An Electromagnetically Actuated Micromachined Loudspeaker for Hearing Aids Applications

We present an electromagnetically actuated micromachined loudspeaker for hearing aid applications. The device has multi-layers of copper-coils, a NiFe soft magnet on polyimide membrane, and a NdFeB permanent magnet on its perimeter. Coil impedance is measured as 1.5 Omega and shows very flat at all over the audio frequency range. The resonant frequency of the loudspeaker is at much away from human audio frequency range to avoid unwanted spike responses. The device operates in low power, only requires tens of milli-ampere; the peak displacement, 7 mum, occurs at 88 mA, which corresponds to 110 dB SPL (Sound Pressure Level). While the micro-speaker generates 106 dB SPL, it consumes only 0.13 mW at 1 kHz, which is more than at least 10 times less power consumption than any existing MEMS (Micro-Electro-Mechanical-Systems) micro-speakers, almost equivalent to existing non-MEMS mini-speakers being used in hearing aids.