This technology requires no electrical signal processing on the sensor surface and uses no conductive coatings. It utilizes ultrasonic sound to sense touches. A SAW sensor is comprised of a sensor substrate which has affixed to it’s perimeter a piezoelectric emitter along with 2 or 3 receivers. Also running along the entire perimeter of the sensor edges are reflection ridges used to bounce ultrasonic sound back and forth across the surface of the sensor face.

To detect touches, the piezoelectric transducer sends out bursts of ultrasonic sound which is reflected by the perimeter ridges back and forth across the entire face of the sensor. Because the speed of sound is somewhat constant, it is known when the origin burst of sound along with all the reflected bursts from the perimeter ridges should arrive at each receiver. If a finger or other sound-absorbing stylus comes in contact with the sensor face, some of that sound originates or reflected will be absorbed and will be missing when the controller expects to hear them arrive at the receivers.

Those missing incidents are what allow the controller interface to determine where the touch would have to be positioned on the sensor face in order to block those sound incidents from arriving at the receivers when expected.

This technology offers 97% light transmission since the sensor substrate is just bare glass. It also offers a very light touch and works well for drag and drop functions. It has a glass surface that is highly durable and is not easily vandalized. It will operate with heavily gloved hands but not with a hard stylus or any implement that can’t absorb sound.

If you scratch it deeply enough though, the ultrasonic waves can fall into the valley of the gouge and bounce off into space causing a dead spot on one side of the scratch. It is susceptible to dirt and dust which slow down or block the ultrasonic sound.

Water droplets interfere with its operation – so can insects attracted to the display's light. It can not be effectively sealed from dirt or moisture as gasketing would block the ultrasonic sound. Open-cell foam gasketing can’t seal from moisture and will still eventually clog with dirt, causing the ultrasonic sound blockage. Changes in humidity and temperature will cause a change in air density affecting the speed at which the ultrasonic sound can travel which can cause problems with accuracy.

H.CONTROLLERS

A D Metro offers a complete line of controllers for its touch screen sensors with software driver support for most major operating systems.

A D Metro CONTROLLER BOARD FEATURES AND BENEFITS:

• Discrete compact controller circuit boards
• Major OS compatibility: Windows, Linux, Mac OS, QNX etc
• Multiple cable and integration options
• USB and RS-232 interface options
• RoHS, FCC and CE compliance

For applications requiring embedded controllers on motherboards, our touch sensors use industry standard interfaces and work with many of the controllers available on the market.