Applications of electromagnetic theory pdf

Complex, novel techniques like diffusion and perfusion imaging, functional imaging have even affected the approach to certain diseases and patients. The advances in hardware have had an impact in the still growing and maturing applications like parallel imaging techniques.

These new advances might start a revolution in patient management and the role of MR in diagnosis of diseases. These statements only prove true if the application and further technological development of MR systems are not constricted by strict occupational exposure limits applicable to the medical personnel working at the MR system.

The clinical benefit of MR scanners for the patient can best be illustrated by reference to the enormous amount of literature on MR in the medical and scientific international journals. Up till now no adverse effects from the exposure of these patients nor from the exposure of the workers to the electromagnetic field created by MR systems is known.

The exposure of patients is not addressed in the European Directive proposal and therefore only mentioned in this memo for illustration. Actual limits for the parameters for patient scanning are given in the IEC particular standard for the safety of MR scanners.

For information, the static magnetic field ceiling value is 4 T for patients for whole body scanning, a number which is based on the clinical experience with 4 T MR scanners at a limited number of hospital sites since For all normal engineering activities these tools can be applied.

For abnormal situation, whereby troubleshooting is required, it may however be unavoidable that these engineers are exposed to higher values then proposed in the draft directive.

The exposure time to the static magnetic field of the operators in the hospital is typically a few minutes per patient. In the worst case they are exposed to the maximum static magnetic field of the magnet, because they must position the patient on the patient support and therefore approach the magnet at a position where the static magnetic field is as high as the main magnetic field of the system. The operators in the hospital are typically not exposed to gradient- and RF- fields, because during the scanning of the patient, the operator is relative far away from the patient at the operator's console of the scanner.

The exposure of the medical staff during interventional MR however is much higher than the proposed limits in the draft directive. For both, the open MR systems and the cylindrical MR systems, the medical doctor can be present near the scanner during a longer time up to one hour or even more and is present in or close to the maximum static magnetic field with his hands and partially with his body.

Since he is present near the patient during scanning, he is also exposed by gradient- and RF-fields. At parts of the body extremities, head they can reach values which can be maximally equal to those applied to the patient. In view of the practical experience up to now, the large installed base for MR scanners at present, the importance of the diagnostic capabilities of these MR scanners for the health care and the weak scientific base for the proposed limiting values, it seems unrealistic and not in the interest of the patients to impose the requirements in the draft directive to medical equipment and MR scanners in particular.

These papers also require permanent training of the personnel, special procedures to be defined and followed or the generation of emergency plans. That means, they are much more specific in addressing the potential hazards in the particular MR vicinity [21]. The Discovery of Microwaves In , the specific heating effect of a high-power microwave beam was accidentally discovered by Percy Spencer, an American self-taught engineer from Howland, Maine. The first food deliberately cooked with Spencer's microwave was popcorn, and the second was an egg, which exploded in the face of one of the experimenters [22].

To verify his finding, Spencer created a high density electromagnetic field by feeding microwave power from a magnetron into a metal box from which it had no way to escape.

When food was placed in the box with the microwave energy, the temperature of the food rose rapidly. On 8 October , Raytheon filed a United States patent application for Spencer's microwave cooking process, and an oven that heated food using microwave energy from a magnetron was soon placed in a Boston restaurant for testing [23]. Microwaves are a form of non-ionizing electromagnetic radiation with a frequency higher than ordinary radio waves but lower than infrared light.

Microwave ovens use frequencies in one of the ISM industrial, scientific, medical bands, which are reserved for this use, so they do not interfere with other vital radio services. Consumer ovens usually use 2.

Water, fat, and other substances in the food absorb energy from the microwaves in a process called dielectric heating.

Many molecules such as those of water are electric dipoles, meaning that they have a partial positive charge at one end and a partial negative charge at the other, and therefore rotate as they try to align themselves with the alternating electric field of the microwaves. Rotating molecules hit other molecules and put them into motion, thus dispersing energy. As noted microwave ovens can operate at many frequencies. Microwave heating is more efficient on liquid water than on frozen water, where the movement of molecules is more restricted.

Compared to liquid water, microwave heating is less efficient on fats and sugars which have a smaller molecular dipole moment. Sugars and triglycerides fats and oils absorb microwaves due to the dipole moments of their hydroxyl groups or ester groups. This can induce temperatures in oil or very fatty foods like bacon far above the boiling point of water, and high enough to induce some browning reactions, much in the manner of conventional broiling UK: grilling , braising, or deep fat frying.

Foods high in water content and with little oil rarely exceed the boiling temperature of water. Microwave heating can cause localized thermal runaways in some materials with low thermal conductivity which also have dielectric constants that increase with temperature. An example is glass, which can exhibit thermal runaway in a microwave to the point of melting if preheated.

Additionally, microwaves can melt certain types of rocks, producing small quantities of molten rock. Some ceramics can also be melted, and may even become clear upon cooling. Thermal runaway is more typical of electrically conductive liquids such as salty water.

Another misconception is that microwave ovens cook food "from the inside out", meaning from the center of the entire mass of food outwards. This idea arises from heating behavior seen if an absorbent layer of water lies beneath a less absorbent drier layer at the surface of a food; in this case, the deposition of heat energy inside a food can exceed that on its surface. This can also occur if the inner layer has a lower heat capacity than the outer layer causing it to reach a higher temperature, or even if the inner layer is more thermally conductive than the outer layer making it feel hotter despite having a lower temperature.

In most cases, however, with uniformly structured or reasonably homogenous food item, microwaves are absorbed in the outer layers of the item at a similar level to that of the inner layers. Penetration depth of microwaves is dependent on food composition and the frequency, with lower microwave frequencies longer wavelengths penetrating further [24].

One variant of the GE Space maker had two taps on the transformer primary, for high and low power modes. Usually choice of power level doesn't affect intensity of the microwave radiation; instead, the magnetron is cycled on and off every few seconds, thus altering the large scale duty cycle.

Newer models use inverter power supplies that use pulse-width modulation to provide effectively continuous heating at reduced power settings, so that foods are heated more evenly at a given power level and can be heated more quickly without being damaged by uneven heating[25]. The microwave frequencies used in microwave ovens are chosen based on regulatory and cost constraints.

The first is that they should be in one of the industrial, scientific, and medical ISM frequency bands set aside for unlicensed purposes. For household purposes, 2. Three additional ISM bands exist in the microwave frequencies, but are not used for microwave cooking.

Two of them are centered on 5. The third, centered on The cooking chamber is similar to a Faraday cage to prevent the waves from coming out of the oven. Even though there is no continuous metal-to-metal contact around the rim of the door, choke connections on the door edges act like metal-to-metal contact, at the frequency of the microwaves, to prevent leakage.

The oven door usually has a window for easy viewing, with a layer of conductive mesh some distance from the outer panel to maintain the shielding. Because the size of the perforations in the mesh is much less than the microwaves' wavelength Conclusion Electromagnetic radiation is a flood of energy through space nearly the speed of light these waves are important in the live. All living organisms on Earth depend on electromagnetic radiation from the sun. There are many types of electromagnetic such as; x-ray, visible, radio waves.

One example of this is an alternating-current AC generator. When rotational mechanical energy turns a coil inside of the generator, it exposes that coil to changes in magnetic field. Those changes induce the production of alternating current voltage — voltage where the current changes directions with a certain frequency — between the two output ends of the coil.

Since no other energy is required other than the mechanical motion of the rotating coil, this type of device can be advantageous in situations where there is a ready source of mechanical energy, such as a steam or gas turbine, or a diesel or gasoline engine. Another advantage of using an electromagnetic energy source is that you can generate either AC or direct-current DC electrical power.

As noted before, an AC generator uses changing magnetic fields to create AC electrical power. A DC generator operates in a similar fashion; however, it requires a few extra pieces to convert AC electrical power to DC. Many DC motors and generators use a device called a commutator to convert the alternating current that comes out of the power generator into current that flows in only one direction, or direct current.

As with an AC generator, many types of DC generators only require a reliable source of mechanical energy to generate electricity. Disadvantages Electromagnetic power sources may not be as useful, or can perhaps be dangerous to use, under certain circumstances. For instance, if you need to have a power source that must have a regulated current output, both AC and DC power generators would need to be run at a non-varying speed.

Further, while a DC power generator produces electrical current that flows in one direction, the electrical current is irregular. To regulate the current produced by a DC generator, you would need additional electrical equipment, such as a battery, a capacitor and an inductor, as well as electronic components called diodes to ensure that the current stays within a regulated range.

Since generators use electromagnetic fields to produce electricity, these fields can be dangerous to some people who use sensitive medical equipment, such as pacemakers. These same electromagnetic fields can also interfere with other electrical and electronic devices, such as cell phones and computers. The electrical energy generation process also produces heat; therefore, it would be best not to use a generator around items or in environments where there is flammable or combustible material.

Some microwave radiation wavelengths can transmit signals out of earths orbit and into space and are used to communicate with satellites. Skin turns darker to so that UV Radiation does not reach the deep skin cells. Sun Beds. Security Pens. Fluorescent Lights. Infrared Radiation. Television uses higher frequency waves than radio program.

Purcell and Morin, Harvard University. Electricity and Magnetism, p 3rd ed. Cambridge University Press, New York. ISBN Traveling electromagnetic waves carry energy, and Browne, Michael Physics for Engineering and Science, p 2nd ed. Visible light constitutes a narrow range of the spectrum, from wavelengths of about nm If the radiation is absorbed by a surface, the momentum drops to zero and a force is exerted on the surface Thus the radiation pressure of an electromagnetic wave is formula.

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Purcell, p "Any number of electromagnetic waves can propagate through the same region without affecting one another. The field E at a space time point is the vector sum of the electric fields of the individual waves, and the same goes for B".

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The Quantum Theory of Fields. We can explain the of visible light; finally, we write our concluding remarks. In equation 1 we can see the complete mathematical base is composed by three sets, but because we are now III. The 10].

We take as an example the shift t1 in the argument of equation we can follow the recipe for quantum Gamow all the members of the following ensemble resonant states. And now, we can build information packs IP that are So each function has changed but the ensemble as a whole functions which represent a part of the signal we want to is invariant under the transformation.

Also if we apply the operator T which gives for each member send with the minimum loss of information. Next, we send separately each translations are multiples of the periods of the carrier, then the modulation will be invariant. At this stage it is f e t by its own device and it is all we need for important to remember that Wiener [6] has pointed out that broadcasting. Now A very important feature is that because of the suppose in addition that we are interested on functions that properties of the modulation process stated in equations 5 are limited to the band from 0 to W cycles per second and 6 , we can recover, for any arbitrary signal, the then we have the following theorem [10]: behavior under spectral representation and under separated Let f t contain no frequencies over W.

Then packs representation. The coefficients X n of the 4d various terms can be considered as coordinates in an Suppose that g t is the signal infinite dimensional "functions space". These two late cases are not only an evidence So we can either talk about g e ' t in 20 as the representation of some element of the new basis functions of self-consistency of the method but a real example of how the highway of the resonances really operates.

To give an example we can use IV. Nowadays there is not any device that could manipulate visible light as occurs with microwaves. So, we must take care that in reading the WS information process, the Figure 1. The former radio broadcasting procedure: modulated translations stated in these equations were multiples of the amplitude. Image given by F. We can also combine the use of as in the former example on equation 2 coming also for resonances with the traditional methods like for example the WS.

Then we can grow the range of application of the MIMO multiple input-multiple outputs [] or simply formalism developed about of that we named vector-matrix to improve time reversal procedures [14]. And Math. Leipzig Vol. Zheludev, What diffraction limit? Rusek et al. IT] 16 Jan Sanayei and A. F View publication stats. Resonance regime on a plasma sandwich simulates a left-hand material broadcasting condition By Jaime A Granados Samaniego. Download PDF.