Thermoacoustic wave generation in multilayered thermophones with cylindrical and spherical geometries

Abstract

A thermoacoustic sound generation model, based on the classical balance equations of the continuum mechanics, is here developed for the cylindrical and the spherical thermoacoustic wave generation. In both geometries, the model considers an arbitrary multilayered structure, where each layer can be fluid or solid and it is characterized by the fully coupled thermo-visco-acoustic response. It means that the viscous behavior and the thermal conduction are considered in each layer. The model is based on a unified representation of cylindrical or spherical thermoacoustic waves, which is valid for both fluid and solid phases. Thanks to the continuity of temperature, particle velocity, normal stress and heat flux between adjacent layers, the model can be implemented by means of a versatile matrix approach, allowing flexible analysis and design of cylindrical or spherical thermophones. Any thermoacoustic variable can be determined at any position, any frequency and for any input power. The results are compared with the models already existing in the literature and the underlying physics is thoroughly discussed. The analysis is focused on the better understanding of the thermoacoustic generation with application to the state of the art of the thermophone technology.

Acoustic Wave Generation in Nanofluids: Effect of the Kapitza Resistance on the Thermophone to Mechanophone Generation Mechanism Transition

“…It can be deduced, via a thorough analysis, that, in the low-frequency range, the thermophone pressure always falls between two asymptotic bounds scaling as and ω, respectively, the actual behavior depending on the thermal parameters and geometry of the system. , Indeed, the ideal behavior, scaling as ω in the low-frequency range, is considered as the ultimate limit for the thermoacoustic efficiency. ,, The high-frequency thermophone regime (whose scaling law varies from 1/ω to , depending on r ) is less studied in the literature since it is not useful for most applications. However, the thermophone asymptotic behavior for large ω can be found, e.g., in refs and , where the near-field sound pressure level is investigated over a wide frequency range. Unfortunately, no comparison is possible for the mechanophone case, for each thermal boundary resistance value.…”

“…In particular, in ref , the concept of the piston model was introduced. In this context, a great deal of effort has been devoted to modeling and improving the thermophone response in the high-frequency range. − The bottom line is that the penetration length of the thermal wave in the fluid decreases as ω –1/2 , ω being the angular frequency with which heat power density is delivered to the nanotransducer. Thus, the capacity to generate an acoustic wave decreases accordingly, and the efficiency of the thermophone mechanism is severely degraded in the high-frequency regime.…”

“…This approach allows us to formally retrieve the interplay of the parameters ruling the thermoacoustic generation in a clear, explicit form. As a matter of fact, operating with a 1D geometry in the frequency domain yields analytical solutions in relatively simple terms (e.g., exponential rather than Bessel functions, as in the case of a cylindrical system 77 ). We provide evidence that there is a specific threshold frequency beyond which the mechanophone becomes more effective than the thermophone.…”

Tuning photoacoustics with nanotransducers via thermal boundary resistance and laser pulse duration

“…In this context, liquid-immersed metal nanoparticles have proven to be efficient photoacoustic generators due to their tunable optical absorption properties [6][7][8][9] , high contrast imaging features 10,11 and biocompatibility 12,13 . Great efforts have been devoted to optimise the parameters allowing a more efficient photoacoustic conversion, such as size, geometry 9,[14][15][16] and transducer materials 17 . Yet, despite its relevance for applications, the combined effects of the pulse temporal width, τ L , [18][19][20] and the thermal boundary resistance [21][22][23] (TBR) tunabilities remain relatively unexplored and lack a thorough rationalization.…”

Ultrafast nano generation of acoustic waves in water via a single carbon nanotube

“…The absorber then launches acoustic waves either by (a) heat transfer to the surrounding water, thus triggering water thermal expansion, or (b) direct thermal expansion of the absorber itself, which acts as a piston for the aqueous medium. In the former case the transducer nano-object is referred to as a thermophone [19] , [20] , in the latter as a mechanophone , see Fig. 1 .…”