Neodymium Magnets in Alternative Medicine

Magnetic fields are all around us and a major part of everyday life. They add greatly to the quality of modern living. The sunlight, which makes life possible, is an electromagnetic field; everything that generates, transmits or uses electricity produces electric and magnetic fields and, of course, the television companies send out their product as electromagnetic radiation.

Some alternative medicine sources state that magnetic fields generated by small permanent magnets could actually improve your health and benefit to your overall well being. Magnet therapy or magnotherapy is a pseudoscientific alternative medicine practice involving the use of static magnetic fields. Practitioners claim that subjecting certain parts of the body to magnetostatic fields produced by permanent magnets has beneficial health effects.

Products include magnetic bracelets and jewelry, magnetic straps, shoe insoles, mattresses, magnetic blankets (blankets with magnets woven into the material), magnetic creams, magnetic supplements, plasters/patches and water that has been “magnetized”. Application is usually performed by the patient.

     gold-plated-torque-magnetic-bangle-large                       magnetic-therapy_950

Fig 1. Magnetic straps                                                           Fig 2. Magnetic bracelet



Fig 3. Magnetic insole


Due to the variety of electromagnetic fields that naturally occur within the body, there is interest in magnet therapy for medical conditions. For example, nervous system transmissions and related muscle contractions are associated with magnetic activity. The heart generates the largest magnetic field in the body. Several other activities in the body are associated with magnetic activity. 

At one time it was thought that abnormal magnetic fields in the body might result in certain disease states and that magnets could play a role in making these magnetic fields normal again.

You may hear that magnets attract the iron in red blood cells, resulting in increased circulation. But this is wrong. The iron in blood cells is not in a magnetic form. However, magnets, in theory, could have an effect on other charged molecules in the blood and other parts of the body.

No scientific evidence has been provided as to these magnets could actually benefit your health and in some cases, these magnets could actually pose a danger. In general, when using neodymium magnets for medical purposes, you should keep in mind these few things:

1) Scientific evidence does not support the use of magnets for pain relief.

2) Do not use magnets as a replacement for conventional medical treatment or as a reason to postpone seeing your health care provider about any health problem.

3) Magnets may not be safe for some people, such as those who use pacemakers or insulin pumps, as magnets may interfere with the devices. Otherwise, magnets are generally considered safe when applied to the skin.

4) Tell all your health care providers about any complementary health approaches you use. Give them a full picture of what you do to manage your health. This will help ensure coordinated and safe care.


References :

David Jeffers, (1996) “Electric and magnetic fields and health”, Structural Survey, Vol. 14 Iss: 1, pp.4 – 8

Park, Robert L. (2000). Voodoo Science: The Road from Foolishness to Fraud. New York, New York: Oxford University Press. pp. 58‚Äď63

Singh, Simon; Edzard Ernst (2008-04-08). “Are we being hoodwinked by alternative medicine? Two leading scientists examine the evidence”. Daily Mail. Retrieved 2009-08-18. (June 23rd, 2014.) (June 23rd, 2014.)

The magnets of the green cars: Sensors

Ever wondered why your laptop turns into sleep when you close it?

It is because of magnetic sensors! There is a magnet on the screen-side, and a sensor on the keyboard-side. When they get close, the sensor feels it and turns a switch.

Picture showing how a sensor on the keyboard-side of the device can be used to detect a magnet on the screen-side, and use the output to switch the power on/off.

Picture showing how a sensor on the keyboard-side of the device can be used to detect a magnet on the screen-side, and use the output to switch the power on/off.  Source: Toshiba


Following last week¬īs post on the use of magnets in motors, this post will be about the magnetic sensors we find in cars.

Lets start at the beginning. There are numerous types of magnetic sensors, and they can be divided into three classes, depending on how they are used in relation to the ever-present magnetic field of the Earth.

There are the sensors for High sensitivity (that are highly sensitive to the magnetic field of the Earth) called MAD, which can detect ferromagnetic objects from long distances. These sensors are used to detect mines, ships and airplanes etc., and are based on the fact that the magnetic fields of ferromagnetic materials (its dipole moment) will distort the field lines of the ambient magnetic field, or create anomalies, why MAD is short for Magnetic Anomaly Detection. See picture below.

Picture showing how MAD (Magnetic Anomaly Detection) works. The dipole moment from ferromagnetic materials will distort the ambient magnet field lines.

Picture showing how MAD (Magnetic Anomaly Detection) works. The dipole moment from ferromagnetic materials will distort the ambient magnet field lines. Source: Lenz, 2006.

Then there are the sensors of Medium sensitivity that are working with (sensing) the Earths magnetic field, and they are known as compasses.
Finally, we have the sensors that are not very sensitive, and it is in this segment we find the two types of magnetic sensors that dominate in cars.

2 main types: The Hall sensor, and the AMR sensor.

The Hall sensor contains a conducting material through which a current is applied, and the voltage across the material is measured. When a magnetic field acts on the system, the voltage will change (the Hall Effect), and indicate the strength of the magnetic field.

AMR is short for Anisotropic Magneto Resistivity, which is the basis for this type of sensor. The main constituent is a Permalloy (80 % Nickel, 20 % Iron) thin film deposited onto a silicon wafer. The films properties are such that the resistivity can change 2-3 % in the presence of a magnetic field. As with the Hall sensor, the voltage (= resistance x current) is measured to indicate the strength of the magnetic field. 

Both these types of sensors are of simple design, cheap to manufacture. There are differences; for example that Hall sensor detects fields that are perpendicular to the current, while AMR senses parallel fields. The AMR has a wider detection area, and are faster, but Hall sensors are still cheaper, and can be smaller (down to a couple of millimetres) why they are more popular. With that said, they are still used for similar applications.

Now, lets focus on the cars again and how these sensors are used in them. We start with the wheel speed sensor.

Connected to the wheels of your car, there is a wheel speed sensor that measures the rotation speed of the pulse wheel (a wheel that is connected to the actual driving wheel, so it has the same speed). A sensor – often a Hall sensor with an incorporated magnet ‚Äď is positioned so that the magnetic field from the magnet ‚Äúcovers‚ÄĚ the cogged pulse wheel. Since the cogged pulse wheel is ferromagnetic, it will change the magnetic field depending on the cog is up or down, and thus also change the output voltage of the sensor. A microprocessor then keeps track of how many ups and downs there has been per time unit, and calculates the speed from that. See picture below.

Picture showing the graph for the output voltage from a Hall sensor next to the Pulse wheel.

Picture showing the graph for the output voltage from a Hall sensor next to the Pulse wheel. Source: Hella

Wheel speed sensors improve comfort and safety

Apart from telling you the speed of your car, the information from the speed sensors can be used to make driving more comfortable, for example with the use of cruise control. You set a speed you want to keep, and when the speed drops below, a signal is sent to the fuel pump to pump harder.

It is also used for safety applications. Heard of ABS? It is short for Anti-lock Braking System, and is a control system that modulates the break pressure in response to the detected wheel speed deceleration. So if you do an emergency break, the wheels won’t lock, instead it makes sure that the car decelerates in a controlled manner, so that the steer ability is not lost and the car won’t slide. (Read more here.)


Ever wondered how the fuel level is measured?

A Hall-type magnetic sensor is installed in the ceiling of the tank, and a floating magnet is put into the tank. The higher the level is, the closer the magnet is to the sensor and the higher the output will be. See picture below.

Picture showing how fuel level can be measured. By using a Hall sensor at the top, the distance to a floating magnet, and thus the level, can be measured.

Picture showing how fuel level can be measured. By using a Hall sensor at the top, the distance to a floating magnet, and thus the level, can be measured. Source: Nagarjuna College


Volvos aims to revolutionise road travel with magnetic sensors

The magnetic sensors can be used for a lot of things. In fact, Volvo thinks that they could
be used to guide tomorrow’s autonomous cars.

The idea is to put magnets into the roads, and then use magnetic sensors on the underside of the car to sense where it’s going and what is in the surroundings. This would improve both comfort and safety.

Video: TomoNews

I bet you wonder which kind of sensor they use?

With car speeds of 90 km/h, the sensors need a sampling rate of 400 readings per second.  And since the sampling rate of the Hall sensor is far from this, they have to use AMR sensors, which are much faster.

Volvo actually built a test road (in Hällered, Sweden) and tried the technology out, and if they can reduce the costs ($24,405 per kilometer highway), the future where we drive autonomous cars might not be that far away after all.


The magnets of the green cars: Motors

¬†EREAN is a European research project that is working on the recycling of NdFeB magnets ‚Äď why today I will discuss how they are used in one of its larger applications. Motors. According to Arnold Magnetics (presentation, 2012), a third of all NdFeB magnets are used in motors.

A large portion of these motors is being used in cars, why I will focus on these today. (Other areas where they come into use are industrial machinery, wind turbines, and electric bicycles)

They are used in order to make the cars more energy efficient, ergonomic, light, environment-friendly and quiet, and have been employed more and more as the demand for these qualities have risen stronger and stronger. Hybrid and electric vehicles use more, but even a normal car today can contain hundreds of magnets, see picture below, where most of the objects that are pointed out are small motors.

A sketch showing that cars contain a lot of magnets.

A sketch showing that cars contain a lot of magnets. Source: Ald-vt

Now, lets see how they work.
Starting with the largest in size, we have the electric motor/generator, which usually contains a couple of kilograms of NdFeB magnets. They come in various designs, but they are all based on what we all know about magnets; that opposite poles attracts, and same poles repels.

A sketch showing how magnets can be used to create rotational movements.

A sketch showing how magnets can be used to create rotational movements. Source: Flantoons

On the picture above we have two magnet wheels, and an iron bar in between. What will happen is that the iron bar attracts the magnets, so they move closer to it. When they come close, the magnets meet each other with same poles, creating a strong repulsion that makes the wheels to continue rotating in that direction. This can be compared with the mechanical gears below.

Mechanical gears.

Mechanical gears. Source:

A good thing about the magnet wheels compared to the gears is that there is no physical contact between the parts, which means that they wont wear and tear, and thus last for a longer period of time. Also, the need for energy input to rotate the wheels is much less for the magnet version.

Now, the actual motors of course don’t look like this. As mentioned, they have various designs, but most of them are based on the same principles. In these, you will find a permanent magnet part (with NdFeB magnets) and an electromagnet part made of coiled copper wires.

An example of an electric motor, disassembled to the right showing the electromagnet-stator and the permanent magnet-rotor.

An example of an electric motor, disassembled to the right showing the electromagnet-stator and the permanent magnet-rotor. Source: Stevens Aero

In the example design above, the copper part is on the inside, with several separate coil sections. On the outside we have the permanent magnet part, also this is made up of several separated magnets, of alternating direction.

When an electric current is sent through one of the copper coils, a magnetic field is produced around it. You can say that it becomes a magnet, an electromagnet. And if this electromagnet comes close to a permanent magnet with same poles facing each other, they will repel, and we will have movement. In this example the inner part is fixed in position (called stator), so the outer part will move (called rotor). We see that it has a bar connected to it, and this is then connected to the wheels and is what makes the car move.

Although there are some disadvantages of the electric motor compared to conventional motors (hard to regulate and control, need for external energy input to start), the advantages are vast. Not only are they more durable as mentioned before, they are extremely quiet, light and small, and energy efficient.

Another good thing about them is that they are versatile. In some cars, they are not only used as motors, but also as generator and when the car is breaking, it takes the kinetic energy and turns it into electrical energy that is then stored in the battery (think of all the energy that is normally turned into heat due to the friction during braking). This is called Regenerative Breaking. (VIDEO)

Another way of saving energy when using an electric motor is to use Start/Stop technology. It will automatically turn off the motor when the car is at standstill (sensed by a magnetic sensor)- for example at traffic lights – and save up to 10% energy. (VIDEO)

When the traffic light turns green, you only have to push the gas pedal to get the motor started again. According to Ombach, if you use Regenerative Breaking and Start/Stop technology, you will reduce the CO2 emissions from your car with 7 %.

Small electric motors for your comfort

The large electric motors are of course only used in hybrid and electric vehicles. But the miniatures are used in all kinds of cars, and they are of similar design, but smaller. While the large motors can contain kilograms of magnets, the small ones are in a range of grams to tens and maybe hundreds of grams. It doesn’t sound a lot, but it will when you take into account that they come in large numbers. According to Ombach, a middle-class car contains on average 36.1 kg of these motors.

Many of the small motors are today made with ferrite magnets, but in the future we will probably see these being replaced with the stronger NdFeB magnets, to reduce weight and size by up to 50 %. (Honkura, 2006)

They are used to adjust your seat so you don’t have to turn the adjustment wheels yourself, as we did in the nineties. They are used to lift and wipe windows, lock doors and pump fuel and also to help you turn the steering wheel, with the so-called Electric Power Steering (EPS) motor that amplifies the turn you make on the wheel. By changing to this technology from the hydraulic system that is used otherwise, you will reduce the CO2 emissions of the whole car with 4.5 % (Ombach).

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As time progress and we want our cars to be cleaner, lighter, and more comfortable, we will see more of the magnet motors (big and small), and more of the NdFeB magnets.

But it is not only motors that bring magnets into your car.

Other applications worth mentioning are speakers (magnets make them vibrate and generate sound) and magnetic sensors, which we’ll discuss next week.

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Until then, drive safe.

Rare Earth Magnets in Magnetic Levitation

Along with several other applications such as electronics goods described in previous posts, permanent rare earth magnets are also needed in special applications such as magnetic levitation. Even though for some people it still sounds like a magic, magnetic levitation concept was first introduced in 1900’s by Robert Goddard and Emile Bachelet [1]. It is a method where an object can be suspended with no other support than magnetic fields or simply it is fighting with and winning against the pull of gravity with invisible magnetism tricks.

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