Nonuniform phase distribution in ultrasound speckle analysis. II. Parametric expression and a frequency sweeping technique to measure mean scatterer spacing

For pt.I see ibid., vol.39, no.3, p.352-9 (1992). The existence of regularly spaced scatterers in the range cell of an ultrasonic imaging system results in speckle with a nonuniform phase distribution. Characteristic phase distributions occur at those particular demodulator frequencies at which the spacing is a multiple of one-quarter wavelength. A demodulator frequency sweeping technique for scatterer spacing estimation has been developed that uses parametric expressions of the phase statistics to detect and to identify scatterers with regular spacings. Changes in these parameters separately identify the mean scatterer spacing when it is an even and an odd multiple of the quarter wavelength of the demodulator frequency. This technique has good tolerance for variations in mean scatterer spacing, and has real-time implementation capability.     

基于 CPLD 的水中主动声探测仪计数检波器设计

从提高水中主动声探测仪检波器的工作性能角度出发, 提出了一种能够克服传统二极管包络检波器缺点的计数检波器, 通过在 1 ms 时间内统计输入信号的脉冲个数, 来区分干扰脉冲和回波信号. 在 Xilinx foundation series3.1 软件平台上, 采用 VHDL(超高速硬件描述语言)和自顶向下的方法, 完成了基于 CPLD(可编程逻辑器件)的计数检波器设计, 并进行了逻辑仿真和水下静态试验. 结果表明, 基于 CPLD 的计数检波器设计功能正确, 具有一定的柔性和可升级性;起到检波和滤波的双重作用, 提高了电路的抗干扰能力;并且通过在整形电路中增加限幅放大器, 可以进一步提高计数检波器的性能.     

Carbon nanotube radio

Here we report experimental results for a carbon nanotube (CNT) based amplitude-modulated (AM) demodulator for modulation frequencies up to 100 kHz. Further, the CNT based demodulator was successfully demonstrated in an actual AM radio receiver operating at a carrier frequency of 1 GHz and capable of demodulating high-fidelity audio. The demodulation originates from the nonlinear current-voltage (IDS vs VDS) characteristic of the CNT, which induces rectification of a portion of the applied RF signal. By properly biasing the CNT such that the operating point is centered on the maximum nonlinear portion of the I-V curve, one can maximize the demodulation effect. This represents a simple application of carbon nanotubes and nanotechnology to the wireless realm.     

Multiple access coding interferometers in wave radio

Wave radios in the past have used passive wide-band with no multiple access (MA) coded interferometer architectures in modulator and demodulator circuits for QPSK digital data transmission and reception. The authors provide information and design insight on the use of MA coded interferometers in modulator and demodulator for UWB wave radio. Wave radio fitted with hardware MA coded interferometers offers MA to users as does CDMA using data codes. Experimental and simulation analyses of coded interferometers show that it is possible to establish a one-to-one wave radio hardware link by means of hardware-based codes (addresses). The number of UWB hardware-coded interferometers investigated is limited to three codes (code 0, code 1 and code 2) for demonstration purposes only.     

Differential synchronous demodulation for small signal amplitudeestimation

A circuit for estimating the amplitude of small signals (in the range of microvolts to a few millivolts) developed initially for an electrical impedance tomography (EIT) data acquisition system is presented. The paper is focused on two points, the accurate demodulation of the difference of two sinewave signals and the common-mode correction of the measurement. The method is oriented for applications in measuring instruments, where a signal source (sinewave oscillator) is assumed to be incorporated. It uses a sample-and-hold circuit, suitably driven, as an amplitude demodulator. One of the advantages of this method is that the realization of the synchronous demodulator (or phase-sensitive detector) does not require a low-pass fitter at the output, resulting in a smaller settling time, that is, in higher speed of measurement. Finally, to improve the accuracy, a self-calibration technique has been developed     

Regularized quadrature and phase tracking from a single closed-fringe interferogram

A new sequential phase demodulator based on a regularized quadrature and phase tracker system (RQPT) is applied to demodulate two-dimensional fringe patterns. This RQPT system tracks the fringe pattern's quadrature and phase in a sequential way by following the path of the fringes. To make the RQPT system more robust to noise, the modulating phase around a small neighborhood is modeled as a plane and the quadrature of the signal is estimated simultaneously with the fringe's modulating phase. By sequentially calculating the quadrature of the fringe pattern, one obtains a more robust sequential demodulator than was previously possible. This system may be applied to the demodulation of a single interferogram having closed fringes.     

Digital Hilbert transformation for separation measurement of thicknesses and refractive indices of layered objects by use of a wavelength-scanning heterodyne interference confocal microscope

A wavelength-scanning heterodyne interference confocal microscope quickly accomplishes the simultaneous measurement of the thickness and the refractive index of a sample by detection of the amplitude and the phase of the interference signal during a sample scan. However, the measurement range of the optical path difference (OPD) that is obtained from the phase changes is limited by the time response of the phase-locked loop circuit in the FM demodulator. To overcome this limitation and to improve the accuracy of the separation measurement, we propose an OPD detection using digital signal processing with a Hilbert transform. The measurement range is extended approximately five times, and the resolution of the OPD is improved to 5.5 from 9 microm without the electrical noise of the FM demodulator circuit. By applying this method for simultaneous measurement of thickness and the refractive index, we can measure samples 20-30-microm thick with refractive indices between 1 and 1.5.     

毛细铜管封装的内嵌式镀金光纤布拉格光栅温度和应力传感器

为了实现复杂、恶劣环境下工程机械表面无损的应力监测方式,实现对大型工程机械的实时动态监测,提出了基于磁控溅射技术的光纤布拉格光栅(FBG)应力传感器封装方法。并对完全嵌套(整个栅区嵌套毛细铜管)和两端嵌套(栅区两端嵌套毛细铜管)两种封装方法开展了研究。从理论分析和有限元仿真的角度比较了传感器的增敏效果,前后结果一致。制备了传感器实物并进行了温度、应力和对比实验。仿真实验结果表明,该模型下FBG传感器能提高约7.5%的灵敏度。温度实验表明第二种封装结构的温度反馈相关系数R2达到了0.99948,在30℃～80℃范围内呈现良好的线性度;应力实验的相关系数R2也达到0.99924,灵敏度为6.14 pm/MPa,在该实验搭建的解调系统下精度达到0.05 MPa,可以快速、精确地解调应力。对比实验表明,光栅解调仪组成的监测系统比应变片组成的监测系统具有更高的精度,最大偏差值减小了59.8%。嵌套毛细铜管的金属化方式结合有机胶固定的封装结构简单、灵敏度和精度高,可以满足大型工程机械表面无损实时健康监测的需求。     

Electric Field Sensing Scheme Based on Matched $ hbox{LiNbO}_{3}$ Electro-Optic Retarders

In this paper, a wideband-electric-field-sensing scheme that uses optically matched integrated optics electrooptic devices and coherence modulation of light is described. In a coherence modulation scheme, the integrated optics sensor detects the electric field and imprints it around an optical delay. The optical delay is generated by a birefringent optical waveguide in a lithium niobate (LiNbO₃) integrated optics two-wave interferometer. The modulated optical delay, acting as an information carrier, is transmitted through an optical fiber channel. At the receiver, light is demodulated by a second integrated optics two-wave interferometer, which also introduces a second optical delay. The optical delays on the sensor and demodulator are matched at the same value. The integrated optics demodulator measures the autocorrelation of light around the optical delay value, and the imprinted electric field is recuperated as a linear variation of the received optical power. The matching of the sensor and demodulator allows a direct detection of the electric field, giving a unique feature to this fiber-integrated optics scheme. The experimental setup described here uses two pigtailed LiNbO₃ electrooptic crystals: one acting as the electric field sensor and the other acting as the optical demodulator. The wideband sensing range on the experimental setup corresponds to frequencies between 0 and 20 kHz.     

Absolute interferometric distance measurement using a FM-demodulation technique

We propose an interferometric method for measuring absolute distances larger than the wavelength. A laser diode is used as a light source. The principle of operation is based on multiple-wavelength interferometry that uses a modulated light source. This method uses the fact that the wavelength of light emitted by the laser diode can be varied by means of the injection current. The modulation of the injection current in combination with the optical heterodyne technique causes a high-frequency phase-modulated detector signal. The phase deviation of the signal is a measure of the optical path difference in the interferometer. By FM demodulation of the detector output with a phase-locked loop demodulator, the optical path difference can be determined directly without the classical ambiguity problem of interferometry. The measuring range in the experiments was limited to 50 mm by the maximum travel range of the used specimen translation stage. Because of the inherent light sensitivity of the method described, the rangefinder can be used for three-dimensional profile measurements on a wide variety of objects, even on diffuse scattering surfaces.     

光纤布喇格光栅的炸药熔铸温度监测研究

为了实现对炸药熔铸过程的温度监测,利用多通道解调仪对炸药熔铸过程温度场进行监测,在炸药熔铸测温的过程中采用了经过特殊封装处理过的光栅传感器。简单介绍了光栅的传感原理、布喇格光栅数据解调仪的原理、实验所用光纤布喇格光栅的封装工艺。将获取的温度数据经Matlab和Origin处理并绘制时间―温度曲线,发现炸药熔铸相变发生的瞬间,温度曲线发生较大的变化。研究结果表明:炸药在熔铸过程中会释放出潜热,在释放潜热时炸药的温度会从88℃上升到90℃,特殊封装后的光纤布喇格光栅传感器能很好地对炸药熔铸过程进行温度测量。     

Real-time holographic baseband frequency demodulator

The multiplicative and low-bandpass filtering characteristics of real-time holograms in photorefractive media are used as a basis for a baseband frequency demodulator by means of holographic homodyne detection. We experimentally demonstrate the demodulation of spatial bandpass signals in the kilohertz regime and homodyne detection in the gigahertz regime.     

A Novel QEPAS with Microresonator in the Open Environment

An improved quartz-enhanced photoacoustic spectroscopy (QEPAS) sensing system for trace gas detection is proposed. The optical fiber Fabry–Perot (F–P) demodulation method is used to replace the conventional electrical one in the QEPAS system. The experimental QEPAS system, which has a microresonator consisting of two stainless steel tubes with a length of 2.3 mm and an inner diameter of 0.9 mm, is implemented to detect the absorption of water vapor in the open environment. The structure parameters of the quartz tuning fork (QTF) are optimized in order to make the sensing system work more stably and reliably. Demonstration experiments are carried out. The vibration signal of the QTF was picked up by the optical fiber F–P demodulator and the conventional electrical scheme at the same time. Normalized noise equivalent absorption coefficients of $4.05\times 10^{-7}\,\text{ cm}^{-1}~{\cdot }~\mathrm{W}~{\cdot }~{\text{ Hz}}^{-1/2}$ and $2.40\times 10^{-6}\,\text{ cm}^{-1}~{\cdot }~\mathrm{W}~{\cdot }~{\text{ Hz}}^{-1/2 }$ are obtained, respectively. The experimental result demonstrates that the sensitivity of the improved QEPAS sensing system with an optical fiber F–P demodulator is about 5.9 times higher than that of the conventional QEPAS system.     

Demodulator of PWM signals

Conclusions The demodulator under consideration possesses high metrological properties and it can be used in systems for transmitting data.Translated from Izmeritel'naya Tekhnika, No. 10, p. 66, October, 1971.     

复合材料弹性模量的激光超声测量方法研究

本文利用激光超声方法来测量碳纤维/环氧树脂复合材料的弹性模量,详细介绍了测量原理和测量系统.利用Q值可调的Nd∶YAG脉冲激光器在复合材料试件中激发超声波,超声波由激光超声接收仪接收,经过解调器后在数字示波器上显示,获取超声声速.根据超声声速与材料弹性模量之间的固有关系,可以反演材料的弹性模量.实验表明,利用激光超声方法获得的测量结果与采用动态法得到的理论参考值相吻合,偏差在3%以内,并且操作简单可行.     

A Cycle-Slip Detector for Phase-Locked Demodulators

Thresholding in a phase-locked demodulator occurs because of cycle slipping between the received signal and the VCO of the PLD. Measurement of rate of occurrence of slips should be an elegant and sensitive method of determining the threshold of a PLL. It is surely a much simpler procedure than attempting to measure output SNR, particularly if the modulation is anything other than a simple sinewave. This paper describes the principles of a slip detector that was built for laboratory measurements.     

Direct conversion receivers using multiport structures for software-defined radio systems

An analytical assessment for multiport structures as direct conversion receivers is presented. A new direct-conversion receiver based on a novel five-port structure suitable for software-defined radio applications is proposed. The five-port architecture provides some advantages compared with previous architectures. Numerical and microwave simulations have been conducted to show its capabilities as a direct demodulator. The proposed five-port has been constructed and the measured results indicate that the five-port receiver introduced can be used effectively as a software-defined radio receiver     

Demodulation of Fiber-Optic Sensors for Frequency Response Measurement

The neural-network-based processing of extrinsic Fabry-Perot interferometric (EFPI) strain sensors was investigated for the special case of sinusoidal strain. The application area is modal or cyclic testing of structures in which the frequency response to periodic actuation must be demodulated. The nonlinear modulation characteristic of EFPI sensors produces well-defined harmonics of the actuation frequency. Relationships between peak strain and harmonic content were analyzed theoretically. A two-stage demodulator was implemented with a Fourier series neural network to separate the harmonic components of an EFPI signal and a backpropagation neural network to predict the peak-to-peak strain from the harmonics. The system performance was tested using theoretical and experimental data. The error for high-strain cases was less than about 10% if at least 12 harmonics were used. The frequency response of an instrumented cantilever beam provided the experimental data. The demodulator processing closely matched the actual strain levels     

A novel differential synchronous demodulator for AC signals

We describe a new analog differential synchronous demodulator for AC signals where (i) the signal is synchronously demodulated using the floating-capacitor technique after being amplified, if necessary, by an AC amplifier with differential input and differential output, thus yielding a very high CMRR; and (ii) the differential-to-single-ended signal conversion is performed after demodulation, that is, on a low-frequency signal that can be amplified by low-cost, high-performance circuits. The possible signal-to-noise ratio degradation because of synchronous sampling is prevented by using bandpass differential filters     

超声位移的激光外差干涉测量

本文介绍了超声位移的激光外差干涉测量的原理，装置和结果，分析了减小探测限和抑制噪声的途径，本装置采有和布喇格衍射盒作为激光的移频装置，锁相环作为调相信号的解调器。