The Aim of the project is to investigate the properties and the propagation characteristics of the electromagnetic wave and microwaves. Since the past few years, there has been an increase in public concern about possible health risks from electromagnetic waves emitted by electronic devices. The first step necessary for an assessment of the potential risks is to investigate the effect of the presence of human bodies on antennas propagation patterns. The propagation characteristics of electromagnetic waves generally depend on the electrical factors of the medium and the presence of the boundaries or interfaces between two media. In free space, at adequately large distance from the source, wave propagation occurs from one end to another. The objective of the paper is to exhibit the selected capability of widely used electromagnetic simulators with a some kinds of antenna and circuit modeling and focus on specific characteristics that are able to make simpler the EM modeling of the structure without lose of fundamental accuracy and decrease computational time. Thus, the aim of the paper is to measure and simulate results or try to come across what the top tool in the market is. The intent of the report is to investigate and analysis the electromagnetic properties of the human tissues.
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For everyday we use electromagnetic waves in electrical appliances. Some category of electromagnetic waves such as radio waves, television waves, and microwaves have vary with it wavelength. Electromagnetic waves consist of mixture of oscillating electrical and magnetic fields, perpendicular to each other. This is difficult to imagine, however the waveform has related characteristics of other types of waves. Before starting our investigation on Electromagnetic waves are the waves going through the space, carrying signal from one place to another. Electrical signals are transmitted from the transfer end to the receiving end in the type of currents and voltages through conductors of transmission lines in the structure of electromagnetic waves through channel structures such as waveguides and optical fibers or in form of electromagnetic waves by radiation in atmosphere. EM waves are produced and carried by oscillating electric charges or by time differing from electric current in a conductor (Nikita, K.S., G.S. Stamatakos, 475). In electromagnetic wave propagation in a space, a varying magnetic field will bring an electric field and vice versa which is propagate with two oscillatory fields, one electric and other magnetic. The section close to the radiating sources is most probable to have high intensity of fields, having both longitudinal and transverse factors concerning the direction of propagation. In general, such places are characterized by difficult field structure comprising reactive and real energies, uneven phase surfaces and unknown field polarization. The exposure of the human body to the electromagnetic waves from Very Low Frequency to Radio frequency range results in induced currents and fields inside the body (P., S. Pisa, E. Puizzi, 254).
Electrical and electronic appliances, wireless communication services are the longest growing field in the world. There is insecurity about the health effects of Electromagnetic waves and some amount of radiation from waves is absorbed by the body and converted to heat by this thermal effect takes place. It consequences in public fear about potential health effects of human exposure to electromagnetic energy and about other potential, so called a thermal effects take place from exposure to frequencies comprise suggestions of slight effects on cells that could have an effect on cancer progress or influences on electrically nervous tissue and it could persuade the function of the brain and nervous tissue (Peter S. Hall, Yang Hao, 2001). There has also been fear about whether there could be effects on brain function, with particular importance on headaches and memory loss. The basic edge of exposure is expressed by the amount called specific absorption rate and it is the time rate at which EM energy is absorbed by an element of organic body mass, and the maximum local SAR, which is the most critical amount in the circumstance of possible health effects of electromagnetic waves radiated, depends on a large number of thing, such as design of the device, its set frequency and antenna input power and direction with respect to the human. The most inspect effect of EM waves on biological tissues increased kinetic energy of the absorbing molecules, thus producing a general heating in the medium.
The waves absorbed by the tissues will generate a temperature rise that is reliant on the cooling means of the tissue. The patterns of the waves fabricate the heating are complex functions of the frequency, source pattern, tissue geometry and dielectric properties of the tissues. When the thermoregulatory capability of the system is go above, tissue damage consequence and the biological system is exposed to microwave radiation, an internal field is making in the structure. The development of model to expect the absorption of electromagnetic energy and the physiologic thermoregulatory response for the human body has advanced for several years.
The electromagnetic waves may be propagated from the transmitter to a remote receiver as a direct wave, ground reflected wave, surface wave or as a sky wave based on the frequencies. The electromagnetic waves shot up into the sky get reflected by the ionized layers and are received on the earth at large distances. This method is subjected to errotic changes in the atmospheric conditions. The ionosphere region encloses gases which are ionized due to solar radiation, all the frequencies which are lower than a critical frequency fc is given by fc = 9 (Nmax)1/2 Hz are reflected back to the receiver, on the earth.
Nmax is the maximum electron density in the ionosphere. Ionosphere reflected waves are used for long remote radio transmit. Since microwave frequencies are greater than fc, microwave signals are not reflected back to the earth, but go through the ionosphere to travel in atmosphere (Julian L.Davis in Springer-Verlag, 1990). The section of the microwaves diffracted around the surface of the earth is point by the ground air interface as a surface wave which gets satisfied and therefore, only propagation of point to point microwave takes place through direct and ground reflected waves in the atmosphere. Since the curvature of the earth and the presence of the other barriers like buildings and trees, microwave signals are satisfied and the range of microwave direct transmission is limited to about 50 km between a transmitter and a receiver.
Electromagnetic waves travels from the transmitted to the receiver as a number of waves. The propagation of the ground wave is travel along the curved path of the earth’s surface and hug to the earth (Alan W. Rudge, 56). They are strongly absorbed and hence cannot travel large distances, the ground reflector waves travel from the transmitter is reflected by the earth and is received. It is not subject to much absorption and can travel longer distance and they are reversed in phase. The direct wave propagates directly from the transmitter to the receiver. The distance between the transmitting and receiving antennas where the electromagnetic waves is reflected earliest is called skip distance. Near the transmitter until the wave is reflected we have a zone of silence called skip zone where no signal is received.
Today electromagnetic waves and the frequency with which it take place are growing with the fast extend of electrical and electronic devices. The automobile used to appreciate the effects of waves is a mathematical model and it measure our sympathetic the occurrence and also may carry out significant properties that are not so readily obvious. An additional, significant lead of a mathematical model is its ability to assist in the design process and that determines whether the form sufficiently represents the occurrence is whether it can be used to expect experimentally observed results. If the calculation of the model does not associate with experimentally practical activities of the phenomenon, it is useless (Jean G. Van Bladel in 2007). However, our ability to solve the equations resultant from the model and extract insight from them quite frequently dictates the estimate used to construct the model. For example, we frequently model nonlinear phenomena with linear estimated form and electromagnetic waves can be confirmed by tuning a radio receiver to a become quiet of the AM band where there is no radio station and placing a calculator with a LED show near the receiver. Today, we identify that almost any tool which operates on the principle of moving an electron from one end to end can be either a basis or a receiver of electrical noise.
The first is the transmitter; it generates the electromagnetic energy in suitable frequency range with the preferred time waveform, superimposes on it details is to be sent, and launches the resultant signal toward the receiver or the region to be detected. The last is the receiver; it recognizes some part of the energy which has been transmitted and takes outs from it the preferred details (Kenneth Frederick Sander, 1988). Propagation is the connection between the transmitter and receiver that is the method whereby the message bearing waves is transferred from the transmitter in the receiver.
An antenna may be thinking of as a short length of a transmission line. When high frequency alternating source is practical at its one end, the resultant forward and reverse traveling waves merge to form a standing wave pattern on the line. However, all the advance energy does not get reflected at the open end, and a small section escapes from the method and is thus radiated. The electromagnetic radiation from the transmitting antenna has two mechanisms, a magnetic field linked with current in the antenna and an electric field connected with the potential. The two fields are perpendicular to each other in space and both are perpendicular to the direction of broadcast of the wave. An electromagnetic wave is level polarized if its electric field is in the horizontal direction. Thus an antenna fixed horizontally fabricates horizontally polarized waves. Similarly a vertical antenna fabricates vertically polarized waves.
Radio signals are have major behavior on radio frequency design antenna and the based on the frequency its travel and reach the antenna. The waves emit in the form of light, ultra-violet and infra red rays, that has under same category but differ in wavelength and frequency. The mechanism of electric and magnetic mechanism in waves that is indivisible and the plane of these mechanisms are at right angles to one another and to the path of motion of the wave.
The electric field consequences from the voltage changes taking place in the antenna which is passing the signal and the magnetic changes consequence from the current flow. It is also initiates that the lines of force in the electric field pass along the similar axis as the antenna, but diffusion out as they progress away from it. This electric field is calculated in terms of the change of possible over a given distance and likewise when an RF antenna obtain a signal the magnetic vary basis a current flow, and the electric field vary basis the voltage changes on the antenna.
There are a number of assets of a wave. The first is its wavelength and this is the distance between points on one wave to the equal point on the subsequently. One of the clearest points to decide is the crest as this can be easily recognized although any point is satisfactory. The second assets of the electromagnetic wave are its frequency and the number of period an exacting point on the wave moves up and down in a given time. The amount of energy that is radiated in space by a transmission line antenna is though, particularly small, unless the wires of the line are properly oriented and their lengths made analogous to the wavelength (Jean G. Van Bladel in 2007). If the two wires of the transmission line are opened up, there is less probability of termination of radiation from the two wire tips and these develop the efficiency of radiation.
The properties of electromagnetic waves identify neither the ionizing or non ionizing radiation and transmit some energy per quantum that they have the capability to split bonds between particles. In the electromagnetic range, gamma rays are radiated by radioactive resources, cosmic rays and X-rays take this property and are called ionizing radiation and the waves whose quanta are inadequate to split molecular bonds are known as non ionizing radiation. Man made causes of electromagnetic waves is found at the fairly extensive wavelength and short frequency end of the electromagnetic field and their quanta are not capable to split chemical bonds. Mobile has non ionizing radiation and frequency range is from 30kHz to 300 GHz are broadly used for telecommunication, comprising broadcast radio and television, and include the radio frequency band.
Interaction with human body:
The electromagnetic fields have a great control on the activities of all the living systems in low reasonably possible theory imposes, in case of extended exposures to low in power system and high frequency in microwave systems and mobile communication fields, some restrictions to the radiated fields by the engineering equipment. On the other hand, some assistances can be in use from the property of the electromagnetic fields on the organism in the hyper thermal technique is recognized for the treatment of the cancer. We need to be confined from the fields, or we require taking help of the optimistic property of these fields, all the property thermal as well as inherited have to be recognized (Scattering of electromagnetic waves, 2001). Similar in industrial appliance, the electromagnetic field calculation permits an improved knowledge of the occurrence, and an optimized design. Hence, there is a vital application for the system of addition of electromagnetic fields. The most important problems that come into view are associated to the objects properties, the living being has very remarkable properties, these properties are not recognized and based on the activities of the person, and this human tissue is an energetic substance at the cell degree; associated to the coupling occurrence, the difficulty is essentially a coupled problem: the thermal result is one of the main property and it is precious by the blood circulation; linked to the geometry, the geometry is complex and one has to obtain into report the situation. The troubles that we have to features with are the detection of the properties of the human being, the coupled difficulty solution and the demonstration of the simulated event.
In this investigation, spherical human skull and dipole antenna were form to investigate the effects of the electromagnetic field of an antenna on human since the impracticality in experiments on human. Local SAR values were intended for two different human head form; single and three-layered spherical form. The application existing here seems to be reliable when comparing the results with the information. The example of energy combination inside an irradiated body is different, and natural reactions are reliant on distribution of energy and the body element that is affected (Jean G. Van Bladel in 2007). The combination rate and the circulation of electromagnetic waves radiate on an organism depend on many aspects are the dielectric work of the irradiated tissue with a inferior water content, take up less of the energy than tissues; the extent of the item comparative to the wavelength of the electromagnetic radiation, shape, geometry, and direction of the object; and pattern of the radiation.
And definitely nobody would desire the lives of patients in a hospital emergency room warned by a break down in the electronic life support systems due to unintended exterior intervention. These are now a few illustration of how an electromagnetic waves cause significant problems and the challenging to resolve the probable divergences between susceptible electronics and a noisy environment, engineers look to make circuits, which are potential receivers, more resistant and those which are possible emitters less noisy.
There are two major exposure has been produced by the electromagnetic radiation and were based on the potential of electromagnetic waves radiation to cause harm or damage through heating of body tissues. While some research had recommended that difficult health effects might occur from exposures lower than those required to produce important heating, the evidence for this was not careful adequate to form a basis for the beginning of exposure guidelines which incorporate basic limitations on the SAR. The SAR is standard over an exposure time and a particular mass tissue depend on the tissue section and the standard times are particular since the time taken for the temperature of tissues to equilibrate when they are showing to the radiation (Leung Tsang, Jin Au Kong, 2001). The waves are supposed to be in the far-field section and the exposures to electromagnetic radiation were designed to prevent illness and damage through heating effects. The preliminary end is the behavioral changes found when experimental were exposed to electromagnetic waves radiation at levels that created a rise in whole body temperature in excess of 1 °C.
Besides safety and the security of communications, there are concern for the reliability of control, computing and measurement method and in addition to perhaps upsetting communication to necessary services, the prospect also be of interfering with such varied electronics as computers, robotics control systems, bullet firing systems, aircraft controls, and microwave ovens.
Antennas for wireless devices are as wide-ranging as the devices and potential comprise external versus embedded, flex printed-circuit boards produced from thin sheet metal, twisted on the product housing using sprayed-on conductive paint, embedded in materials with a high-dielectric constant for size reduction, and so onwards. Apart from the device of the type and pattern of the antenna, performance can be characterized by the Impedance Bandwidth, Efficiency, Directive Gain, Polarization and Radiation Pattern
The antenna is fundamentally a transducer between the typical impedance of the system and the impedance of free space. In isolation, the antenna impedance and the frequencies over which that impedance is preserve are critical and it is necessary that the antenna present a suitable impedance match over the frequency band of process (J. Wiart, C. Dale, M. F. Wong, 477). Antenna impedance and the quality of the impedance match are most frequently characterized by either return loss or Voltage Standing Wave Ratio these two parameters are basically different design of accurately the same impedance data.
Antenna theory and types:
The human body exposed to the electromagnetic waves is accessible as a thick conducting cylindrical scattered of the length L and radius a, placed perpendicularly on the perfect ground (IEEE Std. C95.1-1999). According to the antenna theory and taking into version that the event electric field is tangential to the body and that the ground is entirely conducting, scattered field at the antenna surface is given by
Ez (a,z) = 1/ j4πω ε 0∫ ((∂2 / ∂z2) +k2 ) g E (z, z’, )I( z’ ) dz’
gE (z,z’) = ½Ð¿ ∫ e jkR / R dφ
represent I(z’) is the corresponding axial current distribution in the antenna axis while gE(z,z’) represent the corresponding Green function, k is the free space phase constant, and R is the distance from the source point, to the observation end on the antenna surface, of the form
R = (z – z ‘ )2 + 4 a 2 sin 2 φ/2
The total tangential electric effect at the antenna surface can be written as the sum of the event electric field, produced by the electromagnetic waves transmitter Einc, and the scattered field on the antenna surface Esct
E tot z (a , z) = E inc z (a , z) + E sct z (a , z) .
As the body is defectively conducting, loss in the cylinder can be integrated in the vital equation through the impedance loading the cylinder, as it is planned and total tangential electric field so can be expressed by means of the current I(z) and the impedance per unit length of the antenna ZL(z)
E tot z (z) = Z L (z) I(z) .
The Pocklington integral equation antenna mounted on a perfect ground is given by
E inc z (a, z) = – 1 / j4π4 ε0 ∫ [∂2 / ∂ z2 + k2 ] g E (z, z ‘ )I( z ‘ ) dz’ + Z L (z)I(z) .
According to antenna theory corresponding impedance per unit length of the cylinder is given by
Z L (z) = 1 / a2 πσ ( ka/2) J 0 ( j −1 / 2 ka) / J 0 ( j −1 / 2 ka) J 0 ( j −1 / 2 ka)
where J0 and J1 are the equivalent Bessel functions (Kenneth Frederick Sander, Geoffrey Alexander, 1986).
When this axial current is once known it is probable to conclude the current density, the electromagnetic waves and the power density induced in the body. Using King’s expression the current density inside the body can be measured from the equation
I ( z ) ka J 0 ( j −1 / 2kρ )
J z ( ρ , z) =
a π 2 J 1 ( j ka )
An antenna is a physical device that radiates energy, approximately always with some directional confidence and even an omni-directional antenna will have one or two thin directions where there is a reduction or a void in the radiated energy. The energy leaving an antenna is also polarized significance that the electric field is in a particular direction and theoretically, for proficient transfer of energy between two antennas, their relevant radiation patterns must be optimized in the correct direction and the antennas must be polarized with the same direction. However, in the real world, where line of sight between two antennas infrequently exists, and at frequencies above about 500 MHz, objects in the path between the antennas can significantly alter both the efficient radiation patterns and the polarization. These diffusion properties on the radiation pattern and division are casual, out of control, and typically change continuously with time, qualified antenna position and orientation (Alan W. Rudge, 56). Even if an apparatus is located in a set position, polarization will normally vary with time due to movement of close objects and as a result, while some general concentration must be remunerated to radiation pattern shape and antenna polarization, these factors can be optimized for a exacting situation in wide-ranging way.
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For most antennas, but particularly for an embedded antenna, efficiency is perhaps the most significant performance parameter, assuming the antenna produces a satisfactory return loss over the band of interest. Efficiency is measure of what portion of the power supplied to the antenna, comprising any reflection loss, is really radiated by the antenna. The efficiency of small antennas that are closely embedded into a small result can be affected significantly and nearby grounded conductors and dielectric materials will confine and absorb the near-fields of the antenna and cause important losses (Kenneth Frederick Sander, Geoffrey Alexander, 1986). Types of antenna are Isotropic antenna, which radiates power equally in all directions, dipole antenna typically of two types are Half-wave dipole antenna otherwise called as Hertz antenna, Quarter-wave vertical antenna otherwise called as Marconi antenna and Parabolic Reflective Antenna
As a Dipole antenna is nearer to the plane of the earth, its input resistance diminishes initially because the electric field is being tiny by the ground. As the antenna is brought nearer, the input resistance will rise again since increases in ground loss resistance overcome the decrease due to undersized of the electric mechanism. In excess of a superior conductor such as sea water, the input resistance decreases progressively as the antenna is lowered, accomplishing a significance of zero when the antenna handle the water’s plane.
As a horizontal dipole is raise above the ground, the input resistance enlarge until a maximum assessment of around 90 ohms is accomplish at a height of 3/8 ¬. As the antenna is elevated even higher, the input resistance slowly accelerates approximately the open space value of 73 ohms. Most dipoles in definite setting up demonstrate an input resistance of 50 to 75 ohms, based on the position.
Electromagnetic properties of Human tissues:
The human body functions like an electric machine and it is also very hard in form and the brain is the vital part of the human body and controls switchboard for the whole body system. The various controlling hub in the brain, which takes some magnetic power, control the nervous system as well as the other parts working in the body in which the circulatory system also function likes an electrical generator in which the main part is the heart and equipment some magnetic energy to the whole body through circulation of blood D. Poljak, V. Roje, A. [aroli, 2002). As a result, the brain and the heart are the vital parts of the human body and the heart tissues are have magnetic properties.
The human brain is an extremely organized apparatus, which is a magnificently smart, active and natural hub that controls the implementation of the organs of vision, examination and words as well as the motor and sensory nerves. But all these purpose take place through the brain tissue, which is again said to have a low-coercive phase, recognized as magnetite, the main iron oxide in it (Julian L.Davis in Springer-Verlag, 1990). This possesses a magnetic quality, through which the practice continues and the brain tumor is also said to have this magnetic property.
The brain illustrate not only facts of electrical activity around in but also produce small currents, which cause Brain Waves and it’s usually appear at a occurrence of about 10 per second, but they frequently differ in their frequency and size. This variation differs from man to man and the information of each individual differs in the pattern of his brain waves and it’s measured to be electromagnetic waves, which are transmitted direct to the hands and cause a characteristic difference in handwritings.
The human body is competent of making electricity within itself for its full circumstance and it initiates electromagnetic waves at the rate of 80 million cycles per second, which is beyond the observation of our illustration capacity. All human bodies are constantly release static productions, which may be taken to symbolize either electricity or magnetism (D. Poljak, V. Roje, A. [aroli}, 2002). Human body is like a battery and it requires food and drinks to work as battery and consequently, it is proved that the body of every human being contains some part of electricity and some properties of connected magnetism right from the start to the end of life
Human Phantom models
Since the difficulty in measuring definite SAR in the human body, SAR is predictable by measurement using phantom models. Phantoms are tissue corresponding synthetic materials simulating biological bodies (P., S. Pisa, E. Puizzi, 2002). They may be simple or complex based on the tissue composition as well as the form and all human tissues have electrical characteristics that are varies from air but not so vary between each other. Today, we use the frequencies in cellular technologies in which is dielectric constant is in the array of 40 plus and conductivity is around 1 S/m with respect to the phantom material, both high relative permittivity ε and high dielectric loss tangent are necessary to simulate human tissues.
There are two kinds of methods for preparing simulated high water satisfied tissues such as skin, muscle, various brain tissues, blood and cerebrospinal fluid in the beginning a moist jelly like material consisting of saline water, polyethylene powder and a gelling agent. The other kind of material is a liquid includes water, sugar, salt and a composite called HEC which adjusts the viscosity of the liquid and jelly like material is usually used for SAR estimates with high power relevance using temperature measurements by allowing only one of tissue (Scattering of electromagnetic waves, 2001). The liquid tissue material is enclosed in a shell of the simulated part about 1-3 mm thick classically molded from fiberglass or other plastic material with very low RF absorption. Generally, it is hard to prepare tissue material with the accurate properties, so it is popular to organize the material with rather higher conductivity and lower permittivity to avoid SAR inadequacy.
The electromagnetic waves and carry out their preferred functions without improper ruin from or to the particular electromagnetic background. In other words, the equipment must work without causing intervention or being trouble by interfering from direct current to light frequencies. The causes of electromagnetic waves may be either within the tools with which one is feared, in which case it is known as obstruction and the cause of obstruction is called the emitter and the device disturb by obstruction is called the susceptor (Peter S. Hall, Yang Hao, 2001). In all cases electromagnetic waves arises from a arrangement of three features are source, transmission path, and a device sensitive to the kind of energy being generated, one of which is spontaneous.
The SAR distribution in the phantom is also resultant from the measurement of the temperature increases due to the engrossed RF energy by using a small temperature probe and this technique is appropriate for high RF exposure so that heat transfer within and out of the body does not persuade the temperature considerably (P., S. Pisa, E. Puizzi, 2002).
Commercial Software packages:
The electromagnetic simulation software CST software is the result of many years of research and progress into the most capable and correct computational solutions to electromagnetic design. It includes CST’s tools for the design and optimization of software’s functioning in a extensive range of frequencies stationary to optical. Study may contain thermal and mechanical property, in addition to circuit simulation and all programs are accessible through a common boundary with assist circuit and multi- physics co-simulation. EMPIRE XCcel is one of the most important 3D electromagnetic field simulators and is developed by engineering excellence and it is based on the important Finite Difference Time Domain method which has become an industrial standard for RF and microwave section and antenna design. CST MICROSTRIPES is a dominant 3D electromagnetic simulation tool, used extensively for solving difficult radiation troubles comprising complex antenna structures, installed performance. Ansoft is a most important developer of high- recital electronic design automation software and engineers employ Ansoft software to intend state-of-the-art electronic products, comprising cellular phones, Internet – admittance devices, broadband networking workings and systems, integrated circuits (ICs), printed circuit boards (PCBs), automotive electronic systems, and power electronics.
Scientists are also examining the effects that less than threshold level for body heat arises as a consequence of long-term exposure. To date, no unpleasant health effects from low level, long-term contact to radiofrequency or power frequency fields have been verified, but scientists are actively continuing to research this area. The body has complicated mechanisms to adjust to the many and wide-ranging influences we meet in our situation (J. Wiart,
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