Surface Acoustic Wave
With Surface Acoustic Wave (SAW,) piezoelectric transducers located at different positions of the screen are used to turn the waves of mechanical energy of a touch (vibration) into an electronic signal. The waves are spread across the screen by bouncing off reflector arrays along the edges of the overlay and are detected by two "receivers". The acoustic wave weakens when the user touches the glass with their finger, gloved hand or soft stylus. The coordinates are then determined by the controller circuitry that measures the time at which the amplitude declines. An algorithm to determine the location of the touch based on the transducer signals.
When the panel is touched, a portion of the wave is absorbed. This change in the ultrasonic waves registers the position of the touch event and sends this information to the controller for processing. When sound waves are transmitted across the surface of the display, the following sequence of events occurs:
- Each wave is spread across the screen by bouncing off reflector arrays along the edges of the overlay.
- Two receivers detect the waves.
- When the user touches the glass surface, the user's finger absorbs some of the energy of the acoustic wave and the controller circuitry measures the touch location.
The touch screen itself is made of ordinary glass, giving it good durability and optical clarity. The technology is also well suited to displays that are physically larger. After the initial touch, a motionless finger cannot be detected. However, for the same reason, the touch recognition is not disrupted by any resting objects on the screen (e.g. hand palm or elbows). It has excellent durability that allows it to continue working if scratched since the overlay for the touch sensor is a solid glass display. The disadvantage to this glass overlay is that is breakable and won't work in wash down conditions (e.g. hard rain on the display).
Limitations and considerations
- Because the technology cannot be sealed, it can be adversely affected by surface contaminants and water, making it unsuitable for many industrial or commercial applications. The contaminants can cause dead spots on the screen, requiring periodic cleaning of the sensor and sometimes recalibration.
- Due to the way the technology works it can also be susceptible to data “noise".
Advantages
- No touch overlay or coating required, so no layers that can be worn.
- No brightness or contrast loss, SAW offers superior image clarity and high light transmission.
- Screen can be operated by with a finger, gloved hand (cloth, leather, or rubber), leather or soft stylus. Something hard like a pen doesn't work.
- Durable, scratch-resistant glass surface, continues to work if scratched.
- Vandalism proof, when protected glass is used.
- Antiglare glass option.
- Very long life span. Tested on more than 50 million touches at a single location.
Disadvantages
- The touch screen is not completely sealable, can be affected by large amounts of dirt, dust, and/or water in the environment.
- Display surface needs to be slightly sunk from its mounting bezel
Touch functionality
- Single touch
Product types
- Overlay frame
- Display solution
- Glass window (integrated in glass sheet)
- Chassis screen
Applied in:
SAW ELO 1915L Touch Computer
Partners
