Force-sensing capacitor
`
`A force-sensing capacitor is a material whose capacitance changes when a force, pressure or
`mechanical stress is applied. They are also known as "force-sensitive capacitors". They can provide
`improved sensitivity and repeatability compared to force-sensitive resistors[1] but traditionally required
`more complicated electronics.[2]
`
`Contents
`Operation principle
`Production
`Uses
`References
`
`Operation principle
`
`Typical force sensitive capacitors are examples of parallel plate capacitors. For small deflections, there is
`a linear relationship between applied force and change in capacitance, which can be shown as follows:
`
` is the
` is the area of the sensor and
` is permeability,
`, where
`, equals
`The capacitance,
`distance between parallel plates. If the material is linearly elastic (so follows Hooks Law), then the
`, is
`, where
` is the spring constant. Combining these
`displacement, due to an applied force
`equations gives the capacitance after an applied force as:
`, where
`is the separation between parallel plates when no
`
`force is applied.
`
`This can be rearranged to:
`
`, which is true for small deformations where
`
`, we can
`
`where
`
`, which is constant for a given sensor.
`
`Assuming that
`simplify this to:
`C
`
`It follows that:
`
`CC
`
`We can express the change in capacitance
`
` as:
`
`Samsung Electronics Co. Ltd. et al v. Neodron Ltd
`Exhibit 2004
`IPR2020-00308
`
`

`

`Production
`
`SingleTact makes force-sensitive capacitors using moulded silicon between two layers of polymide to
`construct a 0.35 mm thick sensor, with force ranges from 1 N to 450 N.[3] The 8mm SingleTact has a
`nominal capacitance of 75 pF, which increases by 2.2 pF when the rated force is applied.[3]
`Uses
`
`Force-sensing capacitors can be used to create low-profile force-sensitive buttons. They have been used
`in medical imaging to map pressures in the esophagus[4][5]and to image breast[6][7] and prostate
`cancer.[8]
`References
`1. Martinelli, L; Hurschler, C; Rosenbaum, D (2006-06-01). "Comparison of Capacitive versus Resistive
`Joint Contact Stress Sensors". Clinical Orthopaedics and Related Research. 447: 214–220.
`doi:10.1097/01.blo.0000218730.59838.6a (https://doi.org/10.1097%2F01.blo.0000218730.59838.6a).
`ISSN 0009-921X (https://www.worldcat.org/issn/0009-921X). PMID 16672899 (https://pubmed.ncbi.nl
`m.nih.gov/16672899).
`2. 1943-, Bentley, John P. (1995). Principles of measurement systems (3rd ed.). Harlow [England]:
`Longman Scientific & Technical. ISBN 0470234458. OCLC 30781109 (https://www.worldcat.org/oclc/
`30781109).
`3. "SingleTact Datasheet" (https://www.singletact.com/SingleTact_Datasheet.pdf) (PDF). SingleTact.
`4. US Grant US10961981 (https://worldwide.espacenet.com/textdoc?DB=EPODOC&IDX=USUS10961
`981), Pakrs, Thomas, "High resolution solid state pressure sensor", published 2015-07-14, assigned
`to Sierra Scientific Instruments Inc
`5. "Using Capacitive Force Sensors in Next-Gen Medical Products" (https://www.mdtmag.com/article/20
`16/03/using-capacitive-force-sensors-next-gen-medical-products). Medical Design Technology. 2016-
`03-01. Retrieved 2018-06-21.
`6. Egorov, V.; Sarvazyan, A.P. (2008-09-01). "Mechanical Imaging of the Breast" (https://www.ncbi.nlm.
`nih.gov/pmc/articles/PMC2581459). IEEE Transactions on Medical Imaging. 27 (9): 1275–1287.
`doi:10.1109/tmi.2008.922192 (https://doi.org/10.1109%2Ftmi.2008.922192). ISSN 0278-0062 (https://
`www.worldcat.org/issn/0278-0062). PMC 2581459 (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC25
`81459). PMID 18753043 (https://pubmed.ncbi.nlm.nih.gov/18753043).
`7. "SureTouch" (http://suretouch.us/). SureTouch. Retrieved 2018-06-21.
`8. "Artann Labs" (http://www.artannlabs.com/). www.artannlabs.com. Retrieved 2018-06-21.
`
`Retrieved from "https://en.wikipedia.org/w/index.php?title=Force-sensing_capacitor&oldid=929678101"
`
`This page was last edited on 7 December 2019, at 13:21 (UTC).
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`
`Samsung Electronics Co. Ltd. et al v. Neodron Ltd
`Exhibit 2004
`IPR2020-00308
`
`