How to Shield a Magnet

Magnets continue to play a significant role in various applications and devices. However, there are moments when their magnetic fields or forces must be controlled or limited. And this is where magnetic shielding comes in.

What is Magnetic Shield?

A magnetic shield is a specialized barrier employed to limit or control the magnetic effects of an external magnetic field. The primary purpose of magnetic shielding is to keep specific objects, areas, or even living things from the possible harm of external magnetic fields. To shield magnetic field lines, specialized materials capable of absorbing or redirecting magnetic fields are used.

Magnetic Shield
Magnetic Shield

The Importance of Magnetic Shielding

Uncontrolled magnetic forces can cause harm to living organisms, disrupt the operation of various electronics, or even damage sensitive equipment. However, magnetic shielding offers a reliable solution to all the interferences caused by external magnetic fields, even though some might not be immediately apparent.

Safeguarding Sensitive Electronics

External magnetic fields can greatly distort or disrupt the operation of sensitive electronics like medical equipment and communication devices. This is because unwarranted magnetic forces can distort the currents in electronic circuits.

Deploying a magnetic shield in environments housing sensitive electronics safeguards the key components of these electronics and ensures optimal performance. For instance, installing a magnetic shield near an MRI machine will avert distortion of the imaging area by external magnetic forces leading to accurate results.

Protecting the Health of Living Organisms

When human beings and other living things are continuously exposed to extremely strong magnetic fields, serious health conditions may develop.

For example, workers working on power lines with high voltage can be prone to illnesses caused by excessive magnetic field exposure like cancer. However, incorporating relevant magnetic shielding techniques shrinks their chances of exposure leading to better safety. Magnetic shields can be embedded in their work equipment or protective gear.

Ensuring Accurate Measurements

Interferences caused by external magnetic fields can lead to erratic measurements and results. This can in turn lead to falsified research outcomes in scientific experiments as well as poor product quality in manufacturing.

Implementing feasible magnetic shielding methods can lead to a controlled setting thereby guaranteeing the accuracy of research experiments.

Let us take particle accelerators for instance. The introduction of strong external magnetic fields can impact particle trajectory consequently leading to erratic results. However, with a sophisticated magnetic shield, there is less interference and this translates into accurate results.

Data Protection

Exposing data storage devices like computer hard drives to extreme magnetic forces can lead to corrupted data or complete loss of essential data. This is why most data centers or data storage facilities employ high-end magnetic shielding barriers to protect their servers from external magnetic fields. The shields avert the potential loss of information as well as distortion of sensitive information.

Aerospace Safety

In aviation and aerospace applications, external magnetic fields can have far-reaching consequences on essential components such as navigation and communication equipment.

This can in turn put the lives of crew members in danger thereby underlining the essence of magnetic shielding. Incorporating magnetic shields onto aerospace equipment and electronics counteracts external magnetic fields leading to consistent operation and crew members’ safety.

Improved Functionality of Medical Devices

The proper functioning of medical equipment is vital in ensuring patient safety. This is why medical devices that employ magnetic resonance have to incorporate magnetic shielding to prevent patient endangerment.

For instance, cochlear implants designed to reestablish hearing in human beings constitute electronic components that are sensitive to magnetic forces. Without proper magnetic shielding, these devices can be ineffective and in some instances cause harm to the patient.

Best Materials for Magnetic Shielding

 

Magnetic shielding involves the use of distinct materials characterized by a high permeability. This characteristic allows the materials to soak up external magnetic fields or redirect them to safeguard specific regions and equipment.

They also ensure electromagnetic compatibility in sensitive electronic gadgets. Here are materials best known for blocking magnetic fields.

The Main Magnetic Shielding Materials

Ferromagnetic metals are essentially the most common and effective materials used to make magnetic insulators or shields. The main ferromagnetic materials used for magnetic shielding are nickel, cobalt, and iron.

MU-Metal

Characterized by a high magnetic absorptivity, Mu-metal is one of the most heavily utilized magnetic shielding materials. It is primarily made of iron and nickel and this enhances its magnetic insulation capabilities. Additionally, it boasts of a crystalline structure, which enhances its ability to redirect magnetic field lines.

Steel

Steel is also a common choice when it comes to magnetic shielding since it is ferromagnetic and quite affordable. However, there are specific variations of steel that cannot be magnetized hence they cannot be utilized as magnetic insulators.

Ferrite Materials

Ferrite materials are also widely used to shield magnetic fields and they are basically ceramic materials. They consist of iron oxide mixed with manganese or zinc.

Ferrite magnetic shields can attenuate electromagnetic radiation because of their low electrical conductivity. This explains why they are commonly used in to block magnetic fields in inductors and electricity transformers.

Soft Iron

Soft iron can gain magnetism and lose its magnetic capabilities easily. This makes it an ideal material for magnetic shielding. When placed in the way of a magnetic field, soft iron can redirect the field lines thereby protecting nearby areas and objects from the effects of the magnetic field.

Alternative Magnetic Shield Materials

 

In addition to ferromagnetic materials, which are the primary magnetic shield materials, there are numerous alternatives with novel rewards.

Superconductors

Superconductors such as aluminum can repel magnetic forces particularly when exposed to low temperatures. This is because they experience the Meissner effect, which qualifies their use as magnetic shields.

Their use is however limited by temperature fluctuations. They must be maintained at extremely cold temperatures.

Metglas

Metglas is an alloy that consists of silicon, iron, and boron among other elements. It exhibits a non-crystalline structure, which enhances its coercivity and permeability properties. This consequently qualifies its use as a magnetic shield material.

Carbon-Based Materials

Carbon-based materials such as graphene have remarkable electrical conductivity and this greatly improves their ability to shield magnetic fields. Additionally, graphene exhibits a two-dimensional configuration, which allows it to attenuate magnetic fields and electromagnetic radiation.

Determining Suitable Thickness for a Magnetic Shield

The thickness or broadness of a magnetic barrier directly impacts the level of magnetic blocking attained. This is why selecting the right magnetic shield thickness is as important as selecting the right magnetic field-blocking material. Thicker barriers tend to shield more magnetic field lines.

There is no single formula that can be used universally to calculate the perfect thickness of a magnetic barrier. However, there are certain parameters that can help you determine the right thickness.

Permeability of the Magnetic Shield Material

Permeability simply measures the ease with which magnetic field lines can penetrate the magnetic barrier.

Different magnetic shield materials offer distinct grades of permeability and this makes it difficult to single out a specific thickness as the perfect option. It is however worth noting that highly permeable materials offer better shielding properties.

Magnetic Field Strength

You need to know the strength of the magnetic field you want to shield against. This could be given in units like Tesla (T) or Gauss (G).

Desired Attenuation

Attenuation is the reduction in magnetic field strength as it passes through the shield. You need to decide on the desired level of attenuation, which is often expressed in decibels (dB).

Factors to Consider When Selecting the Suitable Magnetic Shield Thickness

To arrive at the perfect thickness of a magnetic shield, you must take into consideration the following factors. These factors must be weighed against each other to strike the right balance between performance, feasibility, and cost.

The Type of Magnetic Shielding Material Used

The magnetic shield material is the main determinant of a shield’s thickness. It also impacts the effectiveness of the shielding attempt. Different materials exhibit varied permeability and this impacts how well a magnetic barrier can redirect or absorb magnetic fields. Materials with higher permeability demonstrate relatively higher shielding capabilities meaning they do not have to be necessarily thick.

Desired Level of Shielding

Certain applications may necessitate varied degrees of magnetic shielding. For instance, when shielding medical equipment, stronger and thicker shields may be employed since little magnetic interference is needed. The degree of shielding needed is often determined by the sensitivity of the object or area that needs protection from the magnetic fields.

Weight and Size

Although thicker magnetic shields exhibit stronger magnetic blocking capabilities, they can be a little heavier. This can be a major cause for concern for devices that need mobility or applications with limited spaces. This is why it is paramount to strike a balance between the magnetic shield’s thickness and the weight demands or space demands of the application.

Cost Considerations

Cost is a major concern and different shielding materials have varied price tags. Materials such as Mu-metals are relatively pricier than steel magnetic shields.

Similarly, more density consumes more material meaning the cost will be higher. So, in cases where cost-saving is a priority one can opt for a less dense magnetic shield.

Practical Steps in Making Shields That Block Magnetic Fields

Magnetic field-blocking shields can be manufactured using numerous materials and methods. The choice of the manufacturing material and technique is determined by the intended shielding degree and the application requirements. Below is an overview of how to make a magnetic shield:

Material Selection

There is a broad array of materials with magnetic field-blocking capabilities to choose from. The best materials are soft materials like Mu-metals, which do not necessarily have to be dense to be effective.

Material Processing

After settling on a specific magnetic shield material, it is time to process the chosen material. This is typically accomplished using various technologies key amongst them being heat treatment and rolling and annealing. Processing the magnetic shield material equips it with the right magnetic properties to facilitate magnetic shielding.

Shaping

Subsequently, the processed magnetic shield sheets are cut and sized with their intended use in mind. Most magnetic shields assume simple designs but complex designs can also be incorporated.

Joining

The cut magnetic shield sheets are then joined using adhesives or technologies like welding and brazing. It is worth noting that joining does not apply to all magnetic shields. It applies when multiple sheets need to be joined to form a bigger shield.

Coating

Coating is often undertaken as a finishing step and it seeks to enhance the magnetic shield’s appearance. Stronger coats may be applied to elevate the barrier’s resistance to corrosion. Other finishing touches employed could include painting and plating.

Testing

This process is carried out to make certain that the magnetic barrier can meet its set target.  The magnetic shield is placed around the object that needs protection from the magnetic field and exposed to a known magnetic field. The reduction in magnetic flux is then measured using a Gauss meter.

Steps on Shields that Block Magnetic Fields
Steps on Shields that Block Magnetic Fields

How Magnetic Shielding Works?

Magnetic shielding works by blocking or diverting external magnetic fields to keep them from the reach of certain areas, organisms, or devices. Underneath is a breakdown of the processes employed by magnetic shields to stall external magnetic field lines.

Magnetic Shielding
Magnetic Shielding

Diverting Magnetic Field Lines

Magnetic shields are typically placed close to the area or object being protected. The shields draw the magnetic field lines from the external magnetic field towards them thereby diverting them away from the shielded area.

This is made possible because the magnetic shields are made of highly permeable materials.

Generation of Closed Loops

The shielding material forms loops for the magnetic lines and guides them around the protected area.

This keeps the magnetic lines from going into the protected space thereby reducing or stopping the effects of the external magnetic fields. For objects or areas necessitating extreme shielding, thicker magnet shields can be employed. Alternatively, different layers of magnetic shields can be used.

Practical Magnetic Shielding Scenarios

Uncontrolled magnetic fields can interfere with communication signals or compromise essential processes.

Magnetic shielding mitigates the negative implications of magnetic fields on objects, organisms, and regions. This is why magnetic shielding is a popular practice in the following scenarios.

How to Shield a Compass from External Magnetic Field?

To shield a compass from external magnetic forces, wrap it in a vessel made of ferromagnetic material. This could be a Mu-metal or ferrite material.

Usually, the high magnetic permeability of this container will divert external magnetic fields thereby minimizing their influence on the compass needle’s orientation. This will result in unaltered direction readings.

How to Magnetically Shield a Speaker?

To maintain good audio quality, it is important to keep a speaker’s or audio device magnet from the reach of external magnetic fields. This can be accomplished by encasing the respective magnets in highly permeable materials capable of absorbing or redirecting unwanted magnetic forces.

How to Magnetically Shield a Motor?

To stop external magnetic fields from disrupting a motor’s functionality, one needs a motor casing or shield with magnetic properties. The magnetic shield should cover the entire motor to guarantee effective absorption of the external magnetic field lines. This will protect the motor from disruptions likely to be caused by strong uninvited magnetic fields.

How to Magnetically Shield a Wire?

To mitigate electromagnetic interference, which can minimize a wire’s magnetic emissions or negatively impact its performance, one can wrap it using a ferromagnetic shielding tube or tape. The tube will then soak up the external magnetic forces thereby safeguarding the wire.

How to Shield a Strong Earth Magnet?

Strong earth magnets are made of strong earth magnetic materials like neodymium. To maintain the strong magnetic properties of strong earth magnets even within the vicinity of stronger external magnetic fields, simply enclose them in boxes made of ferromagnetic supplies. For instance, a box made of steel.

Conclusion

As you can see, shielding magnets is a practical process. It plays a significant role in many industries. If you want to learn more about laws of magnetism or magnets, contact us now.

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