Papers by Keyword: Photoacoustic

Abstract: Nickel selenide (NiSe) has been synthesized by solid state method and annealed at five different temperatures, ranging from 323 K to 823 K. The annealing effect on NiSe thermal and carrier transport properties were investigated by using open-cell photoacoustic technique. From analysis of its phase signal-frequency, thermal diffusivity, carrier diffusion coefficient, surface recombination velocity and recombination lifetime of the NiSe was determined. The results show that with increasing of the annealing temperature of NiSe sample, the thermal diffusivity and the carrier diffusion coefficient increased. The surface recombination velocity was decreasing as the annealing temperature of the sample increased. The increasing of annealing temperature of the sample also affected the trend of band-to-band recombination lifetime.

Abstract: In photoacoustic (PA) technology, piezoelectrical transducer (PZT) is the most frequently used detector for the PA signal generated by weakly absorbing liquids. Although PZT has high sensitivity, its output signals are distorted and become exponentially damped sinusoidal signal [, which is a barrier to extract correct information of glucose. Therefore it is necessary to find a proper way to extract glucose information. In this paper, a method of parameter estimation based on Laplace wavelet correlation filtering and Least Square Estimation is proposed to extract the information of PA signals, which includes signal decomposition, fitting and glucose parameter extraction. The Laplace wavelet correlation filtering is introduced to decompose piezoelectrical signals into impulse responses of single mode subsystems [2], followed by a Least Square Estimator to fit PA signal and estimate parameters of the exponentially damped sinusoidal model [3]. Good agreement between the fitting model and the PA signal is obtained. Experiments are carried out on finding meaningful parameters indicating glucose among estimated parameters of the exponentially damped sinusoidal model.

Abstract: This paper presents method and performance of the Helmholtz photoacoustic resonant cell and its remodified one which both were designed and tested respectively based on the measurement of the CO₂ contribution of the photoacoustic signal in experiments. The average optical power at the laser operating point was 800mW for the10.653um laser (CO₂ detection). On-line and real time measurement CO₂/N₂ mixtures (CO₂ 300ppm) were then performed. The Helmholtz photoacoustic resonant cell and its remodified one test of the carbodioxide conducted at their respective resonant frequency demonstrated signals about 43mV and 67mV, signal-to-noise (S/N) values about 47dB and 51dB respectively. According to test results, the remodified one also has a better quality factor. All this demonstrate the remodified Helmholtz cell can preferably improve excitation of acoustical signal.

Abstract: This paper presents method and performance of the photoacoustic resonant cell remodified from Helmholtz cavity that can be used to detect photoacoustic signal of multi-gas. This technique has its physical basis in a phenomenon called the photoacoustic effect. The experiment system is composed of a resonant Helmholtz cavity, a sensitive microphone and two infrared lasers with high adsorption capability and specificity to the analyte. In our experiments, the average optical power at the laser operating point is 200mW for the 972nm laser (H₂O detection) and 800mW for the10.653um laser (CO₂ detection), which are modulated at two different frequencies f1=175Hz and f2=125Hz. The remodified Helmholtz resonant on-line and real time measurement of the water vapour (300ppm) and carbodioxide (300ppm) conducted at their respective resonant frequency shown large signals about 4.41mV and 19.77mV respectively. The result demonstrated this cell used to test multi-gas is also feasible.

Abstract: In this paper, the application of photoacoustic methods to study thermal properties of Al-Li alloy is described. The photoacoustic measurements are carried out for thermal properties on Al-Li alloy and studied for various thicknesses. The theoretical basis for quantitative measurements is discussed together with the advantages and limitations of these methods as compared with conventional measurements. Applications to spectroscopic and depth-profile analysis and also to thermal property measurements in Al-Li samples heat-treated at 755K per hour and annealed at 505K are discussed. The results are compared with literature values, and discussed.

Abstract: In Campos oil Basin (Brazil), which is responsible for more than 80 % of the national petroleum production, it is generated a great amount of wastes from deep crude oil extraction related activities. Particularly, the oil sludge waste has been intensely studied in order to search alternatives for the reuse of the waste in treated form in the ceramic industry. the present work focuses on the photoacoustic thermal characterization of sintered ceramic bodies containing up to 5 wt.% added waste. Specimens were uniaxially pressed at 25 MPa, and sintered between 850 °C and 1000 °C. The results of thermal diffusivity indicate that the use of petroleum waste in structural ceramic up to 5 wt.% does not cause significant changes in the structure or composition of the clay/waste system, resulting in great advantages in waste minimization.