UBC Theses and Dissertations

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UBC Theses and Dissertations

Soft capacitive sensors for proximity, touch, pressure and shear measurements Sarwar, Mirza Saquib us


Sensors are devices that convert a physical stimulus into an electrical signal. Mechanical stimuli such as touch, pressure, strain and shear are very important for a plethora of applications. A lot of these application areas, including consumer electronics, sports, health care and robotics, require the sensor to be soft, stretchable and even transparent. In this thesis we demonstrate three capacitive sensors that are each an evolution of the preceding version. The first sensor is a flexible, transparent, proximity and touch sensor based on mutual capacitance technology - the conventional technology used in most touch-screen devices. The novelty in this research is the sensor’s ability to operate while being deformed. This is important for applications where the device is expected to experience a bend or stretch while being interacted with such as in a wearable device and smart clothing. The second sensor in this thesis adds the ability to detect pressure and strain to enable its use in further applications. The sensor uses both mutual capacitance and overlap capacitance to detect the range of stimuli mentioned. The dielectric has cylindrical air gaps that enhance the pressure sensitivity. A 4 X 4 array structure is implemented that demonstrates the detection and differentiation of the different stimuli. However, for artificial skin applications, the ability to sense shear is extremely valuable, for example for helping robots grasp objects. The third sensor developed in this thesis is able to detect proximity and light touch similar to the previous iteration, but with 10X increase in pressure sensitivity (1.3% change in capacitance per kPa applied pressure, compared to 0.13% change for the second sensor) and the ability to detect localized shear (2.2% change in capacitance per kPa of shear stress). The novelty is a patterned dielectric architecture with pillars and sliding supports that enable the top surface of the sensor to slide and buckle like real skin and therefore enable the detection of localized shear. All the sensors use readily available materials (silicone, carbon black and/or polyacrylamide), along with conventional molding and bonding techniques and should be easy to produce in large quantities at low cost.

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