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I am doing preliminary research for my thesis. The thesis involves textile capacitive pressure sensors. I am trying to find out more about how the type of conductive material used affects the capacitance of the sensors so I can better design my thesis. The layer my research will focus on is actually the dielectric layer, but I need to decide on a consistent and reliable sensor design and am a bit overwhelmed by all my options for conductive materials (both in terms of metal and construction method of the material. ie. thread, knitted fabric, woven fabric, etc). Ideally I would just use conductive metal plates for the electrodes, but most likely I will have to make the electrodes out of conductive fabric and an integrative fabric. Any good resources and/or personal experience with picking conductive materials for textile based capacitive pressure sensors would be great. What metals are preferable?

I am new to the site, so if I need to be more specific with my question, please let me know. Thanks in advance.

**Edit: I forgot to add that I am specifically measuring the impact of variations in the spacer material on the outcome of data collected by the sensor, in case that affects anyone's answers.

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Generally you consider the cap characteristic impedance (f) relative to pressure is good for repeatability and hysteresis and start with an error budget , then sensitivity requirements then linearity requirements.

Then as long as the series Conductor Resistance is <<10% preferably <1% at some applied frequency current source then impedance of Cap is linear with amplitude of voltage at that constant sine current.

This is when a good RLC meter is of great value with strain gauges and tensor measurements all automated.

But you could also use an LCO or fixed inductor variable C self resonant oscillator to measure frequency with sufficient gain to overcome the low Q lossy fabric and plot frequency response or frequency of oscillator shift in ppm but then arm hand and body position may interfere with results if not designed geometrically isolated to the pressure of fabric relative to body surface area. And not affected by stray capacitance to earth grounds.

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  • \$\begingroup\$ Is there a particular formula for calculating how the resistance of a conductive material impacts the sensitivity of a capacitive pressure sensor? \$\endgroup\$ – darriage Jul 20 '18 at 23:31
  • \$\begingroup\$ No but it is inverse squared to air gap and proportional to surface area. Search RLC monograph above to get impedance chart \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jul 20 '18 at 23:36
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There are several options but the one that comes first to my mind are piezoresistive materials, especially polyester yarn incorporated with carbon. This material is well documented and a lot of research is done around this material, so this might be a good starting point.

EDIT : Yarn used as the dielectric material between the two plates of the capacitor is more appropriate here.

Readings:

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  • \$\begingroup\$ I am specifically trying to determine the impact of variations within the dielectric spacer layer, on the outcome of data output from the sensor. (ie does this change impact the spacer's distortion, causing a different reading for the same pressure exerted?). Is it best to avoid piezoresistive materials if that is the case? I've only ever worked with piezoresistive sensors and capacitive sensors separately so I don't know much about differentiating between the two effects when measuring for pressure. \$\endgroup\$ – darriage Jul 20 '18 at 20:07
  • \$\begingroup\$ In this case, yarn can be used as the dielectric material (with air). The variation in capacitance is proportional to the mass of the short length of moving yarn between the plates of the capacitor. Piezoresistive are usually in a Wheatstone-bridge configuration. \$\endgroup\$ – dismantl Jul 20 '18 at 20:31

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