Radiometry Technique Research Articles

Preparation and Characterization of Algal Polysaccharides/Magnetite Microparticles Composite Films

Composites of magnetic particles in a polymeric matrix have received increasing interest due to their capacity to respond to external magnetic or electromagnetic fields. Algal polysaccharides such as agar are used extensively as gel-forming agents, thickeners, and stabilizers due to their low cost and high degree of biocompatibility and biodegradability. This study is focused on the preparation and characterization of algal polysaccharides–carbonyl iron composite films. The samples were analyzed using the photothermal radiometry (PTR) technique in the back-propagation emission configuration performing a modulation frequency scan. The amplitude and phase of the PTR experimental data were fitted simultaneously using a one-layer thermal-wave model considering homogeneous optical and thermal properties. The results indicate a systematic increase of the thermal diffusivity and optical absorption coefficient when the magnetic particle content increases. Scanning electron microscopy surface morphology of the agar/carbonyl iron composite indicates that a homogeneous distribution of particles can be obtained with the reported procedure and also provides evidence of agglomeration at high concentrations.

Photothermal and Structural Comparative Analysis of Chitinous Exoskeletons of Marine Invertebrates

Chitinous materials are common in nature and provide different functions including protection and support of many invertebrate animals. Exoskeletons in these organisms constitute the boundary regulating interaction between the animal and the external environment. For this reason, it is important to study the physical properties of these skeletons, in particular, thermal properties. The objective of this study is to investigate the thermal diffusivity of the skeletons of four species of marine invertebrates, Antipathes caribbeana (black coral), Panulinus argus (lobster), Callinectes sapidus (crab), and Limulus polyphemus (xiphosure). Thermal characterization is performed using photothermal radiometry (PTR) and laser-flash techniques. The measurements are complemented with structural characterization using X-ray diffraction. The results using both laser flash and PTR are consistent. These indicate that the thermal properties are strongly dependent on the presence of biogenic minerals (calcium and/or magnesium) and on the crystallinity index of the structure. The thermal-diffusivity values show an increase as a function of the crystallinity index.

Thermal characterization of composites made up of magnetically aligned carbonyl iron particles in a polyester resin matrix

The thermal characterization of composites made up by magnetically aligned carbonyl iron micro-sized particles embedded in a polyester resin matrix is performed using photothermal radiometry technique. The measured experimental data show that the thermal conductivity and thermal diffusivity of the composite, in the direction of the applied magnetic field, increase with the concentration of the particles and are enhanced with respect to their corresponding values for a random distribution of the particles. This thermal enhancement has a maximum at a concentration of particles of 10% and is very low at small and high iron volume fractions, such that for particles concentrations of about 40%, the composite thermal conductivity reduces to its values for random particles. This behavior indicates that for high volume fractions, the effect of the microparticles concentration plays a dominant role over the effect of their alignment. It is shown that the thermal conductivity of the composite can be modeled in terms of the Nielsen model, under an appropriate parameterization of the form factor of the particles. The results of this work could be highly useful for improving the thermal performance of mechanical and electronic devices involving composite materials.

Thermal Conductivity of Composites with Carbon Nanotubes: Theory and Experiment

ABSTRACTIn this work, the thermal conductivity of composites made up of carbon nanotubes embedded in a polyester resin is investigated by comparing experimental data with theoretical predictions. The composite samples were prepared with a random and aligned distribution of carbon nanotubes. Its thermal conductivity is then measured by using the photothermal radiometry technique. The obtained experimental data is accurately described by the proposed theoretical model, which takes into account the size effects of the nanotubes. It is expected that the obtained results can provide useful insights on the thermal design of composites based on carbon nanotubes.

Electronic transport characterization of silicon wafers by combination of modulated free carrier absorption and photocarrier radiometry

A combined modulated free carrier absorption (MFCA) and photocarrier radiometry (PCR) technique is developed to determine simultaneously the electronic transport properties (carrier diffusion coefficient, carrier lifetime, and front surface recombination velocity) of silicon wafers. Comparative computer simulations are carried out to investigate how the experimental measurement errors affect the simultaneous determination of the electronic transport parameters by introducing random or systematic errors into the simulated MFCA and PCR data and statistically analyzing the fitted results, by means of separate MFCA and PCR, as well as the combined MFCA and PCR through fitting the experimental dependences of signal amplitudes and phases to the corresponding theoretical models via a multiparameter fitting procedure, respectively. The simulation results show that with the combined MFCA and PCR the effect of experimental errors on the simultaneous determination of the transport parameters is significantly reduced and therefore the accuracy of the fitted results is greatly improved. Experiments with two c-Si wafers with the three methods were performed and the results were compared. The experimental results showed that the combined MFCA and PCR provided the most accurate fitted transport parameters, in agreement with the simulation results.

Land Geophysical Parameters Retrieval Using the Interference Pattern GNSS-R Technique

In the past years, the scientific community has placed a special interest in remotely sensing soil moisture and vegetation parameters. Radiometry and radar techniques have been widely used for years. Global Navigation Satellite Systems opportunity signals Reflected (GNSS-R) over the earth's surface are younger, but they have already shown their potential to perform these observations. This paper presents a GNSS-R technique, based on Global Positioning System (GPS) measurements, that allows the retrieval of several geophysical parameters from land surfaces. This technique measures the power of the interference signal between the direct GPS signal and the reflected one after scattering over the land, so it is called Interference Pattern Technique (IPT). This paper presents the results obtained after applying the IPT for topography, soil moisture, and vegetation height retrievals over vegetation-covered soils.

Present‐Day Volcanism on Venus: Evidence from Microwave Radiometry

We present new evidence for volcanic eruptions and lava flow emplacement on Venus within the last several decades. An integrated study of a radar‐dark lava flow unit in Bereghinia Planitia on Venus (∼28°E, ∼39°N) based on Magellan data obtained in 1993 reveals a significant apparent microwave thermal emission excess, consistent with increased subsurface temperature due to very recent lava flow emplacement. The flow unit occupies the stratigraphically youngest position in the area and in part is more than 15 years old because it was also observed in the radar map obtained by Pioneer‐Venus in 1978. Analysis of lava flow cooling rates and geological characteristics point to flow material of mafic composition. Future missions can employ this microwave radiometry technique to search for and monitor active volcanism on Venus.

Flower elliptical-orbit constellation exploiting millimetre-wave radiometry and radio occultation for meteo-climatological applications

Abstract. This paper reports on the potential of combining elliptical-orbit Flower constellations with millimeter-wave radiometry and radio-occultation, a mission concept briefly named FloRad2. The advantages of flower constellation with respect to conventional orbits are discussed, including the flexibility ensuring increasing coverage with separate launches. Millimeter-wave radiometry and radio-occultation receivers provide the advantage to design fairly compact payloads that comply well with current technology of mini-satellites. Millimeter-wave radiometry and radio-occultation techniques are somewhat complementary and an optimal combination of these observations results in atmospheric products with enhanced vertical and horizontal resolutions. Thus, the combination of small, light payloads employing millimeter-wave radiometry and radio-occultation with Flower elliptical-orbit constellations may result in an optimal compromise between retrieval performances and system complexity that is ideal for continued long-term missions with meteorological and climatological applications.

Temperature-dependent thermal characterization of Ge2Sb2Te5 and related interfaces by the photothermal radiometry technique

The thermal conductivity of Ge2Sb2Te5 (GST) layers, as well as the thermal boundary resistance at the interface between the GST and amorphous SiO2, were measured using a PhotoThermal Radiometry experiment. The two phase-changes of the Ge2Sb2Te5 were retrieved, starting from the amorphous and sweeping to the fcc crystalline state at 130 °C and then to the hcp crystalline state at 310 °C. The thermal conductivity resulted to be constant in the amorphous phase, whereas it evolved between the two crystalline states. The thermal boundary resistance at the GST-SiO2 interface was estimated to be higher for the hcp phase than for the amorphous and fcc ones.

Radiative defect state identification in semi-insulating GaAs using photo-carrier Radiometry

The photo-carrier radiometry (PCR) technique has been applied to a semi-insulating GaAs wafer for the detection and identification of radiative defects. Due to the ultrafast free carrier recombination lifetime, the conventional carrier-diffusion-wave-based PCR theory was modified to reflect the signal domination by trap emission and capture rates in the absence of diffusion. Defect photoluminescence with photon energies from 0.7 to 1.24 eV was collected and analyzed using photo-thermal temperature spectra and resonant (rate-window) detection combined with frequency scans. Five defect levels were identified self-consistently from the combined rate-window and PCR phase data, and the temperature dependence of the defect photoluminescence quantum efficiency was determined through multi-parameter best fits of the PCR rate theory to the experimental data.

Radiological impact of composite food served at PINSTECH

To determine radiological impact of composite food served at Pakistan Institute of Nuclear Science and Technology (PINSTECH) on its worker, cooked meals were collected during 2000–2007 and analysed by gamma and beta radiometry techniques for naturally occurring radionuclides and fission fragments. The only measurable radionuclide was naturally occurring 40K. Its activity range was 40±1.5 to 182.4±3.8Bq kg−1 with cumulative average value of 89.4±35.1Bq kg−1. Based on annual meals taken by the worker in cafeteria, the measured value gives committed effective dose of 74μSv and estimated cancer risk factor of 1.5×10−4 that is a minor fraction of the total risk of 5×10−3. It depicts that food served at PINSTECH cafeteria is radiologically safe for consumption.

Study of Skin Phantoms by Photothermal Radiometry in Frequency Domain and Multivariate Methods

In this paper the use of the photothermal radiometry technique in the frequency domain (PRTF) and the use of multivariate methods in the study of two types of skin phantoms: (a) one in which skin pigmentation was simulated dyeing the gel phantom and (b) the other consists of exposure of animal skin samples to different degrees of thermal damage. In experiment (a), gel phantoms were prepared with different concentrations of methylene blue (MB). The mean values of the radiometry signal (RS) show significant differences in only those cases in which changes in the concentration of MB were higher than 0.38 mM. This result was confirmed with a t test for independent samples of the data (p < 0.05). The mean values of the amplitude and phase signal do not permit discrimination between phantoms with changes in pigmentation equal to or lower than this value. However, principal component analysis (PCA) demonstrated that it is possible to discriminate between phantoms with changes in molar concentration equal to 0.38 mM (for the phase signal). In the case of experiment (b), the following four groups of pork skin samples were analyzed: one consists of samples of fresh skin, while the other three consist of samples exposed to thermal damage at 45 °C (the exposure time was 4 s) and 80 °C (exposure times were 4 s and 8 s, respectively). The mean values of the RS for each group of samples did not show a clear visual discrimination. However, the t test for independent samples applied to the data demonstrated significant differences only between fresh skin and skin exposure to thermal damage at 80 °C (with exposure times of 4 s and 8 s). PCA was used to discriminate between the four different skin samples.

Effect of laser beam size on measurement contrast of thermophysical gradients in layered structures using thermal-wave techniques

The effect of the laser source spotsize on the measurement sensitivity of layered system using photothermal radiometry (PTR) technique is presented. The beam size effect on the PTR measurement sensitivity is theoretically examined and experimentally demonstrated using a carbo-nitrided C1018 steel sample. The experimental results using a focused beam and an expanded beam for a carbo-nitrided C1018 sample validated the theoretical prediction, according to which the expanded beam showed a much larger magnitude change (contrast) in both amplitude and phase than results with a focused beam.

Studies on natural radioactivity of some Egyptian organic and chemical fertilisers

Radiometry techniques were applied to evaluate the activity and concentration values of 238U, 232Th and 40K in four types of Egyptian made fertilisers. Also, radon and thoron concentration values were estimated for the same samples. The Hyper-Pure Germanium Detection System (HPGeDS) installed at the hot laboratories of Inchas, Cairo, and the Solid State Nuclear Track Detection System (SSNTDS) facility of the Girls' College were used for measurements. A comparative study on the concentration values obtained in this work for the four fertiliser samples is presented.

A Review of ECE Correlation Radiometry Techniques for Detection of Core Electron Temperature Fluctuations

Over the past 15 years, correlation radiometry techniques have been developed to detect the small-amplitude, high-frequency electron temperature fluctuations to which standard electron cyclotron emission measurements are insensitive. In this paper we review the principles of these techniques and summarize recent core electron temperature fluctuation measurements and their impact on understanding turbulent transport.

Two-beam cross-modulation photocarrier radiometry: principles and contrast amplification in semiconductor subsurface imaging

A two-beam photo-carrier radiometry (PCR) technique of semiconductors has been developed. The technique operates on the superposition of superband-gap and subband-gap laser beams which results in the cross-modulation of the backscattered subband-gap laser intensity by the harmonically varying free-carrier-wave density-dependent infrared absorption coefficient. A theory of this two-beam cross-modulation approach and various experimental configurations applied to the imaging of electronic contamination and defects in silicon wafers are presented. Owing to the nonlinear interaction of the two beams, the configuration revealed a new optoelectronic effect, the decrease of the residual subband-gap absorption coefficient due to the decreased carrier capture cross-section brought about by the depletion of occupied band-gap states in the presence of photons produced by radiative recombination. Quantitative values of the optoelectronic constant B associated with the rate of depletion of free-carrier capture cross-section with superband-gap intensity, as well as of IeR, the intensity of radiative recombination emissions, were obtained. These values cannot be measured by conventional PCR or other single-ended optoelectronic techniques. The theory explains the experimental dependence of electronic transport properties on the intensity of the subband-gap beam and accounts for optoelectronic imaging contrast amplification in contaminated or defect semiconductors. The two-beam cross-modulation PCR was further shown to enhance the imaging contrast of a certain electronic contamination type (Fe in p-Si). A dramatic phase contrast enhancement of subsurface defects made by low-dose proton implantation was demonstrated at superband-gap laser intensity levels one order of magnitude lower than possible with single-ended optoelectronic imaging methodologies. This is tentatively attributed to relatively low-injection trap-filling well below optoelectronic trap saturation.

재료의 열확산계수 결정을 위한 광열복사법의 이론적 연구

We analyze in detail axially symmetric theoretical study for the photothermal pulsed radiometry of a cylindrical model. The theoretical solutions describe the transient infrared radiation from the sample heated by short-duration pulsed heating. In the conventional transmission radiometry technique, the excitation source and the detector are on opposite sides of the sample, otherwise in the new single ended radiometry technique, the excitation source and the detector are on same sides of the sample. The analytical solution described for photothermal radiometry in this study would not need to cut or polish samples to measure the thermal diffusivity. Therefore the radial area and axial thickness of samples are not limited. The effects of excitation pulse duration and the area of heat source are discussed.

Measurement accuracy analysis of photocarrier radiometric determination of electronic transport parameters of silicon wafers

Simulations are performed to investigate the accuracy of the simultaneous determination of the electronic transport properties (the carrier lifetime, the carrier diffusion coefficient, and the front and rear surface recombination velocities) of silicon wafers by means of the photocarrier radiometry (PCR) technique through fitting frequency-scan data to a rigorous model via a multi-parameter fitting process. The uncertainties of the fitted parameter values are analyzed by calculating the dependence of the square variance including both amplitude and phase variances on the electronic transport properties. Simulation results show that the ability of the PCR to accurately determine carrier lifetimes gradually decreases for lifetimes longer than roughly 100 microseconds. In case the carrier diffusion coefficient is previously known, the carrier lifetime and front surface recombination velocity can be determined with uncertainties approximately ±20% or less. Experiments with an ion-implanted silicon wafer were performed and the carrier lifetime and front surface recombination velocity were determined with estimated uncertainties approximately ±30% and ±15%, respectively.

Deep subsurface electronic defect image contrast and resolution amplification in Si wafers using infrared photocarrier radiometry

A photocarrier radiometry technique using a secondary subband-gap dc light source is introduced, along with the applications to deep subsurface electronic defect analysis in Si wafers. It is shown that the use of a dc light source, in addition to the modulated laser beam, drastically enhances the potential of the technique in resolving low-level damage otherwise virtually indistinguishable by conventional photothermal techniques. Using this methodology, the overall contrast enhancement was about 386% for amplitude and 5586% in phase over conventional photocarrier radiometry.

Modulated photothermal radiometry applied to semitransparent samples: Models and experiments

Mathematical modeling is presented of the combined conductive and radiative heat transfer occurring in a semitransparent material (STM) subjected to a periodic heat flux. The models rely on the quadrupole method, which is a very powerful tool to obtain analytical solutions in the Fourier or Laplace domain. Photoacoustic or photothermal radiometry techniques are reviewed. Two groups of methods are discussed depending on whether the sample has natural or opaque interfaces to simulate radiative exchanges with the surroundings. The metrological problem of measuring the phonic thermal diffusivity of semitransparent materials is investigated. Theoretical simulations are given. They explain some typical features of the phase-lag signal of temperature responses. Experimental measurements on pure silica validate the results and prove that these methods are efficient for the thermal characterization of STM.