Testing Force & Pressure Deformation of PDMS for Tactile Sensing

Brian Myers, “Testing Force & Pressure Deformation of PDMS for Tactile Sensing”
Mentor: Veysi Malkoc, Biomedical Engineering

Polydimethylsiloxane (PDMS) is the most widely used, silicone-based organic polymer. Silicon wafers are used to design channels, and in our case specific patterns. PDMS is then poured over these wafers and left to harden. When removed, even the smallest of details is left imprinted in the PDMS. By testing the microfabrication’s modes of deformation like stress and strain, we will see which porous structure has the best characteristics for compatibility with a tactile sensor, compared to its original solid structure. An elastic modulus is a quantity that measures an object or substance’s resistance to being deformed elastically (non-permanently) when a stress is applied to it. The elastic modulus of an object is defined as the slope of its stress–strain curve in the elastic deformation region. A stiffer material will have a higher elastic modulus. Stress is defined as the force causing the deformation divided by the area to which the force is applied, while strain is the ratio of the change in some parameter caused by the deformation to the original value of the parameter. Changing the topology of PDMS by adding depressions that may or may not be through holes will drop its modulus of elasticity which then in turn should decrease the stiffness. In theory, this should enhance the sensitivity of a capacitive sensor. Finding the right pattern and dimensions for PDMS to coincide with a sensor will provide electronic feedback based on its deformation. This information can determine the rigidity of materials. For example, this information can help determine if a robotic hand is touching a wood desk versus a pillow. Incorporating this form of tactile sensing to prosthetics allow patients to feel how much pressure to apply to an object, improving functionality and their quality of life.

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