Multifunctional Glass Microfluidic Microwave Sensor Attenuator for Detection of Permittivity and Conductivity With Device Protection

A multifunctional sensor is essential for supporting Internet of Things (IoT) technology. However, many existing sensor technologies are monofunctional, making them challenging to integrate with radio frequency (RF) networks. In addition, several base transceivers operate at high power. To address this problem, our study proposes an asymmetric ring resonator based on a glass substrate for a multifunctional microwave sensor attenuator. The proposed sensor can simultaneously detect permittivity and conductivity while providing protection for high-power RF devices. Our approach uses a specific measurement strategy. Specifically, we utilize a constant transmission coefficient ( ${S} _{{21}}$ ) at a specific frequency for permittivity detection. Simultaneously, we observe changes in the ${Q}$ -factor and the ${S} _{{21}}$ value at a constant frequency for conductivity measurement. Furthermore, the stable ${S} _{{21}}$ response serves as a high-power RF attenuator. In brief, our proposed sensor offers four key advantages: 1) simultaneous detection of permittivity and conductivity changes; 2) operation through a stable microfluidic mechanism with a tiny sample volume of $11.78 \mu \text{L}$ ; 3) high-frequency operation without the need for additional modulators; and 4) independent signal attenuation capabilities to safeguard devices from overpowering RF signals. The measurement results demonstrate the sensor's capability to detect changes in permittivity with a normalized sensitivity of 0.016%. Furthermore, the sensor can sense ultrasmall conductivity values ranging from 0.055 to $0.252 \mu \text{S}$ /cm, with sensitivities of $\Delta {Q}/\Delta \sigma $ = 27.87 and $\Delta \vert {S}_{{21}}\vert /\Delta \sigma $ = 2.49. In addition, the device effectively attenuates overpowering signals, achieving an attenuation of −6.45 dB or transmitting only 22.65%. In conclusion, our study successfully designs a multifunctional sensor device with independent device protection capabilities, addressing the crucial need to protect devices from excessive microwave signal power. This feature makes the sensor well-suited for future IoT technology applications.