Adnen Rajhi

Analytical calculation of the specific absorption rate from cellular phone in some realistic situations

In this paper, we treated analytically the cellular phone antenna radiation parameters in the presence of a human body and the electromagnetic absorption concept by a human body in different realistic talking situations (in free space, in conductive environment, indoor, outdoor) is also investigated. Numerical investigations have been carried out to analyse the EM field coupling problem from cellular phone antenna to a spherical modelled head in different realistic scenarios by using the concept of the coupled integral equations; in which the electric field induced inside the model and the current distribution of the linear antenna can be expressed with coupled integral equations using dyadic Greens function. Some radiation parameters (radiation patterns, input impedance,̃) has been evaluated, and also some investigations on the electromagnetic absorption, which is defined by the local specific absorption rate (SAR) distribution, has been calculated in each scenario for a spherical homogeneous head modelled irradiated by a dipole antenna. Results from different conductive media using the same antenna are compared showing that the SAR parameter is not related only to the radiating device but it depends mainly on the external environment. The resonance frequency of the input impedance is affected when the operator is placed near perfect conductor and will change considerably when the human head is surrounded by perfect conductors and the SAR distribution gives different absorption patterns therefore hazards health problems will be enhanced in such situations.

Novel Conception of a Tunable RF MEMS Resonator

This paper presents a new monolithic microwave integrated circuit (MMIC) based on coplanar waveguide (CPW) design for a tunable resonator based on RF MEMS. This RF structure, which can be used for system on chip (SOC), is constituted with MEMS Bridge placed between two meander inductors and the tenability is controlled by a variable applied DC voltage. Moreover, this device presents a compactness characteristic and the possibility to operate at high frequencies. The resonant frequency and the bandwidth can be changed easily by changing the bridge gap of the RF MEMS. The numerical simulations of this novel structure of a tunable RF MEMS resonator were performed with the electromagnetic solvers CST MWS (Computer simulation Technology Microwave Studio) and validated by the more accurate electromagnetic solver HFSS (High Frequency Structural Simulator). The simulation results, for three different spacing of the bridge gap, show that the tunable frequency band are between 10 and 40 GHz with the two electromagnetic solvers and exhibiting three resonant frequencies (21, 23.1 and 24.6 GHz).The simulation results of the return loss using CST achieves 29 dB with an insertion loss less than 1 dB; However, the HFSS simulation shows similar performance in the resonant frequencies and in the bandwidth giving better results in terms of the return loss (about 35dB instead of 29 dB) and showing a good adaptation.

Indirect influence of lightning EM field induced in a power line on the high frequency transmission line

In this paper the time domain modelling of a transmission line coupling by an external EM fields is described. These fields generated by a nearby lightning stroke induced in an electricity transport and distribution power lines. To model this coupling, we have used the equivalent circuit taking in consideration the different physical concepts based on the theoretical Taylors formulation. The numerical inversion of Laplace transform method is employed to solve the different equations derived from the equivalent circuit models. Results obtained by this model present the response voltages and currents induced in the transmission line used in the mobile telecommunication circuit.

Optimal algorithm for the numerical inversion Laplace transforms method in a multiconductor transmission line system

The current paper presents a study on the numerical method of inversion of Laplace transforms (NILT) to deal with some of EMC problems in MW systems under the Matlab environment. The idea consists in studying the two well used algorithms in NILT, one is called quotient-difference algorithm using expansion of the Fourier series and the other is called epsiv-algorithm using the expansion of Laguerre function, in order to reach an optimal algorithm of the NILT method for different multiconductor transmission line (MTL) systems. The simulation results show that the quotient difference algorithm is most efficient than the epsiv-algorithm in term of rapid convergence to zero with a low relative error; these performances increase significantly the use of Laplace transform inversion by the method of Laguerre in MW circuits.

Conception and simulation of above-IC CPW antenna

The antenna chips becomes very important component in microwave applications and for the wireless communication industry. In this work, different Coplanar Waveguide (CPW) antenna above-IC (integrate circuit) are analyzed and simulated by high frequency structural simulator (HFSS) based on finite element method (FEM). A comparative study has been done on their performances of different types of CPW antenna with some geometrical dimension. Furthermore, the return loss and radiation pattern were investigate in terms of gain radiation and directivity. The simulation results show that it is possible to have multiband CPW antenna by changing the geometry of the radio frequency (RF) patch in the shape of inverse U with a split-ring resonator.

Measurement of water transfer changes during hemodialysis cycle

During the hemodialysis cycle which can be few hours, the actual apparatus of the dialysis does not display the water transfer ratio and since this cycle is around four hours, it is necessary to have the hydratation state of the patient and to avoid the over hydration or the dehydratation states. In this paper, we have investigated the concept of the bioimpedance and the biological body constitutions and its different compartments such as Total Body Water (TBW), Intra-Cellular Water (ICW), Extra-Cellular Water (ECW), Fat Free Mass (FFM), and Fat Mass (FM). During the treatment cycle, there is a variation of the quantity of water and this change of water is slowly varying function leading to small variation of the bioimpedance; therefore we developed a system to detect a small variation of the bioimpedance (order of few milliohms) and to extract and display the different biological compartments. This developed system with an STM 32discovery board displays in the real time the value of the bioimpedance and the calculated body water compositions taking into account the physical data of the patient such as age, sex, weight, length. Finally, the proposed embedded solution can be integrated in the hemodialysis apparatus in the purpose to help the nephrology doctor by giving an information on the over hydratation or the dehydratation states of the patients.

New Experimental Investigation of Magnetic and Electric Fields in the Vicinity of High-Voltage Power Lines

In this paper, the theoretical and experimental characteristics of magnetic and electric fields in the vicinity of high voltage lines are investigated. To realize these measurements and calculations, we have developed some equations for two overhead power line configurations of 150 ㎸ (single circuit, double circuit), based on Biotsavart law, image and Maxwell theories, in order to calculate the magnetic and electric fields. The measurements were done to a maximum distance from the tower of 50 m, at a height of 1m from the ground. These experiments take into consideration the real situations of the power lines and associated equipment. The experimental results obtained are near to that of the Biot-Savart theoretical results for a far distance from the tower; and for a distance close to the power line, the results from the image theory are in good agreement with the experimental results.

EMC immunity test for capacitive shunt RF-MEMS switch

The Radio Frequency Micro-electromechanical system (RF MEMS) has compact geometries and are very used in Monolithic Microwave Integrate Circuit (MMIC) for different important applications with respect to their size and their effectiveness. Its effectiveness can be improved by reducing the Electro Magnetic Interference EMI problem with better Electromagnetic compatibility EMC immunity of the component. This work presents the EMC immunity testing of RF-MEMS for different substrate cases Silicon (Si), Gallium Arsenide (GaAs) and Silicon Carbide (SiC). This MEMS structure is exited by used the electromagnetic solver HFSS (high frequency structural an external parasite line which will induce an EM radiation around the MEMS component; In order to analyze the EM test immunity of the MEMS we simulator) based on finite element method for simulation. For the different substrates, a comparative study of the electric and magnetic fields is exposed and discussed. We have investigated also on the surface current densities on the RF line. The results show that the material SiC has better performances in the immunity test than Si and GaAs substrates.

BER perfermance of GMSK modulation under radio mobile propagation environments

This paper treats the BER performance of GMSK modulation under different radio mobile environments. Studies of GSM performances in various radio mobile environments such as in AWGN channel and in multipath fading channel (one path fading and four path fading cases) were performed. A random data was used as an input to the simulation program in the Matlab environment and the output was stored in the form of Bit Error Rate (BER) as a function of signal-to-noise ratio (Eb/No).

Exprimental investigation of the GSM transmission quality in the vicinity of the power line system

In this paper we have analyzed the GSM (Global System for Mobile communications) transmission quality in the vicinity of the power line system and its EM effect to the RF interface of the mobile telecommunication system. These electric lines and its associated equipments produce the noise around their proximity, which are likely to have dangerous effects on their environment. The characteristic of the power line noise and its correlation with the GSM burst; showing that the considered noise source to the mobile station (MS) and Base Transceiver Stations (BTS) of GSM system is due to the presence of fundamentals and harmonics fields (electric and magnetic fields) in the proximity of power lines functioning at the permanent state; specially the present of the 5th harmonic field which is close to the GSM pulsed field at the frequency 217 Hz. The measurements and simulated results of GSM system were done inside and outside an area of 50m distance from the tower of power line. These experiments take on consideration the two real situations (in the case of the presence of BTS and in the case of the absence of the BTS of the GSM equipments). It has been observed that the effect of the power line on the quality of service (QoS) of GSM signal in idle mode and dedicated mode is more important, and the experimental results show the influence leading to a degradation of the reception level (RxLev) and the reception quality of the GSM signal (RxQual) with an important Frame error rate (FER).