Voice assistants such as Alexa, Siri, Cortana and Google Home will be listening everywhere at this week’s CES 2018 in Las Vegas. While the microphones they use to listen have undergone drastic changes thanks to advances in microelectromechanical systems (MEMS), the speakers they use have remained relatively unchanged, until now.
Among the chaotic cacophony that is CES, look for a small startup called USound that is preparing to generate big waves with an adaptation of MEMS that uses the piezoelectric effect to form the first MEMS silicon micro-speaker. It’s doubtful USound’s speakers will actually be heard above the noise floor at CES, as the speakers are designed for in-ear or near-ear applications.
IoT solution providers should take a close look at these as they can be coupled with MEMS microphones to form a complete ultra-low-power, low-cost, acoustic pick-up and audio output system that can be run off a coin-cell battery. By adding an RF interface, audio signals can be detected and transmitted anywhere, and with appropriate processing it can be filtered and presented to users’ ear canals directly.
The speakers are a breakthrough in the sense that they use silicon manufacturing techniques. They can be miniaturized and produced more efficiently, though MEMS processes are not yet as streamlined as CMOS processes used for semiconductors.
They use a thin-film piezoelectric MEMS technology developed by STMicroelectronics that relies upon the response of the piezoelectric material to electrical stimulus: it bends (Figure 1).
Figure 1. USound’s MEMS-based micro-speaker uses the piezoelectric effect to push a diaphragm and generate audio waves.
This controlled bending of the material, when used in conjunction with appropriate cantilevers and a fully sealed diaphragm, creates a sound wave, albeit at low pressure levels. That said, the full speaker can be made small enough to fit to the top of the ear canal, so that users can still hear ambient sound, while the output from the speaker is coupled almost directly to the eardrum.
USound sees direct application of the technology in augmented reality and virtual reality (AR/VR) systems, though as is often the case, the application of new technology often goes feral once it’s let into “the wild” of creative innovators. The first instantiations of the speaker will be on display at CES (Figure 2), and USound expects to have reference designs available this year.
Figure 2. USound’s micro-speakers will be on display at CES 2018, with development kits expected this year.
While the micro-speakers won’t have the volume levels achievable by typical driver-based speakers, they do greatly reduce size, cost, space and power consumption, while increasing ruggedness and reliability. If higher sound pressure levels (SPLs) are required, the devices can be scaled in number to reach the required SPL. While the devices will be on display, USound hasn’t released any public information regarding SPL or the devices’ audio response curves. Still, the devices open the door to new ways of thinking about how to smartly and discretely present audio.