Basic working principle of a metal detector

Metal detectors are fascinating devices that spot hidden foreign objects from an area or a person. Different types of metal detecting devices work on different working principles.  The science behind most of them remains essentially the same – electromagnetic induction. We constantly rely on the intimate connection between magnetism and electricity every time we use an appliance. Metal detectors, fundamentally work on the same principle. Metal detectors use electricity to create magnetism that creates more electricity somewhere else. Here’s how!

Simply put, a coil in metal detectors is used to interact and attract metallic elements on the ground. This coil receives a re-transmitted field and alarms the user by creating an audible indication in case of the presence of a metal. This coil is also called a transmitter coil.  Let’s delve deeper into this working concept.

As electricity flows through the transmitter coil a magnetic field is generated all around the coil. Once the detector is swept around the ground, the magnetic fields move around too. When the detector meets a metallic object, the magnetic fields get affected in a way that all electrons orbiting around the atoms change. Metal detectors basically induce an electric activity within the metal. What’s more interesting is that this electric charge within the metal in turn creates some amount of magnetism too. This basically causes magnetic field from the detector to transfer onto the metal when you make the metal detector hover over a metallic object. It is this magnetic field around the object that attracts the metal and causes it to pick it up!

Apart from the transmitter coil, most metal detectors also have another coil called the receiver. This coil is usually attached to a circuit containing an audio device or a loudspeaker. When a detector moves over a metallic piece, the magnetic field generated by the metal cuts through the coil. When the metal moves through the magnetic fields it also causes electricity to flow through it. This electricity further flows through the receiver coil thereby producing a beeping sound. Usually the intensity of the beep depends on the proximity between the object and the device. The closer the object, greater is the electromagnetism and louder is the sound! Such a beep is generally an alarm that is raised to indicate the presence of potential metal weapons, coins, foreign objects and the like. Most metal detectors can discriminate between distinct types of targets and can be fixed to overlook undesirable metal objects.