Millimeter wave radar is a radar that can detect in the millimeter wave frequency band. Generally, millimeter wave refers to the frequency domain (1-10mm) of 30~300GHz. The millimeter wave wavelength is between the centimeter wave and the light wave, so it has the advantages of microwave guidance and photoelectric guidance at the same time. Millimeter wave radar uses an atmospheric window (when millimeter waves and submillimeter waves propagate in the atmosphere, the attenuation of their propagation is small, which is caused by the minimal attenuation caused by the resonance absorption of gas molecules, and is affected by natural light and thermal radiation sources. Smaller.
Therefore, millimeter wave radar is of great significance in communications, radar, navigation, remote sensing technology, radio astronomy, and spectroscopy. Using the narrow beam and low sidelobe characteristics of millimeter wave antennas, accurate tracking radars and imaging radars can be realized.
① When the antenna diameter is the same, the millimeter wave radar beam is narrower (generally milliradian measurement level), which can improve the angular resolution and angular accuracy of the radar, and is beneficial to countering electronic interference. Clutter interference, multipath reflection interference, etc.
②Because of the high working frequency, a larger signal bandwidth (such as gigahertz) and Doppler frequency shift can be obtained, which helps to improve the measurement accuracy and resolution of distance and speed, and can analyze target characteristics.
The principle of measuring human breathing and heartbeat by radar is that human activities such as breathing and heartbeat will cause the ups and downs of the chest cavity, which will cause changes in the radial distance between the radar and the measured human body. The breathing and heartbeat signal can be extracted by measuring the change in its radial distance. The detection of human breathing and heartbeat is of great significance in medical monitoring. Such as fire, earthquake and other disaster rescue. Family health monitoring is of great significance. Compared with single-target breathing and heartbeat detection, the difficulty of multi-target breathing and heartbeat detection lies in identifying multiple targets. At present, based on the difference of multi-target recognition domains, this article summarizes them into three categories: distance dimension discriminant method, azimuth discriminant method, and signal domain discriminant method.
It is a straightforward and common method to distinguish the distance based on the difference of the target radial distance. The advantage of this method is that the separation effect is better and the process is relatively simple. The disadvantage is that the radar system requires a higher bandwidth to obtain a higher range resolution; multiple targets cannot be identified in the same range unit. Using the difference in relative azimuth angles of radars, the azimuth information of multiple targets can be identified. The advantage of this method is that it can distinguish multiple targets of the same distance unit, but it needs to use an array antenna, and need to study the corresponding DOA (Direction of Arrival) estimation method and the digital beam forming (DBF) method. Based on the difference of multi-target breathing and heartbeat signals, the multi-target recognition method in the signal domain is recognized. Its advantage is that it can distinguish multiple targets with the same distance unit on the same azimuth angle, but there is a big difference in the breathing and heartbeat signals of multiple targets, and multiple targets are required to be in the same distance unit.
The working frequency of millimeter wave radar is between 30GHz and 300GHz; it has a wide frequency band and can reach up to GHz, so it has a higher range resolution. For example, a radar with a bandwidth of 3GHz has a range resolution of 5cm. The introduction of high-range resolution capability provides a feasible method for multi-target recognition.
In a home environment, the two major difficulties of multi-person monitoring of breathing are:
1) When two or more human targets and the radar are in the same straight line, the radar can only measure the chest undulation information of the human target that is closer;
2) Background clutter interference. There are a large number of large objects in the indoor environment, which hide the echo signals of the human thoracic cavity.
This can be applied to the Ferry Smart 5.8G presence sensing radar module. This series works in the 5.8GHz±75MHz frequency band, integrates a high-performance 32-bit MCU, a single chip directly outputs sensing control signals, a real SoC. Powerful performance, rich algorithms can be used, strong scalability, suitable for high-performance scenarios. It supports a standard UART interface, which can be interconnected with other main controllers or sensors, and can also be used as a main control. It can realize presence sensing based on the detection of human breathing.
Features
FR58L4M32-2020S
? Working frequency: 5.8Ghz±75MHz
? Power supply voltage: 4.5~5.5V
? The forward distance can reach 30 meters
? Equipped with 32-bit MCU
? Strong anti-interference ability and support dense distribution
? Realize presence sensing based on detecting human breathing
? Comply with FCC/CE/SRRC and other wireless certification standards
? Industrial grade, support high and low temperature (-40°-85°) reliability test
? Integrated intermediate frequency processing and filtering
? Flexible pipe angle interface
? Targeted core algorithm protocol
? Support distance adjustment
? Support photosensitive (optional).
The radar can easily meet the following application requirements:
1. High-precision multi-dimensional search and measurement: measure and locate high-precision distance, azimuth, frequency and spatial position;
2. The radar installation platform has a volume. There are strict requirements for vibration and other environments: the millimeter wave radar antenna is small in size, light in weight, and easy to meet the special environmental requirements of different platforms such as portability, missile-borne, vehicle-mounted, airborne and spaceborne;
3. Target feature extraction and classification recognition: millimeter-wave radar with high resolution, wide working frequency band, high-value Doppler frequency response. Short wavelength is easy to obtain target detailed features and clear contour imaging, which is suitable for important tactical requirements for target classification and recognition ；
4. Small target and short-range detection: The light domain corresponding to the short wavelength of millimeter wave is small, so it is more suitable for the detection of small targets than microwave radar. In addition to long-range millimeter-wave radars that specialize in space target observations, millimeter-wave radars are generally suitable for short-range detection below 30 kilometers.
