# Induction coils and contact materials

## Main Question or Discussion Point

Hi, I'm using an induction coil to heat up an electrically conductive material within the coil. However, I'm worried that adjacent electrically conductive materials, which are not within the coil will also have see a heating effect, due to induction not thermal transfer. I want to avoid this as it would draw power from the system reducing the temperature the material I want to heat will achieve.

Thanks so much for your help!

## Answers and Replies

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Simon Bridge
Science Advisor
Homework Helper
Either move the materials farther away or use some sort of shielding.
You may want to try measuring the effect to see if it is important to your design before going to a lot of trouble.

At the moment most shielding materials, which are not electrically conductive, do not seem to be capable of withstanding the temperatures required (2500C). I am trying to determine whether electrically conductive materials (of which there are more available that can withstand those temperatures) can be used instead. This requires determining whether they will have an electromagnet field induced in them and at what distance this is likely to occur.

In essence, does the material have to be INSIDE the coil for a magnetic field to be induced or will a magnetic field be induced in nearby conductive materials.

2500 degrees Celcius are some serious temperature! What is the application if I may ask?

Shielding can be done in two ways. Either by conducting the magnetic flux trough a high permeability conductor ( that is, the flux is confined to inside of the material) or using a high electrical conductive material to shield the object ( induced currents in the conductive material will oppose the magnetic flux, thereby reducing the total flux.)

The latter will use some power from the input power, may be referred to as losses.

If the material you are heating has higher permeability than the insulating material, and it is not saturated, much of the magnetic flux will travel trough the material you are trying to heat, and not the insulating material.

Or you can laminate the insulating material ( like a transformer core).

What about certain types of ceramic materials, they can withstand high temperatures and some are electrical insulating.

The material needs not be inside the coil for currents to be induced. If you google "coil flux lines" and look at the photos, any material crossing the flux lines will have a induced electric field. And if conductive, a induced current.

The magnitude of the flux density a distance from the coil is dependent on the shape, current, materials etc.