Using coded excitation to maintain signal to noise for FMC+TFM on attenuating materials

Lines, David and Mohseni, Ehsan and Javadi, Yashar and Mineo, Carmelo and Wathavana Vithanage, Randika Kosala and Qiu, Zhen and MacLeod, Charles Norman and Pierce, Gareth and Gachagan, Anthony (2019) Using coded excitation to maintain signal to noise for FMC+TFM on attenuating materials. In: 2019 IEEE International Ultrasonics Symposium, 2019-10-06 - 2019-10-09, Scottish Event Campus (SEC).

[img]
Preview
Text (Lines-etal-IEEE-IUS-2019-Using-coded-excitation-to-maintain-signal-to-noise-for)
Lines_etal_IEEE_IUS_2019_Using_coded_excitation_to_maintain_signal_to_noise_for.pdf
Accepted Author Manuscript

Download (480kB)| Preview

    Abstract

    Ultrasonic Non-Destructive Evaluation using Full Matrix Capture (FMC) and Total Focusing Method (TFM) is used for high resolution imaging as every pixel is in optimal focus. FMC excites one element in turn, so operates with lower transmitted energy compared to phased array beamforming. The energy at a reflector is further reduced by the broad directivity pattern of the single element. The large number of Tx/Rx A-scans that contribute to each pixel recover the Signal-to-Noise Ratio (SNR) in the final TFM image. Maintaining this in the presence of attenuating materials is a challenge because relevant information in each Ascan signal is buried in the thermal noise, and the TFM process assumes no quantization effects in the Analogue-to-Digital Converters (ADCs) in each receiver. In-process inspection during Additive Manufacturing (AM) requires ultrasonic array sensors that can tolerate high temperatures, scan over rough surfaces and leave no residue. Dry-coupled wheel probes are a solution, but the tire rubbers are often highly attenuating, causing a problem for FMC+TFM needed to adapt the focus through the rough surface. Common approaches to maintain the SNR are to drop the frequency or to average over multiple transmissions, but these compromise resolution and acquisition rate respectively. In this paper, the application of coded excitation to maintain the SNR in the presence of high signal attenuation is explored.