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CHAPTER 2
AMBIENT RF ENERGY HARVESTING COMPONENTS AND LITERATURE REVIEW
2.1 RECTENNA & ITS COMPONENT A rectenna is a rectifying antenna, a sort of antenna that is used to convert microwave energy or radio frequency energy into direct current signal that can power low sensor devices. They are modelled as a part of wireless power transmission systems that transmit power through radio waves or electromagnetic waves. A basic rectenna, comprises of a microstrip patch antenna with a RF diode. It is nonlinear rectifying element (for example Schottky diode, Zener diode, IMPATT diode.... etc.). The diode rectifies the alternating current or bidirectional current induced in the patch antenna by the RF waves, to generate DC or unidirectional
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2.1.2 RECTIFIER A rectifier is an electrical device that converts bi-directional current or alternating current (AC), to unidirectional current or direct current (DC). This process is called rectification. Rectifiers have many uses including high-voltage direct current power transmission systems, in DC power supplies and in detection of radio signals. There are two types of rectifier, the half wave rectifier and the full wave rectifier. In our case, given the need of matching as the less number of components, half wave rectifier has been used.
2.1.2.1 Half Wave Rectifier The half wave rectifier rectifies only half cycle of the AC input waveform. The half wave rectifier consists of a step down transformer, a diode connected to the transformer and a load resistance connected to the cathode side of the diode.
2.1.2.2 Full Wave Rectifier The circuit of full wave rectifier uses two rectifier elements and the transformer with secondary center tapped. One for the positive half cycle and other for the negative half cycle. The output DC in full wave rectifier is twice that of half wave rectifier and the frequency is twice that of the supply frequency.
2.1.3 IMPEDANCE MATCHING Impedance matching is one of the most eminent part of the RF circuits. It is utilized for the purpose of transferring maximum
A device which supplies electrical energy to an output load is called a power supply. Conversion of one form of electrical power to another desired form and voltage, typically involving converting AC line voltage to a well-regulated lower-voltage DC for electronic devices. Low voltage, low power DC power supply units are commonly integrated with the devices they supply, such as computers and household electronics.
In order to optimize the power delivered to the load to increase the efficiency of the secondary circuit, Rs must be diminished to as low of a value as possible. Likewise, in order to optimize the amount of power being delivered to the secondary circuit through coupling, the primary circuit must increase the amount of power from the source, as well as decrease the resistance in the primary coil itself. The quality factor of the secondary coil is inversely related to the secondary resistance, Rs. The system described is shown in Figure
In fig. 4, the AC signal from the coil is passed through a Cockroft Walton (CW) voltage multiplier. A CW multiplier generates a high DC voltage from a low voltage AC. Hence, it can rectify the received AC voltage, as well as, step up the relatively low voltage. This is a classic multistage diode/capacitor voltage multiplier, which is economically efficient at the same time. The stages can be increased or decreased with ease to get desired output. The final voltage output of the stages, where N is the number of stages –
It is observed that the power factor is maintained closer to unity when the input voltage is reduced from 230V to 110Vrms. Figure 11 (a) and (b) shows the power factor correction of controller for various load condition such as 20% (60W) and 75% (230W). The power factor for the system is found to be 0.84 for light load condition and 0.99 for full load condition. The THD of input current at full load with predominant third and fifth harmonic components are shown in Figure 12(a) and (b).Third harmonics is found to be 4.8% and fifth harmonic component is 4.9% which are well within IEC 61000-3-2 standard during wide range of load variations. The variation in power factor with load is shown graphically in Figure 13(a). It can be inferred from the graph that improved resettable control operates at high power factor for all load condition whereas the conventional PI control has poor power factor under light load conditions. Figure 13(b) shows the comparison between the efficiency of the converter for varying load conditions with the conventional control method and the resettable integrator control. The converter’s efficiency is maintained at 92% for light load conditions and 96% for fully loaded condition with integrator control technique. Thus the improved resettable integrator controller provides a very simple and reliable solution for power factor correction and
1) How is the radiating electric field (or electromagnetic signal) produced when radio stations broadcast? Include a description of what is producing the signal as well as the reasoning behind how this could produce a signal.
(c) Various combinations of capacitor and inductor, such as L-section filter section filter, multiple section filter etc. which make use of both the properties mentioned in (a) and (b) above. Two cases of capacitor filter, one applied on half wave rectifier and another with full wave
Rectifier converts alternating current to direct current the process is known as rectification. The rectifier is an electronic circuit. Rectifier diode lets the electrical current flow in only one direction and is mainly used for power supply operations. They can handle higher current flow than regular ones. The one that is located on switch mode power supply is 800 V and 1 Amp. The diode 3 and 2 will act as open switches, diodes 1 and 4 will act as closed switches and will start conducting the energy coming flowing thru.
AC coupling blocks the DC component of a signal. Therefore, we see the waveform shifted down and centered at 0 volts.
To solve this problems compressed air technology (CAT) was invented, and again the problem in this is input power. The air may be freely available in the atmosphere , but it needs to be compressed to use and the power it needs for compression is electrical energy , which is also a non- renewable energy.
The rectifier is a Ga As Schottky barrier diode that is impedance matched to the dipoles by a low pass filter. The 6 rectifying diodes are connected to light bulbs for indicating that the power is received. The light bulbs also dissipated the received power. This rectenna has a 25% collection and conversion efficiency, but rectennas have been tested with greater than 90% efficiency at 2.45 GHz[4]. The transmission of power without wires is not a theory or a mere possibility, it is now a reality.
This report aims to discuss the working of DC-AC converter for photovoltaic systems and how it has been implemented to convert renewable energy into usable power to be supplied to the load (power supply application).A topology of a two-stage DC-AC converter has been designed in which a boost converter and a full bridge inverter act as an interface between the photovoltaic (PV) array and the power supply applications. A controlled strategy called Maximum Power Point Tracking (MPPT) technique has been used for achieving maximum power output at the load. Various modes of operation of the converter and the inverter are also discussed. MATLAB Simulink environment has been used for designing the circuitry and to observe various waveforms related to the output.
The development of power electronic converters is marked by demands for a simultaneous reduction in Size , losses and power related costs. Historically diode bridge rectifiers with a laSrge capacitor at the dc bus have been used to convert the ac voltage to a dc voltage. But diode bridge rectifiers draw a very high peak current from the ac utility, which is rich in harmonics and thus gives a very poor power factor. Modern AC-DC power supplies utilize power factor correction in order to minimize the harmonics in the input current drawn fiom the utility. The Boost topology is the most popular topology used for power factor correction today. In this paper, power factor correction using boost converters in single phase diode bridge rectifiers is presented.
A transformer cannot operate with direct current(DC). When connected to a Direct Current source, a transformer typically produces a very short output
In this paper a zero voltage switched active network (Fig. 1) used in combination with three-phase ac to dc diode rectifiers is presented. It is shown that by using proposed switching network in three-phase ac to dc boost converter, zero switching losses are obtained while maintaining a unity input power factor. Active network capacitor, Cs, diodes D7, and D8, maintain a zero voltage during turn-off of Q1, and Q2, Capacitor, Cs, discharges through the boost inductors of the circuit thus limiting the rate of rise of current during turn-on. Moreover, the advantage of the proposed active network is that it can maintain a zero voltage switching over the entire range of the duty cycle of the operation. Consequently, boost stage can be used directly to control the dc bus voltage by varying the duty cycle at Constant switching frequency. The resulting advantages include higher switching frequencies, and better efficiency. Finally the operation of the active switching network is verified experimentally on a prototype three-phase ac to dc converter.
Gathering ambient energy from radio frequency is called RF Energy harvesting [1-2]. This includes designing of antenna and some additional circuit that convert EMF radiation into DC voltage so that it can be used to drive low power devices. The concept of wireless power transmission is the basic principle behind RF Energy radiation in free space. The wireless transmission includes Bluetooth, GPS, Satellite communication, Wi-Fi, DTV. The wireless technology reduces cost of installation by eliminating wired transmission thus it is easy for us to carry wireless