Two Ways in Magnetic Gradiometer

Two Ways in Magnetic Gradiometer
Two Ways in Magnetic Gradiometer - RJ Cooper et al.

Atomic magnetometers can filter out background fields to detect weak, nearby radio frequency sources using two new geometries. Researchers have used a variety of techniques to measure magnetic fields, from the first magnetic compasses made of natural magnetite to modern cryogenically cooled superconducting quantum interference devices. Now, two more have been added to these by Robert Cooper of George Mason University in Virginia and his colleagues. They are the first to demonstrate "intrinsic radio frequency gradiometers," variations of a high-precision equipment known as an optically pumped atomic magnetometer. These instruments are suitable for detecting local radio frequency sources that are faint and indistinct from background areas.

How Gradiometer and Magnetometer Work

Earth's magnetic field is measured with a magnetometer and a gradiometer. Local variations in this area, including ore deposits or iron-containing substances such as UXO, cause variations. By measuring this local deviation from the general magnetic field, it is possible to determine the position of ferrous objects and soil layers. A magnetometer called a gradiometer measures changes in the magnetic field (the gradient of the field). This increases measurement accuracy and sensitivity to localized changes in the Earth's magnetic field compared to a magnetometer. Both measurement techniques can be applied to water.

If we go back to our article;

The core of an optically pumped atomic magnetometer consists of a gas of alkali atoms whose spins are aligned by the optical pump, a circularly polarized laser. The spin axis of these atoms is disrupted by the presence of an external magnetic field, which also appears as a shift in the polarization direction of the probe beam, a second, linearly polarized laser transmitted through gas.

In Cooper and his team's instruments, the repeated passage of the probe beam through alkaline gas maximizes the instrument's sensitivity to weak fields. In one configuration, a high-power probe beam travels through the gas in a single M-shaped path, passing twice over two steam cells.

In the other, a low-power beam passes 46 times through a single steam cell along overlapping V-shaped channels.

The researchers place a half-wave plate, an optical component, in the beamline of both devices that rotates the polarization direction of the light 180°. This shift makes field gradients from weak, local sources stand out because it cancels out any polarization signals imprinted on the beam by a uniform background field. Applications such as long-range radio frequency communications and navigation, low-field nuclear magnetic resonance and dark matter exploration can all benefit from measuring such sources.

Source: physics.aps.org/articles/v15/s162

Günceleme: 28/11/2022 10:32

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