A Class D Power Amplifier for Multifrequency Eddy Current Testing Based on Multisimultaneous-Frequency Selective Harmonic Elimination Pulsewidth Modulation

Efficiency and multi-simultaneous-frequency (MSF) output capability are two major criteria characterising the performance of a power amplifier in the application of multi-frequency eddy current testing (MECT). Switch-mode power amplifiers are known to have very high efficiency, yet they have rarely been adopted in the instrumental development of MECT. In addition, switch-mode power amplifiers themselves are lacking in the research literature for MSF. In this paper, a Class D power amplifier is designed so as to address the two issues. An MSF selective harmonic elimination pulse width modulation (MSF-SHEPWM) method is proposed to generate alternating magnetic fields which are rich in selected harmonics. A field-programmable gate array (FPGA) based experimental system has been developed to verify the design. Results show that the proposed methodology is capable of generating high MSF currents in the transmitting coil with a low distortion of signal.