High-resolution synthesized magnetic field focusing and thermal-variation insensitive piezo film force touch sensing systems

Abstract

This paper describes high-resolution synthesized magnetic field focusing (SMF) and thermal-variation insensitive piezo film force touch sensing systems. Firstly, it was recently found that coordinated control of array coil currents makes it possible to focus magnetic field. However, it is hard to predict B-field distribution due to absence of the control system. To solve this problem, overall SMF system including transmitter (Tx), receiver (Rx), and controller was proposed. As a result, a 5 mm resolution at a distance of 20 mm was achieved for the Tx arrayed air coils with spacing of 5 mm, which is about four times sharper than conventional system. In addition, the proposed SMF system allows the designed 5-bit RF barcode array to be fully distinguishable at a 15 mm distance. Secondly, force touch sensing can be improved by replacing the capacitive-type (two-layer) with the piezoelectric-type which consists of only one-layer piezoelectric polymer film. However, the piezoelectric film is fatal in the state of temperature change, due to inherent pyroelectric characteristic. This problem is solved by a proposed system composed of an improved charge amplifier and a digital signal processor. Consequently, the proposed force touch sensing system endures in the situation of ambient temperature change of $100^\circ C$ and has pressure range from 0.3 N to 2.5 N and a linear characteristic.