Milan Honner

Survey of emissivity measurement by radiometric methods

A survey of the state of the art in the field of spectral directional emissivity measurements by using radiometric methods is presented. Individual quantity types such as spectral, band, or total emissivity are defined. Principles of emissivity measurement by various methods (direct and indirect, and calorimetric and radiometric) are discussed. The paper is focused on direct radiometric methods. An overview of experimental setups is provided, including the design of individual parts such as the applied reference sources of radiation, systems of sample clamping and heating, detection systems, methods for the determination of surface temperature, and procedures for emissivity evaluation.

New experimental device for high-temperature normal spectral emissivity measurements of coatings

A new experimental device for normal spectral emissivity measurements of coatings in the infrared spectral range from 1.38 μm to 26 μm and in the temperature range from 550 K to 1250 K is presented. A Fourier transform infrared spectrometer (FTIR) is used for the detection of sample and blackbody spectral radiation. Sample heating is achieved by a fiber laser with a scanning head. Surface temperature is measured by two methods. The first method uses an infrared camera and a reference coating with known effective emissivity, the second method is based on the combination of Christiansen wavelength with contact and noncontact surface temperature measurement. Application of the method is shown on the example of a high-temperature high-emissivity coating. Experimental results obtained with this apparatus are compared with the results performed by a direct method of Laboratoire National d’Essais (LNE) in France. The differences in the spectra are analyzed.

Heat transfer during HVOF deposition

Heat transfer processes during high velocity oxy-fuel (HVOF) deposition of WC coatings are studied. Experiments were conducted with temperature measurement in the substrate by thermocouples. A designed 2D computer simulation model of the spraying process with a moving torch is fitted to match the experimentally obtained temperature evolution. The resulting substrate heat fluxes and corresponding heat transfer coefficients are determined.

A measuring system for experimental research on the thermomechanical coupling of disc brakes

Abstract This paper deals with the introduction of a measuring system for application in research on the thermomechanical coupling of disc brakes. The first part is devoted to a description of the system for fast measurement of the brake disc surface temperature field during braking, which is the main part of the measuring system. The structure of the hardware as well as principles of evaluation of the temperature field are introduced. The second part deals with applications of the system to dynamometer testing rigs and real cars. The third part presents examples of the results. They demonstrate the applicability of the measuring system in experimental research on the behaviour of a disc brake system.

Frictionally Excited Thermoelastic Instability and the Suppression of Its Exponential Rise in Disc Brakes

This paper deals with processes of thermoelastic instability occurring on brake systems that become evident as a non-uniform distribution of temperature with hot spots on contact surfaces. Thermoelastic instability is accompanied by the exponential rising of temperature amplitudes of hot spots during its initial linear phase. The authors discuss different mechanisms of interruption of the growth, based on experimental and computational results. An example of experimental data is presented for the case of a disc brake.

Diagnostics of laser remelting of thermally sprayed coatings using an infrared camera

The fundamental performance limits of coherent optical transmission systems can be observed by a simple optimization between the linear noise and the nonlinear noise generated within the system. Optical Phase Conjugation (OPC) is considered to be one of the promising techniques to compensate for optical fiber’s dispersion and nonlinearity that cause crosstalk between signals traveling through long-haul optical transmission systems, nonlinearity compensation can lead to significant information capacity and distance reach expansion of optical fiber transmission links. To get the full benefit from the deployment of OPC in optical transmission systems, a few considerations must be taken into account, such as: power profile symmetry, fiber’s dispersion slope and Polarization Mode Dispersion (PMD). In this contribution, we will present our simplified theoretical predictions of optical fiber transmission systems performance that deploy mid-link OPC and multiOPC and we will show that the introduction of multi-OPC in an optical transmission system will minimize the impact of uncompensated/nondeterministic signal-signal nonlinear interactions due to fiber’s PMD and signal-noise interactions. We will show wide range of simulation and experimental results that validate the theoretical predictions of system’s performance for various types of links: dispersion managed, dispersion unmanaged, discretely amplified systems and distributed Raman amplified systems. Also, we will present an extensive experimental study shows that the deployment of mid-link OPC can provide a significant reach improvement in asymmetric lumped optical fiber links when optimizing the span length.III-V semiconductors have a direct bandgap that can be tuned through alloy engineering and therefore appear as very interesting for solar-cells, solid-state lighting and high power applications. The performances of current devices may be increased through the use of nanostructures and nanowires which look promising for the integration of high efficiency devices. Nanowires exhibit great properties such as efficient strain relieving capability and large specific area. Growth on silicon substrates and core-shell structures can be considered as well. Still, the production of nanowire-based devices faces material challenges related to morphological, structural, optical and electrical properties which are very linked to the synthesis process. This presentation will focus on Hydride Vapor Phase Epitaxy, which is a growth process implemented in a hot wall reactor using chloride precursors, and showing unique features regarding the growth of III-V and III-Nitride nanowires. For example, self-catalyzed GaAs nanowires were grown on silicon at a fast growth rate (60 µm.h-1) exhibiting a constant zinc-blende crystalline phase, for the potential fabrication of GaAs-based photonic devices on Si. For III-Nitride materials, InGaN nanowires demonstrating the entire composition range were grown by using a method compatible with the standard GaCl-based GaN growth process. Photoluminescence coupled with transmission electron microscopy measurements showed that these nanowires could overcome the so-called green gap and stretch the limits of solar cells efficiency. By taking advantage of the large growth rates anisotropy resulting from the use of chloride precursors, we could freely tuned the shape of GaN wires on masked substrates with (sub)-micrometric apertures.W the popularization of data centre and other bandwidth hungry inter-connect applications, the desired capacity of short reach optical network has exponentially increased to 400 Gbit/s or even more. Recent standardization efforts for 400 G intradata center connections specify link lengths of up to 2 km. 8×56 Gb/s or 4x100 Gb/s could enable such 400 G networks. Relative to coherent detection. Intensity modulation/direct detection (IM/DD) is a good candidate in inter-connect due to its low cost. For 56 and up to 100 Gb/s signal generation, a few modulation formats or schemes, such as pulse-amplitude-modulation (PAM4), discrete multitone (DMT), duobinary and chirp-managed laser (CML) are proposed and experimentally demonstrated. However, considering cost, size and power comsuption, the modulation format should be optimized for different networks to meet different requirements. In this talk, we will discuss this issue how to optimize the modulation formats for different optical networks?

Method for emissivity measurement of semitransparent coatings at ambient temperature

Coatings deposited on a material surface are effective way of changing its surface properties. For increasing or decreasing radiation heat transfer, coatings with high or low emissivity are used. Measurement of spectral emissivity is a fundamental step to effective use of coatings for this application. Up to now the measurement methods are focused on bulk samples and mainly opaque ones. Here we present a method enabling measurement of emissivity of semitransparent coating itself, although it is deposited on a substrate. The method is based on measurement of transmittance and reflectance using an integration sphere system and Fourier transform infrared (FTIR) spectrometer for samples with two different coating thicknesses deposited on transparent substrates. Measured transmittance of the coating indicates spectral regions of potential emissivity differences using different substrates. From all the measured values, spectral emissivity can be characterized for different coating thicknesses. The spectral range of the method is from 2 μm to 20 μm. The measurement is done at ambient temperature enabling measurement of samples sensitive to heating like biomedical or nanocoatings. The method was validated on known bulk samples and an example of semitransparent coating measurement is shown on high-temperature high-emissivity coating.