What is radiation?

All matter is composed of atoms and many atoms are unstable. In fact, over half of the elements in the periodic table including uranium, are in a constant process of rearranging themselves. This is not something that humanity can control.

When the nucleus of an atom attempts to become more stable, it releases energy, known as radiation. Once this happens the original atom changes into When the nucleus of an atom attempts to become more stable, it releases energy, known as radiation. Once this happens the original atom changes into a new atom. In some instances, a new element is formed and in other cases, a new form of the original element, called an isotope, appears. The sponta-neous change in the nucleus of an unstable atom that results in the emission of radiation is called radioactivity and this process of change is often re-ferred to as the decay of atoms.

Radioactive decay is described in half-lives. The time required for 50% of a given radioactive material to disintegrate (or decay) and become a new ele-ment or isotope (i.e. lose one-half of its original level of radioactivity) is known as a half-life. In other words, after one half-life only half of the original material is still around, and after two half-lives only 25% of the original material is still in existence. The half-lives of various substances differ widely, from small fractions of a second to billions of years.

Radiation is energy in the form of sub-atomic particles (protons, neutrons and electrons) or electromagnetic waves. When radiation has enough energy to remove the electrons of atoms with which it interacts, it causes the atoms to become charged, or ionized, and it is called ionizing radiation. Ionizing ra-diation occurs in several forms - as alpha particles, beta particles or neutrons, or in the form of electromagnetic radiation (gamma rays and X-rays). However, people routinely encounter electromagnetic radiation that is not ionizing. It makes up our visible light, radio and television signals, emanates from our computer screens and heats our food in microwave ovens. Yet, because of their low energy, all of these examples are classified as non-ionizing from our computer screens and heats our food in microwave ovens. Yet, because of their low energy, all of these examples are classified as non-ionizing radiation.

What are the sources of radiation?

Radiation is all around us and we are exposed to some form of it every day of our lives. Most natural substances contain radioactive material - soil and rocks, rivers and oceans, food and drinks, our own bodies. A typical backyard, with dimensions of 10 metres by 10 metres and a soil depth of one metre, contains approximately 300 grams of uranium. A typical backyard is therefore slightly radioactive. While uranium emits radiation it is not the only source.

More than 85% of all radiation to which people are exposed occurs naturally, but radiation is also created by our own activities. Take for example the X-rays generated for medical uses. These represent about 12% of the radiation to which we are regularly exposed. Radiation from the nuclear industry is less than 1% of all radiation. A person living at the boundary of a nuclear power plant would receive less radiation each year from living there than re-ceived from a single round-trip flight from Vancouver to Halifax.

A Radio Wave is not a Gamma-Ray, a Microwave is not an X-ray ... or is it?

We may think that radio waves are completely different physical objects or events than gamma-rays. They are produced in very different ways, and we detect them in different ways. But are they really different things? The answer is 'no'. Radio waves, visible light, X-rays, and all the other parts of the elec-tromagnetic spectrum are fundamentally the same thing. They are all electromagnetic radiation.Electromagnetic radiation can be described in terms of a stream of photons, which are massless particles each traveling in a wave-like pattern and moving at the speed of light. Each photon contains a certain amount (or bundle) of energy, and all electromagnetic radiation consists of these photons. The only difference between the various types of electromagnetic radiation is the amount of energy found in the photons. Radio waves have photons with low energies, microwaves have a little more energy than radio waves, infrared has still more, then visible, ultraviolet, X-rays, and ... the most energetic of all ... gamma-rays.

Actually, the electromagnetic spectrum can be expressed in terms of energy, wavelength, or frequency. Each way of thinking about the EM spectrum is Actually, the electromagnetic spectrum can be expressed in terms of energy, wavelength, or frequency. Each way of thinking about the EM spectrum is related to the others in a precise mathematical way.

Electromagnetic waves are transverse, but they are not mechanical. They do not re-quire a medium.

The fact that they are not mechanical means that elec-tromagnetic waves can trans-port energy in a vacuum. As we know from everyday ex-perience, light or electro-magnetic waves can also travel in media such as air, water, and glass.

Electromagnetic waves con-sist of oscillating electric and magnetic fields.

As with mechanical waves, electromagnetic waves carry energy (proportional to the square of the amplitude of the electric and magnetic fields) and have a wavelength and a speed.

The speed of electromagnetic The speed of electromagnetic waves in vacuum is always c, the speed of light ( 3 x 108 meters per second). In other media, the speed is less than c.

γ= Gamma rays Radio wavesHX= Hard X-Rays EHF= Extremely high freq. SX= Soft X-Rays SHF= Super high freq. EUV= Extreme ultraviolet UHF= Ultra high freq. NUV= Near ultraviolet VHF= Very high freq.Visible light HF= High freq.NIR= Near InfraredNIR= Near Infrared MF= Medium freq.MIR= Mid infrared LF= Low freq.FIR= Far infrared VLF= Very low freq. VF/ULF= Voice freq. SLF= Super low freq. ELF= Extremely low freq.

Fastest waves ever photographed

Plasma physicists at the Universities of Texas and Michigan have phoPlasma physicists at the Universities of Texas and Michigan have pho-tographed speedy plasma waves, known as Langmuir waves, for the first time using a specially designed holographic-strobe camera. The waves are the fastest matter waves ever photographed, clocking in at about 99.997% of the speed of light. The waves are generated in the wake of an ultra-intense laser pulse, and give rise to enormous elec-tric fields, reaching voltages higher than 100 billion electron volts/meter (GeV/m). The waves' electric fields can be used to acceler-ate electrons so strongly that they may lead to ultra-compact, tabletop versions of a high-energy particle accelerators that could be a thou-sand times smaller that devices which currently exists only in large-scale facilities, which are typically miles long.

Until now, a critical element necessary for understanding interaction between electrons and accelerating wakes has been missing: the abil-ity to see the waves. The new photographic technique uses two addi-tional laser pulses moving with the waves to image the wakefield ripples, enabling researchers to see them for the first time and reveal-ing theoretically predicted but never-before-seen features. The ability to photograph these elusive, speedy waves promises to be an important step towards making compact accelerators a reality.

Images of a wakefield produced by a 30 TW laser pulse in plasma of density 2.7 x 10̂ 18 cm -̂3. The color image is a 3-D reconstruction of the oscillations, and the grey-scale is a 2-D projection of the same data. These waves show curved wave-fronts, an important feature for generating and accelerating electrons that has been predicted, but never before seen.

What is Scientific Visualization? Scientific visualization, sometimes referred to in shorthand as SciVis, is the representation of data graphically as a means of gaining understanding and insight into the data. It is sometimes referred to as visual data analy-sis. This allows the researcher to gain insight into the system that is stud-ied in ways previously impossible.What it is not- It is important to differentiate between scientific visualiza-tion and presentation graphics. Presentation graphics is primarily con-cerned with the communication of information and results in ways that are easily understood. In scientific visualization, we seek to understand the data. However, often the two methods are intertwined.

From a computing perspective, SciVis is part of a greater field called visu-alization. This involves research in computer graphics, image processing, high performance computing, and other areas. The same tools that are used for SciVis may be applied to animation, or multimedia presentation, for example.

As a science, scientific visualization is the study concerned with the inter-active display and analysis of data. Often one would like the ability to do real-time visualization of data from any source. Thus our purview is infor-mation, scientific, or engineering visualization and closely related prob-lems such as computational steering or multivariate analysis. The ap-proaches developed are general, and the goal is to make them applicable to datasets of any size whatever while still retaining high interactivity. As an emerging science, its strategy is to develop fundamental ideas leading to general tools for real applications. This pursuit is multidisciplinary in that it uses the same techniques across many areas of study..

Wireless System Propagation Modeling

Radio wave propagation is a physical phenomenon that can be de-scribed using electromagnetic wave equations. Like waves travelling away from the spot where a stone has been tossed into a pond, radio waves travel away from the transmitting antenna in all directions (in three dimensions).

Theoretically, it is possible to exactly predict the strength of the signal from any transmitter at any other location if the elements of the propa-gation environment are correctly taken into account. In so-called "free space" (actually a vacuum), there are no elements in the propagation environment and the signal strength at some distance from the trans-mitter can be exactly calculated. Radio wave transmission through outer space is one region where such a simple formulation applies.

For transmitters located on the earth's surface the problem is much more complicated. Every physical entity a radio signal encounters after it leaves the transmitting antenna affects the strength and direction of the signal. The physical entities that impact the signal can be grouped into four broad categories:

1. The atmosphere (or other gaseous media) refracts (bends) and dif1. The atmosphere (or other gaseous media) refracts (bends) and dif-fracts (scatters) the radio waves. Bending changes the direction of the radio wave while scattering generally weakens the wave.

2. Terrain features (hills and mountains) block the radio waves, requir-ing them to diffract over the top or around the sides, weakening the signal on the other side. Radio waves also reflect and scatter off of ter-rain surfaces causing a change in the direction of the radio wave.

3. Like terrain, structures such as buildings, houses, towers, etc. block the radio waves. The waves diffract, reflect, scatter and transmit through structures.

4. The leaves and branches of trees and other types of foliage also weaken radio waves by scattering them, rather than substantially block-ing them as terrain or buildings can do.

As mentioned in the introduction, the atmosphere and terrain have been included for many decades in the propagation models which are designed to predict the strength of radio signals. Only recently has propagation modeling attempted to incorporate information about foli-age and structures and their impact on signal strength.

Figure 1. Radio propagation path without obstructions (open land cover).

Figure 1 shows a representation of a radio wave propagating from a mountaintop transmitter (on the left) to a receiver location in the open (on the right). Although the signal arriving at the receiver will include some reflections from the terrain, the dominant signal is the one that arrives directly from the transmitter. Figure 2 shows the same radio path but with a tree placed in front of the receiver. Because of the tree, the signal is some 9 dB weaker than it is without the tree at a frequency of 870 MHz (a frequency in the cellular phone band). This is the effect of 870 MHz (a frequency in the cellular phone band). This is the effect of groundcover on signal propagation.

Figure 2. Radio propagation with tree obstructions (forest land cover).

When buildings are considered in three dimensions, as shown in Figure 3, the situation becomes considerably more complicated. The radio signal from the transmitter arrives at the receiver by diffracting and reflecting from the four buildings shown in this figure. Because the signals arrive at the receiver via a number of radio paths, the signal at the receiver is often described as a "multipath signal." A multipath signal can have a significant impact on the signal quality or integrity of data which is sent because several versions of the same integrity of data which is sent because several versions of the same signal are arriving at the receiver at different times.

Figure 4. Rays showing multipath signal trajectories in an urban environment.

Figure 5. Signal strength along a route through an urban environment.

As explained above, in complex environments the signal arrives at the receiver via multiple paths and at different times. A quantity often used to described multipath is "RMS delay spread". Figure 6 shows a plot of the predicted RMS (route mean square) delay spread at a mobile unit moving along the same urban route as shown in Figure 5. Notice that the least amount of delay occurs at the point where signal strength is stron-gest in Figure 5.

Figure 3. 3D radio wave propagation over buildings in an urban environment.

As the propagation environment becomes more complex, it is difficult for the propagation model to account for all of these possible radio paths. One approach known as ray-tracing is currently the most viable model for such conditions [2],[3]. With ray-tracing, complex environ-ments such as entire downtown areas can be considered as shown in Figure 4. The signal strength as the mobile user (a cellular phone in a car) moves along a route can also be calculated as shown in Figure 5. Note how the peak in the signal strength occurs due east of the transNote how the peak in the signal strength occurs due east of the trans-mitter, where the path from the transmitter to the mobile is straight down a street with no intervening obstructions (approximately halfway through the route).

Figure 6. RMS delay spread (multipath) along a route through an urban environment.

The Ionosphere and Radio Wave Propagation

The ionosphere is important for radio wave (AM only) propagation....

ionosphere is composed of the D, E, and F layers

the D layer is good at absorbing AM radio waves

D layer dissapears at night.... the E and F layers bounce the waves back to the earth

this explains why radio stations adjust their power output at sunset and this explains why radio stations adjust their power output at sunset and sunrise

Radio waves are part of the electromagnetic spectrum with wavelengths longer than infrared light. Naturally-occurring radio waves are pro-duced by lightning, or by astronomical objects. Artificially-generated radio waves are used for broadcasting, mobile and fixed communica-tions, navigation, computer networks and innumerable other applications. Different frequencies of radio waves have different propagation characteristics in the Earth's atmosphere; long waves may cover a part of the Earth very consistently, shorter waves can reflect off the iono-sphere and travel around the world, and much shorter wavelengths bend or reflect very little and travel on a line of sight.

Immaterials: the ghost in the field

This video is about exploring the spatial qualities of RFID, visualised through an RFID probe, long exposure photography and animation. It features Timo Arnall of the Touch project and Jack Schulze of BERG.

The problem and opportunity of invisibilityRFID is still badly understood as an interactive technology. Many aspects of RFID interaction are fundamentally invisible; as users we experience two objects communicating through the ̒magic̓ of radio waves. This invisibility is also key to the controversial aspects of RFID technology; once RFID antennas are hidden inside products or in environments, they can be invoked or initiated without explicit knowledge or permission.

But invisibility also offers opportunities: the lack of touch is an enormous usability and efficiency leap for many systems we interact with everyday (hence the success of Oyster, But invisibility also offers opportunities: the lack of touch is an enormous usability and efficiency leap for many systems we interact with everyday (hence the success of Oyster, Suica and Octopus cards). But there is also the ̒magic̓ of nearness one of the most compelling experiential aspects of RFID.

As designers we took this invisibility as a challenge. We needed to know more about the way that RFID technology inhabits space so that we could better understand the kinds of interactions that can be built with it and the ways it can be used effectively and playfully inside physical products.

The experimentsIn order to study the readable volume around an RFID reader, we built experimental probes that would flash an LED light when they successfully read an RFID tag. The readable In order to study the readable volume around an RFID reader, we built experimental probes that would flash an LED light when they successfully read an RFID tag. The readable volume is not the same as the radio field, instead it shows the space within the field in which an RFID tag and an RFID reader will interact with each other.

In a dark room, the probes were moved around the various RFID tags and readers that we wanted to study, with a camera taking long-exposure photographs of the resulting pat-terns of light. In this way we could build up layers by slicing through the field in different ways, creating animations that clearly reveal the spatial properties of this interaction.

These experiments were carried out in order to help us flesh out our own models of the technology, and were not intended to be scientifically accurate. So although they accurately reflect the behaviour of the technologies in the situations that we work with, there were no controlled environments or settings for generalisable technical accuracy.

Innovations ID 20The Innovations ID 20 RFID reader has become one of the standard components in a lot of our work, it is small, robust and relatively cheap. So it has been very important for us to gain an understanding of the readable volume it produces when we embed the reader inside products such as Sniff and Skål.

The resulting visualisation shows the way in which we have mapped the boundary of the readable volume, although a tag will read anywhere inside this, we have only mapped the The resulting visualisation shows the way in which we have mapped the boundary of the readable volume, although a tag will read anywhere inside this, we have only mapped the edge for the sake of clarity. From the animation (see the video) we start to clearly see that the readable volume is made up of a strong central sphere, accompanied by a smaller lobe that surrounds the edge of the reader.

Oyster cardMifare cards are one of the largest public applications of RFID, used in many transit systems around the world such as the Oyster and Suica cards. It has become common to have to Mifare cards are one of the largest public applications of RFID, used in many transit systems around the world such as the Oyster and Suica cards. It has become common to have to touch in and touch out of subway stations, and many people have become accustomed to this interaction. So what does the readable volume around an Oyster card look like?

With a square antenna inside the Oyster and the Sonmicro reader, we get an elongated main volume, accompanied by long skinny lobes on each edge of the card. This looks very different from the ID 20 mapping.

OrientationThe first two mappings held the reader and the tag parallel to each other, but we predicted that there would be a higher degree of complexity in the relationship if the tag and the The first two mappings held the reader and the tag parallel to each other, but we predicted that there would be a higher degree of complexity in the relationship if the tag and the reader moved in different orientations. The rig below was built so that we could control the angle between the reader and the tag, which moved along the surface of the table.

There is clearly enormous physical complexity in this relationship, in the animation we can see the volume growing and shrinking, lobes turning into spheres, and vice-versa. But the animation gives us a very clear picture of the ̒throw̓ of the reader onto a single two-dimensional plane, almost like looking at it as a torch.

Parallel and perpendicularParallel and perpendicularTo show the two extremes of the relationship between orientation and the readable volume, we created two mappings, one with the tag parallel to the reader, and the other with the tag perpendicular. We mapped them using two different colours of LED: green for parallel and red for perpendicular.

This image is a composite of the two mappings and it is clear that the readable volume is significantly different. When the tag is perpendicular to the reader, there is a sizeable gap in the middle of the reader where the tag will not read, creating two readable volumes side by side.

ConclusionsWe have been continually challenging the ways in which RFID technology has been framed. It is incredible how often RFID is seen as a long-range ̒detector̓ or how little relevant inWe have been continually challenging the ways in which RFID technology has been framed. It is incredible how often RFID is seen as a long-range ̒detector̓ or how little relevant in-formation is contained in technical data-sheets. When this information is the primary material that we are working with as designers, this is highly problematic. By doing these kind of experiments we can re-frame the technology according to our experience of it, and generate our own material knowledge.

One of the early motivations in this project was the way in which the animations really captured our tacit, embodied knowledge of the readable volume in a visual way, it was almost as if you could wave your hand through the floating green LEDs and feel them. Of course we had felt it hundreds of times in experimenting with tags and readers, but we had never seen it captured in an image, in a way that was communicable to others without having them try an interactive demonstrator. With this visual material, we can communicate about RFID in ways that we couldn̓t previously.

So we hope that this work goes some way towards building better spatial and gestural models of RFID, as material for designers to build better products and to take full advantage of So we hope that this work goes some way towards building better spatial and gestural models of RFID, as material for designers to build better products and to take full advantage of the various ways in which spatial proximity can be used. And with this better understanding we hope to be able to discuss and design for privacy and the ̒leakage̓ of data in a more rigorous way.

The Free Network Visible Net-work project, propose to make visible the interchanged informa-tion between computers of a wireless network connected to In-ternet. The main objective is to ask for the free access to the net and at the same time to make ac-tions in the urban landscape as a way to create new meanings in the public domain.

Our intention is to contribute to the re-definition and re-vitaliza-tion of the concept of public space through the creation of vis-ible connectivity networks that mix the physical public space with the digital public space.

With the territorial demarcation of internet free access areas and the virtual representation of the data that circulate through them, we want to evidence the perception of the city as a morphologic agent that is continuously being changed by the invisible connecchanged by the invisible connec-tions of the communication tech-nologies

Magnetic Movie is a film that explores visible and audible manifestations of radio fields. The film is by Ruth Jarman & Joe Gerhardt of Semiconductor and commissioned by Animate Projects that remains on the forefront of “exploring the relationship between art and anima-tion”.tion”.he secret lives of invisible magnetic fields are revealed as chaotic ever-changing geometries . All action takes place around NASA's Space Sciences Laboratories, UC Berkeley, to recordings of space scientists describing their dis-coveries . Actual VLF audio recordings control the evolution of the fields as they delve into our inaudible surround-ings, revealing recurrent ̒whistlers' pro-duced by fleeting electrons . Are we ob-serving a series of scientific experi-ments, the universe in flux, or a docu-mentary of a fictional world?

Field of beamsIt̓s still the subject of (extensive) debate whether the electric and magnetic fields (EMFs) produced by appliances, cell phones and high-voltage wires contribute to human ill-ness and cancer. For an academic overview, check out the Human Radiation Effects Group, by Professor Denis Henshaw of the University of Bristol. For a visual illustration, look no further than FIELD by artist Richard Box. It̓s a grid of fluorescent light bulbs planted into the ground beneath a series of power lines. When the bulbs glow, it̓s not because of a series of buried wires, or a battery– they light up using the ghost power radiating from the wires overhead.The luminous power of the installation is powered by the weather and passing humans– either of which can make a series of bulbs flicker or power out– but otherwise the bulbs give off a steady glow, come sunset. Planted in the field are a total of 1,301 ready-made fluorescent bulbs. Artist Box came up with the idea for the installation after a conver-sation with a friend who played with such bulbs under power lines as a kid and found that the tubes lit up like light sabres.

The effect is other-worldly, almost post-apocalyptic. It also leaves one wondering: what kind of effect could the power to light 1,301 bulbs have on my body? Which is the point: Box created the installation as Artist-in-Residence at the University of Bristol̓s Physics department, where he worked together with Henshaw. Maybe the fields cause leu-kemia; or maybe they don̓t, but these men are working to shed light on the possible effects that radiation might have on humans.

Scintillation

Scintillation is a remarkable experimental piece by Scintillation is a remarkable experimental piece by young director Xavier Chassaing. This piece stands on it̓s own purely for its visuals, but the technique and craft that went into the production sets this film apart. What looks like film is in fact 35,000 photo-graphs with a mix of 3d mapped projections. Being a young director, Xavier doesn̓t have the facilities and financial backing that a commercial piece will grant. financial backing that a commercial piece will grant. Instead he had to work under what he calls “the clas-sic dogma which is ̒What can you do with what you have… ”̓ I think this sums up Xavier̓s process pretty well. Here is what he had to say to me about his technical process for Scintillation:

What I have was an apartment, a small DSLR camera, a small computer and a small videoprojector. I also made a contraption who looks like a motion control but with the particularity of moving extremely slow who allowed me to take sequences of pictures with long exposure. (1frame per second, with 1 second of exposure). Even the best camera can not compete with this kind of sensitivity if they shoot at normal with this kind of sensitivity if they shoot at normal speed. So, I did everything myself from the 3d ani-mation that I project on object, building the machine, the editing etc..

Built a contraption that acts like a motion control!? Yeah, wow. Xavier also enlisted Mathieu Caulet to help color grade on a flame in the end and worked closely with sound designer Fedaden throughout the entire process to score his piece.

Scintillation reveals that cash flow isn̓t necessarily Scintillation reveals that cash flow isn̓t necessarily the foundation for a great project. In cases when you have nothing, a little ingenuity can make a diamond out of shit. This is an important thing to remember in these times when budgets are being slashed and we all have less to live under the dogma of “what can you do with what you have”?

References and some other useful links:

A Virtual Wave Tank http://www.csesalford.com/drumm/WebPages/WaveTank/DXWaveTank.htm

Electromagnetic Waves Electromagnetic Waves http://learn.uci.edu/oo/getOCWPage.php?course=OC0811004&lesson=005&topic=002&page=21

Fastest Waves Ever Photographed http://www.eurekalert.org/pub_releases/2006-10/aps-fwe_1102706.php

Fictional Radio-Spaces http://www.nearfield.org/2007/12/fictional-radio-spaces

Field of Beams http://www.inhabitat.com/2009/05/02/eco-art-field-of-beams/

Free Network Visible Network http://www.lalalab.org/redvisible/index_en.htm

Frequency Finder UK and Ireland Frequency Finder UK and Ireland http://frequencyfinder.org.uk/index.html

Magnetic Movie http://www.semiconductorfilms.com/root/Magnetic_Movie/Magnetic.htm

Math and Physics Applets http://www.falstad.com/mathphysics.htmlNASA's Imagine the Universe! NASA's Imagine the Universe! http://imagine.gsfc.nasa.gov/docs/science/know_l1/emspectrum.html

Physics Applets http://www.cco.caltech.edu/~phys1/java.html

Radiation http://www.yankeerowe.com/license_radiation.html

Scintillation http://motionographer.com/2009/02/22/scintillation-by-xavier-chassaing/

Sound Wave Motion http://www.silcom.com/~aludwig/images/pwave.gif

The Application of Land Use/Land Cover Data to Wireless Communication System Design http://proceedings.esri.com/library/userconf/proc98/PROCEED/TO550/PAP525/P525.HTM

The Ghost in the Field http://berglondon.com/blog/2009/10/12/the-ghost-in-the-field/http://www.nearfield.org/2009/10/immaterials-the-ghost-in-the-field

The Ionosphere and Radio Wave Propagation The Ionosphere and Radio Wave Propagation http://apollo.lsc.vsc.edu/classes/met130/notes/chapter1/ion2.html

'Touch' (a Research Project) http://www.nearfield.org/

Uranium Science http://www.cameco.com/uranium_101/uranium_science/radiation/

Vortex Basics and Fractals from the Subatomic to the Super Galactic Vortex Basics and Fractals from the Subatomic to the Super Galactic http://www.feandft.com/vortex_basics.htm

Waves in Space Plasmas http://www-pw.physics.uiowa.edu/plasma-wave/tutorial/waves.html

U. S. Inan and A. S. Inan Electromagnetic Waves, Prentice Hall, New Jersey, 1999.

G. M. Nielson, H. Hagen and H. Müller G. M. Nielson, H. Hagen and H. Müller Scientific Visualization: Over-views, Methodologies, Techniques, IEEE Computer Society, California, 1997.

F. H. Read Electromagnetic Radiation, John Wiley & Sons, 1980.