• Proceedings of the Earthquake Engineering Society of Korea Conference
• /
• 1998.10a
• /
• pp.274-285
• /
• 1998

Increasing flexibility and lightness of recently built high-rise buildings make the structures susceptible to loads such as earthquakes and winds. Therefore, higher performance vibration control systems to reduce the vibration levels are demanded more than any time in the past. One of typical active vibration control systems is the active mass damper(AMD). In this paper, an active vibration control system consisting of small shaking table, building model, sensors, signal processing board and AMD is constructed. The dynamic characteristics of these individual systems are investigated through the experimental study. The performance of the active vibration control system is verified through harmonic resonant load excitation on building model.

• The Transactions of the Korean Institute of Electrical Engineers
• /
• v.41 no.8
• /
• pp.947-950
• /
• 1992

At-cut quartz crystal has been applied as chemical vapour sensors. The responses of quartz crystal at 9 MHz coated with phosphatidylglycerol(PG), phosphatidylinositol(PI), phosphatidylethanolamine(PE), phosphatidylserine(PS), and lipid A(LA) are determined for amyl acetate, acetoin, menthone and other organic gases which showed different affinities for each lipid. The identification of odorants depending on the species of lipid used for coating is discussed in terms of the normalized resonant frequency shift pattern.

• Proceedings of the KSR Conference
• /
• 2010.06a
• /
• pp.1861-1867
• /
• 2010

This paper described the positioning algorithm of partial discharge in insulation oil by acoustic method for the application of an on-line diagnosis in oil-immersed transformers. In the experiment, five AE sensors having the resonant frequency of 150 kHz were used, and a signal conditioner was fabricated. A needle-plane electrode system which is composed of a needle with a curvature radius of $10{\mu}m$ and a plane electrode with a diameter of 60 mm was installed to simulate partial discharges in insulation oil. From the time difference of arrival (TOA) of acoustic signal, we calculated the location of partial discharge in insulation oil. In the experiment, an algorithm of positioning of PD occurrence by the time difference of arrival was proposed. From the experimental results, the positioning error of PD calculated by three AE sensors was within 4%.

• Journal of Sensor Science and Technology
• /
• v.24 no.2
• /
• pp.93-95
• /
• 2015

We present an optical detection method for the fundamental vibrational mode of a tuning fork crystal oscillator in air. A focused He/Ne laser beam is directed onto the edge of one vibrating tine of the tuning fork; its vibrating motion chops the incoming laser beam and modulates the intensity. The beam with modulated intensity is then detected and converted to an electrical signal by a high-speed photo-detector. This electrical signal is a sinusoid at the resonant frequency of the tuning fork vibration, which is 32.76 kHz. Our scheme is robust enough that the sinusoidal signal is detectable at up to $40^{\circ}$ of rotation of the tuning fork.

• International Journal of Fuzzy Logic and Intelligent Systems
• /
• v.15 no.3
• /
• pp.200-207
• /
• 2015

This paper proposes an active damping control method for a grid-side converter that has an LCL grid filter in the back-to-back converter. To remove the resonant frequency components produced by the LCL filter, it is necessary to measure the grid current. To do this, sensors must be added. However, it is not necessary to add sensors because the grid current is estimated by designing a suboptimal observer. In order to remove the nonlinearity and to gain fast response of control, both feedback linearization and sliding mode control are applied. The proposed method is verified through a simulation.

• Journal of Advanced Navigation Technology
• /
• v.27 no.4
• /
• pp.469-472
• /
• 2023

If temperature management is required in factory or environmental monitoring, temperature can be measured by connecting various sensors wired or wirelessly. Surface acoustic wave sensors measure temperature using changes in acoustic waves on the sensor surface according to temperature, and are useful for wireless networks. In this paper, in order to build a wireless temperature measurement system in the 900 MHz frequency band, the temperature characteristics of the passive SAW sensor were measured, and the analysis and removal of multipath reflection wave effect inside the high temperature chamber were conducted. The resonant frequency of the SAW sensor was measured, and radio transmission/reception and multipath reflected wave removal techniques were proposed in the shielded chamber.

• Journal of Sensor Science and Technology
• /
• v.5 no.4
• /
• pp.71-79
• /
• 1996

The mechanism of electrochemical polymerization of polypyrrole was analyzed using Q.C.A. via measuring the resonant frequency and resonant resistance of AT-cut quartz crystal, whose electrodes were fabricated with indium tin oxide by sputtering method. The quantity of polymerized polypyrrole was able to be calculated from the resonant frequency and the viscoelasticity of polypyrrole film from resonant resistance. We found that the elastic film is formed at the first stage of the polymerization, but transformed to viscoelastic film later and that this transition repeated at some point. From these results, it was confirmed that the rheological characteristics of electrochemically polymerized polypyrrole thin film can be analyzed using Q.C.A.

• Journal of Sensor Science and Technology
• /
• v.8 no.5
• /
• pp.407-413
• /
• 1999

The resonant frequency of dielectric rod resonator can be calculated very accurately by means of the concept of electric and magnetic walls from the symmetry. But in a real situation, when the supporter is placed in the cavity, asymmetry appears due to the supporter and its dielectric constant. Then we need research into the resonance characteristic of asymmetric dielectric resonator. In this paper, for the dielectric rod resonator which is placed in the asymmetric position in the conducting cavity, the equation for resonance characteristic was derived and the resonant frequency was calculated with the eigenfunction expansion method. We found that the calculated resonant frequency is very accurate when it was compared with the experimental result and that asymmetry affects the resonant frequency more in TM mode than in TE or in hybrid mode.

• Structural Monitoring and Maintenance
• /
• v.1 no.2
• /
• pp.183-195
• /
• 2014

Scour is one of the leading causes of overwater bridge failures worldwide. While monitoring systems have already been implemented or are still being developed, they suffer from limitations such as high costs, inaccuracies, and low reliability, among others. Also, most sensors only measure scour depth at one location and near the pier. Thus, the objective is to design a simple, low cost, scour hole topography monitoring system that could better characterize the entire depth, shape, and size of bridge scour holes. The design is based on burying a robust, waterproofed, piezoelectric sensor strip in the streambed. When scour erodes sediments to expose the sensor, flowing water excites it to cause the generation of time-varying voltage signals. An algorithm then takes the time-domain data and maps it to the frequency-domain for identifying the sensor's resonant frequency, which is used for calculating the exposed sensor length or scour depth. Here, three different sets of tests were conducted to validate this new technique. First, a single sensor was tested in ambient air, and its exposed length was varied. Upon verifying the sensing concept, a waterproofed prototype was buried in soil and tested in a tank filled with water. Sensor performance was characterized as soil was manually eroded away, which simulated various scour depths. The results confirmed that sensor resonant frequencies decreased with increasing scour depths. Finally, a network of 11 sensors was configured to form a distributed monitoring system in the lab. Their exposed lengths were adjusted to simulate scour hole formation and evolution. Results showed promise that the proposed sensing system could be scaled up and used for bridge scour topography monitoring.

• Journal of Sensor Science and Technology
• /
• v.9 no.1
• /
• pp.28-35
• /
• 2000

In this study, we investigated the characteristics of polyurethane synthesis by simultaneously measuring resonant frequency and resonant resistance with a quartz crystal analyzer. The rapid decrease of resonant frequency was appeared because automatic catalytic reaction was caused by the polyurethane formed in initial stage of polyurethane synthesis. In prepolymer(PP) synthesis, the resonant frequency was slowly stabilized after a rapid decrease at a certain point of time. But in segmented polyurethane synthesis in which chain-extender was involved, the resonant frequency increased again after a rapid decrease at a certain point of time. It was considered that this tendency took place because the chain-extender, 1,4-butandiol, caused a soft segment to change to a hard segment. The resonant resistance was used in the analysis of mechanism. From the results, the characteristics of polyurethane synthesis could be analyzed on-line using a quartz crystal analyzer, and the synthesis mechanism could also be interpreted.