Research On The Graphene Loudspeakers Based On Thermoacoustic Effect

This thesis introduces the fabrication of graphene and the study and the use of graphene thermophones.As a novel sonic transducer,the thermophone has many advantages such as wide frequency range and high sound pressure.Graphene has excellent thermal property,electrical property and mechanical property since the graphene has been found.Combining the two characteristics,this thesis develops a graphene thermophone.Fabrication,theoretical model,properties and use of the graphene thermophone are introduced.First,this thesis revises and advances the way of high temperature reduction for graphene fabrication after referring to other ways for graphene fabrication.Graphene has perfect structure,high thermal conductivity and high electrical conductivity,and is reduced by heating with several temperature classifications.Due to the heating,graphene will generate the gasbags on its surface and in its inner.After that,high pressure with different degrees will be used to graphene for removing the gasbags and acquiring the pyknotic graphene.This way can reduce the graphene greatly and avoid the generation of breakage and holes.The structure of graphene is analyzed to investigate degree how the graphene is repaired.In the end,the thermal conductivity,electrical conductivity and flexibility are detected to make sure whether the graphene is appropriate for the thermophone.Then,the fabrication of graphene thermophone is mentioned.And this thesis explores the comparison for alternating current stimulation only and with direct current bias and analyzes the influence on thermophone.The theoretical models for generation of sound,sound directivity and surface temperature are introduced,and some relative experiments about sound pressure,sound directivity and temperature are adopted to verify the rationality.The properties of graphene thermophone are mentioned in the passage about the static characteristics and dynamic characteristics.The static characteristics are measured which include maximal sound pressure level,frequency range,hysteresis,excursion and resistance.And the transient response and frequency transition are also measured by some facilities.The way to improve the sound pressure is discussed and combines with the theoretical model,as a result,declining the thickness of film and changing the substrate with low thermal conductivity are useful.Finally,in order to check the flexibility of the graphene thermophone,the graphene which sticks to the flexible substrate can be put on the cylindrical tubes with different radiuses,and the sound pressure level will be measured.Finally,the thesis mentions the applications of graphene thermophone.An omnidirectional speaker is designed which can transmit the sound around the speaker without decay.So the signals will be more convenient to send.Due to the wide frequency range,we should take advantage of the ultrasonic absolutely,an ultrasonic earphone.This earphone is different from the commercial earphone which can transmit the sound from 20 Hz to 20 k Hz only because of the traditional sound generation principle,its sound frequency range can reach the ultrasonic level.We do an experiment about the reaction of rabbit.The animal presents an obvious characteristic about the ultrasonic signals.So this earphone is used to transmit the signals to animals and command them in some special conditions,such as the dogs rescue the people after earthquake.Combining with the omnidirectional speaker,it can transmit the signals in wide range.