Acoustic Frequency Domain Reflectometry in Waveguides

Acoustic frequency domain reflectometry (AFDR) is a novel sensing technique that employs frequency-modulated continuous wave (FMCW) methods in acoustic waveguide reflectometry. This approach is particularly effective for dispersion and phase compensation due to the method’s frequency domain approach. By applying this compensation, distortion due to waveguide dispersion and frequency sweep nonlinearity is partially deconvolved from the spatial profile of the waveguide. Unlike conventional acoustic FMCW-based methods, AFDR uses a single acoustic transducer for both transmission and reception, which enables the use of lower cost electronic systems than in standard time-domain pulse-echo-based systems. Furthermore, AFDR allows for SNR improvement by extending the sweep time rather than increasing the applied acoustic amplitude, which can aid in small signal detection without signal distortion. AFDR was successfully demonstrated for distributed temperature sensing, achieving a temperature resolution of about 1 °C and a spatial resolution of 20 cm, with a theoretical spatial resolution of about 10 mm, illustrating its scalability in system parameters, sensor density, and methodology. Given its flexibility, simplicity, and low cost, AFDR has significant potential for a wide range of distributed sensing applications using acoustic waveguides.