• Proceedings of the Acoustical Society of Korea Conference
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• 1997.06a
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• pp.53-56
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• 1997

Tonpilz 압전변환기에 관하여 유한요소법을 사용하여 공기중의 동특성 해석과 수중의 방사임피던스를 해석하였다. 공기중에서 트랜스듀서의 구조를 변화시키면서 입력 어드미턴스 특성과 진동모드를 해석하여 압전변환기를 모델링하였다. 음향 윈도우를 압전변환기 전면에 부착한 후 유한요소법(FEM)에 의하여 매질의 영향을 고려한 입력어드미턴스 특성을 해석하였으며, 또한 방사임피던스 계산 루틴을 추가하여 무한 배플의 경계조건하에서 방사 임피던스를 해석하였다. 공기중과 수중에서의 해석을 통하여 Tonpilz 압전변환기 단일 소자의 구조 변경 및 기계 부재의 추가등에 따라 변동하는 변환기의 특성 및 방사 임피던스를 해석하므로서 평면 배열형 음향 트랜스듀서의 설계에 필요한 파라메터를 구할 수있다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.4
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• pp.789-794
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• 2011

A coaxial-cable impedance transformer used in wideband frequency range is generally restricted to the fixed impedance transformation ratio as n2:1 or 1:n2(n: the number of coaxial cables). In this paper, we propose a new coaxial-cable impedance transformer to have an arbitrary impedance transformation ratio. We have fabricated three impedance transformers($50-{\Omega}$ to $25-{\Omega}$, $50-{\Omega}$ to $20-{\Omega}$ and $50-{\Omega}$ to $9-{\Omega}$) to confirm the operation characteristic of the suggested impedance transformer. The reflection characteristics (S11) of the fabricated $50-{\Omega}$ to $25-{\Omega}$ and $50-{\Omega}$ to $20-{\Omega}$ impedance transformer were less than -15dB over about 3-octaves frequency range and the reflection characteristic (S11) of the fabricated $50-{\Omega}$ to $9-{\Omega}$ impedance transformer was less than -15dB over about 1-octave frequency range, respectively.

• Journal of the Korean Society for Nondestructive Testing
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• v.37 no.1
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• pp.37-43
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• 2017

Ultrasonic transducers with high resolution and resonant frequency are required to detect small defects (less than hundreds of ${\mu}m$) by ultrasonic testing. The resonance frequency and resolution of an ultrasonic transducer are closely related to the thickness of piezo-electric materials, backing materials, and the electric impedance matching technique. Among these factors, electrical impedance matching plays an important role because it can reduce the loss and reflection of ultrasonic energy differences in electrical impedance between an ultrasonic transducer and an ultrasonic defects detecting system. An LC matching circuit is the most frequently used electric matching method. It is necessary for the electrical impedance of an ultrasonic transducer to correspond to approximately $50{\Omega}$ to compensate the difference in electrical impedance between both connections. In this study, a 15 MHz immersion ultrasonic transducer was fabricated and an LC electrical impedance circuit was applied to that for having broad-band frequency characteristic.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.18 no.11
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• pp.1767-1773
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• 1993

In this paper, the coupling characteristics as well as the self and the mutual Impedance of a two-element probe-fed stacked circular microstrip array antennas are presented. A full wave analysis for the structure is performed In the spectral domain using the vector Hankel transform(VHT). Also, we presented measured results for the impedance, the coupling characteristics of the antenna and the variation of the coupling with the distance between the two elements. Finally, the calculated and measured results are shown to agree well wlth each other through comparisons.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.26 no.7
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• pp.597-605
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• 2015

Negative impedance converter(NIC)-based non-Foster impedance matching is proposed for an electrically small antenna. The antenna considered in this work is a resistively loaded vee dipole(RVD) antenna, which has considerable reflection at the feed point because of its large negative input reactance. The non-Foster matching circuit built near the feed point consists of two-stage NIC circuit and a capacitor connected between the stages. The NIC is realized by using operational amplifiers(op-amps) and resistors. The circuit is designed by considering of the input impedance according to the finite open-loop gain of the practical NICs. The stability test of the impedance-matched RVD antenna is performed. The non- Foster matching circuit is implemented with the RVD antenna. The measured impedance demonstrates that the proposed non-Foster matching circuit effectively reduces the input reactance of the RVD antenna.

• Journal of Advanced Marine Engineering and Technology
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• v.36 no.1
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• pp.149-156
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• 2012

In this study, we propose a novel transmission line employing inverted PACD (Periodically Arrayed Capacitive Devices) for application to a development of miniaturized passive components on MMIC. The novel microstrip line employing Inverted PACD structure showed a loss much lower than conventional microstrip line. Using the inverted PACD structure, we fabricated a miniaturized impedance transformer on MMIC. the size of the impedance transformer was 0.012 $mm^2$, which is only 1.7% of conventional one. The impedance transformer showed good RF performances in a frequency range of 2.25~6.5 GHz.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.26 no.3
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• pp.283-291
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• 2015

In this paper, a negative impedance converter, the key element of non-Foster matching to enhance the bandwidth of matching high Q-factor passive element, is presented. Proposed negative impedance converter is implemented by the topology of Linvill's transistor negative impedance converter circuit. It is hard to forecast the operation of negative impedance circuit, because it is composed of gain element and positive feedback. Therefore the negative impedance circuit is implemented by hybrid type beforehand to check out the feasibility and it is designed by integrated circuit. The integrated circuit is fabricated by commercial $0.18{\mu}m$ SiGe BiCMOS process, and non-Foster matching is observed at 700~960 MHz band by cancelling the target reactance.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.6
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• pp.582-589
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• 2002

This paper presents 12.2 GHz ~ 12.7 GHz frequency band reflection type 5-bit digital phase shifter with constant insertion loss property that was fabricated with relatively low cost's InGaAs HEMT for amplifier. The unavoidable large insertion loss difference between on and off states of HEMT, when it is designed by conventional design theory based on ideal switching device, is removed by transforming the HEMT impedances at on and off states to other proper values connecting a certain length transmission line to HEMT and then applying the conventional design theory. The fabricated 5-bit digital phase shifter shows very good insertion loss properties of less than 1.5 dB insertion loss difference and -4.5 dB ~ -6 dB insertion loss in 35 phase steps at 12.2 GHz ~ 12.7 GHz. These results verify the design method presented in this paper, which is useful to design phase shifter of constant insertion loss with non-ideal switching device.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.26 no.11
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• pp.1686-1696
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• 2022

The impedance matching circuit design technique based on the phasor plot introduced in this paper is based on the impedance triangle of electric circuit. It is a technique that designs through the construction of a phasor figure using the values given to the matching circuit design. The design pattern is based on L-type, inverted L-type, T-type, and 𝜋-type, and unknown reactance elements are determined through phasor shapes. In this paper, using a design by phasor plot, we design several cases, such as the case where the input and output ports are pure resistance and have reactance. It was confirmed that the design value was verified by serial-parallel equivalent conversion to achieve matching. This design technique can immediately grasp the phase or size of input/output power, so it is expected to be applied mainly in a low frequency band due to rapid design change and application.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2010.04a
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• pp.347-351
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• 2010

판과 같은 구조물의 손상 감지를 위해, 손상 전 구조물의 임피던스 신호를 기저신호(Baseline impedance signal)로 이용하여 직접적으로 비교하지 않는 새로운 개념의 무기저 손상진단 기법(Reference-free impedance method)을 제시한다. 박막 압전소자(이하 PZT)를 판의 상하 표면에 부착시킨 한 쌍의 병치 PZT를 이용하여 손상으로 인해 모드변환을 일으키는 전기역학적 신호(Electro Mechanical Signatures ; 이하 EMS)를 추출한다. 이 연구에서는 스펙트럼 요소법(Spectral Element Method ; 이하 SEM)을 이용하여 주파수 영역에서 병치된 PZT의 EMS를 파악하기 위한 수치해석을 수행한다. 특히, 손상에 의해 발생된 모드변환 EMSMC를 병치된 PZT의 극성에 기인한 신호분해 기법을 적용하여 추출하고, 분해된 모드변환 EMSMC가 손상의 위치와 크기에 따라 받는 영향을 추가로 분석한다.