RFTIRTouch: Touch Sensing Device for Dual-sided Transparent Plane Based on Repropagated Frustrated Total Internal Reflection

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Frustrated total internal reflection (FTIR) imaging is widely applied in various touch-sensing systems. However, vision-based touch sensing has structural constraints, and the system size tends to increase. Although a sensing system with reduced thickness has been developed recently using repropagated FTIR (RFTIR), it lacks the property of instant installation anywhere because observation from the side of a transparent medium is required. Therefore, this study proposes an "RFTIRTouch" sensing device to capture RFTIR images from the contact surface. RFTIRTouch detects the touch position on a dual-sided plane using a physics-based estimation and can be retrofitted to existing transparent media with simple calibration. Our evaluation experiments confirm that the touch position can be estimated within an error of approximately 2.1 mm under optimal conditions. Furthermore, several application examples are implemented to demonstrate the advantages of RFTIRTouch, such as its ability to measure dual sides with a single sensor and waterproof the contact surface.