Plane Source Research Articles

Innovative porous panels made from alpine tree bark-fibre bundles for enhanced acoustic and thermal insulation

ABSTRACT To tackle climate change, raw material shortages and global competition, new technologies should better utilize existing resources. Tree bark, an abundant by-product from Alpine sawmills, offers a promising opportunity despite its heterogeneous nature. In this study, tree bark was homogenised into fibrous material and subsequently processed into novel binder free low-density and therefore porous fibreboards. The aim was to develop effective panels for acoustic and thermal insulation by varying the key parameters bark species, fibre size, density and its variations. The findings highlight the effectiveness of bark fibre-based panelss as thermal and acoustical insulators, achieving densities of 170–330 kg/m³, a noise-reduction coefficient (NRC) exceeding 0.5 for most specimenss, and thermal conductivity below 0.08 W/(m·K). Significant variations in fibre length, density, and tree species indicate the need for tailored manufacturing adjustments. Testing involved impedance tube methods for sound absorption and dynamic plane source tests for thermal properties. This study provides initial validation of this approach, underscoring its potential for future research in utilising tree bark effectively.

Efficient numerical Fresnel diffraction with Gabor frames

Numerical Fresnel diffraction is broadly used in optics and holography in particular. So far, it has been implemented using convolutional approaches, spatial convolutions, or the fast Fourier transform. We propose a new way, to our knowledge, of computing Fresnel diffraction using Gabor frames and chirplets. Contrary to previous techniques, the algorithm has linear-time complexity, does not exhibit aliasing, does not need zero padding, has no constraints on changing shift/resolution/pixel pitch between source and destination planes, and works at any propagation distance. We provide theoretical and numerical analyses, detail the algorithm, and report simulation results with an accelerated GPU implementation. This algorithm may serve as a basis for more flexible, faster, and memory-efficient computer-generated holography methods.

Printed Heating and Temperature-Sensing Film in Transient Plane Source Sensor and Its Application in Measuring Thermal Conductivity

Printed Heating and Temperature-Sensing Film in Transient Plane Source Sensor and Its Application in Measuring Thermal Conductivity

Paley–Wiener partially coherent sources

Starting from the extension to complex arguments of the ordinary Fourier transform (FT) (due to Paley and Wiener) and from results concerning reproducing kernels in Hilbert spaces, we define a new, to the best of our knowledge, class of partially coherent planar sources presenting a structured degree of coherence. Such sources are shown to be of the Schell-model type as far as one of the transverse coordinates is concerned, while they depend on the average value of the orthogonal coordinate of the two points. Some examples are shown in detail, but the proposed approach can be easily extended to infinitely many other sources.

Parallel Bayesian Optimization of Thermophysical Properties of Low Thermal Conductivity Materials Using the Transient Plane Source Method in the Body-Fitted Coordinate.

The transient plane source (TPS) method heat transfer model was established. A body-fitted coordinate system is proposed to transform the unstructured grid structure to improve the speed of solving the heat transfer direct problem of the winding probe. A parallel Bayesian optimization algorithm based on a multi-objective hybrid strategy (MHS) is proposed based on an inverse problem. The efficiency of the thermophysical properties inversion was improved. The results show that the meshing method of 30° is the best. The transformation of body-fitted mesh is related to the orthogonality and density of the mesh. Compared with parameter inversion the computational fluid dynamics (CFD) software, the absolute values of the relative deviations of different materials are less than 0.03%. The calculation speeds of the body-fitted grid program are more than 36% and 91% higher than those of the CFD and self-developed unstructured mesh programs, respectively. The application of body-fitted coordinate system effectively improves the calculation speed of the TPS method. The MHS is more competitive than other algorithms in parallel mode, both in terms of accuracy and speed. The accuracy of the inversion is less affected by the number of initial samples, time range, and parallel points. The number of parallel points increased from 2 to 6, reducing the computation time by 66.6%. Adding parallel points effectively accelerates the convergence of algorithms.

Investigation of the Effect of Copper Nanoparticle Deposition on Low-Carbon Steel using Physical Vapor Deposition for Solar Cooling Application

The use of nanomaterials in solar cooling applications has gained significant attention in recent years. This study aimed to increase thermal conductivity by depositing copper nanoparticles (Cu-NP) on low-carbon steel using thermal evaporation and a physical vapor deposition (PVD) method. Low-carbon steel was selected as the substrate due to its wide use in thermal applications and strong absorption properties. The presence of Cu-NP on the surface was analysed using XRD and thermal characteristics of the thin layer were determined using Thermal Constant Analyzer (TCA) and Transient Plane Source (TPS) measurements. Results showed that the copper nanoparticle coating sample on the carbon steel substrate had better heat emission and absorption compared to the carbon steel alone. It also shows some improvement of around 1% in the thermal conductivity results. This study demonstrates the potential of using Cu-NP deposited on low-carbon steel as a promising material for solar thermal/cooling applications.

UNCOVER: A NIRSpec Census of Lensed Galaxies at z = 8.50–13.08 Probing a High-AGN Fraction and Ionized Bubbles in the Shadow

We present JWST NIRSpec prism spectroscopy of lensed galaxies at z ≳ 9 found behind the massive galaxy cluster Abell 2744 in the UNCOVER Cycle 1 Treasury Program. We confirm the redshift via emission lines and/or the Lyα break for 10 galaxies at z = 8.50–13.08 down to M V = −17.3. We achieve a 100% confirmation rate for z > 9 candidates reported in H. Atek et al. Using six sources with multiple line detections, we find that offsets in redshift estimates between the lines and the Lyα break alone can be ±0.2, raising caution in designing future follow-up spectroscopy for the break-only sources with the Atacama Large Millimeter/submillimeter Array. With spec-z-confirmed sources in UNCOVER and the literature, we derive lower limits on the rest-frame ultraviolet (UV) luminosity function (LF) at z ≃ 9–12 and find that these lower limits agree with recent photometric measurements. We identify at least two unambiguous and several possible active galactic nucleus (AGN) systems based on X-ray, broad Hβ, high ionization lines, and excess in the UV LF. This requires the AGN LFs at z ≃ 9–10 to be comparable or even higher than the X-ray AGN LF estimated at z ∼ 6 and suggests a plausible cause of the high abundance of z > 9 galaxies claimed in the recent photometric measurements is AGNs. One UV-luminous source is confirmed at the same redshift as a broad-line AGN at z = 8.50 with a physical separation of 380 kpc in the source plane. These two sources show emission blueward of Lyα, indicating a giant ionized bubble enclosing them with a radius of 7.69 ± 0.18 pMpc. Our results imply that AGNs have a nonnegligible contribution to cosmic reionization.

Designing a vibration energy harvester for several directions of excitation in planar motion

Abstract Harvesting energy from a mechanical vibration source is always challenging and comes with drawbacks, especially when the vibration input changes direction very often. This research proposes a novel design to harvest energy from a planar mechanical vibration source no matter its direction of oscillation. To achieve this, a spiral beam with a tip mass is designed to be flexible to various directions of the vibration input in a horizontal plane, which is orthogonal to the direction of gravity. An approximate analytical investigation is first performed. Numerical simulations are then conducted using commercial FEA software and the results are in good agreement with the analytical approach. Numerical simulations show that the tip mass acts symmetrically in the plane, although the system is not geometrically symmetric. To experimentally validate the proposed configuration, a 3D-printed prototype device was manufactured and attached to a shaker, which induced a vibrating motion for the tests. A piezoelectric patch was attached to the curved beam to generate electrical energy and measurements of produced open-circuit voltages were taken for different directions of the exciting vibration.

Novel thermally conductive coating for cotton fabrics based on reduced graphene oxide decorated with in situ synthesized silver nanoparticles

The application of thermally conductive materials as coating on fiber surfaces represents an innovative technology solution for conveying heat dissipation capability to IR-opaque textiles. In this work, a sustainable and scalable approach to manufacture a hybrid nanocomposite coating for cotton, formed by Reduced Graphene Oxide (RGO) sheets functionalized by histidine (His) and decorated by Ag nanoparticles (NPs), is reported for increasing thermal conductivity of cotton fabrics. Tens nm in size Ag NPs were synthesized, in situ, at the coordinating sites of the His-RGO modified cotton impregnated by H2O/CH3OH solutions of the AgNO3 precursor, under UV-light exposure, without using chemical reductants. The physical chemical properties of the nanocomposite modified fabrics were comprehensively investigated, integrating chemical, structural and morphological analysis, with characterizations of their thermal, electrical, oxygen permeability, surface wettability and mechanical properties. Thermal conductivity of cotton was measured by Differential Scanning calorimetry (DSC) technique, which was here validated by Transient Plane Source (TPS) method, assessing the effectiveness of DSC in measuring thermal conductivity of textiles. The resulting coating exhibits a thermal conductivity, which was twice as high as untreated cotton, maintaining its breathability, increasing its flexibility, while simultaneously reducing its wettability. This notable enhancement can be attributed to the synergistic effect of the conductive Ag nanostructures formed among the His-RGO sheets within the nanocomposite, and it matches the thermal conductivity achieved by current state-of-the-art methods, while offering additional advantages of being more eco-friendly, scalable, and sustainable. The reported characterization of the structural properties of the achieved coating opens the venue to interesting perspectives towards its application in passive conducting cooling textiles for personal thermal comfort management.

An improved version of PyWolf with multithread-based parallelism support

PyWolf is an open-source software with a graphical user interface that performs numerical simulations of the cross-spectral density function propagation of planar sources using parallel computation through PyOpenCL. In the previous versions of PyWolf, the user could select the OpenCL devices and platforms to perform the parallel computations on several tasks, except for that related to the two-dimensional (2D) fast Fourier transform (FFT) algorithm. The latter task can have a large computation time since one has to perform a large amount of 2D FFTs over 2D slices of a four-dimensional array. The option of using multithread-based computation on these loops and other tasks can be an advantage for multi-core CPUs and can significantly decrease the computation time. Here, I present version 3.0.0 of PyWolf, which adds a multithreading option to be used for the 2D FFT computations. This multithreading option can also be easily implemented in other time-consuming tasks. New version program summaryProgram Title: PyWolfCPC Library link to program files:https://doi.org/10.17632/frjscxypkd.3Developer's repository link:https://github.com/tiagoecmagalhaes/PyWolfLicensing provisions: GPLv3Programming language: PythonSupplementary material: Overview of the main changes with performance results.Journal reference of previous version: Comput. Phys. Commun. 294 (2024) 108899.Reasons for the new version: In the original paper of PyWolf [1] and in the previous version [2], parallel computation was performed only using PyOpenCL. However, in some cases where multiple cores are available in the CPU, multithreading [3] can significantly decrease the computation time of some tasks, for instance, the loops of 2D fast Fourier transforms (FFTs). This new version includes a built-in option for multithreading, enabling users to select the number of threads to be used in the numerical simulation.Summary of revisions: Multithreading support was added to PyWolf and users can now select this feature in PyWolf's graphical user interface and choose the number of available threads to be used in the simulation. In the current version, multithreading is only used for the loops of 2D FFTs but can be easily extended to other tasks. Other small features have been added and some issues have been corrected, namely: (i) a requirements file has been added listing all the libraries used; (ii) some errors associated with file paths have been corrected.Nature of problem: Propagation of partially coherent light from planar sources in the Fresnel or far field approximations using four-dimensional arrays [4,5] demands large memory and computation time. PyWolf uses PyOpenCL to perform parallel computation to reduce time-consuming calculations in the propagation of the cross-spectral density function [4], restricting the memory capacity as the main limitation.Solution method: The open-source toolkit PyOpenCL along with multithreading is used to decrease the computation time. Users can modify and add more features to PyWolf, such as source, propagation, and geometrical models. Custom-made optical components can also be added (e.g., lenses and apertures). The PyQt5-based graphical user interface enables users to easily set the input parameters to simulate their optical setup, plot and export the simulated results, and save or load the simulation session.

Size effect of typical hygrothermal properties test values for building insulation materials

Thermal and moisture properties of building insulation materials are crucial input parameters for analyzing thermal and moisture transfer phenomena in building environments. Accurate determination of these parameters under different conditions is essential for the correct application and assessment of materials and envelope structures. However, numerous factors influence thermal and moisture properties, and while extensive research has been conducted on this topic, the effects of specimen size on typical thermal and moisture property test values remain unclear. To address the issue of unreliable data caused by random specimen sizes in thermal and moisture property testing of building insulation materials, this study selects three materials—expanded polystyrene (EPS), extruded polystyrene (XPS), and foamed cement—as test subjects to explore the size effects on typical thermal and moisture property test values. The results indicate that specimen size significantly affects the test values for typical thermal and moisture properties, with only a few experiments showing negligible size effects for certain materials. For foamed cement, recommended specimen sizes for thermal conductivity testing using the guarded hot plate method and the transient plane source method are 300 × 300 × 30 mm and 50 × 50 × 30 mm, respectively. Except for equilibrium moisture absorption experiments, the weight of other moisture property tests is generally represented by thickness > planar dimensions.

Phase Space Formulation of Light Propagation on Tilted Planes

The solution of the Helmholtz equation describing the propagation of light in free space from a plane to another can be described by the angular spectrum operator, which acts in the frequency domain. Many applications require this operator to be generalized to handle tilted source and target planes, which has led to research investigating the implications of these adaptations. However, the frequency domain representation intrinsically limits the understanding the way the signal is transformed through propagation. Instead, studying how the operator maps the space–frequency components of the wavefield provides essential information that is not available in the frequency domain. In this work, we highlight and exploit the deep relation between wave optics and quantum mechanics to explicitly describe the symplectic action of the tilted angular spectrum in phase space, using mathematical tools that have proven their efficiency for quantum particle physics. These derivations lead to new algorithms that open unprecedented perspectives in various domains involving the propagation of coherent light.

Chuprov invariant for vector-scalar fields of multipole sources in a shallow sea

A computational and theoretical study of the properties of the well-known waveguide invariant S.D. Chuprova (IC) was carried out in a plane-parallel Pekeris waveguide. Unlike earlier works, in which predominantly non-directional (monopole) sources were used as a source, and sound pressure fields (scalar fields) were studied, in this work not only scalar, but also vector fields formed in the waveguide by directional - combined multipole sources with directivity in both horizontal and vertical planes. A differential equation has been obtained that makes it possible to fairly accurately calculate the IC values under different conditions of signal propagation and different depths of sources and receivers. This makes it possible, in a simpler way than “full computer modeling,” to predict the invariance (stability) of the IC when varying both the hydrophysical conditions in the waveguide and the geometry of the experiment. It is shown that the directionality of sources in the horizontal plane has virtually no effect on the properties of the IC, and the directionality in the vertical plane leads to a shift in the fan structure of the signal amplitude fields, but has little effect on the IC values. The properties of the fan structure change in a similar way when using vertical projections of the oscillatory velocity vector - despite the fact that another analytical relation, different from scalar fields, is used to calculate the IC, the IC value is close to (+1) at all frequencies and distances, except those at which new modes or dislocations arise. At these frequencies and in these zones, alternating emissions with different signs and magnitudes occur. It is concluded that the stability of IC allows the application of signal processing algorithms developed for scalar fields and non-directional sources to vector-scalar fields generated, including using directional sources.

Acoustic imaging of geometrically shielded sound sources using tailored Green's functions.

In light of the growing market of urban air mobility, it is crucial to accurately detect the stationary or moving noise sources within the complex scattering environments caused by aircraft structures such as airframes and engines. This study combines conventional and wavelet-based beamforming techniques with an acoustic scattering prediction method to develop an acoustic imaging approach that considers scattering effects. Tailored Green's function is numerically evaluated and used to compute the steering vectors and the specific delayed time used in those beamforming methods. By examining common scenarios where a scatterer is positioned between the source plane and the array plane, it is observed that beamforming in a scattering environment differs from that in free space, leading to improved resolution alongside scattering-induced side lobes. The effectiveness of the developed method is validated through numerical simulations and experimental studies, confirming its improved ability to localize both stationary and rotating sound sources in a shielded environment. This advancement offers effective techniques for acoustic measurement and fault monitoring in the presence of structural scatterers.

Automatic Algorithm Applied for Calculating Thermal Conductivity by Transient Plane Source Method

As a thermal conductivity measurement method, Transient Plane Source (TPS) method has gained much popularity because of its broad applicability, short measurement times, high precision and simple sample preparation. However, the accuracy of thermal conductivity calculations based on temperature rise data is often hindered by factors such as probe thickness, contact thermal resistance, and input power. Currently, there is no standardized criteria for selecting effective temperature rise data for thermal conductivity calculation. Consequently, the accuracy of results are limited by the operator's understanding of the TPS methods, and repeatability of the results is often poor. To address this issue, an automatic algorithm based on the international standard (ISO22007-2:2008) is proposed in this paper. By applying this algorithm to the measurement of different materials, it has been demonstrated that the proposed algorithm can produce more precise and consistent results than the conventional method. Additionally, the integration of the time window function , typically utilized solely for result validation in conventional methods, further enhances the objectivity and reproducibility of the results obtained by the automatic algorithm.

A double-helix plane winding sensor with wire using transient plane source method

The transient plane source (TPS) method is widely used to measure thermophysical properties of various materials, and the high-precision double-helix sensor is a key technology. A novel sensor using an efficient, simple, and low-cost lacquered micron-wire-wound process is proposed to replace traditional complex micro- and nano-etching processes. The TPS test platform was built based on the Wheatstone Bridge theory. A new sensor sample of diameter 5.377 mm was wound with an enameled copper wire of diameter 0.063 mm. Owing to the characteristics of the process, a 1-mm round hole was bored inside the sensor. An analytical solution for the concentric ring heat transfer model of the sensor with a central circular hole structure was derived, and a two-dimensional concentric circle simulation model of the sensor was established. As the number of turns decreased, the average error between the analytical solution of the concentric ring model with a large center hole (LHAS) and that of the traditional concentric circle model (TAS), as well as LHAS and the simulation model, gradually increased. The maximum relative errors between LHAS and TAS, as well as between LHAS and the simulation model, were 23.69 % and 0.1 %, respectively, and the average errors of the absolute maximum were 11.86 % and −0.06 %, respectively. The LHAS exhibited excellent accuracy because of the structural characteristics of the novel sensor. The accuracy of LHAS has been validated by simulation and hot wire method. Temperature rise data of high-borosilicate glass and polytetrafluoroethylene samples at different powers were obtained. The thermal properties of the samples were determined by fitting LHAS and TAS data. The thermal conductivity errors measured by LHAS were smaller than those measured by TAS, the thermal conductivity and thermal diffusivity errors were less than 3.5 % at different powers, and the measured repeatability errors were less than 1 %, indicating the good application prospect of the proposed model.

Extending the Transient Plane Source Scanning method for determining the specific heat capacity of low thermal conductivity materials through a numerical study

In contrast to the conventional Transient Plane Source (TPS) method, the Transient Plane Source Scanning (TPSS) technique allows for the direct determination of the specific heat capacity and requires the use of a specially designed sample holder for accurate measurements. While this method correctly determines the specific heat capacity of samples with moderate and high thermal conductivity, it tends to underestimate the values for those with low thermal conductivity. This paper demonstrates that the underestimated specific heat capacity results from heat loss during the measurement process. To precisely quantify the heat loss, a numerical model based on the finite element method was developed, with key material properties tuned based on measurement data. This model can closely describe the curve of measured thermal response, thereby enabling the precise determination of the specific heat capacity. Consequently, this study introduces a novel approach that incorporates numerical simulation to enhance TPSS measurements of poorly conducting samples, providing a reliable alternative for determining the specific heat capacity.

Experimental study evaluating the performance of thermal conductivity prediction models for air–water saturated weathered sandstone heritage

As a critical parameter, thermal conductivity directly determines the heat transfer and temperature variation within rocks, which can lead to mechanical damage and chemical corrosion. Consequently, understanding the thermal conductivity of stone heritage is vital for assessing their deterioration mechanisms and developing effective conservation strategies. This study obtained sandstone samples from the Yungang Grottoes and subjected them to freeze–thaw cycle experiments to generate weathered sandstone samples. Subsequently, the thermal conductivity of these samples was measured under both dry and water-saturated state using the transient plane source method. To analyze the relationship between air–water saturation, porosity, and thermal conductivity, a saturation influence coefficient was introduced. Thereafter, the effectiveness and applicability of 13 commonly used thermal conductivity mixing law prediction models were evaluated based on experimental data. The results suggested that the influence of water saturation on the thermal conductivity of rocks varies with porosity, and water saturation significantly enhances the thermal conductivity of weathered sandstone. Among the 13 common models, the Geometric mean model was found to be more accurate than other models, with superior performance in both dry (MAE, RMSE, MAPE are 0.148, 0.214, 5.59% respectively) and water-saturated (MAE, RMSE, MAPE are 0.244, 0.170, 8.4% respectively) state. The Albert model demonstrates a good fit in the dry state, whereas the Walsh model (with maximum effect), Ribaud model, and Huang model also exhibit good fitting efficacy in the water-saturated state. This study provides a solid foundation for better predicting the thermal conductivity of weathered stone heritage and developing effective preventive conservation strategies.

Coherence vortices by binary pinholes.

Singularity in a two-point complex coherence function, known as coherence vortices, represents zero visibility with a helical phase structure. In this paper, we introduce a novel technique to generate the coherence vortices of different topological charges by incoherent source transmittance with exotic structured binary pinholes. The binary pinhole structures have been realized by lithography, followed by wet etching methods. We control the transmittance from the incoherent source plane using these exotic apertures, which finally results in a coherence vortex spectrum that features multiple and pure orbital angular momentum modes. The generation of the coherence vortices is achieved within the two-point complex spatial coherence function. The spatial coherence function exhibits the helical phase profile in its phase part, and its absolute part shows a doughnut-shaped structure. A theoretical basis is developed and validated with simulation, and experimental results. The coherence vortex spectra with OAM modes superposed with opposite topological charges, known as photonic gears, are also generated with the proposed theory.

Computational renormalization for thermal conductivity of porous asphalt concrete based on hybrid finite element-neural network method

Thermal conductivity of porous asphalt concrete (PAC) directly affects PAC pavement temperature field, which is closely related to the heat island effect in summer and pavement icing in winter. Due to the large and complex pores and the uneven surface in PAC, there is measurement uncertainty using traditional laboratory tests. In this study, a finite element-neural network (FE-NN) method was proposed to predict the thermal conductivity of PAC based on the three-dimensional (3-D) heterogeneous structure. Additionally, laboratory tests were conducted to measure the thermal conductivity of PAC, fine aggregate mixture (FAM), and basalt aggregate. The results served as input parameters for the FE-NN method and were used to verify its accuracy. Based on the validated method, various factors affecting the thermal conductivity of PAC were analyzed. The analysis results show that, compared to the transient plane source (TPS) method, the backcalculation method can achieve results similar to those obtained with the TPS method for basalt aggregate and FAM, but provides more stable measurements when applied to PAC. The accuracy of the FE-NN method is acceptable, with relative errors of 1.92∼4.34 % compared to the experimental results. Besides, 2-D structural models tend to underestimate the effective thermal conductivity of PAC, with values 83.2∼84.1 % lower than those calculated by 3-D models. When the representative volume element (RVE) sizes are larger than 256×256×256, the variances show little differences and are acceptable. Furthermore, typical aggregate thermal conductivity values were used as input, revealing a nonlinear increase in the effective thermal conductivity of PAC. When the void content increased from 18 % to 24 %, the effective thermal conductivity of PAC decreased by 19.83 %. The effective thermal conductivity of PAC changes more significantly with the thermal conductivity of the aggregate than that with the variation of porosity in an interval. The analysis findings provide insights for better evaluating the pavement temperature field and heat transfer to improve the PAC pavement material designs.