Metal Discovery by Highly Sensitive Microwave Multi-Band Metamaterial-Inspired Sensors

Abstract

A simple, compact, contactless, and high sensitivity metamaterial-inspired sensor has been developed to detect and classify precious transition metals in the S-and C-band regime, using reflection coefficients. A multi-band metamaterial, quadruple concentric circular split ring resonator, is specifically designed as a sensing enhancer, where the additional bands can effectively trigger the electromagnetic properties, as well as enhance the differentiation between the testing metal samples. The proposed sensor was tested on precious transition metals, silver, platinum, and gold thin slabs of various thicknesses, from 0.5 µm to 3 mm. Five resonances were established in the frequency range of 2-8 GHz. Distinguishable frequency responses generated from different metal samples at those five resonances specify the capability of classifying the metal contents and thicknesses.

Design Guidelines for Sensors Based on Spiral Resonators

“…The capacitive coupling between the SR and the probing loop at small distances can be accounted for by adding a distance-dependent term to the expression of the capacitance of the SR as in (10), where C f is the native capacitance of the SR (estimated at a d z beyond which there is no change in the resonant frequency) according to (11) where the native SR resonant frequency, f ∞ , is obtained from numerical simulations at large d z = 30 mm, where this capacitive coupling effect is insignificant. The inductance is calculated in (12) according to [25] for an SR of N turns. The constants in (12) depend on the layout and are obtained for a square planar spiral, µ 0 is the free space permeability, and ρ represents the filling factor and is calculated as the ratio between the difference of the external and internal diameter of the SR to their sum.…”

“…The inductance is calculated in (12) according to [25] for an SR of N turns. The constants in (12) depend on the layout and are obtained for a square planar spiral, µ 0 is the free space permeability, and ρ represents the filling factor and is calculated as the ratio between the difference of the external and internal diameter of the SR to their sum. The additional capacitance C ppc is calculated from (13) in terms of the effective dielectric permittivity of the medium ε 0 between the loop and the SR (modeled here as vacuum which is a valid first approximation since the space between the conductors is occupied as air), the equivalent conductor strip area Ã, and the normal distance d z .…”

“…The terms in expressions (11) and (12) depend on the geometrical parameters with the exception of f 0 that is obtained from a numerical simulation. To calculate the additional capacitance C ppc , an algorithm based on least square fitting was developed to estimate the best fit parameters.…”

“…In frequency-modulated sensors the working principle relies on the simple fact that the resonant frequency is changed due to a change in the measurand; however, the measurement is carried out by means of a wide-band frequency sweep which increases the complexity and cost of the electronics required for signal generation and detection. Frequency-modulated sensors have been used in a variety of applications, such as strain sensors [6], motion detection [7], liquid detection [8], rotation sensors [9,10], methanol concentration [11], and metal detection [12]. These sensors, based on metamaterial unit cell geometries, are capable of providing realtime monitoring of various physical properties and they can operate without any wired connection between the reader and the sensor.…”

Ultra-Thin Nona-Band Polarization Insensitive Metasurface for High-Quality Sensing, EMI-Shielding, and Antenna RCS Reduction

“…A theoretical analysis of a newly structured metamaterial sensor has been done [23] for identification of different variety of oils, fluids, and substances using microwave frequency. To achieve high sensitivity for the identification of valuable metals in the S and C-band, a small size, contactless MM-based sensor is also proposed [24]. Nowadays, Due to its straightforward design and production procedure, low profile planar metasurfaces (MS) are frequently employed in place of traditional microwave absorbers and are used as absorbers in cutting-edge technologies and it has great performance in microwave applications, such as polarisation converter, high-gain antenna, and low RCS.…”