Roger Williams
Radio Corner

Metal Detecting
The Hunt for Gold and Weapons

Metal detectors are devices which electronically generate signals that power a transmitting antenna, sending an electromagnetic field into an area within range of the detector. This range depends upon the strength and force of the signal. The stronger the force of the signal the longer the range. Different types of detectors are manufactured for different applications. The detector is a reporting device, alerting the user that there is a metal of some type present within the transmission field of the unit.

Recent History

Prior to World War II, the use of devices to search for gold and precious metals was an unpredictable process. Various methods were tried using electrical means to search for treasure. Some cumbersome devices actually made a signal or noise when they came into contact with metal. As early as 1930, smaller units were made in kit form which had some success. During this period, companies were producing and marketing detectors based on a number of electrical theories, but they were fairly inefficient. However, with the war, came the need for land mine detectors, causing considerable government-directed research to be done by manufacturers. After the end of the war, a large number of these units were bought as surplus by the civilian population, and the hunt for buried gold and silver was on.

During the '60s and '70s, interest in the use of these devices grew, causing the detector "analyzer" to be developed. By the early '80s, accuracy was improved considerably, along with the ability to identify the types of metals located by the transmitting field. The reduction in their size made them even more "user friendly."

The detectors made today have the ability to pinpoint their targets, measure the depth, and inform the operator if the targeted metal is what he wants to recover. As the equipment becomes more sophisticated the operators too must become more sophisticated in their understanding, application and use of the detectors.

New detection equipment is used for reporting the presence of weapons, often with a simple hand-operated device. While larger units, like walk-through detectors at airports and other places, are placed in areas where security is a high priority.

How Detectors Work

The receiving part of a detector is similar to any radio receiver - capturing radio waves and converting them to sound. In the case of the modern detector, a tone is generated for the user to hear. In the transmitter, a signal is sent to an antenna in a similar fashion to any radio transmitter. The difference is that an electromagnetic field is generated and transmitted by the antenna in all directions. The antennas are circular in shape, and the electromagnetic signals crowd together as they move through them.

This increases the intensity of the signal generated and any distortion of the signal is seen and reported in a mirror image fashion. When the electromagnetic field surrounds a metal surface, small circulating currents called "eddy currents" are created and the losses in the field are seen by the detector and reported to the unit's circuits. The detector then tells the operator that metal has been found, by producing a signal.

Detection of different forms of minerals are reported differently. Iron is non-conductive, for example, the electromagnetic balance of the transmitter and receiver is upset, informing the operator that iron has been detected. Normally, the strength of the electromagnetic field determines the distance of operation as well as the target size and surface area.

In any detector the electromagnetic signal is relatively weak, confining the search area to a radius of only a few feet. Commercially made units can run from $100 to $1,000 for general-purpose detectors. Specialized detectors used for gold nugget hunting, or buried treasure caches - like the one employed by Ted Binions' murderers, in the infamous '999 Las Vegas case, to find his treasure of hundreds pounds of silver - cost upwards of $5,000.

Use of Detectors for Security

The threat of worldwide terrorism has caused law enforcement agencies, at all levels, to turn to various types of metal detectors to enhance public security. As a matter of routine, airports, court houses, legislative houses, post offices, prisons, and many other places are using various types of detection equipment to assist in their security programs in an effort to lessen the possibility of terrorism.


Body scanning detectors: Must be small enough for a single operator to run the unit over the person being searched, and sensitive enough to pickup razor blades, small knives, hatpins, and miniature guns. These items are sometimes concealed in body cavities or in the hair. Because of their small size these battery-powered "wand scanners" have to be used very close to the area being searched.

The antenna size does not allow for a large area of concentration by the magnetic field, and so, although it works the same as the large detectors its area of capture is small. Walk-through units: As a person passes through these systems they are scanned for weapons. bombs, and any contraband. Because of the unit's size the antennas are larger and the signal is greater, so the effectiveness is total. No metal can be concealed from these state-of-the-art detectors. Even metal implants in a person's body triggers these units to the consternation of all involved.

High-end body search equipment: Recently, amplified wand devices with a power supply worn on the belt have been in use, representing another step forward in the fight against terrorism.

Future of the Metal Detector

As the technology of detection develops, the penetration will be greater and results more accurate. There will come a time when airports will be able to count the change in your pocket, and with the metal-containing bills, restaurants could find out if you have enough money in your pocket to pay for your dinner.

As in all electronic development this industry is on the threshold of its greatest technical gains, much of it, sadly, brought about by the necessity to control acts of terrorism here and around the world.

Radioman can be reached for questions at, Joe the Treasure man can be viewed at