Smith chart analysis for transmission line method validation of a simple graphene-based absorber in sugar molecules detection

• Smith chart analysis is applied for the first time to optimize impedance matching in terahertz absorber design. • The proposed graphene-based disk absorber achieves near-perfect absorption (return loss of −55 dB) at 2.5 THz. • The structure exhibits polarization insensitivity and stable absorption up to 75° incident angles. • A practical fabrication approach using CVD-grown graphene and laser patterning enables tunability via chemical potential control. • The device demonstrates promising sensing performance for sugar molecules with sensitivity of 0.482 THz/RIU and Q-factor of 5.45. In this work, a high-efficiency graphene-based disk-shaped terahertz absorber is presented, featuring an innovative use of Smith chart analysis for precise impedance matching — a technique not previously applied in terahertz absorber designs. Unlike conventional validation methods based solely on transmission line (TL) or transfer matrix models, the Smith chart approach enables intuitive, graphical optimization of the absorber parameters, leading to near-perfect impedance matching with free space at 2.5 THz. Using this method in the design of terahertz absorbers will pave the way for the design of absorbers with more complex graphene patterns.Through this method, the absorber achieves exceptional absorption (return loss of −55 dB), strong polarization insensitivity, and robustness up to 75° incident angles. Moreover, the proposed structure shows promising performance in refractive index sensing of sugar molecules, offering a sensitivity of 0.482 THz/RIU and a quality factor of 5.45. The practical fabrication pathway, based on CVD-grown graphene and laser patterning, further supports the real-world applicability of this design. This work highlights the Smith chart as a powerful, practical tool for THz absorber optimization, opening new directions for high-performance terahertz sensing technologies.