Fig. 1. 3D SSPP structures. (a) SSPP bidirectional bending splitter with feeding wire and detecting probe as excitation^[11]; (b) periodic bifurcated slit-decorated structure^[12]; (c) equivalent circuit topology of periodic bifurcated slit-decorated structure^[12]; (d) calculated and simulated dispersion curves of periodic bifurcated slit-decorated structure

Fig. 2. Ultrathin and flexible SSPP transmission line and its propagation properties^[10]. (a) Photograph of flexible transmission line; (b) simulated structure of curved transmission line; (c) simulated near-field result; (d) photograph of curved transmission line; (e) measured near-field result

Fig. 3. Crosstalk suppression using SSPP transmission lines^[16]. (a) Structure of transmission lines; (b) experimental results of transmission and coupling coefficients

Fig. 4. Low-loss properties of SSPP transmission line^[17]. (a) Structure of transmission line; (b) micro-strip line with same size; (c) comparison of measured scattering parameters

Fig. 5. High-efficiency excitation structure of SSPP. (a) High-efficiency conversion between coplanar waveguide and SSPP transmission line ^[33]; (b) high-efficiency conversion between micro-strip and SSPP transmission line ^[34]; (c) simulated and measured S parameters of conversion structure between coplanar waveguide and SSPP transmission line ^[33]; (d) s

Fig. 6. SSPP-based ultra-broadband 3 dB power divider^[40]. (a) Structure diagram; (b) measured transmission and reflection coefficients

Fig. 7. SSPP-based frequency splitter and 3 dB directional coupler^[42]. (a) Structural diagram of frequency splitter;(b) simulated and measured results of frequency splitter; (c) structural diagram of 3 dB directional coupler; (d) simulated and measured results of 3 dB directional coupler

Fig. 8. SSPP-based frequency splitter^[43]. (a) Structural diagram of frequency splitter; (b) simulated electric field distribution at 5.2 GHz; (c) simulated electric field distribution at 10.2 GHz; (d) measured electric field distribution at 5.2 GHz; (e) measured electric field distribution at 10.2 GHz

Fig. 9. SSPP-based ring resonator^[44]. (a) Structural diagram of resonator; (b) simulated electric field distribution at 0.98 THz

Fig. 10. SSPP-based filters. (a) SSPP-coupled filter ^[45]; (b) hybrid band-pass filter composed of anti-symmetric SSPP transmission line and substrate-integrated waveguide ^[46]; (c) compact hybrid band-pass filter ^[47]

Fig. 11. SSPP antennas. (a) Phase-tunable SSPP antenna composed of gradient units ^[51]; (b) SSPP-based antenna array and its feeding network ^[52];(c) odd-mode SSPP antenna ^[53];(d) miniaturized SSPP-based antenna ^[54]

Fig. 12. 3D SSPP structure^[55]. (a) Diagram of periodic corrugated metallic cylinder; (b) diagram of cylinder with equivalent artificial electromagnetic medium

Fig. 13. Ultrathin SLSP structure and its physical properties^[56]. (a) Experimental setup for measuring near-field resonance; (b) near-field response spectra of ultrathin corrugated metallic disk covered by different dielectric pads; (c) simulated near-field responses and patterns; (d) measured near-field responses and patterns

Fig. 14. Physical properties of ultrathin corrugated metallic disk^[57]. (a) Simulated and calculated scattering cross sections of periodic corrugated metallic disk; (b) simulated electric field distribution corresponding to each order resonance

Fig. 15. Resonance spectra of sub-wavelength spiral corrugated metallic disk^[59]. (a) Experimental near-field spectrum and calculated ECS spectrum; (b) electric field distribution of electric LSP resonance; (c) electric field distribution of magnetic LSP resonance

Fig. 16. Measured and simulated resonance spectra of spiral corrugated metallic disk and measured near-field distribution corresponding to each resonance point ^[61]

Fig. 17. Mode hybridization of SLSP^[62]. (a) Two closely spaced spiral corrugated metallic disks; (b) electric field enhancement at gap center; (c) mode resonance frequency and maximum field enhancement versus gap size

Fig. 18. SSPP amplifier^[37]. (a) Anti-symmetric SSPP transmission line; (b) overall structure of amplifier; (c) simulated and measured transmission coefficients; (d)--(g) measured electric field distributions at 14, 16, 18, 20 GHz

Fig. 19. SSPP frequency-doubling generator ^[63]. (a) Structural diagram; (b) measured spectrum; (c) measured electric field distribution when incident fundamental frequency is 8 GHz; (d) measured electric field distribution when output second harmonic frequency is 16 GHz; (e) measured electric field distribution when incident fundamental frequency is 10 GHz; (f) measured electric field distribution when output second harmonic frequency is 20 GHz

Fig. 20. Frequency doubling regulation of SSPPs based on varactor diodes ^[64]. (a) Forward second-harmonic generation; (b) backward second-harmonic generation; (c) unit structure of nonlinear SSPPs

Fig. 21. SSPP-based tunable filter ^[65]. (a) Overall structure; (b) unit structure

Fig. 22. Coupling coefficient regulation among SSPPs ^[66]

Fig. 23. Electronically tunable SLSP structures^[67]. (a) Simulated reflection coefficients; (b) measured reflection coefficients; (c) simulated transmission coefficients; (d) measured transmission coefficients; (e) simulated electric field distributions; (f) measured electric field distributions

Fig. 24. Radio frequency transceiver for SSPP-based wireless communication system with sub-wavelength-spacing dual-channel signals^[68]

Fig. 25. SSPP-based wireless communication with sub-wavelength-spacing dual-channel signals and measured results ^[68]. (a) Schematic of test scenario; (b) test scenario of receiver; (c) test scenario of transmitter; (d) movie signals before transmission; (e) movie signals after transmission through SSPP-based wireless communication system; (f) movie signals after transmission through traditional wireless communication system

Fig. 26. Digital SSPP metamaterial structure ^[69]. (a) Structural diagram; (b) diagram of control unit; (c) dispersion curves

Fig. 27. Multi-bit digital SSPP system loaded by varactor diodes ^[28]. (a) Equivalent circuit model of unit; (b)(c) programmable SSPPs constructed by loading varactor diodes; (d) geometric structure of unit; (e) top view of physical map; (f)(g) bottom view of physical map