Hagerty [22] presented rectenna arrays for broadband ambient EM harvesting and characterized the harvesters from 2 GHz to 18 GHz; rectennas combine impedance matching the RF rectifying circuit and the antenna into Temsirolimus IC50 one compact device, but an array of rectennas may increase the overall size of an EM harvester. Herb [23] and Inhibitors,Modulators,Libraries Vullers [24] have provided a comprehensive state of the art for micro energy harvesting and have explored the various techniques used for harvesting ambient renewable energy.2.?RF to DC Power Converter2.1. Diode RectifierA junction diode equivalent circuit and simple Schottky diode rectifier are shown in Figure 1. RDS is the diode resultant series resistance, CDS is the diode resultant series capacitance, RDP is the diode resultant parallel resistance, CDP is the diode resultant parallel capacitance, Vs is the sinusoidal source voltage and Vc is the voltage across the capacitor.
Figure 1.(a) Diode series equivalent model, (b) Diode parallel equivalent Inhibitors,Modulators,Libraries model, (c) Simple diode detector.The diode capacitive Inhibitors,Modulators,Libraries impedance is mainly due to the junction capacitances provided by the metal, its passivation and the semiconductor forming the diode. AC power incident on a forward biased diode input is converted to DC power at the output. The current-voltage behavior of a single metal/semiconductor diode is described by the Richardson equation [25] as in Equation (1):I=IS(e(qVD/nKT)?1)(1)where I is the current through the diode, IS is the saturation current, q is the charge of an electron, VD is the voltage across the diode, T is the temperature in degrees Kelvin and K is Boltzmann constant.
The voltage equation around the loop can be derived from Figure 1(c) and is given in Equation (2):VD=VS?VC(2)Since the same current flows through the diode and the capacitor, one can find the average current through the circuit by integrating Equation (1) over a time period. By substituting Inhibitors,Modulators,Libraries Equation (2) into Equation (1), VC can be expressed in terms of VS by averaging the diode current to zero. This is given in Equation (3) [26]:VC=KTqln[?0(qVSKT)],(3)where 0 is the series expansion of the sinusoidal source voltage. Equation (3) can further be simplified for very small amplitude VS Entinostat as Equation (4):VC��qVS24KT(4)Equation (4) shows that for a small voltage source, the circuit output voltage is proportional to the square animal study of the input sinusoidal voltage; hence it’s so-called square law operation. Extensions of this model for voltage multipliers and other input signals are presented in [27] and [28]. Equation (4) further confirms that for low input voltage (power �� 10 dBm), an impedance matching network between the source and the diode is necessary to improve the detected output voltage and efficiency.2.2.