A 1.35 m Long 0.18 gf Resolution Differential Capacitive Force Sensor for Contact Force Monitoring

This paper introduces a 1.35 m long differential capacitive force sensor with a small form factor for a catheter integration. The differential force sensor is realized with two polydimethylsiloxane (PDMS) layers having two different rigidity inserted between flexible printed circuit board (FPCB) electrodes. To achieve the higher precision, we also propose the differential driving method which allows the higher driving voltage even in a low supply system, resulting in the higher SNR. By using the driving voltage of 18 Vp-p under 2 V supply system, the proposed sensor interface has accomplished SNR of 58.22 dB at 100 gf and the force error has reduced from 0.24 gf to 0.18 gf with the equivalent capacitance resolution of 22.2 aF. This work has achieved the state-of-art force resolution by using both the differential driving and CP cancellation technique with a miniature sensor. The proposed sensor can be used for a real time contact force measurement during a catheter ablation or the stiffness detection.