• 전력전자학회논문지
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• 제19권4호
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• pp.364-375
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• 2014

Parametric array transducers are used for long-range and highly directional communication in an underwater environments. The power amplifiers for parametric array transducers should have sufficient linear output characteristic and high efficiency to avoid communication errors, system heating, and fuel problems. But the conventional power amplifier with fixed source voltage is very low efficient due to large power loss by the big difference between the fixed source voltage and the amplifier output voltage. Thus to solve the problems this paper proposes the high efficiency power amplifier for parametric array transducers. The proposed power amplifier ensures high linearity of output characteristic by utilizing the push-pull class B type amplifier and furthermore gets high efficiency by applying the envelope tracking technique that variable source voltage tracks the envelope of the amplified signal. Also the paper suggests the detailed circuit topology and design guideline of class B push-pull type amplifier and variable output voltage AC/DC converter. Its characteristics are verified by the detailed simulation and experimental results.

• 전기학회논문지
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• 제67권3호
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• pp.383-390
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• 2018

Piezoelectric micro-machined ultrasonic transducers for highly directional speaker need DC bias voltage. Most existing power amplifiers are not suitable for use in highly directional transducers because they are based on AC. In addition, since the piezoelectric micro-machined ultrasonic transducer has a large capacitive reactance, the power efficiency of the power amplifier is very low. Thus this paper proposes a new high efficiency power amplifier with DC bias voltage. In addition, by designing a matching circuit to compensate the capacitive reactance of the micro-machined ultrasonic transducer, the power efficiency of the power amplifier increases. The operating characteristics of the proposed power amplifier was verified by an experimental prototype. The proposed power amplifier is expected to be widely used in designing and implementing other related power amplifiers.

• 전기학회논문지
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• 제66권8호
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• pp.1215-1221
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• 2017

Parametric array transducers are used for highly directional speaker in an air environments. Piezoelectric micromachined ultrasonic transducers for parametric array transducers need DC-biased voltage driving signals in order to get high-directional quality-sound features. The existing power amplifier such as class A amplifiers has low efficiency and require large volume heatsinks. To overcome the above-mentioned disadvantages of the conventional amplifier, this paper proposes a new power amplifier system. The proposed power amplifier system ensures high linearity of output characteristic by utilizing the push-pull class B type amplifier. Furthermore, the proposed power amplifier system gets high efficiency because it contains the DC-DC converter-type power supply which can perform energy recovery and envelope tracking function. Also the paper suggests the detailed circuit topology. Its characteristics are verified by the detailed experimental results.

• 한국세라믹학회지
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• 제39권9호
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• pp.813-817
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• 2002

Magnetoelectric(ME) laminate composites of $Pb(Mg_{1/3}Nb_{2/3})O_3-PbTiO_3 (PMN-PT)$ and Terfenol-D were prepared by sandwiching single crystals of PMN-PT between Terfenol-D disks. The magnetoelectric voltage coefficient (dE/dH) of the composite was determined to be 10.30 V/cm${\cdot}$Oe, at 1 kHz and under a dc magnetic bias of 0.4 T. The value of dE/dH is ∼80 times higher than either that of naturally occurring magnetoelectrics or artificially-grown magnetoelectric composites. This superior magnetoelectric voltage coefficient is attributed to the high piezoelectric voltage constant as well as the high elastic compliance of PMN-PT single crystal and the large magnetostrictive response of Terfenol-D.

• 센서학회지
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• 제29권5호
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• pp.283-292
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• 2020

Current sensors that use a Hall element and Hall IC to measure the magnetic fields generated in steel silicon core gaps do not distinguish between direct and alternating currents. Thus, they are primarily used to measure direct current (DC) in industrial equipment. Although such sensors can measure the DC when installed in expensive equipment, ascertaining problems becomes difficult if the equipment is set up in an unexposed space. The control box is only opened during scheduled maintenance or when anomalies occur. Therefore, in this paper, a method is proposed for facilitating the safety management and maintenance of equipment when necessary, instead of waiting for anomalies or scheduled maintenance. A Bluetooth 4.0 low-energy current-sensor system based on near-field communication is used, which compensates for the nonlinearity of the current-sensor output signal using a piecewise linear model. The sensor is controlled using its generic attribute profile. Sensor nodes and cell phones used to check the signals obtained from the sensor at 50-A input currents showed an accuracy of ±1%, exhibiting linearity in all communications within the range of 0 to 50 A, with a stable output voltage for each communication segment.

• Journal of Magnetics
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• 제16권4호
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• pp.461-465
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• 2011

Traditional magnetostrictive/piezoelectric laminate composites are generally in the regular geometries such as rectangles or disks. To explore properties of the irregular geometry magnetostrictive/piezoelectric transducer in the fundamental resonant frequency, a step dumb-bell shaped Magnetoelectric (ME) transducer is presented in this study. Both analytical and experimental investigations are carried out for the dumb-bell shaped transducer in the fundamental frequency. Comparing with the traditional rectangular transducer, the theory shows the resonant frequency of dumb-bell shaped transducer is reduced 31%, and the experiment gives the result of that is 37% which is independent of dc magnetic fields. The ratio of magnetoelectric voltage coefficient (MEVC) between the dumb-bell shaped and rectangular shaped transducers in theory is 66% comparing with that of in experiment is varying from 140% to 33% when the dc field is increased from 0 Oe to 118 Oe.

• 전기학회논문지
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• 제56권3호
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• pp.566-570
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• 2007

The specific electrical, optical and acoustic properties of Zinc Oxide (ZnO) are important for semiconductor process which has many various applications. Piezoelectric ZnO films has been widely used for such as transducers, bulk and surface acoustic-wave resonators, and acousto-optic devices. In this study, we investigated etch characteristics of ZnO thin films in inductively coupled plasma etch system with $BCl_3/Ar$ gas mixture. The etching characteristics of ZnO thin films were investigated in terms of etch rates and selectivities to $SiO_2$ as a function of $BCl_3/Ar$ gas mixing ratio, RF power, DC bias voltage and process pressure. The maximum ZnO etch rate of 172 nm/min was obtained for $BCl_3$ (80%)/Ar(20%) gas mixture. The chemical states on the etched surface were investigated with X-ray photoelectron spectroscopy (XPS).

• Journal of Power Electronics
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• 제18권2호
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• pp.558-572
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• 2018

In addition to its modular nature, a Hybrid Modular Multilevel Converter (HMMC) assembled from half-bridge and full-bridge sub-modules, is able to block DC faults with a minimum number of switching devices, which makes it attractive for high power applications. This paper introduces a control strategy based on the Root-Least Square (RLS) algorithm to estimate the capacitor voltages instead of using direct measurements. This action eliminates the need for voltage transducers in the HMMC sub-modules and the associated communication link with the central controller. In addition to capacitor voltage balancing and suppression of circulating currents, a fault tolerant control unit (FTCU) is integrated into the proposed strategy to modify the parameters of the HMMC controller. On advantage of the proposed FTCU is that it does not need extra components. Furthermore, a fault detection unit is adapted by utilizing a hybrid estimation scheme to detect sub-module faults. The behavior of the suggested technique is assessed using PSCAD offline simulations. In addition, it is validated using a real-time digital simulator connected to a real time controller under various normal and fault conditions. The proposed strategy shows robust performance in terms of accuracy and time response since it succeeds in stabilizing the HMMC under faults.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2010년도 춘계학술발표대회
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• pp.54.2-54.2
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• 2010

최근까지는 주로 비정질 실리콘이 디스플레이의 채널층으로 상용화 되어왔다. 비정질 실리콘 기반의 박막 트랜지스터는 제작의 경제성 및 균일성을 가지고 있어서 널리 상용화되고 있다. 하지만 비정질 실리콘의 구조적인 문제인 낮은 전자 이동도(< $1\;cm^2/Vs$)로 인하여 디스플레이의 대면적화에 부적합하며, 광학적으로 불투명한 특성을 갖기 때문에 차세대 디스플레이의 응용에 불리한 점이 있다. 이런 문제점의 대안으로 현재 국내외 여러 연구 그룹에서 산화물 기반의 반도체를 박막 트랜지스터의 채널층으로 사용하려는 연구가 진행중이다. 산화물 기반의 반도체는 밴드갭이 넓어서 광학적으로 투명하고, 상온에서 증착이 가능하며, 비정질 실리콘에 비해 월등히 우수한 이동도를 가짐으로 디스플레이의 대면적화에 유리하다. 특히 Zinc Oxide의 경우, band gap이 3.4eV로써, transparent conductors, varistors, surface acoustic waves, gas sensors, piezoelectric transducers 그리고 UV detectors 등의 많은 응용에 쓰이고 있다. 또한, a-Si TFTs에 비해 ZnO-based TFTs의 경우 우수한 소자 성능과 신뢰성을 나타내며, 대면적 제조시 우수한 균일성 및 낮은 생산비용이 장점이다. 그러나 ZnO-baesd TFTs의 경우 일정한 bias 아래에서 threshold voltage가 이동하는 문제점이 displays의 소자로 적용하는데 매우 중요하고 문제점으로 여겨진다. 특히 gate insulator와 channel layer사이의 interface에서의 defect에 의한 charge trapping이 이러한 문제점들을 야기한다고 보고되어진다. 본 연구에서는 Zinc Oxide 기반의 박막 트랜지스터를 DC magnetron sputtering을 이용하여 상온에서 제작을 하였다. 또한, $Si_3N_4$ 기판 위에 electron cyclotron resonance (ECR) $O_2$ plasma 처리와 plasma-enhanced chemical vapor deposition (PECVD)를 통하여 $SiO_2$ 를 10nm 증착을 하여 interface의 개선을 시도하였다. 그리고 TFTs 소자의 출력 특성 및 전이 특성을 평가를 하였고, 소자의 field effect mobility의 값이 향상을 하였다. 또한 Temperature, Bias Temperature stability의 조건에서 안정성을 평가를 하였다. 이러한 interface treatment는 안정성의 향상을 시킴으로써 대면적 디스플레의 적용에 비정질 실리콘을 대체할 유력한 물질이라고 생각된다.