혐기성 소화 효율 향상을 위한 초음파 주파수의 순차적 적용에 대한 연구

황규대,박성한 대한상하수도학회 2011 상하수도학회지 Vol.25 No.6

The effect of ultrasound pretreatment on sludge degragability was investigated at different condotions: ultrasonic frequency(28, 40, 50kHz), intensity(10, 25, 50W), sonication time(10, 20, 30, 60min). Total suspended solid(TSS) and soluble chemical oxygen demand(SCOD) concentration were measured for the evaluation of pretreatment efficiency. The pretreated sludge was used as the feedstock for anaerobic digestion process. Biogas production and volatile suspended solid(VSS) removal were determined for evaluating the process performance. 1. TSS concentration of the sludge decreased at a constant rate as sonication operation was applied. The degradation rate of TSS increased when ultrasound frequency was decreased from 50kHz to 28kHz and intensity was increased from 10W to 50W. Efficiency of TSS degradation per input energy increased as ultrasonic frequency and intensity were decreased. At the frequency of 28 and 40kHz, SCOD concentration rapidly increased during the initial 30min of sonication time, and then it gradually increased. At 50kHz, SCOD concentration constantly increased for 60min of the sonication time. The SCOD production rate increased with increasing intensity under all ultrasound frequencies. 2. The optimum condition of ultrasound treatment was 28kHz, 50W and 60min for maximizing the biogas production, methane fraction, VSS removal. The highest values in biogas production, methane fraction in biogas, VSS removal were 370ml, 70%, 2.45g, respectively. Methane production rate per input energy increased at ultrasonic frequency and intensity decreased. 3. When raw sludge was pretreated at the condition of ultrasonic frequency of 28 and 40kHz in series, sequential-frequency sonication, intensity of 50W and 60min, biogas production, methane fraction, VSS removal were about the same that of 28kHz single-frequency sonication. When sequential-frequency sonication of 28 and 50kHz was applied in series, biogas production, methane fraction, VSS removal were 356 ~ 423ml, 69 ~ 71%, 2.41 ~ 2.78g, respectively. The pretreatment efficiency of 28-50kHz sequential-frequency sonication which sonication time of 28kHz and 50kHz was 40min and 20min was higher than that of 28kHz single-frequency sonication.

초음파 반사이미지와 고유주파수 변화를 이용한 해상 기초구조물의 세굴도 평가

박기원,변용훈,최창호,이종섭 한국방재학회 2013 한국방재학회논문집 Vol.13 No.2

Local loss of geomaterials, which reduces the sability of the structures, around foundation of offshore structure occurs due to the interaction between water and ground. The objective of this study is to evaluate scouring in offshore foundation structures by using ultrasonic reflection method and natural frequency analyses. Sand-cement mixture is prepared to model the ground, which is encountered the scour depth and the scour shape. Ultrasonic wave and natural frequency are measured according to the scour depth. Ultrasonic transducers are used to measure the ultrasonic wave, and strain guages are used to measure the natural frequency. Ultrasonic transducers are fixed on horizontal movement system and rotational movement system for the change of location. Strain guages are attached on upper part of model monopile. Ultrasonic reflection image and strain responses are monitored in laboratory experiment. Maximum scour depth is estimated by natural frequency, and the characteristics of the scour shape are estimated by ultrasonic reflection image. This study suggests that the ultrasonic scanning and natural frequency analyses may be effectively used to monitor the characteristics of the scour depth and shape. 해상에 구조물이 존재할 경우 유수와 지반의 상호작용으로 인하여 기초구조물 주위의 지반이 국부적으로 소실되는 세굴현상이 발생한다. 본 연구의 목적은 초음파 반사이미지와 고유주파수 측정을 통하여 해상 기초구조물의 세굴도를 평가하는 것이다. 세굴현상을 모사하기 위하여 모래-시멘트 혼합시료를 사용하였으며, 세굴도 변화에 따른 초음파 반사이미지와 고유주파수를 측정하였다. 초음파 반사이미지 측정을 위하여 초점방식의 초음파 트랜스듀서가 사용되었고, 고유주파수 측정을 위하여 전기저항식 변형률계가 사용되었다. 초음파 트랜스듀서는 수평이동장치와 회전이동장치에 고정하여 이동시켰으며, 전기저항식 변형률계는 모형 모노파일의 상단에 부착하였다. 실내실험을 통해 세굴도 변화에 따른 초음파 반사이미지의 변화와 변형률 신호를 관찰하고, 각 단계에서의 세굴특성을 파악하였다. 실험결과, 고유주파수를 이용하여 최대세굴심도의 산정이 가능하였으며, 초음파 반사이미지를 통하여 고해상도 세굴단면의 획득이 가능하였다. 본 논문에서 제시한 초음파 반사이미지와 고유주파수 측정을 통한 세굴도 평가는 해상 기초구조물에서 발생할 수 있는 세굴심도 와 형상을 모니터링하기 위한 매우 효과적인 방법이 될 수 있음을 보여준다.

공간주파수대역에서 기저대역 확장을 통한 원전 대비시험편과 대비 보정 시험편의 초음파 영상 개선

박치승,김선진,Park, Chi-Seung,Kim, Seon-Jin 한국재료학회 2003 한국재료학회지 Vol.13 No.10

Ultrasonic microscope has been used to detect the defects on surface or inner solid. Conventionally, it has used at a single operating frequency. The resolution and quality of the measured images are determined by a characteristic of the transducer of the ultrasonic microscope. The conventional ultrasonic microscope has been used envelope detector to detect the amplitude of reflected signal, but the changes in amplitude is not sensitive enough for specimen with microstructure that in phase. In this paper, we have studied multi-frequency depth resolution enhancement with ultrasonic reflection microscope for the reflectors of a stainless steel reference specimen and a reference calibration block to be used as the material in nuclear power plants for ISI, PSI. Increased depth resolution can be obtained by taking two, three-dimensional images at more that one frequency and numerically combining the results. As results of the experiment, we could get enhanced images with the rate of contrast in proportion and high quality signal distribution for the image to the changing rate of depth for the reflectors of the two kinds of specimens.

드릴링 가공을 위한 초음파 유닛 설계

정안목 한국생산제조학회 2022 한국생산제조학회지 Vol.31 No.6

With the development of new alloys and composites, existing drilling techniques have technical constraints for machining difficult-to-cut materials. To overcome these constraints, researchers have developed various drilling methods, including ultrasonic-assisted drilling (UAD). An ultrasonic spindle with a 30 kHz resonant frequency was designed to apply UAD to hole processing. The resonance frequency and vibration mode were predicted using the finite element method (FEM), and a vibration nodal plane was selected. The resonance frequency and impedance characteristics of the ultrasonic spindle were determined using an impedance analyzer, and an error of approximately 1.9% was predicted using the FEM. Next, the vibration characteristics of the ultrasonic spindle were analyzed using a laser displacement system. The vibration displacement tests showed amplitudes of 39.7 and 0.5 μm at the end of the drilling tool and the nodal plane, respectively. The design validity of the manufactured ultrasonic spindle was demonstrated based on experimental drilling results.

아날로그 로그 검출기를 활용한 C-Scan 고주파 초음파 시스템 구현

이강명(Gang-Myung Lee),박상호(Sang-Ho Park),백광렬(Kwang-Ryul Baek) 제어로봇시스템학회 2020 제어·로봇·시스템학회 논문지 Vol.26 No.4

In this paper, we implement a C-Scan 70 MHz ultrasonic system using an analog log detector, and we conduct experiments with this system. If a system with a 70 MHz ultrasonic system is implemented using conventional methods, the required sampling frequency ranges between 420 MHz to 700 MHz, which is 6 to 10 times the ultrasonic frequency. Instead, we propose a method to detect envelopes using an analog log detector in addition to a double probe structure to create a system with an ultrasonic frequency of 70 MHz. After implementing this system corresponding to the proposed method, we verified the performance of the system through the results. The results indicate that the sampling rate is approximately 0.057 times the ultrasonic frequency, resolving the data collection and storage space problem that is due to the high sampling rate found in high-frequency ultrasonic systems.

Reuse of HPLC Guard Column by Ultrasonic Cleaning

이병대 한국응용과학기술학회 2016 한국응용과학기술학회지 Vol.33 No.3

This study investigated reusability of costly guard column by ultrasonic. It alsoinvestigated various effects that affect to guard column generation by ultrasonic. When investigated30 KHz of frequency, area of ascorbic acid is 73.0% compared to unused guard column. As aresult of investigation of effect of pH, guard column by ultrasonic is effective at alkali area. As aresult of investigation of solvent effect, when ethanol is used, generation rate is 81.9% as of peakarea compared to the case of analysis in un used column. From the result, it indicates thatregenerated guard by ultrasonic is reusable.

초음파 이송시스템의 진행파 제어에 관한 연구

정상화,신상문,김태호,서호진,박진완 朝鮮大學校 機械技術硏究所 2007 機械技術硏究 Vol.10 No.1

Methods of major transport system used in many industry fields are conveyor belt, magnetic levitation system and indexing system. It is an indispensable device in many fields and especially it is very important in the factory automation. However, the conventional transport system can damage precision optical components by the contact force and destroy the inner structure of semiconductor by the magnetic field. The new transport system for transporting without damage is required and the ultrasonic wave transport system has been proposed to replace the conventional transport system. In this paper. the object transport system using the ultrasonic wave is developed. Traveling waves are generated through the use of the ultrasonic wave generator to two ends of the beam. The modelling equation on steady state response of ultrasonic vibration is expressed through normal mode expansion. Natural frequency of flexural beam is estimated. Transport direction of the object is analyzed according to phase difference and frequency. In addition, it is verified by experiment.

초음파에 의해서 가진되어지는 탄성빔의 진행파 제어

정상화(Sang Hwa Jeong),신상문(Sang Moon Shin),김태호(Tae Ho Kim) 한국생산제조학회 2007 한국공작기계학회 춘계학술대회논문집 Vol.2007 No.-

Methods of major transport system used in many industry field are conveyor belt, magnetic levitation system and indexing system. It is an indispensable device in many fields and especially it is very important in the factory automation. However, the conventional transport system can damage precision optical components by the contact force and destroy the inner structure of semiconductor by the magnetic field. The new transport system for transporting without damage is required and the ultrasonic wave transport system has been proposed to replace the conventional transport system. In this paper, the object transport system using the ultrasonic wave is developed. Traveling waves are generated through the use of the ultrasonic wave generator to two ends of the beam. The modelling equation on steady state response of ultrasonic vibration is expressed through normal mode expansion. Natural frequency of flexural beam is estimated. Transport direction of the object is analyzed according to phase difference and frequency. In addition, it is verified by experiment.

Analysis of Thickness Dependence of Nanoscaled Thin Film and Substrate by Ultrasonic Atomic Force Microscopy

Dong-Ryul Kwak 한국정밀공학회 2021 International Journal of Precision Engineering and Vol.22 No.2

Nanoscaled thin films are typically deposited on various substrates to achieve their unique characteristics. These thin fi lm systems can be affected by the thickness variations between the thin fi lm and the accompanying substrate. To investigate the thickness dependence of a nanoscaled thin fi lm system, ultrasonic atomic force microscopy (Ultrasonic-AFM) which can evaluate the localized elastic modulus using the contact resonance frequency of a vibrating cantilever is applied. Copper thin films of low elastic modulus were deposited on silicon substrates of high elastic modulus. By contrast, Si 3 N 4 and Ti thin films of high elastic modulus were deposited on GaAs and glass substrates of low elastic modulus, respectively. Experimental results showed that the thin films with different thickness were affected significantly by the substrate and the contact resonance frequency changes as a result of the varying thickness of the thin films. This research demonstrate that Ultrasonic-AFM may be a novel technique for the nondestructive measurement of nanoscale thin fi lm thickness by considering substrate features.

초음파원자현미경을 이용한 나노스케일 박막 코팅층에 대한 탄성특성 평가

곽동열(Dong Ryul Kwak),조승범(Seung Bum Cho),박익근(Ik Keun Park) 한국생산제조학회 2015 한국생산제조학회지 Vol.24 No.5

Ultrasonic atomic force microscopy (Ultrasonic-AFM) has been used to investigate the elastic property of the ultra-thin coating layer in a thin-film system. The modified Hertzian theory was applied to predict the contact resonance frequency through accurate theoretical analysis of the dynamic characteristics of the cantilever. We coat 200 nm thick Aluminum and Titanium thin films on the substrate using the DC Magnetron sputtering method. The amplitude and phase of the contact resonance frequency of a vibrating cantilever varies in response to the local stiffness constant. Ultrasonic-AFM images were obtained using the variations in the elastic property of the materials. The morphology of the surface was clearly observed in the Ultrasonic-AFM images, but was barely visible in the topography. This research demonstrates that Ultrasonic-AFM is a promising technique for visualizing the distribution of local stiffness in the nano-scale thin coatings.