“Super Ear” really exists! How does the life detection radar “hear” the faint heartbeat under the thick ruins?

Tuchong Creative

When it comes to radar, many people will think of the military, because the earliest radar applications were for military purposes. But there is a kind of radar whose mission is to save lives. This is the life detection radar specially used to detect special objects. Its target is not airplanes, missiles and satellites, but people buried under thick rubble.

Using radar to detect life signs has great application potential, especially in human rescue and medical monitoring. However, the implementation of this technology faces multiple challenges. In order to help you understand the technical challenges I will talk about below, it is necessary to first look at how radar generally works. A typical radar system mainly includes transmitters, receivers, antennas, signal processing units, and display units. The transmitter generates high-frequency electromagnetic waves and transmits them in the direction of the target through the antenna. These electromagnetic waves will be reflected or scattered when they encounter the target. The receiver receives the reflected signal from the target through the antenna and performs preliminary signal amplification and filtering. The antenna is responsible for the transmission and reception of electromagnetic waves, and its performance directly affects the detection capability of the radar system. Highly sensitive and highly directional antennas can effectively improve the detection range and accuracy of the system. The signal processing unit processes the received reflected signal, including filtering, amplification, spectrum analysis, feature extraction and other steps to extract useful target information. The display unit converts the processed signal into visual information, such as images, waveforms or data, for users to observe and analyze.

With this foundation, let's take a look at the challenges that life detection radar needs to face. There are roughly four points: detection signal weakness, environmental interference and noise, target recognition complexity, and the difficulty of achieving technical crossover.

Let's first look at the detection of weak signals. Vital signs such as heartbeat and breathing can cause tiny movements on the surface of the human body. The frequency of these movements is only a few tenths of a hertz and the amplitude is only at the millimeter level. This micro-motion frequency is extremely low, causing its echo signal to be easily drowned out by the inherent noise of the radar system. As Professor Wang Jianqi of the Air Force Medical University put it, "To sense it, it is like separating the sound of a sewing needle falling to the ground from the noisy environment of the market and amplifying it to an audible loudness." The detection of micro-motion signals requires an extremely high signal-to-noise ratio and precise signal processing technology, which is the primary difficulty faced by radar in detecting life signs.

Then, radar signals are interfered with by many factors during propagation, such as walls, metal objects, and even weather. These interferences will cause signal reflection and scattering, making it extremely difficult to extract useful life signature signals from radar echoes. For example, at the rescue site after an earthquake, there are a large number of reflection and scattering sources in the building ruins, which greatly increases the difficulty of signal processing.

In addition, the radar system's own noise and environmental noise are also important obstacles that need to be overcome. In practical applications, how to accurately identify the target and determine its life status is another major challenge. For example, how to distinguish the micro-motion signals of humans and animals, how to determine the life status of trapped people through signals, etc., all require complex signal processing and analysis technologies. The complexity and diversity of life feature signals make target identification very difficult. In response to different scenarios and application requirements, the radar system needs to have a high degree of flexibility and intelligence to cope with various complex situations.

Finally, the technology for realizing radar detection of life characteristics involves the intersection of multiple fields, including radar technology, signal processing, biomedical engineering, etc. It is necessary to comprehensively use a variety of technical means, such as high-frequency microwave technology, digital signal processing, machine learning, etc., to achieve effective detection of life characteristics. Each link requires careful design and optimization, and any error in any link may lead to the failure of the entire system. In addition, the hardware implementation of the radar system also faces challenges, such as high-sensitivity radar antennas, low-noise receiving systems, efficient signal processing units, etc., all of which need to be carefully designed and manufactured.

This is why radar detection of life signatures has long been considered a global challenge.

Since the 1990s, Chinese scientific research teams have begun to explore the use of radar to detect life characteristics. After years of hard work, the team led by Professor Wang Jianqi has successfully developed my country's first biological radar with independent intellectual property rights. This radar can penetrate obstacles, detect the tiny movements of living organisms, and effectively detect trapped people.

In order to capture weak life signals, the team built a new zero intermediate frequency transceiver system, which separated the inherent noise of the system from the echo caused by micro-movements on the body surface by controlling the coherent signal delay. In addition, through in-depth research on the physiological characteristics of life characteristic signals, the team designed a radar transceiver system that is highly sensitive to life signals and solved the matching problem of signal filtering and power amplification.

With the continuous development of technology, the team has achieved a leap forward from biological radar to "perspective glasses". The research team designed and iterated metamaterials - an artificial material that obtains specific physical properties by carefully designing its internal structure rather than relying on the chemical properties of its constituent materials - to turn it into an optically transparent metasurface, which is usually a thin layer composed of tiny structures with special geometric shapes that can control properties such as phase, amplitude and polarization of light, covering the outer layer of the biological radar. When the electromagnetic waves emitted by the biological radar pass through the metasurface, the metasurface can flexibly adjust the propagation direction and characteristics of the electromagnetic waves according to eye movement information to achieve accurate detection of the target. It has achieved the goal of "looking wherever you want to explore", greatly enhancing the flexibility and intelligence level of the equipment, and providing a more convenient solution for disaster relief.

These technological breakthroughs of Chinese scientists have not only remained in the laboratory stage, but have also been tested in actual combat. During the rescue of the 2008 Wenchuan earthquake, Professor Wang Jianqi's team carried bio-radar equipment and successfully detected the life signals of survivors in the ruins, providing valuable information support for the rescue operation. Through field testing, bio-radar can penetrate the ruins of a collapsed three-story building, demonstrating its powerful detection capabilities and application value.

However, we still need to clearly realize that although China has achieved remarkable results in the research of radar detection of life characteristics, there is still a certain gap compared with international advanced technologies. Internationally, research institutions and enterprises such as the United States and Europe started early in the technical research of radar detection of life characteristics and have rich experience and technical accumulation. For example, the micro-motion radar system developed by the Massachusetts Institute of Technology can achieve high-precision vital signs monitoring, and some European companies have also launched commercial life detection radar equipment.

However, China's research in this field is also catching up rapidly. Through independent innovation and technological breakthroughs, the Chinese scientific research team has not only successfully developed high-performance bio-radar equipment, but also achieved rapid transformation from laboratory to practical application. For example, in the search and rescue operations after the Wenchuan earthquake, the bio-radar equipment carried by the Chinese team played an important role and proved its effectiveness in actual rescue. In the future, the technology of radar detection of life characteristics will have broad application prospects. First, in disaster relief, this technology can quickly locate trapped people and buy precious time for rescue. Secondly, in medical monitoring, non-contact radar vital signs monitoring equipment can be used in hospitals and home care to improve the monitoring accuracy and comfort of patients. In addition, this technology can also be applied to security and military fields, such as detecting potential security threats and monitoring battlefield casualties. With the continuous maturity and optimization of technology, the application of radar detection of life characteristics will be more extensive and in-depth. Especially with the support of artificial intelligence and machine learning technology, the intelligence and automation level of this technology will be further improved, bringing more accurate and efficient detection capabilities.

In the field of radar detection of life characteristics, there is both cooperation and competition between China and its international counterparts. Through international cooperation, Chinese scientists can draw on and learn from foreign advanced technologies and experiences to accelerate their own technological development. At the same time, through technological innovation and breakthroughs, China has gradually formed its own advantages and characteristics in this field. China's biological radar and "perspective glasses" systems have unique innovations in performance and application scenarios, providing new ideas and solutions for the development of international radar detection technology. In future development, radar detection of life characteristics technology will continue to play its unique advantages and make greater contributions to the development and security of human society.

This article is a work supported by the Science Popularization China Creation Cultivation Program. Author: Rocket Uncle Science Popularization Creator

Reviewer: Xiao Long, Professor of China University of Geosciences

Produced by: China Association for Science and Technology Department of Science Popularization

Producer: China Science and Technology Press Co., Ltd., Beijing Zhongke Xinghe Culture Media Co., Ltd.