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Extraordinary acoustic transmission via supercoupling and self-interference cancellation
Supercoupling is a widely researched topic in wave engineering, which has been used to build coupling channels that can, in principle, support total transmission and complete phase uniformity, independent of the length of the channel. This has generally been accomplished by employing dispersion in media that display a near-zero index. In the field of acoustics, prior works have required the presence of periodic embedded resonators, such as membranes or Helmholtz resonators, in order to observe near-zero properties. Here it is shown, theoretically and experimentally, that supercoupling can occur in an acoustic channel without the presence of embedded resonators. A compressibility-near-zero (CNZ) acoustic channel was observed to show remarkable properties analogous to those found in electromagnetics. Furthermore, these principles are employed to develop an acoustic power divider, which takes advantage of the CNZ properties of the channel to also exhibit phase invariance at the output. In the next section, another extraordinary acoustic transmission phenomenon is explored, regarding the potential for sending and receiving from a single acoustic transducer at the same time and at the same frequency. This is made possible through an electrical circuit that is designed to cancel self-interfering signals in acoustic measurement systems. Systems that employ self-interference cancellation (SIC) are often referred to as simultaneous transmit and receive (STAR) or in-band full duplex (IBFD) systems, which have recently enabled sending and receiving of Radio Frequency (RF) signals at the same time and at the same frequency. This has led to commercialization efforts with the promise of doubling the throughput of traditional radio systems including Wi-Fi and 5G cellular communications. Prior to these advances, researchers in vibration control explored self-sensing actuator systems, also referred to as sensoriactuators or sensorless control systems. Inspired by these developments, these approaches are combined and extended to explore STAR functionality in an acoustic measurement system. First, self-interference cancellation (SIC) is applied to time-domain measurements to demonstrate the potential for a practical, single-transducer ultrasonic nondestructive evaluation (NDE) system to measure echo returns while it is actively transmitting at the same frequency. Theoretical models and experimental results are presented and discussed.Electrical and Computer Engineerin