• ETRI Journal
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• v.41 no.6
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• pp.850-862
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• 2019

This work investigated three-dimensional (3D) focused microwave thermotherapy (FMT) at 925 MHz for a human tissue mimicking phantom using the time reversal (TR) principle for musculoskeletal disorders. We verified the proposed TR algorithm by evaluating the possibility of 3D beam focusing through simulations and experiments. The simulation, along with the electromagnetic and thermal analyses of the human tissue mimicking phantom model, was conducted by employing the Sim4Life commercial tool. Experimental validation was conducted on the developed FMT system using a fabricated human tissue mimicking phantom. A truncated threshold method was proposed to reduce the unwanted hot spots in a normal tissue region, wherein a beam was appropriately focused on a target position. The validation results of the simulation and experiments obtained by utilizing the proposed TR algorithm were shown to be acceptable. Effective beam focusing at the desired position of the phantom could be achieved.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.14 no.11
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• pp.912-916
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• 2001

Fluxmeter is a measuring instrument the magnetic flux intensity by means of an integration of the voltage induced to a search coil to unit time. It also is required to a precise integrator since the voltage induced to a search coil has a differential value of the flux ${\Phi}$ to unit time. In this study, a bias current which is a main problem of the integrator in a drift troublesome depending on the temperature of a FET is investigated. We have confirmed that the temperature dependence of both the bias current of a integrator using the FET and the reversal saturated current of the minor carrier in a P-N junction of a semiconductor were the same. The property of a commercial integrator goes rapidly down with increasing temperature. The bias current of a FET is increased twice as much with 10$^{\circ}C$ increment. As a result, the low drift integrator could be developed by setting the lower temperature up with a pottier device.

• Electrical & Electronic Materials
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• v.9 no.7
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• pp.668-673
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• 1996

In this paper, (P $b_{1-x}$ L $a_{x}$)(Z $r_{0.52}$ $Ti_{0.48}$) $O_{3}$ (X=0-13[at%]) thin film were prepared by the Sol-Gel method, Multiple PLZT thin films were spin-coated on the Pt/Ti/ $SiO_{2}$Si substrate. The electrical properties of the films were investigated for varying the annealing temperature. In the PLZT(11/52/48) specimens, the dielectric ocnstant of 1236 and the polarization reversal time of 460[nm] were obtained and the breakdown of the film did not occur up to 1*10$^{10}$ cycles at the voltage of 7[V] by the bipolar acceleration. The remanent polarization and coercive field decreased with increasing the content of La in the range of 0-13[at%] and thin film of the PLZT(11/52/48) showed the value of 2.56[.mu.C/c $m^{2}$] and 21.1[kV/cm], respectively.ly.y.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.12C
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• pp.1133-1143
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• 2005

In this paper, we propose an enhanced two-step search scheme for rapid and reliable signal acquisition in UWB systems under multipath channels. The proposed TSS-LS (Two-Step Search scheme with the Linear search based Second step) achieves rapid acquisition performance comparable to the conventional TSS-BS (Two-Step Search scheme with the Bit reversal search based Second step) already proposed by the authors, based on the single-dwell search with two-step thresholds and search windows. However, unlike the TSS-BS which employs the bit reversal search in the second step, the proposed TSS-LS utilizes the linear search in the second step to improve the reliability of signal acquisition. Simulation results with multipath channel models by IEEE 802.15.3a show that the two-step search schemes for the UWB signal acquisition can achieve sig nificant reduction of the required mean acquisition time as compared to general search schemes. In addition, we observe that the proposed TSS-LS achieves quite good bit error rate performance for large signal-to-noise ratios, which is favorably comparable to the case of ideal perfect timing.

• Smart Structures and Systems
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• v.16 no.2
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• pp.281-294
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• 2015

Bolted joint connection is the most commonly used connection element in structures and devices. The loosening due to external dynamic loads cannot be observed and measured easily and may cause catastrophic loss especially in an extreme requirement and/or environment. In this paper, an innovative Real-time Cross-Correlation Method (RCCM) for monitoring of the bolted joint loosening was proposed. We apply time reversal process on stress wave propagation to obtain correlation signal. The correlation signal's peak amplitude represents the cross-correlation between the loosening state and the baseline working state; therefore, it can detect the state of loosening. Since the bolt states are uncorrelated with noise, the peak amplitude will not be affected by noise and disturbance while it increases SNR level and increases the measured signals' reliability. The correlation process is carried out online through physical wave propagation without any other post offline complicated analyses and calculations. We implemented the proposed RCCM on a single bolt/nut joint experimental device to quantitatively detect the loosening states successfully. After that we implemented the proposed method on a real large structure (reaction wall) with multiple bolted joint connections. Loosening indexes were built for both experiments to indicate the loosening states. Finally, we demonstrated the proposed method's great anti-noise and/or disturbance ability. In the instrumentation, we simply mounted Lead Zirconium Titanate (PZT) patches on the device/structure surface without any modifications of the bolted connection. The low-cost PZTs used as actuators and sensors for active sensing are easily extended to a sensing network for large scale bolted joint network monitoring.

• The Journal of the Acoustical Society of Korea
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• v.36 no.1
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• pp.23-29
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• 2017

A concept of a VSA (Virtual Source Array) is the method for an acoustic spatio-temporal focus at a selected location in the outbound direction with respect to the VSA without the need of a probe source as combines a TRP (Time-Reversal Processing) and time-delay and beam-steering. However, in TRP using the VSA concept, it is limited to the critical angle and the short distances relevant to the VSA. In this paper, the waveguide invariant theory is applied to the VSA concept to refocus the received field at ranges greater other than the critical angle and the short ranges by shifting the focused field. The suggested method is verified via numerical simulation, and the results show that the robust acoustic focusing is achieved on the selected location regardless of the limitation on the conventional VSA concept.

• Smart Structures and Systems
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• v.15 no.1
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• pp.135-150
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• 2015

Large concrete structures are prone to cracks and damages over time from human usage, weathers, and other environmental attacks such as flood, earthquakes, and hurricanes. The health of the concrete structures should be monitored regularly to ensure safety. A reliable method of real time communications can facilitate more frequent structural health monitoring (SHM) updates from hard to reach positions, enabling crack detections of embedded concrete structures as they occur to avoid catastrophic failures. By implementing an unconventional mode of communication that utilizes guided stress waves traveling along the concrete structure itself, we may be able to free structural health monitoring from costly (re-)installation of communication wires. In stress-wave communications, piezoelectric transducers can act as actuators and sensors to send and receive modulated signals carrying concrete status information. The new generation of lead zirconate titanate (PZT) based smart aggregates cause multipath propagation in the homogeneous concrete channel, which presents both an opportunity and a challenge for multiple sensors communication. We propose a time reversal based pulse position modulation (TR-PPM) communication for stress wave communication within the concrete structure to combat multipath channel dispersion. Experimental results demonstrate successful transmission and recovery of TR-PPM using stress waves. Compared with PPM, we can achieve higher data rate and longer link distance via TR-PPM. Furthermore, TR-PPM remains effective under low signal-to-noise (SNR) ratio. This work also lays the foundation for implementing multiple-input multiple-output (MIMO) stress wave communication networks in concrete channels.

• Journal of Aquaculture
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• v.1 no.1
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• pp.53-66
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• 1988

Histological study was conducted to determine the initial treatment time and treatment period of hormone for sex reversal in accordance with gonadal development and sexual differentiation in Oreochromis niloticus. The effects of various concentrations and various treatment periods of 17$\alpha$-methyltestosterone (MT) on sex reversal, growth, and condition factor were also evaluated. Paired primodial gonads were formed 9 days after hatching, when germ cells began their gradual multiplication and development into gonial ones. Sex differentiation of gonads either into ovaries or testes became histologically discernible about 20 days after hatching with formation of ovarian cavity and efferent duct. All feed treated with MT at 15 ppm for 10 days or more produced populations of males $95\%$ or above. All male populations were produced at 15 ppm MT for 40 days, and 30 ppm for 30 and 40 days. Growth of hormone-treated-fish was faster than that of untreated ones and the condition factor of hormone-treated-fish was greater than that of untreated ones 77 days after hatching.

• Journal of Aquaculture
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• v.9 no.3
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• pp.279-285
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• 1996

The effects of various concentrations of $17{\beta}-methyltestosterone$ (MT) or $17{\beta}-estradiol\;(E_2)$ on sex reversal, survival and growth rates of olive flounder, Paralichthys olivaceus were investigated. MT and $E_2$ were treated to juvenile flounder for 60 days from 30 (total length : 14.5 mm) to 90 (TL : $10.41\~11.17$ mm) days after hatching. Fish were treated with 0, 1, 10 and 100 ppb of MT or $E_2$ in the rearing water for 2 hours per day. At the time of 200 days after hatching, fish were sampled to examine sex ratio. One hundred pub of MT produced $100\%$ male, however 1 and 10 ppm MT produced 72.5 and $87.2\%$ males. One, 10 and 100 ppb of $E_2$ produced 75.5, 91.9 and $97.2\%$ females, respectively. Survival and growth rates of each experimental group at the end treatment were not significantly different from those of the control (P>0.05).

• Journal of Chest Surgery
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• v.13 no.4
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• pp.346-355
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• 1980

It has been proposed that wide individual variation in response to heparin be not considered in the conventional set protocol for the control of heparin and protamine during extracorporeal circulation. In this paper, two protocol of heparin and protamine therapy were compared to assess the role of the Activated Clotting Time [ACT] in relation to heparin, protamine, and postoperative blood loss and transfusion. The study groups consisted of the 31 patients [adults 15 and children 16] anticoagulated with the conventional heparin protocol and the 31 patients [adults 15 and children 16] anticoagulated with ACT protocol during extracorporeal circulation. In the conventional heparin protocol, two mg of heparin per kg was administered initially with an additional 0.75 mg of heparin per kg every 30 minutes of extracorporeal circulation, and reversal was accomplished with protamine in a dose of 1.5 times the total milligram of heparin. In the ACT protocol, two mg of heparin per kg was administered initially with an additional dose of heparin enough to reach an ACT of 480 seconds [within safe zone 300 to 600 seconds] from the patient`s dose response curve every 1 hour of extracorporeal circulation, and reversal was done with protamine in a dose of 1.3 times the milligram of the residual heparin. The results were summarized as follows. After a dose of 2 mg per kg of heparin, the patient`s ACT varied from 240 to 600 seconds in adults and from 240 t~ 660 seconds in children. In the ACT group the total amount of heparin administered was markedly reduced when compared to the conventional group, and less protamine was required to neutralize heparin. The dose of heparin administered decreased from 7.07 [SE 0.42] mg/kg of the conventional group to 4.92 [SE 0.32] mg/k8 of the ACT group in adults and from 10.17 [SE 1.15] mg/kg to 5.23 [SE 0.24] mg/kg in children, which represent 30.4% and 48.6% decrease respectively. The dose of protamine administered for reversal decreased from 10.6 [SE 0.63] mg/kg of the conventional group to 3.35 [SE 0.35] mg/kg of the ACT group in adults and from 15.7 [SE 1.70] mg/kg to 3.26 [SE 0.27] mg/kg in children, which represent 68.4% and 79.2% respectively. The ratio of protamine to heparin administered in the conventional group was 1.50:1 in adults and 1.54:1 in children, but in the ACT group 0.68:1 in adults and 0.62:1 in children. Postoperative blood loss and transfusion revealed no statistically significant difference between the two groups. Although six patients in the conventional group and one in the ACT group needed re-exploration for continuous hemorrhage, no case of generalized oozing was encountered, and in each case a definite bleeding site was identified. Author would like emphasizing the value of the ACT protocol in controlling heparin and protamine administration during extracorporeal circulation.