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.

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.

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 (T_s)	32/1.58
Wire thickness (t)	2.8/0.0711

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	View Results
Substrate Thickness	Decrease	Lowers the SRF	Decreased Efficiency	View Results
Substrate Type Permittivity (ε_r)	Increase	Lowers the SRF	Efficiency Fluctuates	View Results

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

Substrate Thickness

EFFECTS OF SUBSTRATE THICKNESS CHANGES

Substrate Type

EFFECTS OF SUBSTRATE TYPE CHANGES (ε_r)