基于调制FFT的谐振式SAW传感器快速频率估计算法

针对高动态环境下的谐振式声表面波（Surface Acoustic Wave,SAW）传感器快速精确频率估计,提出一种基于调制快速傅里叶变换（Fast Fourier Transform,FFT）的谐振式SAW传感器快速频率估计算法。对单次谐振式SAW传感器回波信号进行N点取样后进行调制FFT计算,获得回波信号频谱,然后利用最大谱线的两相邻谱线取代I_Rife算法频谱细化后的谱线对频率偏移因子进行估计,最后使用频率偏移因子对最大频谱频率进行修正。该算法较I_Rife算法不需要判断频率修正方向,减少了3N次复数乘法和4（N-1）次复数加法运算,频率估计均方根误差的平均值减小了26%。该算法在提高精度的同时,实现了对谐振式SAW传感器的快速频率估计。     

Broadband phase correction of FT-ICR mass spectra via simultaneous excitation and detection

In typical Fourier transform ion cyclotron resonance (FT-ICR) mass spectra, temporally dispersed excitation and the delay between excitation and detection result in continuous variation of signal phase with frequency in the detected time-domain ion signal. The complex frequency-domain spectrum of such a signal is a linear combination of absorption- and dispersion-mode spectral components with corresponding asymmetric peaks. For this reason, magnitude-mode spectral display is usually employed to yield a phase-independent uniform and symmetrical peak shape at the expense of spectral resolution. In this work, we implement simultaneous excitation and detection to enable Fourier deconvolution to recover absorption-mode spectra for both low- and high-field FT-ICR instruments. These spectra yield resolving power improvement factors approaching the maximum theoretical limit of 2.0, as well as reduction in frequency assignment errors relative to conventional magnitude-mode spectra. The Fourier deconvolution procedure has the additional benefit of correcting for spectral variation resulting from nonuniform power distribution over the excitation bandwidth and the potential benefit of providing useful diagnostic information for interpretation of experimental performance.     

Chemical sensor based on microfabricated wristwatch tuning forks

We report here a chemical sensor based on detecting the mechanical response of a thin (approximately 10-microm) polymer wire stretched across the two prongs of a wristwatch quartz tuning fork (QTF). When the fork is set to oscillate, the wire is stretched and compressed by the two prongs. The stretching/compression force changes upon adsorption of analyte molecules onto/into the polymer wire, which is detected by the QTF with pico-Newton force sensitivity. An array of such sensors with different polymer wires is used for simultaneous detection of several analytes and for improvement of pattern recognition. The low cost (approximately 10 cent) of the QTF, together with that an array of QTFs can be driven to oscillate simultaneously and their resonance frequencies detected with the same circuit, promises a high performance, low cost, and portable sensor for detecting various chemical vapors. We demonstrate here detection of parts-per-billion-level water, ethylnitrobenzene, and ethanol vapors using the QTF arrays.     

结构动力可靠度计算的基于反应功率谱的重要抽样法

提出了受随机地震作用的结构动力可靠度计算的基于反应功率谱的重要抽样法。为了提高动力可靠度计算的效率,利用反应功率谱峰值点对应频率处输入激励幅值的变化对失效概率的影响,提出了利用反应功率谱增大输入激励幅值的方差,达到重要抽样的目的;根据随机振动理论,平稳随机反应功率谱曲线与频域内反应绝对值平方曲线的期望值是相似形,而频域内反应绝对值平方曲线的期望值可以通过Fourier 变换很方便的求出,所以也可利用频域内反应绝对值平方曲线的期望值增大输入激励幅值的方差;重要抽样密度函数可表示为幅值分量概率密度函数连乘的形式,其所采用的输入激励幅值的方差可通过少量的结构分析次数得出。通过对三自由度线性结构及十自由度随机结构的计算,表明该文算法是提高动力可靠度计算效率的有效途径,也是求解随机结构动力可靠度的有效途径。     

A lateral-field-excited LiTaO3 high-frequency bulk acoustic wave sensor

The most popular bulk acoustic wave (BAW) sensor is the quartz crystal microbalance (QCM), which has electrodes on both the top and bottom surfaces of an AT-cut quartz wafer. In the QCM, the exciting electric field is primarily perpendicular to the crystal surface, resulting in a thickness field excitation (TFE) of a resonant temperature compensated transverse shear mode (TSM). The TSM, however, can also be excited by lateral field excitation (LFE) in which electrodes are placed on one side of the wafer leaving a bare sensing surface exposed directly to a liquid or a chemi/bio selective layer allowing the detection of both mechanical and electrical property changes caused by a target analyte. The use of LFE sensors has motivated an investigation to identify other piezoelectric crystal orientations that can support temperature-compensated TSMs and operate efficiently at high frequencies resulting in increased sensitivity. In this work, theoretical search and experimental measurements are performed to identify the existence of high-frequency temperature-compensated TSMs in LiTaO₃. Prototype LFE LiTaO₃ sensors were fabricated and found to operate at frequencies in excess of 1 GHz and sensitively detect viscosity, conductivity, and dielectric constant changes in liquids.     

Phase synchronization of an ion ensemble by frequency sweep excitation in Fourier transform ion cyclotron resonance

The Fourier transform ion cyclotron resonance (FT-ICR) signal is produced by the coherent motion of a population of ions. The ability to produce a well-defined ion packet by excitation of an initially random ion ensemble is a major limiting factor of high mass FT-ICR. Ions must be both resonant and in phase with the applied radio frequency excitation field to be accelerated to radii suitable for detection by FT-ICR. Synchronization of the phase angles of an ensemble of ions occurs by off-resonant acceleration during frequency swept excitation. Results from computer-simulated ion trajectories suggest that phase synchronization of the ion packet prior to resonant excitation results in better spatial definition of the ion ensemble.     

Monolithic miniaturized quartz microbalance array and its application to chemical sensor systems for liquids

We report on the design, fabrication, and application of novel monolithic miniaturized quartz microbalance (QMB) arrays. Up until now, almost all reported resonator arrays (often designated as "electronic noses" or "electronic tongues", respectively, dependent on their application) are assembled from single QMBs. We fabricate arrays with up to 36 QMBs on a single AT-cut quartz blank. Mass sensitive devices based on AT-cut quartz resonators are suitable as (bio)chemical sensors. A frequency shift caused by mass accumulation on the sensor surface increases theoretically with f/sup 2/, hence the detection limits for the application as chemical sensors should be decreased with increasing frequency. Since the quality factor Q of a quartz crystal decreases with f, the frequency stability is reduced, thus limiting mass sensitivity. The mass sensitivity of resonators with different resonant frequencies was examined by means of electrochemical copper deposition on their surface. Subsequently, the manufactured resonators were coated with different layers (polystyrene, amyl-calix[8]arene, /spl beta/-cyclodextrine). In order to examine the applicability of such coatings as sensitive layers, their sensitivities to toluene in water were investigated. Moreover, arrays with up to four different resonant frequencies on one chip were fabricated for comparing the resonator behavior of the same coating at different frequencies. In another test setup, different layers were sprayed onto an array of microbalances having all the same resonant frequency. This allowed for comparing the different coating behavior under equivalent test conditions. Arrays were tested for viscosity measurement to find an optimum resonant frequency.     

Self-Sustained Microwave Absorption Induced by Extremely High Radiation Intensities in Surface Electrons on Liquid Helium

A new nonlinear-optical absorption effect is observed in electrons bound to the liquid helium surface. We study absorption of mm-wave radiation due to resonant excitation of electron bound states. Below 1 K, almost all electrons occupy the ground state. Therefore, the system should be transparent for resonant radiation connecting any two excited states. On the contrary, we observe strong absorption peaks associated with transitions between the first excited and the higher excited states. We show that this anomaly results from the bistability of the electron system induced by extremely high radiation intensities and the long electron relaxation time.     

Magneto-mechanical impedance identification and diagnosis of metallic structures

Magneto-mechanical impedance (MMI) method is implemented for multi-modal structural dynamic identification and diagnosis of metallic structures. Active elements of the method, magneto-elastic active sensors (MEAS), consist of an electrical coil and a permanent magnet facilitating electromagnetic generation and reception of elastic waves via the eddy current mechanism. The paper describes experimental arrangements and proof-of-concept experiments demonstrating availability of structural dynamic features in the MMI response and feasibility of MMI measurements for nondestructive assessment of structural condition. An analytical model describing MMI response of one-dimensional non-ferromagnetic structure is presented. The model includes three distinct contributions: dynamics of the structural element, electromagnetic coupling, and sensor characteristics. Different excitation models for MEAS were considered that account for spatial distribution of the structural load. Effects of structural parameters and sensor characteristic on the MMI signature are investigated and several approaches for improving MMI measurements are suggested. The paper presents examples of MMI monitoring of simple and complex structures. In the reported investigations, MMI spectral features, such as spectral amplitude, frequency shift and redistribution of impedance peaks are explored for structural damage detection and characterization. It is suggested that MMI may facilitate structural diagnostics requiring either embeddable sensors or non-contact transducers.     

非本征光纤法珀传感器的振动特性研究

针对光纤法珀(Fabry-Perot, FP)超声波传感器振动特性,将传感器薄板振动简化为具有集中参数的二阶振动,推导二阶振动方程的集中参数(力阻抗、等效质量、弹性系数、集中力),获得传感器共振频率、振幅灵敏度与结构参数设计关系。测试直径2.52 mm、厚度150 μm玻璃振动薄板在空气、水中的共振频率分别为205 kHz及115 kHz,水介质中共振频率振幅灵敏度约18 pm/Pa。制作的传感器可测试局放产生超声波的最小声压约1 Pa。     

Hydrogen bond acidic polymers for surface acoustic wave vapor sensors and arrays

Four hydrogen bond acidic polymers are examined as sorbent layers on acoustic wave devices for the detection of basic vapors. A polysiloxane polymer with pendant hexafluoro-2-propanol groups and polymers with hexafluorobisphenol groups linked by oligosiloxane spacers yield sensors that respond more rapidly and with greater sensitivity than fluoropolyol, a material used in previous SAW sensor studies. Sensors coated with the new materials all reach 90% of full response within 6 s of the first indication of a response. Unsupervised learning techniques applied to pattern-normalized sensor array data were used to examine the spread of vapor data in feature space when the array does or does not contain hydrogen bond acidic polymers. The radial distance in degrees between pattern-normalized data points was utilized to obtain quantifiable distances that could be compared as the number and chemical diversity of the polymers in the array were varied. The hydrogen bond acidic polymers significantly increase the distances between basic vapors and nonpolar vapors when included in the array.     

Simultaneous real-time imaging of surface and subsurface structures from a single space-frequency multiplexed photodisplacement interferogram

A new parallel photodisplacement technique has been developed that achieves simultaneous real-time imaging of surface and subsurface structures from a single space-frequency multiplexed interferogram, which greatly simplifies the system and the optical alignment. A linear region of photodisplacement is excited on the sample for subsurface imaging by use of a line-focused intensity-modulated laser beam, and the displacement and surface information on reflectivity and topography are detected by a parallel heterodyne interferometer with a charge-coupled device linear image sensor used as a detector. The frequencies of three control signals for excitation and detection, that is, the heterodyne beat signal, modulation signal, and sensor gate pulse, are optimized such that surface and subsurface information components are space-frequency multiplexed into the sensor signal as orthogonal functions, allowing each to be discretely reproduced from Fourier coefficients. Preliminary experiments demonstrate that this technique is capable of simultaneous imaging of reflectivity, topography, and photodisplacement for the detection of subsurface lattice defects at a remarkable speed of only 0.26 s per 256 x 256 pixel area. This new technique is promising for use in nondestructive hybrid surface and subsurface inspection and other applications.     

Extending the longevity of fluorescence-based sensor arrays using adaptive exposure

Fluorescent microbead sensor arrays were prepared to determine sensor array longevity. Sensor longevity is limited by photobleaching of the dyes attached to the microbeads and presents one of the biggest drawbacks of most fluorescent dye-based arrays. Responses of an array of organic vapor sensors were acquired for 2 weeks to evaluate the sensor performance over time. Photobleaching effects were overcome in two ways: (1) by limiting the excitation light power and gradually increasing the power at a rate comparable to the sensor photobleaching rates and (2) by illuminating subsections of the array through an optical slit. Both approaches extended the longevity of a sensor array. During the longevity study, the sensor arrays were employed to test their ability to correctly distinguish between responses to seven vapors. A high classification accuracy (99.8%) was obtained after 17,700 exposures for vapor responses collected over two weeks using only approximately 8% of the array's surface area.     

导电介质交流阻抗测量的自由衰减振荡方法

通过测量导电介质交流阻抗特性参数可实现多种物理或化学量的检测.对一阶传感系统添加电容或电感元件以构成二阶谐振单元,用连续方波脉冲信号激励谐振单元进入自由衰减振荡模式,可同时获取谐振单元的衰减因子和谐振频率.对金属板材的电涡流检测及盐溶液的电导率测量系统分别进行了实验.结果表明,这种方法可有效抑制提离距离或电极引线等非理想因素,在交流阻抗测量技术的传感器化研究方面有很好的应用前景.     

Fracture behavior of wasted activated carbon powder composites

At the Waterworks Bureau (Tokyo Metropolitan Government), activated carbon has been used for filtering water. After being used for the filtering process, it is normally disposed or burned for thermal recycling. However, CO₂ emissions occur during the thermal recycling. This work focuses on the identification of mechanical behavior of recycled wasted activated carbon (WAC) in order to elaborate smart materials having mechanical–electrical functions. Acoustic emission technique (AE) was used intensively as characterization support in which sensors were attached to detect microdamage during bending tests. At first, the resonant frequencies of the specimens were measured using the through-transmission test. The resonant frequencies of the specimens containing low weight fractions of WAC powder were less in comparison to the frequencies of the specimens with higher volume fraction. The frequency analysis was carried out with the projected wavelet transform on the signals detected during bending tests. Obtained data showed that, typically, the first major peaks showed the resonant frequency of the sensors, while the second major peaks exhibited signals indicative of resin cracking. The surfaces of the fractured specimens were analyzed by optical microscopy in order to visualize the crack formation and propagation on the activated carbon composite under flexural stresses. Consequently, fractographic and AE analyses provide better understanding of the failure mechanisms involved.     

A compressive MUSIC spectral approach for identification of closely-spaced structural natural frequencies and post-earthquake damage detection

Motivated by practical needs to reduce data transmission payloads in wireless sensors for vibration-based monitoring of engineering structures, this paper proposes a novel approach for identifying resonant frequencies of white-noise excited structures using acceleration measurements acquired at rates significantly below the Nyquist rate. The approach adopts the deterministic co-prime sub-Nyquist sampling scheme, originally developed to facilitate telecommunication applications, to estimate the autocorrelation function of response acceleration time-histories of low-amplitude white-noise excited structures treated as realizations of a stationary stochastic process. Next, the standard multiple signal classification (MUSIC) spectral estimator is applied to the estimated autocorrelation function enabling the identification of structural natural frequencies with high resolution by simple peak picking in the frequency domain without posing any sparsity conditions to the signals. This is achieved by processing autocorrelation estimates without undertaking any (typically computationally expensive) signal reconstruction step in the time-domain, as required by various recently proposed in the literature sub-Nyquist compressive sensing-based approaches for structural health monitoring, while filtering out any broadband noise added during data acquisition. The accuracy and applicability of the proposed approach is first numerically assessed using computer-generated noise-corrupted acceleration time–history data obtained by a simulation-based framework examining white-noise excited structural systems with two closely-spaced modes of vibration carrying the same amount of energy, and a third isolated weakly excited vibrating mode. Further, damage detection potential of the developed method is numerically illustrated using a white-noise excited reinforced concrete 3-storey frame in a healthy and two damaged states caused by ground motions of increased intensity. The damage assessment relies on shifts in natural frequencies between the pre-earthquake and post-earthquake state. Overall, numerical results demonstrate that the considered approach can accurately identify structural resonances and detect structural damage associated with changes to natural frequencies as minor as 1% by sampling up to 78% below Nyquist rate for signal to noise ratio as low as 10dB. These results suggest that the adopted approach is robust and noise-immune while it can reduce data transmission requirements in acceleration wireless sensors for natural frequency identification and damage detection in engineering structures.     

Development and application of mass sensors based on flexuralresonances in alumina beams

New mass sensors are described, which are based on the change in the flexural resonant frequencies of ceramic cantilever beams subject to piezoelectric excitation. The devices have been fabricated by screen-printing and firing a PZT-based paste on 96% alumina substrates with the methods of thick film technology and are, therefore, low cost and easy to manufacture. Inserted in an electronic feedback loop sustaining and tracking oscillations at one of the resonant frequencies, the sensors work as resonant microbalances with frequency output and can be employed for gravimetric chemical measurements. The beams have been implemented in two different sizes and, as a consequence, operated at different frequencies (about 82 and 149 kHz), in order to vary the mass sensitivity. The sensors' manufacturing and theory of operation are illustrated, and experimental results on their characterization are reported. For the two sensor sizes, mass sensitivities of about -280 and -1200 Hz/mg have been measured, in agreement with theoretical predictions. The influence of temperature has been investigated showing that, for slow thermal drifts, a satisfying degree of compensation can be achieved with a differential configuration. The devices have been successfully applied as sorption sensors for the measurement of air relative humidity (RH) by sensitizing the beams' surface with hydrophilic polymeric coatings. On the basis of past investigations, poly(N-vinylpyrrolidinone) and poly(ethyleneglycol) have been adopted as coating materials, obtaining respective frequency shifts of about 500 and 1400 Hz for RH ranging from 12 to 85%     

超声波在水中衰减的频率效应及其对脉冲回波的影响

超声波在传播中会发生幅值衰减,该衰减不仅与超声波传播的距离有关,还与超声波的频率有关。为了研究高频超声波衰减的频率效应,本文通过脉冲回波法分析脉冲超声波在水中传播反射回波的幅值和频谱变化,研究了超声波在水中传播时幅值衰减与传播距离及其与超声频率之间的关系,通过测量脉冲超声波在水中传播不同距离时的反射回波,并对其进行傅里叶变换,分析了超声波传播衰减的距离效应和频率效应。研究发现:超声波在水中的传播衰减随距离呈指数规律,且不同频率超声波的衰减系数不相同,频率越高,衰减越大,衰减的频率效应可有效解释反射法高频脉冲超声检测中回波脉冲信号的中心频率远低于换能器标称中心频率的现象。     

An interrogation unit for passive wireless SAW sensors based on fourier transform

The application of surface acoustic wave (SAW) resonators as sensor elements for different physical parameters such as temperature, pressure, and force has been well-known for several years. The energy storage in the SAW and the direct conversion from physical parameter to a parameter of the wave, such as frequency or phase, enables the construction of a passive sensor that can be interrogated wireless. This paper presents a temperature-measurement system based on passive wireless SAW sensors. The principle of SAW sensors and SAW sensor interrogation is discussed briefly. A new measurement device developed for analyzing the sensor signals is introduced. Compared to former interrogation units that detect resonance frequency of the SAW resonator by comparing amplitudes of sensor response signals related to different stimulating frequencies, the new equipment is able to measure the resonance frequency directly by calculating a Fourier transformation of the resonator response signal. Measurement results of an experimental setup and field tests are presented and discussed.     

Electronic Scheme for Multiplexed Dynamic Behavior Excitation and Detection of Piezoelectric Silicon-Based Micromembranes

A new concept for a precise compensation of the static capacitance of piezoelectric silicon-based micromembranes is proposed. Combining analog and digital field-programmable gate array hardware elements with specific software treatment, this system enables the parallel excitation and detection of the resonant frequencies (and the quality factors) of matrices of piezoelectric micromembranes integrated on the same chip. The frequency measurement stability is less than 1 ppm (1-2 Hz) with a switching capability of 4 micromembranes/sec and a measurement bandwidth of 1.5 MHz. The real-time multiplexed tracking of the resonant frequency and quality factor on several micromembranes is performed in different liquid media, showing the high capability of measurement on dramatically attenuated signals. Prior to these measurements, calibration in air is done making use of silica microbeads successive depositions onto piezoelectric membranes surface. The mass sensitivity in air is, thus, estimated at, in excellent agreement with the theoretical corresponding value.