Ultrasonic Thickness Measurement Using the Martlet Wireless Sensing System

This paper describes a recent development in ultrasonic thickness measurement for the Martlet wireless sensing system. The newly developed ultrasonic daughter board is capable of a maximum 80 MHz sampling frequency, a significant improvement compared to the 3 MHz sampling frequency in the previous version. The newly implemented analog-to-digital-converter (ADC) module consists of a high-speed ADC chip, a memory chip, and a shift register, transferring the sampled signal to the Martlet motherboard through the serial peripheral interface protocol. The sampling performance of the proposed ultrasonic daughter board is first validated with 1 MHz and 2.5 MHz sine waves. Ultrasonic thickness measurement testing of 25.4 mm thick steel and 8.0 mm thick rusty steel is next conducted using a 2.25 MHz dual element transducer. The proposed ultrasonic daughter board successfully samples the transducer signal, wirelessly sends the sampled signal to a base station, and obtains accurate thickness values. The developed compact, wireless ultrasonic setup has been designed to be integrated into wireless sensor networks containing a diverse array of sensors, and has been designed to be readily integrated with a mobile robot in the future for autonomous structural inspection.