We present the first group of acoustic delay lines (ADLs) at 5 GHz, using the first-order antisymmetric (A1) mode in Z-cut lithium niobate thin films. The demonstrated ADLs significantly surpass the operation frequency of the previous works with similar feature sizes, because of its simultaneously fast phase velocity, large coupling coefficient, and low-loss. In this work, the propagation characteristics of the A1 mode in lithium niobate is analytically modeled and validated with finite element analysis. The design space of A1 ADLs is then investigated, including both the fundamental design parameters and those introduced from the practical implementation. The implemented ADLs at 5 GHz show a minimum insertion loss of 7.9 dB, an average IL of 9.1 dB, and a fractional bandwidth around 4%, with delays ranging between 15 ns to 109 ns and the center frequencies between 4.5 GHz and 5.25 GHz. The propagation characteristics of A1 mode acoustic waves have also been extracted for the first time. The A1 ADL platform can potentially enable wide-band high-frequency passive signal processing functions for future 5G applications in the sub-6 GHz spectrum bands.

The low propagation loss of electromagnetic radiation below 1 MHz offers significant opportunities for low power, long range communication systems to meet growing demand for Internet of Things applications. However, the fundamental reduction in efficiency as antenna size decreases below a wavelength (30 m at 1 MHz) has made portable communication systems in the very low frequency (VLF: 3–30 kHz) and low frequency (30–300 kHz) ranges impractical for decades. A paradigm shift to piezoelectric antennas utilizing strain-driven currents at resonant wavelengths up to five orders of magnitude smaller than electrical antennas offers the promise for orders of magnitude efficiency improvement over the electrical state-of-the-art. This work demonstrates a lead zirconate titanate transmitter > 6000 times more efficient than a comparably sized electrical antenna and capable of bit rates up to 60 bit/s. Detailed analysis of design parameters offers a roadmap for significant future improvement in both radiation efficiency and data rate.

This letter presents the first piezoelectric micromachined ultrasonic transducer (PMUT) based on thin-film lithium niobate (LiNbO 3). The figures of merit (FoMs) of LiNbO 3 as ultrasound sensors and transducers are first studied, showing great prospective as a balanced transceiver platform. Efficient flexural mode excitation is achieved using a proposed lateral-field-excitation (LFE) structure. The implemented device shows a flexural mode at 7.6 MHz, with a high electromechanical coupling (k 2) of 4.2%. Measured quality factor (Q) in vacuum is 2605, indicating the low structural loss, while measured Q in air is 264, suggesting the ultrasound radiation. A dynamic displacement sensitivity of 20.2 nm/V is measured. Upon further optimizations, LiNbO 3based PMUTs are promising candidates for miniature ultrasound applications.

Acoustically driven antennas operating at resonant wavelengths up to 105 times smaller than electrical antennas offer great potential for portable, low power communication systems in the very low frequency and low frequency range. Acoustic antennas with real resonant impedances have been demonstrated to offer orders of magnitude better total efficiency compared to similar sized, subwavelength electrically small antennas exhibiting large reactances. While most acoustic antennas share favorable impedance characteristics offering significant matching efficiency advantages over electrically small antennas, radiation efficiency varies greatly based on the implementation of the acoustically driven antenna. This paper presents a theoretical analysis of the three primary methods for implementing acoustically driven radiating elements, investigating both radiation and matching efficiencies comprising the total antenna efficiency. Radiation from the linear movement of unipolar charge driven both piezoelectrically and capacitively, the piezoelectrically actuated rotation of fixed dipole charges, and from flipping dipoles inside strain driven piezoelectrics are all presented and analyzed in terms of their design parameters and fundamental challenges. The efficiency of each type of acoustic antenna is referenced to an equivalent electrical antenna to benchmark the performance to a more familiar framework. Of the analyzed antenna types, piezoelectric alternating dipole antennas exhibit the most promise, with efficiencies more than a million times greater than electrically small antennas expected as piezoelectric materials, and resonator designs are optimized for acoustic radiation.

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