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Encyclopedia > Magnetometer

A magnetometer is a scientific instrument used to measure the strength and/or direction of the magnetic field in the vicinity of the instrument. To meet Wikipedias quality standards, this article may require cleanup. ...


Earth's magnetism varies from place to place and differences in the Earth's magnetic field (the magnetosphere) can be caused by a couple of things: To meet Wikipedias quality standards, this article may require cleanup. ... A magnetosphere is the region around an astronomical object in which phenomena are dominated or organized by its magnetic field. ...

  1. The differing nature of rocks
  2. The interaction between charged particles from the sun and the magnetosphere

Contents

The Sun is the star of our solar system. ... A magnetosphere is the region around an astronomical object in which phenomena are dominated or organized by its magnetic field. ...

Uses

Magnetometers are used in geophysical surveys to find deposits of iron because they can measure the magnetic pull of iron. Magnetometers are also used to detect archeological sites, shipwrecks and other buried or submerged objects. Electrical resistance map of ancient Aphrodisias EM conductivity survey Magnetic gradiometer map of Prehistoric fire-hearths GPR survey // Overview Geophysical survey most often refers to subsurface imaging techniques used in archaeology. ... General Name, Symbol, Number iron, Fe, 26 Chemical series transition metals Group, Period, Block 8, 4, d Appearance lustrous metallic with a grayish tinge Atomic mass 55. ... An archaeological site is a place (or group of physical sites) in which evidence of past activity is preserved (either prehistoric or historic), and which has been investigated using the discipline of archaeology. ... A shipwreck is the remains of a ship after it has sunk or been beached as a result of a crisis at sea. ...


A magnetometer can also be used by satellites like GOES to measure both the magnitude and direction of the earth's magnetic field. Goes is a municipality and a city in the southwestern Netherlands, in Zuid-Beveland. ... The magnitude of a mathematical object is its size: a property by which it can be larger or smaller than other objects of the same kind; in technical terms, an ordering of the class of objects to which it belongs. ... The term direction can be applied to various topics. ...


Magnetometers are very sensitive, and can give an indication of possible auroral activity before one can even see the light from the aurora. There is a grid of magnetometers around the world constantly measuring the effect of the solar wind on the earth's magnetic field. Prism splitting light Light is electromagnetic radiation with a wavelength that is visible to the eye (visible light) or, in a technical or scientific context, electromagnetic radiation of any wavelength [citation needed]. The elementary particle that defines light is the photon. ... Aurora borealis Polar aurorae are optical phenomena characterized by colorful displays of light in the night sky. ...


Types

Magnetometers can be divided into two basic types:

  • scalar magnetometers measure the total strength of the magnetic field to which they are subjected, and
  • vector magnetometers have the capability to measure the component of the magnetic field in a particular direction.

The use of three orthogonal vector magnetometers allows the magnetic field strength, inclination and declination to be uniquely defined. Examples of vector magnetometers are fluxgates and superconducting quantum interference devices, or SQUIDs. Some scalar magnetometers are discussed below. SQUIDs, or Superconducting Quantum Interference Devices, are used to measure extremely tiny magnetic fields; they are currently the most sensitive such devices (magnetometers) known, with noise levels as low as 3 fT·Hz−½. Some processes in animals produce very small magnetic fields (typically sized between a nanotesla and a microtesla...


A magnetograph is a special magnetometer that continuously records data.


Proton precession magnetometer

One type of magnetometer is the proton precession magnetometer, which operates on the principle that protons are spinning on an axis aligned with the magnetic field. Properties [1][2] In physics, the proton (Greek proton = first) is a subatomic particle with an electric charge of one positive fundamental unit (1. ...


An inductor creates a strong magnetic field around a hydrogen-rich fluid, causing the protons to align themselves with the newly created field. The field is then interrupted, and as protons are realigned with Earth's magnetic field, spinning protons precess at a specific frequency. This produces a weak magnetic field that is picked up by the same inductor. The relationship between the frequency of the induced current and the strength of Earth's magnetic field is called the proton gyromagnetic ratio, and is equal to 0.042576 hertz per nanotesla (Hz/nT). An inductor is a passive electrical device employed in electrical circuits for its property of inductance. ... General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ... Precession refers to a change in the direction of the axis of a rotating object. ... In physics, the gyromagnetic ratio or Landé g-factor is a dimensionless unit which expresses the ratio of the magnetic dipole moment to the angular momentum of an elementary particle or atomic nucleus. ... The nanotesla (nT) is a unit of magnetic flux density equal to 10−9 tesla (unit). ...


Because the precession frequency depends only on atomic constants and the strength of the external magnetic field, the accuracy of this type of magnetometer is very good. Magnetic impurities in the sensor and errors in the measurement of the frequency are the two causes of errors in these magnetometers.


If several tens of watts are available to power the aligning process, these magnetometers can be moderately sensitive. Measuring once per second, standard deviations in the readings in the 0.01 nT to 0.1 nT range can be obtained. thank you. that was good.


Overhauser magnetometer

The Overhauser effect takes advantage of a quantum physics effect that applies to the hydrogen atom. This effect occurs when a special liquid (containing free, unpaired electrons) is combined with hydrogen atoms and then exposed to secondary polarization from a radio frequency (RF) magnetic field (i.e. generated from a RF source).


RF magnetic fields are ideal for use in magnetic devices because they are transparent to the Earth's DC magnetic field and the RF frequency is well out of the bandwidth of the precession signal (i.e. they do not contribute noise to the measuring system). Direct current (DC or continuous current) is the continuous flow of electricity through a conductor such as a wire from high to low potential. ...


The unbound electrons in the special liquid transfer their excited state (i.e. energy) to the hydrogen nuclei (i.e. protons). This transfer of energy alters the spin state populations of the protons and polarizes the liquid – just like a proton precession magnetometer – but with much less power and to much greater extent.


The proportionality of the precession frequency and magnetic flux density is perfectly linear, independent of temperature and only slightly affected by shielding effects of hydrogen orbital electrons. The constant of proportionality is known to a high degree of accuracy and is identical to the proton precession gyromagnetic constant.


Overhauser magnetometers achieve some 0.01 nT/√Hz noise levels, depending on particulars of design, and they can operate in either pulsed or continuous mode.


Cesium vapor magnetometer

A basic example of the workings of a magnetometer may be given by discussing the common "optically pumped cesium vapour magnetometer" which is a highly sensitive (0.004 nT/√Hz) and accurate device used in a wide range of applications. Although it relies on some interesting quantum mechanics to operate, its basic principles are easily explained. General Name, Symbol, Number Caesium, Cs, 55 Series Alkali metals Group, Period, Block 1(IA), 6, s Density, Hardness 1879 kg/m3, 0. ... Fig. ...


The device broadly consists of a photon emitter containing a cesium light emitter or lamp, an absorption chamber containing cesium vapour and a "buffer gas" through which the emitted photons pass, and a photon detector, arranged in that order. The word light is defined here as electromagnetic radiation of any wavelength; thus, X-rays, gamma rays, ultraviolet light, microwaves, radio waves, and visible light are all forms of light. ... General Name, Symbol, Number Caesium, Cs, 55 Series Alkali metals Group, Period, Block 1(IA), 6, s Density, Hardness 1879 kg/m3, 0. ... A gas is one of the four major phases of matter (after solid and liquid, and followed by plasma, that subsequently appear as a solid material is subjected to increasingly higher temperatures. ... In physics, the photon (from Greek φως, phōs, meaning light) is the quantum of the electromagnetic field; for instance, light. ...


Calibration

The basic principle that allows the device to operate is the fact that a cesium atom can exist in any of nine energy levels, which is the placement of electron atomic orbitals around the atomic nucleus. When a cesium atom within the chamber encounters a photon from the lamp, it jumps to a higher energy state and then re-emits a photon and falls to an indeterminate lower energy state. The cesium atom is 'sensitive' to the photons from the lamp in three of its nine energy states, and therefore eventually, assuming a closed system, all the atoms will fall into a state in which the all the photons from the lamp will pass through unhindered and be measured by the photon detector. At this stage the device can be said to be perfectly calibrated. A quantum mechanical system can only be in certain states, so that only certain energy levels are possible. ... The Electron is a fundamental subatomic particle that carries an electric charge. ... In chemistry, an atomic orbital is the region in which an electron may be found around a single atom. ... A semi-accurate depiction of the helium atom. ...


Detection

Given that this theoretically perfect magnetometer is now calibrated it can be exposed to the environment. It is easy to imagine that the environment is constantly emitting quanta of energy and that some of these will pass through the chamber. When they do, they may hit one of our cesium atoms and cause it to jump into a new energy state, which may in turn be one in which it can absorb a photon from our cesium emitter. If this is the case it will cause a decrease in the number of photons reaching our detector and this can be easily recorded. Scaling from this simple example to account for the vast number of energy transactions occurring within the cesium vapour, it is easy to see how the system works. In physics quanta is the plural of quantum. ...


Applications

When removed from an isolated environment, the cesium vapour can never be 'perfectly' calibrated and the system is subject to environmental interference as are all scalar magnetometers. However, by the application of feedback systems and an averaging of the detection rates seen in a benign environment, the instrument can be calibrated sufficiently well in a real-world environment to make it accurate and useful for detection.


SQUID magnetometer

SQUIDs, or Superconducting Quantum Interference Devices, are used to measure extremely small magnetic fields; they are currently the most sensitive vector magnetometers known, with noise levels as low as 3 fT·Hz−0.5 in commercial instruments and 0.4 fT·Hz−0.5 in experimental devices. SQUIDs, or Superconducting Quantum Interference Devices, are used to measure extremely small magnetic fields; they are currently the most sensitive such devices (magnetometers) known, with noise levels as low as 3 fT·Hz−½. While a typical fridge magnet is ~0. ...


These magnetometers require cooling with liquid helium (4.2 K) or liquid nitrogen (77 K) to operate, hence the packaging requirements to use them are rather stringent both from a thermal-mechanical as well as magnetic standpoint. SQUID magnetometers allow one to measure the magnetic fields produced by brain or heart activity (magnetoencephalography and magnetocardiography, respectively). General Name, Symbol, Number helium, He, 2 Chemical series noble gases Group, Period, Block 18, 1, s Appearance colorless Atomic mass 4. ... General Name, Symbol, Number nitrogen, N, 7 Chemical series nonmetals Group, Period, Block 15, 2, p Appearance colorless Atomic mass 14. ... Magnetoencephalography (MEG) is the measurement of the magnetic fields produced by electrical activity in the brain, usually conducted externally, using extremely sensitive devices such as SQUIDs. ... Magnetocardiography (MCG) is a technique to measure the magnetic fields produced by electrical activity in the heart using extremely sensitive devices such as the Superconducting Quantum Interference Device (SQUIDs(. If the magnetic field is measured using a multichannel device, a map of the magnetic field is obtained over the chest...


Early magnetometers

In 1833 Carl Friedrich Gauss, head of the Geomagnetic Observatory in Göttingen, published a paper entitled "On the intensity of the Earth's magnetic field expressed in absolute measure". It described a new instrument that Gauss called a "magnometer" (a term which is still occasionally used instead of magnetometer) [1]. It consisted of a permanent bar magnet suspended horizontally from a gold fibre [2]. A magnetometer is also called a gaussmeter. 1833 was a common year starting on Tuesday (see link for calendar). ... (30 April 1777 – 23 February 1855) was a German mathematician and scientist of profound genius who contributed significantly to many fields, including number theory, analysis, differential geometry, geodesy, magnetism, astronomy and optics. ... General Name, Symbol, Number gold, Au, 79 Chemical series transition metals Group, Period, Block 11, 6, d Appearance metallic yellow Atomic mass 196. ...


External links

  • Dan's Homegrown Proton Precession Magnetometer Page
  • USGS Geomagnetism Program
  • Archaeological Prospectors

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Magnetometers are very sensitive, and can give an indication of possible auroral activity before one can even see the light from the aurora.
One type of magnetometer is the proton precession magnetometer, which operates on the principle that protons are spinning on an axis aligned with the magnetic field.
A basic example of the workings of a magnetometer may be given by discussing the common "optically pumped cesium vapour magnetometer" which is a highly sensitive (0.004 nT/√Hz) and accurate device used in a wide range of applications.
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