碳纳米管-聚二甲基硅氧烷的光声特性

Photoacoustic Properties of Carbon Nanotubes-Polydimethylsiloxane

碳纳米管-聚二甲基硅氧烷(CNT-PDMS)是一种新型的激光超声换能器(LIU-T)复合材料,具有高频率、宽带宽、高振幅的特性。该复合薄膜可作为高效、鲁棒的超声发射器用于诊断和治疗。纳米复合材料的固有结构提供了独特的热、光学和机械性能,这不仅有利于能量转换,而且对脉冲激光烧蚀具有很好的鲁棒性。PDMS聚合物具有高热弹性系数有利于材料的伸缩从而产生超声。研究了几种不同复合薄膜产生的光声信号特性,测试了不同衬底和水介质条件下的光声信号特性。利用碳纳米材料的高吸光性和PDMS聚合物的高膨胀性制作激光超声换能器,不但降低了材料的厚度,还有望产生高频高强度超声信号。实验用硬玻璃衬底厚度约为1 mm,软薄膜衬底厚度在微米级,水介质条件下的厚度为3 mm。在脉冲激光激励下,水介质下软薄膜条件、硬玻璃衬底、软薄膜衬底涂层端面超声压力分别为2.0, 3.9和5.2 MPa。通过一系列的研究得出了结论:(1)软薄膜衬底(3×3)比硬玻璃衬底(3×3)更具有良好的负脉冲,更适合用在光声空化治疗方面;(2)水介质条件下不利于产生高强度光声信号。总而言之,采用激光超声换能器比压电换能器更具有产生高振福,带宽宽的超声信号的潜力,而且提供了一种没有电子等干扰结构的超声激励新方法,有望成为替代压电换能器的新一代激光超声换能器。这种新方法应用在磁声电成像领域可以大大减少超声激励源的干扰。同时,相对于将CNT混入PDMS中的方法,该方法更具有简单方便节省材料等优点。对于硬玻璃传统型衬底,实现的软薄膜衬底能产生较高的声压5.2 MPa,并且中心频率在5MHz,-6 dB超声带宽也相对较宽接近5MHz,相比于早在2014年实现的CNT-PDMS激光超声换能器产生的4.5 MPa声压,本文方法更具有临床应用前景,应用在磁声电成像等方面具有很好的避免电磁干扰效果。

Carbon nanotubes-polydimethylsiloxane(CNT-PDMS)is a new type of laser ultrasonic transducer(LIU-T)composite material with high frequency,wide width and high amplitude.The composite film can be used as an efficient and robust ultrasonic emitter for diagnosis and treatment.The intrinsic structure of nanocomposites provides unique thermal,optical and mechanical properties,which are not only conducive to energy conversion but also robust to pulsed laser ablation.PDMS polymers have high thermoelastic coefficients that allow materials to stretch and produce ultrasound.In this paper,the characteristics of photoacoustic signals produced by several kinds of composite films are studied,the photoacoustic signal characteristics under the different substrate and water boundary conditions were tested.Photoacoustic transducers made of carbon nanomaterials with high light absorption and PDMS polymers with high expansibility not only reduce the thickness of materials but also are expected to generate high frequency and high intensity ultrasonic signals.The thickness of the hard glass substrate realized in this paper is about 1 mm,the thickness of the soft film substrate is at the micron level,and the thickness of water boundary conditions are 3 mm.Under pulsed laser excitation,the ultrasonic pressure at the end surfaces of water boundary conditions and hard glass substrates and soft film substrates was 2.0,3.9 and 5.2 MPa,respectively.Through a series of studies,it is concluded that:(1)soft film substrate(3×3)has better negative pulse than hard glass substrate(3×3),which is more suitable for photoacoustic cavitation treatment;(2)water boundary conditions are not conducive to the generation of high-intensity photoacoustic signals.In a word,compared with piezoelectric transducers,laser-induced ultrasonic transducers have more potential to produce high-amplitude ultrasonic signals with a wide width and provide a new method of ultrasonic excitation without interference structures such as electronics,which is expected to be a new generation of laser ultrasonic transducers to replace piezoelectric transducers.The application of this new method in magneto-acoustic imaging can greatly reduce the interference of ultrasonic excitation sources.At the same time,compared with mixing CNT into PDMS,the method adopted in this experiment is more simple,convenient and material saving.For traditional hard glass substrate,the implementation of soft film substrate can produce high sound pressure 5.2 MPa,and center frequency in 5 MHZ,and-6 dB ultrasound is relatively close to 5 MHz wide bandwidth,compared with the 4.5 MPa pressure produced by the early implementation of CNT-PDMS Photoacoustic transducer in 2014,this paper implementation has more clinical application prospect,applied in Magneto-acoustic electric imaging etc.to avoid electromagnetic interference has the very good effect.