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We present a MEMS microphone that converts the mechanical motion of a diaphragm, generated by acoustic waves, to an electrical output voltage by capacitive fingers. The sensitivity of a microphone is one of the most important properties of its design. The sensitivity is proportional to the applied bias voltage. However, it is limited by the pull-in voltage, which causes the parallel plates to collapse and prevents the device from functioning properly. The presented MEMS microphone is biased by repulsive force instead of attractive force to avoid pull-in instability. A unit module of the repulsive force sensor consists of a grounded moving finger directly above a grounded fixed finger placed between two horizontally seperated voltage fixed fingers. The moving finger experiences an asymmetric electrostatic field that generates repulsive force that pushes it away from the substrate. Because of the repulsive nature of the force, the applied voltage can be increased for better sensitivity without the risk of pull-in failure. To date, the repulsive force has been used to engage a MEMS actuator such as a micro-mirror, but we now apply it for a capacitive sensor. Using the repulsive force can revolutionize capacitive sensors in many applications because they will achieve better sensitivity. Our simulations show that the repulsive force allows us to improve the sensitivity by increasing the bias voltage. The applied voltage and the back volume of a standard microphone have stiffening effects that significantly reduce its sensitivity. We find that proper design of the back volume and capacitive fingers yield promising results without pull-in instability.
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Ferro-electret nanogenerators as flexible microphones
Research on flexible transducers capable of sensing acoustic signals has become increasingly important due to its implications in human interfaces with wearable electronics. The proof-of-concept for a flexible microphone/loudspeaker based on the use of a ferro-electret nanogenerator (FENG) was recently presented. Following that, this work characterizes FENG-based microphones, showing the sensitivity of a 5 cm x 5 cm, single layer FENG to be ∼ .015 mV/Pa. The variance of sensitivity based on surface area is also studied and presented. Polar patterns or directivity is emphasized in this work by studying how various shapes (i.e. flat, concave and convex) affect the output. The spectral information of the output of FENGbased microphone to typical voice input is compared with a commercially available microphone
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- Award ID(s):
- 1854750
- PAR ID:
- 10167458
- Date Published:
- Journal Name:
- IEEE Sensors Conference
- Page Range / eLocation ID:
- 1 to 4
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.1109/SENSORS43011.2019.8956772
