INTRODUCTION:
Energy harvesting (EH) involves
absorbing ambient energy and converting it into electricity to power up the battery/sensors.2
The type of sources of ambient energy is solar energy, tidal energy, wind energy,
thermal energy, electromagnetic energy, mechanical energy, etc. The working principle
is initially an energy harvester converts the incident ambient energy into electrical
energy and then a power management unit (PMU) coverts the obtained energy into a
suitable form for a particular application.3 Even though solar energy
is available abundantly it has some limitations.
Due to its continuous availability, radio frequency (RF)
source is an alter-native. However, it suffers from low incident power levels. A
dedicated source and an efficient RF to DC conversion circuit is needed to improve
this. Extensive availability of RF power and its low power consumption in makes
it as a accurate option for energy harvesting.
The process involved in RFEH is to harvest electrical energy
from RF signals which can be obtained from a dedicated or unknown RF source). Energy
harvesting typically operates in milli-watt or even micro-watt power levels. The
different types of RF energy sources are, namely, Wi-Fi, WLAN, TV/DTV, GSM/cellular
AM, FM, Bluetooth, etc. Since it is present everywhere and all time, it can be used
to power wireless sensor nodes4, wireless body area networks5,
wireless charging systems6, and RFID tags7.
In the case of magnetic resonant wireless power transfer
(WPT) technology, the system topology is the main factor to determining the WPT
characteristics of the system, and recently, different system topologies based on
various composite resonant circuits have been applied in the WPT’s. 1st, characteristics
of the composite resonant circuits is the fundamental circuits of transmitter and
receiver are investigated. In the process, a calculation method of, current ratio,
resonant frequency and quality factor of these circuits are presented and parameters
are clarified. 2nd, the composite resonant circuit-based WPT systems, Possible topologies
of these systems are explored and an equivalent system model of these systems is
proposed. Some applications includes a low-power RF transceiver, for information
transmission or reception, an energy harvester, composed of an RF antenna, an impedance
matching, a voltage multiplier and a capacitor, to collect RF signals and can be
convert them into electricity, A power management module, which decides whether
to store the electricity obtained from the RF energy harvester or to use it for
information transmission immediately.
II.PROPOSED SYSTEM:
The circuit was divided into two sections:
1. Transmitter Circuit
2. Receiver Circuit
The transmitter circuit consists of power supply, boost converter, royer
oscillator and the copper laminated coils. The receiver side had the receiver coil,
rectifier, LCD, PIC microcontroller and the switching circuit that used the CD4066.
The block diagram of the design is shown in Fig 1.
An open helical coil can be approximated with an equivalent series RLC
circuit. If the resistance, the inductance and the capacitance of the single
coil are R, L, and C, the impedance of the coil, 
, is give where 
is an angular frequency. Specifically, the imaginary part
of the coil impedance, 
, can be expressed as shown. Practically, the values of
the self-inductance and of the self-capacitance of the coil remain constant over
the frequency range of operation. Generally the magnetic resonant coupling WPT8
contains two coils: transmission power coil, receiving with load coil, the equivalent
circuit model of a magnetic resonant coupling system gives a reference to analyze
the transfer characteristics9
III. COIL DESGN:
The two coils are needed to be tuned to resonate at the
same frequency also the distance and the angle of orientation for each coil like
less spacing between the two coils, shielding done on their surfaces, ensures effective
and efficient power transfer. It is important to select the type of coil before
adding it to the circuit to be used in both the transmitter and the receiver to
give the best magnetic flux with minimum leakage and less voltage drop, So FEMM
(Finite Element Method Magnetics) is a program based to solve magnetic, electrostatic,
and current flow problems on two-dimensional planar. It also shows the behavior
of electric field intensity and electric flux density10.
IV. DESIGN OPTlM1ZATlON:
Genetic algorithm is the preferred solutions in modeling,
permutising and optimization systems with uneasy dynamics to model. A GA is a very
general algorithm so we can use it every application. Genetic algorithms use the
principles of selection and evolution has a several solutions to overcome the problem.
This algorithm has the first parameters that should be optimized and defined. For
solving a problem GAs does the simulation and gives the survival of the fittest
among individuals over consecutive generation. Each one of the generation has a
population of character strings that are equivalent to the chromosome that are present
in our DNA. Each one of the individual represents a point in a search space and
possible solution. The individuals in the population are then made to go through
a process of evolution.11
The GA is used to optimize coil configuration and resonance
parameters. The calculation of coils self inductances and the mutual inductance
in between them depending on coils configuration using GA. Coupling coefficient
is calculated at 60 cm distance between coils12. During the simulation
process, the gap between each coil wires was optimized to reduce the radiation loss
in given specific fabrication limitations. An integral solver was adopted to reduce
the simulation time, The simulation results yielded the following coil dimensions
as summarized and the radius of the coil is 50 mm, the diameter of the copper wire
is 1 mm, the gap between consecutive turns is 0.2 mm, and the number of turns is
26, to achieve the operation frequency of 13.56 MHz.
Fig 2 Flow chart
Based on the simulation results, the Tx and the Rx coil
prototypes were fabricated with a 1-mm-diameter copper wire utilizing laser cut
acrylic boards for support purposes. A photograph of the fabricated Tx and Rx coils,
the simulated and the measured 
values of the single coil without any other coil in its
proximity, and the measured 
value values for different center-to-center coil distances
identical Tx and Rx coils14.
V. EXPERIMENTAL RESULT:
GAs is among the preferred solutions in modeling and optimization
systems with uneasy dynamics to model. A GA is a very general algorithm that works
well in any search space. Selection and evolution are the two principles of GA to
produce several solutions for a given problem. To use this algorithm, first the
parameters that need to be optimized must be defined. The individuals in the population
are then made to go through a process of evolution. Fig. 2 shows a flowchart of
a GA algorithm.
Fig 3. Experimental results
The GA is used to optimize the coil configuration and the
resonance parameters. the calculation of coils self inductances and the mutual inductance
in between them depending on coils configuration using GA. coupling coefficient
is calculated at 60 cm distance between coils med points as well. In Step 3, the
receiving and sending coils are optimized, following the procedure. In step 3.2,
the total length of the receiving coil must be considered for the RF radiation performance.
If the total length of receiving coil deviates far away from L resonant in, the
receiving coil must be optimized again until the convergence is achieved. In Step
4, the performance of the RF radiation is optimized by adjusting the parameters
of receiving coil and gear like ground in full-wave. The real and imaginary parts
of the input impedance of the antenna are the major concern, respectively. The geometry
of sending coil is slightly adjusted to compensate the deviation in receiving coil
then the parameters of load loop and power loop are optimized according to the influence
of gear-like ground on WPT is investigated by simulation. If the PTE deviation (ΔPTE)
is less than 5% (ΔPTE = PTEcal − PTEsim, PTEcal is the calculated PTE.
PTEsim is simulated PTE by full-wave simulation, the result is acceptable.
VI. CONCLUSION:
As the number of portable electronics devices increases,
the demand for more flexible and reliable power transfer techniques is becoming
more urgent. In order to improve the efficiency of a WPT system, the design of the
circuit and operating frequency must be carefully considered. In this paper, the
possibility of a real-time active MC for biomedical WPT applications is discussed.
First, open helical type coils, which have a self-resonance frequency of 13.56 MHz,
were designed utilizing an EM simulator and characterized through measurements.
Additional operation verification tests conducted for misaligned coil topologies
and for nonsymmetrical Tx–Rx WPT systems featured similar improvement results with
the preliminary well-aligned same-size Tx and Rx configurations. This helps extensive
potential applicability of the proposed real-time automatic matching system to a
variety of WPT applications, especially when there is strong coupling between Tx
and Rx coil causing the frequency split, for example, charging of skin implanted
devices, electrical vehicles, and unmanned aerial vehicles (UAVs). This paper demonstrated
Genetic algorithms based Multi coil (MC) optimization technique to optimize the
circuit design of a WPT system. As the design continues to improve, the technology
will have more potential in many different applications due to its unique features.
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