Simulation of acoustic losses in waveguides for air-coupled ultrasonic phased arrays

Waveguides for ultrasonic air-coupled phased arrays offer grating lobe-free beamforming. However, the interaction between the waveguide and the transducer is not lossless as multiple effects such as thermo-viscosity, reflections and diffraction are introduced. In this work, we analyze these effects with numerical methods in two steps. First, the propagation effects inside a straight waveguide are investigated using a thermo-viscous transient analysis. In order to derive the different acoustic effects, the transient analysis is split in three steps, i.e. simulation without waveguide, with a closed waveguide and with an opened waveguide. Second, a steady state analysis is conducted to derive losses due to inefficient coupling between the transducer and a bent waveguide. As a result, the propagation losses introduced by the waveguide are 10 dB with additional uncertainty of ±3 dB due to the coupling into the waveguide, which is in good agreement with previous measurements of 7.1 dB±1 dB.