A microwave resonator for limiting depth sensitivity for electron paramagnetic resonance spectroscopy of surfaces

Abstract

A microwave Surface Resonator Array (SRA) structure is described for use in Electron Paramagnetic Resonance (EPR) spectroscopy. The SRA has a series of anti-parallel transmission line modes that provides a region of sensitivity equal to the cross-sectional area times its depth sensitivity, which is approximately half the distance between the transmission line centers. It is shown that the quarter-wave twin-lead transmission line can be a useful element for design of microwave resonators at frequencies as high as 10 GHz. The SRA geometry is presented as a novel resonator for use in surface spectroscopy where the region of interest is either surrounded by lossy material, or the spectroscopist wishes to minimize signal from surrounding materials. One such application is in vivo spectroscopy of human finger-nails at X-band (9.5 GHz) to measure ionizing radiation dosages. In order to reduce losses associated with tissues beneath the nail that yield no EPR signal, the SRA structure is designed to limit depth sensitivity to the thickness of the fingernail. Another application, due to the resonator geometry and limited depth penetration, is surface spectroscopy in coating or material science. To test this application, a spectrum of 1.44 μM of Mg2+ doped polystyrene 1.1 mm thick on an aluminum surface is obtained. Modeling, design, and simulations were performed using Wolfram Mathematica (Champaign, IL; v. 9.0) and Ansys High Frequency Structure Simulator (HFSS; Canonsburg, PA; v. 15.0). A micro-strip coupling circuit is designed to suppress unwanted modes and provide a balanced impedance transformation to a 50 Ω coaxial input. Agreement between simulated and experimental results is shown.

Developments in Biodosimetry Methods for Triage With a Focus on X-band Electron Paramagnetic Resonance In Vivo Fingernail Dosimetry

“…Following irradiation, the plates were mounted on a block of 35% polyacrylamide gel wrapped in plastic wrap using thin strips of cellophane tape. The polyacrylamide gel (PAA) provides a good model of the soft tissue that underlies the nail plate (Sidabras et al 2014). Once mounted, the nail plate/polyacrylamide assembly was inserted into the resonator housing and affixed so that the nail plate is oriented directly under the SRA and in contact with a thin Teflon sheet covering the SRA elements.…”

“…This approach would be applicable for all individuals regardless of the availability of sufficient nail length and would avoid the need to process nails to remove the interfering mechanically induced signal in nail clippings which occur when the nail is clipped to collect it from a subject (Reyes et al 2008, Black and Swarts 2010, Wilcox et al 2010, He et al 2011, Trompier et al 2014a, Marciniak and Ciesielski 2016). Configurations for in vivo measurements using X-band EPR techniques and specially designed resonators to localize the 9 GHz microwave field from the resonator to interact only with the keratinized fingernails and not the underlying soft tissues on a portable instrument platform for very convenient use in triage are readily envisioned (Sidabras et al 2014, Grinberg et al 2016). Herein is a description of the current status of our in vivo EPR nail dosimetry instrument and the steps needed to move this forward towards a field ready application.…”

On the Possibility of Miniature Diamond-Based Magnetometers Using Waveguide Geometries

“…There exist several MW resonators designed for electron paramagnetic resonance (EPR) experiments, which are based on standing-wave cavities and are optimised for large samples. For these resonators, B field strengths of the order of a few Gauss are expected and can be uniform over areas similar to the areas of DW1 and DW2 [ 23 , 24 ], making them ideal for implementation with our system. An alternative solution is to employ MW-free magnetometric protocols which are based on the properties of the NV-center ground-state level anti-crossings [ 25 , 26 ].…”

Dielectric-Backed Aperture Resonators for X-Bandin vivoEPR Nail Dosimetry

“…Experiments were performed with one or three Kapton films attached to bleached printer paper to simulate a full nail thickness of 0.8-1 mm. Secondly, depth sensitivity measurements were performed by placing a Rogers 5880 PC board material (equivalent to 90 Gy RIS signal; 0.25 mm thickness) at fixed distance with bleached paper spacers on a finger model (12) . Lastly, in vivo tests were performed using a healthy volunteer's nail with surface-attached Kapton films.…”

“…Recently a surface resonator array (SRA) geometry at X-band (9.5 GHz) was introduced as a means to limit the depth sensitivity to only the nail plate (12) . However, the aperture resonator, which was introduced by Ikeya and his colleagues (13,14) (referred to hereafter as Ikeya et al) for X-band in vivo tooth dosimetry, is potentially an easier approach.…”