Gi-Ho Yun

Numerical analysis of the propagation characteristics of multiangle multislot coaxial cable using moment method

In this paper, multiangle multislot coaxial cable is analyzed qualitatively and quantitatively. This is the extended result of the previous studies of the single-slot coaxial cable. The properties of this cable have been studied by many authors, especially for the surface-wave type. However, the slotted coaxial cable utilizing leaky waves has not been treated rigorously despite its wide use. In this paper, a numerical analysis of a leaky coaxial cable with a multiangle multislot configuration is performed to obtain many useful results, which are impossible to derive employing the approximate model frequently used in this area. Using the moment method, the propagation constant has been obtained for the leaky coaxial cable as a function of various parameters. Several slot configurations are considered to give insight into the properties of coupling loss and transmission loss complicated by simultaneous existence of leaky and surface waves.

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.

Compact Vital Signal Sensor Using Oscillation Frequency Deviation

In this paper, a compact vital signal sensing method using oscillation frequency deviation at 2.4-GHz industrial-scientific-medical band is proposed to detect vital signals, such as heartbeat and respiration signal. The oscillation circuit of the proposed vital sensor system has been realized by a planar resonator, which functions as a positive feedback element, as well as a near-field radiator to sense vital signals, simultaneously. The periodic movement of a body by respiration exercise causes the impedance variation of the radiator within the near-field range. The impedance variation results in a corresponding change in the oscillation frequency, and this variation has been utilized for sensing of the vital signals. In addition, a surface acoustic wave filter and power detector have been used to increase the sensitivity of the system and to transform the frequency variation to voltage waveform. The experimental results show that the proposed vital sensor placed 20 mm from the body can detect the heartbeat waveform very accurately.

Wrist Pulse Detection System Based on Changes in the Near-Field Reflection Coefficient of a Resonator

This letter presents a wrist pulse sensor based on reflection coefficient (S11) from a resonator which is applicable to existing wearable communication devices. The compact resonator is designed on flexible substrate as an RF signal radiator. Since the reflection coefficient from the resonator depends on the distance between the resonator and the wall of the major artery, slight changes in radial artery diameter can be utilized to obtain pulse rate at the wrist. The sensor system is implemented and tested at 2.4 GHz ISM band, and reveals excellent performance in terms of sensitivity as well as convenience as a wearable device compared to conventional piezoelectric or photoplethysmography (PPG) sensor.

Wireless RF Sensor Structure for Non-Contact Vital Sign Monitoring

This paper describes a compact and novel wireless vital sign sensor at 2.4 GHz that can detect heartbeat and respiration signals. The oscillator circuit incorporates a planar resonator, which functions as a series feedback element as well as a near-field radiator. The periodic movement of a human body during aerobic exercise could cause an input impedance variation of the radiator within near-field range. This variation results in a corresponding change in the oscillation frequency and this change has been utilized for the sensing of human vital signs. In addition, a surface acoustic wave (SAW) filter and power detector have been used to increase the system sensitivity and to transform the frequency variation into a voltage waveform. The experimental results show that the proposed sensor placed 20 mm away from a human body can detect the vital signs very accurately.

Wireless RF Vital Signal Sensor Using Autoregressive Spectral Estimation Method

This letter describes a compact and novel wireless vital signal sensor at 2.4 GHz that can detect heartbeat and respiration signals. The oscillator circuit incorporates a planar resonator, which functions as a series feedback element as well as a near-field radiator. The periodic movement of the body during aerobic exercise causes an input impedance variation of the radiator within the near-field range. This variation results in a corresponding change in the oscillation frequency, and this change has been utilized for detection of human vital signals. In addition, a surface acoustic wave (SAW) filter and power detector have been used to increase the system sensitivity and to transform the frequency variation into a voltage waveform. Also, the autoregressive spectral estimation method is applied to achieve precise vital sign detection. The experimental results show that the proposed sensor placed 20 mm away from a human body can detect the vital signals very accurately.

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.

Adaptive burst coherent demodulation for fast flat Rayleigh fading channels

Adaptive burst coherent demodulation scheme is studied. This scheme is suitable for applications having burst slots in fast flat fading environment such as TDMA radio communication systems. It coherently demodulates individual bursts of TDMA symbols using an infinite impulse response (IIR) adaptive phase tracking system. This adaptive structure can track time-varying phase jitter introduced by fast Rayleigh fading channels. So, any modification is not needed in the conventional transmitter. In the receiver, the adaptive parameter set for the highest Doppler frequency considered can be used without changing for lower cases, thus requiring no fading statistics estimation. The error-floors caused by the Doppler spread are lowered up to one third of that in conventional differential detection.