|dc.description.abstract||MEMS technology has ushered in a new era of miniaturized sensors and actuators. Many
smart devices and systems are being developed using these sensors. Home automation
is now a widespread reality owing to the development of affordable miniature devices.
Wearables like smart watches and point-of-care medical devices have brought positive
changes in the healthcare industry. Also, at global scale, these sensors and actuators find
their place in tracking weather changes and remote sensing applications.
Many of these micro and nano systems communicate with humans using
electroacoustic devices. They can take in voice input, process it and give out voice
instructions/suggestions using a system made of microphones and audio speakers.
However, when we compare the sizes of all the different sensors and actuators with the
size of an audio speaker, we see that audio speakers have not really achieved
miniaturization. For example, in a standard smartphone a mini audio speaker is still 8
times larger in volume when compared with a MEMS microphone. An audio speaker is
still struggling to get into micron size range. This further limits the extent to which a
smart device can reduce in size. The size reduction of the audio speaker, if possible, will
lead to an overall size reduction of smart devices. We inspect the intricacies involved in
miniaturization of an audio speaker and explore a possible solution by combining silicon
MEMS technologies with nature inspired design for the same.
In this work, we present two unconventional approaches to build electrostatically
actuated thin audio speakers. First, we present a bio-mimetic micro-speaker inspired by
the sound production mechanism of field crickets. This design uses peripheral actuation
unlike the usual full area actuation in the conventional electrostatic speaker designs or
unlike the electrodynamic speaker designs where the diaphragm is directly actuated by
magnet-coil partially covering the central area of the vibrating diaphragm. Also, as in the
cricket’s sound production mechanism, we design to take advantage of the resonance.
Our speaker essentially uses a silicon diaphragm created by etching out patterned
cavities in the handle layer of an SOI wafer and controlled lateral etch of the buried
oxide to create closely spaced top and bottom annular electrodes for peripheral actuation.
These electrodes are used to drive the diaphragm with audio signal close to its resonance.
The open cavity provides an incredible advantage in terms of increasing the pull-in
voltage enormously. While we demonstrate the working of these micro-speakers with
several audio signals, the development must continue with an array of such speakers for
attaining a flat response over audible frequency range in order to make them
commercially viable. The second novel design to build wafer thin loudspeakers is based
on an accidental discovery we made during testing of the cricket inspired speakers. We
demonstrate how two simple pieces of silicon stacked loosely together and actuated with
appropriate electrical signal produce sound. The theoretical explanation is given behind
the new design idea, whose foundation is electrostatic actuation. Also, a few initial
results for the thin speakers developed with this design are presented||en_US
|dc.rights||I grant Indian Institute of Science the right to archive and to make available my thesis or dissertation in whole or in part in all forms of media, now hereafter known. I retain all proprietary rights, such as patent rights. I also retain the right to use in future works (such as articles or books) all or part
of this thesis or dissertation||en_US
|dc.subject.classification||Research Subject Categories::TECHNOLOGY::Electrical engineering, electronics and photonics::Electronics||en_US
|dc.title||Cricket Inspired micro Speakers||en_US
|dc.degree.grantor||Indian Institute of Science||en_US