Multi-band graphene-nested rings terahertz wave absorber with air gap for sensitive healthcare biosensing applications

A highly sensitive multi-band terahertz wave absorber is proposed, featuring a three-layer structure with a central air gap for blood sample placement, sandwiched by stacked graphene-Kapton layers and backed by a fully reflecting metallic layer. The absorber is modeled using an equivalent impedance circuit and validated by full-wave numerical simulations. The device exhibits seven distinct absorption peaks across the 1 to 9.5 THz frequency range, with absorption levels exceeding 80% for each peak. Sensitivity analysis reveals robust absorption performance with minimal variation against geometrical parameter changes, while demonstrating high sensitivity to refractive index changes within the air gap. Specifically, the absorption spectrum shifts significantly for refractive index variations as small as 0.01, which is critical for non-invasive biosensing applications. These results underscore the absorber’s potential as an accurate, wearable, and reliable building block for healthcare monitoring systems.