Photonic Micro-Mechanical Acoustic Emission Sensors for Untrasonic Non-Destructive Testing

Abstract

Non-Destructive Testing (NDT) of infrastructures has become an increasingly prominent topic in contemporary society with great significance in terms of safety, economy and environmental protection. Acoustic Emission (AE) technology is a representative NDT technology based on passive ultrasonic guided waves, which has the advantages of large coverage, low energy consumption and rapidity but also puts forward higher requirements on performance specifications of sensors, such as sensitivity, bandwidth, signal-to-noise ratio and miniaturization. Silicon photonics employs silicon as an optical medium to create sub-micron precision photonic systems, which provides promising scope for next-generation sensors with ultra-high sensitivity, small footprint and special functionalities. Oriented towards the requirements from AE applications, this project proposes the first silicon photonic micromechanical AE sensor based on micro-machined membranes, with an ambition of replacing the conventional piezoelectric sensors. The prototype design presented in this work includes two options with different cladding materials, which is capable of a peak velocity sensitivity of more than 75dB[V /(m/s)] and a wide operating frequency range of 100 ∼ 1000 kHz. The overall performance of the proposed design is comparable to that of mainstream piezoelectric AE sensors, while the footprint is reduced to about 1/40. In the design process, a complete design methodology for opto-mechanical AE sensors is developed, which allows rapid design with good agreement with simulation results.