Types of Magnetometers

Scalar vs. Vector Magnetometers

Before comparing specific types, it's important to understand the two fundamental categories:

Your smartphone magnetometer is a vector type — it gives you three separate readings (X, Y, Z) from which the total field and compass heading are calculated.

Hall Effect Sensors

The Hall effect sensor is by far the most common magnetometer in the world. Billions are manufactured annually for use in smartphones, automotive systems, industrial equipment, and consumer electronics.

• Type: Vector
• Sensitivity: ~1 µT (microtesla)
• Size: Tiny (1-3 mm chip)
• Cost: Very low ($0.10 - $5)
• Power: Very low (milliwatts)
• Best for: Compasses, proximity sensing, consumer devices, basic metal detection

Learn how Hall effect sensors work in Chapter 2.

Magnetoresistive Sensors (AMR/GMR/TMR)

These sensors detect magnetic fields by measuring changes in electrical resistance. Three sub-types exist, each offering different performance levels:

TMR sensors are increasingly replacing Hall effect sensors in high-end smartphones because they offer much better sensitivity and lower noise while maintaining small size and low power consumption.

Fluxgate Magnetometers

The fluxgate is the go-to instrument for professional geophysical surveys, navigation systems, and space missions. It offers an excellent balance of sensitivity, size, and cost.

• Type: Vector
• Sensitivity: ~0.1 nT (nanotesla)
• Size: Small to medium (finger-sized sensor + electronics)
• Cost: Moderate ($100 - $5,000)
• Power: Moderate (100 mW - 1 W)
• Best for: Geophysical surveys, spacecraft, navigation, archaeology, unexploded ordnance detection

Proton Precession Magnetometers

A proton precession magnetometer measures the precession frequency of hydrogen protons in a fluid, which is directly proportional to the total magnetic field strength.

• Type: Scalar
• Sensitivity: ~0.1-1 nT
• Size: Medium (handheld sensor + console)
• Cost: Moderate ($1,000 - $10,000)
• Power: Moderate
• Best for: Geological surveys, establishing absolute field measurements, base station monitoring

Key advantage: the measurement is based on fundamental physical constants, so it never drifts and doesn't need calibration. This makes it ideal as an absolute reference standard.

Overhauser Magnetometers

An improved version of the proton precession magnetometer that uses the Overhauser effect (dynamic nuclear polarization) to dramatically boost the proton signal.

• Type: Scalar
• Sensitivity: ~0.01 nT
• Size: Medium
• Cost: Moderate to high
• Best for: Geomagnetic observatories, high-precision surveys, military applications

Overhauser magnetometers produce a much stronger signal than standard proton precession types, allowing faster and more sensitive measurements while using less power. They're used in magnetic observatories worldwide for continuous field monitoring.

Optically Pumped Magnetometers

These high-end sensors use laser light and alkali metal vapor (cesium or rubidium) to achieve extraordinary sensitivity. They're among the most sensitive magnetometers that operate at room temperature.

• Type: Scalar (some vector variants exist)
• Sensitivity: ~1 pT (picotesla) — 0.001 nT
• Size: Medium to large
• Cost: High ($10,000 - $100,000+)
• Best for: Space missions, military (submarine/mine detection), airborne surveys, medical imaging

SQUID Magnetometers

Superconducting Quantum Interference Devices are the ultimate sensitivity champions. Nothing else can detect fields as faint as a SQUID.

• Type: Vector
• Sensitivity: ~1 fT (femtotesla) — 0.000001 nT
• Size: Large (requires cryogenic cooling)
• Cost: Very high ($50,000 - $1,000,000+)
• Power: High (cryogenic cooling system)
• Best for: Magnetoencephalography (brain imaging), particle physics, geophysical research, materials science

The extreme sensitivity comes at a price: SQUIDs must be cooled to near absolute zero with liquid helium, requiring bulky and expensive cryogenic equipment.

Search Coil (Induction) Magnetometers

One of the simplest types: a coil of wire that generates voltage when the magnetic field through it changes (Faraday's law of induction).

• Type: Vector (measures field changes, not static fields)
• Sensitivity: Varies widely (depends on coil design)
• Size: Small to large
• Cost: Very low to moderate
• Best for: Measuring AC magnetic fields, electromagnetic interference, geophysical research (pulsations)

Unlike other types, search coils can only detect changing magnetic fields — they produce zero output in a constant field. This makes them ideal for measuring alternating fields and magnetic waves.

Full Comparison Table

Here's a comprehensive side-by-side comparison of all major magnetometer types: