Last-resort for indication of collision. Types include: tactile feelers, tactile bumpers (e.g. spring-loaded tactile bumpers could activate microswitches upon collision) or a distributed surface array
This type of sensor will respond to changes in the amount of emitted energy — after interaction with a target of interest — that is returned to a detector. Will include two transducers (one to emit the energy, and one to receive the energy). Usually transmit longitudinal sound wave of 20-200KHz. The receiver response is function of amplitude of returned energy. This sensor can give us quantitative indicator of distance to target of interest.
Similar to ultrasonic but EM radiation emitted is microwave region of spectrum instead!
This type of sensor again will respond to changes in the amount of emitted energy return after interaction with target of interest. Modulated near-infrared used to reduced effects of ambient light. There are several advantages of this type of sensor vs ultrasonic: reduced time lag as this will propagate at the speed of light rather than sound, easily focussed to eliminate adjacent sensor interaction which would occur with ultrasonic [could be a problem with boat requiring sensors on each side – i.e. ultrasonic receiver may capture energy from unpaired emitter]