Multi-Beam Ultrasonic Transmission from a Single Channel PMUT Array with Cosine-Apodized Amplitude Modulation via Various Top Electrode Areas

Multi-beam ultrasonic transmission (MBUT) is crucial for high-speed imaging and multi-point neural stimulation. However, conventional approaches to obtain the MBUT require complex multi-channel transducers or delay control circuits. In this work, we demonstrated a compact single-channel piezoelectric micromachined ultrasonic transducer (PMUT) capable of generating three distinct beams through cosine-apodized amplitude modulation, which was achieved by varying top electrode areas. The fabricated device with a single-crystal PZT thin film exhibits a resonant frequency of 3.5 MHz in a liquid (Fluorinert, FC-40) and possesses the ability to efficiently produce three beams at steering angles of$\pm 14^{\circ}$and 0°, with the central beam reaching a peak acoustic pressure of$8.7 \text{kPa} / \mathrm{V}$. This electrode-geometry-based modulation methodology provides a simplified and compact solution for realizing multi-beam acoustic transmission, offering significant potential for novel applications, such as scalable neural interfaces and rapid ultrasonic flow detection.