Magnetic sensors have a wide range of applications and have played a significant role in various fields such as the national economy, national defense construction, science and technology, and medical and health care, becoming a major branch of the modern sensor industry. In various aspects such as the application and transformation of traditional industries, resource exploration and comprehensive utilization, environmental protection, bioengineering, and intelligent traffic control, they are playing an increasingly important role. The following is a discussion on the application of some important aspects.

The industrial application of magnetic sensors

Magnetic sensors have found industrial applications in many fields, and the total number of magnetic sensors needed each year is in the billions.

1.1 Motor Industry

Brushless motors have a series of advantages such as small size, light weight, high efficiency, convenient speed regulation, low maintenance, long service life and no electromagnetic interference. The annual demand for them is in the hundreds of millions.

In brushless motors, magnetic sensors are used for the position sensing of rotor magnetic poles and the commutator of stator armature current. Many magnetic sensors, such as Hall devices, Wiegand devices, and magnetoresistive devices, can be used, but the ones that are widely used are mainly Hall devices.

The speed detection and control of motors use rotary encoders, while in the past, optical encoders were mostly used. The use of magnetic encoders has demonstrated an increasing number of advantages and is gradually replacing optical devices. Magnetic sensors can also be used to provide overload protection for motors (mainly Hall current sensors) and torque detection.

1.2 Power Electronics Technology

Power electronic meter technology is a combination of power technology and electronic technology. It can achieve mutual conversion between AC and DC currents and freely adjust current, voltage and frequency within the required range. By adopting these technologies and products, various special power supplies (such as UPS, high-frequency power supplies, switching power supplies, arc welding machine inverter power supplies, etc.) and AC frequency converters can be made (AC frequency converters are used for motor speed regulation and have excellent energy-saving effects). The core of these converter devices is high-power semiconductor devices. Various current sensors based on magnetic sensors are used to monitor, control and protect these high-power devices. Hall current sensors have a fast response speed and rely on the magnetic field to couple with the controlled circuit without being connected to the main circuit. Therefore, they have low power consumption, strong overload resistance, good linearity, and high reliability. They can be used as overcurrent protection drivers for high-power devices and also as feedback devices, becoming a control link in the automatic control loop. The application of conversion technology can save a large amount of energy. In foreign countries, 95% of the electricity used is converted. Although conversion technology has received high attention in China, only 5% of the electricity undergoes this conversion. It is evident that it has a huge application prospect. Among them, the potential absorption of a large number of current sensors is another huge industrial application field for magnetic sensors.

1.3 Energy Management

The automatic detection system of the power grid needs to collect a large amount of data. After being processed by the computer, it monitors the operation status of the power grid, and conducts load distribution adjustment and safety protection. All control links of the automatic monitoring system can be realized by current sensors, transformers and other devices based on magnetic sensors. Hall current sensors have gradually been applied in power grid systems. Electricity meters made of Hall devices have gradually shifted from research and development to practical application. They can automatically charge and display power factor, allowing for timely adjustment to ensure efficient electricity usage.

1.4 Computer Technology and Information Reading and Writing Magnetic Heads

In addition to magnetic tapes and disks, magnetic information recording devices also include magnetic cards, magnetic ink for recording account books, and magnetic records of banknotes, etc. There is a huge demand for magnetic information storage and reading sensors. Induction magnetic heads, thin-film reluctance magnetic heads, amorphous magnetic heads, etc. have all been widely used. As the recording density increases, for instance, up to 100G bytes, magnetic heads with higher sensitivity and spatial resolution are required. Giant magnetoresistance magnetic heads based on multi-layer metal films, amorphous alloy magnetic heads made of amorphous alloy wires, and giant magnetoresistance magnetic heads are all in fierce competition.

1.5 Automotive Industry

In automobiles, a large number of motors are used (each high-end car requires about 40 to 60 motors, and a regular car also has 15. These motors are showing a trend towards brushless motors), and the number of magnetic sensors used is self-evident. Another area that extensively uses magnetic sensors is the ABS system (anti-lock braking system) of automobiles. On average, each car employs 4 to 6 speed sensors, with the majority being inductive speed sensors. The new type of Hall gear sensors that are gradually being promoted, as well as Wirtz devices, amorphous devices, magnetoresistive devices, etc., are about to enter this field.

In addition, there are speed sensors and igniters used for ignition timing in the car engine system. These aspects also mainly use induction sensors. Hall gear sensors and Hall slice switches have already been used in some vehicle models. According to Honeywell, by June 1996, they had supplied 80 million Hall fin switches and 3 million Hall gear speed sensors to the automotive industry. It is predicted that in the future, more than 30 magnetic sensors like Hall sensors will be adopted in a single car.

In fields such as industrial automatic control, robotics, office automation, household appliances and various safety systems, apart from the extensive use of brushless DC motors and AC frequency converters, a large number of magnetic temperature controllers have been employed in devices like refrigerators, air conditioners and rice cookers. By the mid-1980s, the number had exceeded hundreds of millions.

Application and market in the transformation of traditional industries

It is reported that the global market for industrial process control sensors alone reached 26 billion US dollars in 1995. In 2001, the market for SV-GMR heads used in computer HDDS exceeded 400 billion yen (approximately 3.4 billion US dollars). If the new type of micro magnetic sensor is adopted, it will not only make the operation more convenient, but also improve reliability, extend the service life of the device and reduce the cost.

The use of new magnetic sensors can significantly enhance measurement and control accuracy. For instance, the GMI(Giant Magnetoimpedance) magnetic field sensor has the same detection resolution as the commonly used fluxgate magnetometer, but its response speed is twice as fast and its power consumption is only 1% of the latter. If Hall devices are used, their resolution is only 4A/m, while the required external field is over 300 times higher than the former. In stress detection, the sensitivity of SI sensors is 2,000 times higher than that of commonly used resistance wires and 20 to 40 times higher than that of semiconductor strain gauges. For the detection of the piston position in the hydraulic or pneumatic cylinders of industrial machine tools, magnetic sensors composed of permanent magnetic rings and AMR components mounted on the piston rods are widely used. The detection accuracy can reach 0.1mm, and the detection speed can vary from high to low within the range of 0 to 500mm/s. After switching to GMI or SV-GMR sensors, the measurement accuracy can be improved by at least one order of magnitude. In the era of numerical control of machine tools, digital magnetic rulers have helped designers achieve closed-loop control. Magnetic scales with absolute signal output are not affected by noise, fluctuations in power supply voltage, etc., and there is no need to reset the origin. The working state magnetic sensitive switch can also be used to complete the conversion between manual and numerical control.

Rotary magnetic encoders play a crucial role in the detection and control of rotational quantity. They are indispensable important components in the position detection and transmission speed control of CNC machine tools, robots, and factory automation equipment, as well as in the rotational quantity detection of automation equipment and communication devices such as disks and printers. Its detection object is the optical magnetic pattern, which is not affected by oil mist and dust. Therefore, it has higher reliability and longer service life than the most advanced optical encoders at present. It is particularly suitable for applications in automatic welding, painting robots, position detection related to steel, and various metal, wood, plastic and other processing industries. However, optical encoders are still widely used. Due to the fact that these devices are easily affected by dust, oil stains and smoke, they are used in automatic welding, painting robots, textile and processing of steel, wood, plastic, etc., and their reliability is extremely poor. Rotary magnetic encoders composed of AMR, GMR and GMI sensitive components do not have the above-mentioned shortcomings. Therefore, the annual growth rate of their market demand is over 30%. It also has broad application potential in household appliances and energy-saving products, and can be widely used in energy-saving and environmentally friendly products. If micro magnetic encoders and control microcomputers are integrated, it will be more conducive to simplifying the structure of the control system, reducing the number of components and duty cycle volume, which is of great significance in precision manufacturing and processing industries.

Application in environmental monitoring

The prerequisite for environmental protection is to monitor various environmental parameters (temperature, air pressure, atmospheric composition, noise.......). For monitoring, a wide variety of sensors are needed here. It adopts a strong magnetostrictive amorphous magnetic bomb micro magnetic sensor, which can simultaneously measure the temperature and air pressure in a vacuum or closed space. Moreover, it does not require connectors and can be remotely measured and accessed from a distance. It has broad application prospects in food packaging, environmental science experiments and other fields.

Application in Traffic Control

Traffic accidents and traffic congestion are a major problem existing in urban and inter-city traffic. Both at home and abroad, efforts are being made to enhance the development and construction of highway Driving Support systems (AHS), intelligent transportation systems (ITS), and Road Traffic information systems (VICS), among others. Among these new systems, high-sensitivity and high-speed response micro magnetic sensors have a wide range of applications. For instance, GMI and SI sensors with a resolution of up to 1nT can be used to form ITS sensors (for road signs on highways, measuring wheel angles, and the proximity distance of trucks), car passage recorders (for measuring the direction of passage, speed, body length, and vehicle type identification), batch vehicle sensors in parking lots, and acceleration sensors (for measuring the vibration of Bridges and roads when vehicles pass through, etc.).

The Application of Magnetic Sensors in Electronic Compasses

For centuries, people have been using magnetic compasses in navigation. Data shows that as early as over two thousand years ago, the Chinese began to use natural magnets - a type of magnetite - to indicate horizontal directions. The electronic compass (digital compass, electronic compass, digital compass) is a relatively economical electronic instrument for measuring azimuth (heading Angle). Nowadays, electronic compasses are widely used in automobiles and handheld electronic compasses, watches, mobile phones, walkie-talkies, radar detectors, telescopes, star detectors, Muslim Mecca detectors (Muslim clocks), handheld GPS systems, scavengers, weapon/missile navigation (position prediction), position/orientation systems, security/positioning devices. High-performance navigation devices for automobiles, navigation and aviation, video game console devices and other equipment that require direction or attitude display.

The Earth itself is a large magnet. The magnetic field on the Earth's surface is approximately 0.5Oe. The geomagnetic field is parallel to the Earth's surface and always points north. GMR films can be used to make sensors for detecting the geomagnetic field. Figure 5 shows the specific working principle of this sensor. We can fabricate integrated GMR sensors capable of detecting components in both the X and Y directions of the magnetic field. This sensor can be used as a compass and applied to various vehicles as a navigation device. The NVE company in the United States has already applied GMR sensors to the traffic control systems of vehicles. For instance, GMR sensors placed along the side of highways can calculate and distinguish vehicles passing through the sensors. If two GMR sensors are placed separately at the same time, the speed and length of passing vehicles can also be detected. Of course, GMR can also be used at highway toll booths to achieve automatic toll control. In addition, sensors with high sensitivity and low magnetic field can be used in aviation, aerospace and satellite communication technologies. As is known to all, in the military industry, with the development of absorbing technology, military objects can be concealed by covering them with a layer of absorbing material. However, they will generate magnetic fields no matter what. Therefore, the GMR magnetic field sensor can be used to identify concealed objects. Of course, GMR magnetic field sensors can be applied to satellites to detect objects on the Earth's surface and the distribution of mineral deposits beneath. [3]

The Application of Door Magnetic Sensors in Smart Homes

In a smart home access control system, the function of the door magnetic switch is to determine whether the door magnetic is energized. When energized, it becomes magnetic (closing the door), and when de-energized, it demagnetizes (opening the door). The door magnetic is installed on the door and the door frame, while the switch is installed inside the house and used in conjunction with an automatic door closer. Generally, it can withstand a tensile force of 150 kilograms.

Wired door magnets are embedded and more concealed. They sense the opening and closing of doors and Windows and are suitable for sending wired normally closed/normally open switch signals to wooden or aluminum alloy doors and Windows. Door magnets are used to detect whether doors, Windows, drawers, etc. have been illegally opened or moved. It consists of two parts: a wireless transmitter and a magnetic block. The door magnetic system is actually based on the same principle as the bed magnetic system, etc.