I.V.Vovk, V.T.Matsipura Sound radiation by grating formed by coaxial cylindric piezoceramic shells with the end screens. Part IV. Pulse excitation |
Acoustic bulletin, Vol. 5 ¹ 2, (2002) |
| A problem on the sound radiation by grating consisting of coaxial piezoceramical shells and end screens made of acoustically soft truncated cones is solved. The electric excitation of the shells was supposed to be in a form of periodic sequence of radio pulses. On the basis of the obtained solution the vibrational velocities of the shells and the grating's far field were analyzed as functions of time and parameters of radio pulses. It was shown that when all the shells are excited with identical radio pulses, the time dependencies of their velocities (within the action interval of the radio pulse) are essentially different both from the exciting pulse, and from each other. These differences are especially huge in the case when the pulse carrier frequency lays within the limits of resonant frequencies of the shells. It is established that the time trends of pressure changes in the far field are significantly dependent on the direction and are the most expressed in the 45o-sectors, adjacent to the grating's axis of symmetry. It was found that in a pulse-to-pulse interval the pronounced acoustical reverberation is observed. This effect is due to the power interchange between the shells performing free vibrations during this period. Some techniques for practical estimation of the grating's acoustical characteristics under the radio pulse excitation are proposed and demonstrated. It is shown that such estimates satisfactorily fit with the estimates made under monochromatic excitation of the grating. |
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KEY WORDS: radiating grating, pezoelctric shell, screen, far-field, directivity characteristic, pulse excitation |
| TEXT LANGUAGE: Russian |