Liviu Singher

Fourier Transform Infrared—Attenuated Total Reflection Nitrate Determination of Soil Pastes Using Principal Component Regression, Partial Least Squares, and Cross-Correlation

This paper investigates the use of Fourier transform infrared (FT-IR) attenuated total reflectance (ATR) spectroscopy as a fast and simple way for direct determination of nitrate concentration in soil pastes, which would assist precision fertilizer placement and reduce nitrate pollution. Eight types of soils are investigated, with nitrate concentrations ranging from 0 to 1000 ppm-N. The spectral region around the nitrate band (1300–1550 cm−1) is analyzed by (1) principal component regression (PCR), (2) partial least squares (PLS), and (3) cross-correlation with reference libraries that include spectra of pure ions and/or soils. The main obstacle to accurate nitrate measurement appears to be an interfering band present in calcareous soils. This band, which may be due to carbonate, is located around 1450 cm−1 and overlaps with the nitrate band centered around 1370 cm−1. For non-calcareous soils, and in particular for light sandy agricultural soils, PLS and cross-correlation with a reference library containing only spectra of ions in water give similar results (about 8 ppm-N on dry soil basis), while PCR leads to slightly poorer results. When calcareous soils are included in the analysis, the prediction errors are about twice as large. In this case, the best results are obtained using PLS, followed by PCR, while cross-correlation with reference libraries leads to poorer results.

Considerations in bond strength evaluation by ultrasonic guided waves

Acoustic wave propagation in a three‐layer waveguiding configuration is analyzed. Considering an adhesive layer as a waveguide structure, it is shown that the propagation of guided modes is affected by the bonding quality. A comprehensive study demonstrates the possibility of utilizing measurements on guided wave propagation to detect interfacial weakness between an adhesive and adherend.

Bond strength measurement by ultrasonic guided waves

A quasi-static model is proposed for ultrasonic guided waves interaction with imperfect interfaces. Incomplete bonding and the effect of this condition on the velocity is comprehensively discussed. The theoretical model, serves as reference for extracting ultrasonic wave parameters from experimental data. These parameters are correlated to adhesion strength. This work presents the results of a series of experiments with bonds of varying quality and thickness. Ultrasonic surface waves have been generated by a piezoelectric transducer and the detection was performed using an optical interferometer. The optical sensing of the ultrasonic surface waves is used to provide information about the ultrasonic guided waves which propagates along the boundaries between solids. Specifically, the normal component of the ultrasonic wave has been measured for providing information about the bond strength. The challenge of discriminating imperfect bonds was achieved.

Adaptive multiple filtering

The method described represents an attractive compromise between the use of a single filter for a number of image distortions and one filter for each image or distortion of an image. The goal of this work is the generation of a number of filters, each of them being able to recognize a number of distortions. One of the main problems of the filter design is its high sensitivity to internal noise of the system, optical aberrations, etc. In this work, the most common case of image distortion invariance has been considered together with system noise invariance. The simulation results indicate the absence of a false alarm and good identification. The filter generation is based on a learning process in an electro-optical pattern recognition system. The genetic algorithm serves as an optimization method. A binary filter has been selected as the spatial filter. The comparison between a traditional matched spatial complex filter and this adaptive binary filter performance indicates the significant benefits of the latter. Statistical tools were used to estimate and compare the significance of the difference between the output average of a rejection and recognition image sets.

Focused-beam interaction with a phase step.

The interaction of a tightly focused laser beam with a step function is encountered in optical storage media, scanning microscopy, positioning and aligning systems, and various other applications. A theoretical and experimental investigation provides an improved description of the physical process and indicates the possibility of achieving extreme superresolution suitable for certain applications.

Interaction of a guided wave with a nonuniform adhesion bond

This paper presents theoretical considerations for the determination of the diffraction of ultrasonic guided waves propagating in a nonuniform elastic adhesive layer. The nonuniformity results from changes in the adhesion bond characteristics between the adhesive and the adherent layer. The bond strength is assumed to change both locally as well as periodically. The problem is solved by using the perturbation theory. The field of the reflected and transmitted waves is given in natural modes of the elastic waveguide layer. The theoretical model derived serves as a reference for extracting acoustic wave parameters. These parameters are correlated to adhesion strength.

Step height determination by a focused Gaussian beam

The interaction of a focused laser beam with a step on a conducting surface is investigated by a vector method. The 2-D problem is solved by using a model of fictitious current filaments, while 3-D problems are treated by using a model of fictitious dipoles as the sources of the scattered field. Computer simulations indicate a difference between the two polarization components (TE and TM), but with the samples investigated in this work, these differences are too small for practical measurements. The scattered field distribution is found to be strongly dependent on the step height relative to the observation plane and on its position relative to the beam waist. Thus, measurements of the intensity distribution in the observation plane can provide information about these parameters with high sensitivity. Experimental investigation confirms that the height of a step in the range λ/10 to λ/4 can be measured with an accuracy of 5%, including its sign (up or down). The position of the step with respect to the beam can be estimated with an accuracy of about 1/100 of spot size.

Ellipsometry with a stabilized Zeeman laser.

A novel ellipsometric method was introduced in an earlier publication, based on a rotating plane polarized beam. We show that the method is substantially improved by using a stabilized Zeeman laser as the light source.

WAVEGUIDE HOLOGRAPHIC ELEMENTS RECORDED BY GUIDED MODES

Recording holographic optical elements in planar waveguides with both interfering beams being guided modes has certain advantages. We show that such holograms can be efficiently recorded when only a small fraction of the guided modes penetrates the recording material that is deposited outside the main guiding region. An integrated optic wavelength-division demultiplexer is analyzed and implemented as a specific example. In this example the holographic grating also acts as a focusing element; thus no additional collimating or focusing lenses are required.

OPTIMIZATION OF BINARY CIRCULAR FILTERS

A rotation-invariant algorithm based on binary circular filters is developed for optical pattern recognition. The features of the genetic algorithm provide a highly efficient and rapid learning process. During training, the parameters of a circular filter are selected to maximize the distinction between the target and other expected objects in the image. These iteratively designed filters are good discriminators because they utilize all the spatial visual information about the target. Filters that optimize the trade-off between noise robustness and sharpness of the correlation peak can be determined. Binary circular filters when combined with spatial light modulators are appropriate for real-time applications.