High-temperature superconducting multi-band radio-frequency metamaterial atoms

Abstract

We report development and measurement of a micro-fabricated compact high-temperature superconducting (HTS) metamaterial atom operating at a frequency as low as ∼ 53MHz. The device is a planar spiral resonator patterned out of a YBa 2 Cu 3 O 7−δ (YBCO) thin film with the characteristic dimension of ∼ λ 0 /1000, where λ 0 is the free-space wavelength of the fundamental resonance. While deployment of an HTS material enables higher operating temperatures and greater tunability, it has not compromised the quality of our spiral metamaterial atom and a Q as high as ∼ 1000 for the fundamental mode, and ∼ 30000 for higher order modes, are achieved up to 70K. Moreover, we have experimentally studied the effect of the substrate by comparing the performance of similar devices on different substrates.Realization of metamaterials based on sub-wavelength artificial electromagnetic structures has attracted much attention and efforts for a variety of applications 1,2 . This interest applies virtually to the entire span of the electromagnetic spectrum from radio-frequency (RF) up to visible and ultraviolet wavelengths. Nevertheless, at the low-frequency limit, i.e. in the RF regime, where the free-space wavelength of signals ranges from tens of centimeters to meters, the constituent elements of metamaterials, referred to as the metamaterial atoms, are often bulky, which hinders the implementation of scalable RF metamaterials. In addition, RF resonant structures traditionally exhibit low quality factors due to significant dissipation in their bulky structures 3,4 . Since both requirements of scalability/compactness and low dissipation have proved to be challenging to achieve for RF metamaterials, few studies have concerned metamaterials at the low-frequency part of the electromagnetic spectrum 5 . Nonetheless, RF metamaterials have been sought to improve the performance of magnetic resonance imaging (MRI) devices 6,7 , magnetoinductive lenses 8 , microwave antennas 9 , delay-lines 10 , and resonators 11 . Insofar as obtaining RF metamaterials substantially relies on the development of compact and scalable metamaterial atoms that are amenable to conventional microfabrication techniques, many superconducting structures have been recently introduced and tested for metamaterial applications in the RF/microwave regime 12-21 , motivated by their low-losses and deep sub-wavelength sizes.Recently, we have demonstrated superconducting RF metamaterials based on Niobium (Nb) spiral resonators as a viable means to realize efficient metamaterials at low frequencies presenting both a compact physical structure and low loss 22,23 . Given that Nb is a low-temperature superconductor (LTS) whose transition temperature is ∼9.2K, development of analogous superconducting metamaterial atoms capable of functioning at the temperature of liquid nitrogen, 77K, is clearly a technological advantage. Furthermore, accessing a wider range of superconducting temperature allows greater convenience and effectiveness in tuning the properties of the metamaterial ato...

Tunable Negative Permeability in a Three-Dimensional Superconducting Metamaterial

“…constructive and destructive interferences between the direct coupling of the loops and magnetic coupling of the loops to the metamaterial, respectively [35]. We observe higher-order modes corresponding to shorter-wavelength rf-current standing waves in the spiral, which have been extensively studied elsewhere [8,[36][37][38][39]. Above the T c of Nb, superconductivity is lost and the resonance is wiped out at 9.25 K. This demonstrates that such a compact device is not functional if made with thin films of normal metals due to the large ohmic losses.…”

Dielectric resonator method for determining gap symmetry of superconductors through anisotropic nonlinear Meissner effect

“…The first-generation resonator design which satisfies the above requirements is the multi-turn spiral resonator ( Fig.3(a)). [20][21][22][23] The spiral resonator is prepared by patterning a thin-film sample into an Archimedean spiral shape with a photo-lithographic procedure. At its resonant frequencies, this spiral geometry has the advantage that it produces a uniform tangential standing wave current.…”

Effects of Dielectric Substrates and Ground Planes on Resonance Frequency of Archimedean Spirals

“…Planar spirals are used in a variety of RF electronic applications such as filters [1], planar inductors [2], wireless power transfer [3], metamaterials [4], and NMR probe coils [5]. When used as HTS NMR probe coils specifically, and in some other applications, it is typical for the spiral to be mounted on a dielectric substrate [6].…”