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Low-frequency transducers with dry dot contact (or dry point contact (DPC)) allow to overcome the problems of ultrasonic contact in testing of concrete. With the help of these transducers, it is possible to carry out the testing of concrete and other solid materials with longitudinal and shear waves. The principle of operation and device of ultrasonic low-frequency piezoelectric transducers with DPC, which are generating on the surface of solid body normal and tangential oscillatory force are shown. Directional diagrams of acoustic fields of these transducers, waveform of signals and their spectrums are given. Also shown possible areas of application of these transducers, in particular for flaw detection and testing of strength of concrete structures.The ultrasonic testing of concrete and ferroconcrete is possible on the frequencies not more the 150 -200 kHz. Rough, often undulating and porous surface of concrete structures demands special and laborious preparations for achieving the acceptable quality of acoustic contact through the liquid.Testing of the concrete with through-sounding method and more over surface sounding needs the knowledge of the base of sounding with the possible more exactness. To reach that the sizes of probe operating surface should be decreased to the limit. When testing the concrete with the echo method the space selection of the reflector is needed, that can be achieved with the help of big wave size probe or with the help of synthetic aperture focused technique (SAFT). SAFT assumes the usage of small wave size probe. Besides for some purposes, that can be served both with the sounding method and echo method, the transducers with a short duration of transformable impulses and with a low level of self reverberation noise are needed.All these conflicting objectives to ultrasound transducers for testing of the concrete were successfully satisfied by invention of the lowfrequency transducer with dry point contact (DPC).The essence of the DPC is: the size of the acoustic contact zone of oscillating probe surface with the surface of the test object is many times smaller than the length of the ultrasound wave. So when the wavelength is 40 mm (the typical value of wavelength while testing the concrete with ultrasound) the contact with the size of the zone less then 1-2 mm can be considered as point contact. In this case the contact liquid makes no influence on the coefficient of signal transformation and became useless. The transducer acts on the test object surface as a point oscillating force.The principle of DPC is already known for a long time and is used in different low-frequency ultrasound devices [1,2]. For testing the concrete structures the low-frequency transducers with half-waved concentrator are used [3]. The concentrators are the resonant elements that collect oscillations of rather big aperture of transducer in the point of contact.Our low-frequency transducers with DPC differ from the transducers with concentrators by the three main specialties. First, the size of the element th...

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A finite element model has been developed to study the propagation velocity of a horizontally polarized shear waves (SH-waves) in pipes of different diameters depending on geometrical parameters, excitation parameters, physical and elastic properties of the pipe material. The results of studies of the geometric anisotropy of the group and phase velocities of the SH-wave for a pipe with a diameter of 1020 mm with a wall thickness of 16 mm are presented. It has been established that in the case of isotropic properties of the pipe material, the velocity on the outer cylindrical surface in the direction of the envelope is 50 m/s more than on the generatrix. The radiation patterns of the SH-wave are given for the studied pipe size with radiation along the generatrix and envelope of the pipe. The results of experimental studies are in satisfactory agreement with the results of modeling.

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