3D printed acoustic metamaterial filters for the mitigation of inaudible ultrasound attacks on smart speakers

Abstract

Acoustic metamaterials have shown great potential in manipulating acoustic waves with a small footprint and versatile functionality. While their usefulness has been demonstrated in many fields including noise reduction and biomedical ultrasound, not many studies have been done in the field of audible acoustics and speakers. In this work, we show that an acoustic metamaterial-based filter can enhance the security of smart speakers, which are susceptible to inaudible ultrasound attacks due to the shadow effect of the microphones. The filter contains several resonant unit cells which collectively modulate the received signals in the ultrasound spectrum and, thus, mitigate inaudible attacks on smart speakers. On the other hand, normal audible signals are not affected and, therefore, regular functionality is not disturbed. The filtering effect is verified numerically using finite element analysis. Measurements are performed to validate the concept, where it is shown that inaudible ultrasound attacks are effectively blocked when the 3D-printed metamaterial filters are installed. This demonstration shows a possible way to apply acoustic metamaterials in consumer electronics such as smart speakers.