Ultrasonic Modulation–Demodulation-Based Piezoelectric MEMS Speakers—A New Paradigm for Microspeakers

Low-frequency characteristics serve as primary metrics for evaluating the acoustic performance of modern microspeakers. However, conventional microspeakers exhibit flat low-frequency in-ear responses due to their inherent diaphragm displacement–sound pressure relationship, which deviates from ideal human auditory characteristics and fails to meet active noise cancellation requirements. To address this limitation, this study proposes a piezoelectric MEMS speaker that is based on ultrasonic modulation-demodulation principles. This is achieved by dynamic acoustic impedance, where the ultrasonic acoustic source and valve actuators work synchronously. The speaker achieves superior low-frequency performance, featuring a low-frequency sound pressure level of 134 dB at 20 Hz, following the IEC 711 standard. The total harmonic distortion remains below 2% in the 20 Hz to 1 kHz range. The speaker measures only 4 mm $\times 9$ mm in size, and this size is possible due to its source–valve decoupling architecture. Combined with high performance and miniaturization, this technological breakthrough overcomes the performance limitations of conventional speakers and establishes a new paradigm for microspeakers.[2025-0163]