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How does a proton-precession magnetometer measure the strength of Earth’s magnetic field?
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geomagnetic field
The magnetic field of a bar magnet has a simple configuration known as a dipole field. Close to Earth's surface this field is a reasonable approximation of the actual field.
A proton-precession magnetometer measures the strength of Earth’s magnetic field by utilizing the magnetic and gyroscopic properties of protons within a fluid, such as gasoline.1
The measurement process follows these steps:
- Alignment: The magnetic moments of the protons are first aligned by applying a strong magnetic field generated by an external coil.1
- Precession: This external field is then abruptly turned off. As the protons attempt to align themselves with Earth’s magnetic field, they precess—or gyrate—around the field vector because they possess both spin and magnetic properties.1
- Detection: The frequency of this precession is directly dependent on the magnitude of Earth’s magnetic field. The external coil acts as a sensor, detecting a weak voltage induced by the gyration of the protons.1
- Calculation: The period of this gyration is determined electronically. Because the precession frequency is proportional to the field strength, this data allows the device to calculate the magnitude of the field with high sensitivity.12
This method is highly valued in geophysics because it does not require precise alignment, making it ideal for field surveys.1