Speaker
Description
In recent years, loudspeakers that generate audible sound by demodulating an ultrasonic carrier have gained increasing attention. For MEMS applications in particular, this approach offers the advantage of achieving higher sound pressure levels at low frequencies, a regime in which conventional MEMS loudspeakers typically struggle to meet industry requirements. This advantage stems from a fundamental change in the loudspeaker’s operating principle: Classical loudspeakers act as a volume source, whereas modulated ultrasound loudspeakers act as a volume flow source, enabling a +20 dB per decade increase in sound pressure for decreasing frequencies. This fundamentally different operation is achieved by introducing a shutter that demodulates the ultrasound carrier signal in order to create an audible signal. In this contribution, we review the current status of modulated ultrasound principles and outline their challenges in both technological and medical contexts. Besides fabrication, the topics of ultrasound tolerance in humans and animals, simulation methods, design optimization, and sound quality are tackled. Additionally, we compare modulated ultrasound principles with current MEMS loudspeaker designs and identify opportunities and application examples enabled by this new MEMS loudspeaker technology.