The History of Metal Detectors
It’s been a long time since the invention of metal detectors, but there is still much to learn about them. In this blog post, we’ll take a look at what they are and their history.
What is a Metal Detector
A metal detector is a device that detects the presence of metal nearby. This can be done with an electromagnetic field created between two coils, or by detecting emitted radiation from the mineral being detected. The first metal detectors worked by amplifying the current in one coil using an electromagnet to produce a detectable signal, which was then amplified further for listening purposes.
Metal detectors come in a range of form factors, from the common handheld type to large walk-through units. They all work fairly similarly in principle: when a metal object is near enough to the detector, it will alter the current flowing through one or both coils by creating a magnetic field of its own.
These changes are then amplified and displayed or listened to through a speaker, headphones, or a visual display. By moving the coil over the area of interest, an indication will be given as to where the metals are located.
The First Metal Detector
In 1881, a young man named Alexander Graham Bell invented the metal detector as a means to locate the bullet in the body of U.S. President James Garfield. The president had been shot on July 2 and during surgery, doctors located the bullet deep inside his back, but couldn’t find it exactly. Bell suggested using a metal detector to look for the bullet, which they did and were able to successfully recover it.
He discovered that electric currents gave off waves that could be detected with a receiver attached to an electromagnet, and he named it the telephone detector. While working on his early invention, Bell noticed that the needle on his receiver occasionally made moves even though there was no call coming through. He soon realized that this was caused by the electric wires in his room, which created waves when connected to a telephone.
Bell immediately saw the potential in his invention and filed for patents to develop multiple kinds of metal detectors in 1886. The patent described how “invisible metals” like gold could be located by connecting two coils together in a circuit, and the direction of the current in one coil would indicate the location of the metal. However, no one took much interest in his ideas until he demonstrated them in 1891 at an exhibition in Minneapolis, where he successfully located coins hidden beneath boxes.
The First Practical Metal Detector
For centuries, treasure hunters have used various implements to find valuable metal buried in the ground, but none of them have been that effective or reliable – until Charles Hall invented the first practical metal detector in 1918. Using a simple telephone receiver, Hall was able to locate a metal spike driven into the ground which he eventually dug up. At the time of his discovery, no one knew exactly how it worked, but in 1976, scientists at Scripps Institution of Oceanography in La Jolla concluded that the detector operated by emitting electromagnetic pulses and monitoring variations in their echo when they struck a metal object.
The First Walk-Through Metal Detector
In 1966, a walk-through metal detector was developed by American inventor Lloyd Long. He named the device that would revolutionize security as we know it today as The Tracker. It went into commercial use in 1971 and is still used widely throughout airports, courthouses, and jails across the United States.
The First Handheld Metal Detector
In the early 1900s, it was impossible to find any handheld device that could detect metals in the ground. It took until 1950 for Professor Manfred Bowditch of Massachusetts to invent a metal detector that could be used by an individual for this purpose. The metallic detection unit he invented did not need a power supply and was simply a combination of a capacitor coil connected to a crystal radio set.
The Evolution of the Metal Detector
There are several different types of metal detectors on the market today, but some of the most common units are:
- Very Low Frequency (VLF) Metal Detector – This is a highly sensitive unit with an increased frequency range in which it can detect small metal objects that are very far underground. It also has the ability to easily pick up sources of electrical interference without triggering many false alarms.
- Pulse Induction (PI) Metal Detector – This device uses a series of electromagnetic pulses to determine the metal object’s position by measuring the time it takes for the pulse to reach the ground and return. The advantage of this type of unit is that it can detect large objects as deep as several feet underground and even through walls and other solid objects.
Modern Hobby Metal Detectors
One of the most famous hobby detectors is the Fisher F44, which is compact and easy to use. It has an LCD display that shows the depth of any detected metals at all times and an automatic ground balance that makes it easy to find different types of metals even in difficult soil conditions.
Another great hobby unit is the Garrett AT Pro, which uses a PI system with adjustable sensitivity and discrimination levels. It also has a waterproof design that allows it to be used in just about any type of weather condition, along with an external speaker jack for more effective volume control.
In addition to metal detecting on dry land, there are several machines that allow users to find metals underwater.
Underwater Metal Detectors
The most popular among underwater metal detectors is the Garrett Sea Hunter, which was specifically designed for deep-water use with a 20-hour battery pack and bright LCD display. The unit has a maximum detection depth of 100 feet below the surface and comes with three preset programs that can be adjusted for sensitivity and discrimination levels.
Another is the Fisher 1280-X, which is specifically designed for use in shallow water and comes with an attached microphone that allows it to detect metal on land as well. It uses a fixed-coil design at depths of up to 20 feet underwater. Metal Pursuits has an excellent article about the best underwater metal detectors, be sure to check it out.
These are just some of the many hobby metal detectors available on the market today, and there are even units for specific types of metals such as gold and silver. The modern world offers many different options to those looking to get involved with the hobby, which is just another benefit of living in a culture that has embraced technology over the centuries.
Conclusion
In this blog post, we’ve gone over the history of metal detectors and how they have evolved to meet our modern needs.
There are a few different types of units on the market today: VLF (very low frequency) metal detectors, Pulse Induction (PI) metal detectors, and hobby units such as the Fisher F44 or Garrett AT Pro.
In addition to detecting on dry land, hobby metal detectors can be used underwater as well. The most popular underwater metal detector is the Garrett Sea Hunter, which comes with a 20-hour battery, bright LCD display, and 100-foot detection depth.
There are also metal detectors designed for specific metals such as gold or silver.
We hope you enjoyed learning about these devices!
