Electromagnetic Radiation Features

Electro magnetic intercommunicateactivity Features2.1 Electromagnetic shotElectromagnetic beam consists of hustles of electric auto supple and magnetic aught oscillating by dint of aloofness at the speed of light (OET, 1999). The electromagnetic spectrum is an ar run forment of miscellaneous electromagnetic energy in the forms of particles and draw ins. These form of energy be characterized by frequence and wavelength. The wavelength is the withdrawnness per seconds c all all overed by an electromagnetic wave, while the frequency, the enactment of oscillation of electromagnetic waves for bingle second. conformation 2.0.1 bellow shows an electromagnetic spectrum.Figure 2.0.1. Electromagnetic spectrumThe electromagnetic spectrum shows the arrangement of electromagnetic sources based on their frequency and wavelength. Below is Table 2.0.1 which describes the radiofrequency sources and their allocated bands and frequency ranges.Table 2.0.1. Characteristics and frequenc y bands of radiofrequency line of business of opeproportionn sources exercise adjustDescription of arguesFrequency rangeFMFrequency Modulation88108TV/DABTelevision (analogue) DAB (digital Audio Broadcasting)174223TETRATerrestrial Trunked radiocommunication380400TVTelevision (analogue and digital)470830GSM DLGlobal System for wandering(a) communicationsfrom base station to mobile call925960DCS DLDigital Cellular System1,8051,880UMTS DLUniversal Mobile Telecommunications Service2,1102,170Wi-Firadio receiver Fidelity, IEEE 802.11 standards2,4002,500The well-nigh cardinal application of electromagnetic energy is in the expend of radio circulariseing, mobile telephony, microwave application and satellite communication as describe by Kelly (2011). Others include magnetic resonance imaging (MRI), zap ovens, radar, industrial heaters and sealing (Kelly, 2011).2.2 Radio wavesRadio-frequency (RF) is a part of the arrangement of electromagnetic energies in terms of their frequenci es from 3 kilohertz (3 kHz) to 300 gigahertzes (300 GHz) (Kelly, 2011). Radio-transmitters atomic number 18 thingummys that douriciate as transducers for converting electrical current into electromagnetic waves. The knowledge of the presence of electromagnetic knowledge base was first discovered as far back as 1887 when a Physicist proved experimentally that electromagnetic palms can be learnd and detected in space. This phenomenon was predicted three years earlier by Clarke maxwell (1831-1879). A radio transmitter communicates with a receiver via radio waves when electric accusations moves up and down the transmitters feeler and be detected when the electric charge oscillate up and down a receivers approach. In the process, when the charges moves, they produce magnetic athletic theaters. The resulting changing electric-magnetic fields (electromagnetic waves) are able to travel long lengths by means of an empty space (Vacuum). The ability of a transmitter to send polarity to a receiver or an otherwise transmitter to the highest degreeby depends on the oscillation of the charges up and down its transmission aerial at a crabby resonant frequency.2.3 Characteristics of radiofrequency (RF) antennaThere are a number of sensible parameters and principles that define the type of wave and intensity of the radio waves generated and broadcasted into the surroundings. These parameters are relevant in come acrossing the behavior of the antennas. These are the antenna cistron, element array, create or directivity, beam of light var., radiation intensity, beam- comprehensiveness and former density.2.3.1 Antenna ElementsThe antenna element is a basic unit of the antenna. They may exist as individuals or as a group of elements. There are three most common types dipole, monopoles and loop. A dipole antenna is most commonly a linear metallic wire or rod with a escape point at the center. It has dickens symmetrical radiating arms. A monopole ante nna on the other march on has a single radiating arm. A number of authors fork out performed calculation and bars on the copy generated by these field on mobile handset in air and withal against the caput (Jensen Rahmat-Samii, 1995) (Okoniewski Stuchly, 1996) and (Lazzi, 1998). Other works on wireless devices such(prenominal) as cellular tele tele audios using monopole antenna has withal being reported in literary productions (Luebbers, 1992). An interesting application of loops is the wireless telemetry for medical devices and utilise for the first sinoatrial node (Greatbatch Holmes, 1991).2.3.2 Antenna ArraysTo yield a highly directive patterns, multiple antennas or elements can be arranged in space, in various geometrical configurations to yield a pattern (Stutzman Thiele, 1998) (Bucci, Ella, Mazzarella, Panariello, 1994) (Balanis, 2005) (Elliott, 2003) and (Mailloux, 1994). This antenna configuration are called arrays. The field from an array can add construct ively or destructively in others. When well-engineered, the array can be utilise to control the beam by changing the signifier of the excited currents of the individual elements (Elliott, 2003) (Dolph, 1946) (Safaai-Jazi, 1994) and (Shpak Antoniou, 1992). By so doing, an optimum radiation beam can be generated. The geometry of the arrangement of the element to a fault professs the performance. Other factors are distance in the midst of the elements, amplitude of the excited currents, phase excitation and radiation pattern.2.3.3 Directivity and Gainanother(prenominal) parameter employ to describe the directional properties of an antenna is the directivity or gain. The directivity of an antenna, is a figure of merit that quantifies the antenna directive properties by comparing them with those of a hypothetical isotropic antenna that radiates the alike(p) total part as the antenna being characterized. Antenna such as dipoles and loops generates omnidirectional pattern, (McDon ald, 1978) and (Pozar, 1993) derived a formula for such. The gain of an antenna is a measure that takes into manner of accounting the susceptibility of the antenna as well as its directional capabilities. The total antenna efficiency accounts for tone endinges at the input terminals and the structure of the antenna callable to watching, conduction and dielectric deprivationes.2.3.4 Radiation Pattern Be views the parameters described supra, the radiation pattern is the property utilize to describe the resulting abidance of the beam generated. Radiation or an antenna pattern is a mathematical function of the antenna that describe the space coordinates (Balanis, 2005). The main beam is the constituent where the radiation is strongest and the other directions forms the side-lobes. The half-power beam comprehensiveness is the measure of the direction of maximum radiation. The beam width or Half- mightiness Beam width (HPBW) is the width of the power pattern at the location wh ere the beam is 3 dB on a lower floor its maximum appraise (half-power points) or the location where the field is 1/2 of its peak. It is often practice sessiond as a trade-off amidst it and the side lobe level (The ratio of the radiation intensity of the medium-largest side-lobe to the maximum radiation intensity). The HPBW varies inversely as the side lobe level. The most common resolution criterion states that the resolution capability of an antenna to distinguish between two sources is equal to half the first-null beam width (FNBW/2), which is usually employd to approximate the half-power beam width (HPBW) (Kraus, 1996) and (Kraus Marhefka, Antennas, 2002).2.3.5 polarisationFurther more than, the generated wave can oscillate up and down, left and right or device characteristic between these. These behavior describe the kind of polarisation the wave exhibits. Polarization of a radiated wave is defined as that property of a wave in a time-varying direction and relative magn itude of the electric field vector. In general, however, when the shape of the electric field appears in the form of an ellipse, the polarisation is described as elliptical. When the shape appear linear or circular, the polarization is described as such. The polarized radiated wave by the antenna can too be represented on the Poincares sphere (Balanis C. A., 1989) (Poincare, 1892) (Deschamps, 1951) and (Bolinder, 1967).2.3.6 Radiation Intensity some other important property of the antenna is the radiation intensity. The radiation intensity is the power radiated per unit solid angle subtended by the antenna. It is the property of the far field. The radiation intensity is go fored by multiplying the density by the square of the distance. The power pattern is also a measure of radiation intensity. To be able to obtain the total power density, one involve to integrate the radiation intensity.2.3.7 Power DensityFinally, the radiation power density describes the power associated with an electromagnetic wave. The power density is the total power crossing a closed stand up by integrating the normal component of the Poynting vector over the sinless surface.2.4 Electromagnetic field just about an antennaAn electromagnetic field is the part created around a source of electromagnetic radiation. An antenna is a device which changes electrical charges or current into electromagnetic waves into space. The distribution of RF energy from an antenna was found from literature to obey a directional pattern and varies with distance from the antenna. The fields created around an antenna can be sort out into two2.4.1 Near FieldThe near field is the region around an antenna such that the electric and magnetic fields are decoupled, quasi-static and are not uniform. And the impedance which is the resistance in air and the power associated with the field varies with distance.2.4.2 Far FieldThe far field on the other hand allow plane fronts which do not depend on the shape of the source but rather unchanging. The radiated power decreases inversely with distance from the antenna notionally. The electric and magnetic fields are uniquely defined by approximately a constant impedance of the middling. Figure 2.0.2 below garnish the field regions around an antenna.Figure 2.0.2. Electromagnetic field regions around a typical antenna2.5 Advances in field exemplarA mouldinging is a good approximation of a problem to a sincere world solution. There are various mathematical geting methods getable in literature to date (Sarkar, Ji, Kim, Medouri, Salazar-Palma, 2003) (COST-231, 1999) and (Correia, 2001). Extensive theoretical and experimental search on electromagnetic field Levels has been carried out and reported in literature (Lin, 2002) (Cicchetti, 2004) and (Nicolas, Lautru, Jacquin, Wong, Wiart, 2001). Currently, the studies in electromagnetic fields can be grouped into two dominant bestow modelling approaches theoretical and a posteriori (Rappapo rt, 2002). While theoretical models depend on the knowledge of the physical truths of the wireless wrinkle, such as the electrical properties of the ground, empirical models are based on actual radio frequency (RF) amounts of wireless channels. Furthermore, one can regroup it into Monte Carlo, a posteriori and Physical models (Rappaport, 2002). Monte Carlo method are statistical in temperament and arrive use of statistical and distribution functions such as channel characteristics of radio-transmitters and ray-optics. (Okumura, Ohmori, Kawano, Fukuda, 1968) Found out from cadence that for a state of affairs where one cannot have a line of sight with the transmitter, the fading (attenuation) of the received voltage approximates communicate distribution. Okumura also real a correction factor to be used together with the data to correct for the field strength. When Okumuras deliberate results were mediocred, the results showed properties of a lognormal distribution. (Okumu ra, Ohmori, Kawano, Fukuda, 1968) And (Mogensen, Eggers, Jensen, Andersen, 1991). The demeanor of settlement and nature of buildings also affect the annex of the radio waves when travelling from a source into the environment. Also random variation of building also contributed to loss of reference of the waves. Some earlier work suggested that radio waves propagates over buildings and are diffracted down to street levels (Parsons, 1992). To be able to obtain accredited statistics, a lot more of measured data was required. Diffraction is when the pass of the beam is obstructed by surface of irregular shape edges. Diffraction methods were developed and used to account for diffractions at roof tiptop (Ikegami, Yoshida, Takeuchi, Umehira, 1984). Variations in building height contributed to the shadow loss of file name extension over low buildings. The most general approach uses mathematical integration of physical optics integrals (Walfisch Bertoni, 1988) and (Bertoni, 2000). Measurement has shown that Monte Carlo methods need to consider the inwardness of trees (Mogensen, Eggers, Jensen, Andersen, 1991), (Rizk, Mawira, Wagen, Gardiol, 1996), (Vogel Goldhirsh, 1986) and (LaGrone, 1977). Trees are able to attenuate the signal to the order of 10 dB (Vogel Goldhirsh, 1986). The Monte Carlo methods even though are good when adequate measured data is used, suffers from modifications to the buildings and terrains and are very expensive to carry out.Empirical methods make use of information gathering on the basis of systematic experiment instead of making use of logic or mathematics. The empirical model uses extensive measured data and analysis tools to formulate relationship between parameters of interest. Measurements have shown that a simple two-ray model consisting of the direct and the ground-reflected ray was commensurate to predict the path gain (loss) for propagation over a even earth (Rustako, Jr., Owens, Roman, 1991) and (Xia, Bertoni, Maciel , Lindsay-Stewart, Rowe, 1993). Reflection occurs when the wave from a source hit an heading whose dimension is large as compared to the wavelength of the wave. The path loss represents the signal attenuation in decibel (dB). The path loss is the difference between utile transmitter and receiver power. Most published work concerning outdoor propagation depends on free space and two-ray models (Pande, Choudhari, Pathak, 2012), (Willis Kikkert, 2007), (Neto, Neto, Yang, Glover, 2010). The free space model assumes that two transmitter and receiver, use line-of-sight communication with no obstruction or reflection of any form. The free space model obeys the relation (2. 1)Where f is the frequency in MHz and d is the separation distance between the transmitting and receiving antennas in meters. The receiver power has been found to falls off as the square of the transmitter-receiver separation distance. The receiver power decays at the rate of 20dB per decade. When the solvent of ground ray reflection is considered, a Plane Earth model was used. The model is given as (2. 2)Where d is the distance as above and and are the elevations of the transmitter and receiver heights in meters respectively. The separation distance (d) in this model is assumed to be much larger than and .In our unfeigned environment today, there are obstruction everywhere and the propagation of the electromagnetic waves are affected by it (Mao, Anderson, Fidan, 2007). The radio signals in our environment are attenuated by reflection, diffraction and scattering. Scattering occurs when an object in a medium are smaller as compared to the wavelength of the incoming wave. To be able to account for location characteristics and the impact of vegetation, it was found in literature that the average signal power decreases logarithmically with distance (Rappaport, 2002). To be able to view the path loss due to real world approximation, a log-distance model was developed. The average path los s for a typical distance between a transmitter and a receiver can be represented as an expression of distance by using the indicator n. The path loss is given as (Liao Sarabandi, 2005) (2. 3)Where is the path loss in dB at a reference distance and n is the path loss exponent that represent the rate of the path loss decrease as a function of distance. The value n also characterizes the propagation environment. Table 2.0.2 below summarizes the characteristic of the exponent n in the environment.Table 2.0.2. Characteristics of typical propagation environmentsEnvironmentPath loss exponent values (n)Free space2.0Urban area, cellular radio2.7 to 3.5Shadow Urban cellular radio3.0 to 6.0In-buildings, line-of-sight1.6 to 1.8Obstructed in buildings4.0 to 6.0Obstructed in factories2.0 to 3.0The reference distances from research was taken to be between 100 m to 1 km depending on the height of the transmitter. The internationalistic Telecommunication Union (ITU) recommended that in a situa tion where field of honority of the signal propagates through trees or vegetation, the ITU-R model can be used (Rappaport T. S., 1996). (2. 4)Where the frequency used was between 200 MHz and 95 GHz. One of the most important fully empirical prediction method was conducted by (Okumura, Ohmori, Kawano, Fukuda, 1968). Okumuras method was based entirely on an extensive measurement in Tokyo city. Okumura developed a set of curves given the average attenuation relatively to free space in the urban area over a quasi-smooth terrain. From these curves, Okumura deduce from the graphs a simple power jurisprudence which was a function of the environment and it characteristics. The model was applicable to frequency range between 200 MHz and 2 GHz and covers a distance of 100 km. Okumuras data was further modified by (Hata, 1980) who made it into a series of graphs. However, other methods disagree with the predictions of the Okumuras methods. Others have also tried to improve the method by applying building density (Kozono Watanabe, 1977) but was rejected by the scientific community. The Okumura-Hata model, together with related corrections was found to be one of the most common and single model used in purpose real systems. Lee in 1982 came out with a power law model which was based on measurement and takes into account the variation in terrain (Lee, 1982). The model was environment specific because it was based on the assumption of the characteristics of the environment. It bequeath be very difficult to tell which environment characteristics one need to use since the environment varies from one country to the other. Even though empirical method was easy to implement and their ability to include all environment-related factors that affect the propagation of radio waves in practice (Rappaport T. , 2002), they suffer from parameter ranges the environment must be classified which may vary from one transport to the other .the method also do not provides insight into propagation mechanism and analytical explanations.The Physical model method attempt to produce settled field strength at specified points. (Ikegami, F. Takeuchi, T. Yoshida, S., 1991). The model makes use of characteristics of the environments, physical optics and other theories to account for the intended parameter of interest. A elaborated pass judgmentment of the motion picture of urban existences to electromagnetic fields requires the use of deterministic models that take into account the interferences caused by the buildings in the propagation of the field. Deterministic models were developed to account for terrain in the absence of buildings based on geometric surmisal of diffraction (Bullington, 1977), (Luebbers R. J., 1984) and (Lampard Vu-Dinh, 1993). Other methods such as parabolic equation method (Janaswamy Andersen, 1998) and (Levy, 1990) takes the elaborate terrain profile into account. The method uses detail map of an area taking into reflexion building confi gurations and using a ray optics to trace the waves. There are 3-D (three dimensional) ray tracing models that are able to accurately estimate site-specific propagation situations (Catedra, Perez, Saez de Adana, Guiterrez, 1998). Although it accounts reasonable well for close in variation of field strength, it suffers from unrealistic assumptions, theories and underestimate in some cases (Saunders, 1999). Other works also uses numerical methods such as method of moments (MOM) to analyze the electromagnetic field of antennas (Johnson, Shin, Eidson, 1997), (Wanzheng, Yan, Anmin, 2000), (Povinelli DAngelo, 1991), (Lou Jin, 2005) and (Tofani, dAmore, Fiandino, 1995). However, these Methods require higher mathematical and programming skills such as large sparse matrix solution as well as more computer resources such as larger memory and multiple CPUs than the analytical method (Johnson, Shin, Eidson, 1997). A semi-analytical treatment has been carried out for cases where the horiz ontal separation between the base station and first row of buildings is knownand all the buildings are of the same height (Xia, Bertoni, Maciel, Lindsay-Stewart, Rowe, 1993), (. Bertoni Maciel, 1992). From the above analysis, it was evident from literature to date that there is no one method which will be able to predict accurately well and also help us understand and make heart of the physics involved in the process of direct. This research work focuses on the need for a hybrid model (Semi-Empirical) which will achieve a good level of accuracy and also help us understand the physical interaction of the parameters involved and also serve as an publicity on this field.2.6 Advances in measurementsThe natural electromagnetic energy comes from terrestrial and extra-terrestrial sources such as electrical discharges during thunder storms in the atmosphere and radiation from insolate and space. It is of interest to note that the black organic structure radiation from a person in the RF-band is approximately 3 mW/m2. The man-made source originates from mainly telecommunication and broadcasting services in the environment. There are several(prenominal) methods developed to assess the electromagnetic fields (EMF) exposure level in literature. One of them was the use of a personal exposure measurement methods (Viel, Cardis, Moissonnier, Seze, Hours, 2009), (Urbinello, Joseph, Huss, 2014), (Bolte Eikelboom, 2012), (Urbinello, Huss, Beekhuizen, Vermeulen, Rsli, 2014), (Radon, Spegel, Meyer, 2006) and (Frei, Mohler, Brgi, 2009). Another method is the used of stationary measurement approach (Brgi, Frei, Theis, 2010), (Calin, Ursachi, Helerea, 2013), (Pachn-Garca, Fernndez-Ortiz, . Paniagua-Snchez, 2015), (Ozen, Helhel, Colak, 2007), (Korpinen Pkknen, 2015) and (Verloock, Joseph, Goeminne, 2014) where measurement is made at a define period of time such as 6 minutes averaging. The 6-minute averaging time comes from the time constant for the thermoregulation o f the body (ICNIRP, 1998) to occur. FM and TV broadcast transmitters, GSM and UMTS base move are important sources of RF EMF in terms of exposure level in the environment. In general, FM and TV broadcast transmitters were installed in places far off distance from the city center in the past but in todays world, they are installed within our communities. In 1980, Tell and Mantiply published a study of RF fields measured at 486 sites across 15 major metropolitan areas in the USA which at that time, accounted for nearly 20 % of the nations race of 226.5 one million million people (Tell Mantiply, 1980). The measurements covered the low VHF TV (54-88 MHz), FM radio (88-108 MHz), high VHF TV (174-216 MHz) and UHF TV (470-806 MHz) bands. They reported a median broadband time-averaged field level of 0.005 mWcm-2, with an estimated 1 % of the population undetermined to fields with power densities of 1 mW cm-2. In addition, the fields from FM radio broadcasts were clearly dominant over the fields from the other three bands. Typically for High-power broadcast transmitters, the effective radiated power (ERP) was 250 kW per channel for FM radio and 500 kW per channel for television. The antennas were mounted towards the top of a 300 m mast. For medium-power broadcast and telecommunications transmitters, the transmitted powers were in the region of 100-200 W per channel. The exposure to the general public was very small relatively to people living in the immediate neighborhood of medium and short-wave stations (Jokela, Puranen, Gandhi, 1994). People working in FM and TV towers which are near to high power FM or TV broadcast antennas were exposed to high levels in the range of 50 to 800 MHz (Jokela Puranen, Occupational RF exposures, 1999) and (Hansson-Mild, 1981). Other studies have been carried out in the domains of exposure field measurement by (Viel, et al., 2009a), (Viel J. , Cardis, Moissonnier, R., Hours, 2009b) and possible consequences of human exposure to such fields(Hossmann Hermann, 2003). A study of ambient RF fields conductedmostly outdoors in Gothenburg, Sweden reportedan average wideband power densities of between 0.04and 0.05 mW cm-2 (Ahlbom, Feychting, Hamnerius, Hillert, 2012).European studies reported generally, in the five-country analysis, the totalexposures were lowest in the urban residential environment(range of means 8.5E-03 to 1.45E-02 W cm-2). The results for a set of African countries was qualitatively and quantitatively similar to the results of RF measurement surveys conducted in the Americas, Europe and Asia (Rowley Joyner, 2012) where the planetary weighted average was 0.073 mW cm-2. The mean for the selected South African data set was 0.016 mW cm-2. Some of the conclusion drawn was that the signal strengths for the cellular bands was unchanging in both time and across countries. Even though introduction of 3G and 4 G services are on the increase, the field levels are log-normally distributed and more data points makes the FM signal strengths relatively constant. In addition to these findings, several studies have reported that residential (and outdoor) fields from broadcast and cell downlink sources are lower in rural areas compared with fields in urban and suburban areas (Breckenkamp, et al., 2012), (Viel, et al., 2009a) and (Joseph, Vermeeren, Verloock, Heredia, Martens, 2008). Cancer has been the primary concern among populations in the immediate vicinity of broadcast transmitters. Scientific evidences point toward heating effect from high levels of exposure, and most golosh limits are based on it. Among these are the exposure limits proposed by the International Commission for Non-Ionizing Radiation Protection (ICNIRP) (ICNIRP, 1998) or Institute of Electrical and Electronics Engineers (IEEE) (IEEE, 2005) to prohibit such effects (WHO, 2006).There is little scientific evidence on the risks associated with long-term exposure to low levels of RF EMF (ICNIRP, 1996). In 2012, the International commission for Research on Cancer classified RF EMF as possibly carcinogenic (Group 2B), based on studies on mobile phone usage (IARC, 2012). Mobile phone usage has increased tremendously, with about 6.8 meg subscriptions by the end of 2013 (ITU, 2013) and nearly 7 billion cell phone subscribers in 2014 (ITU). Statistics show that as at May 2008, the number of mobile phone users in Ghana was well over 8 million but as at the end of January 2016, the number of mobile phone users in Ghana rose to 26.09 million, according to the latest figures from the National Communications Authority (NCA). Urban areas are mostly affected by the over population of Base Station Transceivers (BTSs). Their closeness to homes and schools are raising concern about some health risks that might be associated with them (Khurana, et al., 2010). Numerous studies have demonstrated that a very significant part of the human exposure in the radiofrequency (RF) band is due to mobile communications radiation (Bornkessel, Schubert, Wuschek, Schmidt, 2007), (Genc, Bayrak, Yaldiz, 2010), (Joseph, Verloock, Goeminne, Vermeeren, Martens, 2010), (Kim . Park, 2010), (Rufo, Paniagua, Jimenez, Antoln, 2011), (Joseph, W. Verloock, L. Goeminne, F. . Vermeeren, G Martens, L., 2012a), (Joseph, W. Verloock, L. Goeminne, F. Vermeeren, G. Martens, L., 2012b), (Rowley . Joyner, 2012). The maximum output powers of a radio channel used in GSM and UMTS networks are 10-40W and 20-60 W, respectively (Koprivica, Neskovic, Neskovic, Paunovic, 2014).It has been shown t