Microfluidic High-Q Circular Substrate-Integrated Waveguide (SIW) Cavity for Radio Frequency (RF) Chemical Liquid Sensing

Abstract

In this study, a high-Q circular substrate-integrated waveguide (SIW) cavity resonator is proposed as a non-contact and non-invasive radio frequency (RF) sensor for chemical sensing applications. The design of the structure utilizes SIW technology along with a circular shape to achieve a high unloaded Q factor, which is one of the important requirements for RF sensors. The resonant frequency of the proposed circular SIW cavity sensor changes when a liquid material or a chemical (microliters) is inserted in the sensitive area of the structure. The sensing of liquid materials with different permittivities is accomplished via the perturbation of the electric fields in the SIW configuration. When a microwell that is 4 mm in radius is installed vertically through the center of the bare circular SIW cavity, the operating frequency varies from 5.26 to 5.34 GHz. Similarly, when the microwell contains ethanol, the frequency shifts from 5.26 to 5.18 GHz, and the amplitude of reflection coefficient is shifted from −29 dB to −17 dB; when the microwell contains mixing deionized (DI)-water, the frequency moves from 5.26 to 4.98 GHz (which is also 0% Ethanol in our study), and the amplitude of reflection coefficient is shifted from −29 dB to −8 dB. A high unloaded Q factor is maintained throughout all experimental results. To demonstrate our idea, different concentrations of ethanol are tested and recorded. The experimental validation yields a close agreement between the simulations and the measurements.

CSRR-Based Microwave Sensor for Dielectric Materials Characterization Applied to Soil Water Content Determination

“…The results shown in Figure 2 indicates that the proposed antenna has a high-quality factor, Q, which can be calculated using Equation (3) [23].…”

Simultaneous Detection of Two Chemicals Using a TE20-Mode Substrate-Integrated Waveguide Resonator

“…For this full-wave simulation, the dielectric properties of 100% ethanol were set as ε r = 5.2 and tan Δ = 0.4 [ 43 ]. The simulated unloaded quality factor Q ≈ 28 was calculated based on the well-known formula as specified in [ 34 , 44 ].…”

“…In [ 28 ], a rectangular SIW cavity was proposed in order to characterize several liquid chemicals, and a frequency shift of 610 MHz was observed. In [ 34 ], a circular SIW cavity (Q ≈ 1080) was proposed as an ethanol sensor, and it showed a frequency shift of 380 MHz. There was a significant improvement in the sensing performance or otherwise miniaturization in each of these SIWs; however, all these sensors had the same limitation of only single-channel sensing per sensor.…”

Planar Inverted-F Antenna (PIFA) Using Microfluidic Impedance Tuner

“…It can be implemented at a less complexity and low cost. Especially, liquid metal in microfluidic channels have been studied for flexible or reconfigurable radio frequency (RF) components [ 9 ], such as filters [ 10 ], sensors [ 11 , 12 ], absorbers [ 13 , 14 ], antennas [ 15 ], and MEMS switch [ 16 ].…”