Ultrasonic Lateral Displacement Sensor for Health Monitoring in Seismically Isolated Buildings.
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The transmitters are immobilized at a fixed point, whereas the receiver set-up is separately arranged on the opposite side.In order to improve measurement accuracy, a correction method that utilizes polynomial approximation is introduced.When five transmitters are arranged, their measurement range is easily extended up to ±60 mm with an accuracy of 0.7 mm.
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PubMed Central - PubMed
Affiliation: Department of Mechanical Engineering, Nagaoka University of Technology, Kamitomioka 1603-1, Nagaoka 940-2188, Niigata, Japan. matsuya@mech.nagaokaut.ac.jp.
ABSTRACT
An ultrasonic lateral displacement sensor utilizing air-coupled ultrasound transducers is proposed. The normally-distributed far field of an ultrasound transducer in a lateral direction is taken advantage of for measuring lateral displacement. The measurement system is composed of several air-coupled ultrasound transducers as a receiver and several transmitters. The transmitters are immobilized at a fixed point, whereas the receiver set-up is separately arranged on the opposite side. In order to improve measurement accuracy, a correction method that utilizes polynomial approximation is introduced. The difference between the corrected lateral displacement and the reference displacement is estimated to be 0.2 mm at maximum for the two transmitters system. A good responsiveness is demonstrated by conducting a dynamic response experiment. When five transmitters are arranged, their measurement range is easily extended up to ±60 mm with an accuracy of 0.7 mm. In both cases, the fluctuations to the measurement ranges show less than 1%. These results indicate that the developed sensor system is useful for measuring relative lateral displacement of a seismically isolated building in the field of structural health monitoring. No MeSH data available. Related in: MedlinePlus |
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Mentions: There is a non-negligible gap between obtained ultrasound intensity distributions and fitted curves that are based on Gaussian approximations as shown in Figure 6b. This gap seems to cause a fluctuation in calculated lateral displacement. So, we introduce a compensation coefficient to the gap as follows:(9)It1=e1(ln(I1I2))⋅I1(10)It2=e2(ln(I1I2))⋅I2where It1 and It2 are normally approximated values that are described on the fitted curve as shown in Figure 6b, e1 and e2 are compensation coefficients for the obtained ultrasound intensities I1 and I2, respectively. Compensation coefficients are expressed as functions of the logarithm of the ratio of I1 to I2 in Equations (9) and (10). Figure 8 shows the values of It1/I1 and It2/I2 by changing the logarithm of the ratio of I1 to I2 to derive the compensation coefficients e1 and e2. For these coefficients, polynomial approximation is applied because the values of It1/I1 and It2/I2 fluctuate greatly as shown in Figure 8. The compensation coefficients are represented as follows:(11)It1/I1=e1(ln(I1I2))=−0.26y6−0.04y5−0.04y4+0.16y3−0.05y2+0.12y−1.10(12)It2/I2=e2(ln(I1I2))=−0.15y6−0.37y5−0.06y4+0.26y3−0.06y2+0.04y+1.00where y shows the logarithm of the ratio of I1 to I2. As shown in Figure 8 and Equations (11) and (12), the compensation coefficients were successfully obtained. Figure 9a shows the corrected ultrasound intensity distribution with the application of Equations (11) and (12). Open circles show corrected values. The solid line shows the fitted curve previously shown in Figure 6b. The fitted curve and the corrected values overlap fairly well. Figure 9b shows the corrected lateral displacement. Open circles show the corrected lateral displacement. The solid line shows the reference displacement. From the Figures, it is clear that the corrected lateral displacement agrees well with the reference. The fluctuation between corrected values and the reference is within 0.20 mm at maximum. Because the fluctuation rate for the 30 mm range corresponds to 0.67%, it is verified that this system has sufficient accuracy for a small displacement region. For the actual measurement activity, a manual stage needs to be arranged under the transmitters or the receiver for the system calibration. After the calibration, the stage should be fixed as a base keeping its position at the origin. |
View Article: PubMed Central - PubMed
Affiliation: Department of Mechanical Engineering, Nagaoka University of Technology, Kamitomioka 1603-1, Nagaoka 940-2188, Niigata, Japan. matsuya@mech.nagaokaut.ac.jp.
No MeSH data available.