GENERATOR OF POWERFUL HIGH-FREQUENCY PACKAGE CURRENT PULSES FOR POWER SUPPLY OF ULTRASONIC ELECTROMAGNETIC-ACOUSTIC TRANSDUCERS
DOI:
https://doi.org/10.31471/1993-9981-2019-2(43)-88-95Keywords:
ultrasonic, electromagnetic-acoustic transducer, flaw detection, field effect transistors, current pulse generator.Abstract
It is possible to increase the sensitivity of electromagnetic-acoustic transducers by three main methods: increasing the induction of a polarizing magnetic field; increase in strength of high-frequency current in the inductor of the converter; using modern methods of processing information packet pulses excited and received from the product. The increase in magnetic field induction of the converter is limited by the capabilities of modern powerful permanent magnets. In addition, there are significant difficulties in monitoring ferromagnetic control samples, due to the large pressing force between the sample and the transducer and sticking of scale to the transducer. Usage of modern processing methods significantly complicates and increases the cost of electromagnetic-acoustic testing devices. Of the selected sensitivityincreasingmethods, the most acceptable way is to increase the power of high-frequency current generators under the condition of excitation of packet pulses. Power supply process of the converter is carried out in two stages. Meander type powerful high-frequency current pulses are excited, which ensures operation of the output transistors in key mode. Isolation of a powerful sinusoidal high-frequency packet current pulse is carried out directly on the electromagnetic - acoustic transducer, the elements of which are included in the resonant circuit with low quality factor. Based on the transistors switched in the push-pull circuit in the key mode, a small-sized generator design has been created that excites a peak current of up to 800 A in the electromagnetic-acoustic transducer and a voltage of up to 3 kV in the transducer in the frequency range 0.3 ... 8 MHz. It was experimentally determined that the new design of the probe pulse generator made it possible to increase the amplitude of pulses reflected from a flat-bottom reflector with a diameter of 2 mm with respect to the interference amplitude by more than 2 times.
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