Basically, is there any way to fully encapsulate an RFIF tag in metal and still have it working? Maybe by using the metal as part of the antenna? Low frequency RFID eg 100kHz?

Material - Platinum. Representative enclosure 40mm x 40mm x 5mm with a wall thickness of 1mm.

  • \$\begingroup\$ Have a look at this Q and A : electronics.stackexchange.com/q/97814/152903 \$\endgroup\$ – Solar Mike Feb 10 '18 at 23:01
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    \$\begingroup\$ does ferrite count as metal? \$\endgroup\$ – Nils Pipenbrinck Feb 10 '18 at 23:14
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    \$\begingroup\$ There are many RFID frequencies. You will need to find one that 'fits' your enclosure top or bottom, and resonates as a 1/4 wavelength antenna (ideally). \$\endgroup\$ – Sparky256 Feb 10 '18 at 23:24
  • \$\begingroup\$ Also the RFID protocol is bidirectional. The device is 'pinged' with a power pulse train to wake up the RFID chip. In return it modulates the pulses so the tag can be read. The usual range for RFID is 1 meter. I would re-think about what you doing. \$\endgroup\$ – Sparky256 Feb 11 '18 at 0:54
  • \$\begingroup\$ what's the approximate size of the enclosure? 40 feet? 40 millimeters? active (battery powered) tag or passive?(wave powered) \$\endgroup\$ – Jasen Feb 11 '18 at 9:24

There will be some attenuation from skin effect and Eddy Current losses dependent on c/fd ratio for d=thickness and speed of light c in air. So 100kHz will be attenuate slightly and result in loss of range, how much depends on material and thickness.

EDIT: Skin Depth of Platinum is twice that of Cu. (better due to conductivity)

Skin depth is defined by 1/e or when the signal is 37% of the original.

\$\delta=\dfrac{1}{\sqrt{\pi f \mu \sigma}}\$ for variables frequency, permeability and conductivity

. enter image description here courtesy Wiki /Zurek's

Eddy Current Losses are defined by;

\$P =\dfrac{π^2B^2_pd^2f^2}{6kρD} \$ where
P is the power lost per unit mass [W/kg]
B is the peak magnetic field [T]
d is the thickness of the sheet or diameter of the wire [m]
f is the frequency [Hz]
k is a constant equal to 1 for a thin sheet and 2 for a thin wire
ρ is the resistivity of the material [Ω-m]
D is the density of the material [kg/m³]

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    \$\begingroup\$ Does a 100kHz near field signal go through a microwave door? (rhetorical) \$\endgroup\$ – Dirk Bruere Feb 11 '18 at 0:22
  • \$\begingroup\$ no. metal will block the signals. you will need slots over the antenna to allow the signal through. \$\endgroup\$ – Jasen Feb 11 '18 at 1:24
  • \$\begingroup\$ and the antenna efficiency of the slot is proportional to the ratio of aperture and wavelength so .. no go. Try 10GHz \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Feb 11 '18 at 1:36
  • \$\begingroup\$ Standard copper foil -- 35micron, or 1.4 mils thick ---has skin effect of 8.9dB (1 neper) at 4MHz. At 100Khz, the attenuation will be sqrt( 100,000 / 4,000,000) smaller, or well under 1dB. \$\endgroup\$ – analogsystemsrf Feb 11 '18 at 3:07
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    \$\begingroup\$ @TonyStewart.EEsince'75 most common RFID tags are near field, not working on wavelength based effects, but simple electromagnetic coupling. \$\endgroup\$ – Jasen Feb 11 '18 at 9:22

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