Guillermo Santiago

Bio: Guillermo Santiago is an academic researcher from University of Buenos Aires. The author has contributed to research in topics: Laser & Photoacoustic effect. The author has an hindex of 10, co-authored 56 publications receiving 281 citations. Previous affiliations of Guillermo Santiago include National Scientific and Technical Research Council.

Photoacoustic detection of NO2 traces with CW and pulsed green lasers

Abstract: Photoacoustic NO2 traces detection based on continuous and pulsed lasers emitting at 532 nm is presented. Both systems were calibrated with known NO2-pure air mixtures. A minimum detectable volume concentration of 20 parts in 109 (S/N=1) and 15 parts in 109 for the resonant and pulsed regime, respectively, were obtained. These values were limited by electrical and acoustical noise of the microphone and electronics. Measurements of NO2 concentrations in urban air are compared with home-manufactured mixtures. Traces of nitrogen dioxide from two different car exhausts are also detected and quantitatively assigned from the calibration curves.

Water-based enhancement of the resonant photoacoustic signal from methane–air samples excited at 3.3 μm

Abstract: Photoacoustic spectroscopy is widely applied for trace-gas detection because of its sensitivity and low detection limit. In a previous work, where we studied the potential application to methane monitoring under a resonant excitation at 3.3 μm, we showed that the signal from methane–nitrogen mixtures decreases with the addition of oxygen. This effect is due to an energy exchange between the ν 4 asymmetric stretching mode of methane and the first metastable level of oxygen. This process makes oxygen accumulate energy, thus hindering the generation of the photoacoustic signal. In this work, we study the possible addition of water, as a good collisional partner of oxygen, in order to obtain a greater sensitivity. We develop a model based on rate equations and find good agreement between theory and measurements. The experiment is carried out with a novel cell of rectangular cross section and a Q factor of 165±1. We find that 0.7 % water content is large enough to obtain a signal as high as in the methane–nitrogen case at atmospheric pressure.

Differential, LED-excited, resonant NO2 photoacoustic system

Abstract: We introduce the application of a differential microphone in an LED-excited photoacoustic system devoted to NO2 measurement. The microphone ports pick up out-of-phase signals generated in two resonators, thus achieving a larger electrical signal and good common mode noise rejection. The reduced noise floor and LEDs with higher optical power, made it possible to measure NO2 down to 60 ppbV, a figure that enables quantifying the amount of such a gas produced by gasoline engines equipped with catalytic converter.

Resonant photoacoustic gas sensing by PC-based audio detection

Abstract: A new and simple technique for data acquisition and processing in an experiment of resonant photoacoustic detection is presented It is based on the use of the sound card of a desk or laptop computer for digitizing the signal from a microphone enclosed in an acoustical cavity and further processing by a high-resolution fast Fourier transform The system is applied to the detection of NO2 traces in air at atmospheric pressure with an amplitude-modulated visible laser and the results are compared with those obtained by a lock-in amplifier For the same acquisition time the results for the ultimate measurable concentration were 50 ppbV with this system and 130 ppbV with a lock-in amplifier

Electromechanical characterization of piezoelectric polymer thin films in a broad frequency range

Abstract: Piezoelectric materials are usually characterized using resonant methods. However, piezoelectric polymers are used in broadband devices, thus requiring characterization over a wide range of frequencies. In this work, we present a non-resonant method for the broadband electromechanical characterization of piezoelectric polymer thin films. The procedure is based on measuring the complex capacitance of a sample of known geometry under three conditions: free, blocked and immersed in a fluid of known acoustic properties. The behaviour of the sample under study is modelled as a one-dimensional transducer and treated as a two-port network that relates the measurable electrical and mechanical variables. Also, the sample is considered as a free-space radiator when immersed in a fluid. The method determines the intensive and the equivalent circuit parameters of piezoelectric polymer films, allowing the characterization of elastic and electrical properties in a broad frequency range. In order to test the method, we performed isothermal capacitance measurements on a sample of poly(vinylidene fluoride) at a temperature of 298 K. The sample was measured along the direction of the poling field and in the frequency range from 10 Hz to 10 MHz. The results given by the method agree with those reported by other authors.

Photoacoustic imaging in biomedicine

Abstract: Photoacoustic imaging is a promising method for visualizing biological tissues with optical absorbers. This article provides an overview of the rapidly developing field of photoacoustic imaging. Photoacoustics, the physical basis of photoacoustic imaging, is analyzed briefly. The merits of photoacoustic technology, compared with optical imaging and ultrasonic imaging, are described. Various imaging techniques are also discussed, including scanning tomography, computed tomography and original detection of photoacoustic imaging. Finally, some biomedical applications of photoacoustic imaging are summarized.

Photoacoustic spectroscopy for analytical measurements

Abstract: Many different techniques, such as UV/vis absorption, IR spectroscopy, fluorescence and Raman spectroscopy are routinely applied in chemical (micro-)analysis and chemical imaging, and a large variety of instruments is commercially available. Up to now, opto- or photoacoustic (PA) and other optothermal (OT) methods are less common and only a limited number of instruments reached a level of application beyond prototypes in research laboratories. The underlying principle of all these techniques is the detection of local heating due to the conversion of light into heat by optical absorption. Considering the versatility, robustness and instrumental simplicity of many PA techniques, it is surprising that the number of commercial instruments based on such approaches is so sparse. The impetus of this review is to summarize basic principles and possible applications described in the literature, in order to foster routine application of these techniques in industry, process analysis and environmental screening. While the terms OT and PA methods cover a very wide range of methods and physical phenomena, this review will concentrate on techniques with applications for analytical measurements.

Analytical devices based on light-emitting diodes – a review of the state-of-the-art

Abstract: A general overview of the development of the uses of light-emitting diodes in analytical instrumentation is given. Fundamental aspects of light-emitting diodes, as far as relevant for this usage, are covered in the first part. The measurement of light intensity is also discussed, as this is an essential part of any device based on light-emitting diodes as well. In the second part, applications are discussed, which cover liquid and gas-phase absorbance measurements, flow-through detectors for chromatography and capillary electrophoresis, sensors, as well as some less often reported methods such as photoacoustic spectroscopy.

Photoacoustic spectroscopy for process analysis

Abstract: Photoacoustic spectroscopy (PAS) is based on the absorption of electromagnetic radiation by analyte molecules. The absorbed energy is measured by detecting pressure fluctuations in the form of sound waves or shock pulses. In contrast to conventional absorption spectroscopy (such as UV/Vis spectroscopy), PAS allows the determination of absorption coefficients over several orders of magnitude, even in opaque and strongly scattering samples. Small absorption coefficients, such as those encountered during trace gas monitoring, can be detected with cells with relatively short pathlengths. Furthermore, PA techniques allow absorption spectra of solid samples (including powders, chips or large objects) to be determined, and they permit depth profiling of layered systems. These features mean that PAS can be used for on-line monitoring in technical processes without the need for sample preparation and to perform depth-resolved characterization of industrial products. This article gives an overview on PA excitation and detection schemes employed in analytical chemistry, and reviews applications of PAS in process analytical technology and characterization of industrial products.

Recent Progress on Infrared Photoacoustic Spectroscopy Techniques

Abstract: Analogous to most new methods in science, photoacoustic spectroscopy (PAS) grew out of an advance in technology, in this case the dramatic improvement in novel light sources, modulators, and acoustic detectors, as well as signal recovery electronics, which in turn was made possible by the development of modern PAS techniques. PAS is a promising technique that can be used to analyze and characterize a broad variety of objects (gaseous, solid, and liquid samples). In the present review, the recent development of infrared PAS limited to the general area of gas-phase analysis techniques since 1990 is summarized, with special emphasis on the development of new or enhanced analytical methodologies based on the use of the photoacoustic (PA) effect to improve the sensitivity of PAS by enhancing signal or reducing noise levels, with regard to PA systems, applications, and conclusions. The applications of these novel PA methods are mainly concerned with molecular spectroscopic, industrial, atmospheric, env...