A reusable robust radio frequency (RF) biosensor with a rectangular meandered line (RML) resonator on a gallium arsenide substrate by integrated passive device (IPD) technology was designed, fabricated and tested to enable the real-time identification of the glucose level in human serum. The air-bridge structure fabricated by an IPD technology was applied to the RML resonator to improve its sensitivity by increasing the magnitude of the return loss (S21). The resonance behaviour, based on S21 characteristics of the biosensor, was analysed at 9.20 GHz with human serum containing different glucose concentration ranging from 148-268 mg dl(-1), 105-225 mg dl(-1) and at a deionised (D) water glucose concentration in the range of 25- 500 mg dl(-1) for seven different samples. A calibration analysis was performed for the human serum from two different subjects and for D-glucose at a response time of 60 s; the reproducibility, the minimum shift in resonance frequency and the long-term stability of the signal were investigated. The feature characteristics based on the resonance concept after the use of serum as an analyte are modelled as an inductor, capacitor and resistor. The findings support the development of resonance-based sensing with an excellent sensitivity of 1.08 MHz per 1 mg dl(-1), a detection limit of 8.01 mg dl(-1), and a limit of quantisation of 24.30 mg dl(-1).
In this letter, microstrip bandpass filters (BPFs) using circular triple‐mode ring resonators with/without stub perturbation are designed and analyzed. The first BPF, with a wide passband and a sharp band rejection, is proposed as a prototype, and stubs are attached to two additional BPFs to introduce perturbation. The effects of the stub perturbation are analyzed and evaluated using both the equations and the equivalent circuits presented in this study. The BPF prototype is equipped with both a circular outer resonator, which operates at one wavelength, and a half‐wavelength open‐ended coupled line with a central connected quarter‐wavelength shunt open stub. Each side of the passband has two transmission zeros, which provides the filter with both good selectivity and good out‐band suppression. Based on this BPF prototype, two additional BPFs are designed with stub perturbation for in‐band (BPF 1) and multi‐band (BPF 2) adjustment.
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