PEMF Helmholtz coils
A while ago I was contacted by a doctor who had a very good understanding about field lines in PEMF coils.
This doctor was actually using a device which came with two coils each with a 2" diameter and he was under the impression that the electromagnetic field lines were homogeneous penetrating the area between the two coils, if placed opposite from each other, not dependent on the distance between them.
This doctor wondered if this indeed could be correct because he did not understand how changing the distance between the coils would influence the electromagnetic field lines between the two PEMF coils.
A German scientist by the name of Helmholtz designed a device to create an almost uniform magnetic field between two coils by placing the them exactly opposite each other.
Taking advantage of the question I received, I explained to this doctor that he was correct and only under specific conditions the so called Helmholtz configuration can be obtained. Working with two coils with very small diameter can only cover half the distance of each coil diameter in order to result in a uniform PEMF field.
Because he wanted to treat larger body parts as well of his patients, like an arm or leg or even stomach, he reasoned that he needed a PEMF system with large coil diameters in order to be able to treat a large area between the two coils with the same electromagnetic field intensity, which is only possible by using a Helmholtz configuration.
Our discussion resulted in a special coil set-up which worked just fine in this PEMF Helmholtz configuration. The generated electromagnetic field lines were now going through the complete stomach of the patient with the same homogeneous intensity! Here follows some explanations on how this works.
The distance between the 2 coils must be equal to half of the diameter of the coils, notice the red arrows.
In this picture two PEMF coils are wired in series.
This means that the electrical current from the source goes into the first coil, comes out, then goes into the second coil in the same direction, comes out and returns to it's source. The resulting PEMF field lines leave the coil perpendicular (= at a right angle to the coils) in the direction of the line marked X.
However if we want to obtain an evenly spread PEMF field, where the intensity is completely equal in the whole area between the two coils, specific conditions must be met.
This explains why it is impossible that an even field can be obtained when using 2 x 2" coils opposite to each other if the distance is more than half the diameter of a coil.
As such the PEMF field distribution is already disturbed when the distance in between such coils exceeds more than 1".
These pictures show how we are able to generate a homogeneous PEMF field between the tips of the two green arrows between the coils. We can now see that the PEMF field lines are traveling straight between the two coils.
Having said this if we need to bridge a distance between two coils of at least 9 inches this requires coil diameters of at least 18 inch! See the red arrows in the picture at the top.
This requires a very large coil area in addition to sufficient power to be able to overcome the distance between these two coils. This in turn requires generation of an amount of power sufficient to drive two of these large PEMF coils.
For this we now need a powerful electrical current, which in turn requires a powerful PEMF generator.
In the picture above we can now see how a Helmholtz PEMF configuration can be obtained, provided the PEMF generator has sufficient energy output. Two flat coils (each with a diameter of 18") positioned one opposite the other will create a homogeneous field between them able to completely penetrate the body. Even values of 40 milli Tesla can be reached.