zForce AIR Touch Sensors detect and trace objects by detecting diffusely reflected infrared light.

Requirements on the object to detect include:

• A minimum reflectance of 30% in the near IR-spectrum is needed for proper signal levels, that is, the object can not be too dark. 
• Object surface must be diffuse. A glossy or mirror-like object may not scatter enough light towards correct receivers in order to generate a reliable detection. 
• An object must be ≥ 5 mm to ensure sufficient signal levels. This is closely related to reflectance. A white, diffuse object may be smaller than a dark, glossy one.