Comparative Study of Different Coil Geometries for Wireless Power Transfer

Inductive coupling wireless power transfer is using time-varying resonant magnetic coupling to transfer the power from the transmitting coil to receiving coil through the air gap for various application such as charging up electric vehicles. However, the main issue is that the design of the coils have led to low mutual inductance and coupling coefficient which will lower the power efficiency as the distance of air gap increases. Therefore, this research is mainly studying and comparing the design of transmitting and receiving coil such as the geometries of the coils in order to investigate the power efficiency, mutual inductance, coupling coefficient and magnetic flux. In this research, a finite element method (FEM) software, Ansoft Maxwell is used to investigate and compare the performance of various designs of coils such as spiral planar coils, square planar coils and pentagon planar coils. In addition, prototypes have been built by using PCB planar coils in shape of spiral, square and pentagon in order to compare the results and performance from simulation. In terms of result, low mutual inductance and coupling coefficient are caused by the distance of air gap. When the distance of air gap is longer, the mutual inductance and coupling coefficient are lower for the three different of coils. And also, magnetic flux is also determined by the geometries of coil where it will affect the mutual inductance which influents the coupling coefficient and power efficienc

Master of Science

thesisThis thesis discusses the design, modeling, and experimental validation of an inductively coupled wireless power transfer (WPT) system to power a micro aerial vehicle (MAV) without an onboard power source. MAVs are limited in utility by flight times ranging from 5 to 30 minutes. Using WPT for MAVs, in general, extends flight time and can eliminate the need for batteries. In this paper, a resonant inductive power transfer system (RIPT), consisting of a transmit (Tx) coil on a fixed surface and a receive (Rx) coil attached to the MAV, is presented, and a circuit is described. The RIPT system design is modeled to determine a suitable geometry for the coils, and the model validated experimentally. It is found that for the MAV used in this work, a suitable geometry of coils is a 19cm diameter planar spiral Tx coil made with 14 AWG copper wire, seven turns, and 5cm pitch paired with an Rx coil made of 16-20AWG wire, 13cm-20cm diameter, 1mm pitch, and one to two turns. A demonstration of an MAV being powered 11cm above the Tx coil with the WPT system in a laboratory setting is presented. The MAV consumes approximately 12 Watts. The overall power efficiency of the RIPT system from RF power source output to MAV motors is approximately 32%

On the relationship of quality factor and hollow winding structure of coreless printed spiral winding (CPSW) inductor

The principle of using hollow spiral winding is not novel, but the study on this topic is far from complete. In this paper, how hollow the central region of the coreless printed spiral winding (CPSW) inductor should be for a given footprint area in order to achieve the maximal quality factor Q max and to maintain high inductance value is explored. A hollow factor based on the ratio of the inner hollow radius and the outer winding radius τ = R in/R out, is proposed as for optimization and quantifying how hollow a spiral winding is. The relationship between τ and Q max, which depends on the operating frequency and the dimensional parameters of CPSW inductor, is established. For a specific operating frequency, it is discovered that if the conductor width is comparable with the skin depth, or the conductors are placed relatively far away from each others, the hollow design of the CPSW inductor has little improvement on Q but reduces the inductance. If the conductor width is much larger than the skin depth and the conductors are closely placed, the hollow spiral design is recommended. The optimal range of τ with which the Q max can be achieved is found to be around 0.45-0.55. © 2006 IEEE.published_or_final_versio