While researching the Carbon Fibre article, I found that one of the characteristics of carbon fibre was that it could shield electro magnetic radiation.
When I tried to understand what that meant, I realized that my understanding of EMR was not good enough to understand what it meant that carbon fibre could shield, so I went back and started filling in the gaps. As it turns out there are a lot of questions un answered and this page is a work in progress.
First Question, What is EMR Electro Magnetic Radiation?
This turned out to be a particularly difficult question to answer.
Depending on what kind of scientist you ask you can get many different answers. This depends on their point of view.
Consider a Rabbit, humour me for a paragraph, there is a point to this. If you ask a clover flower what a rabbit is, she will answer that it's a terrible monster that eats clover. If you ask my grandson, he will say it's a cute friendly animal often kept as pets. If you ask my Italian neighbour, she will likely pull out her grand mama's recipe, while if you ask a slipper manufacturer, he will wax poetic about the soft warm fur. A biologist will likely talk about a medium size herbivore mammal which is quite low in the food chain. Monty Python fans might talk about killer rabbits. The definitions go on depending on who you ask. Everyone is right, but the answers are very different.
Electro Magnetic Radiation is a kind of energy. Remember energy is something that has the potential to do work or cause something to change.
The Formal Definition of Electromagnetic Radiation: "Classically, electromagnetic radiation consists of electromagnetic waves, which are synchronized oscillations of electric and magnetic fields, that propagate at the speed of light through a vacuum."
You cannot separate the "Magnetic" from the "Electrical", together they are EMR.
Wherever you have electricity, then somewhere there is magnetism, and if there is a magnetic field, electrical phenomenon is not far away.
It's been useful to compare EM radiation waves to water waves. In some ways they are very similar. There can be big high waves far apart or short waves close together. They propagate from a point and the further you get, the weaker the effect. Do a cannonball off a dock. It will splash anyone near mightily, but a canoe 100 feet away will be almost unaffected.
There are some major differences. Where as water waves need water to be propagated, Electro Magnetic waves will happily move through a vacuum. This is where it gets a bit fuzzy in my brain. Scientists talk about Photons which behave a bit like particles but are not. They sometimes behave as though they have mass but not really. You are now in the domain of Quantum theory, Einstein, and other lofty science. Quantum, by the way, simply refers to the smallest indivisible quantity unit of energy. In the world of emr the smallest indivisible unit of energy is a PHOTON. You cannot have half a PHOTON.
Quantum theory cannot be explained by normal physical comparisons. You need to understand the math of the system and I am not going there. Good old Wikipedia has an article on Photons that is a useful place to start if you are interested. There are lots of Additional References and links.
EMR, what can it do
For a layman, a more useful way of describing Electromagnetic Radiation is to focus on what it can do, good and bad. In order to understand this a bit better I'm afraid a SMALL BIT OF MATH is useful.
Earlier we said that Electro Magnetic Radiation moves through a vacuum at the Speed of Light. That never changes. If light goes through air, or glass or even water, it slows down. That's why it gets bent. Enyone trying to look at stuff in the water will know that.
Wavelength and Frequency
We know from our analogy with water, that waves have a wavelength, that is the height of a wave, and a frequency, that is how many waves pass a certain spot in a given time period.
Image courtesy of NASA
The wavelength is measured in Meters or fractions of meters. EMR can have very large and very small wavelength. If you look at the diagram, the Gamma Rays on the right, have a wavelength of 10-12. That is very small. The -12 means that the decimal point has been moved over by 12 spots. 0.000 000 000 001 metres. At the left of the scale, Radio waves have much larger wavelengths upwards of 1 metre. There are wavelengths of 1 Kilometre in size at the extreme end.
Image courtesy of LucasVB, Wikipedia commons
The frequency or number of cycles per second, is just a number. This number is given a name: hertz
A frequency of one hertz (1 Hz) is one cycle per second. One hertz just means "one cycle in one second." It's faster to say 1 hertz. If there are 10 waves that go by in one second, then the frequency is 10 Hz. The frequency can be very large or very small.Our gamma rays have tremendously high frequency at 1020 hertz, while our radio waves have a frequency of 104. The higher the frequency the smaller the wavelength and the lower the frequency the larger the wavelength. (more later)
These are the most commonly used units when talking about EMR
Units, or Alphabet Soup
|Name (Symbol)||Base 10||Number|
|Tera (T)||1012||1 000 000 000 000|
|Giga (G)||1010||1 000 000 000|
|Mega (M)||106||1 000 000|
|Micro (µ)||10-6||0.000 001|
|Nano (n)||10-9||0.000 000 001|
|Pico (p)||10-12||0.000 000 000 001|
|Femto (f)||10-15||0.000 000 000 000 001|
|Atto (a)||10-18||0.000 000 000 000 001|
What is the relationship between frequency and wavelength in EMR?
As it turns out, the frequency and the wavelength are closely related. The lower the frequency, the larger the wavelength and vice-versa.
The Relationship of frequency and wavelength is linked to the speed of light such that the frequency x wavelength = speed of light. EMR travels at the speed of light in a vacuum. (Remember we agreed not to fuss too much about the why.)
c stands for Speed of Light which is 299,792,458 metres per second (Rounded up it's approximately 3.00×108 metres per second, or 300,000 kilometres per second)
The Frequency is represented by ν, and the wavelength is represented by λ
So the Speed of Light = Wavelength x Frequency, or c=λν. You can restate the relationship in other forms. c/ν=λ and c/λ=ν
Since the speed of light does not change, it is a constant, then if a wave has a small wavelength it will have a high frequency and if the frequency is low, it will have a high wavelength.
What is the relationship between frequency and Energy?
The relationship of the frequency and the amount of energy is represented by E = hc/λ, We are already familiar with the "c" and "λ": speed of light and the wavelength. E, stands for energy and h is Plank's constant. 6.62607004 × 10-34 m2 kg / s
The Energy equation can also be represented more simply as E=hf so the Energy equals plank's constant times the frequency.
Plank's constant (and various other constants used in physics) is just a way of sorting out the units so that whatever we are multiplying and dividing comes out in units we can work with. It does not change the values, just translates it in units we can work with. Planck's constant h converts the energy of a photon with some wavelength (in meters) into Joules. Which is an energy unit scientists are comfortable working with.
The important things to remember is The higher the frequency the lower the wavelength, and the higher the frequency the higher the energy carried in the wave.
When quantifying the amount of energy of electro magnetic radiation scientists use the electron-volt (symbol eV) is a unit of energy equal to approximately 1.6×10−19 joules. Here is a link to Electron volts explanation The quantities in Joules is so small that the electron volt has been coined to make the numbers easier to work with.
Electromagnetic Radiation Occurs in a range of Frequencies
At the very high end we have the high energy Gamma Rays. At the low frequency end, we have the low energy Radio Waves.
Image from NASA
Here is an image showing the electromagnetic spectrum.
The wavelength of the gamma rays is mind boggling small, while the wavelength of the radio waves can be quite large.
Somewhere in the mid range, (where the eye is in the image,) is the visible spectrum. We are most familiar with the visible range or visible spectrum of electro magnetic radiation. These are the only wavelengths humans can see but of course there are many more on both side of the range. Some animals and insects are much more sensitive to the ultra violet range than we are. Butterflies see much better than we do in that range and use this to identify flowers they can feed on. Other animals and insects can detect infra red, which is also just outside our range, to identify warmer spots either to bite in a vein or to improve night vision.
I often set an infra red camera critter cam to see who visits after dark. In the first photos the animals are often looking straight at the camera. I always suspected that they could see some of the infra red flash. I can't but it's too much of a coincidence that they are often looking with a startled look. The camera makes no noise.
What kind of energy does Electromagnetic radiation carry?
EM radiation can manifest itself in many ways. It can be as simple as heat, or visible light, or UV when we get a sunburn. Radio waves are widely used to carry information, either by changing the frequency (FM, frequency modulation) or changing the wavelength (AM, amplitude modulation). Or simply by bouncing radio waves in Radar. We use EM in cooking in our microwave ovens. Microwaves, which are low energy radio waves can excite our food and cause heat. Radio waves are often used in heat sealers to melt and join plastics and other materials in industrial processes.
The increasingly popular induction cook tops use an electric current to create a magnetic field that extends above the cook top. This in turn generates a current in the ferromagnetic pot and this alternating eddy current causes the pot to heat up because it is not a perfect conductor (it has resistance) and the current going through causes friction thus heat. This is a good example of induction.
"Electromagnetic induction is the production of a voltage (and current) across an electrical conductor in a changing magnetic field."
That is the basis of generators which are just efficient ways of moving an electrical conductor across a magnetic field to produce a voltage and thus current.
If you move a wire across a magnetic field you produce a voltage. This can be see by moving a wire above a magnet and recording the current created using a multimeter. It's also true that if you cause a current to go around a wire, you will create a magnetic field. This is the basis of electro magnets.
Induction can be controlled and wanted or it can occur as an unwanted side effect of electromagnetic radiation.
The scale of this phenomenon can be very small and only affect a small area such as around wires carrying small amounts of current or can be very large and encompass the whole earth (which behaves as a giant magnet with north and a south magnetic poles.)
When there are solar flares, a large amount of Electro magnetic radiation cause oscillating magnetic fields which can disrupt electronic equipment and transformers causing damage and blackouts. Power wires or pipelines can be susceptible to this.
We are immersed in Electromagnetic energy. Much of it comes from our sun but other sources are from deep space, cosmic rays, and from atomic decay of natural minerals. Some of the radiation is man-made. Radio waves are common but there is also a whole collection of EMR that is a by product of electricity pulsing through wires.
Very strong radiation can induce enough voltage and current to deliver electric shocks or or produce sparks.
What exactly is "Radiation"?
We've already talked about Electro Magnetic Radiation. Scientists tend to think of radiation more in terms of what it can do, dangers to life or property rather than just generalized EMR. Radiation becomes quite an ill defined term. We often like to think of radiation in terms of Non Ionizing Radiation and Ionizing Radiation.
Non Ionizing Radiation
Although non-ionizing radiation can excite atoms by making them move faster, (as in microwaves, which excite the water molecules and makes the water warmer,) it doesn't have enough energy to damage atoms. Non ionizing radiation is usually thought of radiation in the area of lower energy UV light, visible light, microwave , radio including cell phones. This does not mean that you cannot be hurt by the effects of the radiation, rather it means that it's not the radiation itself hurting you, rather the EFFECTS. Microwave will excite the atoms and temperature will go up and you can get burned. Same thing happens with the areas around radio antenna and infra red heating lamps.
Although atoms are not modified there can be subtle effects and there is some debate as to the effect and dangers of this.
Ionizing radiation is another thing completely. It has enough energy to change atoms by remove electrons from them, it ionizes them. This can cause a great deal of biological damage. We commonly run into ionizing radiation in X-rays, High energy Ultra Violet, Gamma rays from being high in the atmosphere.
Scientists differentiate between the different kinds of ionizing radiation. They speak of three main types
Alpha Particles (α). Here is a link to a relatively simplified article on α radiation
Beta Radiation (β) Link to Beta particle - radiation
The higher frequency electromagnetic radiation including Ultra Violet, X-ray and Gamma Rays all carry enough radiation to ionize atoms and molecules that is to knock out electrons from their structure thus ionizing them.
Usually lower energy radiation is not considered ionizing. Non-ionizing radiation includes visible light, infra-red, microwave and radio waves are in that group.
Some substances ionize at a much lower energy level than others. Cesium requires only an energy level of about 4 electron volts to ionize, but for the most part 10 electron volts and higher is considered ionizing radiation. This is about the energy put out by 124 nanometers wavelength, UV light. This is a somewhat movable definition depending on who you ask. In Biological systems the amount of energy required to ionize water (33 electron volts, eV,) is the benchmark level.
Some lower energy electromagnetic radiation which is not capable of ionizing atoms or molecules, can nonetheless excite molecules and damage less strong molecular bonds. Sunburn is an example of this but lower energy level radiation can also damage DNA.
Ionizing radiation can cause a number of diseases including Cancer, cognitive decline and heart disease.
Ionizing radiation can come from many sources including man made sources, radiation from space such as cosmic rays and from solar flares. For the most part, we are shielded from such harmful natural radiation by the atmosphere (remember the ozone layer) but in the event of solar storms or frequent traveling in airplanes or in long sojourn in space, we might be exposed to ionizing radiation.Article on Wikipedia on Ionizing Radiation.
Many "radio active" substances emit Electromagetic radiation as they decay.
Electro Magnetic Radiation (EMR) and Health
The dangers of ionizing radiation are well documented and acknowledged. Non ionizing radiation is different. In devices emitting low levels of EMR, it is just very difficult to assess the effects and determine if there is any danger. The range, visible, infra red, microwave and radio frequencies are widely produced.
Heat is one well known effect of electromagnetic fields. This is seen around antennas when high-power transmissions are happening. This is pretty much the same effect as microwave heating. You can get a nasty burn from this.
Various governing bodies are well aware of heat production and limit the exposure to various frequencies and help protect us against thermal damage.
Induced Currents In the same way that a current can be induced in a wire or other conductor, currents can be induced in the human body when exposed to maganetic fields. They can cause tingling sensations or go completely undetected.
The effects of these currents can be detected but the effects are not well understood.
There is some concern that long exposure to low level non-ionizing radiation could be harmful. Radio waves produced by many processes including cell phones use have been pointed out as potentially damaging. Because prolonged exposure is required and it is difficult to demonstrate a cause and effect in a long term exposure case it has not been possible to clearly establish the effect of such devices. So far they are rated as safe when used according to manufacturer's directions.
Many instruments used on boards recreational boats carry warnings. Radar should be installed above human levels, radio, particularly the higher energy range should not be held up to the head but rather spoken into. Even cell phones have recommended distances to the ear/body.
The World Health Organization has issued a warning that mobile phone signals as "possibly carcinogenic to humans". So far no adverse health effects could be established.Wikipedia article on Electromagnetic Radiation and Health
Link to National Cancer Institute (US) on Cell Phones and Cancer Risk page It shows a reassuring lack of evidence between cell phone use and the risk of cancer.
Visible light has been shown to have effects on humans. More recently blue light emitted by LED lights in computer screens for example has been shown to be disruptive to the circadian rhythms and interferes with sleeping. It disrupts the melatonin.
Harvard Medical School has an article about the effects of blue light.
Shielding is a tremendously complex subject because of the various types of Electromagnetic Radiation with vastly different energy content, and because of the many way they interact with various types of shielding materials. Intensity of the radiation also has an effect on the amount of shielding. The first question that comes to mind is WHAT do you need to shield. Gamma Rays and other high energy radiation? X-rays, Ultra Violet, Visible light? Infra red? Microwaves or Radio Waves?
Ideally you want the minimum amount of shielding to work for the radiation you are trying to eliminate. For example, 2 inches of lead might be an effective shield against Ultra Violet damage, it makes very poor and very expensive curtains.
Weight is an issue when you are designing shielding that needs to be lifted to orbit, or in use for airplanes where weight equals cost.
Shielding is an issue microwave manufacturers have solved by making the enclosure of the microwave from metal. The microwaves are too weak to pass through the sheet metal enclosure. Another solution to microwave shielding is the mesh that covers the window. This mesh, or rather sheet with lots of small holes, allow visible light through but blocks the microwaves.
Electromagnetic shielding is used to reduce EM fields or the particles emitted by radiation sources. It is accomplished by enclosing an area or a radiation source with conductive or with magnetic material. Cables are routinely shielded to avoid induction problems while electronic devices are often protected from surrounding equipment by shielding. Electromagnetic shielding that blocks radio frequency electromagnetic radiation is known as RF shielding.
Faraday Cages are enclosures which are shielded by conductive web of material such as copper. They are used in cases where a radiation free area is required. This is often seen in research.
EM Shielding has serious health consideration in cases where exposure can be quite high. It is even more important in cases where the EMR is high frequency ionization radiation.
Space travel and frequent airplane fliers, such as pilots and air crews, are at particular risk. The earth's atmosphere shields the earth from Gamma and other ionizing radiation but the higher up you go the more penetration by dangerous radiation there is.
Other occupations such as X ray technicians, nuclear plant workers, researchers, emergency crews and military personnel.
Here is an interesting article on Materials Used in Radiation Shielding Shielding of Ionization Radiation.
email me if you find mistakes, I'll fix them and we'll all benefit: Christine