The moment you walk inside a railway station or an airport, or check into a hotel, a guy with a wide smile will likely move a piece of electronic equipment all around your body. Sometimes, the process takes much longer, particularly when one is entering an official or government building. Most of you have already guessed that the piece of equipment I’m talking about is a metal detector.
Tale of Invention
The year was 1881. When US President James A. Garfield was shot, the bullet made its way into his body and got stuck there. Unfortunately, doctors were not able to locate it. Alexander Graham Bell (yes, the telephone guy) immediately put together an electromagnetic metal-locating device called an induction balance, which was based on an earlier invention. Unfortunately the bullet couldn’t be found and the President later died. Bell’s device worked to a certain degree, however, and that spontaneous device is said to be the first electromagnetic metal locator.
How does a metal detector work?
You wouldn’t believe it, but it’s actually quite simple.
There is a battery on top of the detector that activates the transmitter circuit (red), which passes electricity from the handle to the transmitter coil at the bottom. As current flows through the transmitter coil, a magnetic field is created around it. Now, when the detector is moved around and there is a metal object (grey object in the image) near the bottom of the detector, the magnetic field of the transmitter coil penetrates through the metal object.
Now, this magnetic field creates a current inside the object, which in turn creates another magnetic field, which the receiver coil (blue) picks up, thereby causing the electricity to flow to the receiver coil on the top, which triggers a buzzing sound.
Bingo! You’ve found something!
This awesome invention has helped us avoid innumerable terrorist attacks over the years. Whenever there is a bomb threat, a bomb squad descends over the area with metal detectors. This handheld device is hovered over the target area and when it detects a metallic object, even if it is kept inside something or buried underground, it beeps to announce that there is some undesirable metal object in the vicinity.
How Deeply Can a Metal Detector Sense?
That answer depends on many factors, including the size, shape and type of the material. Also, larger objects are easier to locate than small ones. Furthermore, the duration for which the object has been underground also impacts its ability to be discovered by the metal detector, as objects buried underground for a long period of time tend to become corroded or decomposed, which makes them difficult to discover.
So, if you were planning to buy an expensive metal detector and go around looking for hidden treasure buried thousands of years ago, you’re in for some real disappointment.
Meanwhile, you can definitely put these detector to other good uses. Below is one such discovery using a metal detector: