Design and Comparison of Resonant and Non-Resonant Single-Layer Microwave Heaters for Continuous Flow Microfluidics in Silicon-Glass Technology

Abstract

This paper presents a novel concept for the co-design of microwave heaters and microfluidic channels for sub-microliter volumes in continuous flow microfluidics. Based on the novel co-design concept, two types of heaters are presented, co-designed and manufactured in high-resistivity silicon-glass technology, resulting in a building block for consumable and mass-producible micro total analysis systems. Resonant and non-resonant co-planar waveguide transmission line heaters are investigated for heating of sub-micro-liter liquid volumes in a channel section at 25 GHz. The heating rates of 16 and 24 °C/s are obtained with power levels of 32 dBm for the through line and the open-ended line microwave heater, respectively. The heating uniformity of developed devices is evaluated with a Rhodamine B and deionized water mixture on a micrometer scale using the microwave-optical measurement setup. Measurement results showed a good agreement with simulations and demonstrated the potential of microwave heating for microfluidics.

Microfluidic Modules Integrated with Microwave Components—Overview of Applications from the Perspective of Different Manufacturing Technologies

“…This technology mostly appears in LOC microsystems, which can be made on, among other things, quartz [ 9 , 45 , 46 , 47 ], silicon [ 48 ], or glass [ 49 , 50 ] substrates. Due to fact that the material, which acts as a microwave circuits’ substrate, should be characterized by high resistivity, the silicon ones are mostly the high-resistive ones [ 51 , 52 , 53 ]. The process of manufacturing microwave devices with microfluidic components usually consists of fabricating thin-layer microwave planar waveguides on a glass or silicon substrate and adding a part constituting a microfluidic channel.…”

“…Due to this, the risk of an unwanted increase in the temperature in parts of microsystems is reduced, which includes some electronic components. Microwaves that use heating are described in [ 51 , 52 , 80 , 81 , 82 ].…”

“…This approach has many advantages, such as the possibility of carrying out the nondestructive tests of the solution and the characterization almost in real-time whilst being able to observe even slight changes in dielectric parameters of the tested material [ 85 , 86 ]. The microwave detection methods can be divided into two groups—the resonant and the nonresonant ones [ 51 , 87 , 88 , 89 ]. The exemplary applications of microwave circuits as a detection include the use of the resonance or differential circuits’ responses to characterize the liquid in the microchannel/microchamber [ 2 , 90 , 91 , 92 , 93 , 94 , 95 ].…”

Experimental Studies of Droplet Formation Process and Length for Liquid–Liquid Two-Phase Flows in a Microchannel

“…Compared with other forms of multiphase microfluidics, liquid-liquid multiphase microfluidic droplets have an additional radial inner vortex and a larger surface area to volume ratio, both of which facilitate enhanced mixing and mass transfer [8,9]. Therefore, liquid-liquid multiphase transport in microchannels has become an important topic in many fields, such as microchemical reactions [10][11][12][13], extraction [14][15][16], oil recovery [17,18], fuel cells [19], microchannel heat transfer [20][21][22][23], carbon capture [24,25], drug transport [26,27], lab on a chip [28][29][30][31], and others.…”

A Stripline-Based Integrated Microfluidic-Microwave Module

“…The common solutions are based on optical [15][16][17], electrochemical [18], acoustical [19] and electromagnetic [20][21][22][23][24] components. Moreover, the microreactors designed for continuous, as well as for digital microfluidics can be found in the literature [25][26][27]. The last area typically includes circuits that are characteristic of the microwave technique.…”