Precision measurements of the propagation velocity of longitudinal ultrasonic waves in solids by resonance method
The possibility of extending the frequency range and functional capabilities of the State primary standard for the units of propagation velocities and damping coefficient of ultrasonic waves in solids GET 189-2014 at reproduction and transfer of the unit of propagation velocity of longitudinal ultrasonic waves in solids by using the resonance measurement method has been studied. This characteristic of solids is used in thickness measurement, flaw detection and other scientific and practical fields. The results of research of the resonance method of measuring the propagation velocity of longitudinal ultrasonic waves in solids are presented. In the experiment, velocity measures made of optical glasses and leucosapphire were used, which allow measuring the velocity in the range of 4000–11200 m/s with its frequency dispersion less than 10–4. Contactless broadband capacitive transducers are used to excitation and registration of the longitudinal ultrasonic waves in the frequency range from 1 to 100 MHz. The accuracy of the measurement results obtained by the resonance method was analyzed in comparison with the laser pulse method used in GET 189-2014. It is established that the absolute error of measurements of the propagation velocity of longitudinal ultrasonic waves in solids by the resonance method, defined as a deviation from conventional true value of a quantity, is not more than 1 m/s depending on the material of the measure, the relative error is less than 10 –4. In the low- frequency range, a monotonic increase in the measured velocity of longitudinal ultrasonic waves was observed when applying a velocity measure made of leucosapphire, which may be due to the physical properties of this material. The obtained results confirm the possibility of extending the frequency range and functional capabilities of GET 189-2014 by using the resonance method of measuring the propagation velocity of longitudinal ultrasonic waves and capacitive transducers, which do not require high (optical) quality of the surfaces of the certified measures.
