Ultrasonic chirp-coded excitation for highly attenuating material testing

Abstract This paper deals with ultrasonic chirp-coded excitation for highly attenuating material testing. We reformulate the expression of gain in signal-to-noise ratio (GSNR) between the compressed signal and short-pulse signal, and propose a method which only needs to adjust the center frequency and bandwidth of chirp. The performance of the chirp-coded method is analyzed and the experimental results match well with the simulation in GSNR and axial resolution except for the main-to-side lobe ratio. Specifically, rubber with an attenuation coefficient of 1.4 Np/(MHz cm) is detected using the transmitting and receiving transducer with a center frequency of 800 kHz. The proposed chirp-coded method has a 4.3 dB GSNR increase to the conventional chirp-coded method, and their axial resolution is approximate to 2.7 μ s, which is close to that of the short-pulse method using a square wave with a 6.25 ns pulse width.