ABSTRACT The photodielectric effect in antimony-doped tin oxide (Sb:SnO2) was observed by using t... more ABSTRACT The photodielectric effect in antimony-doped tin oxide (Sb:SnO2) was observed by using the microwave cavity perturbation method. The results show that the dielectric constant and the losses change upon a long 30 second exposure of 365nm irradiation. On turning off the irradiation, the dielectric constant and losses tend back towards their dark state values though never reach their starting value implying evidence of some permanently excited state within the material.
ABSTRACT A design method for an L-band frequency quadrupler with composite right/left-handed tran... more ABSTRACT A design method for an L-band frequency quadrupler with composite right/left-handed transmission line is proposed. The left-handed transmission line in the proposed frequency quadrupler suppresses the fundamental component ( f 0), while the composite right/left-handed lambda/4 open stub reduces unwanted higher-order harmonics. From the experimental results, unwanted harmonics are suppressed to achieve harmonic distortion of 51lambdadBc minimum with output phase noise of lambda94.34lambdadBc/Hz at 10lambdakHz offset.
ABSTRACT In this paper, a group delay time controller (GDTC) is proposed based on a reflection to... more ABSTRACT In this paper, a group delay time controller (GDTC) is proposed based on a reflection topology employing a parallel resonator as the reflection termination. The design equations of the proposed GDTC have been derived and validated by simulation and experimental results. The group delay time can be varied by varying the capacitance and inductance at an operating frequency. To show the validity of the proposed circuit, an experiment was performed for a wideband code division multiple access downlink band operating at 2.11 GHz to 2.17 GHz. According to the experiment, a group delay time variation of 3 +/- 0.17 ns over bandwidth of 60 MHz with excellent flatness is obtained.
2014 Ieee Mtt S International Microwave Workshop Series on Rf and Wireless Technologies For Biomedical and Healthcare Applications, Dec 1, 2014
ABSTRACT In this paper, a design of truly non-invasive continuous blood glucose monitoring sensor... more ABSTRACT 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.
This paper presents a method to control group delay tine using a resonance circuit. The group del... more This paper presents a method to control group delay tine using a resonance circuit. The group delay time adjuster(GDTA) that can control signal group delay time comprises a variable capacitance and a variable equivalent inductor. These are coupled in parallel at a node and also controlled by two bias voltages separately, A variable equivalent inductor is realized a transmission line terminated a variable capacitor. Group delay time can be controlled by change of capacitance and inductance, but the resonating frequency is fixed. When the proposed GDTA is fabricated on RFID Korean frequency band, a group delay variation is obtained about 3 ns.
In this work, a digital controlled co-channel feedback interference cancellation system is propos... more In this work, a digital controlled co-channel feedback interference cancellation system is proposed to reduce the feedback interference signal in the wireless repeater system. Frequency hopping spread spectrum pilot tone is adopted for the adaptive group delay detection of the feedback path. Amplitude, phase, and group delay of the feedback path are automatically detected and controlled through the comparison algorithm
IEEE Transactions on Microwave Theory and Techniques, 2015
A design of a microwave noninvasive continuous blood glucose monitoring sensor and its interferen... more 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.
2014 IEEE MTT-S International Microwave Workshop Series on RF and Wireless Technologies for Biomedical and Healthcare Applications (IMWS-Bio2014), 2014
ABSTRACT In this paper, a design of truly non-invasive continuous blood glucose monitoring sensor... more ABSTRACT 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.
2011 IEEE MTT-S International Microwave Symposium, 2011
ABSTRACT In this paper, we propose a novel composite negative group delay circuit to reduce the s... more ABSTRACT In this paper, we propose a novel composite negative group delay circuit to reduce the signal attenuation required to obtain negative group delay. It is already known that negative group delay can be obtained in a specific frequency of signal attenuation. For the same negative group delay of -6 ns, the signal attenuation of the conventional circuit is 31.25 dB, while the proposed composite circuit involves signal attenuation of only 13.9 dB. As a result, the number of gain compensating amplifiers can be reduced. This contributes to the efficiency enhancement as well as out-of-band noise reduction and stable operation when integrated into the power amplifier linearization system.
ABSTRACT The photodielectric effect in antimony-doped tin oxide (Sb:SnO2) was observed by using t... more ABSTRACT The photodielectric effect in antimony-doped tin oxide (Sb:SnO2) was observed by using the microwave cavity perturbation method. The results show that the dielectric constant and the losses change upon a long 30 second exposure of 365nm irradiation. On turning off the irradiation, the dielectric constant and losses tend back towards their dark state values though never reach their starting value implying evidence of some permanently excited state within the material.
ABSTRACT A design method for an L-band frequency quadrupler with composite right/left-handed tran... more ABSTRACT A design method for an L-band frequency quadrupler with composite right/left-handed transmission line is proposed. The left-handed transmission line in the proposed frequency quadrupler suppresses the fundamental component ( f 0), while the composite right/left-handed lambda/4 open stub reduces unwanted higher-order harmonics. From the experimental results, unwanted harmonics are suppressed to achieve harmonic distortion of 51lambdadBc minimum with output phase noise of lambda94.34lambdadBc/Hz at 10lambdakHz offset.
ABSTRACT In this paper, a group delay time controller (GDTC) is proposed based on a reflection to... more ABSTRACT In this paper, a group delay time controller (GDTC) is proposed based on a reflection topology employing a parallel resonator as the reflection termination. The design equations of the proposed GDTC have been derived and validated by simulation and experimental results. The group delay time can be varied by varying the capacitance and inductance at an operating frequency. To show the validity of the proposed circuit, an experiment was performed for a wideband code division multiple access downlink band operating at 2.11 GHz to 2.17 GHz. According to the experiment, a group delay time variation of 3 +/- 0.17 ns over bandwidth of 60 MHz with excellent flatness is obtained.
2014 Ieee Mtt S International Microwave Workshop Series on Rf and Wireless Technologies For Biomedical and Healthcare Applications, Dec 1, 2014
ABSTRACT In this paper, a design of truly non-invasive continuous blood glucose monitoring sensor... more ABSTRACT 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.
This paper presents a method to control group delay tine using a resonance circuit. The group del... more This paper presents a method to control group delay tine using a resonance circuit. The group delay time adjuster(GDTA) that can control signal group delay time comprises a variable capacitance and a variable equivalent inductor. These are coupled in parallel at a node and also controlled by two bias voltages separately, A variable equivalent inductor is realized a transmission line terminated a variable capacitor. Group delay time can be controlled by change of capacitance and inductance, but the resonating frequency is fixed. When the proposed GDTA is fabricated on RFID Korean frequency band, a group delay variation is obtained about 3 ns.
In this work, a digital controlled co-channel feedback interference cancellation system is propos... more In this work, a digital controlled co-channel feedback interference cancellation system is proposed to reduce the feedback interference signal in the wireless repeater system. Frequency hopping spread spectrum pilot tone is adopted for the adaptive group delay detection of the feedback path. Amplitude, phase, and group delay of the feedback path are automatically detected and controlled through the comparison algorithm
IEEE Transactions on Microwave Theory and Techniques, 2015
A design of a microwave noninvasive continuous blood glucose monitoring sensor and its interferen... more 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.
2014 IEEE MTT-S International Microwave Workshop Series on RF and Wireless Technologies for Biomedical and Healthcare Applications (IMWS-Bio2014), 2014
ABSTRACT In this paper, a design of truly non-invasive continuous blood glucose monitoring sensor... more ABSTRACT 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.
2011 IEEE MTT-S International Microwave Symposium, 2011
ABSTRACT In this paper, we propose a novel composite negative group delay circuit to reduce the s... more ABSTRACT In this paper, we propose a novel composite negative group delay circuit to reduce the signal attenuation required to obtain negative group delay. It is already known that negative group delay can be obtained in a specific frequency of signal attenuation. For the same negative group delay of -6 ns, the signal attenuation of the conventional circuit is 31.25 dB, while the proposed composite circuit involves signal attenuation of only 13.9 dB. As a result, the number of gain compensating amplifiers can be reduced. This contributes to the efficiency enhancement as well as out-of-band noise reduction and stable operation when integrated into the power amplifier linearization system.
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Papers by Heungjae Choi