Tag Archives: Ultrasonic Technology

Protecting Pedestrians Using Ultrasound Techniques

With vehicular traffic increasing on the roads, pedestrians are shifting to the status of endangered species. Frequent news reports of pedestrians falling victims to collisions with motor vehicles bear testimony to the statement. Now, researchers want to provide a remedy. At the Frankfurt University of Applied Sciences or FRA-UAS, researchers have developed a pedestrian detection sensor that can differentiate a human being from among inanimate matter.

At FRA-UAS, Professors Andreas Pech and Peter Nauth have developed the pedestrian detection system utilizing highly sensitive and efficient ultrasonic sensors. It can discriminate a human being from an object in areas where a collision is likely. Typically, vehicles use such highly cost-effective ultrasonic sensors at their rear to help in parking. The researchers have added an algorithm for recognizing patterns from the signals coming from these sensors. The algorithm, the actual innovation from the researchers, generates a situational analysis within half of a second. This is then used to activate specific protection systems.

In a collision situation, there can be two possibilities. The first could be a vehicle-to-vehicle collision, where the system activates airbags and belt pre-tensioners as it detects an imminent collision with another vehicle. However, if the system determines that the collision situation involves a pedestrian and not a vehicle, it initiates measures that will reduce the impact. These measures could vary, such as, heightening the bonnet to mitigate the impact, providing an exterior airbag to be deployed prior to collision or even reducing the rigidity of the body of the vehicle.

According to the researchers, this pedestrian detection system is relatively more cost-effective in comparison to other systems available in the market. It is possible to retrofit this system even in lower priced vehicles. Moreover, such a pedestrian detection system is also useful in other areas of application. For example, in case of a building fire, where smoke detectors trigger fire alarms, the pedestrian detection system from FRA-UAS can help to locate human beings trapped inside the burning house or apartment.

Application of such a pedestrian detection system can be seen in the crosswalk flasher system installed at the Weaver Lake Elementary School in Maple Grove, Minnesota. The school added the automatic detection system to increase the safety of children who occasionally forget to push the button to activate a flashing beacon before starting to cross the road. The pedestrian detection system uses ultrasonic sensors for detecting the presence of pedestrians waiting at the curb and automatically activates a flashing beacon to alert the approaching vehicles to the presence of the pedestrian.

Ultrasonic detectors emit sound waves of frequency ranging beyond the hearing capabilities of humans. In the presence of moving pedestrians or vehicles, part of the transmitted sound waves reflects back to the receiver. The associated electronics computes the distance and speed of the object from the time and strength of the reflected signal. Ultrasonic detectors detect objects as far away as 30 feet.

The amount of sound energy reflected from the pedestrian depends on the nature of clothes the person is wearing. It also depends on the temperature, pressure, humidity and wind speed at the location.

What Is Ultrasonic Ranging?

Ultrasonic technology has some unique advantages over other types. With ultrasonic methods, you can solve several application problems that become cost prohibitive or simply cannot be solved by other methods. Some of these are: long range detection, broad area detection, widest range of targeted materials and non-contact distance measuring.

In simplest terms, ultrasonic ranging is a method of echo-location. Most of us have used echo-location to know the distance to the cliff producing the echo, the distance of the thundercloud or the depth of a deep well. The principle is simple, note the time taken for the sound to travel and multiply it with the speed of sound. For example, you may hear the sound of thunder 3 seconds after you see the flash. The source of the sound is then 3 times 330 or 990 meters away, as sound travels roughly at 330 meters every second in air. Thunder is visible almost instantaneously, as light travels nearly 1,000,000 times faster than sound does.

The only difference in ultrasonic ranging is the use of sound frequencies that are beyond the range of normal human hearing. Young humans can hear sounds with frequencies ranging from 20 Hz to 20 KHz, with the upper limit dropping off to 15 KHz or even to 10 KHz with advancing age. Frequencies of 30 KHz to 40 KHz are common in ultrasonic ranging.

In ultrasonic ranging, a burst of high-frequency sound is generated, and a timer is started simultaneously. The timer stops as soon as the echo arrives. The burst of sound leaves the transmitter, hits the target object and returns to the receiver. Therefore, it took only half of the total time elapsed for the sound to reach the target object. This half-time multiplied by the speed of sound in the medium gives the distance of the target object from the source of the sound.

Although the sensors for producing the ultrasonic sound and for receiving it may take many complicated shapes depending on the actual application, for general purpose ultrasonic ranging, the sensor module looks like:

The associated electronics on board the sensor module consists of a microprocessor programmed to generate a burst of sound on trigger. The microprocessor also measures the time taken to receive the echo (time of flight) and thereby calculates the distance.

Ultrasonic ranging is mostly used in two ways for locating objects – proximity detection and precise range measurement. In proximity detection, any object passing within the preset range will be detected and the module will generate an output signal. The detection will be independent of object size, material or degree of reflectivity.

Ultrasonic ranging is also used for precise measurements of an object moving to and from the sensor. As explained earlier, the time of flight is measured for calculating the distance between the sensor and the object. By repeatedly sending sonic bursts and measuring the echo received, the distance of change is continuously calculated and displayed.

Depending on the frequency of sound generated by the ultrasonic transducer, the sensing range can vary from a few centimeters to about 10 meters.