PSE-Coated Interdigital Resonator for Selective Detection of Ammonia Gas Sensor

Carbon‐nanotube‐loaded planar gas and humidity sensor

“…These results are consistent with the design philosophy discussed in Section 2. The sensing capability the edge-loaded CNT antenna is also comparable to the reported sensors, [9][10][11][12] while this design offers simplified receiver because tracking frequency shift is easier than impedance as in Reference 9 and is low cost because CNT films are cheaper than Pb-based nanofilms. 12 The data points taken at several time intervals showed a continuous upshift of the frequency as well as increased reflection coefficient, which was as expected because the frequency shift could degrade the matching since the matching circuit was designed for the initial frequency.…”

“…Although there have been a handful of successful gas sensors made of semiconductors, 2 solid electrolytes, 3,4 optical fibers, 5 laser diodes, 6 and nondispersive infrared detectors, 7 applications of those designs were limited by the size of lumped elements, fabrication processes, and the ability to integrate with wireless networks. On the other hand, gas sensors based on planar geometries became a favorable choice with their conformal shapes and lower power consumption 1,8‐12 . The primary mechanism of those reported planar gas sensors has been the utilization of carbon nanotube (CNT) films because of the CNT's sensitivity when exposed to different gases, 13‐15 or by utilizing nanomaterial that changes properties when exposed to certain gases 10‐12 .…”

“…1,[8][9][10][11][12] The primary mechanism of those reported planar gas sensors has been the utilization of carbon nanotube (CNT) films because of the CNT's sensitivity when exposed to different gases, [13][14][15] or by utilizing nanomaterial that changes properties when exposed to certain gases. [10][11][12] As the CNT film changes its conductivity when exposed to different gases, sensing can be achieved by tracking the change of the resonant frequency of a CNT-loaded LC circuit 1 or resonator, 8 or by tracking the change of the antenna's impedance. 9 Despite reported successful demonstrations of such sensors, we found that the sensitivity of the device can be improved and the design can be further simplified by a closer examination of the sensor fundamentals.…”

In-Situ Self-Aligned NaCl-Solution Fluidic-Integrated Microwave Sensors for Industrial and Biomedical Applications

“…Recently, microwave sensors and characterizations have become a popular technique for fluidic and liquid-mixture concentration sensing in various industrial applications, e.g. high-pressure liquid measurements [1]- [2], material moisture content characterizations [3]- [6], continuous process monitoring of biogas plants [7]- [8] and determinations of moisture content in soil [5], [9]- [11]. Moreover, they have also been proven very useful in many healthcare and biomedical applications, e.g.…”

“…With microwave measurement techniques, there are several methods to indicate liquid ingredients from liquid-mixture solutions, e.g., resonance frequency [18], [30]- [32], transmission level [17], [32]- [33], phase and quality factor (Q-factor) [23]. Various liquid-mixture sensors based on microwave technologies have been extensively investigated, such as split-ring resonator [34]- [36], complementary split-ring resonator (CSRR) structures [17], [31]- [32], [37]- [38], interdigital structures [8], substrate integrated-waveguide (SIW) structures [18], waveguide structures [30] and mushroom-like structures [23]. These techniques offer a good measurement accuracy [17]- [18], [31], with, generally, nondestructive measurement and short assay time.…”