On the robustness of coded excitation in ultrasonic acquisition systems

Coded excitation has been shown to be a simple yet effective technique for improving signal quality in ultrasonic active ranging applications. Despite many reported benefits, uptake of coded excitation in industrial applications to date has been minimal. The authors speculate that this can be in part attributed to a lack of understanding of the robustness of the technique in practical use. To combat this, this paper reports on research into the main mechanisms that can introduce performance degradation and describes the effect of the two most important mechanisms, referred to as symbol asymmetry and symbol misalignment. These mechanisms lower output signal quality through the introduction of unexpected signal artifacts, as well as by reducing useful signal amplitude. We show how symbol asymmetry can be introduced through hardware imperfections and the relative degradation severity associated with different imperfection types. We similarly show how symbol misalignment can be introduced when using coded excitation in non-stationary situations. As a result, we formulate the minimum hardware requirements and inspection conditions required to correctly utilise coded excitation such that users can be confident of achieving high quality outcomes. We quantitatively simulate and experimentally verify the output signal degradation across many scenarios to identify the operating conditions that need to be satisfied to ensure that degradation does not exceed an arbitrarily chosen threshold of 40 dB (the noise floor from random noise in our experimental setup).