Explainer
How does a metal detector work?
The coil sends a changing magnetic field into the ground. Metal in that field sets up a weak field of its own. The coil picks it up, and the control box turns it into a tone, and on many models a target ID number.
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The parts that do the work
Three parts do the work. At the end of the shaft, the search coil sends and receives. The control box drives the coil, reads what comes back and sounds a tone. The shaft, with its handle and armrest, holds the coil over the ground.
Inside the coil sit two windings, or one that does both jobs. Garrett's ACE 400 uses an 8.5 x 11-inch DD coil, named for its two D-shaped windings that overlap in the middle.
Parts of a metal detector
- Search coil
- Shaft
- Control box
- Handle
- Armrest
02
From field to tone
On a VLF detector, current through the transmit winding makes a field that swings back and forth thousands of times a second. When the field passes through a coin, it makes small currents flow in the metal. Those currents make a field of their own, and the receiving winding picks it up.
Next, the control box compares what it sent with what it got back. The delay and strength of the reply depend on the metal, its size and its shape. The detector turns that into a tone, and on many VLF models a target ID number.
Soil answers too. Wet salt sand and mineral soil send back their own signal. That is why many detectors offer ground balance, and some a beach mode, like Beach 1 and 2 on the Equinox 900.
03
Single frequency, multi-frequency, pulse induction and ZVT
A single-frequency VLF detector sends one frequency at a time. Garrett's ACE 200 runs 6.5 kHz and reads targets on 0 to 99. Gold models run much higher: 71 kHz on the Fisher Gold Bug 2.
A multi-frequency detector sends several at once and weighs the replies. Minelab calls its version Multi-IQ on the Equinox 900, which also offers single frequencies of 4, 5, 10, 15, 20 and 40 kHz. Pulse induction sends short bursts and listens to how the reply fades. Minelab files the GPX 6000 under pulse induction, with no kHz value published. It gives the GPZ 7000 a fourth label, ZVT, short for Zero Voltage Transmission.
| Model | Technology | Frequencies | Waterproofing | Weight |
|---|---|---|---|---|
| Garrett ACE 200 | Single frequency | 6.5 kHz | CoilWaterproof part | 2.75 lb1.25 kg |
| Minelab Equinox 900 | Multi-frequencyMulti-IQ | 4-40 kHz4, 5, 10, 15, 20, 40 kHz | 16 ftDetector, IP68, 5 m | 2.8 lb1.27 kg |
| Minelab GPX 6000 | Pulse inductionGeoSense-PI | Not published | 3.3 ftCoil only, 1 m | 4.6 lb2.1 kg |
| Minelab GPZ 7000 | ZVTZVT (Zero Voltage Transmission) | Not published | 3.3 ftCoil only, 1 m | 7.32 lb3.32 kg |
Facts from the pages of Garrett and Minelab, read Oct. 16, 2026.
04
What that means when you hunt
Overlap your sweeps: the field is strongest just under the coil. When it sounds, sweep across the spot from another angle, then use a pinpointer once the hole is open.
How to sweep the coil
- Sweep side to side
- Close to the ground
- Target in the field
05
Questions
It does not know. It measures how the reply is delayed and how strong it is. Many VLF models turn that into a number, such as the 0 to 99 scale on Garrett's ACE 200. Different objects can give the same number, so dig what you are unsure of.
A single-frequency VLF detector sends a steady wave at one frequency, such as 6.5 kHz on the ACE 200. Pulse induction sends short pulses and listens to the fading reply, and Minelab publishes no kHz value for its GPX 6000.
Salt water conducts, so wet beach sand sends back a signal of its own. Ground balance, and on some models a beach mode, is there to quiet it.
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