Study and development of a combined method for reducing the size of the uncontrolled near-surface layer during ultrasonic electromagnetic-acoustic testing of ferromagnetic metal products

Ultrasonic methods and tools are widely used in measurements, for quality inspection in industry, research, diagnostics in medicine, etc. Thus, in industry, ultrasonic methods account for more than 60% of all quality control of materials and products. Recently, the electromagnetic-acoustic (EMA) method of ultrasonic testing (UT) has been widely implemented, since it offers significant advantages over traditional methods, which require a contact liquid. EMA provides high performance, requires no clean-up of the surface of a test object (TO), does not require a contact liquid, etc. But there are also disadvantages, one of which is the presence of an uncontrolled near-surface zone caused by free electrical high-frequency oscillations (ringing) in the circuits of the device elements with EMA transducers (EMAT) after completion of the probing pulse. Having analysed existing developments, it has been established that the main method of the ringing suppression is the EMAT load on the resistance of semiconductor elements after completion of the probing pulse. This approach is only partially effective due to the voltage drop on the semiconductor elements during the high-current pulse passage. According to the study it is possible to significantly reduce the duration of the ringing and, accordingly, the size of the uncontrolled near-surface zone by compensating for the accumulated energy in the EMA elements of the device, as well as suppressing the EMAT ringing. A means for generating a group of pulses to ensure the operation of the ultrasonic device has been developed. The effectiveness of the developed control method has been confirmed experimentally.