topic Re: Determination of Optimal Radius of NFC Reader Antenna in NFC
https://community.nxp.com/t5/NFC/Determination-of-Optimal-Radius-of-NFC-Reader-Antenna/m-p/1167261#M7805
<P>Hello <LI-USER uid="62049"></LI-USER> ,</P>
<P> </P>
<P>Yes, you are correct <SPAN>with the mathematics.</SPAN></P>
<P><SPAN>The missing part is L0 of the reader ("L01"): the "single turn" inductance increases with the increasing r. That "reduces the coupling at higher r".</SPAN></P>
<P><SPAN>a simple formula is used like this:</SPAN></P>
<P><SPAN><span class="lia-inline-image-display-wrapper lia-image-align-inline" image-alt="formula.png" style="width: 388px;"><img src="https://community.nxp.com/t5/image/serverpage/image-id/127394iE0DF38589CEC0D86/image-size/large?v=v2&px=999" role="button" title="formula.png" alt="formula.png" /></span></SPAN></P>
<P>D = 2r = diameter of the antenna coil</P>
<P>d = wire diameter (= constant and small compared to D)</P>
<P>If you take this into account, the curve looks like plotted in the slides.</P>
<P>And in fact even in the curve result (as plotted in the slides), it can be seen that the maximum is not exactly at r=x, but slightly below... Still as a thumb rule it fits.</P>
<P> </P>
<P>Have a great day,<BR />Kan</P>
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<P> </P>Wed, 14 Oct 2020 07:53:25 GMTKan_Li2020-10-14T07:53:25ZDetermination of Optimal Radius of NFC Reader Antenna
https://community.nxp.com/t5/NFC/Determination-of-Optimal-Radius-of-NFC-Reader-Antenna/m-p/1149225#M7645
<P>In studying the instructional video 'NFC Antenna Design'</P><P><A href="https://www.nxp.com/design/training/nfc-antenna-design:TIP-NFC-ANTENNA-DESIGN" target="_blank">https://www.nxp.com/design/training/nfc-antenna-design:TIP-NFC-ANTENNA-DESIGN</A></P><P>In terms of the discussion about the determination of optimum radius of RFID reader antenna in relation to distance (10cm) from the tag antenna (at approximately 0:18:19 in the video) and the formula for the coupling coefficient, the mathematics appears to me to indicate that the optimum occurs when the radius is equal to the square root of 2 multiplied by their relative distance (a little over 14cm as opposed to 10cm as the author states). Can anyone help me understand where I am misunderstanding the situation? I simply set the derivative of the formula with respect to r to zero and solved for r. See attached. Thanks.</P><P> </P>Sat, 05 Sep 2020 04:09:22 GMThttps://community.nxp.com/t5/NFC/Determination-of-Optimal-Radius-of-NFC-Reader-Antenna/m-p/1149225#M7645tedj12020-09-05T04:09:22ZRe: Determination of Optimal Radius of NFC Reader Antenna
https://community.nxp.com/t5/NFC/Determination-of-Optimal-Radius-of-NFC-Reader-Antenna/m-p/1149816#M7646
<P>I've linked my OpenOffice ods file worksheet, in case anyone is interested in checking my calculations.</P><P><A href="http://afafa.org/Unlinked/Coupling_Coefficient.ods" target="_blank">http://afafa.org/Unlinked/Coupling_Coefficient.ods</A></P><P>Thanks,</P><P> Ted</P>Mon, 07 Sep 2020 16:36:20 GMThttps://community.nxp.com/t5/NFC/Determination-of-Optimal-Radius-of-NFC-Reader-Antenna/m-p/1149816#M7646tedj12020-09-07T16:36:20ZRe: Determination of Optimal Radius of NFC Reader Antenna
https://community.nxp.com/t5/NFC/Determination-of-Optimal-Radius-of-NFC-Reader-Antenna/m-p/1167261#M7805
<P>Hello <LI-USER uid="62049"></LI-USER> ,</P>
<P> </P>
<P>Yes, you are correct <SPAN>with the mathematics.</SPAN></P>
<P><SPAN>The missing part is L0 of the reader ("L01"): the "single turn" inductance increases with the increasing r. That "reduces the coupling at higher r".</SPAN></P>
<P><SPAN>a simple formula is used like this:</SPAN></P>
<P><SPAN><span class="lia-inline-image-display-wrapper lia-image-align-inline" image-alt="formula.png" style="width: 388px;"><img src="https://community.nxp.com/t5/image/serverpage/image-id/127394iE0DF38589CEC0D86/image-size/large?v=v2&px=999" role="button" title="formula.png" alt="formula.png" /></span></SPAN></P>
<P>D = 2r = diameter of the antenna coil</P>
<P>d = wire diameter (= constant and small compared to D)</P>
<P>If you take this into account, the curve looks like plotted in the slides.</P>
<P>And in fact even in the curve result (as plotted in the slides), it can be seen that the maximum is not exactly at r=x, but slightly below... Still as a thumb rule it fits.</P>
<P> </P>
<P>Have a great day,<BR />Kan</P>
<P><BR />-------------------------------------------------------------------------------<BR />Note:<BR />- If this post answers your question, please click the "Mark Correct" button. Thank you!<BR />- We are following threads for 7 weeks after the last post, later replies are ignored<BR />Please open a new thread and refer to the closed one, if you have a related question at a later point in time.<BR />-------------------------------------------------------------------------------</P>
<P> </P>Wed, 14 Oct 2020 07:53:25 GMThttps://community.nxp.com/t5/NFC/Determination-of-Optimal-Radius-of-NFC-Reader-Antenna/m-p/1167261#M7805Kan_Li2020-10-14T07:53:25Z