• Journal of the Korean Society of Visualization
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• v.22 no.2
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• pp.35-43
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• 2024

Microparticle separation has demonstrated significant potential for biological, chemical, and medical applications. We introduce a surface acoustic wave (SAW)-based microfluidic device for separation of elastic and rigid microspheres based on their property and size. By tuning the SAWs to match the resonant frequencies of certain microspheres, those particles could be selectively separated from the other microspheres. When microspheres are exposed to an acoustic field, they experience the SAW-induced acoustic radiation force (ARF), whose magnitude is dependent on the microparticle size and properties. We modeled the SAW-induced ARF based on elastic sphere theory and conducted a series of experiments to separate elastic and rigid microspheres. We further utilized the acoustofluidic method for the separation of Thalassiosira Eccentrica microalgae based on the differences in their sizes with purity exceeding 90%. We anticipate that our technique will open up new possibilities for sample preparation, detection, and diagnosis in various emerging biological and medical analyses.

• Journal of the Korean Society for Precision Engineering
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• v.27 no.1
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• pp.49-57
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• 2010

This paper describes the design, construction, and fundamental testing of a precision rotational device that utilizes piezoelectric elements as a source of driving force and impact drive mechanism as a driving principle. A novel device structure is designed and the numerical simulations about the static displacement, stress distribution, and mode shape of the designed structure are performed. A fabricated rotational device has been rotated successfully by applying saw-shaped voltages to the piezoelectric elements. The one-step rotational angle was $0.44{\times}10^{-3}$ rad at the applied voltages of 80V. The angular velocities of the device were revealed to be increased as the driving frequency and voltage were respectively increased and the preload was decreased. The device has a feature that it can be translated as well as rotated. An experimental result shows that the device was translated by ${\pm}4.56{\mu}m$ maximum when the 120V sinusoidal voltages with a phase difference of $180^{\circ}$ were respectively supplied to two piezoelectric elements.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.25 no.12
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• pp.1219-1227
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• 2014

For development of the surface acoustic wave bandpass filter(SAW-BPF), we fabricated the high quality ZnO thin films through the step-by-step(double) deposition using two different deposition methods which are pulsed laser deposition(PLD) and RF sputtering techniques. The second growth of ZnO thin films was completed by RF sputtering method on the first ZnO thin films pre-deposited by PLD method. The characteristics of ZnO thin films were analyzed by XRD, SEM and AFM systems. The FWHM of ${\omega}$-scan analysis and the minimum RMS value of surface roughness of step-by-step grown ZnO thin films were $0.79^{\circ}$ and 1.108 nm respectively. As a result, the crystallinity and the preferred orientation of the grown ZnO thin films were kept good quality and the surface roughnesses of those were improved by post-annealing process as comparison with ZnO thin film fabricated by the conventional PLD technique only. Using these proposed ZnO thin films, we demonstrated the RF device such as SAW-BPF, built by the proposed ZnO thin films, shows that it has the bandwidth of 2.98 MHz and the insertion loss of 36.5 dB at the center frequency of 260.8 MHz, respectively.

• Journal of the Korean Society for Precision Engineering
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• v.6 no.2
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• pp.40-46
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• 1989

Recently, the researches on cutting the new material have been done for development of aerospace industrial engineering. Especially, titanium ally is well known as heat resisting, antiwear, anticorrosion and difficult-to-machine materials. Many studies on the analysis of shear angle have been done for improving productivity in cutting these materials. In case of titanium alloy, the saw-toothed type of chip which has wave surface of a triangular form, an eccentric from of a continuous type of chip that is produced in the cutting process, was checked. Nakayama supposed that a maximum shear strewss plane and the shear crack in the free surface made an angle of $45^{\circ}$ .deg. , but it's usually much larger than that. In this paper, the author analyzed the shear conditions of the cutting process in the quick-stopping device with the help SEM-photographs, and measured the hypotenuse angle directly in the photographs of the chips. In conclusion, the author tried to find the shear angle in the cutting process with the saw-toothed chip and compared it with the shear angles which can be calculated from the theories established by others. The results obtained are as follows. 1. In case of the saw-toothed chips, the equivalent cutting ratio can be calculated by using the chip thickness to two-thirds of ramp height. 2. The theory of Ernst-Merchant is not applicable to the titanium and its alloys which does not fractured in accordance with the theory of maximum shear stress. 3. When we cut the titanium alloys which produced the saw-toothed chips, the shear angle can be found with the theories of Rowe-Spick, P.K. Wright and the measurement of hypotenuse angle.

• Journal of IKEEE
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• v.18 no.4
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• pp.586-592
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• 2014

In this paper, high efficiency power management IC(PMIC) with DT-CMOS(Dynamic threshold voltage Complementary MOSFET) switching device is presented. PMIC is controlled PWM control method in order to have high power efficiency at high current level. The DT-CMOS switch with low on-resistance is designed to decrease conduction loss. The control parts in Buck converter, that is, PWM control circuit consist of a saw-tooth generator, a band-gap reference(BGR) circuit, an error amplifier, comparator circuit, compensation circuit, and control block. The saw-tooth generator is made to have 1.2MHz oscillation frequency and full range of output swing from supply voltage(3.3V) to ground. The comparator is designed with two stage OP amplifier. And the error amplifier has 70dB DC gain and $64^{\circ}$ phase margin. DC-DC converter, based on current mode PWM control circuits and low on-resistance switching device, achieved the high efficiency nearly 96% at 100mA output current. And Buck converter is designed along LDO in standby mode which fewer than 1mA for high efficiency. Also, this paper proposes two protection circuit in order to ensure the reliability.

• The Journal of the Acoustical Society of Korea
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• v.16 no.2
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• pp.89-94
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• 1997

A new type SO$_2$ gas sensor with a particular inorganic thin film on SAW devices was developed. The sensor consisted of twin SAW oscillators of the center frequency of 54 MHz fabricated on the LiTaO$_3$ piezoelectric single crystal. One delay line of the sensor was coated with a CdS thin film that selectively adsorbed and desorbed SO$_2$, while the other was uncoated for use as a stable reference. Deposition of the CdS thin film was carried out by the spray pyrolysis method using an ultrasonic nozzle. The sensor could measure the concentration in air less than 0.25 parts per million of SO$_2$. Stability of the sensor turned out to be as good as less than 20ppm, recovery time after each measurement was as short as 5 minutes. Repeatability of the measurement was confirmed through so many reiterated experiments. Hence, the SAW sensor developed through this work showed promising performance as a microsensing tool of SO$_2$. Further work required to improve the performance of the sensor includes enhancement of the reactivity of the CdS thin film with SO$_2$ through appropriate dopant addition, an increase of the center frequency of the SAW device.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.10a
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• pp.793-794
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• 2011

• Journal of International Academy of Physical Therapy Research
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• v.3 no.2
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• pp.458-463
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• 2012

This study is to examine the effects of a feedback breathing device exercise and diaphragm breathing exercise on pulmonary functions of chronic strokes patients. The selection of 20 subjects was divided equally and placed into a experiment group and a control group and the intervention was applied four times per a week for five weeks. In each session, both groups received rehabilitative exercise treatment for 30 minutes, and a feedback breathing device exercise for 15 minutes. In addition, experimental group conducted a combination of diaphragm breathing exercise for 15 minutes. Prior to and after the experiment, patients' pulmonary functions were measured using a spirometer. The pulmonary function tests included FVC, FEV1, FEV1/FVC, PEF, VC, TV, IC, ERV, IRV. With respect to changes in the pulmonary functions of both groups, the experimental group significantly differed in FVC, FEV1, TV, ERV but did not in PEF, FEV1/FVC, VC, IRV. The control group did not significantly differ in any of the tests. There were significant differences in FEV1, FEV1/FVC, TV, ERV between the two groups, but no significant differences in FVC, PEF, FEV1/FVC, VC, IRV between them after the experiment. The experimental group, which conducted a combination of a feedback breathing device exercise and diaphragm breathing exercise, saw their respiratory ability increase more significantly than the control group. The breathing exercise was found to improve pulmonary function in chronic stroke patients.

• Journal of the Korean Society for Precision Engineering
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• v.25 no.11
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• pp.100-106
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• 2008

We have studied the characteristic changes of optical device using imprint lithography. An imprinted structure is inherently involved in residual stress due to the temperature and the pressure cycle during fabrication process. A structure with residual stress undergoes stress relaxation, which leads io dimensional change. Therefore, annealing processes was performed to reduce the residual stress of imprinted polymer channel. Reduction of residual stress was confirmed through dimensional change, birefringence, and the mechanical properties. We have fabricated an optical device, and it saw the optical intensity changes within 0.1% for 1 month.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.40 no.3
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• pp.1-9
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• 2003

In this paper, we designed a highly suppressed sidelobe ladder type RF SAW bandpass filter based on 1-port resonator, for 800 MHz mobile communication system. In order to get the highest device characteristics, we optimized some important parameters such as the electrode thickness, electrode lambda weghting of the reflectors, and static capacitance ratio. Furthermore, we fabricated the Tx and Rx. filter using optimized parameters. Implemented filters can be used in 800 MHz mobile communication system and external impedance matching circuits are not needed. RF filter was fabricated on 36$^{\circ}$LiTaO$_3$ substrates with Al-Cu (W 3 %)and mounted 3.8mm$\times$3.8mm$\times$1.5mm SMD package. Developed filters has 2.3 dB insertion loss in the 25 MHz pass-band, 33MHz with 3-dB insertion loss, stop-band rejection of 30 dB, passband ripple is less than 0.5 The power durability of the filters measured about 3.5W and the maximum temperature variation within -2$0^{\circ}C$~8$0^{\circ}C$ was 0.09 dB/$^{\circ}C$ of 3-dB insertion loss.