DESCRIPTION:

This micro-machined differential microphone utilizes an optical means to convert the sound-induced motion of a diaphragm into an electronic signal.  Because it can be manufactured with high sensitivity and low noise, this lightweight microphone design offers a means to improve hearing aids. 

The majority of high-performance microphones, and particularly miniature microphones used in cellular telephones and hearing aids, use capacitive sensing to detect the diaphragm motion.  This involves detecting the change in capacitance between the pressure-sensitive diaphragm and a back plate electrode.  In order to detect this change in capacitance, it is first necessary to impose a bias voltage between the back plate and the diaphragm.  This voltage creates practical constraints on the mechanical design of the diaphragm that compromise its effectiveness in detecting sound.  This invention overcomes these performance limitations by using an optical detection scheme based on a low-power semiconductor laser and optical gratings incorporated into the microphone diaphragm.  Because the overall compliance of the microphone diaphragm is adjustable over a very wide range, it is possible to achieve high sensitivity and very low noise performance.

The optical design permits the use of much more flexible and smaller diaphragms, which can be made using silicon micro-fabrication techniques.  It also achieves higher signal to noise ratios than are possible in capacitive sensing schemes.  In addition, the microphone has a much lower noise detection floor relatively low power consumption, and is lightweight.

POTENTIAL APPLICATIONS:

Hearing aid and cellular phone applications and high-performance acoustic measurement devices.

KEYWORDS:

miniaturized directional microphone; differential microphone; optical; MEMS; silicon; hearing aid;micro-machining

ADVANTAGES:

It permits the use of much more flexible diaphragms. It also enables the use of much smaller diaphragms than it is currently possible. Lower noise floor.

DISADVANTAGES:

It may cost more to manufacture.

PATENT STATUS:

Patent Pending in the United States (USPTO Ser. No. 11/335,137, filed 1/19/2006)

PUBLICATION:

W. Cui, B. Bicen, N. Hall, S. A. Jones, F. L. Degertekin, and R. N. Miles, “Optical sensing in a directional MEMS microphone inspired by the ears of the parasitoid fly, Ormia ochracea”, Proceedings of 19th IEEE International Conference on Micro Electro Mechanical Systems (MEMS 2006), Jan. 22-26, 2006, Istanbul.