MCR-WPT-PSC Appendix

          On this page we give a little more background information for the design as well as the design process used for MCR-WPT Printed Spiral Coils. For detailed information, click on the button on the right to access the thesis pdf.

Below is a list of all the topics we cover in this page. Click on any of these links to go to that section.

SYSTEM OVERVIEW

The Magnetically Coupled Resonant Wireless Power Transmission (MCR-WPT) coils are also known as Magnetic Inductance and Resonant Coupling coils. These coils are based on a design that was introduced in 2007 by a group of researchers from MIT↗. These researchers used helical coils as the resonators to achieve strong resonant coupling as shown in basic circuit diagram shown below.

Basic circuit diagram of a MCR-WPT coils system connected to a source and load

            From the basic circuit diagram of the system we can see that the first and second coils known as the 1-Source coils (which is connected to the power source) and 2-Sending/Transmitting coil are on the transmitter side, and the third and fourth coils known as the 3-Receiving coil and 4-Load coil (which is connected to the load) are on the receiver side.  The reasons for this configuration is as follows:

  • The inner Source and Load coils are inductively coupled to their respective Sending and Receiving outer coils (which are loosely coupled and magnetically resonant) to externally input into and remove energy from the resonant coils.
  • To obtain the maximum efficiency of the system, impedance matching can be done at either the Source or Load sides of the system.

            To implement this system within the space constraints of a Cellphone, we modified the MCR-WPT coils system which use Printed Spiral Coil (PSC) boards composed of 4 spiral inductors with 2 spiral inductors on each board. The Source and Sending coils on one board and the Receiving and Load coils on the other board as shown in the image below.

Basic MCR-WPT PSC coil structure

            The MCR-WPT coils were the key element of the now obsolete Rezence WPT standard. . The main draw of this technology is the ability to wirelessly power any device at a distance. Another reason that they are desired is that since the coils are impedance matched, they can be tuned to bring the system back into resonance when the separation distance is shorter than the for peak efficiency optimal separation distance known as the Critical Coupling Distance (CCD). This tuning ability and CCD is explained in more details in the background section of the Maximum Peak Detection and Auto-Tuning project and can be accessed by clinking on the button below.
            For more detailed information on the basic theory of the MCR-WPT coils and the design methodology used, check out sections 3.2.1 and 3.2.2 of the thesis respectively. For design specifications and results of our design see sections 3.3.2 and 3.4. Finally for brief overview of the Rezence WPT standard, see section 1.1.1. The thesis can be obtained from the Ryerson University library by clicking the button below.

DESIGN PROTOTYPE PARAMETER SIZING

        We used the following method to detect when the maximum tuning peak is achieved, and determine the separation distance tuning range as described below:

Geometric ParameterInner Coil (mils/mm)Outer Coil (mils/mm)
Diameter 1 (D1)4420/112.25000/127
Diameter 2 (D2)1920/48.82500/63.5
Wire Width (W)50/1.2721/0.533
Wire Spacing (S)10/0.25421/0.533
Number of Turns (N)1 turn7 turns

Inner And Outer Coil Parameter Sizes For Double Layer FR4 MCR-WPT PSC Design For Cellphones.

Geometric ParameterThickness (mils/mm)
PSC Board Thickness (Ts)32/1.58
Wire Thickness (t)2.8/0.0711

PSC Thickness Parameter Sizes For Double Layer FR4 MCR-WPT PSC Design For Cellphones.

Double layer MCR-WPT PSC Parameters

PARAMETER CHANGE EFFECTS ON EFFICIENCY AND SRF

        When designing the MCR-WPT Coils, it is important to understand how changes to each respective parameter affects the efficiency and Self-Resonant Frequency (SRF) of the coils. So in this section we provide a brief overview of these effects.

  • Single layer parameter changes
  • multi-layer parameter changes
  • Effects of adding layers
  • effects of substrate thickness
  • effects of substrate type

CoilParameterChangeBenefitsDrawbacks
InnerDiameterIncreaseImproves efficiency
Improved magnetic flux
Maximum number of outer coil turns reduced
OuterNumber of TurnsIncreaseLowers the SRFInner Diameter may need to be reduced
OuterWire WidthIncreaseLowers the SRF
Reduced DC resistance
Increase in proximity effect resistance
OuterWire SpacingDecreaseLowers the SRFIncrease in proximity effect resistance

Benefits And Drawbacks Of Changing Each Single-Layer MCR-WPT Coil Parameter On SRF & Efficiency Summary With All Other Parameters Constant

More information is provided in section 3.2 of the thesis which can be retrieved by clicking respective button below.
The above summary table is found in section 3.2.2.5

ParameterChangeBenefitsDrawbacks
Number of LayersIncreaseLowers the SRFEfficiency Fluctuates
Substrate ThicknessDecreaseLowers the SRFDecreased Efficiency
Substrate Type Permittivity (εr)IncreaseLowers the SRFEfficiency Fluctuates

Benefits and drawbacks of Multi-Layer MCR-WPT coil parameter changes on SRF & efficiency summary

Effects of changing the number of layers on the SRF and efficiency with a constant PSC board thickness.
Effects of changing the dielectric substrate thickness on the SRF and efficiency of a double layer PSC board.
Effects of changing the type of dielectric substrate on the SRF and efficiency of a double layer PSC board.

More information is provided in section 3.3.3 of the thesis which can be retrieved by clicking respective button below.