In 1960, the first metal detector was established and used in industrial applications and mineral prospecting. A metal detector is an electronic device comprising an oscillator which generates an alternating current passing through a coil generating an alternating magnetic field. When a part of the metal is close to the coil, the eddy current will be induced in the metal object and this generates its own magnetic field. If an extra coil is used to measure the magnetic field, the magnetic field can be changed and detected due to the metal object. Metal detectors are used to detect guns and are also used in the construction industry to identify reinforcing steel bars in pipes, concrete, cables, pipelines buried in walls and floors.
The types of metal detectors are classified into three types, such as BFO (Beat Frequency Oscillation), TR (Transmitter or Receiver) and VLF (Very Low frequency).
Working
The working metal detector is, when the electromagnetic field is transmitted from the search coil to the ground. The metals in the electromagnetic field will be strengthened and will re-send their own electromagnetic. The metal detector comprises a search coil which receives the retransmitted field and alarms the user by generating a metal response. Minelab metal detectors are achieved by discriminating between different types of targets and can be set to ignore unwanted metal objects.
Working a metal detector
Battery
The main purpose of the battery is to provide the power to the detector.
Control box
The control box comprises the electronics of the detector. When the transmission signal is generated, the receive signal is processed and transformed into a destination response.
Search Reel
The electromagnetic field can be transferred by the search coil of the detector to the earth and receives the return of the electromagnetic field of a metallic object.
Electromagnetic field transmission
The transmitted electromagnetic field energizes the metal objects to allow them to be detected.
objective
Here, a target is a metal object that can be detected by a metal detector. In this, the goal is the treasure that is felt and that is a good goal.
Unwanted target
These metal objects are usually attracted by a magnet like nails and also non-ferrous like bottle caps. If the metal detector is set to discard unwanted targets, then the target response will not be generated for those targets.
Receive electromagnetic field
The receiving electromagnetic field is produced from energized targets and is received by the search coil
Objective Response
When the metal detector detects the metal object, it generates an audible sound like a beep. Several Minelab detectors also generate a visual display of target information.
Circuit diagram of the metal detector
The metal detector circuit built with an LC circuit, buzzer and simple proximity sensor. In the LC circuit, the capacitor and the inductor are connected in parallel. When the circuit detects any metal near it, then the circuit activates the proximity sensor and its LED brightness and makes a buzzer.
When this circuit has any resonant frequency from any target that is close to it, then the electric field will be created, which will lead to induce current in the coil and change the S / L in the S / L flow through the Coil.
The value of the sensor can be changed using a variable resistor, which is equal to the LC circuit. When the metal is detected, the circuit will have a new signal and respond accordingly. When the metal object is detected by the coil, the sensor o / p will be 1 mA. When the coil is near the target, then the o / p of the sensor will be around 10mA.
When the output pin is high, resistor R3 will provide a positive voltage to transistor Q1 to turn on the LED, which will glow and generate a buzzer sound. Here, the resistor R2 is mainly used to restrict current flow.