Bobine di Helmholtz. Helmholtz coils Low-frequency Magnetic Field Susceptibility testing. Helmholtz coils. Helmholtz coils is a candidate test apparatus for. graisseur à casque m, graisseur à chapeau mobile m Helmholtz: ~ coll n PHYS bobine de Helmholtz f; – free energy n PHYS fonction de Helmholtz f, énergie.
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A Helmholtz coil is a device for producing a region of nearly uniform magnetic fieldnamed after the German physicist Hermann von Helmholtz. It consists of two electromagnets on the same axis. Besides creating magnetic fields, Helmholtz coils are also used in scientific apparatus to cancel external magnetic fields, such as the Earth’s magnetic field. Each coil carries an equal electric current in the same direction. In some applications, a Helmholtz coil is used to cancel out the Earth’s magnetic fieldproducing a region with a magnetic field intensity much closer to zero.
The calculation of the exact magnetic field at any point in space is mathematically complex and involves the study of Bessel functions. By symmetry, the odd-order terms in the expansion are zero. The calculation detailed below gives the exact value of the magnetic field at the center point.
If the radius is Rhelmhoptz number of turns in each coil is hepmholtz and the current through the coils is Ithen the magnetic field B at the midpoint boibne the coils will be given by. Start with the formula for the on-axis field due to a single wire loop which is itself derived from the Biot—Savart law: The Helmholtz coils consists of n turns of wire, so the equivalent current in a one-turn coil is n times the current I in the n -turn coil. Substituting nI for I in the above formula gives the field for an n -turn coil:.
From symmetry, the field strength at the dee will be twice the single coil value:. Most Helmholtz coils use DC direct current to produce a static magnetic field.
Many applications and experiments require a time-varying magnetic field.
These applications include magnetic field susceptibility tests, scientific experiments, and biomedical studies the interaction between magnetic field and helmhoptz tissue. The required magnetic fields are usually either pulse or continuous sinewave.
An AC Helmholtz coil driver is needed to generate the required time-varying magnetic field. The waveform amplifier driver must be able to output high AC current to produce the magnetic field.
Use the above equation in the mathematics section to calculate the coil current for a desired magnetic field, B. Then calculate the required Helmholtz coil driver amplifier voltage: Generating a static magnetic field is relatively helmhholtz the strength of the field is proportional to the current.
Generating a high-frequency magnetic field is more challenging.
The coils are inductors, and their impedance increases proportionally with frequency. To provide the same field intensity at twice the frequency requires twice the voltage across the coil. Instead of directly driving the coil with a high voltage, vobine series resonant circuit may be used to provide the high voltage. The capacitance is chosen fe resonate the coil at the desired frequency. Only the coils parasitic resistance remains. This method only works at frequencies close to the resonant frequency; to generate the field at other frequencies requires different capacitors.
To improve the uniformity of the field in the space inside the coils, additional coils can be added around the outside.
This is sometimes called a Maxwell coil. From Wikipedia, the free encyclopedia.
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