By Drew Fong
Science Fair Presentation on Magnetic Shielding
I. RESEARCH PROBLEM
When I was travelling in China, I took the Maglev train from the Pudong International Airport to downtown Shanghai. This train uses large electromagnets to levitate over the track. However, magnetic items on the train were not affected by the electromagnet. This made me curious and led me to investigate magnetic shielding.
II. RESEARCH QUESTION
What is magnetic shielding?
What materials are suitable for magnetic shielding?
What are the real-life applications of magnetic shielding in our modern day?
III. BACKGROUND RESEARCH
Magnetic Shielding – How It Works
Many machines today use magnets or electromagnets in order to function. The magnets in these machines affect anything else around it that is made of a magnetic material. This can be dangerous, and it could reduce the efficiency of the machine. In order to subdue the effects of the magnet, the range of the magnet is limited by a magnetic shield. This shield is made of a sheet of magnetic material. This sheet re-routes the magnetic rays and deflects it back to the magnet. A magnetic ray travels from the north pole of a magnet to the south pole, in a circle that curves back to the south pole of the magnet.
Magnetic Shielding Materials – Permeability
When It comes to selecting materials to be used for magnetic shielding, the material has to be permeable. Permeability of a material is the degree to which it allows magnetic field lines to form within it, be absorbed and re-routed.
Magnetic lines can pass through a non-permeable material which has a permeability of zero. Magnetic fields do not form within these non-permeable materials. The magnetic field lines from a magnet pass through cardboard, air and other materials like wood or aluminum foil. A permeable material, however, absorbs and re-routes the magnetic field lines back to the south pole of the magnet.
Objects that aren’t suitable for magnetic shielding have a permeability of 0 or are non-permeable. This means that all magnetic waves can pass through. Materials that are suitable for magnetic shielding would have the permeability of 200-350,000.
The materials used for magnetic shielding are iron, steel, nickel, or cobalt. However, the materials that are most used for magnetic shielding are alloys. When it comes to material selection, designers look for metals that resist the magnetic force, with the shield permanently becoming a magnet over time. The most common alloy would be HyMu 80. It is good for industrial use and is reliable. For magnets with more power, alloy 49 would be used. Alloy 49 is specifically used for machines with massive magnetic power, one of which is the Magnetic Resonance Imaging (MRI) machine.
Applications of Magnetic Shielding
Many machines that use magnets require magnetic shielding implemented in the machine. This is either to increase the efficiency of the machine or make the machine safer for workers. These machines include the MRI machine, large electric motors, space satellites, etc.
Objects that are made of magnetic material are suitable for magnetic shielding.
- Two pieces of wood were sandwiched between two pieces of cardboard, creating a gap for materials to be placed in it.
- Rubber bands were positioned to hold the sandwich together.
- A magnet was placed on top of the cardboard sandwich.
- Two of the materials ( knife and screwdriver ) are tested to see if they are attracted to the magnet and hence, are magnetic in nature.
- Iron nails were held to the bottom of the sandwich. The nails were attracted by the magnet and remained in place.
- Test materials were in turn slotted through the gap in the sandwich, one by one.
- Results were observed.
VI. MATERIALS LIST
- 2 pieces of cardboard
- 2 pieces of wood
- Rubber bands
- Steel knife
- Magnetic putty
- Plastic lid
- Aluminum foil
- Wooden chopsticks
VII. RISK AND SAFETY
- Use a board to shield the falling nails, to minimize the danger of flying nails.
- Extra care should be taken when handling the knife to avoid injury.
VIII. DATA ANALYSIS METHOD
The goal of the experiment is to find out which materials are suitable as a magnetic shield. As each material sample is placed in the gap, it will be observed if the nails fall off.
If the nails fall off, the magnetic field holding them in place would have been re-routed, and the magnetic force on the nails is removed. Hence the material tested is an effective magnetic shield.
“What is Magnetic Shielding?”
“Selecting Magnetic Shielding Materials”
“Effect of Magnetic Materials on Field Lines”
X. ANALYSIS OR DATA OR RESULTS
|MATERIALS||DID THE NAILS DROP?|
|NON-PERMEABLE MATERIALS||PERMEABLE MATERIALS|
|Wooden chopsticks||Steel knife|
My hypothesis was that all items made of magnetic material would be suitable for magnetic shielding. Items that were made of magnetic material were the iron screwdriver, the steel knife, and the magnetic putty. I thought that the iron ore in the magnetic putty would make the material suitable for magnetic shielding. Due to the result, I conclude the iron ore in the putty are too small and too spaced out, allowing the magnetic rays to pass through.
My experiment was a success. Everything went according to plan.
Please view the 3-minute video.
Improvements to Experiment / Further Investigation
More materials should be tested. Non-magnetic metals like copper, zinc, gold, silver, bronze and their alloys can be tested for permeability. From the result of the aluminum foil test, it is likely to be non-permeable and not suitable as magnetic shields.
I would like to thank my father who took the time to purchase the special item – magnetic putty and thick wooden sticks, and my mom who provided overall guidance and tied up all the loose ends.