Ultra-short ultrasonic pulses are a powerful instrument for elastic measuring. A measured value of the delay time between pulses reflected from the both surfaces of a plane-parallel specimen together with data on specimen thickness makes it possible to find elastic wave velocities and elastic modules of the object. Employment of focused ultrasound pulses provides measuring local elastic properties in the frame of such procedure. Measuring the bulk properties is performed with low-aperture (long-focus) probe beams. The focal zone of such a beam is a long cylinder of bounded plane wave; the cylinder cross-section is specified by the focal spot at the specimen face, the length of the focal cylinder is much bigger than the ultrasonic wavelength. So, the diameter of the focal spot determines lateral resolution of measurements, and the focal length put requirements on thickness of specimens under investigation - from a few tenth of millimeter up to some mm at ultrasonic operation frequencies of 50200 MHz.
The focused probe signal penetrates in a solid specimen as convergent beams of longitudinal and transverse waves. Respectively, an echo pattern of the reflected signal involves the signal reflected at the specimen face (B-signal), echo pulses resulted from propagation of the both types of elastic waves in a solid (L- and T-signals) as well as from hybrid mode of propagation (LT-signal). So, focused ultrasonic pulses enable simultaneous measuring both sonic velocities cL and cT (and both elastic modules - bulk K and shear G).
For convergent beams propagation through a plane-parallel object gives different time of propagation between parallel reflecting surfaces for different angular spectrum components of the incident beam. In consequence of the phase delays echo signals L, LT and T change their shape as against the B- signal shape. Difference in shape of the echo pulses causes uncertainty in metering interpulse times. It was shown theoretically the echo pulses are able to take a limited set of well-defined forms. Accuracy of elastic measurements may be essentially enhanced by converting all echo pulses to the unified shape keeping unchangeable their time-scale positions. Such a modified technique can improve metering accuracy of local measuring up to a level of 10-3 - typical for impulse of measuring with plane-wave signals.
Special software has been developed to modify procedure of local elastic measurements with focused impulse ultrasound. Experimental results of the modified technique of local measuring are presented for a set of calibrated specimens. It is shown the obtained data on sonic velocity values are in good agreement with results of conventional plane-wave measurements. Prospects of microacoustical technique application to measuring elastic properties of small-sized and low-dimensional objects are discussed.