Systematic design and experimental demonstration of transmission-type multiplexed acoustic meta-holograms

TL;DR

This paper presents a novel transmission-type acoustic meta-hologram design that enables multiplexed holography at multiple frequencies, demonstrated through experiments with high-quality holograms and ultrasound focusing, advancing acoustic metamaterials applications.

Contribution

The paper introduces a new design strategy for multiplexed acoustic holograms using a transmission-type metamaterial with Fabry-Perot resonant channels, allowing active frequency multiplexing.

Findings

Successfully projected two different holograms at 14 kHz and 17 kHz.

Demonstrated two-channel ultrasound focusing at 35 kHz and 42.5 kHz.

Enhanced information encoding in acoustic metamaterials.

Abstract

Acoustic holograms have promising applications in sound-field reconstruction, particle manipulation, ultrasonic haptics and therapy. This paper reports on the theoretical, numerical, and experimental investigation of multiplexed acoustic holograms at both audio and ultrasonic frequencies via a rationally designed transmission-type acoustic metamaterial. The proposed meta-hologram is composed of two Fabry-Perot resonant channels per unit cell, which enables the simultaneous modulation of the transmitted amplitude and phase at two desired frequencies. In contrast to conventional acoustic metamaterial-based holograms, the design strategy proposed here, provides a new degree of freedom (frequency) that can actively tailor holograms that are otherwise completely passive and hence significantly enhances the information encoded in acoustic metamaterials. To demonstrate the multiplexed acoustic metamaterial, we first show the projection of two different high-quality meta-holograms at 14 kHz and 17 kHz, with the patterns of the letters, N and S. We then demonstrate two-channel ultrasound focusing and annular beams generation for the incident ultrasonic frequencies of 35 kHz and 42.5 kHz. These multiplexed acoustic meta-holograms offer a technical advance to tackle the rising challenges in the fields of acoustic metamaterials, architectural acoustics, and medical ultrasound.