Amplitude and phase calibration of hydrophones by heterodyne and time-gated time-delay spectrometry

Two methods for the amplitude and phase calibration of hydrophones based on time-delay spectrometry are presented: a time-gating technique and heterodyne frequency conversion that allows the phase-locked (i.e., coherent) detection of hydrophone signals. Amplitude and phase of the hydrophone sensitivity are obtained in the frequency range 1-20 MHz. In addition, to show the broad-band capabilities of the methods, amplitude values are measured between 4 and 50 MHz.     

Hydrostatic method for the calibration of hydrophones at excess static pressure

Translated from Izmeritel'naya Tekhnika, No. 10, pp. 51–53, October, 1989.     

Water-air piston hydrophone for calibration of hydrophones of comparatively large sizes

Translated from Izmeritel'naya Tekhnika, No. 4, pp. 63–65, April, 1990.     

基于相位测量的摄像机标定方法

提出一种新的摄像机标定方法,该方法基于2D共面参照物摄像机标定方法和相移技术.首先由摄像机记录已知相位分布的平面,通过相移计算出相位分布.对任意标定平面,两个正交相位分布与平面坐标的对应关系已知,由此可以建立像素坐标与2D平面坐标的一一对应关系.将该已知相位分布的平面在空间中放置不同的位置,分别完成上述测量,即可根据2D共面参照物摄像机标定方法完成摄像机的高精度标定.该方法避开了复杂的标定特征点提取,大大增加了2D标定数据量,提高了标定精度.实验和计算机模拟表明,该方法简单、可靠和精度高.     

A simple method for linearizing nonlinear spectra for calibration

The development and acceptance of spectral calibration methods has been an important success story for the field of chemometrics. This paper contains a new study of a very old calibration method (K-matrix calibration, parallel calibration, or generalized inverse prediction) and partial least squares (PLS), the mainstay of modern chemometrics. We show that with some modest amount of modification, the old method of calibration is comparable, in terms of prediction, to PLS for spectroscopy involving nonlinear spectral responses.     

A k-space method for moderately nonlinear wave propagation

A k-space method for moderately nonlinear wave propagation in absorptive media is presented. The Westervelt equation is first transferred into k-space via Fourier transformation, and is solved by a modified wave-vector time-domain scheme. The present approach is not limited to forward propagation or parabolic approximation. One- and two-dimensional problems are investigated to verify the method by comparing results to analytic solutions and finite-difference time-domain (FDTD) method. It is found that to obtain accurate results in homogeneous media, the grid size can be as little as two points per wavelength, and for a moderately nonlinear problem, the Courant-Friedrichs-Lewy number can be as large as 0.4. Through comparisons with the conventional FDTD method, the k-space method for nonlinear wave propagation is shown here to be computationally more efficient and accurate. The k-space method is then employed to study three-dimensional nonlinear wave propagation through the skull, which shows that a relatively accurate focusing can be achieved in the brain at a high frequency by sending a low frequency from the transducer. Finally, implementations of the k-space method using a single graphics processing unit shows that it required about one-seventh the computation time of a single-core CPU calculation.     

Modification of the comparison method for the moving-source calibration of hydrophones in a shallow sea

The underwater sound field in the vicinity of interference maxima can be approximated locally by a quasi-plane wave. The sensitivity measurement technique discussed in the article calls for measurements to be performed at times when the calibrated and the standard hydrophones reside in the zone of an interference maximum of the sound field generated by a moving radiator. The motion of the latter can be utilized to formulate a simple dynamic algorithm for monitoring the entry of acoustic transducers into the zone of a maximum of the sound field. Translated from Izmeritel'naya Tekhnika, No. 11, pp. 49–52, November, 1999.     

Design technique for nonlinear phase SAW filters using slanted finger interdigital transducers

This paper describes a useful design technique to achieve a nonlinear phase SAW filter using slanted finger interdigital transducers (SFITs) or tapered interdigital transducers which are suitable for wide-band filters in intermediate frequency stages. A required nonlinear phase response in the passband can be obtained by changing center-to-center distances between input and output SFITs along an axis perpendicular to the SAW propagation axis. The design is based on a building-block approach in the frequency domain. A nonlinear phase SAW filter with a center frequency of 70 MHz and a fractional bandwidth of about 10% is demonstrated on x-cut 112.2 degrees y-propagating LiTaO(3 ). Because the substrate has a power flow angle of 1.55 degrees, the SFIT pattern is tilted along that angle. Good agreement between theoretical and experimental results is obtained.     

A local-domain based phase field method for crack propagation

Abstract

The phase field method transfers the crack surface area into a domain integral through a smeared damage parameter. As a result, the fracture energy release rate can be directly incorporated into the energy form without tracking of crack surface, and a minimization approach to optimize the crack shape becomes possible. This nonlocal damage approach requires a fine mesh discretization to capture the damage gradient in the smeared crack zone, which produces a significant degree of freedom problem to optimize over the entire domain. In this research, a local-domain based phase field method is proposed. This method considers only elements in critical regions for energy minimization, whose internal energy are dominant, thus significantly reducing the degree of freedom to be solved. A numerical verification is carried out to demonstrate the feasibility of this approach, and simulations are presented to verify the accuracy of the new method.     

真空比对法校准装置的研究

真空比对法校准装置采用了动态直接比对法、静态直接比对法和静态膨胀法,在一台装置上复合了三种方法,满足了拓宽量程的需求.该装置可以1×105-5×10-4 Pa范围内的各类真空规进行校准,是一种结构简单、操作方便、检定效率高、实用性强的真空标准装置.整套装置由涡轮分子泵、校准容器、副标准真空计和金属膨胀阀等部件组成,主要技术指标符合国际标准化组织和国内有关真空标准的规定.     

Wavelet operators for nonlinear optical pulse propagation

A method that uses discrete wavelet transforms for the solution of evolution equations that describe optical pulse propagation in nonlinear media is presented. The theory of orthogonal wavelet transforms is outlined and applied to the representation of optical pulses. Wavelet transform representations of propagation operators are presented and applied to the nonlinear Schr?dinger equation, yielding results that are indistinguishable from traditional Fourier-based simulations. The compression properties of wavelet representations of optical pulses permit significant improvement in execution speed compared with that of the split-step Fourier method.     

The influence of nonlinear fields on miniature hydrophone calibration using the planar scanning technique

Miniature polyvinylidene fluoride (PVDF) hydrophones used in determining the power and intensity output of ultrasonic fields, including those radiated from diagnostic ultrasound equipment, were calibrated under a variety of field conditions using the planar scanning technique. A diagnostic B-scan piston-type transducer was used as a source, and the output intensity (spatial-peak pulse-average, or SPPA) was varied from 2 to 30 W/cm(2) while the total power was kept constant. The higher-intensity waveforms were significantly nonlinear in the focal region of the source. When the lateral beam profiles of the source (as measured by the hydrophone to be calibrated) were determined by positive-peak-detecting the ultrasonic pulse, the calibrated pressure sensitivity of the hydrophone systematically decreased as the field became progressively more nonlinear. When the beam profiles were measured using the pulse intensity integral, no systematic dependence of the calibration on field linearity was noted. These results imply that measured values of power and intensity of ultrasound diagnostic equipment may be dependent on the methodology utilized to map the lateral beam profiles of the transducer being measured, and the extent of nonlinear effects in the field under characterization.     

Spatial mismatch calibration using circular carrier technique in the simultaneous phase shifting interferometry

In most simultaneous phase shifting interferometry (SPSI) systems, a group of phase shifting interferograms are captured simultaneously at the different physical locations to retrieve the phase. The data of different interferograms should be spatially matched correctly, which is hard to realize by existing methods or this spatial mismatch will lead to phase retrieving error. In this paper, a spatial mismatch calibration method is proposed, where the circular carrier is introduced in the interferograms of the SPSI system, and the modulating phases of any two interferograms can be retrieved by the demodulation technique of circular carrier interferogram. The slope of the difference between these two phases is proportional to the mismatch value, so this error can be extracted and the experiment setup calibrated. The main error sources of the proposed method are analyzed with the conclusion that its match precision can be achieved up to 0.5 pixel. In addition, the simulated interferograms and actual interferograms captured in a SPSI system are processed to validate our proposed method.     

New calibration technique for microwave moisture sensors

A new calibration technique was developed for implementation with microwave moisture sensors. The calibration permittivity function used for this purpose allows computation of moisture content in granular materials with significant differences in shape, dimensions, and composition, independent of bulk density and with temperature compensation. A 3D representation is used to plot the calibration permittivity function as it depends on temperature and moisture content in wheat and corn. For each material, data points form a plane surface. These planes have nearly the same coefficients, which can be utilized for the development of a “universal” calibration method for moisture sensing in natural and manufactured granular materials. Foundations of the method are discussed based on results obtained for wheat and corn over a wide temperature range and at moisture contents of practical interest     

A model/solution-adaptive explicit-implicit time-marching technique for wave propagation analysis

In this work, an explicit-implicit time-marching procedure with model/ solution-adaptive time integration parameters is proposed for the analysis of hyperbolic models. The two time integrators of the methodology are locally evaluated, enabling their different spatial and temporal distributions. The first parameter defines the explicit/implicit subdomains of the model, and it is defined in a way that stability is always ensured, as well as period elongation errors are reduced; the second parameter controls the dissipative properties of the methodology, allowing spurious high-frequency modes to be properly eliminated, rendering reduced amplitude decay errors. In addition, the proposed explicit-implicit approach allows contracted systems of equations to be obtained, reducing the computational effort of the analysis. The main features of the novel methodology can be summarized as follows: (i) it is simple; (ii) it is locally defined; (iii) it has guaranteed stability; (iv) it is an efficient noniterative single-step procedure; (v) it provides enhanced accuracy; (vi) it enables advanced controllable algorithmic dissipation in the higher modes; (vii) it considers a link between the temporal and the spatial discretization; (viii) it stands as a single-solve framework based on reduced systems of equations; (ix) it is truly self-starting; and (x) it is entirely automatic.     

In situ calibration technique for UV spectral radiometers

A technique for calibrating spectral radiometers measuring global (2π sr) irradiance using solar irradiance at the top of the atmosphere as the absolute irradiance reference is reported. In addition to providing a calibration at all measured wavelengths, the technique provides a direct measure of the angular response of the radiometer. For instruments that can be used to measure the ultraviolet-B region, the calibration also provides an estimate of the ozone column amount.