Cylindrical pipes are widely used in industries such as nuclear power plants and micro total analysis systems (mTAS). Measuring the flow rate of fluid in such pipes is critical. Ultrasonic flowmeters are noncontact, nondestructive, and easy-to-use devices, and are therefore widely used. However, typical bulk-wave-based ultrasonic flowmeters cannot be used for pipes narrower than the wavelength of bulk waves. For such pipes, we are currently developing a ''guide wave flowmeter'' that uses guide waves instead of bulk waves. Previously, we theoretically and experimentally investigated a pipe filled with quiescent fluid for all modes [Jpn. J. Appl. Phys. 45 (2006) 4573]. In this study, we expanded our theoretical investigation to a cylindrical pipe containing flowing fluid, and then compared the results with experimental results. Both the theoretical and experimental results revealed that the flow rate can be determined by measuring the sound velocity (propagation time) of guide waves. This is the operating principle of our guide wave flowmeter.
Since scanning probe microscopes scan the probes mechanically along the samples, accuracy of lateral scales of acquired images is mainly determined by the calibration of the movement of the end point of the probes. A dual tunneling unit scanning tunneling microscope (DTU-STM) with an xy stage for simultaneous lateral scanning of both the sample and the scale-reference crystal was developed. It enables calibration of the lateral scale of the sample image under the assumption that the lattice spacing is constant. Accuracy and problems of the proposed method were evaluated by comparing images of graphite simultaneously or consecutively acquired with the DTU-STM. For simultaneously acquired images in the 10 nm range, calibration of drift rates of the tips to the samples, and tilt of the samples to the xy plane were found to be effective in improving the accuracy of comparison measurement to 98.9±1.5%, regardless of orientation. The accuracy marked a higher value of 99.7±0.25% in the direction of the line scan, since the effect of thermal drift is less dominant in the direction. Consecutive single-line scanning of 150 nm with a rate of 380 ms/line, at 30 min intervals, gave an accuracy of over 99.98±0.036%.
Two-dimensional positioning control of the sample stage of a scanning tunneling microscope (STM) was implemented by having an STM tip in register with arrays of atoms of a crystal attached to the sample stage. The position of this reference crystal was modulated with an amplitude of 70 pm (p-p), at a frequency of 3.3 kHz, in the x and y directions consecutively, to obtain the differential of the tunneling current in the two directions. The differential signals were accumulated using two digital integrators and fed to the x and y piezo elements of the sample stage. With such a configuration, the lateral position of the sample stage could be regulated using the crystalline lattice as the scale reference. For example, lateral drift between the sample stage and the tip could be eliminated by aligning an atom of the crystal to the tip. Also, incremental motions of the sample stage could be implemented by having an array of atoms move over the tip. Because the technique offers subnanometer level accuracy, it is a powerful tool for metrological applications as well as for accumulation of weak signals that necessitate averaging without lateral drift of the scanned area.
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