A conclusive role of ordinary transmission for an effective FTIR touch screen

In order to elucidate the physical origins of some drawbacks happening in the application of FTIR (Frustrated Total Internal Reflection) phenomenon, the touch performance has been principally investigated as follows. Assuming a 3 layer thin film of medium1-medium2-medium3 with different refraction indices of n
₁
, n
₂
and n
₃
, respectively, the theoretical analyses prove that FTIR or OT(ordinary transmission) phenomenon may happen when the light goes through medium2 from medium1 to medium3, relying on the relative difference in n
₁
and n
₂
. Namely, FTIR happens at n
₂
=1 (air) and a given incident angle (≥critical angle) whereas the OT appears at n
₂
=1.3 (water). In parallel, the experimental investigations, being phenomenological, also turn out to support the theoretical ones for the above assumption. From these results, one can understand the origins of some wrong operations due to the insensitive touch as well as the coffee drop on screen and the hot source on the other side of the touch plate. Moreover, further discussion regarding how to improve the touch performance is made on the basis of this work.