Integrated Acousto-Optical Temperature Sensor

In this work, we investigate the performance of a novel integrated acousto-optical temperature sensor fabricated in LiNbO₃ and operating with ultrashort light pulses (2 ps). Five parameters (time duration, bandwidth, time intensity maximum, frequency intensity maximum, and output energy on the output pulse converted for the TM mode, as a function of temperature) were observed for the switched pulse at the output of the sensor (TM mode) with and without the presence of an increasing linear self-phase modulation (SPM) profile. Comparing all analyzed parameters, one can conclude that the pulse intensity is presenting the larger variation (100.09%) as a function of the temperature change (24.5 to 400°C) in a configuration without profile. Considering the increasing linear SPM profile, all the analyzed parameters are presenting a significant increase in the percentile variations in the studied range of temperature (24.5 to 400°C). Comparing all the five parameters, in two configurations (with and without the use of linear SPM profile), one can conclude that the time intensity maximum showed to be the most suitable parameter as measurement to be accomplished in a schematic detection for the temperature sensing in the range 24.5 to 400°C. We can conclude that the sensitivity of the AOTS is improving in the configuration with the increasing nonlinearity profile (β = 2) and for higher temperature.     

Adhesives: a new class of polymer coatings for surface acoustic wave sensors for fast and reliable process control applications

Fast and reliable on-line detection of organic vapors for control of chemical processes is a challenging application for a new type of analytical instruments: sensor systems based on an array of differently selective chemical sensors. In this work we present the use of mass-sensitive polymer coated surface acoustic wave sensors (SAWs). The sensors were initially coated with a standard set of polymers consisting of a known composition. But this first approach could not meet all requirements. Therefore, a new class of commercially available polymer coating, namely adhesives, was developed. The coating procedure was optimized and the aging process of the adhesives was carefully investigated. As a result the selectivity for ambitious separation problems arising from similar polarity of the components of typical solvent mixtures could be remarkably increased. The system was then applied in a real testing environment application at a chemical plant: the fast on-line control of a preparative reversed phase process HPLC (RP-PHPLC). Data from this industrial application are shown.     

应用弹性振子点阵模型数值模拟表面带裂痕材料中的激光激发声表面波

本文将激光等效为垂直力源,建立弹性振子点阵模型,并采用数值模拟的方法对线源激光在金属材料中所产生超声及其传播进行了研究,着重针对有无裂痕材料表面上接收到的波形进行了对比和分析。该方法特别适合处理边界问题,因此也易于处理有缺陷材料中的激光超声问题。     

BGO ultra-long SAW convolver

The BGO ultra-long,SAW convolver designed by us is reported.inthis paper.Its interaction time is longer than 53μ_s being the longest one havingbeen reported in literature up to now.It is also possible to design one longerthan 60μ_s.     

Quantitative Determination of Escherichia Coli in Water Sources in the Environment Using a Surface Acoustic Wave Impedance System Modified with a Syringe Filter

A novel surface acoustic wave (SAW) sensor was developed in the study to measure the density of Escherichia coli in water sources in the environment. With a modified syringe filter sealed by a Teflon cover, the sensor system ensured that the CO₂ gas produced by bacteria flowed upward and accumulated at the headspace of the syringe filter. The measurements were obtained by immersing a pair of electrodes into a sealed syringe filter which contained a culture solution containing lauryl sulfate trytose (LST). The changes in frequency of the two electrodes were caused by generation of small CO₂ bubbles on the surface of the electrodes, which were connected in series to a SAW resonator. The signals obtained by the system were 10 times greater than those obtained by conventional SAW systems. The calibration curve of detection time versus density of E. coli showed a linear relationship with a correlation coefficient (R ² ) of 0.9434 over the range of 10² to 10⁷ cells/mL. Further integration of this sensing system with a suitable automated sampling device will enable this device to be used on-site for analysis and field studies.     

Surface vibrational modes in disk-shaped resonators

The natural frequencies and distributions of displacement components for the surface vibrational modes in thin isotropic elastic disks are calculated. In particular, the research is focused on even solutions for low-lying resonant vibrations with large angular wave numbers. Several families of modes are found which are interpreted as modified surface modes of an infinitely long cylinder and Lamb modes of a plate. The results of calculation are compared with the results of the experimental measurements of vibrational modes generated by means of resonant excitation in duraluminum disk with radius of ≈90 mm and thickness of 16 mm in the frequency range of 130–200 kHz. An excellent agreement between the calculated and measured frequencies is found. Measurements of the structure of the resonant peaks show splitting of some modes. About a half of the measured modes has splitting Δ_fsplit/_fmode$\mathrm{\Delta }{f}_{\mathrm{split}}/f_{\mathrm{mode}}$ at the level of the order of 10⁻⁵. The Q-factors of all modes measured in vacuum lie in the interval (2…3) × 10⁵. This value is typical for duraluminum mechanical resonators in the ultrasonic frequency range.     

2D bitmapping approach for identification and quantitation of common base flavor adulterants using surface acoustic wave arrays and artificial neural network data analysis

Arrays of polymer-coated surface acoustic wave microsensors are used in conjunction with a variety of signal-processing algorithms known as artificial neural networks (ANN). This format of data analysis has the capability to characterize complex mixtures of volatile and semi-volatile organic compounds commonly found in base flavors. The approach described, which minimizes the number of training sets while retaining the robustness of an ANN, utilizes a 2D bitmap matrix. The matrix is obtained by converting the time domain kinetics of sensor response into a bitmap. The high data throughput of this approach enables quantitation on the order of ppm of common base flavor adulterants.     

AlGaN/GaN heterostructure-based surface acoustic wave-structures for chemical sensors

We present a new approach in forming of interdigital surface acoustic wave-structures on AlGaN/GaN heterostructure to be applied in chemical sensors technology. This approach uses a selective self-aligned SF₆ plasma treatment of the AlGaN/GaN barrier layer to modify 2DEG density and surface field distribution in the range of interdigital transducers (IDTs) thus enabling SAW excitation. Secondary ion mass spectroscopy was applied to explain the modification of 2DEG density in the plasma treated AlGaN/GaN heterostructure. The initial results in the process technology and characterization are presented.     

Bulk and surface acoustic wave phenomena in crystals: Observation and interpretation

Crystal acoustics is a field that has engaged the attention of theoreticians and experimentalists alike for decades and more. Many striking effects have been revealed, and elegant analytical techniques applied to their interpretation. This article is oriented towards the experimental aspects of the field and the interpretation of the phenomena that have been observed. Particular attention is given to reviewing the techniques that have probed the intricacy of acoustic wave propagation in crystals, including phonon imaging, laser- and capillary-fracture-generated ultrasound, transmission acoustic microscopy and surface Brillouin scattering, and a selection of results obtained with these techniques is presented. Some of these studies pertain to bulk waves and others to surface acoustic waves. The interpretation of far-field observations is carried out within the ray approximation, and elastodynamic Green’s functions are invoked in the interpretation of near-field results. Extensive use is made of the acoustic-slowness and wave surfaces, in particular features such as acoustic axes, with their attendant polarization singularities, and folds in the wave surface.     

Cavities generated by self-organised monolayers as sensitive coatings for surface acoustic wave resonators

Silanisation of quartz substrate surfaces with a mixture of two chlorosilanes, namely trimethylchlorosilane and 7-octenyldimethylchlorosilane, leads to sensitive coatings for volatile organic compounds (VOC) on surface acoustic wave (SAW) devices. In this way we created monolayers of molecular cavities engulfing the analytes according to host–guest chemistry directly on the device surfaces, and also confirmed the occurrence of such cavities by molecular modelling. We monitored the binding process of the silanes by using Fourier transform infrared (FTIR) spectrometry and atomic force microscopy (AFM). In order to increase the stiffness of the cavities, we crosslinked the terminal double bonds of the long spacers by heating the surface in the presence of a radical initiator. Compared to SAW delay lines silanised with trimethylchlorosilane, devices modified with the binary silane mixture lead to substantially higher frequency shifts when exposed to solvent vapour streams. Nearly instantaneous responses can be observed, which e.g. allows xylene detection down to a few ppm. Interaction of o-xylene with a silanised quartz surface Dedicated to Prof. Adolf Neckel on the occasion of his 80th birthday.