A very low frequency (VLF) metal detector is a type of electronic instrument that uses electromagnetic fields to detect the presence of metals or other conductive materials buried underground or hidden within objects. This type of metal detector works by generating a low-frequency electromagnetic field and then measuring the changes in the field that occur when a metallic object comes into proximity with the detector.

VLF metal detectors operate on the principle of electromagnetic induction, which is the phenomenon that occurs when an electric current flows through a conductor and produces a magnetic field around the conductor. In the case of a VLF metal detector, the electric current is provided by a battery or other power source, and the conductor is a coil of wire that is wrapped around a metal rod or other support structure.

When the VLF metal detector is turned on, an electric current flows through the coil of wire, generating a magnetic field around the coil. This magnetic field extends outwards from the coil in all directions, and it extends downwards into the ground. As the VLF metal detector is moved over the ground, the magnetic field encounters any metallic objects that may be buried underground, such as coins, relics, or other valuable items.

When a metallic object comes into proximity with the magnetic field generated by the VLF metal detector, it becomes magnetized by the field. This causes the object to generate its own magnetic field, which interacts with the field generated by the metal detector. The interaction between these two magnetic fields causes a disturbance in the electromagnetic field, which is detected by the metal detector.

The VLF metal detector measures the disturbance in the electromagnetic field and uses this information to determine the presence and location of a metallic object. This information is then displayed on the metal detector's display screen, typically in the form of a visual or auditory signal, such as a change in the tone or volume of a beeping sound, or a change in the color or intensity of a light on the display screen.

Some VLF metal detectors are also equipped with additional features that can help to improve their accuracy and performance. For example, some VLF metal detectors have adjustable sensitivity settings that allow the user to fine-tune the detector's sensitivity to different types of metals, or to different depths underground. Other VLF metal detectors may have ground balance settings that help to cancel out the effects of naturally occurring minerals in the ground, which can interfere with the detector's ability to detect metals.

Overall, a VLF metal detector works by generating a low-frequency electromagnetic field and then measuring the changes in the field that occur when a metallic object comes into proximity with the detector. The VLF metal detector uses this information to determine the presence and location of a metallic object, and it displays this information to the user in a visual or auditory form. VLF metal detectors are a popular tool for treasure hunters, prospectors, and others who are interested in finding valuable metals or other items that may be hidden underground or within objects.