An acoustical method for temperature measurement of large-scale spaces in a wind field is described. The real-time thermometry in a long span of 100 m was realized by the adoption of a bidirectional sound probe as a temperature sensor and a wireless local area network for controlling sensors. The probe mainly consists of two loudspeakers and two microphones. An accurate mean spatial temperature was measured without the interference of the wind in the area by the bidirectional probe. We carried out numerical simulations to confirm the validity of our method. The mean temperature was satisfactorily measured by this principle under various distributions of wind velocity. In field measurements, mean spatial temperature along a 100-m-long baseline was measured by the system with a conventional thermometer as a reference. The temperature change over one hour at 30 s intervals was compared to the change in the reference temperature at the center of the baseline. The results indicated that the system recorded a long periodic change in air temperature without the effects of local turbulence and wind. The advantages of the proposed system compared to a conventional thermometer are real-time, wireless and noncontact measurements.
Abstract Measurement — the act of measuring physical properties that we perform — has the potential to contribute to the successful advancement of sciences and society. To open doors in physics and other sciences, various measurement methods and related applications have been developed, and ultrasound has remained a useful probe, power source, and interesting measurement object for the past two centuries. In this paper, we first summarize the basic principles of ultrasound from the viewpoint of measurement techniques for readers who just have started studying or are interested in the field of ultrasonic electronics. Moreover, we also introduce recent studies — ultrasonic properties of materials, measurement techniques, piezoelectric devices, nonlinear acoustics, biomedical ultrasound, and ocean acoustics — and their trends related to measurement techniques in ultrasonic electronics to provide some ideas for related applications.
Visible light communication is one of the key technologies for intelligent transport systems (ITS). However, current visible light communication systems require high-cost devices, such as high-speed image sensors, to support their high transmission rates. In this paper, we designed a communication system with combination of a low-speed commercial image sensor and a polygon mirror — namely, a fast-blinking light signal is scanned by the polygon mirror and captured as a residual image on the low-speed image sensor — to achieve visible light communication on existing mobile devices with high transmission rates. We also analyzed some required conditions, such as the relationship between the exposure time of the image sensor and the optimal resolution, and conducted experiments for performance evaluation. As a result, we found that the proposed system could achieve a data rate of 120bps, 10 times faster than that of the existing scheme when we compare them using the same image sensor. We also found that the proposed system can achieve a practical bit error rate in a low-noise environment.
Abstract A method of suppressing sound radiation to the far field of a near-field acoustic communication system using an evanescent sound field is proposed. The amplitude of the evanescent sound field generated from an infinite vibrating plate attenuates exponentially with increasing a distance from the surface of the vibrating plate. However, a discontinuity of the sound field exists at the edge of the finite vibrating plate in practice, which broadens the wavenumber spectrum. A sound wave radiates over the evanescent sound field because of broadening of the wavenumber spectrum. Therefore, we calculated the optimum distribution of the particle velocity on the vibrating plate to reduce the broadening of the wavenumber spectrum. We focused on a window function that is utilized in the field of signal analysis for reducing the broadening of the frequency spectrum. The optimization calculation is necessary for the design of window function suitable for suppressing sound radiation and securing a spatial area for data communication. In addition, a wide frequency bandwidth is required to increase the data transmission speed. Therefore, we investigated a suitable method for calculating the sound pressure level at the far field to confirm the variation of the distribution of sound pressure level determined on the basis of the window shape and frequency. The distribution of the sound pressure level at a finite distance was in good agreement with that obtained at an infinite far field under the condition generating the evanescent sound field. Consequently, the window function was optimized by the method used to calculate the distribution of the sound pressure level at an infinite far field using the wavenumber spectrum on the vibrating plate. According to the result of comparing the distributions of the sound pressure level in the cases with and without the window function, it was confirmed that the area whose sound pressure level was reduced from the maximum level to −50 dB was extended. Additionally, we designed a sound insulator so as to realize a similar distribution of the particle velocity to that obtained using the optimized window function. Sound radiation was suppressed using a sound insulator put above the vibrating surface in the simulation using the three-dimensional finite element method. On the basis of this finding, it was suggested that near-field acoustic communication which suppressed sound radiation can be realized by applying the optimized window function to the particle velocity field.
Graphical authentication schemes have the advantage of being more memorable than conventional passwords. Although some image distortion methods have been proposed to prevent the risks of over-the-shoulder attacks (OSAs), these methods cannot prevent camera recording attacks, as the key images are the same each time. In this study, we propose a graphical authentication scheme that generates various distorted images, named Estimating Your Encodable Distorted images (EYEDi). EYEDi generates distorted images by applying several image processing filters to the original images. Moreover, EYEDi estimates the appropriate image processing filter strength based on the authentication data. To measure attack resistance, twenty participants performed three types of attacks (OSA, camera recording attack, and screenshot) 300 times, each using existing methods and EYEDi. The classification error rate of all three types of attacks showed that EYEDi had a lower classification error rate between the legitimate user and attackers. Especially for the screenshot attack, which is the most severe threat model, the existing method was completely broken through, while EYEDi prevented the attacks with a classification error rate of 10%. This result shows that EYEDi can eliminate the screenshot attacker by using the difference in authentication times and a simple improvement in defense performance.
