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Ultrasonic Sensors Are Flourishing. Do You Know Why or How to Make One?

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Learn the basics of ultrasonic sensors and why they are found in so many applications.

Ultrasonic sensors have become commonplace thanks in considerable measure to adoption in early-stage autonomous driving vehicles. Ultrasonic technology uses mostly inaudible sound waves (starting at 20 kHz) to transmit digital data.

Robots represent another area where ultrasonic sensors have found a home, such as robotic vacuum cleaners, lawnmowers and window washers, telepresence robots in offices, and building creation and demolition. These applications and more require robotic devices to find their way around without crashing into walls, furniture, equipment, people, or other robots. Obstacle detection is key to achieving this requirement. A robot must detect or “see” obstacles from a few feet to a few centimeters away to avoid collisions – and in a timely fashion.

Ultrasonic sensors are an inexpensive way to make robots see. The sensors send out sound waves to detect objects. While both glass and most plastics are solid objects that impede sound, acoustically transparent materials work well with ultrasonic sensors. Some acoustically transparent materials are speaker grill cloth and special plastics, and wire screen and mesh.

Most modern vehicles cover the ultrasonic sensor in a particular plastic case to prevent environmental damage to the transducer, i.e., rain, mud, dirt, etc.

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Ultrasonic sensors are covered within special acoustically transparent plastics.

How They Work

The design of a robotic ultrasonic system is similar to collision avoidance and parking systems in cars. For example, ultrasonic sensors are embedded on the sides of a robotic vacuum to give it full 360-degree coverage. The spacing and number of sensors depend on the shape of the vacuum and the field of view of the ultrasonic sensor. As the vacuum – or other robotic devices – roams around a smart home or building, the ultrasonic sensor maps obstructions, calculates the distance from obstacles, and feeds this information to the electronics to navigate around the challenges

Collaborative robots that work side-by-side with humans are yet another application for ultrasonic sensors. Outside of the industrial assembly line factories and warehouse floors, cobots have found acceptance in the medical and hospital halls. In addition to their gentleness, medical cobots and mobile robots can’t be infected by biological coronavirus like COVID-19. Robotic systems have been essential in clinical care, such as disease prevention, diagnosis and screening, and patient care.

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Automotive ultrasonic sensor. (Image Source: TI)

Designing a robot with sound-wave technology requires only a few essential components. Voltage-controlled piezoelectric oscillators are used to generate ultrasonic sound waves. A signal processor and transducer driver chip connect with the transducer to initiate the sound wave, process the return electrical signals, and calculate the needed algorithm for the relevant echoes. A CPU is required to interpret information from multiple ultrasonic sensors around the robot to map obstructions and either stop or help navigate away from them. 

Ultrasonic systems are also being used to improve user convenience and optimize performance for building and residential automation. For example, many products need a way to activate only when required and otherwise remain in sleep mode to conserve power. The device should automatically wake up to perform critical functions upon detecting the early presence of approaching people or other robots. Once detected, these systems would turn lights on or off, adjust heating, ventilation, and air-conditioning (HVAC) system settings, turn on electronic doorbells before they’re pressed, notify homeowners (or recording video), or activate burglar alarms.

Ultrasonic sensing also offers a method for occupancy detection and advanced motion detectors in intelligent buildings. Since ultrasonic technology relies on the strength of a returning echo once a target is struck, it can easily distinguish between the presence of humans versus insects or pets. Once a designated target has been detected via the reflected ultrasonic waves, the conditioned output activates a specific device, e.g., turning on the camera feature in a video doorbell or surveillance camera.

As a side note, another way to determine occupancy is with passive infrared technology. PIR sensors rely on infrared radiation (IR) to detect the presence of heat-emitting beings instead of inanimate objects (e.g., as with ultrasonic sensors). Typically, a pyroelectric sensor measures the average temperature of the surrounding environment, but this measurement is not particularly useful when trying to track motion.

Returning to ultrasonic technology, another popular smart building application is the open parking-spot detection in garages at airports, malls, and other commercial facilities. Once a parked vehicle is detected, the ordinarily green (or open) light mounted on the ceiling will turn read to notified drivers that the spot is occupied.

Do-It-Yourself (DIY)

During the recent pandemic, it was important for people to keep their hands away from their faces. A DIY device would shine a warning light when such behavior is detected to reduce the possibility of infection. The design was prototyped using an Arduino, which controlled an LED through feedback from an ultrasonic proximity sensor. The LED would flash into the user’s peripheral vision, glowing when the sensor detects hands (or other objects) approaching the face. (Image Source: GitHub / Nick A. Bild, MS

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Behavior-changing glasses. (Image Source: GitHub / Nick A. Bild, MS

In addition to giving robots the capability of “sight,” haptic actuators are using an ultrasonic sensor to mimic “feel.” One emerging technology known as contactless haptics doesn’t even require an actuator but rather air-jets or ultrasonic radiation to simulate the feel of actual contact. This means that the user does not have to wear gloves or hold a device to feel the simulated motion or the tactile surface.

The target market for new haptic technologies includes smartphones, gaming, wearables, AR, VR & MR, and other consumer electronics markets, automotive haptics, and various other applications from medical to military and more.

Would you like to design an ultrasonic system? There a plenty of good examples on Youtube, such as this one:

John Blyler is a Design News senior editor, covering the electronics and advanced manufacturing spaces. With a BS in Engineering Physics and an MS in Electrical Engineering, he has years of hardware-software-network systems experience as an editor and engineer within the advanced manufacturing, IoT and semiconductor industries. John has co-authored books related to system engineering and electronics for IEEE, Wiley, and Elsevier.

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