title: Sub-diffraction thin-film sensing with planar terahertz metamaterials.
abstract: Planar metamaterials consisting of subwavelength resonators have been recently proposed for thin dielectric film sensing in the terahertz frequency range. Although the thickness of the dielectric film can be very small compared with the wavelength, the required area of sensed material is still determined by the diffraction-limited spot size of the terahertz beam excitation. In this article, terahertz near-field sensing is utilized to reduce the spot size. By positioning the metamaterial sensing platform close to the sub-diffraction terahertz source, the number of excited resonators, and hence minimal film area, are significantly reduced. As an additional advantage, a reduction in the number of excited resonators decreases the inter-cell coupling strength, and consequently the resonance Q factor is remarkably increased. The experimental results show that the resonance Q factor is improved by more than a factor of two compared to the far-field measurement. Moreover, for a film with a thickness of λ/375 the minimal area can be as small as 0.2λ × 0.2λ. The success of this work provides a platform for future metamaterial-based sensors for biomolecular detection.
authors.affiliation: School of Electrical & Electronic Engineering, The University of Adelaide, Adelaide, SA 5005, Australia. withawat@eleceng.adelaide.edu.au
authors.forename: Withawat
authors.initials: W
authors.lastname: Withayachumnankul
authors.forename: Hungyen
authors.initials: H
authors.lastname: Lin
authors.forename: Kazunori
authors.initials: K
authors.lastname: Serita
authors.forename: Charan M
authors.initials: CM
authors.lastname: Shah
authors.forename: Sharath
authors.initials: S
authors.lastname: Sriram
authors.forename: Madhu
authors.initials: M
authors.lastname: Bhaskaran
authors.forename: Masayoshi
authors.initials: M
authors.lastname: Tonouchi
authors.forename: Christophe
authors.initials: C
authors.lastname: Fumeaux
authors.forename: Derek
authors.initials: D
authors.lastname: Abbott
mesh_terms: D004867:Equipment Design; D019544:Equipment Failure Analysis; D008567:Membranes, Artificial; D055096:Optical Devices; D055053:Terahertz Radiation; D014159:Transducers
chemical_list: D008567:Membranes, Artificial