A study on improving the sound radiation capability of stepped-plate parametric array loudspeakers

It is well known that Parametric Array Loudspeakers (PALs) produce highly directional audible sounds. However, their widespread adoption is hindered by their high cost, which is primarily attributable to the use of an array of ultrasonic radiator units. To address this issue, our research group introduced stepped-plate parametric array loudspeakers (SPPALs) in 2018. SPPALs utilize a single-structure directional ultrasonic radiator, featuring steps of half-wavelength thickness on the radiating plate. This design mitigates the problem of poor directivity, especially at high frequencies, caused by destructive interference resulting from the plate's flexural mode. Moreover, SPPALs can offer cost advantages compared to commercial PALs due to their single structure. However, understanding the vibration characteristics of SPPALs in relation to sound radiation performance is quite challenging due to their various design parameters. In this study, we present an analytical approach that offers a quantitative method for enhanced sound radiation capability. We present a simplified vibration model (SVM), which enables an efficient design process based on a comprehensive analysis of vibration characteristics. By minimizing reliance on finite element method (FEM) simulations, our method expedites the design of various directional speaker systems.