Fig. 1. (a) Unit cell of dual torus toroidal structure; (b) Transmission spectrum at 0.551 THz; (c) Schematic diagram of toroidal dipole formation; (d) Far-field scattering power of multipole

Fig. 2. (a) Transmission spectrum with or without millipore filter under different refractive index; (b)-(e) Magnetic field diagram at resonant frequency point with or without millipore filter under different refractive index

Fig. 3. (a) Optical microscope image of dual torus toroidal structure; (b) Measured transmission spectrum of the proposed chip

Fig. 4. (a) Centrifugation machine diagram; (b) Sample diagram of crude oils after centrifugation

Fig. 5. (a) Experimental schematic diagram based on the dual torus structure; (b)-(g) Experimental procedure diagram

Fig. 6. (a) Experimental transmission spectrum; (b) Bar graph of the relationship between full frequency shift and single frequency shift in the mixture; (c) Frequency shift point diagram and linear fitting diagram of sulfur content; (d) Frequency shift point diagram and linear fitting diagram of residual carbon content