title: Flexible Bond Wire Capacitive Strain Sensor for Vehicle Tyres.
abstract: The safety of the driving experience and manoeuvrability of a vehicle can be improved by detecting the strain in tyres. To measure strain accurately in rubber, the strain sensor needs to be flexible so that it does not deform the medium that it is measuring. In this work, a novel flexible bond wire capacitive strain sensor for measuring the strain in tyres is developed, fabricated and calibrated. An array of 25 micron diameter wire bonds in an approximately 8 mm × 8 mm area is built to create an interdigitated structure, which consists of 50 wire loops resulting in 49 capacitor pairs in parallel. Laser machining was used to pattern copper on a flexible printed circuit board PCB to make the bond pads for the wire attachment. The wire array was finally packaged and embedded in polydimethylsiloxane (PDMS), which acts as the structural material that is strained. The capacitance of the device is in a linear like relationship with respect to the strain, which can measure the strain up to at least ±60,000 micro-strain (±6%) with a resolution of ~132 micro-strain (0.013%). In-tyre testing under static loading has shown the ability of the sensor to measure large tyre strains. The technology used for sensor fabrication lends itself to mass production and so the design is considered to be consistent with low cost commercialisable strain sensing technology.
authors.affiliation: Department of Mechanical Engineering, University of Birmingham, Birmingham B15 2TT, UK. siyangfox@gmail.com.
authors.forename: Siyang
authors.initials: S
authors.lastname: Cao
authors.affiliation: School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT, UK. s.pyatt@bham.ac.uk.
authors.forename: Simon
authors.initials: S
authors.lastname: Pyatt
authors.affiliation: Department of Mechanical Engineering, University of Birmingham, Birmingham B15 2TT, UK. c.j.anthony@bham.ac.uk.
authors.forename: Carl J
authors.initials: CJ
authors.lastname: Anthony
authors.affiliation: Department of Mechanical Engineering, University of Birmingham, Birmingham B15 2TT, UK. aik368@bham.ac.uk.
authors.forename: Ammar I
authors.initials: AI
authors.lastname: Kubba
authors.affiliation: Fusion Innovations Ltd., Research and Innovation Services, Birmingham Research Park, Vincent Drive, Edgbaston, Birmingham, B15 2SQ, UK. A.E.S.Kubba@bham.ac.uk.
authors.forename: Ali E
authors.initials: AE
authors.lastname: Kubba
authors.affiliation: Department of Mechanical Engineering, University of Birmingham, Birmingham B15 2TT, UK. o.a.olatunbosun@bham.ac.uk.
authors.forename: Oluremi
authors.initials: O
authors.lastname: Olatunbosun
keywords: PDMS; flexible; strain sensor; wire bonding