10
Here’s where the second coil comes into play. This “receiver
coil” sits at the end of the detector and is connected to a
loudspeaker or other signaling mechanism. The two coils
are electrically balanced when there is no metal present. But
when the magnetic field around the metallic object interrupts
the electrical current from the coil, it triggers the signal—a
click or beep—that lets you know you have found something.
As the transmitter coil gets closer to the metal, the magnetic
field in the metal gets stronger and the beep gets louder.
• Why do you have to keep the metal detector moving?
Because Maxwell’s Equations tell us that the electromagnetic
relationship works with changing magnetic and electrical
fields, it is important to keep the metal detector’s sensor
moving over the ground.
• How deep can a metal detector’s sensors go?
The depth depends on the strength of the signals (how
powerful your device is) as well as the nature of the soil
you are sweeping. Typically, hobbyists’ detectors can sense
objects between eight and twenty inches deep.
• Why are older objects harder to find?
Metal that has oxidized or corroded does not create as strong
a magnetic field, making the object less likely to be detected.
• How can a metal detector tell what metal is buried?
More sophisticated detectors are able to discriminate
between different metals based on minute differences in the
how the metal responds to the electrical current.