Compact electrodynamics MEMS-speaker

This paper describes the design, fabrication and characterization of an electrodynamic MEMS speaker. The miniaturized speaker consists of a deposited single turn microcoil on a 25 µm thick suspended polyimide diaphragm with a 2.5 mm diameter and a small volume permanent magnet Neodymium-Iron-Boron (Nd-Fe-B). A significant improvement of frequency response to sound pressure level of MEMS-speaker in sealed condition was achieved. The sealed measurement performed in a 1500 mm3 silicon rubber tube resulted in a peak amplitude of 90 dB-SPL at a frequency range of 1, 5 and 10 kHz and experienced magnitude boosting with a value of 25 to 30 dB at frequency below 1 kHz compared to unsealed condition. Peak magnitude level of 92.5 dB-SPL and 110 dB-SPL were achieved at the frequency of 200–500 Hz and 20–60 Hz respectively. The results shows that the fabricated MEMS speaker can be applied in ear canal applications such as hearing aids and music player earphones.