How does a metal detector work?

The metal detector uses a ** transmitter coil and two equal receiving coils to generate a high-frequency variable magnetic field through the oscillator connected by the middle transmitter coil, and the induced voltages of the receiving coils on both sides cancel each other out before the magnetic field is disturbed in the idle state to reach an equilibrium state.

As soon as the metal impurities enter the magnetic field area, the magnetic field is disturbed, this equilibrium is broken, and the induced voltages of the two receiving coils cannot be cancelled out, and the unoffset induced voltages are amplified by the control system and an alarm signal (metal impurities detected) is generated. The system can use this alarm signal to drive an automatic rejection device, etc., to remove metal impurities from the production line.

If ferromagnetic metals appear near the metal circle, then the original magnetic flux of the metal circle will be greatly affected, and once there are non-ferromagnetic metals, then eddy current effect will be generated in the electromagnetic field area, which will also change the original magnetic field distribution. The detector is also equipped with a sensor that sounds an alarm when it detects a change in the magnetic field in the metal ring and the surrounding area, alerting people to the presence of metal underground.

Because the principle of such a metal detector is relatively simple, the "entry threshold" is low, and the sensitivity, working power and accuracy of its electromagnetic transmitter are very limited, so it is not too high, ranging from the simplest few hundred yuan to tens of thousands of yuan, and the corresponding detection depth is not enough, generally within half a meter, there are some good performance, expensive private metal detectors can detect about 1 meter of space underground. Therefore, it is basically impossible to use these detectors to find the "treasures" in the tombs, one is that the detection depth cannot be reached; second, there is nothing that can be done about non-metallic "antiques"; The third is that it is difficult to distinguish between the detected metals, and sometimes it takes a lot of effort to detect and excavate, which turns out to be just iron nails, steel plates, cans and other items, and sometimes find severely corroded metal coins, which generally do not have much value.

If there is metal around the induction coil of a metal detector, it will cause a slight change in the current flowing through the induction coil. Amplify the signal through the amplification circuit, it's as simple as that.

There is also metal in the phone, so it will also be detected.

Working principle: The metal detector is composed of a high-frequency oscillator, an oscillation detector, an audio oscillator and a power amplifier.

The gain potentiometer of the high-frequency oscillator is adjusted to make the oscillator in a critical oscillation state, that is, to make the oscillator oscillate. When the detector coil is close to a metal object, due to the electromagnetic induction phenomenon, eddy currents will be generated in the metal conductor, which will increase the energy loss in the oscillation circuit, weaken the positive feedback, weaken the oscillator in the critical state, and even stop oscillating because it cannot maintain the minimum energy required for the oscillation. If this change can be detected and converted into an acoustic signal, it will be possible to determine whether there is a metal object under the detector coil based on the presence or absence of sound.

The principle of metal detector is to use the principle of electromagnetic induction, using a coil with alternating current to generate a rapidly changing magnetic field. This magnetic field can induce eddy currents inside a metal object. The eddy current in turn generates a magnetic field, which in turn affects the original magnetic field and causes the detector to beep.

The current flowing through the emitting coil creates an electromagnetic field, just as an electric motor produces an electromagnetic field. The polarity of the magnetic field is perpendicular to the plane in which the coil is located. Whenever the current changes direction, the polarity of the magnetic field changes with it.

This means that if the coil is parallel to the ground, then the direction of the magnetic field will constantly alternate, one moment perpendicular to the ground downwards and the other perpendicular to the ground upwards.

As the direction of the magnetic field changes repeatedly underground, it will interact with any conductor target it encounters, causing the target itself to generate a weak magnetic field. The polarity of the magnetic field of the target is exactly the opposite of the polarity of the magnetic field of the emitting coil. If the direction of the magnetic field generated by the emitting coil is perpendicular to the ground downwards, then the magnetic field of the target is perpendicular to the ground upwards.

The working principle of the metal detector is to use alternating current through the coil to generate a rapidly changing magnetic field, so that the magnetic field lines of this magnetic field pass through the metal object and form eddy currents on its surface. The eddy current in turn generates a secondary magnetic field, which in turn affects the original magnetic field and produces a signal that the instrument can receive and identify.

Finally, the signal is processed and amplified to deflect the pointer of the indicator and simultaneously drive the audible indicator to emit an audible signal.

The accuracy and reliability of metal detectors depend on the stability of the electromagnetic transmitter frequency, which is generally used from 8 to 800kHz.

The lower the operating frequency, the better the detection performance of iron; The higher the working frequency, the better the detection performance of high-carbon steel. The sensitivity of the detector decreases as the detection range increases, and the size of the induced signal depends on the size and conductivity of the metal particles.

The belt type is a conveyor belt, and the food is placed on the belt through the probe, and if it contains metal impurities, it will alarm to stop or exclude. The pipeline type is mainly a free-fall type, where the food falls freely, and it will alarm and then discharge after the probe.

The working principle is simply the principle of electromagnetic induction, also known as the principle of eddy current induction.

Usually a metal detector consists of two parts, the inspection coil and the automatic rejection device, with the detection coil as the core part. After the coil is energized, a magnetic field will be generated, and if a metal enters the magnetic field, it will cause a change in the magnetic field, and it is judged that there are metal impurities.

Some products contain water, salt, and other components, which can also interfere with the magnetic field similar to metals. This phenomenon is called the product effect. Such problems can be solved with the product effect compensation function.

When metal is detected, the sensor activates a signal and drives an automatic rejection device, such as a flap, pusher, etc., to remove impurities.

Metal detectors are generally lightweight and consist of only a few components:

1.Stabilizer (optional) – Keeps the device stable while scanning back and forth with the detector.

2.Console.

Contains circuits, control mechanisms, speakers, batteries, and microprocessors.

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Courtesy of electronics.

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GTI1500 Metal Detector.

Most systems will also have a socket for connecting the handset, and some will place the console underneath and the lever and a small display unit on top.

Metal detectors are easy to operate. Once you've turned on the detector, simply let it slowly move over the area you want to search. In most cases, you'll use a coil (search probe) to scan back and forth above the ground in front of you.

If you sweep past the target, the detector will emit a signal that you can hear. More advanced metal detectors are equipped with displays that accurately identify the type of metal found and the depth at which the target is buried underground.

Metals have a reflective effect on electromagnetic waves, and when the electromagnetic waves emitted by metal detectors reach the metal surface, they are reflected and received by metal detectors, so the existence of mines is known.