How does a metal detector work in simple terms?

A metal detector's transmitter coil pushes an oscillating electric current through a wire loop, which creates an alternating magnetic field. When that field passes through a metal object in the ground, it induces a small electric current — called an eddy current — inside the metal, and that eddy current generates its own faint secondary magnetic field. The detector's receiver coil picks up this secondary field, and the control box converts the signal into the tone and target-ID number you hear and see. No metal object, no secondary field, no signal — the whole system runs on electromagnetic induction, the same principle Michael Faraday described in 1831.

What's the difference between VLF and pulse induction detectors?

VLF (Very Low Frequency) detectors run a continuous alternating current, typically 3-30 kHz, and compare the phase shift between the transmitted and returned signal to identify what kind of metal caused it — that phase-shift comparison is what makes target ID and discrimination possible. Pulse induction (PI) detectors instead send short, powerful pulses and measure how long the induced eddy current takes to decay; PI ignores ground mineralization almost completely, which is why gold-prospecting machines like the Minelab GPX 6000 use it, but most PI machines can't tell a nail from a nickel the way a VLF detector can.

How does a detector tell the difference between a coin and a bottle cap?

Through phase shift, not sound alone. Every metal returns a signal at a slightly different phase angle relative to the transmitted signal — highly conductive metals like silver and copper shift one way, low-conductivity metals like iron and foil shift another. VLF detectors measure that phase angle and map it to a target-ID number (usually 0-99), which is exactly what our target ID guide breaks down number by number. The detector isn't identifying the object visually; it's reading how strongly and in what phase the object's eddy current responds.

Why does a metal detector lose depth in mineralized or salt-heavy ground?

Because iron-rich soil and wet salt sand generate their own faint eddy currents, exactly like a real target does, and a VLF detector's receiver coil can't fully separate that background signal from a genuine target. Manufacturers build ground balance controls specifically to cancel this false signal — our ground balance guide covers manual versus automatic tracking — and multi-frequency machines like the Minelab Equinox 900 fight the same problem by running several frequencies simultaneously so at least one cuts through the mineralization.

What does a search coil actually do?

The coil is both the transmitter and the receiver in one housing: an outer winding sends the oscillating field into the ground, and an inner winding (in DD and concentric designs) picks up the returning signal. Coil shape decides how that field is shaped — a Double-D coil overlaps two windings into a wedge field that rejects ground noise better, while a concentric coil nests circular windings into a tighter, more precise cone. Our coil guide covers when each shape wins and how coil size trades depth for target separation.

Is a more expensive detector using fundamentally different physics?

No — every consumer detector still runs on the same electromagnetic induction principle Faraday described nearly 200 years ago. What separates a $180 machine from a $1,700 one is signal processing: multi-frequency engines like Minelab's Multi-IQ transmit several frequencies at once instead of one, faster microprocessors recover from overlapping targets quicker, and better ground balance tracking holds performance in tougher soil. The physics is identical; the electronics reading that physics get dramatically more capable at the top of the range.

How Does a Metal Detector Work? Electromagnetic Induction Explained (2026)

Quick Answer: Every metal detector works through electromagnetic induction: a transmitter coil creates an oscillating magnetic field, that field induces a tiny electric current (an eddy current) in any metal object it passes through, and a receiver coil picks up the faint secondary magnetic field that current generates. VLF detectors (3-30 kHz, the technology in most consumer machines) measure the phase shift of that returning signal to identify the metal type and drive target ID; pulse induction (PI) detectors measure how long the induced current takes to decay instead, which ignores ground mineralization almost entirely but sacrifices most discrimination. No detector “sees” metal — it reads the electromagnetic echo the metal creates.

Ask ten detectorists how their machine works and most will describe what the display shows, not what’s happening in the ground. The actual mechanism is simpler than the marketing around it: one coil sends a signal, a buried object bends it, a second coil catches the bend. Everything else — target ID, discrimination, ground balance, depth — is what a detector’s electronics do with that one basic physical event.

The core mechanism: electromagnetic induction

Step	What happens	Component involved
1. Transmit	An oscillating current runs through the transmitter winding, creating an alternating magnetic field that radiates into the ground	Transmitter coil
2. Induce	The magnetic field passes through a buried metal object and induces a small "eddy current" inside it	Target object
3. Re-radiate	That eddy current generates its own faint secondary magnetic field, distinct from the original transmitted field	Target object
4. Receive	The receiver winding detects the secondary field and passes the signal to the control box for processing	Receiver coil
5. Interpret	The processor compares the phase, strength, and timing of the returned signal to known metal signatures and outputs a tone and target-ID number	Control box / microprocessor

This is the same electromagnetic principle Michael Faraday first described in 1831, and it hasn’t changed since the first practical metal detectors reached hobbyists in the mid-20th century. What has changed is everything downstream of step 5 — modern processors can compare a returning signal against dozens of stored metal signatures in milliseconds, which is what makes numeric target ID and multi-target separation possible on a $300 machine today.

VLF vs. pulse induction vs. BFO: the three technologies

Technology	How it identifies metal	Strength	Weakness	Typical machine
VLF (Very Low Frequency)	Phase-shift comparison between transmitted and returned signal	Real discrimination and target ID	Loses depth in heavily mineralized ground	Garrett ACE 300, Nokta Simplex Ultra
Multi-frequency VLF	Several frequencies transmitted simultaneously, results blended	Discrimination that holds up in salt and mineralized soil	Higher cost, more processing to learn	Minelab Equinox 900
Pulse Induction (PI)	Decay time of the induced eddy current after a pulse	Ignores ground mineralization almost completely; maximum raw depth	Little to no discrimination — digs nearly everything	Minelab GPX 6000, Garrett Sea Hunter Mark II
BFO (Beat Frequency Oscillation)	Audible beat frequency between two oscillators, disturbed by metal	Simple, inexpensive circuitry	Minimal discrimination or depth by modern standards	Mostly obsolete; found in toy-grade detectors only

VLF is the technology behind the overwhelming majority of detectors sold today, from $150 beginner machines to $1,700 flagships, because phase-shift discrimination is what lets a detector tell a nickel from a pull-tab before you dig. Pulse induction trades that discrimination away for raw depth and total immunity to ground mineralization, which is exactly why our gold detecting guide and waterproof detecting guide both lean on PI machines for mineralized gold ground and deep salt-water dive work respectively — situations where VLF’s ground noise problem gets worse than its discrimination advantage is worth.

Minelab Equinox 900 — Best Multi-Frequency VLF

Multi-IQ simultaneous multi-frequency · $999

Transmits multiple frequencies at once instead of a single VLF tone, so at least one frequency keeps working through mineralized or salt-heavy ground.
Full numeric target ID plus adjustable discrimination — the phase-shift processing this guide describes, refined to a 0-99 scale.
Same physics as an entry-level VLF machine, dramatically more processing power reading it.

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Garrett ACE 300 — Best Single-Frequency VLF for Learning the Basics

8 kHz VLF, digital target ID · ~$279

Single 8 kHz frequency keeps the phase-shift signal simple to read while you're learning what target-ID numbers mean.
Digital Target ID cursor shows exactly where a target lands on the 0-99 conductivity scale in real time.
The same core mechanism as the Equinox 900, without multi-frequency's added complexity or cost.

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What decides how deep the signal reaches

The physics in the table above explains whether a detector can sense a target at all; four practical variables decide how deep:

Target size and conductivity. A large, highly conductive object (a silver dollar, a copper pipe) generates a stronger eddy current than a small or low-conductivity one (a thin gold ring, an iron nail), so it’s detectable from farther away — our depth guide breaks this down with Garrett’s own published coil-size figures.
Coil size and shape. A bigger coil radiates a larger magnetic field and reaches deeper on the same target, at the cost of separating nearby targets from each other — the coil guide covers the DD-vs-concentric and size trade-offs in full.
Ground mineralization. Iron-rich soil and wet salt sand generate their own faint eddy currents that mimic real targets, which is the exact noise ground balance exists to cancel — see the ground balance guide.
Frequency. Lower frequencies penetrate deeper but respond less to small or low-conductivity targets; higher frequencies are more sensitive to small gold and jewelry but lose some depth. This is why gold-specific machines often run higher frequencies than general-purpose coin detectors.

The bottom line

Strip away the marketing and every metal detector — from a $120 toy-grade machine to a $5,999 pulse-induction gold rig — runs on the same electromagnetic induction Faraday documented in 1831: a transmitted field induces a current in metal, that current re-radiates its own field, and a receiver coil reads it. VLF detectors turn that signal’s phase shift into the discrimination and target ID most hobbyists rely on; pulse induction machines trade that discrimination for depth and immunity to mineralized ground. Understanding which technology is under the hood explains why a detector behaves the way it does in a given soil — and it’s the same mechanism our coil, ground balance, and target ID guides each dig into from a different angle. New to the hobby entirely? Start with our beginner’s guide before worrying about the physics.