Ultrasonic six-axis deformation sensing

In this paper, we describe a newly developed deformation sensing scheme in a soft medium, which is based on precise encoding and decoding of deformation components into ultrasound wavefronts. It can detect three translational components and three rotational components of displacement around a transmitter position nearly simultaneously. We assume a cell structure that consists of a 2×2 ultrasonic transmitter matrix and a 2×2 ultrasonic receiver matrix, which are placed face to face at a distance of a few tens of wavelengths. All of the transmitter elements are driven sinusoidally and simultaneously, but they are switched into the same, reversed, or quadrature phases to generate a particular shape of wavefront on the receiver matrix. The receiver elements are connected in such a way to obtain amplitude and spatial gradients of the wavefront at a center of the receiver matrix. First, we describe the transduction theory for the six dimensions and show the orthogonality, locality, and simultaneity of this sensing scheme. Then, we describe the fabrication and experimental evaluation of the cell. We also describe a prototype tactile sensor in which a single cell is embedded in a flexible hemispherical fingertip-like body     

应用于热声机械的声波平面传递装置

应用于热声机械的声波平面传递装置,由柔性部分和刚性片部分组成.通过引入柔性结构,将传递声波所必需的弹性部分和惯性部分分开,实现刚性片的平面运动,从而达到声波的平面传递.依据弹性部分的不同形式,声波平面传递装置有3种形式:弹性膜型、折环型和弹性环型.将这种装置应用于热声机械中,可以大大改善热声系统中声波传递的性能,拓展热...     

An aging model for surface acoustic wave devices

The authors present a study of the phase-aging kinetics of a 591.2 MHz quartz-crystal surface acoustic wave (SAW) filter intended for application in an undersea telecommunication system. At aging temperatures from 50 to 140 degrees C, a previously established SAW-device aging model describes the time dependence of the phase aging. The results of an investigation of the temperature dependence of the coefficients in this aging model allows the authors to extend the model, capturing both the time and the temperature dependence of the degradation. They then identify and assess the sources of variation, or error, affecting the data and model, estimate the distributions of the errors, and incorporate these error distributions in the extended aging model. This leads to a composite aging model that describes the time and temperature dependence of the complete phase-aging distribution. The authors use this composite model to predict end-of-life phase-aging distributions, demonstrating that the devices exhibit the high level of stability required by the application.     

Three-dimensional finite-elements modeling and simulation of rotary-draw bending process for thin-walled rectangular tube

According to the characteristics of the rotary-draw bending process of a thin-walled rectangular tube, a three-dimensional finite-elements model of this process is built under the ABAQUS/explicit environment based on the solution of several key techniques, such as contact boundary condition treating, material properties definition, meshing technology, etc. The actions of pressure die, wiper die, clamp die and mandrel are considered in the modeling process. Then the reliability of the model is validated by comparison with experiments in the literature. Furthermore, numerical simulation and analysis of the thin-walled rectangular tube bending process of 3A21 aluminum alloy have been carried out by using the model. The distribution laws of tangential stress in the process have been analyzed. The results show that the maximum tangential stress increases sharply in the initial stage and then keeps nearly constant with the progress of the bending process. The circumferential compressive stress zone is basically unchanged when the bending process becomes stable.     

Crushing analysis and multi-objective optimization design for bionic thin-walled structure

Thin-walled structure has gained increasing attention and been widely used in the field of mechanical engineering due to their extraordinary energy absorption capacity and light weight. In this paper, we introduced a new energy absorbed structure named as bionic thin-walled structure (BTS) based on the structural characteristics of horsetails. In this study, six kinds of BTSs with different cross-sectional configurations under lateral loading conditions were investigated using nonlinear finite element method through LS-DYNA. According to the numerical results, it can be found that the cell number, inner wall diameter and wall thickness of the BTS had significant effect on the crashworthiness of the structure. In order to obtain the optimal design among the six kinds of BTSs, the six BTSs were optimized using a metamodel-based multi-objective optimization method which was developed by employing polynomial regression (PR) metamodel and multi-objective particle swarm optimization (MOPSO) algorithm. In the optimization process, we aimed to achieve maximum value of specific energy absorption (SEA) and minimum value of maximum impact force (MIF). Meanwhile, we also optimized the traditional thin-walled structures, i.e., the circular and square tubes. Based on the comparison of the Pareto fronts obtained by the multi-objective optimizations, we found that the crashworthiness of the BTSs was better than that of the circular and square tubes and the best BTS among the six kinds of BTSs was different when the limit of MIF was different. And, the optimal designs of the BTSs were found to have excellent energy absorption capacity under lateral impact and could be used in the future vehicle body.     

Josephson effect devices and low-frequency field sensing

Three major areas of application of the Josephson effect are recognized; absolute standards, millimetre and sub-millimetre wave sensing, and dc and low-frequency current, voltage, and magnetic field sensing. In the latter area, single junction rf-biased low-inductance loop devices in a number of different forms (junction types and loop geometries) have been developed with sensitivities of the order of 10⁻¹⁵ T (10⁻¹¹ G) or 10⁻¹⁹ V. These sensors are being used in applications as diverse as magnetocardiography and absolute noise thermometry in the millikelvin range. As amplifiers, they are characterized by demonstrated equivalent noise temperatures of less than a few millikelvin, and probably a few microkelvin (theoretical). Highly reliable thin-film loop devices in a number of different forms have been developed in several laboratories, but the more easily-made point-contact devices are probably the most widely used. Many of the characteristics of the devices can be easily interpreted with the aid of a pendulum analogue.     

Ultrasonic wave propagation in temperature gradients

Ultrasonic methods are being developed for sensing and control of high temperature material processes such as welding and solidification. One of the problems in these methods is the distortion of the sound field caused by the change in material properties due to temperature gradients. This paper describes a ray-tracing method for calculating the effects of temperature on ultrasonic propagation in such systems. In the ray-tracing method, the material is conceptually divided into a number of plane layers. The refraction at each layer boundary is calculated from Snell's law using the sound speeds determined from the temperatures of the adjacent layers. The time required for an ultrasonic pulse to traverse each layer is also calculated, allowing the determination of the total time along a particular path. The method is applied to calculating the time of arrival of echoes from various interfaces around a molten weld pool.     

Simulation of surface acoustic wave devices

The Mason crossed-field circuit model is generalized to simulate apodized interdigital transducers without channel division. The apodized transducer model is based on the transmission line model, and the artificial transformer with different voltage and current coupling ratios is used to independently obtain the transfer function and radiation admittance. In addition, a heuristic expression for transformer current ratios is used to approximate the radiation admittance of apodized transducers. Through comparing with the multichannel model, this unichannel model is illustrated to successfully describe the frequency response of apodized interdigital transducers.     

A strategy for chemical sensing based on frequency tunable acoustic devices

A new acoustic sensor geometry, the magnetic acoustic resonant sensor (MARS), is described. The device comprises a circular 0.5-mm-thick resonant plate fabricated from a wide variety of nonpiezoelectric materials and coated on the underside with a 2.5-microm-thick aluminum film. Harmonic radial shear waves over at least a 2 orders of magnitude frequency range can be induced in the resonant plate by enhanced magnetic direct generation using a noncontacting rf coil and NdFeB magnet. Mass loading with adherent aluminum films produced frequency changes of 106 Hz/nm (40.8 Hz/ng-mm(-2)), while contact with viscous fluids resulted in maximum changes of 15 446 Hz/cP. At an operating frequency of 50 MHz, the device detected viscosity changes as low as 0.0006 cP. The adsorption of proteins such as human IgG and the binding of a complementary antigen, goat anti-human IgG, on the upper nonmetallized surface of the device has been monitored with a detection limit of approximately 75 ng/mL. The binding of substrates and allosteric effectors to glycogen phosphorylase b has provided evidence that the device is very sensitive to viscoelastic changes in adsorbed proteins. The MARS device generates radial shear acoustic waves over a broad bandwidth that are unaffected by the conductivity of the solution. These results suggest that simple metal, glass, crystalline, or polycrystalline plates can be used as a new type of tunable acoustic immunosensor.     

螺旋行波管衰减器炭涂层的特性表征

分别采用热解沉积、胶体石墨涂刷和电弧放电法在行波管(TWT)刚玉支撑杆上涂覆了吸波炭涂层,以改善TWT稳定性.通过一种带孔窄频-高波-道管的实验装置,应用无向量网络解析器实施反射和透射波测量,测得6.0GHz频段涂层杆的衰减程度.并利用一种软件高频结构模拟器(HFSS)进行了模拟.结果表明:胶体石墨涂层显示出最大的损失或吸光率.是适宜的衰减器涂料.HFSS模拟的结果与实验结果吻合.     

Ultrasonic wave propagation in carbon fibre-reinforced plastics

The attenuation and velocity of the longitudinal and shear waves in unidirectional carbon/epoxy composites have been measured as a function of the fibre volume fraction over the frequency range, 1.84 to 11.9 MHz, using the pulse-echo technique. The decrease of attenuation with fibre volume fraction suggested that the high attenuation in the composites was caused by viscoelastic losses in the epoxy matrix rather than scattering losses by the fibre. The attenuation increased with frequency, while the velocity was found to be independent of frequency.     

Ultrasonic wave transmission in periodically undulated plates

This study focuses on quantifying the change in phase speed of waves transmitting through periodically undulated plates under pass band interaction. A perturbation technique is used to analyze the transmission of horizontally polarized guided waves in elastic plates with sinusoidal periodicity at their outerfaces. Phase speed of transmitting modes is presented as a function of various parameters, including outerface wavenumber, undulation amplitude, degree of undulations symmetry about the periodically undulated plate midplane, plate average thickness, and frequency of propagation.     

Discrete control of resonant wave energy devices

Aiming at amplifying the energy productive motion of wave energy converters (WECs) in response to irregular sea waves, the strategies of discrete control presented here feature some major advantages over continuous control, which is known to require, for optimal operation, a bidirectional power take-off able to re-inject energy into the WEC system during parts of the oscillation cycles. Three different discrete control strategies are described: latching control, declutching control and the combination of both, which we term latched-operating-declutched control. It is shown that any of these methods can be applied with great benefit, not only to mono-resonant WEC oscillators, but also to bi-resonant and multi-resonant systems. For some of these applications, it is shown how these three discrete control strategies can be optimally defined, either by analytical solution for regular waves, or numerically, by applying the optimal command theory in irregular waves. Applied to a model of a seven degree-of-freedom system (the SEAREV WEC) to estimate its annual production on several production sites, the most efficient of these discrete control strategies was shown to double the energy production, regardless of the resource level of the site, which may be considered as a real breakthrough, rather than a marginal improvement.     

超声A扫描信号建模及其缺陷识别方法研究

针对超声检测中A扫描信号依靠经验评定结构缺陷、识别缺陷类型困难等问题,提出一种A扫描信号建模方法,计算出缺陷A扫描信号。该方法基于超声检测系统建立A扫描信号数学模型,应用多元高斯声束法计算模型中缺陷表面超声波传播质点速度,运用基尔霍夫近似理论描述模型中缺陷散射振幅,从而获得缺陷超声A扫描信号。应用CSII-1/20标准试块平底孔(缺陷)超声A扫描表明:该方法计算获得试块平底孔5#(缺陷)A扫描信号与试验测量结果在缺陷位置和幅度基本吻合,是识别结构孔洞类缺陷的一种有效方法。     

Sensitivity of Lamb wave sensors in liquid sensing

The differences of the sensitivities of liquid- and solid-sensing of Lamb wave sensors are discussed. It is shown that the sensitivity of S₀ mode in liquid sensing is much smaller than that in solid sensing, and also much smaller than that of the A₀ mode     

Versatile sensing devices for self-driven designated therapy based on robust breathable composite films

Flexible wearable electronics were developed for applications such as electronic skins,human-machine interactions,healthcare monitoring,and anti-infection therapy.But conventional materials showed impermeability,single sensing ability,and no designated therapy,which hindered their applications.Thus it was still a great challenge to develop electronic devices with multifunctional sensing properties and self-driven anti-infection therapy.Herein,flexible and breathable on-skin electronic devices for multifunctional fabric based sensing and self-driven designated anti-infection therapy were prepared successfully with cellulose nanocrystals/iron(Ⅲ)ion/polyvinyl alcohol(CNC/Fe³⁺/PVA)composite.The resultant composite films possessed robust mechanical performances,outstanding conductivity,and distinguished breathability(3.03 kg/(m²·d)),which benefited from the multiple interactions of weak hydrogen bonds and Fe³⁺ chelation and synergistic effects among CNC,polyaniline(PANI),and PVA.Surprisingly,the film could be assembled as a multifunctional sensor to actively monitor real-time physical and infection related signals such as temperature,moisture,pH,NH3,and human movements even at sweat states.More importantly,this multifunctional device could act as a self-driven therapist to eliminate bacterial by the release of Fe³⁺,which was driven by the damage of metal coordination Fe-O bonds due to the high temperature caused by infection at wound sites.Thus,the composite films had potential versatile applications in electronic skins,smart wound dressings,human-machine interactions,and self-driven anti-infection therapy.