Noise of piezoelectric accelerometer with integral FET amplifier

Since significant progress has been achieved in the development of low-noise piezoelectric (PE) accelerometers with integral FET amplifiers, detailed noise analysis of the system PE transducer-FET amplifier, and obtaining the engineering formula for its noise floor has become vital. As a result of this analysis, the formula for the noise floor of PE accelerometers in terms of acceleration spectral density is obtained at wide frequency band. Noise floor of the low-noise PE accelerometer comprising low-noise JFET charge amplifiers with some particular parameters of the PE transducer and the JFET amplifier was measured. The theoretical and experimental curves of the PE accelerometer's noise floor have a good correlation with each other at frequencies from 1 Hz to 10 kHz. The contribution of the different noise sources to the overall noise floor is shown. Those noise sources include the mechanical-thermal noise and electrical-thermal noise of the PE transducer and all main noise sources of FET amplifiers: the thermal noise voltage of the FET biasing resistor, the thermal noise of the series resistor between the PE transducer and the gate of the FET, the channel thermal noise voltage, the 1/f noise voltage, and the shot noise current in the gate circuit. At low frequencies, the f/spl les/50 Hz noise floor is determined mainly by the FET biasing resistor's thermal noise and the PE transducer's electrical-thermal noise. At frequencies from about 50 Hz to about 1 kHz, the contribution of the PE transducer's electrical-thermal noise dominates over the amplifier's noise sources by a factor of less than 2. At frequencies above 1 kHz, noise floor is determined mainly by the JFET channel thermal noise and the PE transducer's electrical-thermal noise.     

高g值加速计和压电式力传感器的动态校准

本提出一种高g值加速度计的动态校准方法和装置,其最大加速度峰值超过100000g。这套装置还可以对压电式力传感器进行动态校准。中给出两个加速度计加速度峰值的二十余次实验结果,以及加速度计与力传感器的冲击响应实验曲线。同时,还求出它们的动态数学模型（包括差分模型、传递函数、频率特性）和动态性能指标。此外,还讨论了本的4个创新点。     

Cymbal and BB underwater transducers and arrays

The cymbal is a miniaturized class V flextensional transducer that was developed for use as a shallow water sound projector and receiver. Single elements are characterized by high Q, low efficiency, and medium power output capability. Its low cost and thin profile allow the transducer to be assembled into large flexible arrays. Efforts were made to model both single elements and arrays using the ATILA code and the integral equation formulation (EQI). Millimeter size microprobe hydrophones (BBs) have been designed and fabricated from miniature piezoelectric hollow ceramic spheres for underwater applications such as mapping acoustic fields of projectors, and flow noise sensors for complex underwater structures. Green spheres are prepared from soft lead zirconate titanate powders using a coaxial nozzle slurry process. A compact hydrophone with a radially-poled sphere is investigated using inside and outside electrodes. Characterization of these hydrophones is done through measurement of hydrostatic piezoelectric charge coefficients, free field voltage sensitivities and directivity beam patterns. Electronic Publication     

Design and Calibration of an Integration-Free Accelerometer-Based Joint-Angle Sensor

A methodology has been developed for indirect, noncontact, and dynamic sensing of angles for robotic applications. Two accelerometers are placed on the adjacent links close to the joint axis, and their outputs are processed to estimate the joint angle. In the proposed technique, the joint angles are obtained without integrating the accelerometer outputs. To ensure accuracy of accelerometer readings, two calibration procedures for the accelerometers are presented, which can easily be implemented in place. Both these methods solve a nonlinear least squares problem to adjust the offset parameters of the accelerometers. The accelerometer-based angle sensor is particularly suitable for the harsh working environment of heavy-duty manipulators, where conventional contact-type angle sensors cannot be deployed or problems are associated with their use. The performance of the new sensor is studied and compared with the performance of digital resolvers in two applications, involving the position control and dynamic payload measurement of a miniexcavator. The experimental results attest to the efficiency and accuracy of the new angle-sensing mechanism.     

Effect of Telemetry Channel Noise on the Output of Accelerometers

The noise in the FM telemetry channel may decrease significantly the accuracy of accelerometer readings. The noise effects in both digital and analog accelerometers are examined in this paper. A maximum-likelihood estimate of the accelerometer output is made and the mean-square error of the estimate is evaluated. It is shown that the digital accelerometer is superior to the analog accelerometer in the presence of noise. Two methods of reducing the mean-square error are suggested.     

压电加速度传感器Hn估计校准方法

针对压电加速度传感器灵敏度校准过程中噪声对校准结果的影响难以消除的问题,结合Hn估计方法,利用其多次求互相关函数并求平均值的特性对系统噪声进行抑制。用"半长法"进行互相关计算,对多组采样信号进行互相关计算后再用FFT法进行功率谱计算,可得到功率谱的无偏估计。实验结果证明,利用该方法可提高压电加速度传感器灵敏度校准结果的准确度。     

A sensitive differential capacitance to voltage converter forsensor applications

There is a need for capacitance to voltage converters (CVC's) for differential capacitive sensors like pressure sensors and accelerometers which can measure both statically and dynamically. A suitable CVC is described in this paper. The CVC proposed is based on a symmetrical structure containing two half ac bridges, is intrinsically immune to parasitic capacitances and resistances, is capable of detecting capacitance changes from dc up to at least 10 kHz, is able to handle both single and differential capacitances, and can easily be realized with discrete components. Its sensitivity is very high: detectable capacitance changes of the order of 2 ppm of the nominal value (24 aF with respect to a nominal capacitance of 12 pF) result in a measured output voltage of 1.5 mV. However, due to drift the absolute accuracy and resolution of the CVC is limited to 3.5 ppm. A differential accelerometer for biomedical purposes was connected to the CVC and showed a sensitivity of 4 V/g. The measured rms output voltage noise in the frequency range of 2-50 Hz is 750 μV, resulting in a signal to noise ratio of 75 dB at an acceleration of 1 g in the frequency range of 2-50 Hz     

Chemical sensors based on micromachined transducers with integrated piezoresistive readout

We demonstrate an approach for the development of chemical sensors utilizing silicon micromachined physical transducers with integrated piezoresistive readout. Originally, these transducers were developed and optimized as sensitive accelerometers for automotive applications. However, by applying a chemically responsive layer onto the transducer, we convert these transducers into chemical sensors. These transducers are attractive for chemical sensing applications for several key reasons. First, the required sensitivity of the chemical sensor can be achieved by choosing the right spring constant of the transducer. Second, the integrated piezoresistive readout of the transducer is already optimized and is very straightforward, providing a desired reproducibility in measurements, while not requiring bulky equipment. Third, chemically responsive film deposition is simple due to the ease of access to the transducer's surface. Fourth, such transducers are already available for another (automotive) application, making these sensors very cost-effective. The applicability of this approach is illustrated by the fabrication of highly sensitive CO2 sensors. To study hysteresis effects, we selected high CO2 concentrations (10-100% CO2) to provide the worst-case scenario for the sensor operation. These sensors demonstrate a hysteresis-free performance over the concentration range from 10 to 100% vol CO2, have detection limits of 160-370 ppm of CO2, and exhibit a relatively rapid response time, T(90) = 45 s. Importantly, we demonstrate a simple method for cancellation of vibration effects when these physical transducers, initially developed as accelerometers, are applied as chemical sensors.     

加速度计稳定性测试的补偿技术

介绍了加速度计稳定性的测量装置及方法。由于环境因素可以对稳定性测试产生影响,因此对加速度计的工作温度、基础水平倾角的影响进行了分析。通过研究加速度计温度误差模型,确定了建模方法。在稳定性试验中,使用高精度铂热电阻测量加速度计的工作温度,对加速度计的模型方程系数和输出进行温度补偿;使用地震前兆倾斜仪监测基础水平倾角变化,对加速度计零位输出进行补偿。     

基于栅结构谐振器的X和Y轴加速度及Z轴角速度的组合测量

本文利用一由两个相互垂直的加速度计组成的栅结构谐振器来同时测量z轴和Y轴的加速度以及z轴的输入角速度．此谐振器利用变面积电容进行检测,具有良好的线性度及快速的信号响应．此谐振器的x轴及Y轴的加速度计的谐振频率分别为1．9315kHz和1．8403kHz．在初始状态下,Ⅳ轴的加速度计被驱动进入谐振状态,且Y轴的加速度随着x轴的加速度计一起振动．当=轴存在角速度输入时,Y轴的加速度计会相应地沿Y轴进行振动,而x轴及Y轴的加速度会改变相应轴上加速度计的平衡位置．测试结果表明,此器件的z轴角速度灵敏度为16mV／（（9）·s-1）,x和Y轴的加速度灵敏度分别为49mV／g和244mV／g．z轴角速度输出的噪声等效角速度为0．0138（s·／Hz-1）,x和Y轴加速度输出的噪声等效加速度为0．42X10-3g／／Hz和0．074X10-3。g／√Hz．     

基于输出预估自抗扰策略的加筋壁板结构多模态振动主动控制

针对加筋壁板结构中存在的模型难以精确确定和多模态外界干扰等问题,基于加速度传感器,提出了一种不依赖结构精确数学模型的多模态线性自抗扰振动主动控制(Linear Active Disturbance Rejection Control)策略。由于加速度传感器和压电驱动器的异位配置不可避免地使得整个控制系统存在时延。为解决该问题,利用Smith预估器的原理,引入输出预估器来补偿时延,这样设计的自抗扰振动主动控制器能够很好地解决时延对结构振动性能的影响。基于dSPACE实时仿真平台、利用加速度传感器、压电片驱动器,设计并建立四面固支压电加筋壁板结构实验系统,对提出的控制方法进行试验比较研究。最后的试验结果表明,采用提出的具有输出预估功能的自抗扰振动控制器,能够快速有效地抑制结构的多模态振动。     

Modeling of piezoelectric sensor fidelity

Ideal piezoelectric sensors should measure the response of a structure in a nonintrusive manner. The size of the sensor should be relatively small and its properties well matched to the structure. The voltage response of a piezoelectric sensor embedded in a fluid loaded plate structure is modeled using a hybrid finite element approach. The structure is excited by an obliquely incident acoustic signal. Finite element modeling is used for the structure and the fluid surrounding the transducer region, and a plane wave representation is invoked to match the displacement field on a mathematical boundary. On this boundary, continuity of field derivatives is enforced by using a penalty factor and to further achieve transparency at the mathematical boundary, drilling degrees of freedom (d.o.f.) are introduced in the finite element representation. Another novel feature in the FEM is the use of solid elements for the acoustic fluid augmented by an irrotational constraint to render the fluid inviscid. Numerical results are presented for the sensor response of an immersed plate structure. The voltage excited in the piezoelectric sensor is studied as a function of sensor and host material properties, size of sensor, and poling direction of the sensor with respect to the structure. The effect of multiple sensors on one another is also studied. It is found that piezoelectric sensors can be nonintrusive and sensitive to the characteristics of the structure     

基于机械品质因数的全波压电超声换能器设计

针对全波压电超声换能器常规设计方法存在的尺寸参数较多、计算较复杂等问题,研究了一种利用机械品质因数设计全波压电超声换能器的方法。基于压电超声理论推导了全波压电超声换能器的频率方程,利用电学理论推导了全波压电超声换能器各组成部分的等效电路,利用等效电路求取了在任意等效截面处的等效机械阻抗,进而推导出全波压电超声换能器各部分尺寸参数与其机械品质因数的关系式。利用机械品质因数及频率方程的等高线图,对全波压电超声换能器各部分尺寸进行了设计计算。利用ANSYS对该尺寸全波压电超声换能器的谐振频率进行了仿真分析,结果表明所设计的全波压电超声换能器的谐振频率具有较高的精度,满足工程应用的要求。     

On the conventional boundary integral equation formulation for piezoelectric solids with defects or of thin shapes

In this paper, the conventional boundary integral equation (BIE) formulation for piezoelectric solids is revisited and the related issues are examined. The key relations employed in deriving the piezoelectric BIE, such as the generalized Green's identity (reciprocal work theorem) and integral identities for the piezoelectric fundamental solution, are established rigorously. A weakly singular form of the piezoelectric BIE is derived for the first time using the identities for the fundamental solution, which eliminates the calculation of any singular integrals in the piezoelectric boundary element method (BEM). The crucial question of whether or not the piezoelectric BIE will degenerate when applied to crack and thin shell-like problems is addressed. It is shown analytically that the conventional BIE for piezoelectricity does degenerate for crack problems, but does not degenerate for thin piezoelectric shells. The latter has significant implications in applications of the piezoelectric BIE to the analysis of thin piezoelectric films used widely as sensors and actuators. Numerical tests to show the degeneracy of the piezoelectric BIE for crack problems are presented and one remedy to this degeneracy by using the multi-domain BEM is also demonstrated.     

Increasing the Information Content of a Linear Accelerometer Based on Incremental Measurements of the State Parameters of the Primary Transducer

A quantum model of the states of the primary transducer of an accelerometer is proposed. By means of the model it is possible to increase the information content of linear accelerometers on the basis of quantum measurements of the parameters of states that do not occur in the complete set.     

Development of novel optoelectromechanical systems based on"transparent metals" PBG structures

Developed a novel smart optoelectromechanical structure, fabricated using a multilayer, metal-dielectric photonic band gap (PBG) structure. We discuss innovative devices with electrically controllable optical properties that can be used as sensors with optical output signals for applications in harsh or hostile environments (pressure sensors, micro gravimeter, or micro accelerometer) or as optical modulators and optical limiters. Theoretical models of these novel devices together with experimental prototypes have been developed, and characterization of the devices has been performed. Moreover, microelectromechanical devices have been studied for application to this field and are presented. In particular, the problem of realizing highly sensitive accelerometers has been addressed, and it will be shown that the proposed approach allows detecting displacements of a few nanometers     

Damping of compression and shear piezoelectric accelerometers byelectromechanical feedback

It is shown that the very pronounced resonance peak in the frequency entirely by a simple modification of existing accelerometers, providing them with an electrical sensor output as well as an electrical actuator input, and using a charge amplifier in a feedback path between the sensor output and the actuator input. Because a piezoelectric accelerometer is normally read out by a charge amplifier, no extra circuitry (expense) is necessary to provide this electromechanical feedback. It is shown that a maximally flat response (Butterworth) can be obtained with little peaking (approximately 2 dB) and excellent dynamic stability, which makes the acceleration usable up to its resonance frequency     

基于并联机构的六维加速度传感器的方案设计及建模研究

提出一种新的基于并联机构的压电式六维加速度传感器的设计方案,即用并联机构充当传感器的弹性体结构,压电陶瓷同时充当传感器的敏感元件和并联机构的移动副,弹性球铰链代替传统的球面副.分别在质量块、外壳及地面上固结坐标系,基于多体系统理论推导两两之间位姿关系的解析表达式.运用牛顿-欧拉法建立系统的动力学方程,通过引入辅助角速度并用四元数来描述旋转矩阵和角速度矢量,将其转化成两个一阶常微分方程组的初值问题,并运用改进的欧拉算法进行求解,实现了六维加速度的完全解耦.针对四元数的违约问题,运用矩阵广义逆理论提出了一种有效的可重复运行的修正算法.利用建立的解耦模型及其算法对实例进行了求解,数据处理总时间小于采样点时间跨度,且理论计算值与ADAMS仿真数据吻合得很好;另外,通过试验进一步验证了设计方案的合理性以及数学模型的可靠性.     

A reduced modal parameter based algorithm to estimate excitation forces from optimally placed accelerometers

This paper presents a time domain technique for estimating dynamic loads acting on a structure from acceleration time response measured experimentally at a finite number of optimally placed accelerometers on the structure. The technique utilizes model reduction to obtain precise load estimates. The structure essentially acts as its own load transducer. The approach is based on the standard equilibrium equations of motion in modal coordinates. The modal parameters of a system – natural frequencies, mode shapes and damping factors – can be estimated experimentally from measured data, analytically for simple problems, or using the finite element method. For measurement of the acceleration response, there can be a large number of locations on the structure where the accelerometers can be mounted, and the precision with which the applied loads are estimated from measured acceleration response may be strongly influenced by the locations selected for accelerometer placements. A solution approach, based on the construction of D-optimal designs, is presented to determine the number and optimum locations of accelerometers that will provide the most precise load estimates. An improvement in the algorithm, based on reduced modal matrix, is further proposed to reconstruct the input forces accurately. Numerical examples that help understand the main characteristics of the proposed approach are also presented. The numerical results illustrate the effectiveness of the proposed technique in accurately recovering the loads imposed on discrete as well as continuous systems.