ABOUT HEAD WAVES AND UNDER-SURFACE LONGITUDINAL WAVES, RADIATED BY THE NORMAL PROBE WHICH IS TAKING PLACE ON A FREE FLAT SURFACE OF THE ELASTIC ENVIRONMENT

On the basis of integrated representations Fourier–Bessel a component of displacement of elastic waves, radiating by the normal converter which is taking place on a free flat surface of the elastic environment, receives analytical estimations of displacement a under-surface longitudinal and head (it is surface-longitudinal) waves. Components of displacement a under-surface longitudinal wave are the sum a component in approximation of geometrical acoustics (GA), the diffraction amendments to this approximation and the amendments which are taking into account influence of feature when the parameter of integrated representation is equal to wave number of a longitudinal wave. Components of displacement of a head wave are defined as the sum appropriate diffraction amendments for a component of displacement of a volumetric longitudinal wave in approximation GA and a component of displacement of a lateral wave. The maximum of amplitude of displacement a under-surface longitudinal wave in angular area of a direction of distribution near to a free surface of environment is caused by one of local maxima of the directivity characteristic of the normal probe. Thus dependence of change of amplitude of this wave of distance wave from the centre of the probe practically corresponds to similar dependence for displacement of a volumetric longitudinal wave in GA approximation. Quantitative estimations of maxima of amplitude of displacement under-surface longitudinal and head waves concerning the greatest amplitude, radiated by the normal probe of a volumetric longitudinal wave.

TO A QUESTION ABOUT QUASIBAND OF ACOUSTIC AXIS OF THE ANGLE BEAM PROBE

On the basis of modelling an acoustic path of the angle beam probe with a reflector as a side drilled hole influence of two factors resulting to quasiband of acoustic axis of the angle beam probe is shown, first of which is connected to change of amplitude echo signal owing to attenuation of a shear wave in the environment due to absorption and dispersion, and the second factor – with change of amplitude owing to a divergence of wave fronts radiated and received elastic waves. Influence of the first factor is increased with growth of attenuation and depth of reflector, and the second – on increase of distance up to a reflector practically does not depend. Quantitative estimations have revealed a ratio of influence of both factors on size of a angle quasiband of acoustic axis on value of factor of attenuation of shear waves. Reduction of an angle quasidand with increase of radius piezoplate of the angle beam probe is shown at constant operation frequency, that is at narrowing the directivity characteristic of the probe.

Interferometric Processing of Acoustic Information by Using Extended Antennas in Dispersing Media

The theory of interferometric processing of acoustic information by using extended antennas in media with frequency dispersion is presented. The dependence between the two-dimensional spectral density of the two-fold Fourier transform of the interference pattern formed by a moving noise source and the aperture and angular structure of the received field is analyzed. The gain factor, directivity characteristic, and noise immunity of processing are estimated. Depending between the input signal/noise ratio on the antenna element and the maximal range of the noise source is obtained. This maximal range allows stable detection and estimation of direction, radial velocity, range and depth are close to real values. Numerical simulation results are presented and discussed.

THE INFLUENCE OF A CRITICAL ANGLE ON AN ORIENTATION OF RADIATION OF A SHEAR WAVE THE ANGLE BEAM PROBE

In a far field it is received asymptotic expression of displacement of the shear waves transmitted in the elastic environment by the angle beam probe in view of features of radiation of such waves under a angle of probe, coming nearer to the third critical. At sufficient remoteness from a critical corner this expression passes in received earlier in geometroacustical approximation. The estimations carried out for steel have shown, that for converters with nominal angles of probe 37 – 40 influence of this critical angle causes increase of an angle of registration of a maximum of the signal, observed earlier experimentally. This feature is influenced as distance up to points of registration of a shear wave, and with working frequency of the angle beam probe and its size piezoplate (width of the directivity characteristic).

Design and Analysis of a Quasi-Yagi Antenna for an Indoor Location Tracking System

In this paper, a quasi-Yagi antenna for an indoor location tracking system is proposed. The performance of the proposed antenna was verified by testing it using an indoor location tracking system. To improve the bandwidth and gain, two parasitic directors were added near the dipole. The performance verification of the proposed antenna is explained, along with a performance comparison of the VSWR (voltage standing wave ratio) radiation pattern and the realized gain. The proposed antenna was connected to an NVA-R661 module of Xethru Inc. for indoor location tracking. The proposed antenna exhibited a wide bandwidth of 4.36 GHz by satisfying a VSWR ≤ 2 from 5.03 to 9.39 GHz, the maximum gain was 6.46 dBi in the 8 GHz band. The radiation pattern exhibited a good directivity characteristic within the proposed band. The location tracking result of a moving target clearly describes the route of the target along a moving line.

The Study on Broad Directivity Characteristic of Piston Transducer with Finite Baffle

Transducer with large directivity and high transmitting sensitivity is designed and fabricated. It is a sandwich transducer with composite horn and it has a finite baffle. A novel model considering the dimension of baffle is deduced, the directivity of transducers are calculated under different conditions. The computations of models agree with the experimental data well. The maximum transmitting voltage response level of the sandwich transducer is 143dB (1V/μPa) and the directivity is up to 99°(-3dB) at the resonance frequency of 75.6kHz.

Effect of Guide’s Acoustic Parameters on Vertical Directivity of the Marine Ambient Noise

The vertical directivity characteristic of ambient noise is one inherent characteristic of the ocean in shallow water. And it includes the information of guide’s acoustic characteristic information. The marine guide is composed of sea water; seabed and surface boundary, there into, the acoustic parameters of seabed are hardly obtained exactly. In this paper, the model of vertical directivity for ambient noise is established. Based on the ray theory of sound propagation, the influence of guide’s acoustic parameters which include sound speed, density and attenuation coefficient on vertical directivity of marine ambient noise is simulated. The results are propitious to analysis and command the characteristics of ambient noise, and valuable to accelerate the exertion of acoustic equipment performance.