Modelling and Measurements of the Microwave Dielectric Properties of Microspheres

Abstract

A microwave microstrip sensor incorporating a split ring resonator is presented in this paper for microsphere detection and dielectric characterization within a microfluidic channel. Split ring resonator (SRR) sensor of three different radii, but with approximately equal gap dimensions to change their sensitivity, were designed and fabricated, of resonance frequencies 2.5, 5.0 and 7.5 GHz. To validate the SRR sensors, two sizes of polystyrene microspheres were tested, of diameters 15 and 25 . Measurements of changes in resonance frequency and insertion loss of the odd SRR mode were related to the dielectric contrast provided by the microspheres and their host solvent, here water. COMSOL Multiphysics was used to model the sensors, and good agreements were found between the simulated and measured results.

Dual Mode Microwave Microfluidic Sensor for Temperature Variant Liquid Characterization

“…In this case K Q = 1.60. From (10) and (11), the resonant frequency and the quality factor in the case of the empty capillary of port 3 can be found instantaneously from the measurements of port 2 as function of temperature. To demonstrate how temperature drifts can result in large errors in extraction of complex permittivity, we assume room temperature (25°C) as the reference temperature to calibrate our results.…”

“…In [9], the error frequency shift of a resonator due to temperature dependence of the sample's dielectric properties was determined by using reference measurements in which the resonator does not need cooling. Another idea was proposed in [10] and [11], where an unperturbed mode can be used to assess and correct for very small temperature changes. However, there is still a small influence of the sample on this mode, which complicates the correction process.…”

“…A new, versatile sensor is proposed in this paper whose novelty lies in it having a reference resonator, spectrally separated from the measurement mode. Its reference resonant frequency is insensitive to the presence of the dielectric sample, more so than the aforementioned case [10], [11] and so can be used to monitor the temperature changes and hence to adjust ("calibrate") the dielectric measurements accordingly. Such separation of the spectral responses of the measurement and reference sensors is accomplished by the design, which uses different resonators for each function, while allowing for simultaneous excitation.…”

An innovative microwave cavity sensor for non-destructive characterisation of polymers

“…Microwave based sensing is relatively a new and developing technology. Microwave based permittivity measurements of the material and sensing for material characterisation has been much in use in the research for over couple of decades [5,6]. Microwave frequencies at a single and multiple modes have been utilised by researchers such as Ren et al [7,8] and Meng et al [9] to characterise the dielectric properties of various materials with and without the influence of high temperature (up to 1000°C).…”

Microwave-to-terahertz dielectric resonators for liquid sensing in microfluidic systems

“…Planar resonators, multiple resonator filter structures and even metamaterials are attractive because of their high electric fields within capacitive gaps, like in coplanar waveguides, lumped element LC resonators or split ring resonators [8,9]. Microfluidic fabrication technology enables the integration of metal electrodes within microfluidic channels.…”