PI "Pulse Induction" metal detectors are a less common type of metal detector that have found their home mostly among hobbyists. PI metal detectors work well in the water, on beaches and in gold fields. Many hobbyists swear by pulse PI technology. Pi metal detectors are definitely in a class of their own!
How Pulse Induction Works

PI "Pulse Induction" metal detectors can work by using one coil working solo or by using many coils working together. The coil or coils work to generate bursts "Pulses" of current through a coil. These pulses of current generate a magnetic field when the pulse reaches its peak the magnetic field is reversed and collapses very suddenly. The end result of this process is a sharp electrical spike. The sharp electrical spike that this type of metal detector creates lasts for a very short time, ruffly a few microseconds "one millionth of a second!" This process convinces another current to run through the coil. This current is called the reflected pulse and is extremely short, lasting only about 30 microseconds. Another pulse is then sent and the process is repeated. The number of pulses that a metal detector sends out varies greatly between metal detectors and their settings. The variation can be anywhere from about a few dozen pulses per second, to a thousand or more.

When a pulse induction metal detector is passed over a metal object, the pulse creates a reverse magnetic field in the metal object. The pulse's magnetic field then collapses, causing the reflected pulse, the magnetic field of the object makes the metal detector take longer for the reflected pulse to completely disappear. This information is sent to a sampling circuit that is set to measure the length of the reflected pulse. After the sampling circuit of the metal detector measures the length of the pulse it then compares it to the expected length and makes a determination of whether or not a metal object has interfered with the pulse.

The sampling circuit then sends the weak signals to a device call an integrator. The integrator reads the signals from the sampling circuit, amplifying and converting them into direct current. The direct current's voltage is connected to an audio circuit, where it is changed into a tone that the metal detector uses to indicate that a target object has been found.

Pulse induction metal detectors are not very good at discriminating between metals which is why they have some limited applications. VLF is a choice technology for most types of metal detectors and offers the greatest dependability and accuracy.