Water-immune ftir touch screen

A method, comprising:

• directing, from a light source, a first light beam having a first angle characteristic and a second light beam having a second angle characteristic into an upper substrate layer comprising a first index of refraction, the first angle characteristic being greater than the second angle characteristic;
• filtering the first light beam out of the upper substrate layer with an optically clear adhesive layer comprising a second index of refraction, the optically clear adhesive layer being situated below the upper substrate layer, the second index of refraction being greater than or approximately equal to an index of refraction for water and less than an index of refraction for human skin;
• and
• detecting at a light detector the second light beam after propagating through the upper substrate layer.

A water-immune frustrated total internal reflection (FTIR) touchscreen system, comprising:

• a FTIR touchscreen comprising an optically clear adhesive layer situated between lower and upper substrate layers, wherein the upper substrate layer is configured to propagate a light beam, and wherein an index of refraction of the optically clear adhesive layer is greater than or approximately equal to an index of refraction for water and less than an index of refraction for human skin;
• a display situated below the FTIR touchscreen;
• and
• a processor configured to determine an attenuation in the detected propagated light beam resulting from a touch event in the touch area.