RECONSTRUCTIONS OF PHASE SPECTRUM AND TRANSIENT RESPONSES OF SPHERICAL PIEZOELECTRIC TRANSDUCER

In this paper,a simple method deriving the transfer function of a spherical piezoelectric transducerhas been given.Transient responses have been obtained from the analytical expression of transferfunction by using FFT.Calculated results show that the impulse response of the spherical piezoelectrictransducer also exhibits the minimum phase behaviour and so the phase spectrum of its transfer func-tion can be reconstructed from the amplitude spectrum by using the Hilbert transform,the reconstruct-ed phase spectrum is in good agreement with that calculated from the analytical expression of transferfunction directly. Based on above-mentioned results,the phase spectrum of transfer function of a F42-c spherical pic-zoelectric transducer has been reconstructed from the measured values of its amplitude spectrum for thefirst time.The reconstructed phase spectrum is basically consistent with the measured values of phasespectrum. In addition,the impulse response and step response of F42-c spherical piezoelectric tra     

A STUDY OF THE SOUND REFLECTION FROM POROUS MATERIAL BY IMPULSE METHOD

This paper presents a study of the reflection of sound pulse from porous material when the im-pulse sound source and receiver are located on a line perpendicular to the surface of the material.The transfer functions of reflected sound waves were calculated from the experimental incident and thereflected sound pulses by use of DFT.The impulse response of reflected sound waves can be calculatedtheoretically under the assumption of idealized porous material.Both local reacting and extendedreacting materials were taken into account in the calculations. comparison of the calculationsfor spherical waves and plane waves provides a measure of the effect of spherical waves on thetransfer function of reflected sound waves.For a layer of porous material the reflections in thematerial are studied.     

THE SYSTEM GAIN OF MULTICHANNEL WIENER FILTER

As a pre-processing technique,the Wiener filter can be used to suppress strong interference and noise.The general solution of optimum transfer function has been found for the multichannel system.By using aninverse matrix formula,a simple expression of optimum transfer function can be derived in the case that onlyone interference is present.The formula for calculating the system gain is presented.The asymptoticperformance of system gain as input interference to signal ratio increasing to infinite is evaluated.When theinterference is distorted not only in phase but also in amplitude as well,the system gain can be evaluated insome particular cases.The results of numerical calculation are given in this paper.     

MULTIDIMENSIONAL COUPLED VIBRATIONS OF PIEZOELECTRIC VIBRATORS——PURE PIEZOELECTRIC VIBRATORS

In this paper,the fundamental modes of two- and three-dimensional coupled vibrations ofvarious piezoelectric ceramic vibrators,including the rectangular cross-sectional bar,the rectangularplate,the finite solid cylinder and hollow cylinder,are analyzed by using the apparent elasticitymethod,and some quite simple analytic formulae for the resonant frequencies of the above-men-tioned various piezoelectric vibrators are obtained,These formulae have been used to calculatethe variations of frequency constants with the geometric size of the vibrators,and the calculatedresults are in satisfactory agreement with the published experimental results and results calculatedby using various other methods,including the finite difference method,finite element method andRitz variational method.These formulae are quite simple,and the resonant frequencies or the geo-metric size of the vibrators can be rapidly calculated by using a scientific calculator instead of acomputer,so this method is more convenient for engineering     

An impulse technique of measuring insertion loss of open screens

An impulse response technique has been investigated by application to the open screens for obtaining sound transmission loss. The measurements of such screens according to ISO 140 were also presented. The predicted results calculated by a model which is based on Huygen's principle and Kirchhoff's formulation have shown good agreements with the results obtained by impulse method. The method requires no specialist acoustic facilities and measurement systems can be portable.     

Optical transfer function analysis of circular-pupil wavefront coding systems with separable phase masks

This paper proposes a simple method to achieve the optical transfer function of a circular pupil wavefront coding system with a separable phase mask in Cartesian coordinates.Based on the stationary phase method,the optical transfer function of the circular pupil system can be easily obtained from the optical transfer function of the rectangular pupil system by modifying the cut-off frequency and the on-axial modulation transfer function.Finally,a system with a cubic phase mask is used as an example to illustrate the way to achieve the optical transfer function of the circular pupil system from the rectangular pupil system.     

PSPICE controlled-source models of analogous circuit for Langevin type piezoelectric transducer

The design and construction of wide-band and high efficiency acoustical projector has long been considered an art beyond the capabilities of many smaller groups. Langevin type piezoelectric transducers have been the most candidate of sonar array system applied in underwater communication. The transducers are fabricated, by bolting head mass and tail mass on both ends of stacked piezoelectric ceramic, to satisfy the multiple, conflicting design for high power transmitting capability. The aim of this research is to study the characteristics of Langevin type piezoelectric transducer that depend on different metal loading. First, the Mason equivalent circuit is used to model the segmented piezoelectric ceramic, then, the impedance network of tail and head masses is deduced by the Newton's theory. To obtain the optimal solution to a specific design formulation, PSPICE controlled-source programming techniques can be applied. A valid example of the application of PSPICE models for Langevin type transducer analysis is presented and the simulation results are in good agreement with the experimental measurements.     

Measurement of Specimen Thickness by Using Electron Holography and Electron Dynamic Calculation with a Transmission Electron Microscope

A method of transmission-electron microscopy for accurate measurement of specimen thickness has been proposed based on off-axis electron holography along with the dynamic electron diffraction simulation.The phase shift of the exit object wave with respect to the reference wave in vacuum,resulting from the scattering within the specimen,has been simulated versus the specimen thickness by the dynamic electron diffraction formula.Offaxis electron holography in a field emission gun transmission-electron microscope has been used to determine the phase shift of the exit wave.The specimen thickness can be obtained by match of the experimental and simulated phase shift.Based on the measured phase shift of the [110] oriented copper foil,the thickness can be determined at a good level of accuracy with an error less than-10%.     

Constrained high-order statistical blind deconvolution of spectral data

A constrained high-order statistical algorithm is proposed to blindly deconvolute the measured spectral data and estimate the response function of the instruments simultaneously. In this algorithm, no priorknowledge is necessary except a proper length of the unit-impulse response. This length can be easily set to be the width of the narrowest spectral line by observing the measured data. The feasibility of this method has been demonstrated experimentally by the measured Raman and absorption spectral data.     

Equivalence of MTF of a turbid medium and radiative transfer field

The equivalence of the modulation transfer function (MTF) of a turbid medium and the transmitted radiance from the medium under isotropic diffuse illumination is demonstrated. MTF of a turbid medium can be fully evaluated by numerically solving a radiative transfer problem in a plane parallel medium. MTF for a homogenous single layer turbid medium is investigated as illustration. General features of the MTF in the low and high spatial frequency domains are provided through their dependence on optical thickness, single scattering albedo, asymmetrical factor, and phase function type.     

ECHO STRUCTURE OF SOUND SCATTERING BY A FINITE ELASTIC CYLINDER IN WATER

In this paper the echo structure of short pulse from finite solid elastic circular cylinder is investigated.Itis emphasized that in the case of oblique incidence the echoes still include two kinds of scattering wave:(1).Geometrical scattering waves,namely corner waves.(2).Elastic scattering waves,i.e.waves related with theelasticity of cylinder.The geometrical scattering waves are the waves reflected form the discontinuities ofcylinder,and essentially independent of the material of cylind.Using Kirchhoff approximation therepresentation of corner waves from rigid cylinder has been derived.In the case of oblique incidence theelastic scattering waves differ from the circumferential waves for an infinite cylinder.Two sorts of echoescaused by the reradiation of elastic surface wave have been obeerved in experiments;the radial surfacebackscattering wave and the longitudinal surface backscattering wave,They can be identified according to the arriving time and appearing angle,and the results of a comparable obse     

Wideband tunable optoelectronic oscillator based on a single-bandpass microwave photonic filter and a recirculating delay line

A wideband tunable optoelectronic oscillator(OEO) based on a tunable single-bandpass microwave photonic filter(MPF) and a recirculating delay line is proposed and experimentally demonstrated. The MPF is formed by cascading a finite impulse response filter and an infinite impulse response filter, which can enhance the quality factor of the MPF and suppress the side modes of the OEO. The frequency response of the tunable MPF is theoretically analyzed. By placing the MPF into the OEO, tunable microwave signals from 10.3 GHz to 26.7 GHz and a 100 MHz step tunability are experimentally demonstrated. The phase noise is-113 dBc∕Hz@10 kHz. The results agree well with the theory.     

Broadband energy harvesting via magnetic coupling between two movable magnets

Harvesting energy from ambient mechanical vibrations by the piezoelectric effect has been proposed for powering microelectromechanical systems and replacing batteries that have a finite life span. A conventional piezoelectric energy harvester （PEH） is usually designed as a linear resonator, and suffers from a narrow operating bandwidth. To achieve broadband energy harvesting, in this paper we introduce a concept and describe the realization of a novel nonlinear PEH. The proposed PEH consists of a primary piezoelectric cantilever beam coupled to an auxiliary piezoelectric cantilever beam through two movable magnets. For predicting the nonlinear response from the proposed PEH, lumped parameter models are established for the two beams. Both simulation and experiment reveal that for the primary beam, the introduction of magnetic coupling can expand the operating bandwidth as well as improve the output voltage. For the auxiliary beam, the magnitude of the output voltage is slightly reduced, but additional output is observed at off-resonance frequencies. Therefore, broadband energy harvesting can be obtained from both the primary beam and the auxiliary beam.     

A large area plastic scintillation detector with 4-corner-readout

A 760 mm × 760 mm × 30 mm plastic scintillation detector viewed by photomultiplier tubes(PMTs)from four corners has been developed, and the detector has been tested with cosmic rays and γ rays. A positionindependent effective time Teff has been found, indicating this detector can be used as a TOF detector. The hit position can also be reconstructed by the time from the four corners. A TOF resolution of 236 ps and a position resolution of 48 mm have been achieved, and the detection efficiency has also been investigated.     

Lensless Wiener–Khinchin telescope based on second-order spatial autocorrelation of thermal light

The resolution of a conventional imaging system based on first-order field correlation can be directly obtained from the optical transfer function. However, it is challenging to determine the resolution of an imaging system through random media, including imaging through scattering media and imaging through randomly inhomogeneous media, since the point-to-point correspondence between the object and the image plane in these systems cannot be established by the first-order field correlation anymore. In this Letter, from the perspective of ghost imaging, we demonstrate for the first time, to the best of our knowledge, that the point-to-point correspondence in these imaging systems can be quantitatively recovered from the second-order correlation of light fields, and the imaging capability, such as resolution, of such imaging schemes can thus be derived by analyzing second-order autocorrelation of the optical transfer function. Based on this theoretical analysis, we propose a lensless Wiener–Khinchin telescope based on second-order spatial autocorrelation of thermal light, which can acquire the image of an object by a snapshot via using a spatial random phase modulator. As an incoherent imaging approach illuminated by thermal light, the lensless Wiener–Khinchin telescope can be applied in many fields such as X-ray astronomical observations.     

CHARACTERISTICS OF A UNIFORM PIPE ARRAY AND ITS APPLICATION TO INFRASONIC RECEPTION

In this paper the acoustic behaviour of a uniform pipe array,one end of which is connected to aninfrasonic transducer and the other is terminated with an acoustic impedance,is discussed.Both theo-retical analysis and computation of the response of the pipe array are given.Influenes of the impedan-ces at the terminal and of the transducer on the response are shown.By using these results the frequen-cy and phase responses and the directivity can be calculated as a plane sound wave pass across thearray. The pipe array is used for detecting the infrasonic or gravity waves in wind noise.A model of windnoise is established and its average power spectrum density function and coherence can be computed.Based on the theoretical analysis of the pipe array,some imporvement in the signal-to-noise ratioof infrasonic waves in the wind noise back-ground can be got by calculation.Results of a numericalexample obtained by computer programme are given.It is found that there is a significant improve-ment in the period range     

Double sinusoidal phase modulating laser diode interferometer for thickness measurements of transparent plates

A double sinusoidal phase modulating (SPM) laser diode interferometer for thickness measurements of a transparent plate is presented. A carrier signal is given to the interference signal by using a piezoelectric transducer, and the SPM interferometry is applied to measure the thickness of a transparent plate. By combining the double-modulation technique with the Bessel function ratio method, the measurement error originating from Sight intensity fluctuations caused by the modulation current can be decreased greatly. The thicknesses of a glass parallel plate and a quartz glass are measured in real time, and the corresponding experimental results are also given.     

Nuclear Level Density and Thermodynamic Functions for Nuclei with Static Deformation

The level densities of even-odd and even-even isotopes^161,162Dy,^166Er and ^171,172Yb were calculated using microscopic theory of interacting fermions and compared with experiments.It is found that the data can be well reproduced with level density formalism for nuclei with static deformation.The nuclear temperature as well as the reproduced with level density formalism for nuclei with static deformation.The nuclear temperature as well as the entropy of nuclear system as a function of excitation energy has been extracted from the BCS theory.It is shown that the entropy exhibits an S-formed shape as a function of excitation energy.This is interpreted as a phase transition.Procedure of treating the even-odd and even-even nuclear systems has been presented and discussed.     

Gauss-Newton based kurtosis blind deconvolution of spectroscopic data

The spectroscopic data recorded by dispersion spectrophotometer are usually degraded by the response function of the instrument. To improve the resolving power, double or triple cascade spectrophotometer and narrow slits have been employed, but the total flux of the radiation decreases accordingly, resulting in a lower signal-to-noise ratio (SNR) and a longer measuring time. However, the spectral resolution can be improved by mathematically removing the effect of the instrument response function. Based on the Shalvi-Weinstein criterion, a Gauss-Newton based kurtosis blind deconvolution algorithm for spectroscopic data is proposed. Experiments with some real measured Raman spectroscopic data show that this algorithm has excellent deconvolution capability.