Capacitive MEMS Microphone Optimized for PAS Applications
Abstract
To derive an optimum design of a MEMS microphone in any application (i.e. photoacoustic instrumentation), it is important to understand the underlying physics that govern the behavior of the device. In addition, one must have a good understanding of the specific requirements imposed on the device in the intended application. In the particular case of photoacoustic detection, signal-to-noise ratio is the overwhelmingly important parameter. Other parameters such as size and required operating voltage may be compromised to achieve the best possible signal-to-noise ratio. An important property, to be shown below, is the low sensitivity to vibration in MEMS microphones due to a much smaller mass of inertia of the sensing diaphragm, when compared to state-of-the-art conventional microphones. In photoacoustic detection, a microphone is used to detect the minute thermal expansion/pressure wave generated in a gas due to molecular absorption, and subsequent release, of energy generated from a light source 1,6. This method is very well suited for molecular fingerprinting, since the absorption versus applied light energy/wavelength is uniquely dependent on the exact molecular structure. The measurement, in which light of various wavelengths is applied, to map the molecular absorption, is referred to as photoacoustic spectroscopy (PAS). Current PAS instrumentation utilizes state-of-the-art conventional microphone technology in combination with high powered light sources to maximize the sensitivity of the system. It is well known from literature (such as 2), that electrostatic, or capacitive, microphones have the highest sensitivity and the lowest self-noise of the known detection principles. while conventional capacitive microphones provide excellent signal-to- noise ratio, there is a significant problem with vibration-borne artifacts.
Document Details
- Document Type
- Technical Report
- Publication Date
- Apr 18, 2005
- Accession Number
- ADA433491
Entities
People
- John F. Mcclelland
- Michael B Pedersen