Polarization-Based Gigahertz Near-Field Bio-Sample Detector Prepared by Integrated-Passive-Device Fabrication.

Far-field detection has been widely used in biomedical diagnosis, security inspection, such as MRI, ultrasonic, SPECT, X-ray, etc. However, the near-field detection has yet to be well established. This paper proposed a sensor structure with series inductance and capacitor. The inductance is a differential-transformer-type inductor formed by winding two spiral inductors. The interdigital capacitor is redesigned and placed inside the inductor to reduce its overall size. With the presence of the digital capacitor, the resonance shifts to the lower frequency, and the amplitude of return loss is increased. The micro-fabricated resonator was realized through integrated passive device technology for sensitive detection and characterization of glucose. The experimental results verified the performance of the proposed biosensor as the radio frequency multi-parameter bio-detector, such as the resonance frequency and the reflection coefficient. The detection results vary in response to deionized water, following by the iterative measurements of the changing glucose concentrations (from 50 to 150 mg $\cdot $ dL $^{-1}$ ). The concentration of glucose solution changes from 50 mg $\cdot $ dL $^{-1}$ to 150 mg $\cdot $ dL $^{-1}$ . The experimental results show that the amplitude changes 32.1 dB, and the phase changes 60.88° at 1 GHz. The results indicate the proposed microwave sensor has an excellent biosensing performance.