From the Blog
Several different kinds of metal detectors exist, I will explain how they work while trying not to get too technical. There are three major classes of metal detectors available.
The first type of metal detector is the PI, which stands for Pulse Induction. Pulse induction means that you are creating an electromagnetic pulse that exits the coil, builds off a target, then returns to the coil giving a report on the target it hit.
Pulse induction detectors are usually more sensitive to smaller and deeper targets. The down side is they also pick up more trash targets and have a difficult time telling good goals apart from bad targets.
Another detector type is the VLF, which stands for Very Low Frequency. This kind of detector is versatile and commonly used. It uses phase demodulation to discriminate between types of metallic objects like iron and gold. It does a good job at telling the difference between good objects, like gold and treasure, and trash such as nails, bottle caps etc.
Yet another is the BFO, or Beat Frequency Oscillator. The beat frequency oscillator is a low cost circuit design. It has two coils, one at the end of the arm of the detector and one in the control box on the handle. These coils form a pair of tuned oscillators. The oscillators are tuned so that the difference in their frequencies is an exact multiple of each other. The presence of any metallic object will produce a change in either oscillator and thus produce an audible beat frequency harmonic tone.
Each of these technologies has trade-offs, usually between cost and their ability to sense small valuable objects. Newer advances are coming every day. Most of these are in the area of using special digital signal processing of the return signal. Every constructive object has a specific signature spectrum that tells a bit more about the object and can also be filtered out to separate junk (iron & aluminum) from Gold Treasure. As technologies advance the price for more capable equipment drops. This in turn opens new depths and more trashy areas to be hunted for treasure.
Please remember to hunt responsibly, avoid trespassing and fill your holes when you are finished. Enjoy hunting for buried treasure!