Differential Microwave Microfluidic Sensor Based on Microstrip Complementary Split-Ring Resonator (MCSRR) Structure

Review of Recent Microwave Planar Resonator-Based Sensors: Techniques of Complex Permittivity Extraction, Applications, Open Challenges and Future Research Directions

“…Further research should be undertaken to investigate the mathematical modelling based on machine learning approaches to analyse the measured data quickly and with high accuracy. Recently, mathematical tools based on Neural Networks (NNs) were employed for complex permittivity extraction, and this is due to their strong learning ability and high accuracy [ 20 , 21 , 22 , 23 , 24 ]. Figure 2 demonstrates the general structure of a neural network where there are three layers.…”

“…The final layer is where we obtain the result performed by the hidden layer. A Back-Propagation Neural Network (BP-NN) was presented in [ 23 ] where the genetic algorithm was used to obtain the initial optimal values of the network weights in the training process, while the BP-NN was used to find the optimum solutions with these initial weights. The authors used the input data as the relative permittivity of the tested sample and the normalized quality factor.…”

“…Two PDMS channels were used, where one was considered as the reference channel and the other one as the measurement channel for the liquid under test. However, the proposed sensor by Gan et al [ 23 ] requires two resistors to be soldered, which increases the fabrication cost and circuit size and makes it inconvenient. Furthermore, the resonance of the reference channel might be affected to some extent due to the timing difference when loading the liquid sample compared to the measurement channel.…”

“…This review shows the recent development of various studies and examples of applications of microwave planar sensors in material characterization. It includes the mathematical models for complex permittivity extraction [ 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 ], sensing application examples of microwave sensors [ 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , …”

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

“…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 ].…”