Standard Installation for the Transmission of Units of Sound Pressure in the Ultrasonic Frequency Range
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ACOUSTIC MEASUREMENTS STANDARD INSTALLATION FOR THE TRANSMISSION OF UNITS OF SOUND PRESSURE IN THE ULTRASONIC FREQUENCY RANGE
А. Е. Isaev, А. М. Polikarpov, S. V. Sil’vestrov, and N. G. Shcherblyuk
UDC 534.6
We present information about a standard installation used for the calibration of hydrophones at frequencies of 0.1–3.0 MHz. The installation is created with an aim to extend the frequency range of the GET 55-2017 State Primary Standard to the region of high-frequency ultrasound. The necessity of development of this installation is justified. We briefly consider basic principles of its operation and the possibilities of measurements. The requirements to the characteristics of ultrasonic transducers are discussed. In the choice of standard transducers, we give priority to their time stability because, in the course of transmission of the unit with the help of a tone signal, the uniformity of the frequency characteristic of sensitivity of the transducer is not of primary importance. To reduce the influence of directivity, we use a precise four-coordinate system of positioning of the transducers, which includes the possibility of control of their mutual positions with the help of a laser beam. We also consider the problems connected with the possibility of passing to higher frequencies. Keywords: hydroacoustics, high-frequency ultrasound, standard, calibration, hydrophone.
Introduction. As a natural result of the development of hydroacoustic technologies, we can mention the use of increasingly high frequencies for practical purposes. Thus, in the megahertz band, the length of acoustic waves in water is smaller than 1 mm, which makes it possible to emit short pulses with steep fronts, form narrow sound beams, and increase the productivity of information transmission systems due to the application of broadband signals. Ultrasound is used for the precise determination of distances to obstacles in automobile rear park systems. In a similar way, it is used for the purposes of laying of underwater pipelines. The requirements to the directional diagram are, in this case, not so severe as, e.g., for echo sounders (sonars). A sonar used for fishing must not only detect the presence of fish but also determine its location, i.e., must have an acceptable directional diagram. Moreover, the emitter of a sound-imaging device characterized, unlike other devices, by high space resolution (up to 1° in the angular coordinate and several centimeters in the distance), which makes it possible not only to select a mark in the direction to the object but also to determine its shape, must meet severer requirements. The working frequency of a domestic sound-imaging device with an angular resolution of 0.9 × 0.9° is equal to 1 MHz [1, 2]. To improve the characteristics of sonars, the researchers use more and more complex signals and, at the same time, the requirements to monitoring of the shape of emitted acoustic signal become more strict. To construct a three-dimensional image in the holographic system of acoustic imaging, it is necess
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