Acoustic phased arrays are capable of steering and focusing a beam of sound via selective coordination of the spatial distribution of phase angles between multiple sound emitters. Constrained by the principle of reciprocity, conventional phased arrays exhibit identical transmission and reception patterns which limit the scope of their operation. This work presents a controllable space–time acoustic phased array which breaks time-reversal symmetry, and enables phononic transition in both momentum and energy spaces. By leveraging a dynamic phase modulation, the proposed linear phased array is no longer bound by the acoustic reciprocity, and supports asymmetric transmission and reception patterns that can be tuned independently at multiple channels. A foundational framework is developed to characterize and interpret the emergent nonreciprocal phenomena and is later validated against benchmark numerical experiments. The new phased array selectively alters the directional and frequency content of the incident signal and imparts a frequency conversion between different wave fields, which is further analyzed as a function of the imposed modulation. The space–time acoustic phased array enables unprecedented control over sound waves in a variety of applications ranging from ultrasonic imaging to non-destructive testing and underwater SONAR telecommunication.
Broadband nonreciprocal linear acoustics through a non-local active metamaterial
The ability to create linear systems that manifest broadband nonreciprocal wave propagation would provide for exquisite control over acoustic signals for electronic filtering in communication and noise control. Acoustic nonreciprocity has predominately been achieved by approaches that introduce nonlinear interaction, mean-flow biasing, smart skins, and spatio-temporal parametric modulation into the system. Each approach suffers from at least one of the following drawbacks: the introduction of modulation tones, narrow band filtering, and the interruption of mean flow in fluid acoustics. We now show that an acoustic media that is non-local and active provides a new means to break reciprocity in a linear fashion without these deleterious effects. We realize this media using a distributed network of interlaced subwavelength sensor–actuator pairs with unidirectional signal transport. We exploit this new design space to create a stable metamaterial with non-even dispersion relations and electronically tunable nonreciprocal behavior over a broad range of frequencies.
more » « less- NSF-PAR ID:
- 10303679
- Publisher / Repository:
- IOP Publishing
- Date Published:
- Journal Name:
- New Journal of Physics
- Volume:
- 22
- Issue:
- 6
- ISSN:
- 1367-2630
- Page Range / eLocation ID:
- Article No. 063010
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract -
null (Ed.)Acoustic devices have played a major role in telecommunications for decades as the leading technology for filtering in RF and microwave frequencies. While filter requirements for insertion loss and bandwidth become more stringent, more functionality is desired for many applications to improve overall system level performance. For instance, a filter with non-reciprocal transmission can minimize losses due to mismatch and protect the source from reflections while also performing its filtering duties. A device such as this one was originally researched by scientists decades ago. These devices were based on the acoustoelectric effect where surface acoustic waves (SAW) traveling in the same direction are as drift carriers in a nearby semiconductor are amplified. While several experiments were successfully demonstrated in [1], [2], [3]. these devices suffered from extremely high operating electric fields and noise figure [4], [5]. In the past few years, new techniques have been developed for implementing non-reciprocal devices such as isolators and circulators without utilizing magnetic materials [6], [7], [8], [9]. The most popular technique has been spatio-temporal modulation (STM) where commutated clock signals synchronized with delay elements result in non-reciprocal transmission through the network. STM has also been adapted by researchers to create non-reciprocal filters. The work in [10] utilizes 4 clocks signals to obtain a non-reciprocal filter with an insertion loss of -6.6 dB an isolation of 25.4 dB. Another filter demonstrated in [11] utilizes 6 synchronized clock signals to obtain a non-reciprocal filter with an insertion loss of -5.6 dB and an Isolation of 20 dB. In this work, a novel non-reciprocal topology is explored with the use of only one modulation signal. The design is based on asymmetrical SAW delay lines with a parametric amplifier. The device can operate in two different modes: phase coherent mode and phase incoherent mode. In phase coherent mode, the device is capable of over +12 dB of gain and 20.2 dB of isolation. A unique feature of this mode is that the phase of the pump signal can be utilized to tune the frequency response of the filter. Under the phase-incoherent mode, the pump frequency remains constant and the device behaves as a normal filter with non-reciprocal transmission exhibiting over +7 dB of gain and 17.33 dB of isolation. While the tuning capability is lost in this mode, phase-coherence is no longer necessary so the device can be utilized in most filtering applications.more » « less
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Metamaterials based on mechanical elements have been developed over the past decade as a powerful platform for exploring analogs of electron transport in exotic regimes that are hard to produce in real materials. In addition to enabling new physics explorations, such developments promise to advance the control over acoustic and mechanical metamaterials, and consequently to enable new capabilities for controlling the transport of sound and energy. Here, we demonstrate the building blocks of highly tunable mechanical metamaterials based on real-time measurement and feedback of modular mechanical elements. We experimentally engineer synthetic lattice Hamiltonians describing the transport of mechanical energy (phonons) in our mechanical system, with control over local site energies and loss and gain as well as over the complex hopping between oscillators, including a natural extension to nonreciprocal hopping. Beyond linear terms, we experimentally demonstrate how this measurement-based feedback approach makes it possible to independently introduce nonlinear interaction terms. Looking forward, synthetic mechanical lattices open the door to exploring phenomena related to topology, non-Hermiticity, and nonlinear dynamics in nonstandard geometries, higher dimensions, and with novel multibody interactions.more » « less
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The existing concepts of non-reciprocity in propagation of acoustic or elastic waves are based either on nonlinear effects, or on local circulation of linear elastic fluid that leads to red or blue Doppler shift, depending on the direction of sound wave. The same concepts exist for electromagnetic non-reciprocity, where external magnetic field may produce the effect similar to local rotation of the medium. These two concepts originate from two known methods of breaking a time-reversal symmetry (T-symmetry), that is necessary for observation of nonreciprocal wave propagation. Both concepts require additional electrical or mechanical devices to be installed with their own power sources. Here we propose to explore viscosity of fluid as a natural factor of the T-symmetry breaking through energy dissipation. We report experimental observation of the nonreciprocal transmission of ultrasound through a water-submerged phononic crystals consisting of several layers of aluminum rods arranged in a square lattice. While viscous losses break the T-symmetry, making the wave propagation thermodynamically irreversible, the transmission remains reciprocal if the scatterers are symmetrical. To generate different energy losses for opposite directions of propagation, the P-symmetry of the crystal is broken by using asymmetric scatterers. Due to asymmetry, two sound waves propagating in the opposite directions produce different distributions of velocity and pressure that leads to different local absorption. Dissipation of acoustic energy occurs mostly near the surface of the scatterers and it strongly depends on surface roughnesses. Using two phononic crystal with smooth and rough aluminum rods we demonstrate low (2-5 dB) and high (10-15 dB) level of non-reciprocity within a wide range of frequencies, 300-600 kHz. Experimental results are in agreement with numerical simulations based on the Navier-Stokes equation. This nonreciprocal linear device is very cheap, robust and does not require energy source.more » « less
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