"Fuzzy tap-testing" sensors for material health-state characterization

A smart sensor for structural health monitoring, based on piezoelectric tactile sensors and soft-computing signal-processing techniques, is presented in this paper. The proposed probe, made by tubular translating piezoceramic elements, stimulates the surface of the object under test and analyzes the local viscoelastic response produced at the moment of tapping. An automatic and "real-time" strategy, based on the processing of a class of features, extracted from the time-domain responses of the developed tactile probe, is proposed in order to classify the damages compromising the health status of a material. Suitable software procedures, based on fuzzy logic and implemented on a dedicated microcontroller, elaborate the input data in order to realize the desired classification task. A specific application is reported here in order to validate the proposed sensing device. It consists of the "detection of damages induced in composite structures"; in particular, a coupon of quasi-isotropic carbon epoxy material, subjected to various aggressions, has been considered. Different damages such as delaminations, induced by calibrated impacts, and burning, induced either by contact with a hot body or by simulated lightning impact produced by electric sparks, have been considered. The results obtained are quite interesting in view of the simple structure of the measurement system proposed here with respect to other classical approaches.     

Transparent and flexible tactile sensors based on graphene films designed for smart panels

With the development of the human–computer interaction, smart panel requires more of lightweight and transparency. However, most smart panels have been developed based on bulky metal materials and integrated external circuits, which lack flexibility and transparency. Here we demonstrate an ultrathin and flexible tactile sensor based on few-layer graphene films (GFs). The optical transmittance of the sensor is up to 80% in the visible range, which provides optical transparency enough for an aesthetic view. The sensor is assembled through a very simple method consisted a polyethylene terephthalate substrate and two unconnected GFs. The as-assembled sensors can reflect one-dimensional (1D) touch position with a high sensitivity of 0.23 mm^?1. The tactile sensor can be used in the monitoring of finger touch, as well as in the detection of liquid temperature. The GFs-based tactile sensor was transferred on the glass substrate to form a smart window, which can warn of a rainy weather coming without sacrificing the window visual functionalities. In addition, a flexible smart panel has been assembled only connect two external circuits and succeed in reappearing the 2D touch path.     

Tactile sensor based on piezoelectric resonance

We discuss here the realization of tactile sensors based on the principle of change in piezoelectric resonance frequency with the applied pressure. An array of electrodes has been adopted on either side of the PZT material to have independent resonators. The common areas sandwiched between the electrodes and excitable at resonance frequency of the PZT material are used to form the sensitive area of the tactile sensor. The electrodes were deposited using sputtering technique. Tactile sensors with 3/spl times/3, 7/spl times/7, and 15/spl times/15 array of electrodes are developed with different electrode dimensions and separation between the electrodes. The tactile sensor has been interfaced to computer for the convenience of automatic scanning and making it more user interactive. The tactile sensors developed with different spatial resolution were tested for different shaped objects placed in contact with the sensor. The 3/spl times/3 matrix tactile sensor showed relatively poor spatial resolution, whereas the 15/spl times/15- matrix tactile sensor showed improved spatial resolution. The sensor with 7/spl times/7 matrix elements was tested for its sensitivity to different extents of applied force/pressure. The output response study carried out on the sensors indicated that these sensors can provide information not only about the extent of force/pressure applied on the object, but also the contour of the object which is in contact with the sensor.     

基于压电智能材料的自适应吸声实验研究

提出了用压电材料进行水下主动宽带低频吸声的方法,用PVDF复合智能材料作为主动吸声系统中的吸声材料,在滤波-X LMS算法基础上,研究了一种在工程中实现简便的次级通道建模方法——通道时延估计法。构建了数字时延控制系统,直接从实际声场中分离入射声波与反射声波作为控制系统的参考信号和误差信号,在脉冲声管中进行了管道声有源吸声控制实验。实验结果表明,在施加控制的情况下PVDF压电智能材料能有效地对低频入射声进行吸收。     

可变摩擦力触感移动终端的汉语盲文编码设计

在智能触屏移动终端上表达盲文是一件具有深刻现实意义但又充满挑战的工作。为了让视障人士能够通过摸读智能触屏移动终端上的盲文来获取信息,提出了3种基于可变摩擦力触感的移动终端通用汉语盲文编码方法,分别为通用盲文编码方法、声调嵌入编码方法及4行2列编码方法。基于压电传感器的超声震荡波可在物体表面产生可变摩擦力触感的原理,在智能移动终端上实现汉语盲文触感编码。通过对12名盲人用户进行2次系统实验,从摸读效率、摸读准确率和用户满意度方面对编码方法进行可用性评估。首先,对3种编码方法进行可用性评估(实验1),然后基于实验1的结果,挑选4行2列编码方法与基于向右滑动摸读方式的振动马达触觉反馈编码方法进行可用性对比(实验2)。实验1结果显示,3种编码方法的平均摸读效率分别为8.82,4.91,4.12 s/汉字,平均摸读准确率分别为98.6%,96.8%,98.6%,4行2列编码方法在用户满意度方面的综合得分最高。实验2结果表明,与基于向右滑动摸读方式的振动马达触觉反馈编码方法相比,4行2列编码方法的摸读效率、摸读准确率及用户满意度更高。综上所述,采用4行2列编码方法能够在移动终端上实现对通用汉语盲文的编码和摸读,可为视障人士在智能移动终端上摸读汉语盲文提供新思路。     

Skin-like tactile sensor arrays for contact stress field extraction

Continuous scanning of variable contact forces occurring during object exploration and manipulation by means of miniature sensors is becoming increasingly important in medical prosthetics and orthotics, advanced robotics, teleoperation and telepresence. In this paper a system able to provide robots with tactile sensitivity is presented. Skin-like tactile sensor arrays, which are selectively sensitive to stress-tensor components and are based on piezoelectric polymer technology, have been implemented. The basic characteristics of the sensors, together with the mechanical devices and the electronics developed for setting up the artificial tactile system, are described. An investigation of the expected responses of the sensor has been carried out by modelling the mechanics of object-sensor interaction and by finding the stress solutions of a forward elastic contact problem. The system has been tested by comparing the theoretical results with data measured experimentally from the sensor.     

Dual-Mode Capacitive Proximity Sensor for Robot Application: Implementation of Tactile and Proximity Sensing Capability on a Single Polymer Platform Using Shared Electrodes

In this paper, we report a flexible dual-mode capacitive sensor for robot applications which has two sensing capabilities in a single platform; tactile and proximity sensing capability. The sensor consists of a mechanical structure based on PDMS (Polydimethylsiloxane) and a mesh of multiple copper electrode strips. The mesh is composed of 16 top and 16 bottom copper strips crossed each other to form a 16 $,times,$16 capacitor array. The proposed sensor is able to switch its function from tactile sensing to proximity sensing or vice versa by reconfiguring the connection of electrodes. The tactile sensing capability has been demonstrated already and reported in our previous paper (Lee , 2006); therefore, in this paper, we will demonstrate the feasibility of the proximity sensing capability and the dual-mode operation of the proposed sensor in detail. The capacitance change caused by an approaching object has been estimated through simulation of multiple two-dimensional models as an initial study. The measured data have shown similar trends with the simulation results. We tested various materials from conducting metals to a human hand for proximity measurement. The fabricated sensor could detect a human hand at a distance up to 17 cm away from the sensor. We also have successfully demonstrated the feasibility of dual-mode operation of the proposed sensor in real-time exploiting a custom designed PCB, a data acquisition pad, and Labview software.      

智能材料工艺与结构中的先进传感器的发展

建立复合材料成型过程的智能化在线监控系统,有效地调整生产工艺,科学设计和优化生产工艺,可以有效地提高生产质量,降低生产成本。除生产工艺智能化外,还需建立材料结构的智能化体系,从复合材料固化成型、材料生产到材料应用整个过程均实现智能化,将开辟材料科学研究的新途径。建立智能材料工艺与结构体系需要先进的性能优良的传感器,本文以智能材料体系为背景阐述了各种传感器技术性能及发展方向。     

Harsh environments minimally invasive optical sensor using free-space targeted single-crystal silicon carbide

To the best of our knowledge, for the first time, a single-crystal silicon carbide (SiC)-based minimally invasive smart optical sensor suited for harsh environments has been designed and demonstrated. The novel sensor design is based on an agile wavelength source, instantaneous single-wavelength strong two-beam interferometry, full optical power cycle data acquisition, free-space targeted laser beams, multiple single-crystal-thick SiC optical front-end chips, and multiwavelength signal processing for unambiguous temperature measurements to form a fast and distributed smart optical sensor system. Experiments conducted using a 1550-nm eye-safe band-tunable laser and a 300-/spl mu/m coating-free thick SiC chip demonstrate temperature sensing from room temperature to 1000/spl deg/C with an estimated average 1.3/spl deg/C resolution. Applications for the proposed sensor include use in fossil fuel-based power systems, aerospace/aircraft systems, satellite systems, deep-space exploration systems, and drilling and oil mining industries.     

A Novel Thick-Film Piezoelectric Slip Sensor for a Prosthetic Hand

The ability to mimic the tactile feedback exhibited by the human hand in an artificial limb is considered advantageous in the automatic control of new multifunctional prosthetic hands. The role of a slip sensor in this tactile feedback is to detect object slip and thus provide information to a controller, which automatically adjusts the grip force applied to a held object to prevent it from falling. This system reduces the cognitive load experienced by the user by not having to visually assess the stability of an object, as well as giving them the confidence not to apply unnecessarily excessive grip forces. A candidate for such a sensor is a thick-film piezoelectric sensor. The method of fabricating a thick-film piezoelectric slip sensor on a prototype fingertip is described. The construction of experimental apparatus to mimic slip has been designed and analyzed to allow the coefficient of friction between the fingertip and the material in contact with the fingertip to be calculated. Finally, results show that for a coefficient of friction between the fingertip and grade P100 sandpaper of approximately 0.3, an object velocity of 0.025plusmn0.008 ms^-1 was reached before a slip signal from the piezoelectric sensor was able to be used to detect slip. It is anticipated that this limiting velocity will be lowered (improved) in the intended application where the sensor electronics will be powered from a battery, connections will be appropriately screened, and if necessary a filter employed. This will remove mains interference and reduce other extraneous noise sources with the consequence of an improved signal-to-noise ratio, allowing lower threshold values to be used in the detection software     

Low-coherence Michelson interferometric fiber-optic multiplexed strain sensor array: a minimum configuration

A minimum configuration Michelson fiber-optic low-coherence interferometric quasi-distributed sensing system is proposed that permits absolute length measurement in remote reflective sensor arrays. The sensor's reflective signal characteristics have been analyzed, and the relationship between intensities of light and number of sensors is given for evaluation of multiplexing potential. The proposed sensing scheme will be useful for the measurement of strain distribution. An important application may be strain monitoring in smart structures. Experimentally, four-sensor array has been demonstrated.     

MEMS Endoscopic Tactile Sensor: Toward In-Situ and In-Vivo Tissue Softness Characterization

The superiority of endoscopic surgery over traditional open surgery in many areas has encouraged researchers to tackle a few shortcomings that are associated with the current state of minimally invasive surgical procedures. Among the shortcomings of minimally invasive surgery (MIS), the lack of sense of touch was the motive of the present work. Therefore, this research was aimed at restoring tactile sensing capabilities by developing a microelectromechanical systems (MEMS) tactile sensor for integration with existing MIS graspers. The tactile sensor is able to measure force, force position and also the softness of the grasped object. The transduction element, a uniaxial polyvinylidene fluoride (PVDF) film, was characterized before the microfabrication of the corrugated sensor. A finite-element model of the sensor system and soft material was also developed. The simulation results were compared with those of the experimental tests and the comparison showed good agreement.     

Wireless Industrial Monitoring and Control Using a Smart Sensor Platform

A wireless smart sensor platform (based on patent pending technologies, Ramamurthy ) targeted for instrumentation and predictive maintenance systems is presented. The generic smart sensor platform with "plug-and-play" capability supports hardware interface, payload and communications needs of multiple inertial and position sensors, and actuators, using a RF link (Wi-Fi, Bluetooth, or RFID) for communications, in a point-to-point topology. The design also provides means to update operating and monitoring parameters as well as sensor/RF link specific firmware modules "over-the-air." Sample implementations for industrial applications and system performance are discussed     

Study on electromechanical characterization of piezoelectric polymer PVDF in low-frequency band

Polyvinylidene fluoride (PVDF), a piezoelectric polymer material, is well known as one of the best smart materials to be used for tactile sensors in robots for its good performance. It has been used in many applications including sensors, actuators and surface acoustic wave (SAW) devices. This paper presents an experimental setup and experimental procedures for studying the electromechanical characterization of piezoelectric polymer films, by which the electromechanical characterization of the PVDF films under quasi-static loads and dynamic loads in a wide range of frequency can be researched. Through quasi-static tests, the stress–strain relationships of PVDF films in different directions were obtained. Furthermore, the viscoelastic and piezoelectric properties of PVDF films were analyzed based on the measurement results of dynamic tests under low frequency from 5 Hz to 200 Hz, and some suggestions of the applications of PVDF piezoelectric films in robot tactile sensor are presented.     

光纤缠绕式应变传感器

研究了一种可用于机敏复合材料与结构状态监测的本征型强度调制光纤应变传感器,它由两根以上多模光纤相互缠绕绞合形成。分析了该传感器的应变传感原理,得到其既能测量拉应变、又能测量压应变的结论。传感器对应变的响应具有良好的线性和重复性,灵敏度高,无迟滞现象。对植入碳纤维/环氧复合材料内的光纤缠绕型应变传感器的实验结果与理论分析一致,表明该传感器是适合于机敏复合材料与结构状态监测的较为理想的光纤传感器。     

Large‐Area All‐Textile Pressure Sensors for Monitoring Human Motion and Physiological Signals

Wearable pressure sensors, which can perceive and respond to environmental stimuli, are essential components of smart textiles. Here, large‐area all‐textile‐based pressure‐sensor arrays are successfully realized on common fabric substrates. The textile sensor unit achieves high sensitivity (14.4 kPa^?1), low detection limit (2 Pa), fast response (≈24 ms), low power consumption (<6 µW), and mechanical stability under harsh deformations. Thanks to these merits, the textile sensor is demonstrated to be able to recognize finger movement, hand gestures, acoustic vibrations, and real‐time pulse wave. Furthermore, large‐area sensor arrays are successfully fabricated on one textile substrate to spatially map tactile stimuli and can be directly incorporated into a fabric garment for stylish designs without sacrifice of comfort, suggesting great potential in smart textiles or wearable electronics.     

Piezoelectric Vibration-Type Tactile Sensor Using Elasticity and Viscosity Change of Structure

We propose a new tactile sensor utilizing piezoelectric vibration. This tactile sensor has a high sensitivity, wide measurement range, pressure resistance, flexibility, and self-sensing function. This tactile sensor comprises two piezoelectric materials. One is used for the vibration of the sensor element and the other is used for the measurement of the change in mechanical impedance induced by an external force. We achieved the wide measurement range by implementing two ideas. One was to apply the external force to the sensor element through an elastic body and the other was to use two or more modes of vibration. Moreover, for the elastic body, it is preferable to use a material whose elasticity and viscosity are easily changed by an external force, such as a gel. In this study, first, this tactile sensor was analyzed, and then its characteristics were derived. The analytical results qualitatively corresponded to the experimental results. Next, a prototype tactile sensor was fabricated and evaluated. The evaluation results showed that this tactile sensor can measure a pressure of 2.5 Pa or less and a pressure of 10 kPa or more and its pressure resistance is 1 MPa or more.     

Systems,structures and people

Five days listening to world experts talking on the topic of smart materials and structures leaves an amazing amount of material to be digested. One of the major issues is the multidisciplinary breadth of field covered. This ranges through modelling, signal processing and control; smart sensor technology and measurement; electroactive polymer actuators and devices; smart systems for bridges, structures and highways, damping and isolation; active materials behaviour and mechanics; smart electronics, MEMS and nanotechnology; smart structures and integrated systems to the industrial and commercial applications of smart structure technologies.     

Skin-Inspired Thermosensitive Tactile Sensor Based on Thermally Conductive and Viscous Interface Composites for Rocks

Achieving high thermal conductivity and exceptional interfacial adhesion simultaneously in thermosensitive tactile recognition sensors poses a significant challenge. A copolymer, poly([[(butylamino)carbonyl]oxy]ethyl-ester)-co-polydimethylsiloxane (referred to as PP), is synthesized and subsequently complexed with alumina particles coated with liquid metal (LMAl₂O₃) to prepare a composite material called PP/LMAl₂O₃ with high thermal conductivity and strong interfacial adhesion to address this challenge. The best thermal conductivity (4.43 W m⁻¹ K⁻¹), electrical insulation (10⁻⁶–10⁻⁷ S m⁻¹), and adhesion properties derived from hydrogen bonding (1316 N m⁻²) are obtained by adjusting the volume fraction of PP and LMAl₂O₃ in PP/LMAl₂O₃. PP/LMAl₂O₃ with high thermal conductivity and high interface adhesion can efficiently transfer heat between thermal flux sensors and the objects being sensed, reliably detecting small thermal flux variations and ensuring accurate thermal flux measurements. In this study, PP/LMAl₂O₃ is used to make up thermosensitive tactile sensor. Surprisingly, PP/LMAl₂O₃ demonstrates high thermal signal sensitivity for tactile recognition applications, allowing the smart thermosensitive tactile sensor system to distinguish unknown rock materials even in the dark. Overall, PP/LMAl₂O₃ may function as a fundamental material in thermosensitive tactile sensors for lithology identification.     

A feasible noise estimation algorithm for resource-limited sensor systems

Fault tolerance and self-checking capabilities are key features of modern smart sensors, which often require the integration of additional signal processing facilities. In high-volume production areas such as automotive applications, however, optimized controllers are employed that typically have only limited computing resources. This paper examines several algorithms to assess the noise in a quasi-closed loop measurement channel under the assumption that the stimulus can be held constant during noise measurement. Starting from the definition of standard deviation, we propose several modifications and obtain an easy-to-implement algorithm relying entirely on addition and shift operations. Numerical experiments based on simulated and measured noise verify the practicability of the approach. The proposed algorithm has already been successfully implemented in a capacitive angular speed sensor system for automotive applications.