A device that will respond to a metal is called metal detector. 1960s is the era where this device is produced in industrial environment. This device is usually used for mining industry.
Gerhard Fisher developed a system which is called as radio direction-finding that is used for accurate navigation. This system works well but there were anomalies in an area which is contained ore-bearing rocks. Gerhard Fisher is the first person who patented a this kind of detector.
A new design of detector comes with coil. The original design consists of two identical coils which are placed on the top of one another. This design was developed into a new invention which could extinguish the mineralization effect on the ground.
The new innovation of metal detector allows the user to adjust the discrimination, sensitivity, threshold volume, track speed, etc. Nowadays, this device is fully computerized.
This device is usually used to find knife and gun but mostly used in land mines. Some people also use this in archeology and treasure hunting. The construction industry also uses this device to detect foreign bodies in food and steel on a wire, pipes, and wall. After a war, this machine is used to find booby trap in a certain area.
A metal detector that consists of an oscillator is the simplest form. The oscillator produces an alternating current which passes through a coil producing an alternating magnetic field.
This device is good for treasure hunting. You can use this under the water to find any metal materials. Every detector for metal has its own ability and range. You may find the most sensitive detector if you want to find a small metal thing in a certain area.
You may need to find the most appropriate detector based on your primarily needs. It depends on the thing that you want to hunt and where you hunt.