Electrically stretched capacitive membranes for stiffness sensing and analyte concentration measurement

A novel method for stiffness sensing is developed using an electret capacitive sensor. The electret membrane is coated with a recognition layer that responds with a change in its stiffness/elasticity in the presence of a target analyte. Since the electret membrane is stretched by electrostatic pulling towards a metallic base plate, a change in stiffness of the composite membrane results in deflection of the membrane. This deflection is measured as a change in capacitance of the sensor. The sensitivity of the sensor to stiffness changes depends on the strength of the preset electric field. The developed sensor operates in a quasi-static mode and eliminates the need for resonant monitoring. The sealed capacitive sensor is ideal for monitoring analytes in both gas and liquid environments. The final sensor package with the capacitance measurement circuitry has a low power consumption (<30 mW). A proof-of-concept carbon dioxide gas concentration sensor is developed by coating the electret sensor with a single-walled nanotube film whose stiffness changes in the presence of carbon dioxide. Experimental results prove the viability of the sensing technique.