Aliev Ali E, Codoluto Daniel, Baughman Ray H, Ovalle-Robles Raquel, Inoue Kanzan, Romanov Stepan A, Nasibulin Albert G, Kumar Prashant, Priya Shashank, Mayo Nathanael K, Blottman John B
Alan G. MacDiarmid NanoTech Institute, University of Texas at Dallas, Richardson, TX 75083, United States of America.
Nanotechnology. 2018 Aug 10;29(32):325704. doi: 10.1088/1361-6528/aac509. Epub 2018 May 15.
The combination of smooth, continuous sound spectra produced by a sound source having no vibrating parts, a nanoscale thickness of a flexible active layer and the feasibility of creating large, conformal projectors provoke interest in thermoacoustic phenomena. However, at low frequencies, the sound pressure level (SPL) and the sound generation efficiency of an open carbon nanotube sheet (CNTS) is low. In addition, the nanoscale thickness of fragile heating elements, their high sensitivity to the environment and the high surface temperatures practical for thermoacoustic sound generation necessitate protective encapsulation of a freestanding CNTS in inert gases. Encapsulation provides the desired increase of sound pressure towards low frequencies. However, the protective enclosure restricts heat dissipation from the resistively heated CNTS and the interior of the encapsulated device. Here, the heat dissipation issue is addressed by short pulse excitations of the CNTS. An overall increase of energy conversion efficiency by more than four orders (from 10 to 0.1) and the SPL of 120 dB re 20 μPa @ 1 m in air and 170 dB re 1 μPa @ 1 m in water were demonstrated. The short pulse excitation provides a stable linear increase of output sound pressure with substantially increased input power density (>2.5 W cm). We provide an extensive experimental study of pulse excitations in different thermodynamic regimes for freestanding CNTSs with varying thermal inertias (single-walled and multiwalled with varying diameters and numbers of superimposed sheet layers) in vacuum and in air. The acoustical and geometrical parameters providing further enhancement of energy conversion efficiency are discussed.
由无振动部件的声源产生的平滑、连续声谱、柔性有源层的纳米级厚度以及制造大型共形投影仪的可行性引发了人们对热声现象的兴趣。然而，在低频时，开放碳纳米管片（CNTS）的声压级（SPL）和声产生效率较低。此外，易碎加热元件的纳米级厚度、它们对环境的高敏感性以及热声发声实际所需的高表面温度使得独立的CNTS需要在惰性气体中进行保护性封装。封装能使低频声压按预期增加。然而，保护外壳限制了电阻加热的CNTS以及封装器件内部的散热。在此，通过对CNTS进行短脉冲激励来解决散热问题。结果表明，能量转换效率总体提高了四个多数量级（从10提升到0.1），在空气中1米处声压级为120 dB re 20 μPa，在水中1米处声压级为170 dB re 1 μPa。短脉冲激励能使输出声压随输入功率密度大幅增加（>2.5 W/cm）呈稳定线性增长。我们对具有不同热惯性（不同直径和叠加层数的单壁和多壁）的独立CNTS在真空和空气中不同热力学状态下的脉冲激励进行了广泛的实验研究。讨论了能进一步提高能量转换效率的声学和几何参数。
