This is a design of a bifilar coil, meaning that when this design is fabricated on a two-layer printed circuit board (PCB), there will be a single bifilar coil.
This designs differs from the others in that a single coil is devoted to one layer and the board itself is the dielectric between the top and bottom coils.
This design requires that an external wire connect the inner terminal of one coil to the outer terminal of the other coil (with the added benefit of being able to insert a tuning capacitor in between the two coils.)
The theory is that when you drive the coil with a sine wave at its resonant frequency, it can transfer power at its greatest efficiency.
The beauty of this design is that it is parametric.
Both coils are concentric and wind in the same direction. Therefore the magnetic field from each coil section combines uniformly with the other coil resulting in a stronger, cohesive field.
Additionally, this design differs in that the two coils are directly sandwiched together via the board's dielectric such that the capacitance is stronger between the coils.
This shows the various layers on a small (100mm x 100mm) coil to highlight the wiring and various layers of the PCB:
In this design, coils can be created with varying board size, trace widths, and gaps between traces. As a result, this parametric design could theoretically be used for coils of any manufacturable size (from microscopic on up).
In this section, we will document emperically-measured resistances and resonant frequencies of fabricated coils as they become available.
Here is a large (400mm x 400mm) PCB with 92 windings per coil:
and measurements on the coil:
It has 2.0mm trace width, 2.0mm pad diameter, 1.0mm drill hole diameter, and 0.15mm trace gap. Its board thickness is 0.6mm.
Please visit Master Ivo's YouTube channel to see some novel uses of bifilar coils.
Here is a small (100mm x 100mm) PCB with 21 windings per coil:
It has 2.0mm trace width, 2.0mm pad diameter, 1.0mm drill hole diameter, and 0.15mm trace gap.
It measures 2.8Ω, 0.07mH, and 222pF. Its board thickness is 1.6mm.
Coil 3 is a large (400mm x 400mm) PCB with 45 windings per coil.
It has 4.0mm trace width, 4.0mm pad diameter, 1.5mm drill hole diameter, and 0.15mm trace gap.
It measures 9.1Ω, 1.23mH, and 7460pF. Its board thickness is 0.8mm.
Enjoy!
Copyright 2019 Glenn M. Lewis. All Rights Reserved.
Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at
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