachined ultrasonic transducer (pMUT) array based on the monocrystalline Pb(Zr, Ti)O3 (Mono PZT)-based thin film, and demonstrated its application as the ultrasound imager. At first, we optimized the island-shaped design as an individual element, and then developed the fabrication process based on the control of the edge shape of an insulative polymer pattern. As a result, the hexagonally arranged arrays with 372 elements at the maximum were fabricated successfully, of which the diameter and pitch were 70 mu m and 120 mu m, respectively. The resonance frequency, displacement sensitivity, and quality factor in air measured approximately 5.4 MHz, 175 nm/V and 175, respectively. This array exhibited low crosstalk. The actuation of the unaddressed element was less than 10 % of that of the addressed one. In addition, the deviations on the resonance frequencies and displacement sensitivities were as small as only 2 % and 15 %, respectively. Then, the basic acoustic performance in a medium FC-70 was evaluated by using the minimum unit array composed of 5 columns. Also, the transmitting beamforming of a focused ultrasonic burst wave was done by applying driving voltages with a time delay. Finally, an ultrasonic imaging for a metallic object was demonstrated by mechanically scanning the object.
查看更多>>摘要：This work presents the control of a piezoelectric interface that combines two vibration modes of a plate to render the haptic feeling of a button click. By principle, the two vibration modes create an elliptical motion of particles of a beam that can induce a lateral force to the fingerpulp. In this device, the synchronization of the modes' vibrations is essential, and can be obtained with a closed loop control. In the paper, we present the control in the (d,q) frame, because it can ensure the dynamic performances to achieve a compelling haptic feedback, yet being robust besides the external disturbances produced by the user's finger. The proposed method could achieve a 2 ms response time, and the haptic feedback was perceived by 100% of users in a psychophysical study.
查看更多>>摘要：The superconductor/magnetoresistance (MR) mixed magnetic sensor, which is composed of a superconducting magnetic flux transformation amplifier (SMFTA) and a MR sensitive element, has extremely great development potential in weak magnetic field detection because of its excellent sensitivity, simple structure and small size. However, it still lacks an effective method to study the spatial distribution of the magnetic field produced by SMFTA. Here, a finite element simulation method was proposed to study the magnetic field amplification effect of the SMFTA. Several factors affecting the magnetic field amplification were studied via this simulation method. Furthermore, mixed magnetic sensors with three typical sizes were successfully fabricated, and the experimentally measured magnifications of the three sensors were basically consistent with the simulation values, demonstrating the reliability of this simulation method. Our works are expected to pave a meaningful way for the SMFTA design and promote the development of superconductor/MR mixed magnetic sensors.
查看更多>>摘要：Introduced by Fabio Sauli in 1997, the Gas Electron Multiplier (GEM) technology is commonly used in many high energy physics experiments. It has proven unique value in many scientific domains and adaptability to new research tasks. Typically, the GEM detectors are made with polyimide films (GEM foils and readout plate), halogen-free FR4 epoxy resins (supporting and stretching structures), conductive copper layers, etc. Because of outgassing and ageing, those components release in time residues of dust, moisture, and vapors. The residues pollute the gas mixture and consequently degrade the detector's working parameters. To avoid such a problem, devices can be constantly flushed by pure gas from an external source. This solution is not optimal for autonomous space detectors because of volume and weight limitations. The paper describes the successive work to develop an autonomous GEM detector without a gas mixture circulation system. As a solution, the use of Low Temperature Cofired Ceramics (LTCC) materials was proposed and validated. The dedicated LTCC readout plates were manufactured and tested, and results are presented.
查看更多>>摘要：We propose a long-period fiber grating (LPFG) humidity sensor based on two kinds of spider silks. Both spider dragline silk (SpDS) and spider egg-case silk (SpECS) for sensor preparation are produced by the Araneus ven-tricosus. SpDS can contract up to half the original length in the axial direction when the ambient relative hu-midity (RH) increases due to its supercontraction property. However, the length of SpECS axial contraction is much smaller than that of SpDS as RH increases, because SpECS does not have the supercontraction property like SpDS. We fabricated a LPFG by irradiating a single-mode fiber with a high-frequency CO2 laser. One end of LPFG is fixed by ultraviolet glue, and the other end is inserted into the quartz round tube without fixing. Therefore, the unfixed end of LPFG serves as the movable end to ensure that the direction of movement of LPFG is controllable. In addition, SpDS and SpECS exert pull forces on LPFG in two opposite directions, and the overall structure forms an X shape. When the ambient RH increases, the length of SpDS becomes shorter due to the supercontraction property. It changes the structure curvature of LPFG, leading to the transmission spectrum shift. When the RH decreases, SpECS provides a recovery pull, like a spring, that restores SpDS to a taut state when it relaxes. The curvature of LPFG is reduced, and the transmission spectrum shifts in the opposite direction. Therefore, we monitor the RH by observing the wavelength shift of the transmission spectrum. Our sensor achieves humidity detection with -0.2039 nm/%RH sensitivity in the 50%RH-80%RH range. Additionally, we can adjust the amount and length of the two spider silks to increase the maximum detection humidity range closer to 100% RH at the expense of reduced sensitivity. The proposed humidity sensor has the advantages of reversibility, good repeatability, and environmental friendliness.
Wang, Chao-NanPeng, Ming-XingYue, Li -JuanYang, Xuan-Yu...
9页
查看更多>>摘要：The development of high sensitivity acetone gas sensor is of great significance for air quality monitoring and diagnosis of diseases. Herein, ZIF-8 derived ZnO@CeO2 heterojunction was prepared by simple hydrothermal method to achieve ppb level detection of acetone. ZnO was decorated on the surface of CeO2 matrix by using ZIF8 as sacrificial template, which was beneficial to enlarge the specific surface area and generate abundant oxygen vacancies (OV). ZnO@CeO2-1 min composites show excellent sensing performance towards acetone detection, with low detection limit (240 ppb), high response (32 for 100 ppm acetone) and good stability. Particularly, the electronic modulation of ZnO@CeO2 heterojunction increases the resistance variation during the sensing process, and OV increases the carrier concentration of sensitive materials, providing more active sites. The synergistic effect of the construction of ZnO@CeO2 heterostructure and the surface Ov can effectively improve the sensing performance. Our study provides an ingenious strategy to produce ZnO@CeO2 nanostructures as well as new insights for the detection of acetone.
查看更多>>摘要：Machine learning techniques have significantly enhanced signal handling and prediction accuracy in electronic skins by facilitating the extraction of useful information hidden in the sensory outputs. We present a polymer sensor with four irregularly shaped electrodes enabling energy-efficient sensing and improved data interpretation. We first compute the resistance change for the sensing element under pressure. The finite element method is used to solve the three-dimensional nonlinear elasticity. The electric potential distribution is simulated using an arbitrary Lagrangian-Eulerian formulation. We then build reduced-order models for detecting pressure distribution for different pressure cases. The inverse models built using deep neural networks showed good prediction accuracy and resolution. The irregular arrangement of the electrodes resulted in low correlation coefficients between the input resistances, and therefore, efficient predictions of the four-electrode sensor. It is demonstrated that the present four-electrode sensor could replace at least four sensors in an array. For arbitrary pressure distributions over a 2 x 2 surface resolution, a model is trained with a mean accuracy of 22 Pa in the range of 1-20 kPa. Additionally, for a single square-shaped pressure with arbitrary magnitude and surface area, position prediction accuracies of 99% and 96% are obtained at 4 x 4 and 8 x 8 resolutions, respectively. Moreover, the models showed low sensitivity to the uncertainty in the measured signals.
查看更多>>摘要：The capacitance-based stress self-sensing in asphalt without device or functional constituent incorporation is reported for the first time, with relevance to smart pavements. Stress sensing enables weighing. Without the incorporation, the technology is applicable to existing and new pavements, and gives low cost, high durability, large sensing volume and maintained mechanical properties. Linearity of the capacitance with the normal compressive stress occurs for stress ranging from 2 Pa to 60 Pa. The ability to sense such low stress enables the sensing of even children. Nonlinearity at > 60 Pa involves the slope of the capacitance-stress curve decreasing. Monotonic and reversible capacitance increase with stress occurs for stress <= 600 Pa, with complete reversibility up to stress >= 2100 Pa. The electrodes are aluminum foil bonded to the asphalt with a thin bitumen interlayer. With coplanar electrodes (the stress not applied to the electrodes), the in-plane capacitance increases upon compression, presumably due to the compaction of the part of the asphalt near the plane of the coplanar electrodes. With sandwiching electrodes (the stress applied to the electrodes), the through-thickness capacitance increases reversibly upon compression, due to the decrease in the thickness of the bitumen interlayer. The coplanar electrodes enable self-sensing, and, compared to the sandwiching electrodes, they give much greater sensitivity and are more amenable to practical implementation. The sensing is based on the fractional change in capacitance, so the thickness of the asphalt or bitumen interlayer does not matter. The capacitance-based stress sensing is superior for asphalt than cement-based materials of prior work, due to the greater stiffness of the latter.
查看更多>>摘要：Recently, carbon nanotube (CNT) yarns produced by the continuous spinning method have triggered significant interest owing to their excellent strength and electrical and thermal conductivities. Hence, they can be used for energy storage in ion batteries, supercapacitors, energy harvesters, and sensors. This study aims to develop a "bifunctional yarn " to let both energy input and output function heterogeneously while it is working. A buckypaper type of CNTs took advantage of a technique called "biscrolling technology, " which was used to load up to 90 wt% or more of a guest material. Furthermore, performances of iron (Fe3O4 ) as the guest material in the bifunctional yarn were significantly considered owing to its magnetic force, attraction/repulsion as a soft magnet, and high supercapacitor due to large potential window, specific high capacitance, and different valence states, simultaneously. This study demonstrates that the fabricated "bifunctional yarn " acts as a magentic torsional actuator and supercapacitor simultaneously. The bifunctional yarn in the magnetic torsional actuator wirelessly produced torsional actuation of a maximum of 1200 due to application of magnetic field; two symmetrically bifunctional yarns with 90 wt% of Fe(3)O(4 )loading coated by quasi-solid-state of poly (vinyl alcohol) (PVA)-LiCl gel electrolyte can be configured in parallel as a supercapacitor.
NSTL
Elsevier