声波测井压电换能器多频点阻抗匹配技术研究

针对声波测井压电换能器的多频点阻抗匹配技术展开研究,首先采用多模态等效电路精确描述了换能器的导纳特性;然后通过分析多模态阻抗匹配理论,设计电感-电容复合阻抗匹配网络,并结合换能器等效电路进行参数优化和电路仿真。实验表明,相比于换能器没有阻抗匹配的测试结果,该阻抗匹配技术可大幅提高换能器在谐振频率附近多个频率处的有功功率,频带内的有功功率平均提高了30倍,从而改善换能器的激励带宽和激励效率,提高测井仪器的适应性、探测深度和分辨率。     

Frequency encoding of resonant mass sensors for chemical vapor detection

Chemical vapors can be detected by a resonant mass sensor array with selective absorption coatings implementing a frequency encoding method. The sensor array consists of sensor elements with different frequencies for their identifications in the frequency response obtained with a pulse Fourier transform detection scheme. Zero-loading resonance frequencies are chosen so that frequency shift due to absorption is bounded within a predefined region so that there is no overlap of peaks and all peaks can be assigned to the correct elements at any operation conditions. Mechanical oscillations of all or selected numbers of the sensor elements are excited by application of an excitation signal. Free oscillation decay signals from all or selectively excited sensor elements are detected and digitized. The free oscillation decay signal is subjected to a spectral analysis routine converting into a frequency spectrum, in which frequency shifts due to absorption of chemical vapors can be obtained. The implementation of the frequency encoding method with pulse Fourier transform detection to resonant mass sensors allows simultaneous multisensor detection, fast data acquisition speed, high signal-to-noise ratio by coaddition of raw data, flexible excitation, reduced complexity of electronic hardware, application of advanced data/spectral analysis algorithms, and realization of many other advantages by the introduction of the pulse Fourier transform method. A practical chemical vapor sensing system is demonstrated experimentally by use of nine frequency-encoded and polymer-coated sensors.     

Mode structure effects in optical resonance excitation

The dependence of the excitation strength on the longitudinal mode structure of a pulsed, resonant excitation field is examined. As an experimental test case, resonance ionization signal fluctuations are studied with a two-step excitation of strontium. Successive ionization signals, the corresponding pulse energies, and the mode structures of the resonant step laser pulses are recorded. The large signal fluctuations, up to 120%, cannot be explained by the modest (1-3%) pulse-energy fluctuations of either the resonant or the photoionizing field. In the case of weak excitation, the fluctuations in the signal correlate strongly with the intensity in a narrow frequency band around the resonance. In this weak-field region, the experimental correlation curves, i.e., the correlation between the signal and the spectral intensity versus the frequency, agree well with calculations based on a simple linear-response model. With the aid of correlation analysis a resonance can be localized with a single-moderesolution. As the resonant field is increased the correlation between the signal and single-mode intensity diminishes and almost disappears at full saturation. However, also in the saturation region, the correlation technique can be applied to localize a resonance with a resolution much better than that determined by the laser linewidth.     

Reference phase shifter for testing electronic phase meters type ÉF-1 (F2-1)

Conclusions It will be seen from analyzing (2') that the above methods of testing electronic phase meters can also be applied for testing digital phase meters (from 0 to 180°) by using more precise and higher-quality capacitance standards (for instance, capacitance boxes ME-1, ME-3 [5] KVM-4S [6], etc.), and a nonreactive resistance box type R-58, whose range extends to 5000 Hz, or a box consisting of nonreactive resistors UNU [7]. In the latter case the actual values of the resistors should be used, thus extending the frequency error testing range up to radio frequencies (without taking into consideration the shunting effect of the tested phase meter's input circuit).The reference phase shifter can be fed from Soviet-made oscillators (for instance, GZ-33, GZ-4A, etc.) by checking their frequency against a crystal oscillator type KG-A by means of an oscilloscope (for instance, ÉO-7 etc.) or a digital frequency meter (for instance, Ch3-3A, Ch3-4A, etc.).The testing will then be correct, provided that the input impedance of the tested digital phase meters retains a value of not less than Z_in=5 M.The value of Z_in drops with frequency, and this limits the phase meter's testing range.The electronic phase meters type ÉF-1 (F2-1) tested by this method at the plants which use them have all without exception subsequently passed their state testing at the VNIIM.Translated from Izmeritel'naya Tekhnika, No. 4, pp. 74–76, April, 1970.     

Development of circuit for measuring both Q variation and resonant frequency shift of quartz crystal microbalance

Although frequency shift is often used for QCM (Quartz Crystal Microbalance) measurement, Q of a resonator also varies when viscous loading occurs. However, it is difficult to measure Q variation in real time in comparison with resonant frequency shift. Furthermore, oscillation frequency shift deviates from real resonant one in case of large viscous loading. Here, the authors have developed the circuit based upon motional admittance method for measuring both Q variation and real resonant frequency shift. It was applied to a quartz resonator gas sensor, and its Q variation was measured by this circuit. Moreover, it was compared with a conventional oscillation circuit and the frequency shift of the former was remarkably different from that of the latter in case of large Q variation. When a quartz resonator coated with PEG20M (PolyEthylene Glycol 20M) membrane was exposed to water vapor, its Q decreased from 38700 to 3650 and a frequency shift of the oscillation circuit was only about one sixth of this circuit.     

Chirp excitation of ultrasonic probes and algorithm for filtering transit times in high-rangeability gas flow metering

The signal processing used in an ultrasonic high-rangeability gas flow meter using times of flight is presented. The flow meter under discussion uses a combination of continuous wave and chirp signals to measure at low flow velocities, below 20 m/s, and chirp signals alone to measure high flow velocities, above 20 m/s. Because of the need for a pulse compression technique in the signal waveform design the technique of pulse compression and the choice of signal waveforms are discussed. The advantages and disadvantages of amplitude weighting vis-a-vis frequency domain manipulations of the waveforms are also discussed. To eliminate spurious times of flight, a special filtering technique is used, based on assessing the gradient of ascendingly ordered time series of time-of-flight measurements. A summary of user experience with high-rangeability gas flow meters in use on different offshore platforms and in refineries is given. Long-term tests that examined the accuracy of the high-rangeability flow meter are also described.     

基于分支电路的主动-被动混合式结构振动控制

研究了压电智能结构振动控制问题。采用基于分支电路的主动-被动混合的控制方法对结构振动进行抑制，通过在控制器中设置主动电感使得分支电路的谐振频率在一定范围内可以连续调节，以适应激励频率的变化。给出了系统的模型及控制算法，并进行了仿真及实验研究。仿真及实验研究的结果表明该方法能有效地抑制结构振动，并且其鲁棒性明显好于Filter-x算法。     

On the establishment of a method for characterization of material microstructure through laser-based resonant ultrasound spectroscopy

Noncontacting, laser-based resonant ultrasound spectroscopy (RUS) was applied to characterize the microstructure of a polycrystalline sample of high purity copper. The frequencies and shapes of 40 of the first 50 resonant vibrational modes were determined. The sample's elastic constants, used for theoretical prediction, were estimated using electron backscatter diffraction data to form a polycrystalline average. The difference in mode frequency between theory and experiment averages 0.7% per mode. The close agreement demonstrates that, using standard metallurgical imaging as a guide, laser-based RUS is a promising approach to characterizing material microstructure. In addition to peak location, the Q of the resonant peaks was also examined. The average Q of the lasergenerated and laser-detected resonant ultrasound spectrum was 30% higher than a spectrum produced employing a piezoelectric transducer pair for excitation and detection.     

EMS频率对应电能表计量误差值精确测量的方法

针对目前电能表EMS试验中人工干预过多、驻留时间无法确定等问题，提出一种与EMS频率相对应的电能表计量误差值精确测量的方法。利用该方法可使EMS频率点与电能表计量误差值——匹配，同时可动态设置驻留时间，提高测量数据的精确性和测量速度，并以实例说明该方法的有效性。     

SAW impedance elements

In the past few years a new class of SAW devices has been under development based on the use of one port SAW resonators as lumped elements with their impedance strongly changing in a frequency range of effective SAW excitation. These `SAW impedance elements' can be connected in ladder type, balanced bridge type, or others types of networks to provide desired filter characteristics. In this paper the admittance characteristics of a single element are analyzed using coupling of mode (COM) model simulations. It is found that resonant type characteristics of a long transducer can be described by very simple formulas. The frequency gap between resonance and anti-resonance, important for filter design, is determined practically by the ΔV/V parameter of the piezoelectric substrate used, while the minimum magnitude of the impedance at the resonant frequency is determined by the SAW attenuation. The internal reflections only shift the resonance to the left edge of the stopband not changing other characteristics. A case of a synchronous resonator comprising a relatively short transducer and two reflectors placed on both sides of it is also analyzed. This type of impedance element has smaller frequency shift between resonance and anti-resonance points     

1.52-GHz micromechanical extensional wine-glass mode ring resonators

Vibrating polysilicon micromechanical ring resonators, using a unique extensional wine-glass-mode shape to achieve lower impedance than previous UHF resonators, have been demonstrated at frequencies as high as 1.2 GHz with a Q of 3,700, and 1.52 GHz with a Q of 2,800. The 1.2-GHz resonator exhibits a measured motional resistance of 1 MOmega with a dc-bias voltage of 20 V, which is 2.2 times lower than the resistance measured on radial contourmode disk counterparts at the same frequency. The use of larger rings offers a path toward even lower impedance, provided the spurious modes that become more troublesome as ring size increases can be properly suppressed using methods described herein. With spurious modes suppressed, the high-Q and low-impedance advantages, together with the multiple frequency on-chip integration advantages afforded by capacitively transduced micromechanical resonators, make this device an attractive candidate for use in the front-end RF filtering and frequency generation functions needed by wireless communication devices.     

Gough-Stewart并联机构谐振频率特性试验研究

对具有不同结构参数的Gough-Stewart并联机器人机构进行典型位姿下的脉冲激励试验,研究系统谐振频率随结构参数和位姿的变化规律。首先,按照一定的结构参数装配机构,在上平台的结构特征点布设加速度计。然后,在典型位姿进行脉冲激励,记录特征点空间三个自由度方向上的加速度响应,利用分析软件求解频率响应函数曲线,并进行谐振频率辨识,分析谐振频率随位姿的变化情况。最后,改变结构参数重新装配机构,重复试验过程,分析谐振频率随结构参数的变化情况。研究结果可作为机器人动态优化设计与控制器设计的参考。     

A simple programmable frequency meter for low frequencies withknown nominal values

A meter which can be used to measure instantaneously the frequencies of various signals, such as power line frequencies, heart rates, and motor speeds, by only choosing the proper clock and nominal frequencies is described. The technique is based on using an up/down counter operating in the down mode only, resulting in minimum timing signals. Thus the meter is designed with a minimum number of digital integrated circuits. Two frequency meters for heart rate and power line frequency measurements are discussed. A prototype of the proposed meter is built and tested for various frequencies     

1/f frequency noise of 2-GHZ high-Q thin-film sapphire resonators

We present experimental results on intrinsic 1/f frequency modulation (FM) noise in high-overtone thin-film sapphire resonators that operate at 2 GHz. The resonators exhibit several high-Q resonant modes approximately 100 kHz apart, which repeat every 13 MHz. A loaded Q of approximately 20000 was estimated from the phase response. The results show that the FM noise of the resonators varied between S_y (10 Hz)=-202 dB relative (rel) to 1/Hz and -210 dB rel to 1/Hz. The equivalent phase modulation (PM) noise of an oscillator using these resonators (assuming a noiseless amplifier) would range from L(10 Hz)=-39 to -47 dBc/Hz     

薄膜电容真空计电源的研究

介绍了利用交流电桥和相敏检波（PSD）原理设计的薄膜电容真空计电源的电路实施方案、主机电路结构和实测性能，对其中关键的小电容测量方法进行了深入的研究，在8h内测量，电容差值的漂移可小至10－3pF。主机结构采用微机控制和真空计模块化设计，可构成复合真空计或用于组装其他真空计。初步测试结果表明，这种真空计用单规管可以实现从大气至1Pa，覆盖五个数量级的真空度测量。     

一种计算热计量仪表误差的简便方法

热计量仪表中各组成部分的准确度对其热量计量准确度起着至关重要的作用。目前的有关标准与规程只给出了热计量仪表误差极限的计算方法 ,并由此确定其准确度等级。实际上 ,热计量仪表的误差并不是其各部分组件误差的代数和。文中根据热计量仪表误差计算的基本方法 ,提出了一种计算热计量仪表准确度的简化法 ,具有一定的准确性 ,便于在实际测量中使用     

一种谐振式传感器频率特性测试平台

谐振式传感器的谐振频率和Q值可以通过其频率特性计算得到,因此需要有一种通用的测试平台来测量各种不同谐振式传感器的频率特性.本文描述了一种谐振式传感器频率特性测试平台,并提出了一种采用间歇激励方法测试谐振式传感器谐振频率的新方法,采用线性调频信号激励谐振式传感器,传感器自由振动状态下的振动频率即是传感器的谐振频率;测得传感器自由振动状态下的振动频率,即可得到谐振式传感器的谐振频率.     

Resonant Magnetoelectric Effect with Strongly Nonlinear Magneto-Elastic Coupling in Magnetoelectric Laminate Composites

Considering the complex strongly nonlinear coupling characteristic of the magnetostrictive strain and magnetization under the excitation of the bias magnetic field and the pre-stress in the giant magnetostrictive material, this paper adopts the nonlinear magnetostrictive constitutive model and the equivalent circuit method to establish a strongly nonlinear resonant magnetoelectric (ME) effect theoretical model for the ME laminate composites compounding by the giant magnetostrictive material and the piezoelectric material. For the L-T mode magnetostrictive/piezoelectric/magnetostrictive (MPM) ME laminate, the predicted results coincide well with the experiment results of the resonant frequency and the resonant ME field coefficient varying with the external magnetic field when the pre-stress degenerates to zero in our model. The agreement indicates the proposed theoretical model validity. On the basis, we use the theoretical model to forecast the varying characteristic of the resonant ME field coefficient and the resonant frequency effect under the influence of the different bias magnetic field and the pre-stress in ME laminate composites. And we also predict that the resonant ME coefficient and the resonant frequency appear "reversal" with the pre-stress increasing. After that, the influence of the different volume ratio on the ME effect and resonant frequency is analyzed. Particularly, a resonant frequency value not influenced by the volume ratio with increasing bias magnetic or pre-stress occurs. This research can provide theory basis for improving the resonant ME conversion performance and for controlling the resonant frequency under the excitation of the bias conditions (i.e. the bias magnetic field and the pre-stress) for the ME devices (i.e. sensor, transducer, microwave device and so on).     

Surface adsorbate fluctuations and noise in nanoelectromechanical systems

Physisorption on solid surfaces is important in both fundamental studies and technology. Adsorbates can also be critical for the performance of miniature electromechanical resonators and sensors. Advances in resonant nanoelectromechanical systems (NEMS), particularly mass sensitivity attaining the single-molecule level, make it possible to probe surface physics in a new regime, where a small number of adatoms cause a detectable frequency shift in a high quality factor (Q) NEMS resonator, and adsorbate fluctuations result in resonance frequency noise. Here we report measurements and analysis of the kinetics and fluctuations of physisorbed xenon (Xe) atoms on a high-Q NEMS resonator vibrating at 190.5 MHz. The measured adsorption spectrum and frequency noise, combined with analytic modeling of surface diffusion and adsorption-desorption processes, suggest that diffusion dominates the observed excess noise. This study also reveals new power laws of frequency noise induced by diffusion, which could be important in other low-dimensional nanoscale systems.     

Effect of various pulse wave forms for pulse-type magnetic flux pump

The excitation current of magnetic pole windings in magnetic flux pump needs to be generated by a control system. In this paper, the control system of pulse-type high temperature superconducting magnetic flux pump is discussed in detail. The control system consists of a control circuit and a drive circuit. A direct current power supply is the unique power supply of the drive circuit. The control circuit is powered by a computer through a USB interface of the computer. The control circuit receives commands from the computer and controls the drive circuit to generate different pulse waves. Each pulse wave generates a unique pulse-type traveling magnetic field and will pump magnetic flux into the superconducting loop. Experiments have been performed to examine the pumping effect of different pulse waves on both MgB₂ and Bi-2223 superconducting loops using the proposed control system, and the best pulse wave has been found. The experimental results show that the magnetic flux pump can compensate current decay up to 32.5 A for MgB₂ loop and 129 A for Bi-2223 loop. It indicates that the control system of the pulse-type magnetic flux pump is effective and feasible.