How to select helmholtz coil magnetic field, solenoid coil magnetic field and electromagnet

            At present, the commonly used type of magnetic field generator, generally have fixed magnetic field, Helmholtz coil, spiral pipe coil, and electromagnetic field generator. Fixed magnetic field, standard magnetic field is composed of a plurality of permanent magnets, through the magnetic field loop, to produce a constant magnetic field in the gap, the magnetic field size is generally hundreds of gauss and thousands of gauss, can be used for gauss meter calibration.
            Helmholtz coil, is made up of two flat coaxial single-coil, produce spherical homogeneity between coil magnetic field, by changing the current size to change uniform area size of the magnetic field, a magnetic field is adjustable, high uniformity, high sensitivity, great homogeneity, the magnetic field is generally below 1000 gs, two-way magnetic field, according to the direction of the magnetic field, magnetic field size can design one dimensional helmholtz coils, one dimensional compensating helmholtz coil and the three dimensional helmholtz coil, etc., can produce dc magnetic field, magnetic field communication.
            Solenoid coil magnetic field by a single spiral line, to produce long garden bar uniform magnetic field in the coil, change the homogeneity of magnetic field by changing the current size of the size, but the uniformity compared with the helmholtz coil is a bit poor some of electromagnet, is made up of two flat coaxial single-coil, every coil magnetic field derived from pure iron, to produce uniform magnetic field in the two pieces of pure iron gap, by changing the current size of the changing magnetic field, a magnetic field is adjustable, homogeneous area is big, strong magnetic field characteristics, the highest magnetic field up to 10 t. To sum up, we select the appropriate type of magnetic field according to magnetic field category, magnetic field size, uniform area size and uniformity