Design of a ferrite rod antenna for harvesting energy from medium wave broadcast signals

Radio frequency (RF) energy harvesting is an emerging technology that has the potential to eliminate the need for batteries and reduce maintenance costs of sensing applications. The antenna is one of the critical components that determines its performance and while antenna design has been well researched for the purpose of communication, the design for RF energy harvesting applications has not been widely addressed. The authors present an optimised design for such an antenna for harvesting energy from medium wave broadcast transmissions. They derive and use a model for computing the optimal antenna configuration given application requirements on output voltage and power, material costs and physical dimensions. Design requirements for powering autonomous smart meters have been considered. The proposed approach was used to obtain the antenna configuration that is able to deliver 1 mW of power to 1 kΩ load at a distance of up to 9 km, sufficient to replace batteries on low-power sensing applications. Measurements using a prototype device have been used to verify the authors simulations

Analytical Approach to the Calculation of Parasitic Capacitance between Winding Turns

At high frequencies, winding components behave differently than at low frequencies. Therefore, suitable models are required which can predict coil performances over the whole possible range of frequencies they can be operated. Inductors used in power electronic conversion, magnetic sensors, EMC equipments, and also motor windings can experience frequency levels above several hundreds of kHz where parasitic resistance and capacitance can affect significantly their intended operation. One of the main problems is modeling turn-to-turn capacitance of coils both for single- and multiple-layer windings. The lumped parameter models used in literature for HF inductor simulation are based on simplified approaches to the turn-to-turn and turn-to-core capacitance calculation. In this paper, an analytical approach based on conformal mapping to calculate the exact solution for the turn-to turn and turn-to-core capacitances for coils with different geometrical structures is introduced

An efficient algorithm for the formulation of state equations and output equations for networks with ideal switches

A novel algorithm for the computer formulation of state equations and output equations for linear dynamic networks containing ideal switches is proposed. The state equation and output equation are obtained directly from each topology of the network and its element laws for all cases with no restriction and without the necessity to resort to an iterative procedure. The proposed method is efficient and easy to be implemented in a computer code

Fault generated transients in MHD channels

Flow transient in MHD linear channels are analyzed by means of a quasi-one-dimensional time dependent model. Medium size MHD channelsboth in segmented Faradayandin diagonal connection are utilized for the present study. Plasma flows derived from the natural gas combustion with a mass flow rate of 25 kg/s in the subsonic regime and with a mass flow rate of 45 kg/s in the supersonic regime, are considered. Transients generated by the transition from the nominal operating condition to short circuit, by the transition from the nominal operating condition to open circuit and by a sudden interruption of the seed supply are analyzed

Magnetohydrodynamic transients in MHD generators

Models for the investigation of transients MHD flows are presented in this paper. Both the study of transients caused by the finite flow time of the plasma through the channel and by transitions between different operating conditions of the generator are considered. The analysisof physical phenomena as plasma relaxation and non-uniformities belong to the first case. Transients originated by changes of the operating conditions and faults are of the second case. In order to perform the mentioned study, one-dimensional and two-dimensional time dependent models have been set up. The models are presented in this note. The analysis of the transient during the start up of a linear gas fired generator is shown

Multifrequency optimization of multilayered shields

A procedure for the optimization of planar multilayered shielding structures for magnetic fields, at frequencies for which the quasimagnetostatic description can be adopted, is presented in this paper. The optimum thickness of multilayered shields is found under the constraint of a minimum threshold value for the magnetic shielding effectiveness (SE) at a certain distance from a given source. The design of the shield with respect to the number and type of layers is carried out adopting the particle swarm optimization (PSO) method. Multilayered shields composed of selected materials are considered, and the optimal configuration in a source of a periodic triangular-wave current at the frequency of 10 kHz is investigated

Time-dependent quasi-onedimensional flow models for linear magnetohydrodynamic generator channels

A time-dependent quasi-one-dimensional approximation of a magnetohydrodynamic (MHD) compressible flow in a linear channel has been considered. for the numerical solution of the problem three different algorithms have been utilized (MacCormack's, Godunov's and Casulli's algorithms). they are based on the finite-difference method. these models are utilized for the prediction of the behavior of electrical, thermal, and dynamic quantities during transients and during the occurrence of faults in MHD channels. A comparison of the methods when analyzing a load variation for a Faraday channel is considered

Optimization of magnetic multilayered shields

In this paper a procedure for the optimization of multilayered shields for low-frequency magnetic fields is presented. The shield is optimized with respect to the total volume of the composing materials, being the magnetic flux density magnitude at test points in the shielded region smaller than a given threshold value. For simplicity, shields composed of two different materials only are considered. The number and thickness of the shield layers belong to the set of the control variables. Only one layer thickness at a time is allowed to vary. The procedure is repeated for the different multilayered shield configurations, starting from the single-layer ones for each material, until the optimum shield volume is reached

Electrical stresses during transients in linear MHD channels

Electrodynamical (electric field, current density, electrical power density), hydrodynamic (shear stress) and thermal (heat flux density towards the walls) stresses in a linear segmented Faraday MHD channel have been investigated by means of numerical methods for the startup procedure, a transient from the open circuit (k=1) conditions to loads with K=0.5 (optimum load) and 0.3. The main characteristics of the MHD channel were chosen corresponding to a sample having been investigated before. It has been found that the hydrodynamical and thermal stresses manifest no increase due to the transient when compared with their steady state values. However, at k≠0.5 these can be larger than at k=0.5. In contrary to this, the electrical stresses show unwanted increases at k=0.3. Therefore, it is important to work at k=0.5. Several results of the calculations have been plotted graphically. Some recommendations for the channel design have been given