When background noise is horribly loud – in a tank, on an airport runway or aircraft carrier – ordinary microphones are useless. Even mics that clamp to the throat or skull are no good because the noise vibrates the sensor.
So four inventors deep in the heart of US Defence territory, in Maryland and Virginia, have come up with a mic that is clamped to a back tooth. This, they say, shields it from external vibration while still picking up speech from the jaw bone.
The team provides an example of the problems that background noise can cause. In Afghanistan, a device with an external microphone is used by soldiers to automatically translate English battlespeak into the local language, Dari. But background noise can lead to misinterpretation.
In the new device, a vibration sensor is set in resin and moulded to fit like a dental cap or plate. A low-power radio link transmits audio to a higher-power transmitter built into ear-muff headphones, so wearers hear their own voice as it is sent to others.
A push-to-talk function is provided by a tongue-operated switch. The inventors say the system works in noise up to 160 decibels, which is louder than a jet aeroplane taking off. They also note that the mic works inside gas masks and that encryption can be added for security. The mic can be removed for cleaning to avoid infection.