• Journal of Biomedical Engineering Research
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• v.40 no.5
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• pp.151-157
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• 2019

An acoustofluidic device using conductive liquid-based electrodes was developed for malaria parasite separation from white blood cells. In this device, the electrode channels filled with a conductive liquid were used to generate standing surface acoustic waves (SSAWs) in a fluidic channel, which can overcome the limitation of conventional patterned metal electrodes. Separation performance of the device was evaluated using fluorescent polystyrene particles with two different sizes (2 and $10{\mu}m$ diameters), which were successfully separated. In addition, a mixture of malaria parasites and white blood cells were also efficiently separated with high purity of ~98% in the CL-SSAW device at the flow rate of $12{\mu}l/min$.

• Plant Journal
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• v.4 no.3
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• pp.54-59
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• 2008

The resonance of boiler is caused by exciting force in the gas path and it generates the vibration by the harmony of boiler's dimensional factor. According to trending toward the boiler of increasing capacity and a bigger size, it has a problem of the vibration at back-pass heating surfaces. We can predict such vibrations as comparison between vortex frequency and gas column's natural frequency. We can't rely on the method for the past decades because of changing parameters, such as an allowable error, gas temperature, gas velocity, Strouhal number. We can reduce the vibration to use the seasoning effect and change the operating condition in coal fired boiler but it's not essential solution. When the vibration occurred in the model boiler, we must measures the acoustic pressure and frequency of places for considering the means. So far, we confirmed the problem from field measures and theoretical analysis about the acoustic vibration of boiler. We installed anti-acoustic baffle in a existing boiler to change the acoustic natural frequency at the cavity, which results in reducing the acoustic vibration. The first, we prove that the acoustic resonance is caused by harmonizing vortex shedding frequency of tube heat surface with acoustic natural frequency of cavity in the range of 650~750 MW loads. The second, the acoustic resonance at the back-pass heating surface has the third order of acoustic natural frequency at the second economizer. We install five anti-acoustic baffles at the second economizer to reducing the resonance. We confirm considerably reducing the acoustic vibration of boiler during the commercial boiler.

• Proceedings of the SAREK Conference
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• 2006.06a
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• pp.471-476
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• 2006

Thermoacoustic refrigerators are operated with acoustic power to pump heat. The acoustic standing wave displaces the gas In the channels of the stack while compressing and expanding. The thermal interaction between the osillating gas he surface of the stack generates an acoustic heat pumping. in this study, a thermoacoustic refrigerator is composed of a resonator of 4cm diameter, stack of plates, heat exchangers and cooling part. Length of the hot heat exchangers, the stack of plates and the cold heat exchanger are 9mm, 8mm and 6mm respectively. Using helium as a coolant at frequency of 516Hz, the cold-part temperature of exchanger fell to $-19.0^{\circ}C$ after 1hours.

• Journal of Soil and Groundwater Environment
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• v.21 no.1
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• pp.80-85
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• 2016

Acoustic cavitation can induce various sonochemical effects including pyrolysis and radical reactions and sonophysical effects including microjets and shockwave. In environmental engineering field, ultrasound technology using sonochemical effects can be useful for the removal and mineralization of recalcitrant trace pollutants in aqueous phase as one of emerging advanced oxidation processes (AOPs). In this study, the effect of liquid height, the distance from the transducer to the water surface, on sonochemical oxidation reactions was investigated using KI dosimetry. As the liquid height/volume increased (40~400 mm), the cavitation yield steadily increased even though the power density drastically decreased. It was found that the enhancement at higher liquid height conditions was due to the formation of standing wave field, where cavitation events could stably occur and a large amount of oxidizing radicals such as OH radicals could be continuously provided.

• Journal of the Korean Society for Nondestructive Testing
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• v.36 no.5
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• pp.370-376
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• 2016

Corrosion on the surface of a structure can generate cracks or cause walls to thin. This can lead to fracturing, which can eventually lead to fatalities and property loss. In an effort to prevent this, laser imaging technology has been used over the last ten years to detect thin-plate structure, or relatively thin piping. The most common laser imaging was used to develop a new technology for inspecting and imaging a desired area in order to scan various structures for thin-plate structure and thin piping. However, this method builds images by measuring waves reflected from defects, and subsequently has a considerable time delay of a few milliseconds at each scanning point. In addition, the complexity of the system is high, due to additional required components, such as laser-focusing parts. This paper proposes a laser imaging method with an increased scanning speed, based on excitation and the measurement of standing waves in structures. The wavenumber of standing waves changes at sections with a geometrical discontinuity, such as thickness. Therefore, it is possible to detect defects in a structure by generating standing waves with a single frequency and scanning the waves at each point by with the laser scanning system. The proposed technique is demonstrated on a wall-thinned plate with a linear thickness variation.

• The Journal of the Acoustical Society of Korea
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• v.42 no.5
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• pp.412-421
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• 2023

Ultrasound brain stimulation is spot-lighted by its capability of inducing brain cell activation in a localized deep brain region and ultimately treating impaired brain function while the efficiency and directivity of neural modulation are highly dependent on types of stimulus waveforms. Therefore, to optimize the types of stimulation parameters, we propose a cell-cultivable ultrasonic transducer having a series stack of a spin-coated polymer piezoelectric element (Poly-vinylidene fluoride-trifluorethylene, PVDF-TrFE) and a parylene insulating layer enhancing output acoustic pressure on a glass-coverslip which is commonly used in culturing cells. Due to the uniformity and high accuracy of stimulus waveform, tens of neuronal cell responses located on the transducer surface can be recorded simultaneously with fluorescence microscopy. By averaging the cell response traces from tens of cells, small changes to the low intensity ultrasound stimulations can be identified. In addition, the reduction of stimulus distortions made by standing wave generated from reflections between the transducers and other strong reflectors can be achieved by placing acoustic absorbers. Through the proposed ultrasound transducer, we could successfully observe the calcium responses induced by low-intensity ultrasound stimulation of 6 MHz, 0.2 MPa in astrocytes cultured on the transducer surface.

• The Journal of the Acoustical Society of Korea
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• v.20 no.5
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• pp.69-75
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• 2001

In this paper, a fast and easy impedance matching method, which could give the impedance matching component for the general 1 or 2-port network was introduced. First, the entire network structure was defined which consists of the network part to be matched and the impedance matching part composed of inductors and capacitors. Next, the transmission matrix and input and output impedances of the entire network from the terminal impedance conditions were calculated, then the exact solutions for the matching components were obtained. To verify the efficiency of this method, this method was applied to the CDMA If band withdrawal weighted SAW transversal filter, and investigated the effects of the impedance matching before and after, through the simulation and experiment. As the result, the performance of a fractional bandwidth of 1.2%, insertion loss of 29 dB, and VSWR of 80 have improved to a factional bandwidth of 1.8％, insertion loss of 9 dB, VSWR of 3 at 85.38 MHz center frequency. The result shows that this impedance matching method could be used in the SAW devices and other types of 1 or 2-port network.