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Most people recognize magnets as toys or materials with limited applicability like fridge magnets or simple magnets to hold papers when attached to a metal surface. What many people do not know is that in fact magnetic materials (magnets) have a wide range of applications in many areas of our lives like medical services, security devices, communications, transportation and even nowdays magnetic materials are wide use in areas like jewelry where the development of magnetic bracelets and earrings has changed the way people conceive magnetism. Here is presented a review of the main applications that magnetic materials have in the modern world and the future applicability of the new types of materials that are produce these days.
Compasses
Compass represent a traditional application of magnets. A compass is an instrument use to measure directions using as reference the earth's magnetic poles. The frame of reference consists of the four cardinal points, north, south, east and west. The magnetic compass interacts with the earth magnetic field, which is like a giant bar magnet, pointing towards the magnetic poles of the earth.
The Chinese were the first to note these phenomena because their lack of knowledge about the electromagnetic forces that cause this effect. The compass was invented during the Han Dynasty between the second century BC and the first century AD and was only used for navigation by the eleventh century. Later on it was introduced to Europe where was replaced by the dry compass. In the 20th century the liquid-filled magnetic compass was introduced. The invention of the compass was certainly one of the most important creations in the history of humanity.
Magnetic Resonance Imaging (MRI)
MRI is a technique broadly use nowdays in medicine for the diagnosis of different diseases like cancer. It main use relations on the construction of images of internal organs of the body avoiding the use of surgery to find and diagnose the disease. Because the body is composed of mainly water molecules, MRI uses the properties of water in the presence of a high magnetic field to produce an anatomical image of specific areas of the body, being especially useful for the imaging of the brain, muscles and the heart . In a MRI device a magnetic field is used to make hydrogen atoms in water molecules resonate at a given frequency and then a radiofrequency pulse is applied changing the energy state of the spins. When the radiofrequency pulse stops, electromagnetic signals are emitted due to the relaxation of the spins; this is detected by the instrument and an image is formed taking advantage of tissue contrast.
Magnetic nanoparticles
Nanoparticles and nanomaterials consist of materials with sizes less than 100 nanometres. Many types of nanoparticles like quantum dots, liposomes, gold nanoparticles, carbon nanotubes and magnetic nanoparticles are design today for different applications in medicine and industrial processes. Among these materials, magnetic nanomaterials have been widely used for the detection of cancer and many other diseases. Magnetic particles can be used to enhance the signals caused by the water molecules in the body when a magnetic field is applied like described in MRI, so these nanoparticles serves as contrast agents for MRI. Besides that, they can also use to kill cancer tumors by means of hyperthermia. Hyperthermia consist of the production of heat by very small magnetic particles when a magnetic field is applied. This heat can be use to kill cancer cells specifically after accumulation of the small particles in a tumor and is being research nowdays as an alternative to traditional methods to treat cancer like radiotherapy.
Alarms
Many burglar alarms are based on the use of magnets. Basically these alerts consist of a contact switch which responds to changes in the environment sending a signal to a noise making device. A permanent magnet is installed in the frame of a door or a window together with a magnetized material in other part of the window or door creating a connection between the two materials once the alarm is activated. When something disrupted the magnetic field created between the magnet and the metal by opening the door or the window, the alarm is activated.
Magnetic levitation trains or MAGLEV trains
MAGLEVS trains consist of a mode of transportation based on the use of powerful magnetic fields to suspend, guide and propel trains by using magnets instead of mechanical methods like wheels, axles and bearings. As this fast vehicles are lifted from the ground by magnetic forces they are claimed to move faster, smoother and quietly and require less maintenance in respect to wheeled trains. Acceleration and deceleration can be achieved faster as the system is claimed to not rely on friction.
Speakers
Speakers consist of a wire carrying an alternate current. When the wire is located in the magnetic field of a circular permanent magnet (that surrounds the wire) it experiences a force that generates sound waves by compression and rarefaction of the air surrounding the device. This vibrates a cone shaped diaphragm that reproduces the sound generated at the source.
Other uses of magnetic devices include credit and debit cards, televisions, electric guitars, electric motors and toys and represent an important factor in the development of new technologies for different purposes around the world.
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