Magnetometer

6 Key excerpts on "Magnetometer"

• 

  eBook - ePub

  Space Microsystems and Micro/Nano Satellites

  • Zheng You(Author)
  • 2017(Publication Date)
  • Butterworth-Heinemann

    (Publisher)

  Chapter 9

  Magnetometer Technology

  Abstract

  The Magnetometer is a sensor for measuring magnetic induction. The Magnetometer plays a large role in all types of aircraft and spacecraft. This chapter introduces the concept, function, and application of Magnetometers, and the application of microMagnetometers in Nanosat. The chapter presents how to design, fabricate, and calibrate a MEMS Magnetometer as an example of an AMR Magnetometer.

  Keywords

  Magnetometer; MEMS; geomagnetic field; spacecraft; AMR

  9.1 Summary

  9.1.1 Concept, Function, and Application of Magnetometers

  The Magnetometer, also known as a magnetic sensor, is a sensor for measuring magnetic induction (magnetic field intensity), which is an important sensor component in all types of aircraft and spacecraft. It also has been widely used in other fields, such as industry, agriculture, national defense, as well as biology, medicine, aerospace, interplanetary research, etc., and currently almost no field of technology is immune from magnetic field measurement [1 ,2] .

  The Magnetometer plays a more important role in the development, research, operation, management, and maintenance of defense equipment and weapons. For example, magnetic sweeping, ship degaussing, weapons search, magnetic wave communication, magnetic detection, magnetic guided missiles, as well as underwater mines, landmines, bomb detectors, and magnetic navigation, etc., are all inseparable from magnetic field measurement techniques. In addition, the Magnetometer has the characteristic that other types of sensors do not have of being able to work normally under severe and limited conditions.

  In the field of aeronautics, the Magnetometer can be used to measure the geomagnetic field vector information of the position of the aircraft body, such as airplanes and satellites. And, according to the reference model for the Earth’s magnetic field and local magnetic field, the angle information of a certain precision can be obtained through an algorithm, therefore, the Magnetometer is widely used in aircraft attitude determination systems, especially in microsatellites, such as nanosatellites and picosatellites, etc. [3 ,4]

  Sign up to read

  Learn more about book
• 

  eBook - PDF

  Electrical Measurement, Signal Processing, and Displays

  • John G. Webster(Author)
  • 2003(Publication Date)
  • CRC Press

    (Publisher)

  For further information on this subject, see [8, 9]. The Fluxgate Magnetometer The fluxgate Magnetometer has been and is the workhorse of magnetic field strength instruments both on Earth and in space. It is rugged, reliable, physically small, and requires very little power to operate. These characteristics, along with its ability to measure the vector components of magnetic fields over a m m = -˚ ¸ ` ˆ fl ˜ ¨ ˛ ˝ ˝ ø ß oe oe a w c F 1 2 l l L n d t l l = + ( ) m m p 0 2 2 4 e w c m m e c a w c = + + ˚ ¸ ` ˆ fl ˜ ( ) -[ ] 1 1 2 d d t f l l f l l l l l l l l w c w c w c w c ( ) = -( ) -( ) + ( ) 1 9088 0 8672 1 1217 0 8263 2 3 . . . . Magnetic Field Measurement 12 -11 0.1 nT to 1 mT range from dc to several kHz, make it a very versatile instrument. Geologists use them for exploration and geophysicists use them to study the geomagnetic field (about 20 m T to 75 m T on the Earth’s surface). Satellite engineers use them to determine and control the attitude of spacecraft, scientists use them in their research, and the military uses them in many applications, including mine detection, vehicle detection, and target recognition. Some airport security systems use them to detect weapons. The Fluxgate The heart of the Magnetometer is the fluxgate . It is the transducer that converts a magnetic field into an electric voltage. There are many different fluxgate configurations. Two of the more popular ones are shown in Figure 12.7. A very comprehensive explanation of the fluxgate principle and the different fluxgate configurations is given in [10]. The ring core fluxgate is constructed from a thin ribbon of easily saturable ferromagnetic material, such as 4-79 Permalloy wrapped around a bobbin to form a ring or toroid. As shown in Figure 12.8, an alternating current is applied through a coil that is wound about the toroid. This creates a magnetic field that circulates around the magnetic core.

  Sign up to read

  Learn more about book
• 

  eBook - ePub

  Geophysical Electromagnetic Theory and Methods

  • Michael S Zhdanov, Michael S. Zhdanov(Authors)
  • 2009(Publication Date)
  • Elsevier Science

    (Publisher)

  Measurement of the magnetic components of the electromagnetic field is in many ways more difficult than measurement of the electric components. Many varieties of sensitive Magnetometers have come into use in geophysics; each has advantages and shortcomings which must be considered in designing any given electrical method which requires knowledge of the magnetic field.

  Magnetic balances

  The oldest form of Magnetometer is the magnetic balance, no different in principle than the compasses used by early mariners. In a magnetic balance, a magnetized piece of ferromagnetic material is suspended in such a way that the torque exerted by the ambient magnetic field on the suspended magnetic material is balanced against gravity. Figure 11.15 shows an arrangement for measuring a horizontal component of the magnetic field with a magnetic balance. A bar magnet is balanced vertically on a knife edge. The suspension of the magnet is constructed in such a way that the center of gravity is below and to the left of the suspension point. The torque exerted by the horizontal component of the magnetic field normal to the axis of the wedge on the magnetic moment of the magnet rotates the magnet until it is balanced by the force of gravity attempting to rotate the magnet about its point of suspension. In Figure 11.15 , if the strength of the horizontal component of the magnetic field increases, even slightly, the component of weight contributing to the gravitational torque, and when the magnet has rotated far enough, the two torques come into balance. In a typical sensitive magnetic balance the actual amount of rotation is small, probably less than a degree. The rotation can be detected using a light beam reflected from a mirror mounted on the magnet with the motion of the light beam being recorded on a moving strip of film.

  Figure 11.15 Principle of a magnetic balance. A magnetized rod of moment 2mL is balanced at a point slightly offset from its center of gravity. The rod rotates until the gravitational torque about the point of suspension, Mg, balances the torque imposed by the action of the horizontal component of the magnetic field on the magnet, 2mLH. The rotation needed to bring the two torques into balance is a measure of the horizontal component of magnetic field strength, H

  Sign up to read

  Learn more about book
• 

  eBook - ePub

  An Introduction to Geophysical Exploration

  • Philip Kearey, Michael Brooks, Ian Hill(Authors)
  • 2013(Publication Date)
  • Wiley-Blackwell

    (Publisher)

  magnetic variometers . There were several types, including the torsion head Magnetometer and the Schmidt vertical balance, but all consisted essentially of bar magnets suspended in the Earth’s field. Such devices required accurate levelling and a stable platform for measurement so that readings were time consuming and limited to sites on land.

  7.6.2 Fluxgate Magnetometer

  Since the 1940s, a new generation of instruments has been developed which provides virtually instantaneous readings and requires only coarse orientation so that magnetic measurements can be taken on land, at sea and in the air.

  The first such device to be developed was the fluxgate Magnetometer , which found early application during the second world war in the detection of submarines from the air. The instrument employs two identical ferromagnetic cores of such high permeability that the geomagnetic field can induce a magnetization that is a substantial proportion of their saturation value (see Section 7.2). Identical primary and secondary coils are wound in opposite directions around the cores (Fig. 7.10 ). An alternating current of 50–1000 Hz is passed through the primary coils (Fig. 7.10(a) ), generating an alternating magnetic field. In the absence of any external magnetic field, the cores are driven to saturation near the peak of each half-cycle of the current (Fig. 7.10(b) ). The alternating magnetic field in the cores induces an alternating voltage in the secondary coils which is at a maximum when the field is changing most rapidly (Fig. 7.10(c) ). Since the coils are wound in opposite directions, the voltage in the coils is equal and of opposite sign so that their combined output is zero. In the presence of an external magnetic field, such as the Earth’s field, which has a component parallel to the axis of the cores, saturation occurs earlier for the core whose primary field is reinforced by the external field and later for the core opposed by the external field. The induced voltages are now out of phase as the cores reach saturation at different times (Fig. 7.10(d) ). Consequently, the combined output of the secondary coils is no longer zero but consists of a series of voltage pulses (Fig. 7.10(e)

  Sign up to read

  Learn more about book
• 

  eBook - PDF

  Sensor Analysis for the Internet of Things

  • Michael Stanley, Jongmin Lee(Authors)
  • 2022(Publication Date)
  • Springer

    (Publisher)

  The geomagnetic field varies over the surface of the earth from approximately 25– 65 T . A Magnetometer is used to measure magnetic field strength. You can subdivide magne- tometers into vector Magnetometers and total field (scalar) Magnetometers. The former measures 14 2. SENSORS the 3D vector components of a magnetic field, whereas the latter measures the magnitude of the vector magnetic field. Alternately, you separate Magnetometers based on the physical proper- ties used to make measurements. Examples include Hall effect sensors, current sensors, and magnetoresistive sensors. The proper choice of Magnetometer type depends on the application. However, investigating all these variations is out of the scope of this book. We will focus on one recent technique—tunneling magnetic resistance (TMR), which is well suited for measuring the Earth’s magnetic field. TMR is based upon the magnetic tunnel junction (MTJ) illustrated in Fig. 2.6. The MTJ includes two magnetic layers separated by a thin insulating layer which allows tunneling when a voltage is applied. One of the two magnetic layers is called the “pinned (or, fixed) layer.” It is permanently magnetized in one direction. The other magnetic layer is called the “unpinned (or, free) layer.” As the Magnetometer moves, changes in ambient magnetic fields will affect the unpinned layer. The tunneling current is maximized when the fields of these two layers are aligned in parallel, whereas the current is minimized when they are aligned in antiparallel. The tunneling current, therefore, affects the MTJ resistance change as given by R ap NUL R p R p D 2 P 1 P 2 1 NUL P 1 P 2 ; (2.18) where R p and R ap denote the resistances when the two magnetic layers are aligned in parallel and antiparallel, respectively, and P 1 and P 2 are the spin polarizations of the two magnetic layers. Physically, each MTJ device can be optimized to sense magnetic fields in a specific di- rection.

  Sign up to read

  Learn more about book
• 

  eBook - PDF

  Thin Film Magnetoresistive Sensors

  • S Tumanski(Author)
  • 2001(Publication Date)
  • CRC Press

    (Publisher)

  Figure 3.7 The two-sensor electronic compass design and the method of the simple determination of eight magnetic field directions (Philips Technical Information). sensor system designed for compass application. In this system eight major compass directions can be detected. Typical comparators can be used to obtain eight different signals transferred to the display. Figure 3.8 presents a similar compass circuit using three sensors able to detect the direction with 30° resolution. All magnetoresistive sensors might be directly used as a Magnetometer device because their output signal is proportional to magnetic field strength. Several authors have described magnetoresistive sensors designed as magnetic field sensors 1 . But the Magnetometer, as an instrument for measuring the magnetic field, should be equipped with many additional circuits to perform calibration, compensation of the parasitic fields, correction of errors, calculation of the vectorial components etc. Actually apart from the HMR2300 digital Magnetometer of Honeywell there are no other available magnetoresistive Magnetometers (unlike for example the numerous models of Hall-sensor Magnetometers). All manufacturers of MR sensors offer many application notes allowing users to construct such instruments. Tumanski (1984) analysed and tested various circuit principles of the magnetoresistive Magnetometers. The four main ideas of such Magnetometers are presented in figure 3.9. The simplest one is the circuit with a DC supply voltage of the sensor and a direct longitudinal stabilizing field. The major drawbacks of such circuit are difficult to overcome – temperature offset drift and small immunity from the orthogonal field component. This last disadvantage may be reduced by applying the magnetic feedback technique. Thus the Magnetometer presented in figure 3.9(a) may be recommended as a simple device, with modest sensitivity and resolution, but of large frequency bandwidth.

  Sign up to read

  Learn more about book