The qualities of an electromagnetic field

This article was found on http://www.helium.com

It was written by Ian Loft

Created on: September 07, 2008

In the early 1990's I worked in a power station where my job required frequent excursions into the generator room, inside control booths, behind the alternators and around the huge power bus bars carrying many hundreds of amps of electric current. I soon learned to leave my wallet in which credit cards and electronic identification cards on which magnetic strips activated various readers locked in my desk draw because proximity to power generating equipment and high currents exposed them to electromagnetic fields and they became very quickly corrupted.

Few people today realize the importance of magnetic fields and their underpinning of almost all electronic applications in today's world of gadgets, automatic functions, motors, generators, transformers, decoders, electronic filters and speakers just to name a few. Each of these devices or appliances incorporate magnetic fields in various ways and at different frequencies, for example speakers are designed to operate across a limited range of audio signals while a transformer employs the fundamental principle of mutual induction that enables us the ability to boost or reduce power and current.

So what is a magnetic (electromagnetic) field? In simple terms it is possible to visualize a magnetic field by comparing it to a stream of water. The current flows in one direction and vary in strength much as a magnetic field can vary in strength, and where the direction of flow is from north and south poles. This can be demonstrated using a bar magnet and fine iron filings scattered on a piece of paper. Place the magnet under your paper and scatter filings across the top. As you rotate the magnet underneath you will see the field shape and orientation by the way filings line up and form around the magnet shape.

An electromagnetic field is simply a field induced by way of applying electrical current. In the wire itself an electromagnetic field surrounds the core and this field can be increased to incredible strengths by winding the conductor around an iron core. Ever dropped a small screw down an inaccessible place and wondered how to retrieve it? Try this: find a length of find insulated wire say about four or five feet in length. Wrap it tightly around a long screwdriver and use a little sticky tape to hold it in position. Ensure both ends come out close to the handle; you can wind the wire up and down in several layers to increase the power. Bare ends and clamp, screw or solder them to a battery holder (AA size is sufficient), and include a single throw switch. When you insert a battery and close the switch you will have a very effective electromagnet careful the wire does not heat up too much. A brief flick of the switch is usually enough to magnetize your screwdriver but if this is not enough then insert your screwdriver down where you dropped what you are trying to retrieve then close the switch.

Electromagnetic fields are used in alternative current (AC ) applications where induction enables proportional increase and decrease in voltage and current. This enables power boosted to many thousands of volts at a small current to be transmitted hundreds of miles then reduced in voltage (with a proportional increase in current) for domestic and industrial use. This becomes possible because the reversing of field direction (north and south orientation) many times a second is picked up by wires coiled tightly around the magnet (usually an iron core). This process is called induction and is one of the most fundamental principles of electromagnetic field applications universally employed across power and electronic industries.

Audio applications employ two fundamental qualities of electromagnetic fields: frequency combined with the properties of the magnetic core used. The electromagnetic field dynamics of audio engineering are truly a feat of scientific magic enabling hi-fidelity replication of sound improving as new core materials offer improved frequency control.

Electromagnetic fields pass through almost all solid matter which means it is possible to conceal the source for purposes such as security alarms where a balanced electromagnetic field will activate an alarm when the field is broken (door opened) or the field is disrupted by someone attempting to disable it using a metallic object. The density of the solid will vary the distance an electromagnetic field is projected moreover it takes a significant amount of energy to project a magnetic field over a relatively short distance however modern technology is gradually improving field projection with less power.

In all and without launching into esoteric mathematical explanations describing properties of an electromagnetic field it is clear that most of the technology we take for granted today would not be possible without the exploitation of basics such as mutual induction, permeability (ability to pass through solid matter) and frequency response where effects of frequency induce vibrations (sound). As you read this be aware that within your computer there are billions of tiny cells in which individual electromagnetic fields oriented in combinations of north and south orientation make it all possible but that is another story!