A novel non-contact vital-sign sensing algorithm for use in cases of multiple subjects is proposed. The approach uses a 24 GHz frequency-modulated continuous-wave Doppler radar with the parametric spectral estimation method. Doppler processing and spectral estimation are concurrently implemented to detect vital signs from more than one subject, revealing excellent results. The parametric spectral estimation method is utilized to clearly identify multiple targets, making it possible to distinguish multiple targets located less than 40 cm apart, which is beyond the limit of the theoretical range resolution. Fourier transformation is used to extract phase information, and the result is combined with the spectral estimation result. To eliminate mutual interference, the range integration is performed when combining the range and phase information. By considering breathing and heartbeat periodicity, the proposed algorithm can accurately extract vital signs in real time by applying an auto-regressive algorithm. The capability of a contactless and unobtrusive vital sign measurement with a millimeter wave radar system has innumerable applications, such as remote patient monitoring, emergency surveillance, and personal health care.

In this paper, a microwave fluidic glucose sensor based on dual complementary split ring resonators (CSRRs) with a switching circuit is proposed for non-invasive and continuous glucose concentration detection. A CSRR has been designed to detect subtle changes in the dielectric constant of glucose solutions, and the electric field distribution is utilized to determine the effective sensing region. In a well-controlled environment, the glucose concentration can be detected by tracking the transmission coefficient of the designed CSRR. However, because the variations in dielectric constant with the glucose concentration are very small, the environmental factors (i.e., ambient temperature and relative humidity) can be dominant compared to the glucose concentration. To qualify the effect of the environmental factors, the variation in the transmission coefficient of the CSRR has been measured when the ambient temperature condition is varied from 293 K to 313 K and the relative humidity is varied from 30% to 90% inside temperature- and humidity-controlled chamber. Moreover, the environmental effects are calibrated out using two identical CSRRs with the switching circuit: one detects changes in the glucose concentration, while the other operates as a reference for environmental factors. After the elimination of the environmental effects, glucose concentrations in the range of 0 mg/dL to 400 mg/dL have been measured, and the sensitivity is 0.008dB/(100mg/dL). In addition, the reproducibility of the proposed sensor is verified by repeated measurements. It is demonstrated that the proposed sensor can detect glucose concentrations under practical environmental conditions

In this paper, a fluidic glucose sensor that is based on a complementary split-ring resonator (CSRR) is proposed for the microwave frequency region. The detection of glucose with different concentrations from 0 mg/dL to 400 mg/dL in a non-invasive manner is possible by introducing a fluidic system. The glucose concentration can be continuously monitored by tracking the transmission coefficient $S_{21}$ as a sensing parameter. The variation tendency in $S_{21}$ by the glucose concentration is analyzed with equivalent circuit model. In addition, to eradicate the systematic error due to temperature variation, the sensor is tested in two temperature conditions: the constant temperature condition and the time-dependent varying temperature condition. For the varying temperature condition, the temperature correction function was derived between the temperature and the variation in $S_{21}$ for DI water. By applying the fitting function to glucose solution, the subsidiary results due to temperature can be completely eliminated. As a result, the $S_{21}$ varies by 0.03 dB as the glucose concentration increases from 0 mg/dL to 400 mg/dL.

A real-time humidity sensor based on a microwave resonator coupled with a poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) conducting polymer (CP) film is proposed in this paper. The resonator is patterned on a printed circuit board and is excited by electromagnetic field coupling. To enhance the sensitivity of the sensor, the CP film is located in the area with the strongest electric field in the resonator. To investigate the performance, the proposed sensor is placed alongside a reference sensor in a humidity chamber, and humidity is injected at room temperature. The experimental results indicate that the electrical properties of the resonator with the CP film, such as the transmission coefficient (S₂₁) and resonance frequency, change with the relative humidity (RH). Specifically, as the RH changes from 5% to 80%,S₂₁and the resonance frequency change simultaneously. Moreover, the proposed sensor exhibits great repeatability in the middle of the sensing range, which is from 40% to 60% RH. Consequently, our resonator coupled with the CP film can be used as a real-time humidity-sensing device in the microwave range, where various radio-frequency devices are in use.