In the past, the loudspeakers for in-ear headphones and hearing aids didn’t exactly shine with regard to their hi fidelity properties. But the innovative MEMS version produces true sound shower effects. It can be seen and heard at Fraunhofer (Hall C5 Booth 426) at electronica this week.
MEMS sensors are the “sensory organs” of mobile devices. With their help, smartphones recognize position and movement while tiny MEMS microphones record noises and voice. But the loudspeakers are not yet “MEMS.” In spite of their similarity to microphones – the same principle but in reverse – they lag behind electromagnetism. This is despite the fact that non-linear signal conversion, bad performance in the low and high frequency ranges due to too much mass and design-related self-resonance seriously limit the sound quality.
On the other hand, innovative MEMS micro loudspeakers from Fraunhofer ISIT and Fraunhofer IDMT (Hall C5 Booth 426) promise a balanced, impressive sound with outstanding brilliance in the high frequency range. On an area of just 4 x 4 millimeters they cover a frequency range from 20 Hz to more than 20 kHz and when used for in-ear headphones, generate a sound pressure level of 110 decibels (dB). That’s similar to the sound of a chainsaw at a distance of one meter. At lower bandwidths, it can even surpass the pain threshold of 130 dB.
MEMS loudspeakers are also much smaller than conventional ones, they cost less to produce, and consume less energy. This makes them ideal for battery-operated mobile devices.
MEMS loudspeakers based on the piezo principle
MEMS (Micro-Electro-Mechanical Systems) is a microchip technology that allows both electronic circuits and mechanical devices to be manufactured on a silicon chip with dimensions in the thousandth millimeter range in large numbers and at a low cost.
The finished micro loudspeaker then works according to the piezoelectric principle. When a voltage is applied, materials deform, in other words, they convert electrical energy into motion. If you apply an alternating voltage to the drive structures that consist of a piezoelectric layer, which is just two thousandth of a millimeter thick, and extremely thin silicon membranes, they start to vibrate. In the loudspeakers, these mechanical deflections displace the surrounding air and thus generate sound waves.
Micro loudspeaker from Austria
It’s not only Fraunhofer that is developing MEMS loudspeakers. Austrian startup USound (as reported previously) seems to be ahead, at least in terms of commercialization. Together with STMicroelectronics (Hall C3 Booth 101) they began shipping the first silicon micro loudspeakers at the start of this year. In the project, USound provided the design, while the thin film piezo technology came from STMicroelectronics.
USound GmbH_Finalist Fast Forward Award 2018
USound began mass production just recently and has found a prominent distribution partner in Digi-Key (Hall B5 Booth 165). Flex, STMicroelectronics, and AT&S plan to produce several million units each year, initially for in-ear headphones. This will be followed by wearables and, ultimately, smartphones.
Because of their outstanding properties, MEMS loudspeakers could become the most important development in the area of miniature loudspeaker technology for many years. The MEMS expert among the analysts, Yole Développement, calculates the current overall market for micro loudspeakers at USD 8.7 billion and expects silicon-based MEMS products to gain more market shares.
The applications include smartphones, wearables, augmented reality (AR) / virtual reality (VR), and even medical products. At present, Fraunhofer scientists are working on loudspeakers based on new piezoelectric high-performance materials that will reduce power consumption even more. The form factor will also be reduced considerably in the future. This will make the loudspeakers even more attractive from a price aspect and could create completely new areas of application in acoustics.
Yole Développement Webcast Acoustic MEMS and Audio Solutions