An electronic device that measures the distance of a target object by emitting ultrasonic sound waves, and converts the reflected sound into an electrical signal is known as an ultrasonic sensor. Ultrasonic waves travel faster than the speed of sound i.e audible to a human. By sending the sound wave at a frequency above the human range of hearing the ultrasonic sensors works. Two main components of ultrasonic sensors are the transmitter and the receiver. The transmitter is the component that emits the sound using piezoelectric crystals. The receiver is the component that encounters the sound after it has traveled to and from the target. The transducer of the sensor acts as a microphone to receive and send the ultrasonic sound. To receive the echo and to send a pulse ultrasonic sensors use a single transducer. The sensor determines the distance to a target by measuring time lapses between the sending and receiving of the ultrasonic pulse. It sends an ultrasonic pulse which travels through the air and if there is an object, it will come back to the sensor. The distance can be calculated by calculating the travel time and the speed of sound. To detection of clear objects, ultrasonic sensors are a great solution. Regardless of the color, surface, or material unless the material is very soft like wool, as it would absorb sound ultrasonic sensors can detect the presence of the objects. Ultrasonic sensors DO NOT work at very high temperatures or pressures or locate objects moving about in a 3-dimensional space. They can not measure farther than about 70 feet. Ultrasonic sensors are commonly used with micro-controller platforms like Raspberry Pi, ARM, Arduino, and Beagle Board. Ultrasonic sensors are also used as proximity sensors. Ultrasonic sensors are also used in manufacturing as well as in obstacle avoidance systems.
There are a total of four types of ultrasonic sensors
The drip-proof type
It is named as drip-proof type cause these sensors have a closed structure that allows the sensor to be used even in environmental conditions where water can drip on it. These types of sensors can only be used for automotive applications. A single sensor performs both transmission and reception. The internal structure inhibits resonance.
The high-frequency type operates at frequencies up to 300 kHz. These sensors are used for only the applications employing double-feed detection. In applications employing double-feed detection, this enables sensors to face each other at short distances
Open structure type
In lead type sensor the top has an open structure and inside are a unimorph piezoelectric oscillator and a horn, resulting in high sound pressure and high sensitivity. They are capable of both short and long-range distance detection. They can also be used to detect moving objects by using the doppler effect to detect fluctuations in the received waveform.
For surface mounting of these types of sensors compact and low-profile configuration suitable. Allowing for distance detection in confined spaces, transmission-reception is of combined type.