Bone Conduction Microphones

New patented surface mount micro-electromechanical systems (MEMS) microphone enhances hearing experience in most difficult environments over the standard microphones. It works by sensing the vibration signals precisely and reliably transmitted through bone and hence do not pick up the surrounding noise. Its small size allows it to easily fit and provide design flexibility in various types of applications.

What Is Bone Conduction

Bone Conduction was discovered by the famous 18th century compose, Ludwig van Beethoven who was almost completely deaf in his early twenties. He found a way to hear the piano through his jawbone.

Most sounds are heard by our eardrums, but we can also hear through our bones in which case it bypasses eardrum, and vibrations are transmitted directly to the inner ear, which is connected to our auditory nerve, which then transmits the sound to our brain. We hear our own voice differently as both mediums are involved – air and bone conduction as opposed to someone else hearing us!

Bone conduction microphone can be really advantageous for user with hearing aid needs or is surrounded by noise. Care should be taken to mount the microphone such that noise is not transferred to the device.

Customer can also combine the best of two microphone types to overcome limitations and develop an array using air conduction microphones with bone conduction microphones to offer best user experience.

Circuit Design

Slight variances in power supply voltage do not affect the sensitivity of PUI Audio’s MEMS microphones. As such, a circuit designer only needs to ensure that the voltage output of the power supply is within the voltage range called out in the MEMS microphone specifications.

Unlike traditional ECM microphones, MEMS microphones do not require the use of a bias resistor between the power supply and the microphone. MEMS microphones have an independent output that is separate from the voltage input. It is recommended to decouple the noise of the power supply from the MEMS microphone by using a 0.1µF capacitor at C1 in the diagram below. A DC-blocking/high-pass filter capacitor should be placed between the MEMS output pin and the CODEC/ADC/preamplifier’s input pin, C2 in the diagram below. Values between 1µF and 3µF are often used, where the larger the capacitor value, the higher the frequency at which the high-pass filter’s corner frequency is placed.

In the event of electromagnetic interference, place a resistor that matches the microphone’s impedance between the amplifier’s unused differential input and the microphone’s ground.