Gel Impedance Used as a Pressure Sensor: Preliminary Results

Pressure sensing by measuring the impedance of soft matter, like hydrogels and rubber, has so far posed the problems of low conductivity and hysteresis. Further modifications in the materials to enhance their properties are needed. A pressure sensor using a simple gelatin/agarose double network gel placed between two Ag/AgCl electrodes is presented. The impedance spectra from 100 Hz to 1 MHz were investigated and admittance calculated. Both response time and hysteresis were also investigated. All the experiments were made using an impedance analyzer from Zurich Instruments. Results showed that the lowest standard deviation is at 3.5 kHz. It was found that the admittance increases exponentially from 7.9 to approximately 11.7 mS with increasing the mechanical load at 3.5 kHz. The highest hysteresis of about ±7.6% was found to be at zero load. The measured response time of the gel impedance was approximately 0.5 s, which makes the double network gel feasible for real time pressure monitoring. Mechanical tests measuring the force on the gel due to deformation showed little influence of the gel structure on the impedance. Thus it was concluded that the change of the distance in between the electrodes is responsible for the impedance change of the gel. Calibrations will be necessary for practical applications, since the gel impedance changes as environmental conditions change. This sensor showed better results as compared to conductive rubber published in the literature. It can be concluded that agarose/gelatin gels provide a cheap and easy to fabricate pressure measuring device.