Gauss meter
Fluxgate Magnetometer
Superconducting Quantum Interferometer (SQUID)
Atomic Magnetometer
Proton Magnetometer
Optical Pump Magnetometer
Flux meter
Magnetoresistor
Magnetic resonance method
magneto-optical effect
Focus on the first 6 types (1-6) of magnetometers, because these 6 types of magnetometers are more commonly used, and the last 4 types (7-10) are only briefly introduced.
1. Gaussmeter
1 Principles of Physics
Gaussmeter is an instrument based on the principle of the Hall effect (as shown in the figure below). The Hall probe of the Gauss meter generates a voltage due to the Hall effect in the magnetic field. After measuring the voltage, the magnetic field to be measured can be calculated.
2 Instrument parameters
Instrument accuracy: generally 0.05%-2% of the range
(Remarks: Meter accuracy = maximum value of absolute error/meter range × 100%)
Measuring range: generally 1 G ~ 1 T magnitude
It is suitable for measuring relatively large magnetic fields, such as hundreds of Gauss or even Tesla, and measuring permanent magnets is a very good tool; however, it is not suitable for measuring weak magnetic fields, such as measuring the geomagnetic field, which is very inaccurate.
Meter bandwidth
Generally 0Hz ~ dozens of KHz
3 Hall probes
The size of the probe is relatively small, about 1 to 2mm, and the measured magnetic field is the average value within this size range
Measurement dimension It is easy to integrate a three-dimensional Hall probe within a size of 1 to 2 mm, so the general Gauss meter can measure the three-dimensional magnetic field, which is the advantage of the Gauss meter.
4 Instrument applications
Used to measure the magnetic field of magnets; more suitable for measuring relatively large magnetic fields.
Hall Effect
When the magnetic field is perpendicular to the semiconductor sheet, the electrons are deflected by the Lorentz force, creating a potential difference (called the Hall voltage) on both sides.
2. Fluxgate magnetometer
Instrument parameters
The resolution is generally in the order of 0.1nT, which is far beyond the reach of a Gauss meter!
In the measurement process of the fluxgate magnetometer, a positive measurement is sometimes used, and then the probe is reversed to measure once. Data processing: add the two results and divide by 2. The purpose is to eliminate the magnetic field offset.
Meter Accuracy 0.5% of reading
The measuring range of the instrument is in the order of 0.1nT to tens of thousands of nT, covering the range of the geomagnetic field. But it cannot measure such a strong magnetic field as a permanent magnet!
Instrument bandwidth DC 0Hz ~ 1KHz magnitude
The residual magnetism of the probe is in the order of 1nT. When you buy this, you must explain it clearly to the manufacturer! Otherwise, the residual magnetism of the probe provided by the manufacturer is often relatively large ~10nT, such as the China Metrology Institute.
Points to pay attention to when purchasing: Explain with the company whether to measure the DC magnetic field or the AC magnetic field. I have used a fluxgate magnetometer purchased from China Metrology Institute with only a few Hz bandwidth. If you want to measure power frequency magnetic field noise, you need to purchase a high bandwidth fluxgate magnetometer.
In particular, we need to measure the power frequency magnetic field noise, and we must purchase a high-bandwidth fluxgate magnetometer. I have seen an engineering team help a university laboratory to detect ambient power frequency magnetic field noise, using a "Stefan Mayer Instruments" three-dimensional fluxgate magnetometer, the noise is less than 1pT/root Hz
Probe size
The size of the probe depends on whether it is a uniaxial or triaxial magnetic field measurement. Uniaxial probes are much smaller than triaxial probes.
Three-dimensional probe: generally in the order of 2cm ~ 3cm, you can refer to Bartingdon (Bartingdon, this is the best brand in the world, but the price is relatively high)
Uniaxial probe: generally on the order of 1cm, or even smaller, the one I have used is 8mm.
3 Principles of Physics
To understand how a fluxgate magnetometer works:
First of all, we need to clarify a question "what is a hysteresis loop"?
Secondly, figure out the nonlinearity of the hysteresis loop (also known as the magnetic saturation phenomenon, or the fluxgate effect, or the transformer effect);
Finally, the principle of fluxgate magnetometer is deduced through Faraday's law of electromagnetic induction;
