Twenty Examples of Magnetism

Twenty Examples of Magnetism

Vincent Marché

Vincent Marché

Vincent Marché graduated first in electronics, and then went on to refine his skills at business school. After more than 10 years in the industry, working on product marketing and sales of sensors, switches and electronic devices, he fell into a melting pot called electrical engineering simulation. Supporting FluxTM electromagnetic simulation software since 2009, he is passionate about the large fields of applications addressed by simulation tools and the application expertise of the users. He is constantly looking for solutions that address the innovation needs of electrical engineers. Since the recent acquisition of Cedrat by Altair, he manages the promotion of electromagnetic applications, electrical engineering and e-Mobility.
Vincent Marché

Twenty Examples of Magnetism at Work

  1. Refrigerator magnets- artwork & messages
  2. Refrigerator magnets- to seal and close the doors
  3. Metal machine shop holding devices
  4. Scrap yard and steel mill lifting
  5. Separation of materials
  6. Radiation Isotope creation
  7. Pure Physics research
  8. Motors- automotive, lawn mower, kitchen mixer
  9. Incontinence- bladder valve replacement
  10. Dentures
  11. Levitation of trains
  12. Navigation via the compass
  13. Store and library item security tags
  14. Shark Navigation
  15. MRI for moisture & fat content analysis
  16. MRI for body and organ images
  17. Transmission Line transformers
  18. Recording heads- VCR, audio & video cassettes, hard & floppy disk drives
  19. Recording media- VCR, audio & video cassettes, hard & floppy disk drives, Magneto-optic disks
  20. Credit cards & ATM bank cards

Magnetism exists in two forms, it exists in objects and in air. When magnetism is observed in objects it is represented by a group of things called ‘dipoles’, and it is referred to by the letter “m”. When magnetism is observed in air, it is simply called ‘an applied field’, and it is referred to by the letter “h”.

dipole is a small unit of magnetization which consists of a strength and a direction. Dipole 1 (see figure 1) has a specific strength (designated by the area of the circle), and a direction similar to one o’clock. Dipole 2 (see figure 2) has a strength to be twice that of dipole 1, and its direction is similar to nine o’clock. A magnetic object exhibits a total magnetization (m) which is dependent upon the combination of all the dipoles within the object.

Dipole 1

Figure 1- Dipole 1

Dipole 2

Figure 2 -Dipole 2

An applied field generally exists because of either one of the two following reasons. Reason no. 1 – an object’s overall magnetization is formed in such a way that it sends some of its strength into the surrounding air. Reason no. 2 – electricity passing through a wire generates an applied field. It is important to note that both of these forms of an applied field can coexist; either cooperatively or uncooperatively . As with the dipole, an applied field has a strength and a direction. Applied field 1 (see figure 3) has a strength designated by the length of its arrow, and a direction similar to three o’clock. Applied field 2 (see figure 4) has a strength designated to be one half that of applied field 1 and a direction similar to six o’clock.

 Applied field

Figure 3 – Applied field 1

Applied field

Figure 4- Applied field 2

Each group of dipoles depicted in Figure 5a and Figure 5b represents some different magnetic scenarios or situations. If one considers that each of these situations may exist in any magnetic object, then certain combinations of dipole groups can be used to define the two basic magnetic object types; a hard object, and a soft object.

dipoles
dipoles
dipoles

Figure 5a- Group of dipoles representing a hard object

hard object is one which would best be described as having behavior associated with a sequence of events corresponding to first ‘A’ then ‘ B’ and then ‘C’. ‘A’ describes a group of dipoles in an object where no applied field is present; each dipole is oriented in a unique position. ‘B’ describes a group of dipoles in an object , where an applied field is present; each dipole is aligned with the applied fieldsimilar to three o’clock. ‘C’ describes a group of dipoles in an object, where the applied field of ‘B’ has just been removed; please note that some of the dipoles have not returned to their original positions in ‘A’, but have taken on a new unique position.

dipoles
dipoles
dipoles

Figure 5b- Group of dipoles representing a soft object

soft object would best be described if its behavior was associated with a sequence of events corresponding first to ‘A’ and then ‘B’ and finally ‘D’. ‘A’ describes a group of dipoles in an object, where no applied field is present; each dipole is oriented in a unique position. ‘B’ describes a group of dipolesin an object , where an applied field is present; each dipole is aligned with the applied field similar to three o’clock. ‘D’ describes a group of dipoles in an object, where the applied field of ‘B’ has just been removed; please note that all of the dipoles have returned to their original positions in ‘A’.

The applied field changed the nature of both the hard and soft objects. The hard object retained some of the new features created by the applied field while the soft object retained none of the new features created by the applied field. These behaviors define the essential difference between hard and softobjects, and also clearly establishes which object should be used to accomplish the examples of magnetism at work.

The laws of physics require that all matter exists in its lowest possible energy state. This means that as environmental conditions change, matter will adapt in order to remain at the lowest possible energy state. A magnetic object may experience thousands of environmental situations where a change in applied field implies a new environment situation.

There are two main kinds of hard objects. The first kind of hard objects are called permanent magnets, and the second kind are called recording media. Both kinds of hard objects share the ability to store (or retain) energy although each stores this energy in a different manner.

Permanent magnets are objects constructed with a special group of combined minerals. These minerals once united generally do not exhibit magnetism until the magnet is charged with the process described above. The entire object exhibits the same character in cooperation and the object is used a stored energy device.

Recording mediums are objects constructed with a different group of specially combined minerals. Although different, these objects generally do not exhibit any magnetism until they also experience a sequence of events similar to the process described above. The difference here is that the applied fieldused; it supplies a concentrated amount of energy to a very small localized portion of the object. This makes it possible to store energy in different locations on the object. In fact, it is possible to store energy in designed patterns on the object; which corresponds directly to the information an individual is trying to archive on the recording medium.

Basically, there is only one kind of soft object. Specially combined minerals are used for these objects too; although as mentioned earlier, these objects do not retain any energy. None the less, they are very useful, because they have an ability to organize and sometimes amplify the energy from an applied field when it is present.

The energy commonly associated with magnetism is quite useful for creating large amounts of both attractive and repulsive forces. The following diagrams are useful in depicting the differences between the two kinds of forces, and the situations necessary for directional changes to result. Repulsion is designated by the letter ‘R’ (see figure 6) and attraction by the letter ‘A’ ( see figure 7). The forces which result in either case, are a direct result of the dipoles trying to reduce their energies to the lowest possible state. Usually this requires some kind of motion; either attraction or repulsion. Should one of the interaction dipoles be fixed in place, then the dipole which is free of constraint will be the only one to move.

Repulsion

Figure 6- Repulsion between dipoles

Attraction

Figure 7- Attraction between dipoles

Now onto the examples …

1. Refrigerator magnets – artwork & messages :

A refrigerator magnet is a hard object, and more specifically a permanent magnet. When this magnet is held in your hand, it has adapted to its present situation and rests in its lowest possible energy state. If you now move this magnet toward the refrigerator door (which is a soft object) you have given the magnet a new environmental condition or situation. The magnet will adapt itself in order to reach the new lowest possible energy state. Specifically it will do this by sending a portion of its’ energy into the refrigerator door which will absorb it. This energy minimization process illustrates what was described above as attraction; the refrigeration magnet will be attracted to the refrigerator door. One can take advantage of this attractive force and use the magnet to hold artwork or messages to the door; there will however be a limit to the weight which the magnet can support.

2. Refrigerator magnets – to seal and close the doors :

The refrigerator manufacturers use the knowledge described above to not only close the door when it gets reasonably close to the refrigerator frame but also to pull the door, which has a permanent magnet gasket along the inside edge, very snugly to the refrigerator frame. This accomplishes two things; it allows the owner the freedom to no slam the door closed, and it provides an extremely effective thermal seal.

3. Metal machine shop holding devices :

In a machine shop it is paramount that pieces of metal be held firmly in place. If this is accomplished, accidents and mistakes are less frequent and less damaging. By utilizing the same knowledge from above, it is possible to produce attractive forces which are large enough to do two things. One, the attractive forces are sufficient enough to hold a piece of metal heavier than the actual magnet itself, and two, the attractive forces are able to withstand additional forces created from the various machine operations. A requirement of these attractive forces is that they can be turned on and off upon request. This requires a clever diversion of the magnet energy away from the held metal.

4. Scrap yard and steel mill lifting :

In a scrap yard or steel mill, it is necessary to lift and relocate large quantities of metal. As the metal is largely steel, it is a soft object. With the knowledge mentioned earlier, magnetism is used to accomplish this task. A very large crane using either an electro-magnet or an assembly of hard magnetic objects on the end of its cable is able to pick up, relocate, and release the steel pieces.

5. Separation of materials :

Mines of various types use magnetism to separate the materials being collected. Attractive forces, similar to those described earlier, are placed near a conveyor transporting the mined materials. As the soft magnetic objects move by the magnetic assembly they are drawn away from the conveyor containing the desired material and diverted to the collection area. Various degrees of sophistication are available enabling the mine to be quite selective in their collection and separation of materials.

6. Radiation isotope creation :

Many forms of medical research utilize radiation in the form of isotopes. These isotopes are used to isolate and observe various forms of medical problems; diabetes, cancer, and AIDS are but a few examples. Most of these isotopes are manufactured; they are not abundant in their natural forms. The knowledge presented above is actually used to produce these isotopes. A device called an acceleratorprovides an element ( like phosphorus) with a tremendous amount of energy causing the element to change state and to emit radiation in order to minimize its energy.

7. Pure Physics research :

Subatomic Physics experiments utilize magnetism to create and observe the smallest structures of matter. Attractive and repulsive forces are generated by magnetism in controlled environmental chambers. Responses are predicted for certain structures of matter under controlled circumstances. Observation of the actual responses clarifies or disproves the predictions. This enables society to gain a clearer understanding of what matter consists of, and better equips us to solve the future problems.

8. Motors – automotive, lawn mower, kitchen mixer :

Motor manufactures utilize the same knowledge from above to produce rotation in their motors. A motor is divided into several wedge shaped areas. Synchronized electrical signals generate small attractive forces which rotate the motor from one wedge region to the next. The speed of the motor is directly related to the rate at which the electrical signals are repeated.

9. Incontinence-bladder valve replacement :

Unfortunately, some people suffer an inability to urinate on demand; this is a form of incontinence. In an effort to assist these people, artificial bladder valves have been developed. These valves are surgically implanted inside the individual. The valve contains a fluid which contains quantities of a soft object dispersed uniformly throughout the fluid. A permanent magnet producing an attractive force is then used to move the valve and open the urinary tract.

10. Dentures :

A new form of denture adhesion utilizes the knowledge from above. Small pieces of permanent magnet are surgically implanted in an individual’s gums, and pieces of soft objects are placed in selected portions of the denture. When the denture is then put in place, adhesion results from the attraction.

11. Levitation of trains :

Magnetic repulsion is used to levitate trains. One set of very strong dipoles (The train) experience a repulsive force from another set of dipoles (The track). As a result the train moves as far away from the track as possible, and is at least partially levitated. This levitation reduces the resistance that the train experiences in order to move (friction). The train will then require less fuel to move from one station to the next and can move at faster speeds as well.

12. Navigation via the compass :

Navigation using a compass is accomplished because the earth generates magnetism. Geographically the top of the globe is labeled the ‘North Pole’, and the bottom the ‘South Pole’. Currently the earth’s ‘North Pole’ is magnetically a south pole, and the earth’s ‘South Pole’ is magnetically a north pole. A compass at location ‘A’ on Earth will point to the earth’s ‘North Pole’. If we consider the attractive knowledge that we have learned from above it becomes apparent that the end of the compass labeled with an ‘N’ must be magnetically a north pole, and the end of the compass labeled with a ‘S’ must be magnetically a south pole. This configuration for the compass allows it to minimize its energy pointing to the Earth’s ‘North Pole’, which of course provides our directional reference.

13. Store and library item security tags :

For security measures it is necessary to determine whether an object (either a book in a library or a pair of jeans in a store) leaves a designated area without permission. This monitoring can be done with magnetism. As we have seen, a group of dipoles can have unique responses to their environment. Some soft objects and some combinations of hard and soft objects in a mosaic pattern exhibit such unique responses, that they can be used as ‘tags’. If a person leaves the designated area appropriately, the tag is neutralized or removed. If they do not, then the ‘tag’ triggers the detection systems, and an alarm sounds notifying authorities of the problem.

14. Shark navigation :

Sharks navigate in the ocean in reference to the earth’s ‘North Pole’ and ‘South Pole’. As they swim, they are regularly moving their heads from side to side. It has been discovered that they have small sensing elements in their heads which convert the earth’s magnetic energy into electrical impulses. These impulses are used by the shark to maintain a directional reference for navigation.

Nuclear magnetic resonance also occurs as a result of energy minimization. Physicists long ago hypothesized a unique set of environmental conditions which would in effect cause a magnetic dipoleto precess and then continually spin like a top (or resonate) in order to minimize its energy. Free dipoles in the presence of the following unique environmental conditions will produce magnetic resonance; a strong alignment applied field in a direction similar to twelve o’clock, and a pulsed (short duration) oscillating applied field is in the direction similar to three o’clock. (see figure 8 ) The pulsed oscillating applied field is in the form of a sine function at a frequency somewhere in the radio frequency range (several million cycles per second). Frequency determines how many times a function is repeated in a set amount of time. The faster the frequency, the faster the function changes, and the more cycles which will have been produced.

Magnetic Resonance
Magnetic Resonance
Figure 8 : Applied Field Conditions for Magnetic Resonance 

 

The outcome of the above hypothesized experiment has provided us with an extremely important observation tool which is noninvasive; this means that the material or object being observed is not altered or destroyed. This technique is called Magnetic Resonance Imaging (MRI).

15. MRI for moisture & fat content analysis :

Magnetic resonance is used by food manufactures (like Pepperidge Farm) to monitor and optimize the water and fat content in their ingredients in order to determine and maintain taste and shelf life. Small amounts of materials are placed in a device which duplicates the above conditions. The resonance response is monitored and directly correlated to either water or fat content. This is accomplished because water and fat both contain magnetic dipoles and their response is different enough to be distinguished.

16. MRI for body & organ images :

Magnetic resonance is used to produce 3D images of the organs in the body with a clarity and a resolution exceeding that of the conventional x-ray, and without the use of harmfully penetrating x-rays. The production of, a useful image requires an even more special set of conditions than that described above. The alignment of the applied field is still required, but this field now has two components, a uniform ‘field and a gradient field. A uniform field is a field which has a magnitude over a volume like a 16 inch diameter sphere which differs from the average by only 30 or 40 parts per million (ppm), or alternatively by only .003 or.004 percent (%) anywhere in the sphere. The gradient field is a field which changes linearly with distance from the center of the sphere as one moves to the edge of the sphere. This gradient field provides a means of determining spatial relations during the image production, and thus is a major contributor to the increase in clarity and resolution that a MRI provides. The uniform field and the gradient field are used simultaneously to align the dipoles in the observation region. These dipoles minimize their energies by aligning with the field. Now the pulsed field is introduced; as described above the dipoles will resonate in order to best minimize their energies. This resonance is monitored and recorded as an electrical impulse. A sequence of different gradient fields will be applied covering the entire organ area of interest. Once all of the data has been collected (this takes close to one hour) it is processed by a powerful computer to produce the 3D image.

17. Transmission Line transformers :

Soft magnetic objects are used by the power companies. The large transformers (both residential and industrial) convert energy from one form into energy of another form. Specifically they transform voltage at one magnitude into a voltage of 110 or 220 volts, which are the typical household appliance voltages. Transmission lines contain several thousand volts, and a transformer containing softmagnetic objects is used to turn this large amplitude of voltage into the 110 and 220 volts used in your house.

18. Recording heads – VCR, audio & video cassettes, hard & floppy disk drives :

A special coding sequence is used to accomplish information storage. This coding sequence requires that energy (in the form of applied fields) be presented to storage media in small organized areas. Softmagnetic objects are used to channel this magnetic energy into appropriate locations in order to accomplish the information storage.

19. Recording media- VCR, audio & video cassettes, hard & floppy disk drives :

As mentioned previously, recording media is a hard magnetic object. These form of media are used extensively in our everyday lives either directly or indirectly. The desired information is saved to the magnetic material for our retrieval later. We are also able to record and re-record as we desire with no degradation in performance or capabilities.

20. Credit cards & ATM bank cards :

Most credit cards contain a strip of hard magnetic object on the back of the card. This strip contains coded information; specifically, your name(s), account number(s), and probably a few other special items. When you make a purchase with a credit card it is now rare for the clerk to have to talk to anyone to clarify your ability to purchase an item. Instead the clerk will pass your card through a small box. This box is an intelligent interface between the store and the credit card office. Your credit card information is read of of your card by the small box, and is then directly passed to the credit card computer via a telephone line. The clerk then will enter your purchase amount, and wait for an approval number. If you use an automatic teller machine (ATM), the ATM will access your account information from your card and then will prompt you to initiate bank transactions. Any of your selections are computer controlled and fully automated and all initiated by magnetics.

Vincent Marché

About Vincent Marché

Vincent Marché graduated first in electronics, and then went on to refine his skills at business school. After more than 10 years in the industry, working on product marketing and sales of sensors, switches and electronic devices, he fell into a melting pot called electrical engineering simulation. Supporting FluxTM electromagnetic simulation software since 2009, he is passionate about the large fields of applications addressed by simulation tools and the application expertise of the users. He is constantly looking for solutions that address the innovation needs of electrical engineers. Since the recent acquisition of Cedrat by Altair, he manages the promotion of electromagnetic applications, electrical engineering and e-Mobility.