• 한국전자파학회논문지
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• 제27권2호
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• pp.163-169
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• 2016

본 논문에서는 소형 모바일 기기에 적용이 가능하도록 코일형 및 루프형 공진기의 평면화를 통해 소형화하여 자기공진형 무선전력전송 시스템을 구축하였다. 제안된 디스크형 이중코일공진기(disk type double coil resonator)는 아크릴 기판(acrylic substrate)의 양면에 얇은 구리 재질을 2 mm의 넓이(width)와 1 mm의 간격(pitch)으로 8번 감은 수의 나선코일패턴을 설계하여 최외각단을 연결한 구조이다. 이 공진기는 구리 재질의 패턴 길이에 의한 유도용량과 각 양쪽 나선코일패턴간의 아크릴 사이에 발생하는 정전용량을 이용하여 6.78 MHz에서 공진한다. 공진기에 설계된 나선코일패턴의 크기는 최외각 지름이 9 cm로 소형화 되었다. 급전 및 부하공진기로 사용되는 루프는 5 mm 굵기의 동선을 이용하여 지름 10 cm의 단일 루프로 구현하였다. 또한, 6.78 MHz에서 공진할 수 있도록 3,300 pF 커패시터(capacitor)를 직렬로 연결하였다. 디스크형 이중코일공진기의 특성을 알아보기 위해 다양한 공진기 재배열을 통해 시스템을 구성 및 측정하였으며, 소형 무선전력전송 시스템의 최대 전송효율은 35.67 %를 보였다. 제안된 공진기의 구조를 통해 더 작은 소형화 구조 설계가 가능할 것으로 기대된다.

• 대한물리의학회지
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• 제13권2호
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• pp.129-135
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• 2018

PURPOSE: The imbalance of pretibial muscles can be a factor contributing to the development of pes planus. However, no study has yet compared the muscle activity of the tibials anterior (TA) to that of the extensor digitorum longus (EDL). The purpose of this study was to determine whether there are differences in the electromyographic (EMG) TA and EDL amplitude indexes (AIs) between normal and pes planus feet. METHODS: A total of 14 subjects with normal feet and 15 subjects with bilateral pes planus participated in this study. TA and EDL muscle activities were measured using a wireless EMG system and the angles of ankle dorsiflexion and eversion of the subtalar joint were measured using a universal goniometer during active ankle dorsiflexion in the prone position. AI was calculated as follows: $\text{amplitude_{TA}-amplitude_{EDL}/(amplitude_{TA}+amplitude_{EDL})}/2{\times}100$. RESULTS: The AIs of the TA and EDL were significantly lower in pes planus feet than in normal feet (p<.05). The angle of subtalar eversion was significantly greater in pes planus feet than in normal feet during active ankle dorsiflexon (p<.05). However, there was no significant difference in the angle of ankle dorsiflexion between normal feet and pes planus feet (p>.05). CONCLUSION: This study showed that TA muscle activation was lower in pes planus feet than in normal feet, resulting from greater eversion range of motion during active ankle dorsiflexion. We suggest that the imbalance of ankle dorsiflexors must be considered in pes planus management.

• Korean Circulation Journal
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• 제54권3호
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• pp.140-153
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• 2024

Background and Objectives: Although a single-lead electrocardiogram (ECG) patch may provide advantages for detecting arrhythmias in outpatient settings owing to user convenience, its comparative effectiveness for real-time telemonitoring in inpatient settings remains unclear. We aimed to compare a novel telemonitoring system using a single-lead ECG patch with a conventional telemonitoring system in an inpatient setting. Methods: This was a single-center, prospective cohort study. Patients admitted to the cardiology unit for arrhythmia treatment who required a wireless ECG telemonitoring system were enrolled. A single-lead ECG patch and conventional telemetry were applied simultaneously in hospitalized patients for over 24 hours for real-time telemonitoring. The basic ECG parameters, arrhythmia episodes, and signal loss or noise were compared between the 2 systems. Results: Eighty participants (mean age 62±10 years, 76.3% male) were enrolled. The three most common indications for ECG telemonitoring were atrial fibrillation (66.3%), sick sinus syndrome (12.5%), and atrioventricular block (10.0%). The intra-class correlation coefficients for detecting the number of total beats, atrial and ventricular premature complexes, maximal, average, and minimal heart rates, and pauses were all over 0.9 with p values for reliability <0.001. Compared to a conventional system, a novel system demonstrated significantly lower signal noise (median 0.3% [0.1-1.6%] vs. 2.4% [1.4-3.7%], p<0.001) and fewer episodes of signal loss (median 22 [2-53] vs. 64 [22-112] episodes, p=0.002). Conclusions: The novel telemonitoring system using a single-lead ECG patch offers performance comparable to that of a conventional system while significantly reducing signal loss and noise.

• 대한의용생체공학회:의공학회지
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• 제43권2호
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• pp.124-130
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• 2022

In this paper, we proposed a portable electronic cardiogram and stethoscope (ECGS) that can simultaneously perform the electrocardiogram (ECG) and auscultation tests to increase the reliability of diagnosis of heart disease. To measure the ECG and heart sound (HS) at the same time, three ECG electrodes and a microphone sensor were combined into a triangular shape with a width of 90 mm and a height of 97 mm that can be held in one hand. In order to prevent skin problems when they contact the patient's skin, a capacitive coupled electrode was selected as the ECG electrode and a silicone material was used in a chest piece with the microphone sensor. For the signals measured from the electrodes and the chest piece, filters were respectively configured to pass only the signals of 0.01-100 Hz and 20-250 Hz, which are frequency bands for ECG and HS. The filtered ECG and HS analog signals were converted into digital signals and transmitted to a PC using wireless communication for monitoring them. The HS could be auscultated simultaneously using an earphone. The monitored ECG had an SNR of about 34 dB and a P-QRS-T waveform is clearly visible. In addition, the HS had an SNR of about 28 dB and both S₁ and S₂ are clearly visible. It is expected that it can aid doctors' inexperience in analyzing the ECG and HS.

• Journal of electromagnetic engineering and science
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• 제11권1호
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• pp.16-26
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• 2011

This paper presents high power and high efficiency Doherty amplifiers for 2.345 GHz wireless broadband (WiBro) applications that use a Nitronex 125-W ($P_{3dB}$) GaN high electron mobility transistor (HEMT). Two- and three-way Doherty amplifiers and a saturated Doherty amplifier using Class-F circuitry are implemented. The measured result for a center frequency of 2.345 GHz shows that the two-way Doherty amplifier attains a high $P_{3dB}$ of 51.5 dBm, a gain of 12.5 dB, and a power-added efficiency (PAE) improvement of about 16 % compared to a single class AB amplifier at 6-dB back-off power region from $P_{3dB}$. For a WiBro OFDMA signal, the Doherty amplifier provides an adjacent channel leakage ratio (ACLR) at 4.77 MHz offset that is -33 dBc at an output power of 42 dBm, which is a 9.5 dB back-off power region from $P_{3dB}$. By employing a digital pre-distortion (DPD) technique, the ACLR of the Doherty amplifier is improved from -33 dBc to -48 dBc. The measured result for the same frequency shows that the three-way Doherty amplifier, which has a $P_{3dB}$ of 53.16 dBm and a gain of 10.3 dB, and the saturated Doherty amplifier, which has a $P_{3dB}$ of 51.1 dBm and a gain of 10.3 dB, provide a PAE improvement of 11 % at the 9-dB back-off power region and 7.5 % at the 6-dB back-off region, respectively, compared to the two-way Doherty amplifier.

• 한국전문물리치료학회지
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• 제12권4호
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• pp.26-32
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• 2005

This study was purposed to provide basic information on the correct application of a wheelchair's backrest angle by investigating the change in cardiopulmonary function according to backrest angle during propulsion. This study examined the effects of the wheelchair's backrest angle on the cardiopulmonary function by varying the angle to $0^{\circ}$, $10^{\circ}$ and $20^{\circ}$ with a propulsion velocity of 60 m/min. The experimental parameters were respiration rate, oxygen consumption rate and oxygen consumption rate/kg which were measured by a portable wireless oxygen consumption meter (COSMED, $K4b^2$). The results of the study were as follows: 1) There were no statistically significant differences in respiration rates due to changes in the wheelchair backrest angle (p>.05). 2) There were statistically significant differences in oxygen consumption rates due to changes in the wheelchair backrest angle (p<.05). 3) There were also statistically significant differences in the oxygen consumption rate/kg due to changes in the wheelchair backrest angle (p<.05). In conclusion, changes in the backrest angle of wheelchairs during propulsion influences oxygen consumption rates and heart rates, while respiration rates are not affected. Therefore, a training program for good seating and posture needs to be provided, and the wheelchair seating system should be equipped with the unadjustable-angle wheelchair to reduce the functional load on the cardiopulmonary system.

• 대한물리의학회지
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• 제9권4호
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• pp.347-354
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• 2014

PURPOSE: This study was to examine changes in muscle activity of lower extremity shoes sole form (high heels, shoes with curved out sole, house shoes). METHODS: The subjects of this study were 12 women in their twenties. They put three kinds of shoes (high heels, shoes with curved out sole, house shoes) and walked 5m. The muscles activities of lower extremity muscles (rectus femoris, vastus medialis, tibialis anterior, gastrocnemius medial part) were measured using a wireless electromyogram (EMG). Rectus femoris was attached to 1/2 position at the distance between ASIS and knee bone and vastus medials was attached to 2cm from upper inside of knee bone. Tibialis anterior was attached to 75% position above line connecting knee joint and ankle joint and gastrocnemius medial part was attached to 3 5% position above knee joint and ankle. RESULTS: It was found that there were significant differences in changes of muscles activities of lower extremity muscles (rectus femoris, vastus medialis, tibialis anterior, gastrocnemius medial part) on shoes sole forms (p<.05). All lower extremity muscles were showed high muscles activities, when high heels wear (p<.05). Wearing shoes with curved out sole was showed high muscle activity of tibialis anterior and lower muscle activity of gastrocnemius medial part compared with wearing house shoes (p<.05). CONCLUSION: Shoes sole form should be considered when patients with knee and ankle joint problems choose shoes because muscles were showed different activities according to shoes sole forms.

• 한국전기전자재료학회논문지
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• 제21권4호
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• pp.311-320
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• 2008

In this paper, a 2.4 GHz low-voltage CMOS double-balanced down-conversion mixer using neutralization technique has been proposed and verified by circuit simulations and measurements. The grounded source structure was used for low-voltage operation. The neutralization technique was used to improve a conversion gain. The proposed mixer is fabricated in $0.25{\mu}m$ CMOS process for a 2.4 GHz wireless receiver. The mixer consumes 1.94 mW and gives conversion gain of 5.66 dB, input IP3 of 0.7 dBm and P1dB of -11.2 dBm at 1.5 V power supply. Measured results for the designed mixer show improved conversion gain of 2.86 dB over conventional mixer of grounded source structure.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2008년도 하계학술대회 논문집 Vol.9
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• pp.184-184
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• 2008

In this paper, a power divider with a multi-band and broadband are designed and fabricated using an InGaP/GaAs process. The design of this divider is based on multi-band because it is important in the next generation IMT-Advances system. In this design, power divider is fabricated with the frequency of 824 MHz to 894 MHz, 1.8 GHz to 2.2 GHz and 2.3 GHz to 2.4 GH for cellular, personal communication system (PCS) and Wireless Broadband Internet (WiBro). The topology of the designed power divider is based on the multi-section and fabricated using integrated passive device (IPD) library of nanoENS Inc. It is measured using network analyzer.

• 대한전자공학회논문지TC
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• 제37권2호
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• pp.7-16
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• 2000

본 논문에서는 p-persistent CSMA 방식의 IEEE 802.11 MAC 계층 프로토콜을 모델링 하였다. 그리고 renewal 이론을 적용하여 수학적으로 분석한 Basic CSMA/CA 프로토콜, CTS/RTS 프로토콜 그리고 은닉 노드를 고려한 Basic CSMA/CA 등의 성능분석모델을 제안하였다. 제안한 분석 모델을 이용하여 throughput을 구한 결과, active 노드 수가 적거나 패킷의 길이가 짧을 때는 Basic CSMA/CA 프로토콜 방식이, active 노드 수가 많거나 패킷의 길이가 길 때는 CTS/RTS 프로토콜 방식이 우수하였다. 또한 active 노드 수가 적은 경우가 많은 경우 보다 은닉 노드의 영향을 적게 받았다.