The iTouch controller uses ultrasonic waves on the CRT faceplate to develop a digital map of the surface. Each X- or Y-axis has a transmitting and receiving piezoelectric transducer and a set of reflector stripes on the outside edge of the CRT. The touchscreen controller sends a five-megahertz burst to the transmitting transducers that convert the electrical signal into surface acoustic waves — mechanical waves that propagate in the surface of materials such as glass. A special pattern of reflector stripes diverts the burst to create a uniform density of acoustic wave energy across the surface of the CRT.

A light touch with a finger, gloved hand, or soft stylus absorbs a portion of the wave. The resulting change in the received signal is analyzed by the controller and digitized into X and Y coordinates. In addition to sensing the location of a touch, surface wave is the only touch technology that can also sense the pressure of a touch — the Z-axis — by measuring how much signal was absorbed.

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