Editing Metal detector (section)

=== Discriminators and circuits ===
The development of [[transistor]]s, discriminators, modern search coil designs, and [[Wireless|wireless technology]] significantly impacted the design of metal detectors as we know them today: lightweight, compact, easy-to-use, and deep-seeking systems. The invention of a tunable induction device was the most significant technological advancement in detectors. Two [[Electromagnetically induced acoustic noise|electro-magnetically]] tuned coils were used in this method. One coil serves as an [[Rf transmitter module|RF transmitter]], while the other serves as a receiver; in some situations, these coils may be tuned to [[Frequency|frequencies]] ranging from 3 to 100&nbsp;kHz.

Due to eddy currents induced in the metal, a signal is detected when metal is present. The fact that every metal has a different phase response when exposed to alternating current allowed detectors to differentiate between metals. Longer waves (low frequency) penetrate the ground deeper and select for high conductivity targets like [[silver]] and [[copper]], while shorter waves (higher frequency) select for low conductivity targets like [[iron]]. Unfortunately, ground [[mineralization (geology)|mineralization]] interference affects high frequency as well. This selectivity or discrimination allowed the development of detectors that can selectively detect desirable metals.

Even with discriminators, avoiding undesirable metals was difficult because some of them have similar phase responses (for example, [[Tin foil|tinfoil]] and [[gold]]), particularly in alloy form. As a result, tuning out those metals incorrectly increased the chance of missing a valuable discovery. Discriminators also had the downside of lowering the sensitivity of the devices.