Orbital Angular Momentum Multiplexing in Space–Time Thermoacoustic Metasurfaces

Abstract

Multiplexing technology with increased information capacity plays a crucial role in the realm of acoustic communication. Different quantities of sound waves, including time, frequency, amplitude, phase, and orbital angular momentum (OAM), have been independently introduced as the physical multiplexing approach to allow for enhanced communication densities. An acoustic metasurface is decorated with carbon nanotube patches, which when electrically pumped and set to rotate, functions as a hybrid mode‐frequency‐division multiplexer with synthetic dimensions. Based on this spatiotemporal modulation, a superposition of vortex beams with orthogonal OAMs and symmetric harmonics are both numerically and experimentally demonstrated. Also, flexible combinations of OAM modes with diverse frequency shifts are obtained by transforming the azimuthal phase distributions, which inspires a mode‐frequency‐division multiplexing approach that significantly promotes the communication capacity.

Generation of time-varying orbital angular momentum beams with space-time-coding digital metasurface

“…An additional degree of freedom in controlling OAM with a time-varying profile can be used to enhance communication capacity as an immediate application. 42 Moreover, the inhomogeneous OAM profile in both the spatial and temporal domains can also be potentially useful for obtaining unconventional particle trapping, sorting dynamics, and controlling particle trapping stability. 43 In summary, we have experimentally generated time-varying OAM beams by a space-time-coding digital metasurface in the microwave regime.…”

Tunable, reconfigurable, and programmable acoustic metasurfaces: A review

“…As shown in Figure 2C, different transmission or phase delay properties were achieved by varying the helical unit cells such as by using a screw-nut mechanism to allow the length of the spiral channel to be changed to slow down the propagating waves in a tunable manner (Zhao et al, 2018). This concept was later extended to the dynamic rotation process by leveraging structures and effects such as with nested resonant rings (He et al, 2022), a passive linear vortex (Wang et al, 2022a), electrically pumped carbon nanotubes (Jia et al, 2022), rotational Doppler effect (Wang et al, 2022b), and a tunable perfect sound absorption metasurface (Liu et al, 2021). There have been some research reports dealing with this issue, such as that of Liang et al (2020), who presented a systematic strategy to control AMs based on helical-structured metamaterials.…”

“…In this procedure, a rotational system drives the metasurface to rotate steadily such that the phase-adjustable and high-transmittance units are periodically arranged along the azimuthal direction, forming a spiral phase distribution for the incident plane. Jia et al (2022) constructed an AM decorated with carbon nanotube patches as spatiotemporal modulators to function as a hybrid mode frequency division multiplexer. Dynamically tuning the thermo-acoustic phase generation was proposed with the help of manipulation of the electric phase delays, and it was substantiated that the acoustic pressure amplitude remained uniform, while its phase accumulation doubled the electrical one.…”

Spatiotemporal Acoustic Communication by a Single Sensor via Rotational Doppler Effect

“…Multiplexing technology has been proposed as an efficient solution to promote the transmission capacity in acoustic communication, [ 3 ] including frequency‐division multiplexing, time‐division multiplexing, and so on. As an emergent branch of multiplexing technology, orbital‐angular‐momentum‐division multiplexing [ 4 , 5 , 6 , 7 , 8 ] based on acoustic vortex beams [ 9 , 10 , 11 , 12 , 13 ] has attracted broad attention owing to its intrinsic orthogonality, infinite dimensionality of its Hilbert space and compatibility with existing multiplexing technologies. As a consequence, each vortex beam of different topological charge l plays as an orthogonal OAM channel, [ 6 ] which can boost the transmission capacity by integrating with other state‐of‐the‐art communication technologies, for example, the combination of OAM and multiple input multiple output technologies [ 14 ] has been proposed to further increase the communication speed, and mitigate the crosstalk with the equalization algorithm.…”

“…[ 27 ] Importantly, the rotational Doppler effect builds the bridge between the angular momentum and frequency. A mode‐frequency‐division method has been proposed by rotating the OAM sources to generate multiple frequency signals, [ 4 , 32 ] where the harmonic frequency waves may asynchronously propagate due to the dispersion. [ 33 ] Apart from the rotating source, we recognize that the vortex beams of identical frequency but different OAM orders can play as the multiplexed carries, which can be efficiently separated in the frequency domain and simultaneously measured by a single sensor, getting rid of the field‐scanning, insertion loss, spatial overlapping, and propagation dispersion.…”