# PCB coil designs

In researching how to design a planar rectangular PCB coil, I've come across numerous papers describing many topologies, except for a rectangular one. Square, hexagonal, circular are common ones, but a description of a rectangular does not seem to exist.
For a square one, there is a relationship between the outer "diameter" and the inner "diameter" at the end of the spiral. But, I think this assumes the lenght of each side of the outer loop is the same, which is not the case for a rectangular coil. I'm wondering why the rectangular geometry is not covered in any of these papers. Is it an obvious extension of the square one (but apparently not obvious to me), or is there something that makes it a much more complex analytical problem than the square one?

Edited- per request, references include in question. Also added comment.

References:

https://www.researchgate.net/publication/3442132_Design_of_planar_rectangular_microelectronic_inductors_IEEE_Trans_Parts_Hybrids_Packag

http://www.edn.com/design/components-and-packaging/4363548/A-new-calculation-for-designing-multilayer-planar-spiral-inductors

http://www.ti.com/lsds/ti/analog/webench/inductive-sensing.page

http://www.scirp.org/journal/PaperDownload.aspx?DOI=10.4236/cs.2013.42032)Design

Also, wanted to add that after giving this some thought, it occurred to me that maybe I can just approximate the inductance of the rectangular coil by scaling the square-coil's inductance by the ratio of the areas of the coils. For example, if the square-coil's area is 4 times the area of the rectangular one, could I just divide the inductance of the square coil by 4 to approximate the inductance of the rectangular one?.

• Could you include your research references in the question? Mar 8, 2016 at 18:17
• @Daniel, sure:1) link Design_of_planar_rectangular_microelectronic_inductors_IEEE_Trans_Parts_Hybrids_Packag 2) link A-new-calculation-for-designing-multilayer-planar-spiral-inductors 3)link Ti Analog Webench Mar 9, 2016 at 20:07
• 4)[link]scirp.org/journal/PaperDownload.aspx?DOI=10.4236/… and Optimization of Printed Circuit Board Inductors for Wireless Power Transfer System Mar 9, 2016 at 20:10
• Also, wanted to add that after giving this some thought, it occurred to me that maybe I can just approximate the inductance of the rectangular coil by scaling the square-coil's inductance by the ratio of the areas of the coils. For example, if the square-coil's area is 4 times the area of the rectangular one, could I just divide the inductance of the square coil by 4 to approximate the inductance of the rectangular one?. Mar 9, 2016 at 20:15
• @jrive, you should modify your question to include this information rather than adding it in the comments. Mar 10, 2016 at 21:50

## 2 Answers

I have found this paper by ST Microelectronics very informative for rectangular coils. (Pg 10-13)

Page 11 talks about a software tool called antenna.exe that can be used to calculate rectangular planar antenna inductances. The software can be found here: http://www.st.com/web/catalog/tools/FM147/SC1871/PF257519

here is one example: "Jow, Uei-Ming, and Maysam Ghovanloo. "Design and optimization of printed spiral coils for efficient transcutaneous inductive power transmission." IEEE Transactions on biomedical circuits and systems 1.3 (2007): 193-202."

It's a bit old but the model and optimization steps they used is quite inspiring.

• Can you also quote the section which helps answering the OP question better.? Jan 22, 2017 at 17:34