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Presentation on theme: "Magnetometer"— Presentation transcript:

1 Magnetometer

2 Nuclear magnetic resonance - Magnetometers
Various magnetometers use NMR effects to measure magnetic fields, including proton precession magnetometers (PPM) (also known as proton magnetometers), and Overhauser magnetometers. See also Earth's field NMR.

3 Magnetometer 'Magnetometers' are measurement instruments used for two general purposes - to measure the magnetization of a magnetic material like a ferromagnet, or to measure the strength and, in some cases, the direction of the magnetic field at a point in space (also known as a 'gaussmeter' or 'survey magnetometer').

4 Magnetometer The first magnetometer was invented by Carl Friedrich Gauss in 1833 and notable developments in the 19th century included the Hall Effect which is still widely used.

5 Magnetometer - Laboratory magnetometers
Unlike survey magnetometers, laboratory magnetometers require the sample to be placed inside the magnetometer, and often the temperature, magnetic field, and other parameters of the sample can be controlled

6 Magnetometer - SQUID (Superconducting quantum interference device)
SQUIDs are a type of magnetometer used both as survey and as laboratory magnetometers. SQUID magnetometry is an extremely sensitive absolute magnetometry techniques. However SQUIDs are noise sensitive, making them impractical as laboratory magnetometers in high DC magnetic fields, and in pulsed magnets. Commercial SQUID magnetometers are available for temperatures between 300 mK and 400 Kelvin, and magnetic fields up to 7 Tesla.

7 Magnetometer - Inductive Pickup Coils
Inductive pickup coils measure the magnetization by detecting the current induced in a coil, due to the changing magnetic moment of the sample

8 Magnetometer - VSM (Vibrating Sample Magnetometer)
VSM (Vibrating Sample Magnetometers) detect the magnetization of a sample by mechanically vibrating the sample inside of an inductive pickup coil or inside of a SQUID coil

9 Magnetometer - Pulsed Field Extraction Magnetometry
Pulsed Field Extraction Magnetometry is another method making use of pickup coils to measure magnetization

10 Magnetometer - Torque Magnetometry
Magnetic torque magnetometry can be even more sensitive than SQUID magnetometry. However, magnetic torque magnetometry doesn’t measure magnetism directly as all the previously mentioned methods do. Magnetic torque magnetometry instead measures the torque τ acting on a sample’s magnetic moment μ as a result of a uniform magnetic field B, τ=μ×B.

11 Magnetometer - Torque Magnetometry
A torque is thus a measure of the sample's magnetic or shape anisotropy

12 Magnetometer - Faraday Force Magnetometry
This can be circumvented by varying the gradient field independently of the applied DC field so the torque and the Faraday Force contribution can be separated, and/or by designing a Faraday Force Magnetometer that prevents the sample from being rotated.

13 Magnetometer - Optical Magnetometry
Optical magnetometry makes use of various optical techniques to measure magnetization

14 Magnetometer - Gaussmeters or Survey magnetometers
Gaussmeters measure the magnetic field at a point in space. They can be divided into scalar devices which only measure the intensity of the field and vector devices which also measure the direction of the field.

15 Magnetometer - Gaussmeters or Survey magnetometers
Gaussmeters are widely used for measuring the Earth's magnetic field and in geophysical surveys to detect magnetic anomalies of various types. They are also used militarily to detect submarines. Consequently some countries, such as the USA, Canada and Australia classify the more sensitive magnetometers as military technology, and control their distribution.

16 Magnetometer - Gaussmeters or Survey magnetometers
Gaussmeters can be used as metal detectors: they can detect only magnetic (ferrous) metals, but can detect such metals at a much larger depth than conventional metal detectors; they are capable of detecting large objects, such as cars, at tens of metres, while a metal detector's range is rarely more than 2 metres.

17 Magnetometer - Gaussmeters or Survey magnetometers
In recent years magnetometers have been miniaturized to the extent that they can be incorporated in integrated circuits at very low cost and are finding increasing use as compasses in consumer devices such as mobile phones and tablet computers.

18 Magnetometer - Early Gaussmeters
In 1833, Carl Friedrich Gauss, head of the Geomagnetic Observatory in Göttingen, published a paper on measurement of the Earth's magnetic field.

19 Magnetometer - Early Gaussmeters
It described a new instrument that consisted of a permanent bar magnet suspended horizontally from a gold fibre. The difference in the oscillations when the bar was magnetised and when it was demagnetised allowed Gauss to calculate an absolute value for the strength of the Earth's magnetic field.

20 Magnetometer - Early Gaussmeters
The Gauss (unit)|gauss, the CGS unit of magnetic flux density was named in his honour, defined as one Maxwell (unit)|maxwell per square centimeter; it equals 1×10−4 Tesla (unit)|teslas (the SI unit).

21 Gaussmeters can be divided into two basic types:
Magnetometer - Types Gaussmeters can be divided into two basic types:

22 Magnetometer - Types *Scalar (mathematics)|Scalar magnetometers measure the total strength of the magnetic field to which they are subjected, but not its direction

23 Magnetometer - Types *Euclidean vector|Vector magnetometers have the capability to measure the component of the magnetic field in a particular direction, relative to the spatial orientation of the device.

24 Magnetometer - Types A vector is a mathematical entity with both magnitude and direction. The Earth's magnetic field at a given point is a vector. A magnetic compass is designed to give a horizontal compass bearing|bearing direction, whereas a vector magnetometer measures both the magnitude and direction of the total magnetic field. Three orthogonal sensors are required to measure the components of the magnetic field in all three dimensions.

25 Magnetometer - Types They are also rated as absolute if the strength of the field can be calibrated from their own known internal constants or relative if they need to be calibrated by reference to a known field.

26 A magnetograph is a magnetometer that continuously records data.
Magnetometer - Types A magnetograph is a magnetometer that continuously records data.

27 Magnetometer - Types Magnetometers can also be classified as AC if they measure fields that vary relatively rapidly in time ( 8,000 USD) and were once widely used in mineral exploration. Three manufacturers dominate the market: GEM Systems, Geometrics and Scintrex. Popular models include G-856, Smartmag and GSM-18 and GSM-19T.

28 Magnetometer - Types For mineral exploration, they have been superseded by Overhauser and Caesium instruments, both of which are fast-cycling, and do not require the operator to pause between readings.

29 Magnetometer - Overhauser effect magnetometer
An Overhauser magnetometer produce readings with a 0.01 nT to 0.02 nT standard deviation while sampling once per second.

30 Magnetometer - Caesium vapour magnetometer
The optically pumped caesium vapour magnetometer is a highly sensitive (300fT/Hz0.5) and accurate device used in a wide range of applications. It is one of a number of alkali vapours (including rubidium and potassium) that are used in this way, as well as helium.

31 Magnetometer - Caesium vapour magnetometer
The device broadly consists of a photon emitter containing a caesium light emitter or lamp, an absorption chamber containing caesium vapour, a buffer gas through which the emitted photons pass and a photon detector, arranged in that order.

32 Magnetometer - Caesium vapour magnetometer
This theoretically perfect magnetometer is now functional and so can begin to make measurements.

33 Magnetometer - Caesium vapour magnetometer
In the most common type of caesium magnetometer, a very small AC magnetic field is applied to the cell

34 Magnetometer - Caesium vapour magnetometer
Both methods lead to high performance magnetometers.

35 Magnetometer - Applications
The caesium magnetometer is typically used where a higher performance magnetometer than the proton magnetometer is needed. In archaeology and geophysics, where the sensor sweeps through an area and many accurate magnetic field measurements are often needed, the caesium magnetometer has advantages over the proton magnetometer.

36 Magnetometer - Applications
The caesium magnetometer's faster measurement rate allows the sensor to be moved through the area more quickly for a given number of data points. Caesium magnetometers are insensitive to rotation of the sensor while the measurement is being made.

37 Magnetometer - Applications
The lower noise of the caesium magnetometer allows those measurements to more accurately show the variations in the field with position.

38 Magnetometer - Vector magnetometers
Vector magnetometers measure one or more components of the magnetic field electronically. Using three orthogonal magnetometers, both azimuth and dip (inclination) can be measured. By taking the square root of the sum of the squares of the components the total magnetic field strength (also called total magnetic intensity, TMI) can be calculated by Pythagoras's theorem.

39 Magnetometer - Vector magnetometers
Vector magnetometers are subject to temperature drift and the dimensional instability of the ferrite cores. They also require levelling to obtain component information, unlike total field (scalar) instruments. For these reasons they are no longer used for mineral exploration.

40 Magnetometer - Rotating coil magnetometer
The magnetic field induces a sine wave in a rotating coil. The amplitude of the signal is proportional to the strength of the field, provided it is uniform, and to the sine of the angle between the rotation axis of the coil and the field lines. This type of magnetometer is obsolete.

41 Magnetometer - Hall effect magnetometer
The most common magnetic sensing devices are Solid state (electronics)|solid-state Hall effect sensors. These sensors produce a voltage proportional to the applied magnetic field and also sense polarity. They are used in applications where the magnetic field strength is relatively large, such as in anti-lock braking systems in cars which sense wheel rotation speed via slots in the wheel disks.

42 Magnetometer - Magnetoresistive devices
These are made of thin strips of permalloy (NiFe magnetic film) whose electrical resistance varies with a change in magnetic field. They have a well-defined axis of sensitivity, can be produced in 3-D versions and can be mass-produced as an integrated circuit. They have a response time of less than 1 microsecond and can be sampled in moving vehicles up to 1,000 times/second. They can be used in compasses that read within 1°, for which the underlying sensor must reliably resolve 0.1°.

43 Magnetometer - Fluxgate magnetometer
Fluxgate magnetometers were invented in the 1930s by Victor Vacquier at Gulf Research Laboratories. Vacquier applied them during World War II as an instrument for detecting submarines, and after the war confirmed the theory of plate tectonics by using them to measure shifts in the magnetic patterns on the sea floor.

44 Magnetometer - Fluxgate magnetometer
A fluxgate magnetometer consists of a small, magnetically susceptible core wrapped by two coils of wire

45 Magnetometer - Fluxgate magnetometer
A wide variety of sensors are currently available and used to measure magnetic fields. Fluxgate compasses and gradiometers measure the direction and magnitude of magnetic fields. Fluxgates are affordable, rugged and compact. This, plus their typically low power consumption makes them ideal for a variety of sensing applications. Gradiometers are commonly used for archaeological prospecting and unexploded ordnance (UXO) detection such as the German military's popular Foerster.

46 Magnetometer - Fluxgate magnetometer
The typical fluxgate magnetometer consists of a sense (secondary) coil surrounding an inner drive (primary) coil that is wound around permeable core material

47 Magnetometer - Fluxgate magnetometer
There are additional factors that affect the size of the resultant signal. These factors include the number of turns in the sense winding, magnetic permeability of the core, sensor geometry and the gated flux rate of change with respect to time. Phase synchronous detection is used to convert these harmonic signals to a DC voltage proportional to the external magnetic field.

48 Magnetometer - SQUID magnetometer
SERF atomic magnetometers demonstrated in laboratories so far reach competitive noise floor but in relatively small frequency ranges.

49 Magnetometer - SQUID magnetometer
Geophysical surveys use SQUIDS from time to time, but the logistics of cooling the SQUID are much more complicated than other magnetometers that operate at room temperature.

50 Magnetometer - Spin-exchange relaxation-free (SERF) atomic magnetometers
At sufficiently high atomic density, extremely high sensitivity can be achieved. Spin-exchange-relaxation-free (SERF) atomic magnetometers containing potassium, caesium or rubidium vapor operate similarly to the caesium magnetometers described above, yet can reach sensitivities lower than 1 fT Hz-½. The SERF magnetometers only operate in small magnetic fields. The Earth's field is about 50 Tesla (unit)|µT; SERF magnetometers operate in fields less than 0.5 µT.

51 Magnetometer - Spin-exchange relaxation-free (SERF) atomic magnetometers
The technology can also produce very small magnetometers that may in the future replace coils for detecting changing magnetic fields

52 Magnetometer - Uses Gaussmeters have a very diverse range of applications, including locating objects such as submarines, sunken ships, hazards for tunnel boring machines, hazards in coal mines, unexploded ordnance, toxic waste drums, as well as a wide range of mineral deposits and geological structures

53 Magnetometer - Uses Depending on the application, magnetometers can be deployed in spacecraft, aeroplanes (fixed wing magnetometers), helicopters (stinger and bird), on the ground (backpack), towed at a distance behind quad bikes (sled or trailer), lowered into boreholes (tool, probe or sonde) and towed behind boats (tow fish).

54 Magnetometer - Archaeology
Magnetometers are also used to detect archaeological sites, shipwrecks and other buried or submerged objects. Fluxgate gradiometers are popular due to their compact configuration and relatively low cost. Gradiometers enhance shallow features and negate the need for a base station. Caesium and Overhauser magnetometers are also very effective when used as gradiometers or as single-sensor systems with base stations.

55 Magnetometer - Archaeology
The TV program Time Team popularised 'geophys', including magnetic techniques used in archaeological work to detect fire hearths, walls of baked bricks and magnetic stones such as basalt and granite. Walking tracks and roadways can sometimes be mapped with differential compaction in magnetic soils or with disturbances in clays, such as on the Great Hungarian Plain. Ploughed fields behave as sources of magnetic noise in such surveys.

56 Magnetometer - Auroras
Magnetometers can give an indication of auroral activity before the light from the Auroral light|aurora becomes visible. A grid of magnetometers around the world constantly measures the effect of the solar wind on the Earth's magnetic field, which is then published on the K-index.

57 Magnetometer - Coal exploration
Whilst magnetometers can be used to help map basin shape at a regional scale, they are more commonly used to map hazards to coal mining, such as basaltic intrusions (Dike (geology)|dykes, sill (geology)|sills and volcanic plugs) that destroy resources and are dangerous to longwall mining equipment. Magnetometers can also locate zones ignited by lightning and map siderite (an impurity in coal).

58 Magnetometer - Coal exploration
The best survey results are achieved on the ground in high-resolution surveys (with approximately 10 m line spacing and 0.5 m station spacing). Bore-hole magnetometers using a Ferret can also assist when coal seams are deep, by using multiple sills or looking beneath surface basalt flows.

59 Magnetometer - Coal exploration
Modern surveys generally use magnetometers with Global Positioning System|GPS technology to automatically record the magnetic field and their location. The data set is then corrected with data from a second magnetometer (the base station) that is left stationary and records the change in the Earth's magnetic field during the survey.

60 Magnetometer - Directional drilling
Magnetometers are used in directional drilling for oil or gas to detect the azimuth of the drilling tools near the drill. They are most often paired with accelerometers in drilling tools so that both the inclination and azimuth of the drill can be found.

61 Magnetometer - Military
For defensive purposes, navies use arrays of magnetometers laid across sea floors in strategic locations (i.e. around ports) to monitor submarine activity. The Russian 'Goldfish' (titanium submarines) were designed and built at great expense to thwart such systems (as pure titanium is non-magnetic).

62 Magnetometer - Military
Military submarines are degaussed by passing through large underwater loops at regular intervals in a bid in order to escape detection by sea-floor monitoring systems, magnetic anomaly detectors and mines that are triggered by magnetic anomalies

63 Magnetometer - Military
Submarines tow long sonar arrays to detect ships, and can even recognise different propeller noises. The sonar arrays need to be accurately positioned so they can triangulate direction to targets (e.g. ships). The arrays do not tow in a straight line, so fluxgate magnetometers are used to orient each sonar node in the array.

64 Magnetometer - Military
Fluxgates can also be used in weapons navigation systems, but have been largely superseded by GPS and ring laser gyroscopes.

65 Magnetometer - Military
Magnetometers such as the German Forster are used to locate ferrous ordnance. Caesium and Overhauser magnetometers are used to locate and help clean up old bombing/test ranges.

66 Magnetometer - Military
UAV payloads also include magnetometers for a range of defensive and offensive tasks.

67 Magnetometer - Mineral exploration
Magnetometric surveys can be useful in defining magnetic anomalies which represent ore (direct detection), or in some cases gangue minerals associated with ore deposits (indirect or inferential detection). This includes iron ore, magnetite, hematite and often pyrrhotite.

68 Magnetometer - Mineral exploration
First world countries such as Australia, Canada and USA invest heavily in systematic airborne magnetic surveys of their respective continents and surrounding oceans, using airplanes such as the Shrike Commander.

69 Magnetometer - Mineral exploration
to assist with map geology and in the discovery of mineral deposits

70 Magnetometer - Mineral exploration
Where targets are shallow ( 200 m), aeromag anomalies may be followed up with ground magnetic surveys on 10m to 50 m line spacing with 1 m station spacing in order to give the best detail (2 to 10 m pixel grid) (or 25 times the resolution prior to drilling).

71 Magnetometer - Mineral exploration
Magnetic fields from magnetic bodies of ore fall off with the inverse distance cubed (dipole target), or at best inverse distance squared (magnetic monopole target). One analogy to the resolution-with-distance is a car driving at night with lights on. At a distance of 400 m one sees one glowing haze, but as it approaches, two headlights, and then the left blinker, are visible.

72 Magnetometer - Mineral exploration
There are many challenges interpreting magnetic data for mineral exploration. Multiple targets mix together like multiple heat sources and, unlike light, there is no magnetic telescope to focus fields. The combination of multiple sources is measured at the surface. The geometry, depth or magnetisation direction (remanence) of the targets are also generally not known, and so multiple models can explain the data.

73 Magnetometer - Mineral exploration
Potent by Geophysical Software Solutions [] is a leading magnetic (and gravity) interpretation package used extensively in the Australian exploration industry.

74 Magnetometer - Mineral exploration
Magnetometers assist mineral explorers both directly (i.e. gold mineralisation associated with magnetite, diamonds in kimberlite pipes) and, more commonly, indirectly, such as by mapping geological structures conducive to mineralisation (i.e. shear zones and alteration haloes around granites).

75 Magnetometer - Mineral exploration
Airborne Magnetometers detect the change in the Earth's magnetic field using sensors attached to the aircraft in the form of a stinger or by towing a magnetometer on the end of a cable. The magnetometer on a cable is often referred to as a bomb because of its shape. Others call it a bird.

76 Magnetometer - Mineral exploration
Because hills and valleys under the aircraft will cause the magnetic readings to rise and fall, a radar altimeter is used to keep track of the transducer's deviation from the nominal altitude above ground. There may also be a camera that takes photos of the ground. The location of the measurement is determined by also recording a GPS.

77 Magnetometer - Oil exploration
Seismic methods are preferred to magnetometers for oil exploration although magnetic methods can give a preliminary idea.

78 Magnetometer - Magnetic surveys
Systematic surveys can be used to in searching for mineral deposits or locating lost objects. Such surveys are divided into:

79 Magnetometer - Magnetic surveys
* Aeromagnetic survey

80 Magnetometer - Magnetic surveys
Aeromag datasets for Australia can be downloaded from the [ GADDS database].

81 Magnetometer - Gradiometer
Because nearly equal values are being subtracted, the noise performance requirements for the magnetometers is more extreme.

82 Magnetometer - Gradiometer
Gradiometers enhance shallow magnetic anomalies and are thus good for archaeological and site investigation work. They are also good for real-time work such as unexploded ordnance location. It is twice as efficient to run a base station and use two (or more) mobile sensors to read parallel lines simultaneously (assuming data is stored and post-processed). In this manner, both along-line and cross-line gradients can be calculated.

83 Magnetometer - Position control of magnetic surveys
In traditional mineral exploration and archaeological work, grid pegs placed by theodolite and tape measure were used to define the survey area. Some UXO surveys used ropes to define the lanes. Airborne surveys used radio triangulation beacons, such as Siledus.

84 Magnetometer - Position control of magnetic surveys
Non-magnetic electronic hipchain triggers were developed to trigger magnetometers. They used rotary shaft encoders to measure distance along disposable cotton reels.

85 Magnetometer - Position control of magnetic surveys
Modern explorers use a range of low-magnetic signature GPS units, including Real-Time Kinematic GPS.

86 Magnetometer - Heading errors in magnetic surveys
Magnetic surveys can suffer from noise coming from a range of sources. Different magnetometer technologies suffer different kinds of noise problems.

87 Magnetometer - Heading errors in magnetic surveys
Heading errors are one group of noise. They can come from three sources:

88 Magnetometer - Heading errors in magnetic surveys
Some total field sensors give different readings depending on their orientation. Magnetic materials in the sensor itself are the primary cause of this error. In some magnetometers, such as the vapor magnetometers (caesium, potassium, etc.), there are sources of heading error in the physics that contribute small amounts to the total heading error.

89 Magnetometer - Heading errors in magnetic surveys
Console noise comes from magnetic components on or within the console. These include ferrite in cores in inductors and transformers, steel frames around LCD's, legs on IC chips and steel cases in disposable batteries. Some popular MIL spec connectors also have steel springs.

90 Magnetometer - Heading errors in magnetic surveys
Operators must take care to be magnetically clean and should check the 'magnetic hygiene' of all apparel and items carries during a survey. Acubra hats are very popular in Australia, but their steel rims must be removed before use on magnetic surveys. Steel rings on notepads, steel capped boots and steel springs in overall eyelets can all cause unnecessary noise in surveys. Pens, mobile phones and stainless steel implants can also be problematic.

91 Magnetometer - Heading errors in magnetic surveys
The magnetic response (noise) from ferrous object on the operator and console can change with heading direction because of induction and remanence. Aeromagnetic survey aircraft and quad bike systems can use special compensators to correct for heading error noise.

92 Magnetometer - Heading errors in magnetic surveys
Heading errors look like herringbone patterns in survey images. Alternate lines can also be corrugated.

93 Magnetometer - Image processing of magnetic data
Recording data and image processing is superior to real-time work because subtle anomalies often missed by the operator (especially in magnetically noisy areas) can be correlated between lines, shapes and clusters better defined. A range of sophisticated enhancement techniques can also be used. There is also a hard copy and need for systematic coverage.

94 NMR - Magnetometers Various magnetometers use NMR effects to measure magnetic fields, including Magnetometer#Proton precession magnetometer|proton precession magnetometers (PPM) (also known as proton magnetometers), and Magnetometer#Overhauser_magnetometer|Overhauser magnetometers. See also Earth's field NMR.

95 Proton magnetometer The 'proton magnetometer', also known as the Magnetometer#Proton_precession_magnetometer|proton precession magnetometer (PPM), uses the principle of Earth's field NMR|Earth's field nuclear magnetic resonance (EFNMR) to measure very small variations in the Earth's magnetic field, allowing ferrous objects on land and at sea to be detected.

96 Proton magnetometer It is used in land-based archaeology to map the positions of demolished walls and buildings, and at sea to locate wrecked ships, sometimes for recreational diving.

97 Proton magnetometer PPMs were once widely used in mineral exploration. They have largely been superseded by Magnetometer#Overhauser effect magnetometer|Overhauser effect magnetometers and alkali vapour (Magnetometer#Caesium vapor magnetometer|cesium, rubidium, potassium) or helium magnetometers, which sample faster and are more sensitive.

98 Proton magnetometer - Principles of operation
A direct current flowing in a solenoid creates a strong magnetic field around a hydrogen-rich fluid (kerosine, and decane is popular, and even water can be used), causing some of the protons to align themselves with that field

99 Proton magnetometer - Principles of operation
[ Requirements for obtaining high accuracy with proton magnetometers]

100 Proton magnetometer - Principles of operation
The frequency of Earth's field NMR for protons varies between approximately 900Hz near the equator to 4.2kHz near the geomagnetic poles. These magnetometers can be moderately sensitive if several tens of watts are available to power the aligning process. If measurements are taken once per second, standard deviations in the readings is in the 0.01 nT to 0.1 nT range, and variations of about 0.1 nT can be detected.

101 Proton magnetometer - Principles of operation
For hand/backpack carried units, PPM sample rates are typically limited to less than one sample per second. Measurements are typically taken with the sensor held at fixed locations at approximately 10 meter increments.

102 Proton magnetometer - Principles of operation
The two main sources of measurement errors are magnetic impurities in the sensor, errors in the measurement of the frequency and ferrous material on the operator and the instruments, as well as rotation of the sensor as a measurement is taken.

103 Proton magnetometer - Principles of operation
Portable instruments are also limited by sensor volume (weight) and power consumption. PPMs work in field gradients up to 3,000 nT m−1 which is adequate from most mineral exploration work. For higher gradient tolerance such as mapping banded iron formations and detecting large ferrous objects Overhauser magnetometers can handle 10,000 nT m−1 and Caesium magnetometers can handle 30,000 nT m−1.

104 Proton magnetometer - Proton magnetometer in archaeology
In 1959, with the support of the Society, Black purchased a magnetometer built specifically for archaeological work from the Oxford Archaeometric Laboratory.

105 Proton magnetometer - Proton magnetometer in archaeology
This work, which was the first systematic use of a proton magnetometer for archaeological research in North America, was reported by both Johnston and by Black.

106 Proton magnetometer - Further reading
*Black, G. A. and Johnston, R. B., A Test of Magnetometry as an Aid to Archaeology, American Antiquity, Vol. 28, pp , 1962.

107 Proton magnetometer - Further reading
*Black, G. A., Angel Site: An Archaeological Historical, and Ethnological Study, 2 vols., Indiana Historical Society, Indianapolis, 1967.

108 Proton magnetometer - Further reading
*Johnston, R. B., Proton Magnetometry and its Application to Archaeology: An Evaluation at Angel Site, Indiana Historical Society, Prehistory Research Series, Vol. IV, No. II, 1962.

109 Proton magnetometer - Further reading
*Smekalova T. N., Voss O., Smekalov S. L. Magnetic Surveying in Archaeology. More than 10 years of using the Overhauser GSM-19 gradiometer, Wormianum 2008.

110 Magnetic immunoassay - Magnetometers
A simple instrument can detect the presence and measure the total magnetic signal of a sample, however the challenge of developing an effective MIA is to separate naturally occurring magnetic background (noise) from the weak magnetically labeled target (signal)

111 Magnetic immunoassay - Magnetometers
Beyond this requirement, MIA that exploits the non-linear magnetic properties of magnetic labels Magnetic Immunoassays, P.I.Nikitin, P.M

112 Magnetic immunoassay - Magnetometers
This technology,makes magnetic immunoassay possible in a variety of formats such as:

113 Magnetic immunoassay - Magnetometers
*vertical flow tests allowing for the interrogation of rare analytes (such as bacteria) in large-volume samples

114 Magnetic immunoassay - Magnetometers
It was also described for in vivo applications Quantitative real-time in vivo detection of magnetic nanoparticles by their nonlinear magnetization, M. Nikitin, M. Torno, H. Chen, A. Rosengart, P. Nikitin Journal of Applied Physics (2008) 103, 07A304 and for multiparametric testing.

115 Vibrating sample magnetometer
A 'vibrating sample magnetometer' or VSM is a scientific instrument that measures magnetic properties, invented in 1955 by Simon Foner at Lincoln Laboratory MIT

116 SPICAV - Magnetometer 'MAG': The magnetometer is designed to measure the strength of Venus's magnetic field and the direction of it as affected by the solar wind and Venus itself

117 MEMS magnetometer - Introduction
Magnetic field sensors|Magnetic field sensing can be categorized into four general typesLenz, J., Edelstein, A.S., Magnetic sensors and their applications

118 MEMS magnetometer - Introduction
There are many approaches for magnetic sensing, including Hall effect sensor, magneto-diode, magneto-transistor, Magnetoresistance|AMR magnetometer, Giant magnetoresistance|GMR magnetometer, magnetic tunnel junction magnetometer, magneto-optical sensor, Lorentz force based Microelectromechanical systems|MEMS sensor, Electron tunneling|Electron Tunneling based MEMS sensor, MEMS compass, Nuclear precession magnetic field sensor, optically pumped magnetic field sensor, fluxgate magnetometer, search coil magnetic field sensor and SQUID magnetometers|SQUID magnetometer

119 MEMS magnetometer - Lorentz-force-based MEMS sensor
This type sensor relies on the mechanical motion of the MEMS structure due to the Lorentz force acting on the current-carrying conductor in the magnetic field

120 MEMS magnetometer - Voltage sensing
Beroulle et al.Beroulle, V.; Bertrand, Y.; Latorre, L.; Nouet, P

121 MEMS magnetometer - Voltage sensing
Herrera-May et al.Herrera-May, A.L.; García-Ramírez, P.J.; Aguilera-Cortés, L.A.; Martínez-Castillo, J.; Sauceda-Carvajal, A.; García-González, L.; Figueras-Costa, E

122 MEMS magnetometer - Voltage sensing
Kádár et al.Kádár, Z.; Bossche, A.; Sarro, P.M.; Mollinger, J.R

123 MEMS magnetometer - Voltage sensing
Emmerich et al.Emmerich, H.; Schöfthaler, M. Magnetic field measurements with a novel surface micromachined magnetic-field sensor. IEEE Tans. Electron Dev. 2000, 47, fabricated the variable capacitor array on a single silicon substrate with comb-figure structure. The reported sensitivity is 820 Vrms/T with a resolution 200 nT at the pressure level of 1mbar.

124 MEMS magnetometer - Frequency shift sensing
Another type of Lorentz force based MEMS magnetic field sensor utilize the shift of mechanical resonance due to the Lorentz force applying to certain mechanical structures.

125 MEMS magnetometer - Frequency shift sensing
Sunier et al.Sunier, R.; Vancura, T.; Li, Y.; Kay-Uwe, K.; Baltes, H.; Brand, O

126 MEMS magnetometer - Frequency shift sensing
Bahreyni et al.Bahreyni, B.; Shafai, C

127 MEMS magnetometer - Optical sensing
The optical sensing is to directly measure the mechanical displacement of the MEMS structure to find the external magnetic field.

128 MEMS magnetometer - Optical sensing
Micromachined polysilicon resonating xylophone bar magnetometer

129 MEMS magnetometer - Optical sensing
Keplinger et al.Keplinger, F.; Kvasnica, S.; Hauser, H.; Grössinger, R

130 MEMS magnetometer - When the temperature increases, the Young’s modulus of the material used to fabricate the moving structure decreases

131 Spacecraft magnetometer
There are ongoing missions using magnetometers, including attempts to define the shape and activity of Saturn's core

132 Spacecraft magnetometer
Magnetometers were taken to the Moon during the later Apollo 16|Apollo missions

133 Spacecraft magnetometer
Spacecraft magnetometers basically fall into three categories: fluxgate, search-coil and ionized gas magnetometers. The most accurate magnetometer complexes on spacecraft contain two separate instruments, with a helium ionized gas magnetometer used to calibrate the fluxgate instrument for more accurate readings. Many later magnetometers contain small ring-coils oriented at 90° in two dimensions relative to each other forming a triaxial framework for indicating direction of magnetic field.

134 Spacecraft magnetometer - Magnetometer types
Magnetometers for non-space use evolved from the 19th to mid-20th centuries, and were first employed in spaceflight by Sputnik 3 in A main constraint on magnetometers in space is the availability of power and mass. Magnetometers fall into 3 major categories: the fluxgate type, search coil and the ionized vapor magnetometers. The newest type is the Nuclear Overhauser effect|Overhauser type based on nuclear magnetic resonance technology.

135 Spacecraft magnetometer - Fluxgate magnetometers
Fluxgate magnetometers are used for their electronic simplicity and low weight. There have been several types of fluxgate used in spacecraft, which vary in two regards. Primarily better readings are obtained with three magnetometers, each pointing in a different direction. Some spacecraft have instead achieved this by rotating the craft and taking readings at 120° intervals, but this creates other issues. The other difference is in the configuration, which is simple and circular.

136 Spacecraft magnetometer - Fluxgate magnetometers
Venera 4, Venera 5|5, and Venera 6|6 also carried magnetometers on their trips to Venus, although they were not placed on the landing craft.

137 Spacecraft magnetometer - Vector sensors
This spacecraft was equipped with a single vector-fluxgate magnetometer.

138 Spacecraft magnetometer - Search-coil magnetometer
NASA The benefit of these magnetometers is that they measure alternating magnetic field and so can resolve changes in magnetic fields quickly, many times per second

139 Spacecraft magnetometer - Search-coil magnetometer
In 1997 the US created the Fast Auroral Snapshot Explorer|FAST that was designed to investigate aurora phenomena over the poles.[ A-04 Tri-Axial Fluxgate and Search-coil Magnetometers - FAST Mission] National Space Science Data Center, NASA And currently it is investigating magnetic fields at 10 to 30 Earth radii with the THEMIS satellites[ A Search coil magnetometer - Themis-A] National Space Science Data Center, NASA THEMIS, which stands for Time History of Events and Macroscale Interactions during Substorms is an array of five satellites which hope to gather more precise history of how magnetic storms arise and dissipate.[ A Themis-A] National Space Science Data Center, NASA

140 Spacecraft magnetometer - Heavy metal mdash; scalar
The magnetometer was fouled accidentally which caused it to overheat, it worked for a period of time but 52 h into the mission transmission went dead and was not regained.[ A-01 RB-Vapor and Fluxgate Magnetometers] National Space Science Data Center, NASA Ranger 1 and 2 carried a rubidium vapor magnetometer, failed to reach lunar orbit.

141 Spacecraft magnetometer - Helium
Similar in accuracy to the triaxial flux-gated magnetometers this device produced more reliable data.

142 Spacecraft magnetometer - Other types
'Magnetometer#Overhauser_magnetometer|Overhauser magnetometer' provides extremely accurate measurements of the strength of the magnetic field. The Orsted (satellite) uses this type of magnetometer to map the magnetic fields over the surface of the earth.

143 Spacecraft magnetometer - Other types
On the Vanguard 3 mission (1959) a 'proton processional magnetometer' was used to measure geomagnetic fields. The proton source was hexane.[ A-01 Proton Processional Magnetometer] National Space Science Data Center, NASA

144 Spacecraft magnetometer - Configurations of magnetometers
Ironically satellites launched more the 20 years ago still have working magnetometers in places where it would take decades to reach today, at the same time the latest equipment is being used to analyze changes in the Earth here at home.

145 Spacecraft magnetometer - Uniaxial
Search coil magnetometers were used on Pioneer 1, Explorer 6, Pioneer 5, and Deep Space 1.

146 Spacecraft magnetometer - Diaxial
Explorer 10 had two fluxgate magnetometers but is technically classified as a dual technique since it also had a rubidium vapor magnetometer.

147 Spacecraft magnetometer - Triaxial
(ALSEP).[ C Lunar Surface Magnetometer - Apollo-12 Lunar module] National Space Science Data Center, NASA[ C-04 Lunar Surface Magnetometer] National Space Science Data Center, NASA The magnetometer continued to work several months after that return module departed. As part of the Apollo 14 ALSEP, there was a portable magnetometer.

148 Spacecraft magnetometer - Triaxial
The MESSENGER mission has triaxial ring-coil magnetometer with a range of +/ mT and a sensitivity of 0.02 mT, still in progress, the mission is designed to get detailed information about Mercurian magnetosphere.[ A MESSENGER] Space Science Data Center, NASA] The first use of spherical magnetometer in three axis configuration was on the Orsted (satellite).

149 Spacecraft magnetometer - Dual technique
Each type of magnetometer has its own built in 'weakness'. This can result from the design of the magnetometer to the way the magnetometer interacts with the spacecraft, radiation from the sun, resonances, etc. Using completely different design is a way to measure which readings are the result of natural magnetic fields and the sum of magnetic fields altered by spacecraft systems.

150 Spacecraft magnetometer - Dual technique
The other device is a vector/scalar helium magnetometer.[ SPACECRAFT - Cassini Orbiter Instruments - MAG] The RCFGM is mounted 5.5 m out on an 11 m boom with the helium device at the end.

151 Spacecraft magnetometer - Dual technique
Explorer 6 (1959) used a search coil magnetometer to measure the gross magnetic field of the Earth and vector fluxgate.,[ Experiments Explorer 6] National Space Science Data Center, NASA however because of induced magnetism is the space craft the fluxgate sensor became saturated and did not send data. Future missions would attempt to place magnetometers further away from the space craft.

152 Spacecraft magnetometer - Dual technique
This satellite and Grm-A1 carried a scalar cesium vapor magnetometer and vector fluxgate magnetometers.[ A-01 Scalar Magnetometer Magsat mission] National Space Science Data Center, NASA[ A-02 Vector Magnetometer Magsat mission] National Space Science Data Center, NASA The Grm-A1 satellite carrier the magnetometer on 4 meter boom

153 Spacecraft magnetometer - Dual technique
The CSC fluxgate magnetometer is located inside the body and associated with a star tracking device

154 Spacecraft magnetometer - By Mounting
The simplest magnetometer implementations are mounted directly to their vehicles. However, this places the sensor close to potential interferences such as vehicle currents and ferrous materials. For relatively insensitive work, such as compasses (attitude sensing) in Low Earth orbit, this may be sufficient.

155 Spacecraft magnetometer - By Mounting
Magnetometer booms for vector instruments must be rigid, to prevent additional flexing motions from appearing in the data

156 Spacecraft magnetometer - By Mounting
Some vehicles mount magnetometers on simpler, existing appendages, such as specially-designed solar arrays (e.g., Mars Global Surveyor, Juno (spacecraft)|Juno. This saves the cost and mass of a separate boom. However, a solar array must have its cells carefully implemented and tested to avoid becoming a Electromagnet|contaminating field.

157 Attitude control - Magnetometer
A magnetometer is a device that senses magnetic field strength and, when used in a three-axis triad, magnetic field direction. As a spacecraft navigational aid, sensed field strength and direction is compared to a map of the Earth's magnetic field stored in the memory of an on-board or ground-based guidance computer. If spacecraft position is known then attitude can be inferred.

158 Proton precession magnetometer
The 'proton magnetometer', also known as the 'proton precession magnetometer' (PPM), uses the principle of Earth's field NMR|Earth's field nuclear magnetic resonance (EFNMR) to measure very small variations in the Earth's magnetic field, allowing ferrous objects on land and at sea to be detected.

159 Proton precession magnetometer - Principles of operation
A direct current flowing in a solenoid creates a strong magnetic field around a hydrogen-rich fluid (kerosine and decane are popular, and even water can be used), causing some of the protons to align themselves with that field

160 Proton precession magnetometer - Proton magnetometer in archaeology
This was the first systematic use of a proton magnetometer for archaeological research in North America.

161 Ingo Swann - Magnetometer psychokinesis tests
Swann said he focused his attention on the interior of the magnetometer and was getting nothing.Mind-Reach: Scientists Look at Psychic Ability by Russell Targ Harold Puthoff, A Delta book, Dell Publishing Co

162 Ingo Swann - Magnetometer psychokinesis tests
Then there are different versions of the following events

163 Ingo Swann - Magnetometer psychokinesis tests
More supportive sources say that Heberd supports Puthoff's version that in the second instance Heberd suggested he would be more impressed if Swann could stop the field change altogether. Heberd denies he told James Randi that he never suggested it.

164 Ingo Swann - Magnetometer psychokinesis tests
[ A Skeptical Look at James Randi by Michael Prescott] Swann recalled he heard, “Can you do that again?” from Puthoff. Swann said his feats frightened some doctoral candidates, claiming that two virtually ran from the room and one collided with a totally visible structure support.

165 Ingo Swann - Magnetometer psychokinesis tests
No evidence exists to support Puthoff's claim that the effect was repeated at will under observation.

166 Ingo Swann - Magnetometer psychokinesis tests
Though Swann was to spend a year at SRI, in their book, Targ and Puthoff present no further data and, Swann did not mention he was involved in any other PK experiments with the magnetometer than those that occurred and were recorded on June 6, 1972.

167 Ingo Swann - Magnetometer psychokinesis tests
Immediately after, Puthoff wrote a brief paper in a draft form

168 Magnetic field sensors - Types of magnetometer
Magnetometers used to study the Earth's magnetic field may express the vector components of the field in terms of declination (the angle between the horizontal component of the field vector and magnetic north) and the inclination (the angle between the field vector and the horizontal surface).

169 Magnetic field sensors - Types of magnetometer
Absolute magnetometers measure the absolute magnitude or vector magnetic field, using an internal calibration or known physical constants of the magnetic sensor. Relative magnetometers measure magnitude or vector magnetic field relative to a fixed but uncalibrated baseline. Also called variometers, relative magnetometers are used to measure variations in magnetic field.

170 Magnetic field sensors - Types of magnetometer
Survey magnetometers are used to measure magnetic fields in geomagnetic surveys; they may be fixed base stations, as in the Intermagnet|INTERMAGNET network, or mobile magnetometers used to scan a geographic region.

171 For More Information, Visit: The Art of Service

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