Yunseog Hong

Noncontact Proximity Vital Sign Sensor Based on PLL for Sensitivity Enhancement

In this paper, a noncontact proximity vital sign sensor, using a phase locked loop (PLL) incorporated with voltage controlled oscillator (VCO) built-in planar type circular resonator, is proposed to enhance sensitivity in severe environments. The planar type circular resonator acts as a series feedback element of the VCO as well as a near-field receiving antenna. The frequency deviation of the VCO related to the body proximity effect ranges from 0.07 MHz/mm to 1.8 MHz/mm (6.8 mV/mm to 205 mV/mm in sensitivity) up to a distance of 50 mm, while the amount of VCO drift is about 21 MHz in the condition of 60 °C temperature range and discrete component tolerance of ±5%. Total frequency variation occurs in the capture range of the PLL which is 60 MHz. Thus, its loop control voltage converts the amount of frequency deviation into a difference of direct current (DC) voltage, which is utilized to extract vital signs regardless of the ambient temperature. The experimental results reveal that the proposed sensor placed 50 mm away from a subject can reliably detect respiration and heartbeat signals without the ambiguity of harmonic signals caused by respiration signal at an operating frequency of 2.4 GHz.

A Label-Free Biosensing Platform Using a PLL Circuit and Biotin-Streptavidin Binding System

This paper proposes a novel RF biosensor that utilizes a frequency synthesizer associated with a microstrip open-loop resonator for label-free biomolecular detection. The RF biosensor consists mainly of a resonance-assisted transducer and a phase locked loop (PLL) circuit. In this work, the performance of the RF biosensor is validated using the well-known biotin-streptavidin binding system. When biotin is bound to streptavidin, the input impedance of the resonator is varied, resulting in a change in the oscillation frequency. The concentration of the streptavidin is ultimately detected by a voltage signal of the PLLs loop filter with simple measurement equipment. According to the experimental results, the RF biosensor has revealed excellent sensitivity ( ~ 61 kHz/ngml(-1)) and a low detection limit ( ~ 1 ng/ml), as well as a rapid response. These results demonstrate that the RF biosensor can be an effective sensing platform for label-free detection in a biomolecular binding system.This paper proposes a novel RF biosensor that utilizes a frequency synthesizer associated with a microstrip open-loop resonator for label-free biomolecular detection. The RF biosensor consists mainly of a resonance-assisted transducer and a phase locked loop (PLL) circuit. In this work, the performance of the RF biosensor is validated using the well-known biotin-streptavidin binding system. When biotin is bound to streptavidin, the input impedance of the resonator is varied, resulting in a change in the oscillation frequency. The concentration of the streptavidin is ultimately detected by a voltage signal of the PLLs loop filter with simple measurement equipment. According to the experimental results, the RF biosensor has revealed excellent sensitivity ( ~ 61 kHz/ngml-1) and a low detection limit ( ~ 1 ng/ml), as well as a rapid response. These results demonstrate that the RF biosensor can be an effective sensing platform for label-free detection in a biomolecular binding system.

A Proximity Coupling RF Sensor for Wrist Pulse Detection Based on Injection-Locked PLL

In this paper, a proximity coupling RF sensor based on injection-locked phase-locked loop (PLL) for wrist pulse detection is proposed. The sensor is composed of two main parts: a free-running oscillator and a PLL synthesizer containing a voltage-controlled oscillator. The free-running oscillator is built with a two-port microstrip line resonator (inter-digital electrodes), which acts as part of a transducer that can transform the expansion or contraction of the radial artery into an impedance variation. Measurements show that the impedance variation of the resonator due to changes in the radial artery causes a frequency change of up to 0.74 MHz in the free-running oscillator. For the PLL part, the frequency change can be transformed to a variation in dc voltage by injection of the modulated signal from the wrist pulse into a phase-locked oscillator. The variation of the loop-control voltage, in one cycle of the pulse, is approximately 10-15 mV peak-to-peak. Our sensor is demonstrated to be an effective noncontact and noninvasive scheme for wrist pulse detection.

A gas sensor using double split-ring resonator coated with conducting polymer at microwave frequncies

In this research, a gas sensor using double split-ring resonator (DSRR) incorporated with conducting polymer (CP) is proposed at microwave frequencies (Ku-band). The DSRR fabricated on printed circuit board (PCB) is excited by a high-impedance microstrip line, and the CP is coated inside of an inner circle of the DSRR. Electrical characteristics of the CP can be deviated by an interaction between CP and a target gas, and then this deviation of electrical characteristic is demonstrated by S21 frequency response of the DSRR. To examine the performance of the proposed sensor, 100 ppm ethanol (C2H5OH) gas is exposed at room temperature. According to the measured result, the S21 resonance frequency of the DSRR is shifted by 220 MHz and simultaneously, the resonance amplitude is changed by 0.79 dB level. It is clearly found that the DSRR with CP material can be a good candidate for a sensitive gas sensor operating at microwave frequencies.

A reflection type gas sensor using conducting polymer as a variable impedance at microwave frquencies

In this paper, a gas sensor using a reflection type variable attenuator structure with conducting polymer (CP) is represented. A common gas sensing mechanism is to measure the conductivity or resistance of the CPs when it is exposed to gas. Because conductivity of the CPs varies due to the gas. A novelty in this paper is that the proposed sensor has employed the CPs as impedance-variable transmission lines that cause the impedance mismatching with conventional hybrid coupler. This structure can be thought as a variable attenuator or phase shifter. Experiment is conducted with 100 ppm ethanol gas at a temperature of 28°C and relative humidity of 80% (humidity condition). As a result the amplitude of S11 and the frequency satisfying ∠S21 = -360° is shifted about 2.875 MHz. It is that this reflection type sensor represented.

Proximity coupled vital sign sensor based on phase locked loop under injection

In this paper, a phase locked oscillator under injection is designed with proximity coupled vital sign sensor at 2.4 GHz. The proposed system is composed of a sensor oscillator with a planar resonator, a voltage controlled oscillator (VCO), and a phase locked loop (PLL) synthesizer. The planar resonator functions not only as a series feedback component to an oscillator but also as a detector which measures respiration and heartbeat signal. The input impedance of the planar resonator varies with the distance between the human body and the planar resonator. This impedance variation changes the oscillation frequency of the sensor oscillator. The sensor oscillator injects its output into the VCO so that the VCO is locked to the sensor oscillators frequency. Then the PLL applies the control voltage to the VCO to prevent frequency shifting by vital signs. Therefore, the VCO control voltage reflects vital signs. Measurement results prove that this sensor can detect vital sign up to 40 mm away from a subject.

High-frequency characteristics of conducting polymer for gas-sensor

In this paper, we report the intrinsic characteristics of conducting polymer for gas-sensor at high frequency region, i.e., 500 MHz to 10 GHz. To investigate the high-frequency characteristics of conducting polymer (CP), a coplanar waveguide electrode (CPW) is utilized. First, a CPW without CP, i.e., an open CPW, is simulated by a full-wave electromagnetic solver. From the simulated and measured result, we find that the open CPW shows clearly capacitive component. For a CPW with CP, it shows constant transmission characteristic of approximately 3-4 dB level at overall frequency region. This indicates that CP may be a good sensing material for detection of various gases or vapors in the high frequency region because its electrical properties can be sensitively varied with surface modification of gas absorption and desorption. As a result, if CP is possible to realize the various radio-frequency (RF) circuits and devices, we suggest that it can be used for diverse RF gas- as well as bio-sensing applications.

Vital Sign Sensor Based on Second Harmonic Frequency Drift of Oscillator

In this paper, a vital sign sensor based on impedance variation of resonator is proposed to detect the respiration and heartbeat signals within near-field range as a function of the separation distance between resonator and subject. The sensor consists of an oscillator with a built-in planar type patch resonator, a diplexer for only pass the second harmonic frequency, amplifier, SAW filter, and RF detector. The cardiac activity of a subject such as respiration and heartbeat causes the variation of the oscillation frequency corresponding impedance variation of the resonator within near-field range. The combination of the second harmonic oscillation frequency deviation and the superior skirt frequency of the SAW filter enables the proposed sensor to extend twice detection range. The experimental results reveal that the proposed sensor placed 40 mm away from a subject can reliably detect respiration and heartbeat signals.

RF Gas Sensor Using 4-Port Hybrid Coupler with Conducting Polymer

In this paper, a gas sensor using a modified hybrid coupler structure with conducting polymer which operates at 2.4 GHz is represented. Conducting polymers are used to the gas sensing material in proposed sensors. The conducting polymer varies its electrical property, such as work function and conductivity corresponding to the certain gas. To verify this variation of electrical property of conducting polymer at microwave frequencies, the conducting polymer is incorporated with the hybrid coupler structure, and this proposed sensor operates as reflection type variable attenuator and variable phase shifter. The conducting polymer is employed as impedence-variable transmission lines that cause a impedance mismatching between the general transmission line and conducting polymer. The experiment was conducted with 100 ppm ethanol gas at temperature of and relative humidity of 85 %. As a result, the amplitude deviation of is 0.13 dB and the frequency satisfying

Differential radial power combiner using substrate integrated waveguide

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