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.

Active and Tunable Metamaterials

“…MAs can be achieved at most of the frequency region by selecting the unit cell dimensions accordingly. The existence of such a huge operating spectral range enables the applications of MAs in various fields such as energy harvesting and thermal emitting and sensing [53][54][55]. Recently, various designs have been reported for MAs [56][57][58][59][60] and the corresponding numerical analysis and theory methods can be referred to, e.g., in [61][62][63][64].…”

Metamaterial-based microfluidic sensor for dielectric characterization

“…Substances under test include solid dielectrics [2,3,4], liquids [5,6], and biomolecules [7,8,9], developed in the form of solid or liquid films. Most of the studies have merely investigated the function of metamaterial resonators for detecting the presence and/or estimating the amount of the sample.…”

Invited Article: Terahertz microfluidic chips sensitivity-enhanced with a few arrays of meta-atoms

“…26 Since the fs laser beams are focused at the output surface of the NLOC, the beam diameter of the generated THz waves is approximately the same size as that of the focused beam spot which overcomes the diffraction limit of THz waves. 26 By setting samples in the vicinity of the THz generation spot on the 2D-THz emitter, THz-TDS and THz-imaging have been successfully achieved on the samples of sub-THz wavelength scale, such as dielectric thin-film, 27 a human hair strand, 28 metallic small apertures, 29 THz meta-atom, 30 and nanoparticles. [31][32][33] Therefore, it is interesting to see if this technique can be also applied to the measurements of trace-amount of liquid solutions.…”