Abstract
A device for measuring biological small volume liquid samples in real time is appealing. One way to achieve this is by using a microwave sensor based on reflection measurement. A prototype sensor was manufactured from low cost printed circuit board (PCB) combined with a microfluidic channel made of polymethylsiloxane (PDMS). Such a sensor was simulated, manufactured, and tested including a vacuum powered sample delivery system with robust fluidic ports. The sensor had a broad frequency band from 150 kHz to 6 GHz with three resonance frequencies applied in sensing. As a proof of concept, the sensor was able to detect a NaCl content of 125 to 155 mmol in water, which is the typical concentration in healthy human blood plasma.
Highlights
Microwave sensors are defined as sensors that transmit an electromagnetic wave through the sample or allow a measuring wave to be reflected from the sample and acquire data in the form of scattering parameters (S-parameters), which include wave magnitude and phase information
The sensing electrode can be integrated on basic electronic materials/substrates like printed circuit board (PCB) or ceramic, this can make the design of the sensor difficult
The actual sensing part was an interdigitated electrode (IDE) which had dimensions related to the microfluidic channel
Summary
Microwave sensors are defined as sensors that transmit an electromagnetic wave (typically between 300 MHz–300 GHz) through the sample or allow a measuring wave to be reflected from the sample and acquire data in the form of scattering parameters (S-parameters), which include wave magnitude and phase information. A typical microwave sensor that employs the 1-port measurement principle uses a coaxial line sensor structure. This is a powerful method which includes mathematical formulae for calculating the dielectric properties of samples [2,3]. Commercial sensors using this principle are available, such as the Speag DAK (Dielectric Assessment Kit) [4]. There is electromagnetic simulation software available which can be used as a powerful tool for designing custom probes for specific tasks [5]
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