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.

Influence of camber angle on tire tread behavior by an on-board strain-based system for intelligent tires

“…In recent years, there has been an increasing amount of literature on the possibility of getting information from tire deformation or other parameters by using different technologies. For instance, Surface Acoustic Wave (SAW) sensors [3][4][5], optical sensors [6][7][8][9], piezoelectric sensors [10,11], accelerometers [12][13][14][15] or capacitive sensors [16][17][18][19][20]. Although they demonstrated the capability to provide information about tire working conditions from tire behaviour, they usually have some limitations such as energy consumption, robustness or dependency of the tire-rim relative position.…”

A Strain-Based Method to Detect Tires’ Loss of Grip and Estimate Lateral Friction Coefficient from Experimental Data by Fuzzy Logic for Intelligent Tire Development

“…Overall, they analyze the tire’s deformation by measuring sidewall deflection, tire tread deformation, acceleration, etc. by means of different sensors such as Surface Acoustic Wave (SAW) sensors [ 15 , 16 , 17 ], optical sensors [ 18 ], piezoelectric sensors [ 13 , 19 ], accelerometers [ 20 , 21 ] or capacitive sensors [ 22 , 23 , 24 , 25 ]. Although all of them demonstrated the capability to provide information about tire working conditions from tire behavior, they usually have some limitations such as energy consumption, robustness or dependency of the tire-rim relative position.…”

Tire strain piezoelectric energy harvesters: a systematic review

“…After exploiting a capacitive strain sensor with 0.013% resolution, Cao et al [38] mounted the sensor inside a tire treadwall. The sensor's capacitance sensitivity was reported to be 76 fF for every 10,000 microstrain.…”