The magnitude of this frequency shift is used to measure sensitivity, often reported in units like THz/RIU (refractive index unit). For example, one terahertz metamaterial absorber achieved a sensitivity of 2.537 THz/RIU, meaning the resonance frequency shifts by 2.537 THz for each unit increase in refractive index. In a biomedical context, sensors have shown sensitivity values up to hundreds of GHz/RIU, with strong responsiveness in the refractive index range typical for biological samples (n ≈ 1.3–1.39).