Design of an improved signal conditioning circuit for ionic polymer sensors based on the streaming potential hypothesis

Abstract

Ionic polymer transducers also known as ionic polymer metal composites belong to the family of electroactive polymer transducers. Electroactive polymers are flexible and lightweight devices that operate as sensors and actuators without having any internally moving parts. The absence of moving parts offers a more efficient and cost-effective transducer with increased reliability. As actuators, ionic polymer transducers have the ability to generate bending strains on the order of 5% when +2 V potential is applied across their thickness. However, as sensors, the ionic polymer transducer has superior sensitivity as compared to other electroactive polymer materials. This is especially true when a charge or current amplifier is used as the signal conditioning circuit. These sensors operate in a wide spectrum and specifically at small strains. In this article, a new signal conditioning circuit is designed with superior sensing capabilities compared to the conventional circuit. In the new design, the ionic polymer transducer is biased with a small voltage on the order of 5 to 25 mV. Experimental results demonstrate a 27% enhancement in the current generated and the signal-to-noise ratio as compared to the conventional circuit. Furthermore, this circuit enables the use of ionic polymer transducer polymers with larger capacitance compared to the previous current sensing circuit. Earlier research demonstrates that the capacitance of an ionic polymer transducer is proportional to its actuation performance, and it is believed to affect the sensing performance. To increase the capacitance, the direct assembly process is used in the fabrication of ionic polymer transducer. Previously, using the conventional current amplifiers, it was impossible to use a direct assembly process–fabricated ionic polymer transducer with a large capacitance as a sensor, since it would saturate the operational amplifier circuit. In this study, three types of operational amplifier circuits are investigated, and their ability to bring the sensor to a short-circuit condition is measured. The signal-to-noise ratio of the operational amplifiers is measured and the OP177 has proved to be the best in both experiments.