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 the  Class-E Power amplifier.

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

background and purpose of mcr-wpt printed spiral coils

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 list

Parameter sizes for double layer FR4 MCR-WPT PSC design for cellphones..

Parameters Inner Coil (mils/mm) Outer Coil (mils/mm)
Diameter 1 (D1)

4420/112.2

5000/127

Diameter 2 (D2)

1920/48.8

2500/63.5

Wire Width (W)

50/1.27

21/0.533

Wire Spacing (S)

10/0.254

21/0.533

Number of Turns (N)

1 turn

7 turns

PSC board thickness (Ts)

32/1.58

Wire thickness (t)

2.8/0.0711

Double layer MCR-WPT PSC Parameters

Effects of parameter changes 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.

Effects Of Single-Layer Parameter Changes

Benefits and drawbacks of changing Single-Layer MCR-WPT coil parameters on SRF & efficiency summary

Coil Parameters Change Benefits Drawbacks

All other parameters remain constant

Inner

Diameter

Increase

  • Improves efficiency
  • Improved magnetic flux

Maximum number of outer coil turns reduced

Outer

Number of Turns

Increase

  • Lowers the SRF

Inner Diameter may need to be reduced

Outer

Wire Width

Increase

  • Lowers the SRF
  • Reduced DC resistance

Increase in proximity effect resistance

Outer

Wire Spacing

Decrease

  • Lowers the SRF

Increase in proximity effect resistance

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

Effects Of Multi-Layer Parameter Changes

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

Parameters Change Benefits Drawbacks Simulation Results

All other parameters remain constant

Number of Layers

Increase

Lowers the SRF

Efficiency Fluctuates

Substrate Thickness

Decrease

Lowers the SRF

Decreased Efficiency

Substrate Type Permittivity (εr)

Increase

Lowers the SRF

Efficiency Fluctuates

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

Number of Layers

EFFECTS OF CHANGING THE NUMBER OF LAYERS

Effects of changing the number of layers on the SRF and efficiency with a constant PSC board thickness.

Substrate Thickness

EFFECTS OF SUBSTRATE THICKNESS CHANGES

Effects of changing the dielectric substrate thickness on the SRF and efficiency of a double layer PSC board.

Substrate Type

EFFECTS OF SUBSTRATE TYPE CHANGES r)

Effects of changing the type of dielectric substrate on the SRF and efficiency of a double layer PSC board.