Search

The use of the angular spectrum method (ASM) to simulate the reflection of airborne ultrasound beams from a thin membrane separating air from a mixture of air and another gas is examined. The main advantage of this method is its high computing speed and efficiency for practical design calculations, suitable for sensing applications. The implemented ASM code is validated against custom Rayleigh integral code in a pure propagation simulation. In addition, ultrasound beam reflection calculations using ASM with finite element numerical results and experimental measurements are compared, finding good agreement in both cases. Then, ASM is used to estimate the sensitivity of specular reflection signals to variations in the composition of the incidence medium as a function of the angle of incidence. Conditions for which a reflection signal using inexpensive commercial ultrasound emitter/receiver at 40 kHz, in a simple configuration, offer a high enough sensitivity suitable for monitoring air quality indoors are found.

In this work we investigate an efficient method for calculating the reflected and transmitted acoustic fields from diffracting ultrasound beams incident to a gas/gas interface. The study is motivated by the application to gas sensors of an experimental setup consisting of a 40 kHz acoustic incident beam at oblique angles to an interface separating two gases. The numerical method consists of performing a plane wave expansion of the incident beam using standard Fourier transform methods. Expressions for the reflected and transmitted acoustic fields are obtained in terms of integrals of simple kernels. These can be performed numerically in a straightforward way. The main approximation in this method comes from guessing the acoustic pressure field at a plane just in front of the ultrasonic emitter. We compare calculations of this Plane Wave Expansion Method (PWEM) with finite element method simulations in a 2D geometry, finding good qualitative agreement. Among the advantages of the PWEM we have that there is no need to calculate the whole acoustic fields in a large volume, compared to the wavelength of the frequency used, while still considering rigorously diffraction effects. We present calculations for airborne ultrasound reflection measurements of interest in developing novel acoustic gas sensors.

The aquifer recharge area that supplies water to Mexico City is being protected with the implementation of land use restrictions and with the use of payment schemes for maintaining environmental services (PES). In order to assess the effects of PES in the conservation soil area, the chemical and isotopic compositions of water from springs were characterized and the water baseline chemistry was established to provide a useful standard to monitor the water resources and to support the decision-making under current water management policies. A total of 32 water samples taken in four field surveys, during the dry and rainy season, and background chemical data from different information sources, were studied. The water salinity increases from southwest to northeast towards the urbanized area. The chemical composition of water is due to the occurrence of natural chemical interactions between water and rocks in aquifers and to the presence of effluents generated by human activities. In the forest area, water chemistry has not changed significantly over the past three decades and there are no major discernible trends in the compiled water chemistry data, suggesting that PES has contributed in part to maintain the initial condition in the aquifer recharge area. The natural reference levels proposed have allowed the current chemical conditions in the system to be understood and can be implemented to monitor water resources in the area of conservation soil in the Sierra de Las Cruces with an acceptable degree of reliability. Fil: Zabala, Maria Emilia. Universidad Nacional del Centro de la Provincia de Buenos Aires. Rectorado. Instituto de Hidrología de Llanuras - Sede Azul. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto de Hidrología de Llanuras - Sede Azul; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Martinez, Sandra Edda. Autoridad de Cuenca Matanza Riachuelo; Argentina Fil: Perevochtchikova, María. El Colegio de Mexico; México Fil: Sandoval Romero, G. Eduardo. Universidad Nacional Autónoma de México; México Fil: Aponte, Nidya. Universidad Nacional Autónoma de México; México

The objective of this paper is to compare two gyrocompass' schemes for the detection of Earth's true north. These schemes are refered to as dynamic and static methods. We present a model to characterize the sensitivity of each model as a function of the output signal of the sensor element. We use a fiber optic gyroscope (FOG) as the sensor element.

An interferometric system of volume optics and fiber optic were constructed and proved, showing the instrumentation technique made for these devices, supported in the new technologies of optical detection, amplification, analogical and digital filtrate and single data acquisition. Based on the Sagnac's effect of volume optics and fiber optic, the interferometer of Sagnac has many applications, nevertheless the methods of construction, design and instrumentation for the sensors manufacture of based on both designs are not very well‐known, is for that reason that in this work approaches some of the methodologies for the design and construction of these devices, obtaining higher sensitivity and better contribution in its respective interferometric paths, for the sensing of different physical parameters in which they are applied. We used the single design for each interferometer, proposing the best detection limit for each one. The data acquisition was made with the proposal to obtain quick results, using the audio card of a PC, obtaining a real time measurements and digital processing of the signal in a single way.

In this work an implementation of angular sensor movements is made based on the Sagnac effect, made it in volume optics, using a detection method of the interference lines and its amplified pattern. The new devices of sensing through optical systems, have given a new vision of measurement and instrumentation, guiding to new studies on designs and prototypes of themselves. An example of these developments is the advance in devices of sensing in fiber optic, such is the fiber optic gyroscope (FOG) which is based on the Sagnac effect. This device has a great sensitivity because the area enclosed by the interferometric ring, is through a fiber optic coil, which increases the sensitivity and diminishes the size of the device. It is possible to indicate that in previous years, with the technology then existing, the utility to use the Sagnac effect like a gyroscope was very limited, because it was just employed to measure angular movements of great magnitudes and with very big areas, since there was not the optical detection systems of the great sensitivity that now exist or coherent sources with high power, indispensable elements in the implementation of the system. For that reasons, the application of this effect began to grow with the development of the fiber optic, and was possible diminish the size and increase the area of the device. Thus the Sagnac effect in volume optics was relegated by the fiber optic interferometer. Nevertheless using the new electronic systems of amplification and optoelectronic devices that now exist, we have rescued the Sagnac effect in volume optics to make measurements of angular velocities in an interferometric system of 0.25m2. For this work, was necessary to create a detection system of great quality, this was made using a detection method of the interference lines and amplification of the interferometric pattern.

Throughout all this paper we are going to analyze one application of the optical beam deflection method (OBDM), the procedure for its development, as well as its ideal implementation to reach measurements of displacements that could be the most accurate and of the smaller scale possible, this condition is essential for the magnitude of the results to evaluate. We also give an application of the OBDM such as a fine particle densimeter principally in solids. This present work will analyze the laser beam deflection technique, the procedure to apply, as well as its ideal implementation in order to obtain measures of displacements that can sense to the most exact and the smaller possible scale, obtaining results from microns, micrometers and even, until nanometers. Our objectives that are considered in this investigation are two: the first one is to build a device based on this technique, make accurate measures on a very low scale, which could be reliable and in the order of scale of microns until nanometers. The second objective that we are searching is to obtain an alternative method for verify the values of density that some substances that are hard to get like titanium oxide.

Most of the investigations that exist about the interferometer of Sagnac in our days, are made through fiber optic, which has the great advantage of having a big area size in very little space wound in a nucleus. The first interferometers of Sagnac, were used for very big angular speeds measures, it didn't have the advances to carry out detections of small signs, because the measurements systems like photo-detectors, amplifiers, filters, etc. didn't have the capacity of the systems that now exist. That is one reason that our experiments are based on the electronic advances, to make detections of phase changes of until less than 0.1 nm with area of 0.025 m 2 . Besides we proposed changes in the original interferometer diagram, adding some elements that can help s to achieve a bigger sensibility, accuracy and reduction of noise. Another of the advantages of use an interferometer of Sagnac, is work directly with the beams that travel through it, because we can observe the behavior from the optic road to external physical effects, like angu lar velocity or speed and little movements. Finally the acquisition devises and the software were used for calculate the angular frequency of the sensor directly from the experiment and know the parameters of the movement. Keywords : Fiber optic gyroscope, Sagnac’s interferomete r, optic interference, electronic stage.

We propose a simple technique for determining the refractive indices of highly absorbing materials. This method uses two transmittance measurements at oblique incidence. A theoretical analysis of the proposed method is presented. The refractive index of water was experimentally determined with a relative error ranging from 0.12% to 1.3%. We discuss the extension of this method to spectroscopic measurements.

Most of the investigations that exist about the interferometer of Sagnac in our days, are made through fiber optic, which has the great advantage of having a big area size in very little space wound in a nucleus. The first interferometers of Sagnac, were used for very big angular speeds measures, it didn't have the advances to carry out detections of small signs, because the measurements systems like photo-detectors, amplifiers, filters, etc. didn't have the capacity of the systems that now exist. That is one reason that our experiments are based on the electronic advances, to make detections of phase changes of until less than 0.1 nm with area of 0.025 m2. Besides we proposed changes in the original interferometer diagram, adding some elements that can helps to achieve a bigger sensibility, accuracy and reduction of noise. Another of the advantages of use an interferometer of Sagnac, is work directly with the beams that travel through it, because we can observe the behavior from the optic road to external physical effects, like angular velocity or speed and little movements.

Throughout all this paper we are going to analyze one application of the optical beam deflection method, the procedure for its development, as well as its ideal implementation to reach measurements of displacements that could be the most accurate and of the smaller scale possible, this condition is essential for the magnitude of the results to evaluate. We also give and introduction of the optical beam deflection method, it is characteristics and some of their latest applications as an auxiliary technique on research and commercial fields. This present work will be analyzed the laser beam deflection technique, the procedure to apply, as well as its ideal implementation in order to obtain measures of displacements that can sense to the most exact and of smaller possible scale, obtaining results from microns, micrometers and until nanometers. The importance of this work resides in that the technique although is simple and has easy implementation, the results that can hurtle they are very reliable; thanks to it, the laser beam method of deflection has been not only diffused in many fields of the science and the technology of the optics, but also in those where its application is innovating. This has ended up being a technique of huge utility on interdisciplinary use and has been used to measure physical parameters in a great variety of experiments.