LF - 125 kHz HF - 13.56 MHz

Those frequencies refer to the magnetic field that is used to induce a voltage in the transponder. Can the magnetic fields actually interfere with EM waves in the vicinity?

  • 2
    \$\begingroup\$ I challenge you to create a 13.56MHz magnetic field without emitting EM \$\endgroup\$ – PlasmaHH Oct 10 '18 at 19:53

All electromagnetic stuff can be described using the four Maxwell equations:

$$\begin{align} \nabla\cdot \textbf D &= \rho_V\\ \nabla\cdot \textbf B &= 0\\ \nabla \times \textbf E &= -\frac{\partial \textbf B}{\partial t} \\ \nabla \times \textbf H &= \frac{\partial \textbf D}{\partial t} + \textbf J \end{align}$$

The 3rd equation will tell you that a changing magnetic field will always be accompanied by an electric field. The 4th equation says that a moving electric field will always coexist with a magnetic field in free space. The two together mean radiation, and you can't pull them apart.

So there isn't really such a thing as "magnetic waves", only electromagnetic waves.

  • \$\begingroup\$ Corollary: there is no such thing as a "magnetic loop" or H-field antenna. All antennas respond to both E and H fields of an EM wave. Even if they're "shielded"... \$\endgroup\$ – tomnexus Oct 11 '18 at 4:36
  • \$\begingroup\$ What about loop antennas, with the wiring surrounded by a copper pipe, that Efield shield broken at one point, to avoid being a shorted turn? Hewlett Packard used this for 60KHz WWVB time-frequency standard receivers. \$\endgroup\$ – analogsystemsrf Oct 11 '18 at 4:58
  • \$\begingroup\$ I am not an expert in loop antenna's, but this question seems to address your issue. \$\endgroup\$ – Sven B Oct 12 '18 at 13:57

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