Textile-Based Sensors for Inspection of Composite Materials

The monitoring of mechanical deformation and damage of composite materials is normally performed by established analytical methods,such as strain gauges and opt...     

Analysis of a Direct Interface Circuit for Capacitive Sensors

We present the theoretical analysis and performance results of a direct microcontroller unit (MCU) interface circuit for capacitive sensors based on the charge-transfer method, when stray capacitances are considered. The interface circuit can implement two alternative two-point calibration techniques that reduce the effects of stray capacitance, temperature, and MCU parameters that depend on the power supply voltage. The best measurement deviation achieved from 0 $^{circ}hbox{C}$ to 50 $^{circ}hbox{C}$ and for power supply voltage from 4.0 to 5 V is below 0.01 full-scale range (FSR) for the two subranges from 10 to 100 pF and from 100 pF to 1 nF and 0.08 FSR for the subrange from 2 to 10 pF.      

Capacitive Transduction for Liquid Crystal-Based Sensors, Part I: Ordered System

In this paper, the theory for tracking the average molecular orientation of a liquid crystal (LC) material via capacitive sensing of anisotropic media is presented. The candidate LC sensor structure utilizes interdigital electrodes. Two capacitive measurements in orthogonal direction can track the director axis of nematic LC material in a homogenous ordered LC film. The sensitivity for the sensor at different alignments is studied. The candidate sensors have been fabricated and experimentally verified. Both experimental and calculated values for capacitances of selected interdigital fingers sensor structures are presented.     

Self-Powered Sensors for Monitoring of Highway Bridges

The task of structural health monitoring (SHM) of aging highway bridges and overpasses is important not only from the point of preventing economic losses from traffic delays and detours but also is a matter of preventing catastrophic failures and loss of human life. In recent years, wireless sensor technologies have been used extensively to develop SHM platforms for bridges. A limitation of wireless sensors is the finite life span of batteries and high cost of battery replacements, which make such systems prohibitively expensive in many cases. Energy harvesting is a solution capable to alleviate this problem. A novel wireless sensor system is presented that harvests vibrations of the bridge created by passing traffic, which is converted into usable electrical energy by means of a linear electromagnetic generator. Utilization of an electromagnetic generator allows harvesting of up to 12.5 mW of power in the resonant mode with the frequency of excitation at 3.1 Hz, in this particular design. The novelty of the system also includes tight integration of the power generator and a smart algorithm for energy conversion that switches between the low-power mode and the impedance matching mode. Finally, results of field experiments are presented in which the wireless system is operated exclusively by the harvested energy of vibration on a rural highway bridge with low traffic volume.     

Smooth Contact Capacitive Pressure Sensors in Touch- and Peeling-Mode Operation

Capacitive (C) pressure sensors typically sense quadratic changes in $C$ as a pressure difference $(P)$ deflects a flexible conducting diaphragm near a rigid ground plane. Touch-mode capacitive pressure (C-P) sensors, where the conducting diaphragm touches a dielectric coated ground plane, often show a more linear response, but with less sensitivity, particularly at low-$P$ . Initial contact of the diaphragm often occurs at a critical $P$. Until $P_{rm crit}$ is reached, the sensitivity is typically too low for accurate measurements. In this work, two different types of electrodes with “parabolic” and “donut” cavity-shapes have been designed, fabricated, and tested to achieve high-sensitivity at low-pressures. A flexible conducting diaphragm touches the bottom electrode smoothly, and both cavity shapes permit initial contact at a zero-pressure differential. This type of C-P sensors can have touch-mode and peeling-mode operations. The sensitivities of these sensors in two operation modes were measured, and their resolutions were smaller than 0.1 Pa at a mean pressure of ${10} ^{5}~{rm Pa}$. Both sensors in two modes have the resolution over total-pressure less than ${10} ^{-6}$, which is difficult to achieve at atmospheric pressure.      

Capacitive Humidity Sensors With High Sensitivity and Subsecond Response Times

Capacitive-based humidity sensors were fabricated using coplanar interdigitated electrodes coated with nanostructured TiO₂ thin films produced by glancing angle deposition. In this letter, we show that increased sensitivity (nF/%RH) is obtained by decreasing the electrode periodicity or by increasing the planar area of the electrodes, or both. The devices were sensitive over a wide range of relative humidity levels (<1% to >92%) and exhibited extremely fast, subsecond response times. Typical adsorption and desorption response times were measured to be <220 and >400 ms, respectively     

Intraocular Pressure Monitoring Sensors

Continuous measurement of intraocular pressure is important in the detection and treatment of glaucoma. While a point check of intraocular pressure in a doctor's office using indirect measurements such as the tonometer is helpful, it is inadequate to track circadian variation. Circadian variation is an independent risk factor in addition to elevated pressure levels. This paper is aimed at providing an up-to-date review of various intraocular pressure sensing techniques and in vivo sensor design approaches. The basic operating principles of various implantable sensors are reviewed and categorized into groups to delineate their differences. A discussion is presented identifying the drawbacks of existing designs and key design questions are proposed for future progress.     

Capacitive Transduction for Liquid Crystal Based Sensors, Part II: Partially Disordered System

This paper presents the capacitive transduction technique involved with liquid crystal (LC) based sensors in partially disordered systems. These sensors have the potential applications in chemical and biological systems. The theory for tracking the average molecular deformation (state of alignment) and degree of ordering of anisotropic and partially disordered LC film via capacitive sensing is investigated. This system is modeled using the Q-tensor approach in modeling uniaxial LC material. The proposed sensor design is an interdigitated electrodes structure. Transverse and fringing capacitances as function of the molecular deformation are calculated. It is verified that three capacitance measurements are required to track the average molecular orientation and the degree of disorder in the LC film. The sensitivity for the sensor at different alignments and ordering degree is also studied. Toward practical sensor, neuro-fuzzy system is modeled to simulate the capacitive transduction and to monitor the LC profile. Sensors are fabricated and tested. Both the experimental and calculated capacitances are presented and compared.      

Textile-Based Electrogoniometers for Wearable Posture and Gesture Capture Systems

This paper introduces a method for detecting joint angles by using piezoresistive strain sensitive materials, as carbon loaded rubbers are. Materials used can be screen-printed onto fabrics to provide garments with a sensing apparatus able to reconstruct human postures and gestures. The main differences between this approach and the previous ones, and the core of this work, is the rigorous proof that for small local curvatures of the layers the constituting electrogoniometers, the resistance depends only on the total curvature of the layers and not on the particular form that the sensor keeps in adherence with the human body. In this paper, we show that the hypothesis of small local curvature does not severely restrict the set of angles which can be detected.      

Evanescent Field Fiber-Optic Sensors for Humidity Monitoring Based on Nanocoatings

The transmitted optical power of two different fiber optic based structures when a nanofilm is being deposited onto them is experimentally studied. The technique used to build the nanofilms is Electrostatic Self Assembly (ESA), which has been widely reported in the literature. For the shake of comprehensibility, the comparative analysis of this phenomenon is accomplished for a particular sensing measure, humidity. The two structures selected towards development of practical humidity evanescent field sensors are hollow core fibers and tapered optical fibers. Some preliminary experimental studies of depositing humidity sensitive thin films and demonstrating their feasibility are presented. Depending on the working point selected, up to 10dB of variation in the optical output power is obtained when the environmental humidity changes. Both configurations exhibit similar dynamic behavior and response times shorter than 300msec, making these evanescent field sensors good candidates to monitor human breathing     

Full Wheatstone Bridge Spin-Valve Based Sensors for IC Currents Monitoring

Full Wheatstone bridge spin-valve-based electrical current sensors at the IC level are presented. Prototypes with different geometrical parameters have been designed, fabricated and fully characterized. DC characterization has been carried out, for measurement of insertion losses, linearity, voltage offset and sensitivity. Current ranges from 10 $mu{rm A}$ to 100 mA can be covered with these sensors with excellent linearity and sensitivities above 1 ${rm mV}/({rm V}cdot{rm mA})$ . AC characteristics have also been analyzed and bandwidths exceeding 100 kHz are demonstrated. Moreover, the temperature coefficients have been extracted in the range of $-20^{circ}{rm C}$ to $+60^{circ}{rm C}$. In order to highlight the design properties, dependence of the sensor's performance with external magnetic perturbations and self-heating have also been measured and quantified. The associated errors are in the range of 1%–2% of the full scale.      

Silver Nanowire Electrodes: Conductivity Improvement Without Post-treatment and Application in Capacitive Pressure Sensors

Nano-Micro Letters - Transparent electrode based on silver nanowires (AgNWs) emerges as an outstanding alternative of indium tin oxide film especially for flexible electronics. However, the...     

面向结构健康监测的传感器数量及位置优化研究

在能够反映结构特性的重要位置布置合理数量的传感器不但可以有效地降低结构健康监测成本,还可以提高监测系统处理信息的效率.根据结构系统可观性,分别给出了观测一般结构和重频结构的前若干阶目标模态所需要最少传感器数量的估计方法.提出一种选用Frobenius范数求最大化Fisher信息矩阵的方法,阐述了求最大化Fisher信息矩阵等价于选取具有最大能量的节点模态向量子集的结论.在此基础上并结合传感器优化布置的多重标准,提出基于节点能量和模态保证准则的传感器优化布置方法.数值算例的结果验证了该方法的正确性和有效性.     

Continuous-Flow System for On-Line Water Monitoring Using Back-Side Contact ISFET-Based Sensors

A multiparametric continuous-flow system for on-line monitoring of water based on ISFET sensors is described. The ISFETs used have silicon nitride as gate material, and the electrical contacts are placed on the back side of the chip. This is a technological improvement that allows for a more compact ISFET packaging and greatly increases the lifetime of the sensor compared with planar type ISFETs, since the electrical parts are separated from the chemical environment. A special probe has been designed in order to encapsulate and apply these ISFETs into the flow system. Further, a reference electrode based on standard Ag/AgCl technology has been constructed according to the ISFET probe design in order to integrate both sensors in the same flow-through cell. These probes can be easily replaced in the flow system and are made of cheap and easily mechanized materials. Using these flow-through sensors, a continuous-flow system for the determination of pH, NH(4)(+), Ca(2+), and NO(3)(-) in waters has been designed. The system configuration is based on a modular design (one setup for each parameter and a common sampling channel), which allows simple manipulation and maintenance as well as a good flexibility for different analytical requirements. A study of the system characteristics was performed by following the specifications for water monitoring. Under the conditions established for the flow system, a sampling rate of 20 h(-)(1) was obtained for each parameter, and long-term stabilities of at least 3 weeks of daily work for ISFET sensors and 5 months for the reference electrode have been achieved. The response performances obtained show the feasibility of the BSC ISFET probe use in continuous-flow monitoring.