Design and Optimization of Printed Antennas for Wireless Powering

The aim of present research was design and optimization of printed spiral inductor coils as the antennas for wireless powering. Power transfer was limited to some milliwatts over several centimeters with mega Hertz range frequency for low power consumer products like desktop accessories or packaging. Generally, the efficiency of power transferring through printed antennas is less than conventional coils because of some characteristics of conductive inks and printing processes. In this thesis, design and optimization of printed antennas based on printing limits was considering. Geometrical parameters of spiral antennas and the effect of them on inductive powering were reviewed. Three layouts for screen printing of the antennas were represented: Preliminary layout for practical tests on fine line printing and dimensional characteristics of antennas; Comparative layout for comparison between electromagnetic characteristics of antennas; and a Final layout for using in wireless powering. Two types of mesh screens and three types of conductive silver inks were applied for printing the samples on PET substrates. Characterization of printed samples was done by application of a network analyzer based on reflection method in frequency range of 100 Hz to 40 MHz. The magnitude and phase angle of impedance spectrum were plotted and the inductance, resistance, and parasitic capacitance were calculated based on equivalent RLC model. The first resonance frequency of most of antennas was included in the frequency range of measurement. The phase angle did not exceed 90° in all of the samples. The resonance frequency improved extremely by increasing the track width and decreasing the number of turns. Application of different inks could significantly change the impedance value. The measurements showed that the proximity effect losses could be more effective than skin effect in printed samples. Also, by increasing the track length or turn numbers, the parasitic capacitance and inductance could be increased. The results represented that the quality factor could be a problematic factor for comparison between different geometries. Figure-of-merit was applied for comparison between different antennas based on overall area of the antennas. The overall area was substituted with ink area to represent the ratio of efficiency to ink consumption. The FOM of printed antennas in present research was relatively less than PCB antennas that could be caused by high resistive losses of conductive inks. Finally, the functionality of printed antennas was represented by a demonstrator. Also, a concept for software workflow for the design of printed antennas was represented.