If science and technology can realize this kind of sci-fi vision, it will bring very important practical significance. For example, after an earthquake, houses collapsed and buildings turned into rubble. Unfortunately, people and animals may be buried in the rubble. In this case, rescuers will desperately look for signs of life in the ruins. Imagine if rescuers can “see through” the rubble, find the survivors under the rubble, measure their vital signs, and even directly generate images of the victims, this will bring about a qualitative change in disaster relief.
In fact, this reality may not be so far away from us. With the “through-wall perspective radar technology”, this will soon become possible. Early versions of the technology can show whether a person is in the room. It has been in use for several years. There are also technologies that can measure vital signs under certain conditions.
Avery Fastey is an electrical engineer who studies electromagnetic communication and imaging systems. He and other engineers are using high-speed computers, new algorithms, and radar transceivers that can collect large amounts of data to bring real-life technology closer to the “perspective eye” effect of Superman. This emerging technology can determine how many people are behind a wall or obstacle, where they are, what items they may be carrying, and in military use, it can even determine what type of armor they may be wearing.
Radar that can see through walls
”Radar” was originally an English acronym for radio detection and ranging. Like mobile phones, radar uses electromagnetic waves, which use radio waves to send signals that travel at the speed of light. If the signal meets an object, such as an airplane, it will be reflected back to the receiver. After a certain delay, the reflected wave can be seen on the radar screen, which can be used to estimate the position of the object.
In 1842, the Austrian physicist Christian Doppler described a phenomenon now known as the “Doppler effect”. It said that the change of signal frequency is related to the speed and direction of the signal source. For example: when an ambulance approaches you, passes by you and then moves away, you can feel its alarm tone change.
To use radar to track objects on the other side of the wall, the key is to have a very sensitive antenna that can receive greatly weakened reflected radio waves.
Emergency rescue radar life detector
Working principle of through-wall radar
Doppler radar uses this effect to compare the frequency of the transmitted and reflected signals to determine the direction and speed of moving objects, such as thunderstorms and speeding cars. The Doppler effect can be used to detect tiny movements, including chest movements related to heartbeat and breathing. In this case, the Doppler radar will transmit a signal to the human body, and the reflected signal will be different due to inhalation or exhalation, and even due to heart rate. Therefore, this technology can accurately measure these vital signs.
When the wave hits a solid wall (such as a plaster wall or a wooden wall), part of it will be reflected from the surface, while the remaining part can pass through the wall, especially the relatively low frequency radio. If the emitted wave encounters a metal object or a human body, it can be completely reflected back because the human body has a high water content and is highly reflective.
When the radar receiver is sensitive enough (of course, much more sensitive than the ordinary radar receiver), it can receive the reflected signal through the wall. Using mature signal processing technology to filter out the reflections of static objects such as walls and furniture, signals that people are really interested in can be separated, such as various useful information such as the location of the person.
The radar sensor function is getting stronger and stronger
In the past, the ability of radar technology to assist in disaster management and law enforcement has been limited because it did not have enough computing power and speed to filter out background noise in complex environments such as gravel and generate real-time images.
But today, radar sensors have the ability to collect and process large amounts of data, even in harsh environments, and can generate high-resolution images of targets. Through complex algorithms, they can display data in near real-time. This requires a high-speed computer processor to process a large amount of data quickly, and it also requires a broadband circuit that can transmit data quickly, thereby increasing the resolution of the image.
The latest developments in millimeter-wave wireless technology, from 5G to 5G+ and even higher configurations, may help to further improve this technology, using a wider bandwidth to provide higher resolution images. Wireless technology will also speed up data processing time and greatly reduce latency.
Fasai’s laboratory is developing a high-speed method for remotely depicting the electrical characteristics of walls. This helps calibrate radar waves and optimize antennas to make it easier for waves to pass through walls and minimize wall obstruction. The team also developed software and hardware systems to achieve near real-time analysis of big data in the radar system.
Have the power of “superman”
At present, due to the limitation of antenna size, low-frequency radar systems that can see through walls are usually “behemoths.” The wavelength of the electromagnetic signal is related to the size of the antenna. Scientists have been working hard to push the penetration radar technology to higher frequencies in order to build smaller and more portable systems.
These through-wall fluoroscopy radars can track the movement of the individual as well as the heartbeat and breathing rate. This technology can also be used to determine the overall layout of a building from a distance, and even go deep into the wall to confirm the location of pipes and wires, and to detect hidden weapons and booby traps.
In addition to providing tools for disaster response, law enforcement, and the military, this technology can also be used to monitor the elderly or obtain vital signs of patients with infectious diseases from outside the ward.
In the future, people also hope that it can be combined with more technologies. For example, someone is even studying a kind of through-wall perspective radar, which can generate sufficiently accurate facial images for the facial recognition system to accurately recognize. In this way, people may truly have the power of “superman”.