The feasibility of using a focusing ultrasonic transducer as a sound pressure receiver is discussed. It is shown theoretically that, at certain angular apertures of the receiver, its output signal is proportional to the sound pressure in the field point coincident with the receiver center of curvature. The receivers of this type have been demonstrated suitable for remote measurements of field spatial distribution of plane and focused ultrasonic radiators. Data are presented on the experimental testing of focused receivers in measuring acoustic fields in water, air, and certain samples of biological tissues. The instruments are sufficiently universal and allow the measurement not only of acoustic fields, but also of temperature increments in locally heated media, as well as permit one to follow the initiation and development of ultrasonic cavitation and study nonlinear effects. The remote sensing ability and high sensitivity of focused ultrasonic receivers allow their practical use in biomedical acoustics for noninvasive measurements.

Abstract. The article describes the mathematical model and the method and results of simulation modeling of the drive of lifting of the downhole motor from the well. The system of differential equations takes into account the elastic properties of a long mechanical line (tubing string), as well as non-linearity: friction, variable elasticity, pressure limitation. Transient and frequency characteristics are obtained.

Remote generation of shear waves in tissues by a focused ultrasonic beam is the basis of a new acoustic method of medical diagnostics, namely, shear wave elasticity imaging [A. P. Sarvazyan, U.S. Patent No. 5,606,971, 1997]. The feasibility of SWEI was demonstrated recently in experiments with optical and NMR detection of ultrasonically induced shear waves in tissue phantoms. In the present study an SWEI system with ultrasonic detection of shear waves was designed and tested. The shear wave was excited inside an inhomogeneous tissue phantom using radiation force generated by the reflection of ultrasound from internal inhomogeneity. A focusing transducer of 6 cm in diameter and with 6-cm focal length was used. The carrier frequency was 2 MHz, and the intensity was varied in range from 10–30 W/cm2. The rectangular envelope was 0.2 ms in duration. Induced shear motion was evaluated using a 10-μs-long 3-MHz ultrasonic pulse by measuring the time delay for the pulse backscattered by moving inhomogeneities in the tissue. Maximum displacement in the propagating shear wave was over 10 μm, which agrees with theoretical predictions.

It is known that the difference in shear modulus for normal tissues and for pathological ones can reach two or three orders. This is the basis for the development of a very sensitive medical diagnostics method. Shear stresses inside of tissue can be excited by a focused ultrasound. The efficiency of this process is the main problem. The phenomenon of shear wave excitation by a focused acoustical beam has been studied experimentally and theoretically. In the experiment a shear wave has been excited in rubberlike material (transparent polymer) by powerful focused ultrasonic beam in a pulsed regime. The registration of the shear deformation has been performed by means of an optical beam, which was focused at a target in the thickness of polymer sample. Temporal profiles of a shear wave have been registered at different distances from the focal region. The measured value of shear wave velocity was in a good agreement with its theoretical prediction. A theoretical model of shear wave generation by a beam of a longitudinal wave has been developed. An analytical expression for the pulse response function was derived which allows one to study the spatial and temporal characteristics of the shear wave.

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