Last Updated On July 9th, 2018
Wondering what type of metals can metal detectors detect? While you may have seen those yesteryear movies detecting every metal that you can imagine, it cannot.
Metal Detectors and Its Use
When we hear the word “metal detectors”, various things come to our mind. Metal detectors detect the presence of metallic objects with the help of electromagnetic field. They come in several forms like hand-held, walk through, and vehicle mounted. They are used at entrances to airports, malls, offices and other places requiring security.
So How Does It Work?
A metal detector contains a coil inside. When electricity is passed thorough the coil, then a magnetic field is generated.
- When you move the detector over the metal then a magnetic field, other than the one present in the metal, is generated.
- The detector picks up this second magnetic field.
- The detector has one more coil called the receiver coil which connects to the loudspeaker.
- The second magnetic field cuts through the coil. So when you move the detector over the metal, the electricity flows through the coil making the beep sound in the detector.
Types of Metal Detectable By Metal Detectors
All types of metals are detectable, but their strength of detectability varies.
1. Ferrous metals
These metals contain iron and steel. They can be easily attracted to a magnet and very are conductive. It is because of these properties that they are easily detectable by metal detectors. These metals tend to increase the inductance of the search-coil which makes it an easy detection by any simple metal detector.
Some examples of ferrous metals are paper clips, staplers, screws, nails and various other things.
2. Non-Ferrous Metals
Unlike ferrous metals, they do not contain iron. They are non-magnetic and more resistant to corrosion than ferrous metals. Though they have no magnetic properties but they are good or excellent conductors which make them a relatively easy metal to detect.
You would require approximately more than 50% of a non-ferrous metal to be equally dateable to a ferrous metal.
Some examples of non-ferrous metals are aluminium, copper, gold and silver.
One surprising thing is that chewing gum wrappers can also set off a metal detector. The wrappers are made of aluminium foils which are easily detectable by the metal detectors.
3. Stainless Steel
These metals come is various forms ranging from magnetic to completely non-magnetic. The conductivity of this metal can also vary but is generally low. These properties make stainless steel a poor metal detector.
In general, a stainless steel should be having a 1.5 to 2 time the surface area of a ferrous metal to be detected by a metal detector. Sometimes the properties of the stainless steel are modified by machining. This increases the magnetic effect making it an easy detector by metal detectors.
The non-magnetic stainless steel not detectable is type 302, 304 and 316.
So, what type of metals can metal detectors detect?
Today, there are continuous efforts being made in order to detect all type of metals. New technologies have come into place that almost and always detects all types of metals. So, next time when going through security do remember to put coins, watches and all the small things in the tray.