Ceramic Microphones

What are Ceramic Microphones?

We can say that ceramic microphones are a modern version of crystal (piezoelectric) microphones that originated in the late 1960s. They were considerably more stable and shock-resistant than electromagnetic microphones (Madaffari & Stanley, 1996). Ceramic microphones operate based on sound moving a diaphragm connected to a piezoelectric material by a strut or pin. Movement of the diaphragm causes the connecting pin to deform the (ceramic) piezoelectric material, producing a varying voltage across it. Ceramic microphones had internal preamplifiers for boosting the microphone output signal and providing a low output impedance, which was necessary for their use with transistor amplifiers.

Piezoelectric

Ceramic microphones are sometimes loosely classified as piezoelectric. The transducer mechanism uses a special polarized ceramic such as barium titanate. It generates an electrical potential. His conversion is similar to a piezoelectric effect. However, the mechanism differs in both compressive and extensive strains, producing the same potential polarity. If untreated, such a transducer would produce a highly distorted output. The equivalent of an offset strain occurs in the material by a process called polarization (not identical to that for the capacitor type). This offset linearizes the output. Retention of polarization is temperature dependent. At a critical elevated temperature, you lose polarization.

Tough Microphones

The stressed force is divided by a linkage to a diaphragm that moves in response to sound pressure. Such microphones are more rugged than capacitor or electret microp ones. Even when used in dosimeters, they can survive rough treatment. They are also significantly less susceptible to impairment by condensation of atmospheric moisture. Ceramic microphones are more susceptible to excitation by vibration, have higher noise filter floors, and have a more limited high-frequency response when compared to the capacitor and electret types. Though they can be made in higher grades, they are commonly available for type 2 instruments. These limitations are acceptable for dosimetry, and people use them in such applications because of their desirable properties.

Barium Usage

As mentioned above, the Barium titanate was the material of choice for a ceramic mic element. (See U.S. Patent 2,640,165, issued May 26, 1953.) Lead Titanium Zirconate was also used. A crystal mic element, a Rochelle salt crystal, was used. This type of salt crystal could not withstand temperatures above 130 degrees F. Also, direct moisture or a humid environment would eventually damage the salt crystal. A ceramic element was far more tolerant of high temperature and humidity. The advantages of the ceramic element eventually led to the elimination of the Rochelle salt crystal as a mic element.