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(a) Receiver current as a function of time delay for the smooth wire (red curve) and the helical groove structure (blue curve). (b) Amplitude spectra of the time domain data in (a) together with the spectrum of another nominally identical helical sample (green curve, displaced for clarity). The arrows indicate the three azimuthal modes of the helical groove structure. The spectrum of the Sommerfeld wave (red curve) on the smooth wire extends to .
Dispersion relation of the surface EM modes supported by a PEC wire of radius inscribed with a triangular cross-section helical groove of pitch . The groove has width and depth . The upper row of insets displays electric field magnitude maps evaluated at the three band edges, (left), 0.320 (center), and 0.349 THz (right). The next lower row corresponds to the first mode at 0.280 THz (left) and the second mode at 0.180 THz (right). The map in the lowest row is for the first mode at 0.180 THz.
FIT simulations of the propagation of surface EM modes on a 9.6 cm long wire. The metawire is modeled as a PEC wire of radius tightly wound on a straight PEC wire of the same dimensions. The helix pitch is . Main panel shows the spectra of at four points close to the wire surface (, , , , and ) located 1.5 cm away from the illuminated end. Right insets show in a cross section at the three obtained from FDTD calculations (from top to bottom: 0.305, 0.320, and 0.349 THz). These frequencies are shown in the main panel by cyan arrows and the corresponding frequencies in the experimental spectra are indicated by black arrows.
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