Thermal Wave Interference Research Articles

Thermally driven hybrid metastructure for multi-functional surface acoustic wave engineering

Acoustic wave engineering through solid mediums are essential for improving or optimizing the performances of various platforms, such as biomedical and industrial applications. Metamaterials or metasurfaces have been recently developed to artificially manipulate the wave propagation passing through mediums. However, they only conduct one fixed function passively, determined by the structure design for the particular wavelength, and their fabrication involves high-cost and complex procedures. Here, we report a thermally driven hybrid metastructure (HMS) for actively controlling surface acoustic waves. The HMS is designed as the layered structure of a thermoresponsive polymer (TP), thermal metamaterials (TMs) and an intermediate layer (IL) made of silica aerogel. For providing multi-functions, TPs conduct the considerable elastic modulus changes and corresponding wave manipulation at a certain glass transition temperature while TMs enable the programmed heating configuration, and the IL mitigates thermal and acoustic wave interference. By introducing the IL, the entire energy of the propagating wave is captured at the interface and interference between the wave and thermal energy is prevented, which directly reflects the temperature control through the TMs into the TP heating configuration. Versatile functions of programmable wave engineering including omnidirectional wave focusing-collimation through modified Luneberg lenses, dual-functioning focusing-bifurcation, and double refraction through 3-phase wave steering are demonstrated using the proposed HMS implemented by the temperature gradient design of TMs. This work will inspire tunable and scalable platforms for active controls of wave propagation enabled by thermal energy as a driving force.

Propagation and interference of thermal waves in turbulent thermal convection

We observe propagation and interference of two coherent thermal waves in the highly turbulent core of convective Rayleigh-B\'enard flow of cryogenic helium gas generated by top and bottom boundaries with harmonically oscillating temperatures. When the same amplitude of modulation is applied to both plates at slightly different frequencies, the resulting temperature interference pattern in the turbulent core shows a periodic increase and decrease in amplitude. If the observed time record of thermal wave interference were converted to corresponding pressure oscillations and shifted to higher frequencies, one would hear the acoustic beats often used, e.g., in tuning stringed musical instruments.

Development of a Generalized Photothermal Measurement Model for the Layer Thickness Determination of Multi-Layered Coating Systems

In this article, a general model for 1D thermal wave interference is derived for multi-layered coating systems (with n∈N coating layers) applied on a thermally thick substrate. Such a model means the first step to building a non-contact photothermal measurement device that is able to determine the coating thickness of each layer. Test objects are to be illuminated on the surface using planar, sinusoidal excitation waves with fixed frequencies leading to the generation of thermal waves inside the object. Due to the multi-layered structure, each of these thermal waves is reflected and transmitted at layer interfaces. This process leads to infinitely many wave trains that need to be tracked to formulate the final surface temperature as a superposition of all waves. A mathematical and physical formulation of thermal wave interference is needed to model this process and relate the dependencies of the layer thicknesses, the materials, and the frequencies to the phase angle data, which then can be measured using, e.g., an infrared camera. In practice, the thermal properties of the layers might be unknown, which makes the process even more difficult. This article presents a concept to determine the thermal properties in advance. Finally, numerical experiments are presented that demonstrate the feasibility of the introduced layer thickness determination process.

Significant enhancement of thermal conductivity in segregated(GnPs&MWCNTs)@Polybenzoxazine/(Polyether ether ketone) -based composites with excellent electromagnetic shielding

• Segregated structural composites assist in thermal conductivity enhancement. • Segregation provides more conductive reflective interfaces for shielding. • Polybenzoxazine modification increased polymer-filler interfacial interaction. • Hybrid fillers improve the interconnected filler transmission network. With the rapid development of integration and multi-functionality of electronic devices, polymer-based composites with thermal management and electromagnetic wave interference (EMI) are in urgent demand. Herein, a segregated structure multi-walled carbon nanotubes-graphite nanosheets/polyetheretherketone (PEEK) composite modified by polybenzoxazine (PBZ) have been fabricated via vacuum-assisted filtration and melting-point pressing methods. Different sizes of PEEK composite granules would yield different thermal conductivity (TC) and EMI performance of the resulting segregated composites. The TC of (GnPs&MWCNTs)@PBZ/PEEK with the grain of 200 meshes reach up to 3.38 (through plane) and 6.27 W/(m·K) (in plane) at 19.84 vol% filler loading, which is 1400% and 2600% higher than that of pure PEEK, respectively. The obtained composites also exhibit excellent EMI shielding effectiveness (54.4 dB), electrical conductivity, and thermal stability. Based on the Agari modeling, it is demonstrated that the more compact heat chain network is formed for segregated composites rather than fillers randomly distributed composites. This study provides a viable approach for enhancing the thermal conductivity of polymers-based composites with EMI capability.

Overshooting phenomena of heat conduction in suspended graphene

Recent experiment and theoretical results show that thermal wave is more likely to occur in the low dimensional nonmetallic materials, such as graphene. In this article, based on the Guyer-Krumhansl model we derive the occurrence condition of the overshooting phenomenon in suspended graphene. This condition indicates that at the temperature 100 K if the size of suspended graphene is within the required range of about micro to millimeter, phonon transport is in the under-damped free oscillation regime and the overshooting can occur. Furthermore, we find that the overshooting phenomenon induced by the interference of thermal waves can cause the temperature in the heat conduction medium three times more than that of the temperature at the boundary, and the effective thermal conductivity of suspended graphene is more than six times of its bulk counterpart. Finally, an experimental plan to demonstrate the overshooting phenomenon (or second sound) in suspended graphene is proposed.

Improvement of the Technique for Predicting the Temperature Modes of Low-Potential Geothermal Wells

The experience of operating geothermal thermal power plants shows that during the first 5 years, their economic performance deteriorates, because there is a change in the temperature field of the soil. It is also important to consider: seasonal cyclical changes in the heat load and possible reversal of the heat flow when switching from heating to air conditioning and vice versa. An option is considered, which, when the coolant fills the well, directly contacting the surface of the casing. During well operation, seasonal or technological changes in well load are taken into account. The well is operating in reverse mode. The conditions for calculation are determined by the alternation of the periods of turning on the heat pump with the cyclical periods of stopping, determined by the season. Research have shown that as a result of longterm operation of a geothermal well in a cyclic mode of thermal loading, there are changes of a temperature field of the rock surrounding a well, with effect of interference of thermal waves, leading to accumulation of heat. Based on the processing of the results obtained criterion equations for calculating the dimensionless temperature of the well at the time of completion of the cycle of heat supply or removal, as the corresponding largest temperature difference heat pump. The received equations allow to specify calculation of technical and economic indicators taking into account duration of geothermal well operation and its mode.

The non-capacitor model of leaky integrate-and-fire VO2 neuron with the thermal mechanism of the membrane potential

The study presents a numerical model of leaky integrate-and-fire neuron created on the basis of VO2 switch. The analogue of the membrane potential in the model is the temperature of the switch channel, and the action potential from neighbouring neurons propagates along the substrate in the form of thermal pulses. We simulated the operation of three neurons and demonstrated that the total effect happens due to interference of thermal waves in the region of the neuron switching channel. The thermal mechanism of the threshold function operates due to the effect of electrical switching, and the magnitude (temperature) of the threshold can vary by external voltage. The neuron circuit does not contain capacitor, making it possible to produce a network with a high density of components, and has the potential for 3D integration due to the thermal mechanism of neurons interaction.

Discriminate the substrate crack under sprayed coatings using ultrasonic infrared thermography

It has always been a challenge for most non-destructive testing (NDT) methods to discriminate the crack defects in substrate beneath sprayed coatings, owing to the interruption to testing signal by coating cracks. Ultrasonic infrared thermography (UIT) was employed to solve this problem in the current work. Coating crack and substrate crack were regarded as heat sources lying at different depth when excited by ultrasonic vibration. Coherent interference of thermal waves emitted from coating crack and substrate crack was introduced theoretically, and phase deviation (PD) of mixed thermal wave on surface was draw out as the discriminating feature for the deeper heat source, scilicet the substrate crack. Finite element modelling (FEM) results suggested that PD was more intensive in lower frequency range than that in higher frequency range. The proposed PD feature was validated experimentally with a plate specimen in which coating crack and substrate crack generated artificially under controlled monaxial cycle tensile load, experimental results were in qualitative agreement with FEM results. In addition, both FEM results and experimental results indicated that PD was insensitive to the heating intensity of crack defects under ultrasonic excitation, which was deemed to be a main unrepeatable parameter in UIT.

Thermal conduction in polymeric nanofluids under mean field approximation: role of interfacial adsorption layers

Polymeric nanofluids of TiO2/PVA (polyvinyl alcohol) and Cu/PVA have been prepared by dispersing nanoparticles of TiO2 or metallic copper in PVA. The thermal diffusivities and thermal conductivities of these nanofluids have been measured as a function of particle loading following a thermal wave interference technique in a thermal wave resonant cavity. It is found that in both cases thermal conductivity increases with particle concentration, with Cu/PVA nanofluids showing a much larger increase. The results have been compared with the corresponding values calculated following different theoretical models. Comparison of the results with model-based calculations shows that the thermal conductivity variations in these nanofluids are within the framework of the classical mean field theory including the formation of thin interfacial adsorption layers around nanoparticles. Although the molecular weight of PVA is very high, it is found that the adsorption layer thickness is limited by the hydrodynamic radius of the nanoparticles. It is found that particle clustering followed by interfacial layering accounts for the larger increase in thermal conductivity found for Cu/PVA compared to TiO2/PVA.

Dependence of particle size on the effective thermal diffusivity and conductivity of nanofluids: role of base fluid properties

Effect of nanoparticle size on effective thermal diffusivity and conductivity of polymeric and water based nanofluids are investigated following thermal wave interference technique. Two sets of nanofluids, prepared by dispersing TiO2 nanoparticles, with average sizes in the range 5–100 nm, in polyvinyl alcohol and water show opposing particle size dependences. Variations are explained invoking effective medium theory, including size of nanoparticles, molecular weight of base fluid and effects associated with it.

Photoacoustic monitoring of thermal wave interference effects during the formation of polymeric thin films from solutions

In this work, the potential of photoacoustic (PA) technique in the analysis of the formation of polymer films by evaporation from aqueous solutions is explored. Experiments are performed using different aqueous volume fractions of two different polymers, PEDT:PSS and a white liquid glue. The liquid sample is deposited on a metallic substrate attached to a modified PA cell that allows the monitoring of the evaporation process and development of the polymeric film. It is shown that when the thickness of the sample is of the order of the thermal diffusion length, maxima and minima of the PA signal, due to thermal wave interference effects, are observed. In the last stage of the process, the PA signal reaches a stable value which depends on the thickness of the formed film. The kinetics of the polymeric film formation, the dependence of the evaporation rate of the solvent as well as the final thickness of the polymeric film is discussed. These results can be useful in establishing a methodology for the photothermal monitoring and thermal characterization of the development of polymeric films from solutions.

Thermal wave interference as the origin of the overshooting phenomenon in dual-phase-lagging heat conduction

In the present work, the overshooting phenomenon is investigated based on the one-dimensional dual-phase-lagging heat conduction model. The thermal wave interference is found to trigger the overshooting of temperature field. A condition for the occurrence of overshooting phenomenon is established for the one-dimensional dual-phase-lagging heat conduction in a finite medium. According to this condition, the overshooting phenomenon may occur in heat conduction across gold films with the thickness ranging from 4.8555 nm to 19.581 μm.

On the modulation frequency dependence of the photoacoustic signal for a metal coated glass-liquid system

Abstract We show that the front photoacoustic signal due to a sample consisting of a glass plate with a metal coated surface, at which thermal waves are generated by periodical light absorption, enhances for certain modulation frequencies when the other glass surface is covered with a liquid sample. This contradicts the intuitive expectation based on the assumption that the liquid provides a new channel for heat conduction thereby decreasing the substrate temperature. Experimental results are shown and the described effect is explained using a thermal wave interference model.

Dual-reference photothermal imaging for the estimation of thermal effusivity of solids

A photothermal imaging method for the fast measurement of thermal effusivity of solids is suggested. On the basis of the principles of thermal wave interference in a layered medium, we have derived the conditions for a linear variation of the phase difference with effusivity for a sample–reference substrate assembly coated with an optical absorber. Exploiting this linearity, a dual-reference scheme has been introduced for simultaneously normalizing the instrumental offset and coating parameters out of effusivity estimation. As a means of improving accuracy and reducing sample size, three ranges of measurement within 5000–40 000 W s1/2 m−2 K−1 are used. For the absorber, we have used spin or spray coated carbon layers whose reliability has been verified using common-mode-rejection-demodulation-assisted photothermal imaging. Once set for an effusivity range and coating parameters, a threshold frequency can be found, below which the method offers the assumed accuracy. Typical error is 2.8–3.8% in most measurements and the technique turns out to be an easy and fast scheme, which can be implemented with minimum instrumentation and computation. The method has been demonstrated for the effusivity evaluation of hardened steel as a function of the quenching time.

Measurement of Thermal Parameter using Non-Contact Photopyroelectric Method

In the standard photopyroelectric technique, a precise control of thermal coupling fluid between the solid sample and the sensor is sometimes difficult, and yet an important factor in sample characterization. In this paper, we propose a non-contact photopyroelectric configuration for thermal diffusivity measurement of solids by considering the phenomena of thermal wave interference. We adopted the thermal wave interferometry, which was extensively discussed by Bennett and Patty in the photoacoustic signal generation, to our photopyroelectric signal generation in a thermally thick condition for a nondestructive testing. A normalization procedure has been used to eliminate a number of media parameters of photopyroelectric cell that otherwise needed to be known before one can determine thermal diffusivity of the sample. The thermal diffusivities obtained for Al, Cu, and Ni samples were close to literature values and thus justified the proposed model.

Comparison of plasma wave models in photoacoustics

Plasma wave effect describes the influence of diffusion and irradiative recombination processes of excess carriers on the instantaneous temperature distribution in the sample. This temperature field is responsible for a series of effects observed experimentally. The most important element for the computations of the plasma wave effect is the formula for the spatial temperature distribution in the sample. The aim of this paper was: to investigate and compare differenttemperature distribution formulae, derive another temperature distribution formula with the thermal wave interference method ofBenett and Patty and simplify the notations to make the formula more convenient and practical.

Normalisation procedure in thermal wave approach of thermal diffusivity measurement of solids using pyroelectric sensor

The theory of thermal wave interference in generation of photoacoustic signal suggested by Bennett and Patty [Appl. Opt. 21 (1982) 49] was applied to measure thermal diffusivity of optically opaque sample using photopyroelectric technique. To determine thermal diffusivity with precision, one needs to work with frequencies high enough in order to be in a thermally thick regime. However, this condition cannot always easily be fulfilled due to the great attenuation of the amplitude signal at high frequency resulting in decrease in signal-to-noise ratio. In this work, we proposed thermal diffusivity measurements to be carried out with the thermal wave probing starting from the sample–pyroelectric interface towards the thermally thick region of the sample. Reflection of thermal wave in the pyroelectric coatings, which was ignored in previous models, was considered in the generation of photopyroelectric signal. Normalisation procedure was used to eliminate the number of media parameters of photopyroelectric cell that otherwise need to be known before one can determine the thermal diffusivity of the sample. With the appropriate sample–pyroelectric detector dimension, the thermal diffusivity of any solid sample is readily being determined. The method was experimentally tested for aluminum, copper, and nickel, and the values obtained were close to the literature values.

Normalisation procedure in thermal wave approach of thermal diffusivity measurement of solids using pyroelectric sensor

The theory of thermal wave interference in generation of photoacoustic signal suggested by Bennett and Patty [Appl. Opt. 21 (1982) 49] was applied to measure thermal diffusivity of optically opaque sample using photopyroelectric technique. To determine thermal diffusivity with precision, one needs to work with frequencies high enough in order to be in a thermally thick regime. However, this condition cannot always easily be fulfilled due to the great attenuation of the amplitude signal at high frequency resulting in decrease in signal-to-noise ratio. In this work, we proposed thermal diffusivity measurements to be carried out with the thermal wave probing starting from the sample–pyroelectric interface towards the thermally thick region of the sample. Reflection of thermal wave in the pyroelectric coatings, which was ignored in previous models, was considered in the generation of photopyroelectric signal. Normalisation procedure was used to eliminate the number of media parameters of photopyroelectric cell that otherwise need to be known before one can determine the thermal diffusivity of the sample. With the appropriate sample–pyroelectric detector dimension, the thermal diffusivity of any solid sample is readily being determined. The method was experimentally tested for aluminum, copper, and nickel, and the values obtained were close to the literature values.

Monitoring of gas diffusion in air using the TWI technique: Thermal diffusivity measurements made easy

The thermal wave interference technique (TWI) has been explored in recent years for the investigation of the thermal and transport properties of gases and liquids. In this article we address ourselves to the quantitative understanding of the transient thermal wave interference signal of air:hydrocarbon vapor mixtures. This is the situation one faces when placing a given portion of liquid hydrocarbon inside an initially air-filled thermal wave interference. What is observed in this case is the thermal wave interference signal decay as a function of the time as a result of the change of the gas thermal diffusivity with time due to the increase of the hydrocarbon vapor concentration in air. In this article we show that value of the thermal diffusivity of the saturated mixture is readily obtained from the saturation value of the normalized signal amplitude, without the need of performing the conventional L scan.

Measurement of mass diffusivity in air using thermal wave interference detection

A discussion on the use of the thermal wave interference (TWI) for the monitoring of the transient of hydrocarbon in air is presented. The thermal wave signal was modeled using the logarithm-mixing model for the thermal diffusivity of a two-phase gas system in which the hydrocarbon vapor concentration in the air-filled TWI cell is a varying function of time. The time varying hydrocarbon vapor concentration was described assuming the simple Fick’s model for mass diffusion of the hydrocarbon vapor in the stagnant air column of the TWI cell. The transient TWI signal amplitude data fitting yielded two parameters, namely, the saturation concentration and the characteristic diffusion time. From the corresponding values of the diffusion time the hydrocarbon mass diffusivities were straightforwardly obtained.