A dual-planar-coil miniature dynamic microphone, one of the electro-acoustic transducers working with the principle of the electromagnetic induction, has been realized by semiconductor micro-processing and micro-electro-mechanical system (MEMS) techniques. This MEMS microphone mainly consists of a 1 μm thick diaphragm sandwiched by two spiral coils and vibrating in the region with the highest magnetic flux density generated by a double magnetic system. In comparison with the traditional dynamic microphone, besides the miniaturized dimension, the MEMS microphone also provides 325 times the vibration velocity of the diaphragm faster than the traditional microphone. Measured by an audio analyzer, the frequency response of the MEMS microphone is only 4.5 dBV Pa −1 lower than that of the traditional microphone in the range between 50 Hz and 20 kHz. The responsivity of −54.8 dB Pa −1 (at 1 kHz) of the MEMS device is competitive to that of a traditional commercial dynamic microphone which typically ranges from −50 to −60 dBV Pa −1 (at 1 kHz).

Traditional ribbon microphones cannot be miniaturized owing to the sensitivity of the microphone in proportion to its ribbon length. A novel symmetrical voice coil instead of the traditional ribbon is proposed, designed, and optimized. The new structure of ribbon microphones was fabricated by microelectromechanical systems (MEMS) technology, which allows increasing the effective coil length while reducing the diaphragm dimension. The obtained results present a voice coil length of 77.5 mm under a limited ribbon length of 17 mm. Compared with the conventional ribbon microphones (with ribbon length 50 mm and voice coil length 50 mm), the diaphragm dimension was reduced but its effective length was increased by about 55%, from 50 mm to 77.5 mm. Moreover, the magnetic flux density in the air gap of the magnetic circuit by simulations and experiments is measured to be at 5.1 and 5 kG, respectively. (C) 2009 Society of Photo-Optical Instrumentation Engineers. [DOI: 10.1117/1.3142971