中国微米纳米-微纳结构对电容式柔性压力传感器性能影响的研究

设计制备出三明治结构的电容式柔性压力传感器,并对其性能进行研究.该传感器以银纳米线为电极材料,聚二甲基硅氧烷(PDMS)为柔性衬底,同时采用毛面玻璃和光面玻璃分别作为柔性衬底的制备模板,制备出微纳结构和平面结构的PDMS薄膜.然后采用喷涂法制备AgNWs/PDMS复合电极,以另外一层PDMS为介电层,将两电极面对面封装,得到电容式柔性压力传感器,最后系统研究了传感器的电极微纳结构对器件性能的影响.本文研究表明,具有微纳结构的AgNWs/PDMS复合薄膜传感器的灵敏度为1.0 kPa-1,而平面结构的AgNWs/PDMS复合薄膜传感器的灵敏度为0.6 kPa-1,由此可知具有微纳结构的柔性衬底能够显著提高器件的灵敏度.     

基于电容-电阻转换原理的柔性压力传感器

目前,基于碳基纳米材料的柔性压力传感器凭借着其便携性、柔韧性、生物相容性和低成本等特点,在智能医疗、人机交互和智能机器人等领域有着广泛的应用前景,但如何使其在具有较大量程范围的同时保持较高灵敏度,仍是一个严峻的挑战。提出一种基于氧化石墨烯/碳纳米管（Graphene Oxide/Carbon Nanotube, GO/CNT）复合敏感层的柔性压力传感器,同时以热塑性聚氨酯弹性体（Thermoplastic Polyurethanes, TPU）多孔海绵作为传感器骨架。该GO/CNT@TPU柔性压力传感器的量程范围为0～60 kPa,基于电容-电阻转换原理,当受到较小压力（0～5 kPa）时,传感器以电阻感知为主,灵敏度为0.05777 kPa^-1;当受到较大压力（5～60 kPa）时,传感器以电容感知为主,灵敏度为0.33213 kPa^-1。从而有效地实现了传感器的在宽量程内的高灵敏度检测。     

基于 ＧＮＰｓ/ ＰＤＭＳ 复合薄膜的柔性压阻传感器制备及性能研究

目前柔性压力传感器已被用于众多领域,其中压阻薄膜是柔性压力传感器的核心。本文将石墨烯纳米片（GNPs）与聚二甲基硅氧烷（PDMS）复合,通过倒模的方法制备压阻薄膜,经测试,GNPs浓度为8%时,材料具有较好的性能。以此为基础,制备了压敏结构间距为1.2 mm,直径大小为1.0 mm的GNPs/PDMS基压阻传感器,经测试,所制备的传感器加载响应为340 ms,卸载响应速度为260 ms,并具有较好的稳定性,同时,基于该压阻式柔性压力传感器实现了人体手腕关节处压力信号的测试。     

柔性温度压力仿生皮肤的模块化设计与实现

为实现电子仿生皮肤的模块化设计,以石墨烯纳米片制备薄膜温敏传感器,同时,以炭黑/硅橡胶复合材料为弹性电介质、有机硅导电银胶为柔性上极板设计电容式力敏传感器,在此基础上,以聚酰亚胺为柔性基体,提出一种可用作智能机器人仿生皮肤的全柔性温度/压力触觉传感器,并设计成具有可拼接特点的模块化阵列结构.介绍柔性温度/压力触觉传感器的结构设计、检测机理以及信号采集与处理系统.通过温度、压力及温度/压力复合感知实验表明,该柔性温度/压力复合式触觉传感阵列及信号提取系统可实现触觉感知功能,为可穿戴式人工皮肤的研究提供了一种设计方案.     

一种新型CMOS电容式绝对压力传感器的设计

提出了一种新型的采用标准CMOS工艺结合MEMS后处理工艺加工的电容式绝对压力传感器.传感器结构部分是由导体/介质层/导体组成的可变电容器.电容的上下极板分别为CMOS工艺中的多晶硅栅和n阱硅,中间介质层为栅氧化层.在CMOS工艺加工完之后,利用选择性的体硅腐蚀、pn结自停止腐蚀以及阳极键合等MEMS后处理工艺来得到传感器结构.与传统的电容式压力传感器相比,这种结构具有更大的初始固有电容,这样可以抑制寄生电容的影响,从而简化检测电路的设计.文中,应用多层膜理论模型分析了传感器的结构,并利用ANSYS有限元分析对模型进行了验证,并利用电容变化模型分析了传感器的灵敏度.对于边长为800 μm的敏感方膜,初始电容值为1 104pF,传感器灵敏度为46 fF/hPa.同时,本文给出了传感器的电容检测电路的设计.     

基于RFID的无线无源柔性压力传感器研究

提出了一种基于RFID反向散射耦合原理的无线无源柔性压力传感器。该传感器以铁氧体薄膜作为反射层,柔性海绵作为中间层,RFID标签作为数据传输层。通过有限元方法对传感器的增益和杨氏模量进行仿真,并使用压力测试系统测量传感器的灵敏度,最后得到了同样的结论：在相同厚度下中间层为低密度海绵的传感器灵敏度更高。此外对传感器进行了一系列性能测试,得到传感器最大工作距离为10 cm,在温度测量范围(25℃～45℃)误差为0.91%,在湿度测量范围(43%RH～82%RH)误差为0.89%。该无线无源柔性压力传感器结构简单、生产成本低,增加了无线无源传感器在近场范围内的测量距离。在医用绷带压力检测、足底压力检测等智能医疗领域具有良好的应用前景。     

基于柔性电极结构的薄膜电容微压力传感器

基于柔性电极结构,本文设计、制作了薄膜电容微压力传感器,在阐述传感器工作原理的基础上,提出了两种设计思路,即基于柔性纳米薄膜的电容式微压力传感器和具有微结构的柔性电极薄膜电容式微压力传感器,并结合传感器的结构和柔性材料的加工特性,进一步提出了相应的力敏特性材料结构优化思路和加工流程,利用该流程得到了一种结构轻薄、工艺简单、高灵敏度的微压力传感器。经测试,本文制作的压力传感器的灵敏度能够达到218 fF/mmHg,在智能穿戴和可植入压力检测等领域显示出较好的应用前景。     

基于银膜-石墨烯复合膜对称结构的SPR传感器研究

针对棱镜激励银膜SPR传感器灵敏度虽然较金膜结构高,但易被氧化、稳定性较差的缺点,提出一种棱镜耦合激励银膜－石墨烯－介质－石墨烯－银膜复合膜对称结构的SPR传感器,增加石墨烯膜层,解决银膜SPR传感器易氧化导致稳定性下降问题,采用角度调制的方法对SPR传感结构进行了性能参数分析,研究了金属材质、石墨烯以及检测介质的厚度对传感性能的影响。结果表明,银膜相比金膜,具有更好的共振效果,灵敏度较高,通过调节检测介质的厚度,可以改变角度的调节范围,实现了传感器的可调性,对称传感结构可以产生双共振峰SPR曲线,为分布式传感提供了可供参考的依据,石墨烯优化并提高了传感器的稳定性和检测灵敏度。     

石墨烯柔性压力/应变传感器的研究进展

柔性压力/应变传感器可以贴附在物体表面,测量其表面压力或应变,可用于人体脉搏检测、表情识别和运动监测等,在健康监护、医疗诊断等方面有广阔的发展空间.石墨烯柔性压力/应变传感器比普通压力/应变传感器性能更为优异,其测量范围宽、灵敏度高且尺寸仅为纳米级.综述了石墨烯压力/应变传感器在近几年来的研究进展及应用情况,重点讨论了基于石墨烯材料的电容法、激光诱导法、3D海绵法、纸基法、水凝胶法的压力/应变传感器的制备方法及性能差异.最后简要指明石墨烯柔性压力/应变传感器未来的研究方向.     

基于LCP衬底的柔性湿度传感器研究

介绍了一种新型柔性电容式湿度传感器.该柔性电容式湿度传感器采用液晶高分子聚合物(LCP)作为衬底,金属铜(Cu)作为叉指电极,聚酰亚胺(PI)作为湿度传感器的湿敏介质.LCP衬底的应用使得该传感器具有良好的柔性和可弯曲性.该柔性湿度传感器与传统硅基湿度传感器相比较具有成本低廉、结构简单、制作方便等优点.该柔性湿度传感器在25℃下的平均灵敏度为0.04%pF/%RH,最大回滞为±4.16%RH,其平均灵敏度在25℃~70℃范围内受温度影响较小.在25℃下其响应时间和恢复时间分别为36 s和39 s.该柔性湿度传感器可以应用于环境湿度检测、人工电子皮肤系统和可穿戴设备等领域.     

Yager’s new class of implications Jf and some classical tautologies

Recently, Yager [R. Yager, On some new classes of implication operators and their role in approximate reasoning, Information Sciences 167 (2004) 193-216] has introduced a new class of fuzzy implications, denoted J_f, called the f-generated implications and has discussed some of their desirable properties, such as neutrality, exchange principle, etc. In this work, we discuss the class of J_f implications with respect to three classical logic tautologies, viz., distributivity, law of importation and contrapositive symmetry. Necessary and sufficient conditions under which J_f implications are distributive over t-norms and t-conorms and satisfy the law of importation with respect to a t-norm have been presented. Since the natural negations of J_f implications, given by N_Jf(x)=J_f(x,0), in general, are not strong, we give sufficient conditions under which they become strong and possess contrapositive symmetry with respect to their natural negations. When the natural negations of J_f are not strong, we discuss the contrapositivisation of J_f. Along the lines of J_f implications, a new class of implications called h-generated implications, J_h, has been proposed and the interplay between these two types of implications has been discussed. Notably, it is shown that while the natural negations of J_f are non-filling those of J_h are non-vanishing, properties which determine the compatibility of a contrapositivisation technique.     

Forest carbon densities and uncertainties from Lidar, QuickBird, and field measurements in California

Greenhouse gas inventories and emissions reduction programs require robust methods to quantify carbon sequestration in forests. We compare forest carbon estimates from Light Detection and Ranging (Lidar) data and QuickBird high-resolution satellite images, calibrated and validated by field measurements of individual trees. We conducted the tests at two sites in California: (1) 59 km² of secondary and old-growth coast redwood (Sequoia sempervirens) forest (Garcia-Mailliard area) and (2) 58 km² of old-growth Sierra Nevada forest (North Yuba area). Regression of aboveground live tree carbon density, calculated from field measurements, against Lidar height metrics and against QuickBird-derived tree crown diameter generated equations of carbon density as a function of the remote sensing parameters. Employing Monte Carlo methods, we quantified uncertainties of forest carbon estimates from uncertainties in field measurements, remote sensing accuracy, biomass regression equations, and spatial autocorrelation. Validation of QuickBird crown diameters against field measurements of the same trees showed significant correlation (r = 0.82, P < 0.05). Comparison of stand-level Lidar height metrics with field-derived Lorey's mean height showed significant correlation (Garcia-Mailliard r = 0.94, P < 0.0001; North Yuba R = 0.89, P < 0.0001). Field measurements of five aboveground carbon pools (live trees, dead trees, shrubs, coarse woody debris, and litter) yielded aboveground carbon densities (mean ± standard error without Monte Carlo) as high as 320 ± 35 Mg ha^− 1 (old-growth coast redwood) and 510 ± 120 Mg ha^− 1 (red fir [Abies magnifica] forest), as great or greater than tropical rainforest. Lidar and QuickBird detected aboveground carbon in live trees, 70-97% of the total. Large sample sizes in the Monte Carlo analyses of remote sensing data generated low estimates of uncertainty. Lidar showed lower uncertainty and higher accuracy than QuickBird, due to high correlation of biomass to height and undercounting of trees by the crown detection algorithm. Lidar achieved uncertainties of < 1%, providing estimates of aboveground live tree carbon density (mean ± 95% confidence interval with Monte Carlo) of 82 ± 0.7 Mg ha^− 1 in Garcia-Mailliard and 140 ± 0.9 Mg ha^− 1 in North Yuba. The method that we tested, combining field measurements, Lidar, and Monte Carlo, can produce robust wall-to-wall spatial data on forest carbon.     

A technique for monitoring SO2 in combustion exhausts: Use of a non-Nernstian sensing element in combination with an upstream catalytic filter

Detection of sulfur dioxide (SO₂) at high temperature (600–750 °C) in the presence of some interferents found in combustion exhausts (NO₂, NO, CO₂, CO, and hydrocarbon (C₃H₆)) is described. The detection scheme involves use of a catalytic filter in front of a non-Nernstian (mixed-potential) sensing element. The catalytic filter was a Ni:Cr powder bed operating at 850 °C, and the sensing elements were pairs of platinum (Pt) and oxide (Ba-promoted copper chromite ((Ba,Cu)_xCr_yO_z) or Sr-modified lanthanum ferrite (LSF)) electrodes on yttria-stabilized zirconia. The Ni:Cr powder bed was capable of reducing the sensing element response to NO₂, NO, CO, and C₃H₆, but the presence of NO₂ or NO (“NO_x”, at 100 ppm by volume) still interfered with the SO₂ response of the Pt–(Ba,Cu)_xCr_yO_z sensing element at 600 °C, causing approximately a 7 mV (20%) reduction in the response to 120 ppm SO₂ and a response equivalent to about 20 ppm SO₂ in the absence of SO₂. The Pt–LSF sensing element, operated at 750 °C, did not suffer from this NO_x interference but at the cost of a reduced SO₂ response magnitude (120 ppm SO₂ yielded 10 mV, in contrast to 30 mV for the Pt-(Ba,Cu)_xCr_yO_z sensing element). The powder bed and Pt–LSF sensing element were operated continuously over approximately 350 h, and the response to SO₂ drifted downward by about 7%, with most of this change occurring during the initial 100 h of operation.     

First-principles calculations of binary Al compounds: Enthalpies of formation and elastic properties

Systematic first-principles calculations of energy vs. volume (E-V) and single crystal elastic stiffness constants (c_ij’s) have been performed for 50 Al binary compounds in the Al-X (X = Co, Cu, Hf, Mg, Mn, Ni, Sr, V, Ti, Y, and Zr) systems. The E-V equations of state are fitted by a four-parameter Birch-Murnaghan equation, and the c_ij’s are determined by an efficient strain-stress method. The calculated lattice parameters, enthalpies of formation, and c_ij’s of these binary compounds are compared with the available experimental data in the literature. In addition, elastic properties of polycrystalline aggregates including bulk modulus (B), shear modulus (G), Young’s modulus (E), B/G (bulk/shear) ratio, and anisotropy ratio are calculated and compared with the experimental and theoretical results available in the literature. The systematic predictions of elastic properties and enthalpies of formation for Al-X compounds provide an insight into the understanding and design of Al-based alloys.     

Influence of doping BiYO3 and Nb2O5 on PTCR characteristics of BaTiO3 thermistor ceramics

Nb₂O₅-doped (1 − x)Ba_0.96Ca_0.04TiO₃-xBiYO₃ (where x = 0.01, 0.02, 0.03 and 0.04) lead-free PTC thermistor ceramics were prepared by a conventional solid state reaction method. X-ray diffraction, scanning electron microscope, Agilent E4980A and resistivity-temperature measurement instrument, were used to characteristic the lattice distortion, microstructure, temperature dependence of permittivity and resitivity-temperature dependence. It was revealed that the tetragonality c/a of the perovskite lattice, the microstructure and the Curie temperature changed with the BiYO₃ content. In order to decrease the room temperature resistivity, the effect of Nb₂O₅ on the room temperature resistivity was also studied, and its optimal doping content was finally chosen as 0.2 mol%. The 0.97Ba_0.96Ca_0.04TiO₃-0.03BiYO₃-0.002Nb₂O₅ thermistor ceramic exhibited a low ρ_RT of 3.98 × 10³ Ω cm, a typical PTCR effect of ρ_max/ρ_min > 10³ and a T_c of 153 °C.     

Estimating Siberian timber volume using MODIS and ICESat/GLAS

Geosciences Laser Altimeter System (GLAS) space LiDAR data are used to attribute a MODerate resolution Imaging Spectrometer (MODIS) 500 m land cover classification of a 10° latitude by 12° longitude study area in south-central Siberia. Timber volume estimates are generated for 16 forest classes, i.e., four forest cover types × four canopy density classes, across this 811,414 km² area and compared with a ground-based regional volume estimate. Two regional GLAS/MODIS timber volume products, one considering only those pulses falling on slopes ≤ 10° and one utilizing all GLAS pulses regardless of slope, are generated. Using a two-phase(GLAS-ground plot) sampling design, GLAS/MODIS volumes average 163.4 ± 11.8 m³/ha across all 16 forest classes based on GLAS pulses on slopes ≤ 10° and 171.9 ± 12.4 m³/ha considering GLAS shots on all slopes. The increase in regional GLAS volume per-hectare estimates as a function of increasing slope most likely illustrate the effects of vertical waveform expansion due to the convolution of topography with the forest canopy response. A comparable, independent, ground-based estimate is 146 m³/ha [Shepashenko, D., Shvidenko, A., and Nilsson, S. (1998). Phytomass (live biomass) and carbon of Siberian forests. Biomass and Bioenergy, 14, 21-31], a difference of 11.9% and 17.7% for GLAS shots on slopes ≤ 10° and all GLAS shots regardless of slope, respectively. A ground-based estimate of total volume for the entire study area, 7.46 × 10⁹ m³, is derived using Shepashenko et al.'s per-hectare volume estimate in conjunction with forest area derived from a 1990 forest map [Grasia, M.G. (ed.). (1990). Forest Map of USSR. Soyuzgiproleskhoz, Moscow, RU. Scale: 1:2,500,000]. The comparable GLAS/MODIS estimate is 7.38 × 10⁹ m³, a difference of less than 1.1%. Results indicate that GLAS data can be used to attribute digital land cover maps to estimate forest resources over subcontinental areas encompassing hundreds of thousands of square kilometers.     

Restricted arc-connectivity of digraphs

Since interconnection networks are often modeled by graphs or digraphs, the edge-connectivity of a graph or arc-connectivity of a digraph are important measurements for fault tolerance of networks.The restricted edge-connectivity λ^′(G) of a graph G is the minimum cardinality over all edge-cuts S in a graph G such that there are no isolated vertices in G−S. A connected graph G is called λ^′-connected, if λ^′(G) exists.In 1988, Esfahanian and Hakimi [A.H. Esfahanian, S.L. Hakimi, On computing a conditional edge-connectivity of a graph, Inform. Process. Lett. 27 (1988), 195-199] have shown that each connected graph G of order n?4, except a star, is λ^′-connected and satisfies λ^′(G)?ξ(G), where ξ(G) is the minimum edge-degree of G.If D is a strongly connected digraph, then we call in this paper an arc set S a restricted arc-cut of D if D−S has a non-trivial strong component D₁ such that D−V(D₁) contains an arc. The restricted arc-connectivity λ^′(D) is the minimum cardinality over all restricted arc-cuts S.We observe that the recognition problem, whether λ^′(D) exists for a strongly connected digraph D is solvable in polynomial time. Furthermore, we present some analogous results to the above mentioned theorem of Esfahanian and Hakimi for digraphs, and we show that this theorem follows easily from one of our results.     

On the Sum Coloring Problem on Interval Graphs

In this paper we study the following NP-complete problem: given an interval graph G = (V,E) , find a node p -coloring such that the cost is minimal, where denotes a partition of V whose subsets are ordered by nonincreasing cardinality. We present an O(m χ (G) + n log n) time ε -approximate algorithm (ε < 2) to solve the problem, where n , m , and χ #(G) are the number of nodes of the interval graph, its number of cliques, and its chromatic number, respectively. The algorithm is shown to solve the problem exactly on some classes of interval graphs, namely, the proper and the containment interval graphs, and the intersection graphs of sets of ``short' intervals. The problem of determining the minimum number of colors needed to achieve the minimum over all p -colorings of G is also addressed. Received February 1, 1996; revised August 22, 1997.     

d-Dimensional Range Search on Multicomputers

The range tree is a fundamental data structure for multidimensional point sets, and, as such, is central in a wide range of geometric and database applications. In this paper we describe the first nontrivial adaptation of range trees to the parallel distributed memory setting (BSP-like models). Given a set of n points in d -dimensional Cartesian space, we show how to construct on a coarse-grained multicomputer a distributed range tree T in time O( s / p + T _c (s,p)) , where s = n log ^d-1 n is the size of the sequential data structure and T _c (s,p) is the time to perform an h -relation with h=Θ (s/p) . We then show how T can be used to answer a given set Q of m=O(n) range queries in time O((s log m)/p + T _c (s,p)) and O((s log m)/p + T _c (s,p) + k/p) , where k is the number of results to be reported. These parallel construction and search algorithms are both highly efficient, in that their running times are the sequential time divided by the number of processors, plus a constant number of parallel communication rounds. Received June 1, 1997; revised March 10, 1998.