Heungjae Choi

Design of Dual-Band Bandpass Filter Using DGS With Controllable Second Passband

In this letter, the application of a variable characteristic impedance transmission line that can be used to design a dual-band bandpass filter (BPF) is presented. The proposed filter offers a fixed first passband and a controllable second passband. The tuning of the second passband is achieved by varying the characteristic impedance of the shunt open stub of stub loaded resonator (SLR) with the help of a defected ground structure (DGS) transmission line and varactor diodes. In order to validate the theoretical predictions and simulated results, a two stage dual-band BPF with three transmission zeros was implemented and experimentally verified.

Design and In Vitro Interference Test of Microwave Noninvasive Blood Glucose Monitoring Sensor

A design of a microwave noninvasive continuous blood glucose monitoring sensor and its interference test results are presented. The novelty of the proposed sensor is that it comprises two spatially separated split-ring resonators, where one interacts with the change in glucose level of a sample under test while the other ring is used as a reference. The reference ring has a slightly different resonant frequency and is desensitized to the sample owing to its location, thus allowing changes in temperature to be calibrated out. From an oral glucose tolerance test with two additional commercially available sensors (blood strip and continuous glucose monitor) in parallel, we obtained encouraging performance for our sensor comparable with those of the commercial sensors. The effects of endogenous interferents common to all subjects, i.e., common sugars, vitamins (ascorbic acid), and metabolites (uric acid) have also been investigated by using a large Franz cell assembly. From the interference test, it is shown that the change in sensor response is dominated by changes in glucose level for concentrations relevant to blood, and the effects of interferents are negligible in comparison.

Adaptive Coupling of Resonators for Efficient Microwave Heating of Microfluidic Systems

An electronically adaptive coupling technique is presented for a microwave microstrip resonator to improve the efficiency of liquid heating in a microfluidic system. The concept is based on feeding the resonator with two synchronized inputs that have a variable phase shift between them. A Wilkinson power divider and phase shifter were designed and fabricated for this purpose. Both simulation and measurement (using chloroform as an exemplar liquid) demonstrated that the adaptive coupling can be used to optimize the heating efficiency of the liquid.

A Research on the Magnitude/Phase Asymmetry Measurement Technique of the RF Power Amplifier Based on the Predistortive Tone Cancellation Technique

This paper proposes a novel memory effect measurement technique in RF power amplifiers(PAs) using a two-tone intermodulation distortion(IMD) signal with a very simple and intuitive algorithm. Based on the proposed predistortive tone cancellation technique, the proposed measurement method is capable of measuring the relative phase and magnitude of the third-order and fifth-order IMDs, as well as the fundamental signal. The measured relative phase between the higher and lower IMD signal for specific tone spacing can be interpreted as the group delay(GD) information of the IMD signal concerned. From the group delay analysis, we can conclude that an adaptive control of GD as well as the magnitude and phase is a key function in increasing the linearization bandwidth and the dynamic range in a predistortion(PD) technique.

Development of a RF waveform stress test procedure for GaN HFETs subjected to infinite VSWR sweeps

An RF waveform stress test has been developed in order to assess device degradation caused by the infinite VSWR conditions that could result from the removal of a protection isolator. The proposed stress test involves both DC and RF characterization of a device, before and after an RF stressing mechanism is applied. The procedure was first applied with the device being stressed whilst driving into its optimum impedance and secondly with the device being stressed by one of the three potential failure regions that result from an infinite VSWR sweep.

Design of continuous non-invasive blood glucose monitoring sensor based on a microwave split ring resonator

In this paper, a design of truly non-invasive continuous blood glucose monitoring sensor which uses a pair of microwave split ring resonators is presented, operating around 1.4 GHz. The rings are made from silver coated copper wire. In addition to the sensing ring, a reference ring is added which operates at a higher frequency. This is used to take into account the temperature dependent expansion of the ring and to calibrate out any effects due to changes in temperature. The proposed sensor made up of the pair of rings is directly attached onto the skin in the abdominal area by using an adhesive patch. For validation, we have tested the proposed sensor simultaneously with two commercially available sensors (blood strip and continuous glucose monitor) over 12 hour periods with 3 food events, with encouraging correlation of our blood glucose results with those of the commercial sensors.

Continuous class BJ power amplifier with DGS output matching

This paper presents the design, implementation, and experimental evaluation of a high efficiency continuous Class BJ mode power amplifier, using a compact defected ground structure (DGS) to provide the necessary output matching and harmonic termination for broadband operation. Detailed consideration has been given to the DGS microstrip line impedance and corresponding equalization network, in order to achieve the required fundamental and harmonic matching. The method is demonstrated through design and realization of an amplifier using a commercially available 10W GaN HEMT transistor that achieves efficiencies above 70% over a 600MHz bandwidth with an output power of at least 40 dBm.

Group Delay Time Matched CMOS Microwave Frequency Doubler

PURPOSE: A ground delay time matched CMOS microwave frequency multiplier is provided to adjust a phase error between two input signals of an XOR gate by controlling a group delay time with voltage controlled delay line. CONSTITUTION: In a ground delay time matched CMOS microwave frequency multiplier, a hysteresis comparator(100) receives an input signal and converts a sinusoidal wave into a square wave. The hysteresis comparator controls a duty cycle of the square wave according to a change of a control voltage constant. A delay element(200) is installed at an output terminal of the hysteresis comparator. The delay element delays the square wave inputted through the hysteresis comparator by 90°, and a voltage controlled delay line(300) is installed in parallel with the delay element. The voltage controlled delay line compensates the group delay time of the delay signal outputted through the delay element according to the change of the control voltage. An XOR gate(400) outputs a desired amplified signal through two signals inputted from the delay element and the voltage controlled delay line.

Microwave noninvasive blood glucose monitoring sensor: Human clinical trial results

In this paper, a microwave non-invasive blood glucose monitoring system operating at around 1.4 GHz is designed and its performance in terms of accuracy and repeatability is evaluated by a clinical trial involving 24 human subjects, with and without diabetes. Direct comparison with the most accurate benchtop glucose analyzer shows the exceptional accuracy and repeatability of the proposed system.

A high power high efficiency integrated solid-state microwave heating structure for portable diagnostic healthcare applications

This paper presents a novel approach for designing solid-state microwave heating arrangement designed for portable and field-deployable microwave assisted health-care diagnostic application. The arrangement contains a purpose-build TM010 mode Circular microwave cavity driven by a 10W-LDMOS power transistor as microwave source. In this method, the natural impedance environment of the resonant cavity has been considered as a function of temperature, and used to present the inherent optimal loading conditions to the 10W LDMOS power transistor for achieving high-efficiency operation over the operational bandwidth of the cavity resonator. Significant reduction in the output matching network complexity using simple microstip series lines and straightforward integration into a microwave resonant cavity makes this structure suitable for portable health-care diagnostic applications. In this demonstrator, an in-built directional coupler has also been included at output stage of power amplifier to measure the RF power and to reduce the physical size of the microwave heating arrangement. Measurement results show more than 60% Power Added Efficiency, above 40dBm output power and above 20dB Gain over the targeted Bandwidth and expected temperature variation.