Suggestions on conductive materials for textile capacitive pressure sensors

Question

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.

Answer 1

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.

Answer 2

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:

• Study of Structure and Properties of Polyester/Carbon Blends for Technical Applications

• Piezoresistive Response of Integrated CNT Yarns under Compression and Tension: The Effect of Lateral Constraint

• Textile capacitors as pressure sensors

• Design, Development and Characterisation of Piezoresistive and Capacitive Polymeric Pressure Sensors for use in Compression Hosiery