The Hall Effects Priya

8/13/2019 The Hall Effects Priya

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Discovery

The physics behind it

Applications

Personal experiments

Richard Beck - Physics 141A, 2013 2


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Observed in 1879

Edwin Herbert Hall

Discovered 18 years before

the electron


Via Wikimedia Commons (public

domain)


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Just basics: The change in magnetic

field induces a current, the change

in intensity and direction of the

current can measure the velocity

and direction object producing the

magnetic field.


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The basic physical principle underlying

the Hall effect is the Lorentz force. When

an electron moves along a direction

perpendicular to an applied magneticfield, it experiences a force acting normal

to both directions and moves in response

to this force and the force effected by

the internal electric field


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Mobile charges pressed to one side from

Lorentz force, immobile charges unaltered

Creates internal electric potential, known asHall voltage.

For simple metals, is V =

6

Note: t refers to the thickness of the metal along the direction of the B-field


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1. Electrons2. Hall element, or Hall sensor3. Magnets4. Magnetic field5. Power source


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From Non-Destructive Testing (NDT) Resource Center


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Magnitude parameter:

In metals:

In semiconductors:



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Classical Picture: only electrons moving in

same average direction in both hole (p-type)

and electron (n-type) conductivity.

Opposite sign indicates that electrons in

valence bands move in opposite direction

than previously thought.



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Measurement can tell about charge carrier

mobility, concentration

Conversely, knowing the above allows forsensitive measurement of an external B-field

Resistant to outside contaminants unlike

optical, electromechanical testing



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This sensor measures the thickness of

nonferrous materials with 1% accuracy bysandwiching the material being measuredbetween a magnetic probe on one sideand a small target steel ball on the otherside [6].

It measures up to 10 mm. The Hall effectsensor is used to measure the magneticfield, as a dc measurement; ac Hall effectmeasurements can be made moreprecisely because they eliminate bias andare done with less noise


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Switches

Sensors

Absolute field

Differential field Special-Purpose


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Hall Effect sensors capable of switching very

fast, does not distort like capacitative or

inductive sensors

Contactless sensing



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Used expansively in rotating systems

Anti-lock brakes, motor feedback, ignition


Via Power Systems Design, Ltd. Via Draper, 2005


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Hall Effect thruster

Trap electrons in a magnetic field, electrons

ionize propellant, creates thrust



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Sensor only devise

Good only in close proximity

Must have a reference pointMagnetic field must be present

Must be calibrated


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Quantum Hall Effect

Spin Hall Effect

Anomalous Hall Effect



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Quantization of normal Hall Effect

Seen at low temperature, high magnetic field

Very precise, magnitude determined by

Landau levels and electron interaction


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Separation of electron spins in current-

carrying object, no magnetic field needed

Predicted in 1971, observed in 2004 viaemission of circularly polarized light

Universal, present in metals and

semiconductors at high and low temperature


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Ferromagnetic materials have internal

magnetic field

Much larger than normal Hall Effect, but not

well understood ; Possible Berry-phase effect


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The Hall Effects Priya