I Ultrasonic Radar Sensor
​
Ultrasonic radar sensors are widely used sensing hardware in the automotive field, such as the reversing radar on our cars, which uses it.

Its principle of action is that the transmitter sends out ultrasonic waves, which are reflected when encountering obstacles and are received by the receiver, thus obtaining the specific distance between obstacles. However, the scattering angle of ultrasonic waves is large, not conducive to long-distance recovery of signals, so the working distance of the ultrasonic radar is not very far, between 0.1-3 meters with high accuracy. However, it should be noted that ultrasonic radar is susceptible to weather conditions, the propagation speed of different weather is different, and the speed of the car is also a factor affecting the accuracy.

Ⅱ Millimeter Wave Radar Sensor
​
The wavelength of millimeter wave radar sensor is between 1mm-10mm, with strong penetrability, can easily penetrate plastic, paint and other materials. Therefore, millimeter wave radar sensors are often installed in the bumper, and even on the body side skeleton. It works by transmitting millimeter waves out, reflecting them when they encounter an object, and then being accepted by the reflector, which calculates the distance through the time difference.

Unlike ultrasonic radar, millimeter wave radar because of strong penetration, foggy days, dust, smoke and other environments have no effect, the only thing to pay attention to is the rainy days, will be affected by the slightest, but the overall performance is still better than ultrasonic radar. In addition, millimeter wave radar detection distance is also farther, up to 200 meters. Because of this, millimeter-wave radar is also a key part of the high-speed cruise distance-keeping function.
​
However, millimeter-wave radar also has some small shortcomings, that is, in the detection of pedestrians such as reflective surface of small objects, millimeter-wave radar is easy to false alarms. For this problem, car companies have also done the corresponding “remedy”, such as through the combination of detection with high-precision camera.

Ⅲ Lidar Sensor
​
The signal emitted by LIDAR sensor is not sound waves but laser beams. The system can determine a lot of information by comparing the signals reflected back from the target, such as target distance, orientation, height, speed and even shape and other parameters. In addition, LIDAR has a relatively long detection range, up to 500 meters in the automotive sector.

In addition to its long detection range, LIDAR is also characterized by its ability to detect lane lines. LIDAR relies on the unique intensity of the reflected light signal to distinguish lane lines. In terms of working principle, it is simpler and more secure.

Automotive millimeter wave radar sensor is currently categorized mainly by operating frequency, mainly focused on 24G, 60G, 77G, 79GHz. these operating frequency bands are not simply controlled by the OEM or equipment parts suppliers, but there is a special counterpart of the national regulations, the radar's frequency in any one country is subject to strict control.
 
In addition, millimeter wave radars are also categorized according to their operating modes, with pulsed and continuous wave types. The former sends out waves intermittently, and the latter sends out waves continuously outward to detect the position of objects, and the former has basically been eliminated due to its general functional effect.
 
The latter is roughly divided into CW (constant frequency continuous wave, only speed can not measure distance), FSK (frequency shift keying continuous wave, can detect the specific and speed of a single target), FMCW (frequency modulated continuous wave, can be realized on multiple targets to measure the distance and speed) several kinds of function with the order of progress, of course, the cost is also progressive.

ⅠWhere is millimeter wave radar generally arranged on a car?
​
Considering that millimeter wave radar is mainly used to detect the distance between the front and rear of the car as well as the angle, it is installed on the front side on most products.
​
A part of the car models are integrated behind the logo. Considering that the signal quality has to be guaranteed, the surface of the logo in this part of the car models is mostly very smooth and does not have the three-dimensional effect of the traditional logo design.

Another part of the model is installed in the center of the front bumper, which is relatively simple and direct, and the signal quality is also guaranteed.
​
However, considering its installation position is too far down, most of the application models are SUVs and other products with slightly higher ground clearance.

Ⅱ The working principle of millimeter wave radar sensor
​
Like all radars, millimeter wave radar works by sending out waves through a vibrator, bouncing back after touching an object, being received by the receiving antenna, and calculating the distance to the front vehicle based on the time difference after sampling, filtering, and converting.

Of course, most of the current vehicle millimeter wave radar can be calculated together with the speed of the car, the principle is to send out the millimeter wave is not a fixed frequency, but the frequency of the emitted waveform according to the time change, that is, variable frequency.
​
This can be based on the returned waveform time difference and cycle length according to the Doppler effect to calculate the speed of the car.

Ⅲ How millimeter wave radar sensors are used in smart connected vehicles

Millimeter wave radar is only related to two functions in most scenarios on vehicles, one is ACC cruise and the other is AEB active braking.

One of the ACC cruise needs millimeter wave radar will be the distance between the front car and the speed difference between the two cars to determine whether the speed judgment is in a reasonable range, occurring too close or the front car speed is too slow to slow down in time to keep a fixed distance from the front car, i.e., to follow the car driving.
​
If there is no vehicle detected in front of the vehicle is quite simple, according to the set speed can be driven.

AEB active braking is relatively simple, if the vehicle in front of you is too slow or there is a foreign object in front of you, after the distance determination, you can brake directly with the maximum force, on the one hand, to avoid accidents, and on the other hand, if you can't avoid it, you can also reduce the consequences of accidents, in order to improve the safety of driving.

The principle of using millimeter wave radar sensor to realize virtual mouse is to control the movement and clicking operation of the mouse by detecting the movement of the user's finger. Specifically, the millimeter wave radar can detect the position and movement trajectory of the user's finger in space, and then convert this information into the mouse's moving and clicking operations. For example, when the user's finger moves in space, the millimeter wave radar can detect changes in the position of the finger and convert these changes into movement operations of the mouse; when the user's finger makes clicking motions, the millimeter wave radar can detect the clicking motions of the finger and convert these motions into clicking operations of the mouse.

Smart Home
In the field of smart home, the use of millimeter wave radar to realize the virtual mouse can provide users with a more convenient way of interaction. Users can control the switch, brightness, temperature and other operations of smart home devices through finger movement, without the need to use the traditional remote control or cell phone APP.

Virtual Reality and Augmented Reality
In the field of virtual reality and augmented reality, the use of millimeter wave radar to realize virtual mouse can provide users with a more natural and intuitive interaction experience. Users can control the movement of objects in the virtual scene, menu selection and other operations through the movement of fingers, without the need to use the traditional handle or keyboard.

Medical field
In the medical field, the use of millimeter wave radar to realize the virtual mouse can provide more convenient interaction for the disabled or patients with limited mobility. Patients can control the operation of medical equipment through finger movement, such as adjusting the height and angle of the hospital bed, without the need to use traditional buttons or handles.
​
Industrial Control
In the field of industrial control, the use of millimeter wave radar to realize the virtual mouse can provide a safer and more convenient way for workers to interact. Workers can control the operation of industrial equipment, such as starting, stopping, adjusting the speed, etc., through the movement of their fingers without direct contact with the equipment, thus reducing the occurrence of workplace accidents.

Infrared, ultrasonic, camera, and other sensors can be used for gesture scanning perception (and voice control), and millimeter-wave radar sensors are also gradually exploring a number of emerging areas to expand the viability of radar sensors. Gesture scanning sensing in hoods, although niche, also has room for survival.
 
Most of the researchers only consider the definition and recognition rate of gesture actions, while few of them consider the effect of human motion on the accuracy of gesture recognition. Human motion and gesture actions are difficult to distinguish in 24G radar with low resolution. Some schemes are to limit the sensing distance of human gestures, such as limiting it to 40 cm, only gestures within 40 cm are detected, and at the same time require that the human body can not be close. But this approach is hardly acceptable for hood sensing and most other gesture recognition applications.

Low-cost radar sensors mainly detect the motion of the gesture, such as forward, backward, left, right, up, down, drawing circles, etc., and the gestures must be dynamic (not considering ISAR imaging). Its outputs are the distance, speed, angle, and power of the gesture changes over a period of time, and their correlation of these information.

Non-contact radar sensor for controlling light switches also include the following:

1. Bluetooth or Wi-Fi enabled smart switches
These can be controlled via a mobile app on your smartphone or other compatible devices. You can turn the lights on or off remotely from anywhere as long as you have an internet connection. For example, when you're about to arrive home, you can turn on the lights in advance using your phone to make the house more welcoming.
 
2. Motion sensor switches
These detect movement in the area and automatically turn the lights on when motion is detected and turn them off after a period of no movement. They are commonly used in areas like staircases and storage rooms where hands-free operation is convenient and energy savings can be achieved.
 
3. Voice-activated switches
Integrated with virtual assistants like Amazon Alexa or Google Assistant, these switches respond to voice commands to turn lights on or off. For instance, simply saying "Turn on the lights" can activate the lights without any physical contact.

There are both contact and non-contact radar sensors for humans to control light switches.
 
The contact ones are touch buttons, touch screens, and touch wireless remote controls. Among them, touch buttons and touch screens require the human body to operate very close to the touch point, and the position is relatively fixed. Touch wireless remote control can be controlled within the range of wireless signals, the human body can not be fixed operating position, but need to carry the remote control.
 
Non-contact are infrared sensors (temperature control), cameras, microphone sensors (voice control), microwave radar sensors, and so on. These sensors do not need to touch the button, and do not need to carry a remote control, only need the human body into the sensor sensing range, you can turn on or off the lights sensorlessly.
 
Contact methods of electric light control, such as dual-control switches, are the most used configurations in modern homes. Bedroom into the door immediately press the first switch to turn on the lights, sleep lying down and then the second switch to turn off the lights, the wiring structure is shown in the figure below:

In addition to the bedroom, up and down the stairs, inside and outside the bathroom also exist in this type of installation. The biggest advantage of this approach is that the system structure is simple, stable control, easy to operate, and the user has a strong sense of operation. However, the shortcomings of this way is that multiple lines need to be laid to realize the dual-control function.

Non-contact switch control, the use of microwave sensing to achieve a person to light up, people go out of the light function. Thus avoiding the cost of dual-control switches and wiring, but also reduces the user's dependence on the switch, do not need to look for the switch in dark environment where the switch is, and then go to touch it.
 
 
The other one is a microwave sensing radar for power connection type, which realizes the de-switching of the electric light, the electric light only needs to be connected to the zero wire and the fire wire, free of wiring, and the integration of the control switch and the electric light. You don't need to worry about the cost of wiring and aging, as you can avoid bad switch wiring, do not need wall grooving.
 
 
Most of the radar sensor lights are installed in corridors, aisles, and these locations because these locations do not need radar to determine human consciousness, they only need to monitor the presence of a human body. The scene in the bedroom is the presence of people who may not need to turn on the light, and may also need to turn on the light after turning off the light.
 
A switch signal can be triggered by a triggering method, which makes the radar perceive the awareness of human behavior, thus controlling electric lights. By using proximity gesture recognition, the radar from the previous integrated lamp out, respectively, installed in the entrance and bedside, through the gesture to perceive the human body movement, to achieve non-contact control.
 
You can also integrate the near-end gesture perception function into the bedside lamp or make a separate discrete perception module, placed in the bedside, while the light inside the perception of the radar is still retained. When a person enters the room will automatically turn on the light, the person leaves the room will automatically turn off the light. If a person does not need to turn on the light in the room, he or she can wave the sensing module with a gesture, and if a person needs to turn on the light, he or she can also wave the sensing module with a gesture. Of course, the priority for waving the sensing module with a hand gesture will be higher than that inside the electric light.
 
This perception module can not only control lamps, desk lamps, curtains, fans, air conditioners, stereos, TV screens, projectors, sweeping robots, washing machines, and so on, through proximity gesture sensing, to achieve integrated control of smart devices. You only need to define a lot of gestures, and at the same time ensure that each gesture can have a high degree of recognition accuracy. In the past, smart devices could also be controlled by voice or wifi, but radar is also a solution that doesn't require speech and is friendlier to people with speech impediments.

Evaluating the effect of radar sensor application in elevator system can be done in the following aspects:
 
1. Passenger waiting time: by installing radar sensors, the system is able to detect whether there are passengers waiting outside the elevator, thus reducing the unnecessary dwell time and improving the response speed of the elevator.
 
2. Operation efficiency: The radar sensor can detect whether there are passengers inside the elevator and the number of passengers, which helps the system to decide the operation strategy of the elevator, such as skipping certain floors when there are no passengers, or deploying more elevator services when there are many passengers, thus improving the overall operation efficiency.
 
3. Energy consumption: Through intelligent detection and scheduling, radar sensors help reduce ineffective elevator operation and lower energy consumption.
 
4. Full load rate: Radar sensors can more accurately monitor the number of passengers in the elevator, helping to increase the full load rate of the elevator and reduce the number of elevator round trips.
 
5. Failure rate and maintenance: Radar sensors can be used to monitor elevator operating conditions and predict potential failures, thereby reducing the probability of failure and optimizing maintenance schedules.
 
6. Passenger experience: Passenger experience is enhanced by reducing wait times and improving operational efficiency.
 
7. Data monitoring and analysis: Data collected by radar sensors can be used for long-term monitoring and analysis to further optimize the performance of the elevator system.
 
8. Safety: Radar sensors help detect abnormalities inside and outside the elevator, improving elevator safety.
 
9. Cost-benefit analysis: Evaluate the relationship between the installation and maintenance costs of radar sensors and the efficiency gains and energy savings they bring.
 
10. Practical application cases: Evaluate the effectiveness and feasibility of radar sensors by analyzing the application cases of radar sensors in actual elevator systems.
 
11. Compliance with technical specifications: Check whether the radar sensor system complies with the relevant technical specifications and standards, such as the Technical Specification for Elevator Intelligent Sensing and Warning System.
 
12. Intelligent level: Assess the contribution of the radar sensor system to the level of elevator intelligence, such as whether it supports remote monitoring, fault warning, data analysis and other functions.

Ⅰ Requirements
Taking an elevator in a high-rise building in a big city, the following situations can happen:
(1) Someone on certain floors presses the elevator, but then suddenly leaves for something else, causing the elevator to stay, which is very common in life.
(2) It is also common in life that the elevator is already packed with people but still stays on the floor where someone pressed the elevator but can no longer carry anyone else.
(3) Some high-rise buildings will exist 4 to 6 elevator devices, multiple button operation, will lead to the existence of multiple elevators to the same floor, but at this time the passengers have been carrying the first to arrive at the elevator to leave, after arriving at the elevator belongs to an empty trip.
(4) Some people will press the wrong elevator but will not cancel it in time, but the elevator will still lift to the wrong floor after stopping at the right floor, which is more common when going up the stairs.
Although the current elevator is smart enough, it has not completely solved the above problems, as well as other problems that the blogger has not thought of.
 
Ⅱ Solution
It just occurred to me that millimeter-wave radar for human detection has been studied for more than 10 years, especially in the last 5 years the outbreak of a large number of human presence detection radar, multi-target tracking and head counting radar, etc., their costs have been very low. If the characteristics of millimeter wave radar can be used, it should be able to solve the problem of elevator intelligent linkage to a certain extent:
(1) If the elevator is already stuffed with people, it will only go down but not up;
(2) If there is no one outside the elevator door, then don't stay;
(3) If there is no one inside the elevator, then keep silent.
This not only saves electricity, but also accelerates the passengers' riding experience, so that they will not be annoyed because the elevator is always doing some useless work, especially during the peak period of commuting.
 
Ⅲ Implementation Program
(1) Install a headcount radar inside the elevator, which requires high-resolution radar. Do better with cameras.
(2) Each floor to install a low-cost human presence detection radar can be, 24GHz radar sensor can be, after all, a lot of floors, the deployment of the cost is very high.
(3) Finally, link the data from the radar with the elevator control system, while ensuring the stability of the system and the correct functionality of the system can be.

Parking assistance sensors are integrated into vehicles to help drivers park more accurately by detecting surrounding obstacles. These sensors provide real-time feedback, often through visual or audible alerts, to help the driver find a parking space. The goal is to minimize the chance of a collision, even in challenging conditions with multiple moving objects around the vehicle.
 
Parking assistance systems typically use various technologies, each with its own advantages and disadvantages. Currently, one of the most popular technologies is ultrasonic sensors, which can detect objects at close range but have some performance drawbacks. Radar sensors, an emerging parking technology, offer more advanced features that help overcome the performance drawbacks of ultrasonic sensors and lead to new features and applications.
 
The ultrasonic parking sensor emits high-frequency sound waves that are undetectable to the human ear. When sound waves hit an object, such as a wall or another vehicle, they bounce back to the sensor. By measuring the time it takes for the sound waves to return, the sensor can determine the object's distance based on the known speed of sound. If the object is within a critical distance, the system alerts the driver with an audible alarm. Typically, four or six ultrasonic sensors are integrated into the bumper to provide a 180-degree field of view.
 
Radar sensors emit electromagnetic waves and analyze the reflected signals to determine the distance, horizontal and vertical angles, and speed of objects within the vehicle. Millimeter-wave radar technology uses electromagnetic waves in the millimeter wavelength range, with the standard frequency being 79 GHz for exterior automotive applications. Once the sensor emits waves, they propagate through the air and reflect off objects in their path, such as other vehicles, walls, or pedestrians.

The sensor receives the reflected waves and calculates the distance of each detected object from the vehicle based on the time it takes for the reflected waves to return. Today's radar sensors use MIMO (Multiple Input Multiple Output) technology with multiple transmitters and receivers, providing a larger field of view and the ability to detect all objects in a single scan, including distance, angle to the sensor, and their relative speed.
​
When comparing ranges, millimeter wave radar outperforms ultrasonic sensors at both minimum and maximum detectable distances. Millimeter-wave radar sensors can detect objects up to 5 centimeters from the vehicle, while ultrasonic sensors have a detection distance of 10-20 centimeters. Ultrasonic sensors have a maximum range of about 8 meters, with some systems reaching 20 meters. In comparison, radar sensors can detect objects up to 60 meters away from a person and up to 100 meters away from a vehicle with a field of view (FoV) of 180°.
 
Field of View (FoV) is the width of a sensor's field of view and is typically measured in degrees. Radar parking sensors typically have a 120°horizontal FoV, but the new generation of millimeter-wave radar sensors have a horizontal FoV of up to 180°, covering the entire area behind the vehicle.