Firstly, in the traditional magnetic detection, the induction coil is used as the sensitive element. The characteristic is that it does not need to be electrified in the coil, and generally only plays a sensitive role in the moving permanent magnet or current carrier. Later, it was developed to form an oscillation circuit with coils. Such as mine detectors, metal foreign body detectors, fluxmeter for measuring magnetic flux, etc. Fluxgate, vibrating sample magnetometer. Hall sensor Hall sensor is a device based on Hall effect. Hall effect: When charged carriers are subjected to an external magnetic field perpendicular to the carrier plane, they are subjected to Lorentz force and tend to gather to both sides. Due to the accumulation of free electrons (more on one side and less on the other), a potential difference is formed, which is more obvious in semiconductor materials prepared by special processes. Thereby forming a Hall element. Early Hall effect material Insb (indium antimony). In order to enhance the sensitivity to magnetic field, semiconductor group IIIV elements have been applied to materials. In recent years, in addition to Insb, there are silicon substrates and gallium arsenide. Due to its working mechanism, Hall element devices are all made into full-bridge devices, and their internal resistance is about150Ω ~ 500Ω. For linear sensors, the working current is about 2~ 10mA, and the constant current power supply mode is generally adopted. The typical operating current of Insb and silicon-based Hall elements is 10mA. The typical operating current of gallium arsenide is 2 mA. As a low-weak magnetic field measurement, we hope that the lower the working current required by the sensor itself, the better. (Because there is a magnetic field around the power supply, errors are introduced to varying degrees. In addition, the current sensor is very sensitive to temperature, with large current and self-heating problem. (Temperature rise) will lead to sensor zero drift. In addition to the compensation circuit, these aspects are also constantly improving in materials. There are two main types of Hall sensors, one is a switching device, and the other is a linear Hall element. The former is greater than the latter in structure (variety), dosage and yield. The response speed of Hall element is about 1us. Magnetoresistive sensor Magnetoresistive sensor and magneto-sensitive diode are another kind of magneto-sensitive sensor derived from Hall sensor. The semiconductor materials used are basically the same as those used by Hall. However, the mechanism of this kind of sensor on magnetic field is different, and the direction of carrier movement in the sensor is in the same plane as the detected magnetic field. By the way, Hall effect and magnetoresistance effect coexist. When manufacturing Hall elements, efforts should be made to reduce the influence of magnetoresistive effect, and when manufacturing magnetoresistive devices, efforts should be made to avoid Hall effect (a nonlinear term in the calculation formula). In the application of magnetoresistive devices, the control of temperature drift is also the main contradiction. In terms of device preparation, magnetoresistive devices are different from Hall, so the early products are single magnetoresistance. Due to the large temperature drift, a single arm (two magnetoresistors in series) is mainly used to compensate the temperature drift. At present, there are also full-bridge products, but the usage (use) is slightly different from that of Hall element. It is reported that the response speed of magnetoresistive devices is the same as that of Hall 1uS. Magnetoresistive sensor is powered by a constant voltage source (but it also needs a certain current) because its working mechanism is different from Hall's. When the subsequent circuits are different, the requirements for power supply stability and internal noise are also different. Fourth, the application of magnetic sensor: the volume of magnetic sensor (unit): magnetic sensor is designed and manufactured as a detection magnetic field. The general concept of detection is: measuring the magnetism of a certain point in the magnetic field. The definition of a point is infinitesimal in geometry. In magnetic field detection, because the area, volume and gap size of the magnetic field are all limited, we hope that the area of the magnetic sensor is smaller and more accurate than that of the magnetic field to be measured. In the technology of magnetic field imaging, the smaller the element volume, the more pixels are collected in the same area. The higher the resolution and clarity. In the measurement of surface magnetic field and the detection of multi-stage magnets, such requirements are needed in the magnetic grid ruler. According to the working mechanism of magnetic sensor, in order to improve the sensitivity, there are corresponding requirements for the geometric shape in the magnetic field, which is contradictory to the requirements of "point". In the technical exchange with foreign experts, it was learned that in 1999, Russian experts indicated that they had made a probe with a volume of 0 .6mm (made by several research institutes). The United States also has corresponding products, each about 70 dollars. Whether it is the highest level at present has not been reported. It is also difficult to require the verticality of probe package in the measurement of two-dimensional field and three-dimensional field. & gt