Abstract
This paper reports on a sensor based on multi-element complementary split-ring resonator for the measurement of liquid materials. The resonator consists of three split rings for improved measurement sensitivity. A hole is fabricated at the centre of the rings to accommodate a hollow glass tube, through which the liquid sample can be injected. Electromagnetic simulations demonstrate that both the resonant frequency and quality factor of the sensor vary considerably with the dielectric constant and loss tangent of the liquid sample. The volume ratio between the liquid sample and glass tube is 0.36, yielding great sensitivity in the measured results for high loss liquids. Compared to the design based on rectangular split rings, the proposed ring structure offers 37% larger frequency shifts and 9.1% greater resonant dips. The relationship between dielectric constant, loss tangent, measured quality factor and resonant frequency is derived. Experimental verification is conducted using ethanol solution with different concentrations. The measurement accuracy is calculated to be within 2.8%, and this validates the proposed approach.
Highlights
Complex permittivity is one fundamental electromagnetic property of dielectric materials [1]
In situ measurement of dielectric constant and loss tangent for liquid materials is in active demand
It is still difficult to distinguish small changes in permittivity. Another complementary split ring resonator (CSRR)-based liquid sensor working at 200–330 MHz is reported for dielectric measurement of different density ethanol [30]
Summary
Complex permittivity is one fundamental electromagnetic property of dielectric materials [1]. The resonant cavity method is sensitive to low-loss and low-permittivity samples with high accuracy. New dielectric measurement techniques shall be developed for high-permittivity and high-loss liquid samples with sufficiently high sensitivity. Sensors reported by Kiani et al [16] can measure the dielectric constant of liquids, but not the loss tangent. It is still difficult to distinguish small changes in permittivity Another CSRR-based liquid sensor working at 200–330 MHz is reported for dielectric measurement of different density ethanol [30]. For measuring liquid samples with εr in the range of 1–90, the circular CSRR structure is a better choice, in the high-permittivity range
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