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Ultrasonic metal detector

Ultrasonic metal detector

A. Goshev , Rostov-on-Don

In the practice of treasure hunters, most metal detection cases turn out to be “empty”, that is, the item found is a simple rusty piece of iron, and a lot of time is spent on work to extract it. In order to free the searchers from unnecessary work and give them the opportunity to determine its name immediately upon detection of the metal, this scheme was developed.

The scheme of the ultrasonic metal detector is shown in fig. 1. The principle of its action is based on the property of magnetostriction, which manifests itself as a change in the size of a metal object under the action of mechanical force on it in a constant magnetic field.

The emitter - the BQ 1 piezoelectric element acts on the ground or building structures that most often hide the desired object by ultrasound with a frequency of 6 MHz. The radiation wavelength is such that the particles of the crystal lattice of semiconductor-type substances, such as silicon, calcium, etc., or molecules of substances such as carbon, chlorine, etc., that make up the soil or walls of houses, come to a non-equilibrium state. It is characterized on the one hand by the transmission of the mechanical action of ultrasound from particle to particle, and on the other hand by the appearance of the so-called “fluidity” state of substances in the ultrasonic field. As a result, metal objects appear to be suspended or freely floating in the area of ​​"fluidity".

The substance in the state of "fluidity" re - radiates the ultra - wide spectrum of ultrasonic vibrations (Fig. 2) with an average frequency of 6 MHz, and the bandwidth reaches 5 MHz. In the lower part of the band, there are frequencies of magnetostriction resonances of the most frequently sought for metals, which are indicated by spectral components (Fig. 2). Metal objects are excited at frequencies of natural resonances that are different from others, while the amplitude of resonant radiation exceeds the noise background of the "fluidity", which allows for their detection.

The metal detector design (Fig. 1) consists of a transmitter assembled on a domestic K174KHAZA microcircuit on a three-point capacitive with parametric frequency stabilization on a VT 1 transistor, a multichannel receiver in the form of a line of Al ... A 6 frequency detection indicators on a microcircuit type MC34119R ( DA 2). The transmitter, powered by one or two flat batteries, is loaded onto a BQ 1 piezoelectric emitter, which is mounted on an electrical steel steel with a weight to increase the operating frequency 2 kg .

The same piezoelectric element BQ 2 is used to receive ultrasonic vibrations, so it is placed on a similar platform next to the transmitting, and for decoupling the radiation frequency, their adjoining ribs are laid with rubber. From the piezoelectric element, the input signal goes to the receiving modules of channels A 1 ... A6, which differ only in the tuning frequency of the input electromechanical filters, which for aluminum (A1) is 3245 kHz, for copper (A 2 ) 3872 kHz, for iron (A3) 4731 kHz, for silver (A4) 5278 kHz, for gold (A5) 5621 kHz and for platinum (A6) 5722 kHz.

If there is a signal at the input of the channel amplifier that exceeds the noise level, the signal is detected, amplified and makes the relay K 1 turn on , which turns on the light signaling, indicating the presence of a metal of a certain name. At the same time, an audible alarm is activated in the indicator circuit by supplying power to the AF2 DA2 generator through a decoupling VD 2 diode.

The design of the metal detector is simple, however, the oscillating system of the transmitter and the filters of the receiver require careful tuning by methods widely known to amateurs.

Parts and structural elements are intentionally available to facilitate repetition of the structure.