Scaling acoustic directional couplers using 3D printing

Abstract

Acoustic directional couplers permit separation of forward and reverse sound pressure waves. This separation opens the way to traceable, precision acoustic reflection measurements. In order to span the audio spectrum, multiple couplers will be required as each coupler only operates slightly over one octave. To reach 20 kHz or above requires very small, mechanically-precise construction. We achieve this precision using 3D printing techniques. The Lagasse design method was used by Pennington to create a coupler that operated over a designed range of 1-2 kHz. This design was scaled to create an acoustic directional coupler with a designed range of 10-20 kHz. Because frequency scales inversely with the size of the coupler, the coupler needs to be built with a very high degree of precision. The coupler was therefore designed and modeled in SolidWorks and 3D printed to high precision. Characterization of the couplers was achieved using two distinct methods. The first, a preliminary measurement method to test the hypothesis and the second, a high precision automated measurement. The automation was scripted in python on a Ubuntu Linux distribution. Future work may include an Acoustic coupler to be used in ultrasound, to do this the coupler would need to be scaled a further 2.5 times. This would likely prove difficult as the wavelengths at 50 kHz are in the order of mm, comparable with those of electromagnetic waves at 44 GHz.