There are three types of ultrasonic-sensing applications:

• Ranging Measurement: Periodically records the distance of one or more objects moving to or from the sensor within each time-of-flight transaction. The rate at which the distance updates is dependent on how long the sensor waits in the echo-listen mode. The longer the sensor waits for the echo, the further the detectable range.

  Examples: Ultrasonic park assist sensors, obstacle avoidance sensors in robotics, level transmitters

  Further reading: Ultrasonic Terrain-Type and Obstacle Detection for Robotic Lawn Mowers tech note (SLAA910).

• Proximity Detection: A significant change to the ultrasonic echo signature corresponds to a physical change to the sensing environment. This binary approach of ultrasonic sensing is less dependent on range, and more dependent on echo signature stability.

  Examples: Cliff and edge detection in robots, object detection, vehicle detection in parking space, security, and surveillance systems

  Further reading: Using Ultrasonic Technology for Smart Parking and Garage Gate Systems tech note (SLAA911).

  Figure 1-2 Echo Response for Vehicle Presence
• Surface Type Detection: Using raw ultrasonic echo data, and not the time-of-flight measurement, material softness and hardness can be indirectly measured with ultrasonic measurements. Ultrasonic sound waves bounce off harder surfaces towards the transducer with fewer losses, which provides a stronger echo response in return. Softer objects, like foam and carpet, absorb many of the sound waves and provide a weaker echo response.

  Examples: Floor type detection in vacuum robots, terrain type detection in robotic lawn mowers

  Further reading: Ultrasonic Floor-Type and Cliff Detection on Automated Vacuum Robots tech note (SLAA909).

Figure 1-3 Ultrasonic Surface Type Detection