Photoacoustic Properties Of CNT-PDMS Composite Films Under Long Pulse Laser Irradiation

Underwater communication based on acoustic waves is an important means to realize long-distance wireless communication in the ocean.In order to solve the deficiencies of the piezoelectric transducer used in the traditional underwater acoustic communication such as large volume,complicated electrical connection,and the need for waterproof measures,at the same time,in order to obtain lower frequency acoustic waves to meet the transmission distance requirements of underwater acoustic communication.In this paper,CNT-PDMS composite film photoacoustic transducer is constructed and its photoacoustic characteristics under the action of long pulse laser are studied.The photoacoustic properties of the CNT-PDMS composite film under the action of a long pulse laser were studied theoretically.Based on the heat conduction equation,the mathematical model of the temperature field inside the film was established with the equal heat flux as the boundary condition,and the physical models of the stress,strain and exiting acoustic waves inside the film were established by the thermoelastic mechanics theory and the thermoacoustic coupling theory.The variation law of temperature,thermal expansion stress,acoustic pressure and frequency spectrum of CNT-PDMS composite film with geometrical parameters of composite film and incident laser parameters was studied by simulation.The results show that the long pulse laser acting on CNT-PDMS composite film can produce medium or high frequency acoustic wave.For example,when the pulse width of incident laser is 100?s,the center frequency of outgoing acoustic wave is 6875 Hz.The CNT-PDMS composite film under the action of a long pulse laser pulse sequence,the acoustic pressure and frequency spectrum of the emitted acoustic wave vary with the duty cycle of the laser pulse sequence.It is concluded that the acoustic pressure amplitude of each acoustic wave in the acoustic wave sequence is the same as that of a single pulse laser,and that the frequency spectrum components of the acoustic wave sequence are determined by the duty cycle of the laser pulse sequence and the laser pulse width.A variety of CNT-PDMS composite films with different structures were produced,and a acoustic field measurement system was built.The test results show that adding a thin layer of PDMS between the CNT-PDMS composite film and the glass substrate can increase the acoustic pressure amplitude of the emitted acoustic wave by 10%.Increasing the mass fraction of CNT from 3% to 6% and 9% can increase the acoustic pressure amplitude of the emitted acoustic wave again by 11.5% and 16.2%.The measured amplitude and frequency spectrum of the emitted acoustic pressure of CNT-PDMS composite film are in good agreement with the simulation results.