Dual-function terahertz metamaterial absorber based on microfluidic structures.

In recent years, terahertz metamaterial sensors have shown great potential in label-free biosensing; yet, the detection of high-absorption liquid samples that are sensitive to terahertz waves remains a significant challenge. In this study, a dual-function absorber capable of dynamically switching between broadband absorption and high-sensitivity sensing is proposed based on the microfluidic technology and phase change characteristics of vanadium dioxide (VO). Compared with traditional terahertz microfluidic sensors, this structure differs in that it incorporates a VO film as a separation layer in the sensor cover plate and a VO square resonator on top. This configuration not only exhibits high-sensitivity sensing but can also function as an absorber for broadband absorption. When VO is in the metallic state, the structure acts as a broadband absorber with an absorption rate exceeding 90% across the 1.09-3.02 THz range. When VO is in the insulating state, the structure functions as a microfluidic sensor, achieving an absorption rate above 99.9% at 1.438 and 2.068 THz, with nearly perfect absorption and refractive index sensitivities of 532 and 785 GHz/RIU, respectively; the quality factor is 17.6 and 23.5, respectively, indicating excellent sensing performance. Moreover, due to the symmetry of the metal micro-structured layer and the VO square resonator, the device exhibits polarization insensitivity and stability at large incident angles. In summary, this structure significantly broadens the applications of traditional absorbers and sensors and holds promise for future applications in electromagnetic cloaking, energy harvesting, and biomedical detection.