• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• 제24권12호
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• pp.1205-1214
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• 2013

Recently spaceborne SAR systems are increasing image resolution and frequency. As a high quality image resolution, the wider bandwidth is required and a wideband signal generator with RF component is very complicated and RF impairments of device is increased. Therefore, it is very important to improve performance by reducing these errors. In this study, the transmission signal of the wideband signal generator is applied to the phase noise, IQ imbalance, ripple gain, nonlinear model of high power amplifier. And we define possible structures of wideband signal generator and measure the PSLR and ISLR for the performance assesment. Also, we extract error of the amplitude and phase from the waveform and use a quadratic polynomial curve fitting and examine the performance change due to nonlinear device. Finally, we apply a high power amplifier predistortion method for non-linear error compensation. And we confirm that distortion in the output of the amplifier by intermodulation component is decreased by 15 dB.

• International Journal of Fluid Machinery and Systems
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• 제8권4호
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• pp.264-273
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• 2015

This presentation describes an experimental approach for the detection of cavitation in hydraulic machines by use of ultrasonic signal analysis. Instead of using the high frequency pulses (typically 1MHz) only for transit time measurement different other signal characteristics are extracted from the individual signals and its correlation function with reference signals in order to gain knowledge of the water conditions. As the pulse repetition rate is high (typically 100Hz), statistical parameters can be extracted of the signals. The idea is to find patterns in the parameters by a classifier that can distinguish between the different water states. This classification scheme has been applied to different cavitation sections: a sphere in a water flow in circular tube at the HSLU in Lucerne, a NACA profile in a cavitation tunnel and two Francis model test turbines all at LMH in Lausanne. From the signal raw data several statistical parameters in the time and frequency domain as well as from the correlation function with reference signals have been determined. As classifiers two methods were used: neural feed forward networks and decision trees. For both classification methods realizations with lowest complexity as possible are of special interest. It is shown that two to three signal characteristics, two from the signal itself and one from the correlation function are in many cases sufficient for the detection capability. The final goal is to combine these results with operating point, vibration, acoustic emission and dynamic pressure information such that a distinction between dangerous and not dangerous cavitation is possible.

• Transactions of the Korean Society of Mechanical Engineers B
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• 제27권10호
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• pp.1385-1392
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• 2003

An electromagnetic flowmeter(EMF) was developed and its characteristics were compared with a commercial EMF. The developed EMF was designed as the 100 mm nominal diameter. A signal processing circuit was also developed for generating the magnetic field and converting the flow signal to flowrate and flow quantity. In order to obtain a more stable and reliable flow signal, the double magnetizing frequency was adopted for magnetizing the coil of the EMF. For the characterization of the developed EMF, the uncertainty of calibrator was estimated within $\pm$0.5 %. The evaluation procedure of the uncertainty followed the ISO Guide to the Expression of Uncertainty in Measurement. It was found that the flow signals between the electrodes were about $\pm$60-$\pm$300$\mu$V, which were sufficient for the discrimination of flowmeter and the protection of noise. The test results against the calibrator showed the good linearity in the range of 3 ㎥/h and 70 ㎥/h. A commercialized design of the EMF based on the current study will be technically more competitive in domestic and foreign market.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• 제25권6호
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• pp.440-446
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• 2015

Acoustic signal is emitted from a vessel and received by a cylindrical array sensor at some distance from the vessel. Acoustic signal is the source for a cylindrical array sensor which is designed to detect the acoustic signal. Cylindrical array sensors seldom have an ideal hydrodynamic shape and are not sufficiently robust to survive without some protection and they are normally housed in a sonar dome. Reflected signals by some structure inside a sonar dome make unwanted signals. Therefore, an acoustic baffle is used to minimize unwanted signals. The performance of the acoustic baffles can be determined from the acoustic numerical analysis at the design stage. In this study, finite element method was used to analyze the acoustic field around the cylindrical array sensor and baffle effects. The baffle performance can be defined the echo reduction. To show the baffle performance, the specimens were made for pulse tube test and echo reductions were measured during the test. In this paper, the effect of echo reduction of the acoustic baffle was discussed.

• Korean Journal of Optics and Photonics
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• 제5권1호
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• pp.158-165
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• 1994

A fiber optic voltage sensor is demonstrated with a new signal processing scheme that displays the magnitude and the waveform of applied voltage with immunity from the signal frequency change. The sensor is based on a Mach-Zehnder interferometer with a PZT phase modulator as a sensing element. We observed a linear relationship between applied voltage and the number of fringe shift during a half cycle of the ac signal. The temperature dependence of the sensor output is experimentally evaluated over the temperature range from $-20^{\circ}C to 80^{\circ}C$. It is demonstrated that the detrimental polarization modulation effect can be overcome by using polarization maintaining fibers or a half-wave plate. plate.

• Journal of the Institute of Convergence Signal Processing
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• 제11권4호
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• pp.298-302
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• 2010

Extracorporeal circulation support system is a device for repiratory and heart failure treatment, and there have been many trials for development and clinical application in the world. These devices need to be careful while using is air embolism. Air embolism can be a lethal complication of surgical procedures during which venous pressure at the site of surgery is sub-atmospheric or air is forced under pressure into a body cavity or using extracorporeal circulation support system. To solve the problem, we developed the air detector using relative dielectric constant change. In experiments with a mock circulation system, the proposed system showed a signal difference depending on the amount of air in the tube.

• Korean Journal of Optics and Photonics
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• 제3권2호
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• pp.123-132
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• 1992

We designed and constructed the Cs beam tube which consists of a Ramsey cavity, four C-field rods, fluorescence detecting systems, and etc. for developing an optically pumped Cs atomic clock. A semiconductor laser was used for optical pumping and probing in the Cs beam. We observed Ramsey resonance signal by detecting the fluorescence signal in the probing region as the microwave frequency injected into the Ramsey cavity was scanned near 9192.6 MHz which corresponds to the "clock transition" of Cs atoms. We found that the linewidth of the Ramsey signal was 200 Hz, the magnetic field intensity was $8.61\muT$ when the current of 0.8A flowed in the C-field rods, and the second order Zeeman shift by the magnetic field was 3.17 Hz.s 3.17 Hz.

• Smart Structures and Systems
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• 제19권2호
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• pp.181-194
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• 2017

In order to investigate the interface debonding defects detection mechanism between steel tube and concrete core of concrete-filled steel tubes (CFSTs), multi-physical fields coupling finite element models constituted of a surface mounted Piezoceramic Lead Zirconate Titanate (PZT) actuator, an embedded PZT sensor and a circular cross section of CFST column are established. The stress wave initiation and propagation induced by the PZT actuator under sinusoidal and sweep frequency excitations are simulated with a two dimensional (2D) plain strain analysis and the difference of stress wave fields close to the interface debonding defect and within the cross section of the CFST members without and with debonding defects are compared in time domain. The linearity and stability of the embedded PZT response under sinusoidal signals with different frequencies and amplitudes are validated. The relationship between the amplitudes of stress wave and the measurement distances in a healthy CFST cross section is also studied. Meanwhile, the responses of PZT sensor under both sinusoidal and sweep frequency excitations are compared and the influence of debonding defect depth and length on the output voltage is also illustrated. The results show the output voltage signal amplitude and head wave arriving time are affected significantly by debonding defects. Moreover, the measurement of PZT sensor is sensitive to the initiation of interface debonding defects. Furthermore, wavelet packet analysis on the voltage signal under sweep frequency excitations is carried out and a normalized wavelet packet energy index (NWPEI) is defined to identify the interfacial debonding. The value of NWPEI attenuates with the increase in the dimension of debonding defects. The results help understand the debonding defects detection mechanism for circular CFST members with PZT technique.

• Proceedings of the KSME Conference
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• 대한기계학회 2004년도 추계학술대회
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• pp.1116-1121
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• 2004

In this study, the effect of central fuel injection on a coaxial laminar $CH_{4}/air$ flame was experimented at the defined premixing condition(${\Phi}=1.90$, ${\sigma}=50/75/100%$, x/D=10). The partial premixing parameter are the equivalence ratio that total fuel is fixed at 200cc/min, the fuel split degree which means the percentage of fuel entering the outer tube to the total amount, and the mixing distance indicating the nonreactant mixture's homogeneity between inner tube top and burner exit. The object is to investigate the flame structure and chemiluminescence characteristics of laminar partial premixed flame as changing mixing parameters. The radical signal was acquired from ICCD camera and PMT. Each intensity was compared with Abel inverted value for measuring the effect of background light on the peak signal location and the intensity at central preheat zone. The results show that the peak location of each radical was broaden as the fuel split degree increasing because the mixing quality was enhanced. and $OH^{\ast}$ is a good indicator for flame front between reaction and preheat zone. At last $CH_{2}^{\ast}$ has the same tendency with $CH^{\ast}$ but a thinner reaction zone than $CH^{\ast}$ due to a rapid decay on the burned gas side.

• Transactions of the Korean Society of Mechanical Engineers B
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• 제40권9호
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• pp.613-620
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• 2016

In order to scrutinize the fluid conductivity effects on the electromagnetic flowmeter(EMF) characteristics, a small scale EMF was designed and fabricated. The measuring tube has a $3mm{\times}4mm$ rectangular cross-section, 9 mm length, and a $2mm{\times}3mm$ plate electrode and a ${\Phi}1.5mm$ point electrode. The design parameters, such as the magnetizing frequency and the number of coil turns, and the diameter were optimized. The EMF was tested with a gravimetric calibrator and showed good linearity in the range of 0 to $1.17{\times}10^{-5}m^3/s$. The fluid conductivity was varied between 3 and $11{\mu}S/cm$, and the magnitude of the flow signal was proportional to the fluid conductivity and the wetted area of the electrode. The design information and the test results provide flow measurement techniques for very low flowrate.