Suppression of transient processes in the oscillatory circuit of the NQR spectrometer

A simple device intended for suppressing transient processes in the oscillatory circuit of the nuclear quadrupole resonance spectrometer operating at 0.5–10 MHz is described. The transient process duration is reduced by applying active damping to the circuit immediately after the excitation pulse terminates. The switching time is ≤0.1 μs. At 3.3 MHz, the transient process duration is reduced by a factor of 5.     

A Signal Preamplifier of the Piezoelectric Vibration Transducer of the Cantilever of an Atomic-Force Microscope

An electronic circuit for amplitude and phase measurements of the forced vibrations of the tip of the scanning atomic-force microscope by the current flowing through the piezoelectric cell exciting these vibrations is described. The circuit allows the electronic correction of the Q factor (width of the resonance peak) of the driven oscillatory system tip-piezoelectric cell (for example, a crystal tuning fork), and, as a result, reduction by a factor of 2–50 of the settling time of the parameters of tip vibrations reflecting its interaction with the studied surface. The output signal of the described circuit corresponds to the current through the piezoelectric cell. Due to the proposed correction of the capacitive component of the piezoelectric cell's current, the phase range of the output signal observed upon attainment of the tuning-fork resonance frequency has increased from several degrees to a 180° theoretically expected value.     

迟滞非线性振荡压实系统动态响应分析

分析了振荡压实中材料发生弹塑性变形而表现出的迟滞非线性,建立了一种新的振荡压实非线性动力学模型。在一次近似的前提下,利用等效线性化方法,将迟滞恢复力转化为等效刚度和等效阻尼表示,根据谐波平衡原则求出了单自由度振荡压实系统的频响方程。数值求解表明,随着激励幅度的增大系统出现软化趋势,共振点随激励变化而漂移。将等效线性化的结果推广到二自由度振荡压实系统,得到了频响方程组。     

3D spectral analysis for vibration signals by wavelet-based demodulation

In this paper, a wavelet-based demodulating function is proposed to apply in 3D spectral analysis for vibration signals. In the function, there are three parameters required to assign for adjustment and designation of the filtering passband, which are the low cut-off frequency, the high cut-off frequency and the dilation. Accordingly, it would be convenient to apply in the high-frequency resonance technique. In addition, by sweeping the filtering passband from a low-frequency band to a high-frequency band, a 3D spectrum could be constructed to describe how energy distribution between the instantaneous frequency and the filtering passband for a vibration signal. The 3D spectrum would be helpful to give a clear view of both characteristic frequencies and system resonances, and possesses the advantage of minimising the interventions by the end-user.     

A Radio-Frequency High-Temperature Superconducting Magnetometer

A radio-frequency high-temperature superconducting magnetometer is described. It is based on the generation of combination frequencies in a nonlinear ceramic-superconductor sensor with a resonance circuit at its input. Measurements at the combination frequency allows for an improvement of the noise and frequency characteristics as compared to a magnetometer based on the generation of the second harmonic in the superconductor. The instrument has a level of intrinsic noise of (2–4) × 10^–8 Oe/Hz^1/2 within a frequency range of 17 kHz.     

A power supply for a technological installation

A voltage changer for the power supply of an ultrasonic piezoelectric transducer is designed on the basis of a resonance inverter. The output filter designed on the basis of a series-resonant circuit with parallel and series compensation ensures matching of the changer to the load. The changer ensures a load current of 0.5A±10% within a wide range of the load resistance (from 50 to 400 Ω) at an input voltage of 220 V±15% with automatic tuning to the frequency of the load mechanical resonance. The changer output power is 100 W, and the output current is a sinusoid with a frequency of 22±2 kHz.     

水轮发电机组短路故障时机电耦联的扭振问题研究

首先采用一种统一的机电耦联的新方法，找到发电机组机电耦联系统的微分方程组，经变换得到方程组的解，进行数值计算，得到三相短路、两相线间短路及一相对中短路时各机、电变量的变化规律。得知短路时电磁力矩很大，其振荡频率为50Hz或100Hz，幅值可达到额定扭矩的数倍，甚至更高，故要引起很大的冲击扭振应力，当轴系扭振固有频率接近50Hz或100Hz时，会发生强烈的共振。并进行了实验研究，说明理论结果和实验结果相吻合。研究结果对水轮发电机组轴系的安全运行有重要的应用价值，对轴系的设计有指导价值。     

一种可调低通有源滤波器的设计

给出了一种用单片机控制、通带边界频率可调、适用于较高频率的有源滤波器的设计方法。以一个通带边界频率调整范围为190k～505kHz，调整步长为15kHz。滤波器的阻带衰减大于50dB的滤波器设计为例进行了说明。实测结果表明，该设计方案具有较低的元件参数灵敏度。     

多带隙联合的声子晶体滤波梁弹性波传播特性

提出了一种包含Bragg散射、整体局域共振和局部局域共振机理的多带隙联合声子晶体滤波梁,通过传递矩阵法与Bloch定理求得无限周期结构各阶带隙为0～170 Hz、180～262.6 Hz、552.3～597 Hz、974～1 563 Hz、1 903～2 667 Hz;并调节结构参数,得出带隙调制规律和带隙机理。同时,与其他3种工况声子晶体梁带隙特征进行对比分析,证明了声子晶体滤波梁在带隙宽度、丰富度以及弹性波衰减率方面均有着相对优势,具备更好的过滤或抑制结构中弹性波的性能。此外,求解近声子晶体滤波梁的振动传递系数,得出在各阶带隙范围内,弹性波的传播存在明显衰减,验证了带隙的存在。最后为探究弹性波在带隙/通带范围内的波动模式,分别提取位于带隙/通带范围梁体位移分布,发现在带隙频率范围内的弹性波沿波动方向快速衰减,表现出带隙特性;通带频率范围内的弹性波无明显变化或衰减,表现出通带特性。     

Development of adaptive eddy-current instruments for flaw sizing

The design of an eddy-current transducer (ECT) equipped with an oscillatory circuit was developed; interrelations between the voltage fed to the flaw detecting and measuring module and flaw parameters, operating gap, frequency, and tilt angle of the ECT were studied theoretically and experimentally. Different methods of ECT signal filtering and approximation of obtained magnitudes are considered. Instruments developed for eddy-current inspection are represented.     

High-frequency nuclear quadrupole resonance apparatus for use in pressure cell

A high-frequency NMR apparatus for use in pressure cell is described. All components of the resonance circuit are set in the pressure cell. This method makes the resonance frequency much less influenced by large stray capacitance residing at the electrical feedthrough of the pressure cell. With the use of this apparatus, a pressure-induced neutral-ionic phase transition in DMTTF-QBr(4) was successfully observed by (79)Br nuclear quadrupole resonance, whose resonance frequency is ～300 MHz.     

DESIGN OF TEMPERATURE CONTROLLED QUARTZ CRYSTAL MICROBALANCE SYSTEM

In this study, the dual modulated quartz crystal microbalance (QCM) with heating and cooling control has been developed for the quantitative determination of biological molecules, as a biosensor. On the other hand, since, the Sauerbrey formula is misprinted in some publications, the correct form of formula is also discussed. The proposed QCM biosensor has three main parts, which are the oscillator circuit, temperature control circuit, and the differential frequency measurement unit. Colpitts oscillators with the buffer amplifier, microcontroller (PIC16F877) for the temperature control circuit and a peltier element were used for heating and cooling inside the developed system. Differential frequency measurement is a known technique to compensate environmental effects causing instability of crystals. For this reason, one of the crystals is implemented with oscillatory circuits, i.e., the detector; the other one is used as the reference. The designed system was tested between 8°C and 50°C and frequency shift versus temperature is observed at 0.5 ppm/°C over a given temperature range.     

700kHz/1.2MHz非调谐式振荡器

在对传统的振荡器电路的分析比较基础上,提出并设计一种非调谐式振荡器。该振荡器利用迟滞比较器控制电容充电、放电的时间来产生振荡时钟,从而得到所需要的振荡波形。电路结构简单,面积小,易于集成,可以根据不同的控制信号,工作于1.2 MHz或700 kHz。Cadence Spectre仿真结果表明,该电路基本符合设计指标。     

Fuzzy classifier for fault diagnosis in analog electronic circuits

Many studies have presented different approaches for the fault diagnosis with fault models having ±50% variation in the component values in analog electronic circuits. There is still a need of the approaches which provide the fault diagnosis with the variation in the component value below ±50%. A new single and multiple fault diagnosis technique for soft faults in analog electronic circuit using fuzzy classifier has been proposed in this paper. This technique uses the simulation before test (SBT) approach by analyzing the frequency response of the analog circuit under faulty and fault free conditions. Three signature parameters peak gain, frequency and phase associated with peak gain, of the frequency response of the analog circuit are observed and extracted such that they give unique values for faulty and fault free configuration of the circuit. The single and double fault models with the component variations from ±10% to ±50% are considered. The fuzzy classifier along the classification of faults gives the estimated component value under faulty and faultfree conditions. The proposed method is validated using simulated data and the real time data for a benchmark analog circuit. The comparative analysis is also presented for both the validations.     

Magneto-sensor circuit efficiency incremented by Fourier-transformation

In this paper detection by recognized intelligent algorithm for different magnetic films with the aid of a cost-effective and simple high efficient circuit are realized. Well-known, magnetic films generate oscillating frequencies when they stay a part of an LC- oscillatory circuit. These frequencies can be further analyzed to gather information about their magnetic properties. For the first time in this work we apply the signal analysis in frequency domain to create the Fourier frequency spectra which was used to detect the sample properties and their recognition. In this paper we have summarized both the simulation and experimental results.     

低频正弦波形发生器仿真与设计

利用核磁共振方法勘查地下水就是利用一个铺在地面上的线圈发射并接受NMR信号，线圈中需通入某一谐振频率(拉莫尔频率即氢质子在地磁场中的旋进频率)的正弦波作为激发源。欲获得合适的正弦波，分析了谐振电路的频率特性，对低频正弦波形发生器进行仿真，得到相应的仿真结果，从而设计了实际发射电路，并通过室内实验获得与仿真电路一致的结果，解决了将直流电源能量转化为交流能量发射的实际需要。该正弦波形发生器优点在于发射波形没有衰减，且发射电流持续时间可调节。     

双层串联微穿孔板吸声体设计理论及应用研究

在微穿孔板吸声体理论的基础上,基于电力声类比等效电路法建立了双层串联微穿孔板吸声体理论分析模型,分析了双层串联微穿孔板吸声体的共振频率ωs与参数k1、r1的关系。将共振频率ωs与前腔深度D1做为两项设计指标,结合单层微穿孔板吸声体的设计方法,提出了一种双层串联微穿孔板吸声体的设计思路,简化了设计工作。     

基于XPE的变尺度级联随机共振系统研究

随机共振作为一种新颖的信号处理手段在各个领域得到了广泛应用,在随机共振的基础上讨论了级联随机共振的构成方式,采用模拟电路的形式对其进行实现,并基于该电路构成嵌入式变尺度级联随机共振系统.此系统硬件采用ETX技术,可以对CPU主板功能进行全新整合,软件上通过定制XPE操作和采用EWF技术,加强了系统的稳定性,同时变尺度算法和最佳级联随机共振判断程序在系统中的移植可以使之在较高频率的场合准确应用.最后给出了应用实例,验证了该系统对信号提取的准确性.     

管道震击破坏弱信号放大与带通滤波

管道震击破坏已经成为引起油气输送管道泄漏的最主要因素.采用高灵敏度的加速度传感器采集微弱的震击破坏声信号,阐述了基于AD620仪表运算放大器放大电路设计和2阶带通滤波器的设计方法.通过Multisim对设计的电路进行了仿真,并且在管道敲击破坏实验中取得了理想的效果.