Thermal Cavity Research Articles

A radioisotope thermophotovoltaic converter with nanophotonic emitters and filters

Radioisotope thermophotovoltaic (RTPV) systems convert the heat of decay of radioisotopes into electricity via thermally radiated photons. In this work, we report the performance analysis of the RTPV system incorporating a cubic-shaped thermal cavity including 1.04kg of Plutonium-238 (238PuO2) and nanophotonic emitters facing low bandgap photovoltaic (PV) cells. The performance of RTPV was investigated by varying the nonidealities of nanophotonic emitters and filters and with introducing a weighting factor (W) that quantifies the benefit of each nanophotonic component. Unlike previous studies, we varied the packing factor (PF) defined by the volume ratio between the radioisotope and the overall thermal cavity, then investigated the effects of the PF on the conversion efficiency, optimal configuration, and radiation safety. Our results show that it is crucial to reduce the nonidealities of nanophotonics at low energy photon level (below the PV cell bandgap) to achieve a high conversion efficiency. With the current state-of-the art nanophotonics including 2D tantalum photonic crystal (PhC) emitter and tandem filter which using interference and plasma filter, we show that the RTPV has the potential to achieve ∼30% of conversion efficiency and surpass the conversion efficiency of conventional radioisotope thermoelectric generators (RTGs) with the same PF (∼10%). The increase in the PF from 10% to 70% provide approximately 23% of further increase in RTPV efficiency while limiting the increase in the total radiation dose only by ∼10%. This work will help the development of high efficiency nanophotonic RTPV converters.

Entanglement of atoms passing consecutively through one-mode cavity

In this paper we investigated the entanglement dynamics of a pair of two-level atoms passing through a vacuum or thermal cavity one after another. We assumed that two atoms were initially prepared in separable coherent or entangled states. Using the exact solution of the density matrix evolution equation we calculated the time dependence of negativity for models with one-and two-photon interaction between atoms and the cavity field. For the two-photon model we took into account the dynamical Stark shift. We have found that the degree of atom-atom entanglement can be controlled by the Stark shift and cavity mean photon numbers.

Study of fire-resistance of reinforced concrete slab of a new type

Reinforced concrete structures with complex inner geometry under the effect of high temperatures considering void former materials were examined. The analysis of strain-stress state of new type of architectural and construction system ‘Monofant’ under the effect of high temperature heating in standard fire mode, considering the change of design pattern was carried out. Numerical study of concrete slab with given reinforcement and complex inner geometry was carried out with use of software packages based on finite element method. Temperature fields throughout the depth of cross section of the slab of new type of architectural and construction system ‘Monofant’ upon heating in standard fire mode for time interval 0-240 min. were obtained. The carrying capacity of sections exposed to high temperatures was determined by deformation method. Offered the algorithm that considers the transformation of design patterns depending on temperature values and excessive pressure in thermal insulation cavities taking into account influence of deformation fields on temperature distribution.

Multi-spectral image processing for the measurement of a spatial temperature distribution on the surface of a laser-heated microscopic object

In this paper, we demonstrate that combining a laser heating (LH) system with a tandem acousto-optical tunable filter (TAOTF) allows us to measure the temperature distribution (TD) across a laser-heated microscopic specimen. Spectral image processing is based on one-dimensional (1D) non-linear least squares fitting of the Planck radiation function. It is applied for determining the temperature T at each point (x, y) of the specimen surface. It is shown that spectral image processing using the 1D non-linear least squares fitting allows measurement of the TD of the laser-heated microscopic specimen with higher precision and stability than those of the conventional linear least-squares fitting of the Wien approximation of Planck’s law.

RELATIVISTIC THEORY OF EXCITATION AND IONIZATION OF HEAVY ALKALI RYDBERG ATOMS IN A BLACK-BODY RADIATION FIELD: NEW DATA

The combined relativistic energy approach and relativistic many-body perturbation theory with the zeroth Dirac-Fock potential approximation are used for computing the thermal Blackbody radiation ionization characteristics of the alkali Rydberg atoms, in particular, the rubidium and caesium in Rydberg states with principal quantum number n = 20-100. Preliminary application of theory to computing ionization rate for the Rydberg sodium atom in the have demonstrated physically reasonable agreement between the theoretical and experimental data. The accuracy of the theoretical data is provided by a correctness of the corresponding relativistic wave functions and accounting for the exchange-correlation effects.

Thermodynamic properties of the blackbody radiation: A Kaniadakis approach

The thermodynamic properties of the blackbody radiation are revisited, for the first time, within the theoretical framework of the κ-statistics introduced by Kaniadakis. Using the κ-counterpart of the Bose–Einstein distribution, generalized expressions for the free energy, the entropy, the specific heat, and the pressure are obtained. All quantities are shown to recover their standard expressions in the limit κ→0. The reexamination of the thermodynamic properties of the blackbody radiation shows that it emits more energy with an increase of the value of |κ| in comparison with the standard Planck radiation law. Moreover, the effects of the deformed Kaniadakis statistics are shown to be more appreciable for high temperatures. Our results could be used as a theoretical support for experimental studies implying blackbody radiation such as the study of microwave background radiation.

Increasing the thermal conductivity of silicone based fluids using carbon nanofibers

Heat transfer in silicone fluids loaded with high thermal conductivity carbon nanofibers was studied using photoacoustics and thermal wave resonator cavity. It is shown that heat transport depends strongly on volume fraction of carbon nanofibers; in particular, a low loading percentage is enough to obtain significant changes in thermal conductivity. Theoretical models were used to determine how heat transfer is affected by structural formations in the composite, such as packing fraction and aspect ratio (form factor) of carbon nanofiber agglomerates in the high viscosity fluid matrix. Our results may find practical applications in systems, in which the carbon nanofibers can facilitate heat dissipation in the electronic devices.

Exact research on the theory of the blackbody thermal radiation.

After studying the normalized Planck equation in depth, a brand-new type of spectrum curves of blackbody thermal radiation is given. Two important parameters of the new type curves, namely relative width RWη and symmetric factor RSFη, are defined. The paper points out that the experimental verification of the parameters has three significant applications: (1) Giving a method to measure temperature by detecting the radiation wavelength. (2) Determining the blackbody grade. (3) The temperature obtained from the law of the blackbody thermal radiation can be used as a criterion.

Room temperature direct-bandgap electroluminescence from a horizontal Ge ridge waveguide on Si**Project supported by the National Basic Research Program of China (Grant No. 2013CB632103), the National Natural Science Foundation of China (Grant Nos. 61176013 and 61036003), and the Science Fund from Beijing Science and Technology Commission, China (Grant No. Z151100003315019).

We report a lateral Ge-on-Si ridge waveguide light emitting diode (LED) grown by ultrahigh vacuum chemical vapor deposition (UHV-CVD). Direct-bandgap electroluminescence (EL) of Ge waveguide under continuous current is observed at room temperature. The heat-enhancing luminescence and thermal radiation-induced superlinear increase of edge output optical power are found. The spontaneous emission and thermal radiation based on the generalized Planck radiation law are calculated and fit very well to the experimental results. The Ge waveguides with different lengths are studied and the shorter one shows stronger EL intensity.

Design of CMOS‐MEMS broadband infrared emitter arrays integrated with metamaterial absorbers based on CMOS back‐end‐of‐line

A new design of complementary metal–oxide–semiconductor microelectromechanical systems (CMOS-MEMS) broadband infrared (IR) emitter arrays with integrated metamaterial absorbers (MAs) developed by the CMOS back-end-of-line is presented. The IR emitter array is a promising broadband thermal radiation source for integrated gas sensors. Novel IR emitter arrays are designed using the Central Semiconductor Manufacturing Corporation 0.5 μm 2-poly-3-metal CMOS process. To improve the low emissivity that is commonly seen in CMOS-MEMS type IR emitters due to the inherited low emissivity of SiO2 and SiN in CMOS process, we newly adopted tri-layer metal–insulator–metal (MIM) and four-layer insulator–MIM (IMIM) MA by using the CMOS back-end metal layers and inter-layer dielectrics, thereby to excite multi-mode surface plasmon polariton resonances. The emitter integrated with IMIM MA can be electrically modulated up to 344 Hz, as theoretically predicated from thermal properties of the emitters and the radiation properties calculated based on Planck's radiation law. Simulated emissivity spectra through FEM show that the multi-mode resonances in CMOS MIM and IMIM MAs enhance emissivity and broaden the waveband effectively.

Probing interstellar turbulence in cirrus with deep optical imaging: no sign of energy dissipation at 0.01 pc scale

Diffuse Galactic light has been observed in the optical since the 1930s. We propose that, when observed in the optical with deep imaging surveys, it can be used as a tracer of the turbulent cascade in the diffuse interstellar medium (ISM), down to scales of about 1 arcsec. Here we present a power spectrum analysis of the dust column density of a diffuse cirrus at high Galactic latitude (l ~ 198 deg, b ~ 32 deg) as derived from the combination of a MegaCam g-band image, obtained as part of the MATLAS large programme at the CFHT, with Planck radiance and Wise 12 micron data. The combination of these three datasets have allowed us to compute the density power spectrum of the HI over scales of more than three orders of magnitude. We found that the density field is well described by a single power law over scales ranging from 0.01 to 50 pc. The exponent of the power spectrum, gamma=-2.9 +- 0.1, is compatible with what is expected for thermally bi-stable and turbulent HI. We did not find any steepening of the power spectrum at small scales indicating that the typical scale at which turbulent energy is dissipated in this medium is smaller than 0.01pc. The ambipolar diffusion scenario that is usually proposed as the main dissipative agent, is consistent with our data only if the density of the cloud observed is higher than the typical values assumed for the cold neutral medium gas. We discuss the new avenue offered by deep optical imaging surveys for the study of the low density ISM structure and turbulence.

Probabilistic Cloning of two Single-Atom States via Thermal Cavity

We propose a cavity QED scheme for implementing the 1 → 2 probabilistic quantum cloning (PQC) of two single-atom states. In our scheme, after the to-be-cloned atom and the assistant atom passing through the first cavity, a measurement is carried out on the assistant atom. Based on the measurement outcome we can judge whether the PQC should be continued. If the cloning fails, the other operations are omitted. This makes our scheme economical. If the PQC is continued (with the optimal probability) according to the measurement outcome, two more cavities and some unitary operations are used for achieving the PQC in a deterministic way. Our scheme is insensitive to the decays of the cavities and the atoms.

Dynamics for atoms successively passing a cavity in the presence of the initial atomic entanglement

We investigated the dynamics of entanglement between atoms successively passing a cavity and interact with a thermal cavity field. We considered the situation when atoms are initially prepared in a pure entangled state. Using the exact solution of density matrix evolution we calculated the negativity for different values of cavity mean photon numbers. We shown the possibility to save the initial atomic entanglement even for a thermal cavity field with relatively high temperature.

Thermal dissociation cavity attenuated phase shift spectroscopy for continuous measurement of total peroxy and organic nitrates in the clean atmosphere.

A thermal dissociation cavity attenuated phase shift spectroscopy (TD-CAPS) instrument was developed for measuring total peroxy nitrates (PNs) and organic nitrates (ONs) concentrations in the clean atmosphere. This instrument is easy to operate and can be applied to continuous measurement of PNs and ONs. A continuously measurable system is convenient to perform observations, especially in remote areas. Three lines (NO2, PNs, and ONs lines) were used for thermal dissociation. The NO2 line contains a quartz tube that is not heated, while the PN and ON lines contain quartz tubes that are heated at 433 K and 633 K, respectively. The concentrations of NO2, NO2 + PNs, and NO2 + PNs + ONs can be obtained from the NO2, PN, and ON lines, respectively. The lower limit values of the detection limit (3σ) for PNs and ONs were estimated to be 21 parts per trillion by volume with an integration time of 2 min. PNs were selectively thermally decomposed in the PNs line and formed NO2 quantitatively. In the ONs line, both PNs and ONs were thermally decomposed to produce NO2 quantitatively, but partial decomposition of HNO3 at 633 K interfered with the ONs measurement. Therefore, a HNO3 scrubber is required before the ONs line. Continuous observations were conducted with the TD-CAPS instrument in a remote area, and the instrument performed well for obtaining PNs and ONs concentrations.

Nanophotonics-enabled smart windows, buildings and wearables

AbstractDesign and production of spectrally smart windows, walls, roofs and fabrics has a long history, which includes early examples of applied nanophotonics. Evolving nanoscience has a special role to play as it provides the means to improve the functionality of these everyday materials. Improvement in the quality of human experience in any location at any time of year is the goal. Energy savings, thermal and visual comfort indoors and outdoors, visual experience, air quality and better health are all made possible by materials, whose “smartness” is aimed at designed responses to environmental energy flows. The spectral and angle of incidence responses of these nanomaterials must thus take account of the spectral and directional aspects of solar energy and of atmospheric thermal radiation plus the visible and color sensitivity of the human eye. The structures required may use resonant absorption, multilayer stacks, optical anisotropy and scattering to achieve their functionality. These structures are, in turn, constructed out of particles, columns, ultrathin layers, voids, wires, pure and doped oxides, metals, polymers or transparent conductors (TCs). The need to cater for wavelengths stretching from 0.3 to 35 μm including ultraviolet-visible, near-infrared (IR) and thermal or Planck radiation, with a spectrally and directionally complex atmosphere, and both being dynamic, means that hierarchical and graded nanostructures often feature. Nature has evolved to deal with the same energy flows, so biomimicry is sometimes a useful guide.

Determination of ionization efficiencies of thermal ionization cavity sources by numerical simulation of charged particle trajectories including space charge

An in-house developed code, Sofie, and the methods used for numerical determination of the ionization efficiency of thermal ionization cavity (TIC) sources up to intermediate temperatures (<2500K for cavity dimensions of a few millimetres) are presented, thus, creating a tool to identify cavity geometries offering better ionization efficiencies and to aid in matching the ion beam produced by a TIC source to the ion optics of a beam line or a mass analyser as used in conventional thermal ionization mass spectrometry (TIMS).Essential is the code’s ability to approximate the solution of Poisson’s equation, in which the space charge predominantly originates from electrons thermally emitted from the inner cavity walls. The assumption of a quasi-neutral plasma forming in the volume of the cavity is no longer valid at lower temperatures and/or cavity dimensions, and charged particles can be regarded as moving freely throughout the cavity only interacting via the electrostatic potential shaped by the particles’ space charge. Under such conditions the geometry of the cavity has got a large effect on the ionization efficiency of sample atoms loaded into the source. The code also allows the simulation of surface adsorption and re-emission of various particle species simultaneously, making the calculation of ionization efficiencies possible by determining the currents of sample ions and neutral atoms out of the cavity. The validity of the code is successfully demonstrated by simulating problem sets, for which analytical solutions exist, and also by reproducing experimental data from TIC sources found in the literature. The necessity of including space charge in such simulations is demonstrated. A non-exhaustive search for a best cavity geometry has been performed and a geometry has been identified that could enhance the ionization efficiency by up to a factor of 100 over the ionization efficiency of the Saha-Langmuir equation, which corresponds to the efficiency achievable with conventional flat filament TIMS sources.

A stack bonded thermo-pneumatic micro-pump utilizing polyimide based actuator membrane for biomedical applications

This paper presents a simple and low-cost fabrication method of thermo pneumatic micropump with very thin polyimide (Pi) membrane. The measurement and functional testing of the whole micropump system is investigated as well. The thermo-pneumatic micropump consists of three main components, such as micro heater, thin film membrane with thermal cavity and planar valve with diffuser nozzle. Three different processes were used to fabricate the micropump due to different material used in each component. The thin polyimide membrane acts as an actuator and actuated by thermal expansion volume in thermal chamber. The diameter and the thickness of the actuator diaphragm are 2 mm2 and 3.5 µm, respectively. The meniscus motion in the outlet tube is observed with a microscope image video and the flow rate of the micropump is calculated through the frame analysis of the recorded video data. The flow rate range of the micropump is about 770 pL to 12.5 nL at approximately 33.5–63.5 °C, when the input voltage of 2–12 V applied to the micro heater. This flow rate range is suitable to be used with artificial kidney function, nano pipet and other biomedical application.

Near-field radiative thermal control with graphene covered on different materials

Based on the structure of double-layer parallel plates, this paper demonstrates that thermal radiation in near field is greatly enhanced due to near-field effects, exceeding Planck′s blackbody radiation law. To study the effect of graphene on thermal radiation in near field, the authors add graphene layer into the structure and analyze the ability of graphene to control near-field thermal radiation with different materials. The result indicates that the graphene layer effectively suppresses the near-field thermal radiation between metal plates or polar-dielectric plates, having good ability of thermal insulation. But for doped-silicon plates, depending on the specific models, graphene has different control abilities, suppressing or enhancing, and the control abilities mainly depend on the material graphene is attached to. The authors also summarize some common rules about the different abilities of graphene to control the near-field thermal radiation. In consideration of the thickness of 0.34nm of monolayer graphene, this paper points out that graphene plays a very important role in controlling the near-field thermal radiation.

Integrated photonic crystal selective emitter for thermophotovoltaics

Converting blackbody thermal radiation to electricity via thermophotovoltaics (TPV) is inherently inefficient. Photon recycling using cold-side filters offers potentially improved performance but requires extremely close spacing between the thermal emitter and the receiver, namely a high view factor. Here, we propose an alternative approach for thermal energy conversion, the use of an integrated photonic crystal selective emitter (IPSE), which combines two-dimensional photonic crystal selective emitters and filters into a single device. Finite difference time domain and current transport simulations show that IPSEs can significantly suppress sub-bandgap photons. This increases heat-to-electricity conversion for photonic crystal based emitters from 35.2 up to 41.8% at 1573 K for a GaSb photovoltaic (PV) diode with matched bandgaps of 0.7 eV. The physical basis of this enhancement is a shift from a perturbative to a nonperturbative regime, which maximized photon recycling. Furthermore, combining IPSEs with nonconductive optical waveguides eliminates a key difficulty associated with TPV: the need for precise alignment between the hot selective emitter and cool PV diode. The physical effects of both the IPSE and waveguide can be quantified in terms of an extension of the concept of an effective view factor.

Imaging system based on a tandem acousto-optical tunable filter for in situ measurements of the high temperature distribution.

We present, to the best of our knowledge, the first experimental demonstration of a new imaging system for in situ measurement of the two-dimensional (2D) distribution of the surface temperature of microscopic specimens. The main component of the system is an imaging tandem acousto-optical tunable filter (TAOTF) synchronized with a video camera. A set of TAOTF spectroscopic images (up to a few hundreds) is taken by the TAOTF imaging system to fit the measured spectral curves in each pixel to the Planck radiation function and determine the temperature and emissivity of the sample using the gray body approximation. It is experimentally shown that this technique provides aberration-free spectral imaging suitable for precise multispectral imaging radiometry (MIR).