As wireless devices proliferate and systems gain processing power, the demand grows for those devices and systems to accept real-world sound inputs such as voice commands. There’s also a need for the same in applications such as microphones in true wireless stereo (TWS) earbuds. In many cases, micro-electromechanical systems (MEMS) sensors are stepping up, with system manufacturers taking advantage of MEMS sensors’ high sensitivity to vibration and low current consumption in low-power mode.
It’s into this framework that Knowles brings the V2S200D multimode digital vibration sensor, a miniature device offering a single-bit, pulse-density-modulation (PDM) output.
Derived from the company’s SiSonic MEMS technology, the device comprises a transducer, a low-noise input buffer, and a sigma-delta modulator. With its high vibration sensitivity, the V2S200D can pick up audio via bone conduction in earbuds, wearables, and other applications requiring flat response to vibration and high acoustic isolation.
Expanding Applications for Vibration Sensors
While the V2S200D vibration sensor is worthy of consideration in these voice-call microphones, that’s not its only application. Recently, a series of live demonstrations showed the range of apps that the device can serve. Because it's sensitive to vibration as opposed to acoustic sound pressure, the V2S200D can go places that a conventional microphone would not necessarily fill the bill (see figure).
For example, consider the conventional stethoscope used by doctors and nurses to listen to the human heart, a device that's remained unchanged for many decades. In keeping with today’s trend of deploying electronics in medical applications, the V2S200D can sense the vibration generated as a heartbeats. Those vibrations are rich in low-frequency signals. Once acquired, they can be processed with noise suppression to further refine the signal.
In automotive applications, one might use a sensor like the V2S200D to pick up and transmit voice commands or emergency-vehicle sirens from a vehicle’s exterior. It can, for example, be placed on or inside a side-view mirror, where sound waves propagating through air impact the mirror’s surface, causing it to vibrate sympathetically for the sensor to acquire. Placing the sensor within the mirror provides high environmental robustness.