Sound fields radiated from a linear phased array based on analytical solutions of transient elastic waves

Beam characteristics of a linear phased array transducer are critical to its engineering applications as well as to its design. This paper proposes a method for the theoretical calculation of ultrasound field radiated by a linear phased array coupled to an elastic solid by a longitudinal wave couplant. In this case, the ultrasound field can be determined by superposition of the exact and analytical solutions of transient elastic waves induced by a number of discrete line sources normally acting on an elastic half-space. Based on the theoretical calculation, this work investigated the influences of several important parameters in a linear array transducer, such as wave length, array size, ratio of element width to inter-element spacing, to the ultrasound field characteristics. Interesting phenomena and useful results are obtained, which provide fast and accurate guidance for linear phased array transducer design. It also satisfies diverse and specific demands for actual engineering testing using arrayed transducers.     

空气耦合超声检测复合材料研究综述

复合材料普遍具有高比强度、高比刚度、高模量、耐腐蚀等优异性能,广泛应用于飞机机翼、导弹外壳、航空发动机壳体等部位。制造和服役过程中各类缺陷影响复合材料的力学性能和服役性能,必须采用有效的方法准确检测和评估复合材料中各类缺陷。空气耦合式超声检测具有完全非接触、非侵入、无损伤和无需耦合剂的特点,能够很好地运用于复合材料的在线和在位检测。该文就近年来空气耦合超声检测技术的研究现状进行了系统综述,简明扼要地分析和介绍了当前空气耦合超声检测的研究热点及进展,重点介绍了1-3型压电复合材料换能器、信号处理技术、相控聚焦式空气耦合超声检测、超声在复合材料的传播特性及其与缺陷交互作用的研究现状,探讨了空气耦合超声无损检测技术与仪器的发展方向,总结了目前空气耦合超声检测的研究热点问题,最后展望了空气耦合超声检测的发展趋势和应用前景。     

Large scale sonochemical processing: aspiration and actuality

It has been recognised for many years that power ultrasound has great potential in a wide variety of processes in the chemical and allied industries. Some of these processes have been known for many years and continue to flourish as major commercial applications, e.g. plastic welding and cleaning. Others, like ultrasonic drilling, while showing great potential have not been widely exploited to date. The potential for the industrial use of power ultrasound is enormous, and yet industry seems somewhat reluctant to adopt it. In this article the existing uses of power ultrasound in processing are reviewed and the potentials are explored.     

多卜勒计程仪

本文简要回顾多卜勒计程仪的发展和用途，分析了多卜勒计仪为导航设备的优点，工作原理，主要性能及组成部件，最后介绍了多卜勒计程仪在我国的设计情况。     

Direct optical sensors: principles and selected applications

In the field of bio and chemosensors a large number of detection principles has been published within the last decade. These detection principles are based either on the observation of fluorescence-labelled systems or on direct optical detection in the heterogeneous phase. Direct optical detection can be measured by remission (absorption of reflected radiation, opt(r)odes), by measuring micro-refractivity, or measuring interference. In the last case either Mach–Zehnder interferometers or measurement of changes in the physical thickness of the layer (measuring micro-reflectivity) caused, e.g., by swelling effects in polymers (due to interaction with analytes) or in bioassays (due to affinity reactions) also play an important role. Here, an overview of methods of microrefractometric and microreflectometric principles is given and benefits and drawbacks of the various approaches are demonstrated using samples from the chemo and biosensor field. The quality of sensors does not just depend on transduction principles but on the total sensor system defined by this transduction, the sensitive layer, data acquisition electronics, and evaluation software. The intention of this article is, therefore, to demonstrate the essentials of the interaction of these parts within the system, and the focus is on optical sensing using planar transducers, because fibre optical sensors have been reviewed in this journal only recently. Lack of selectivity of chemosensors can be compensated either by the use of sensor arrays or by evaluating time-resolved measurements of analyte/sensitive layer interaction. In both cases chemometrics enables the quantification of analyte mixtures. These data-processing methods have also been successfully applied to antibody/antigen interactions even using cross-reactive antibodies. Because miniaturisation and parallelisation are essential approaches in recent years, some aspects and current trends, especially for bio-applications, will be discussed. Miniaturisation is especially well covered in the literature.     

Reusable conductimetric array of interdigitated microelectrodes for the readout of low-density microarrays

Low-density protein microarrays are emerging tools in diagnostics whose deployment could be primarily limited by the cost of fluorescence detection schemes. This paper describes an electrical readout system of microarrays comprising an array of gold interdigitated microelectrodes and an array of polydimethylsiloxane microwells, which enabled multiplexed detection of up to thirty six biological events on the same substrate. Similarly to fluorescent readout counterparts, the microarray can be developed on disposable glass slide substrates. However, unlike them, the presented approach is compact and requires a simple and inexpensive instrumentation. The system makes use of urease labeled affinity reagents for developing the microarrays and is based on detection of conductivity changes taking place when ionic species are generated in solution due to the catalytic hydrolysis of urea. The use of a polydimethylsiloxane microwell array facilitates the positioning of the measurement solution on every spot of the microarray. Also, it ensures the liquid tightness and isolation from the surrounding ones during the microarray readout process, thereby avoiding evaporation and chemical cross-talk effects that were shown to affect the sensitivity and reliability of the system. The performance of the system is demonstrated by carrying out the readout of a microarray for boldenone anabolic androgenic steroid hormone. Analytical results are comparable to those obtained by fluorescent scanner detection approaches. The estimated detection limit is 4.0 ng mL⁻¹, this being below the threshold value set by the World Anti-Doping Agency and the European Community.     

Reflector-based phase calibration of ultrasound transducers

Recently, the measurement of phase transfer functions (PTFs) of piezoelectric transducers has received more attention. These PTFs are useful for e.g. coding and interference based imaging methods, and ultrasound contrast microbubble research. Several optical and acoustic methods to measure a transducer’s PTF have been reported in literature. The optical methods require a setup to which not all ultrasound laboratories have access to. The acoustic methods require accurate distance and acoustic wave speed measurements. A small error in these leads to a large error in phase, e.g. an accuracy of 0.1% on an axial distance of 10 cm leads to an uncertainty in the PTF measurement of ±97° at 4 MHz. In this paper we present an acoustic pulse-echo method to measure the PTF of a transducer, which is based on linear wave propagation and only requires an estimate of the wave travel distance and the acoustic wave speed. In our method the transducer is excited by a monofrequency sine burst with a rectangular envelope. The transducer initially vibrates at resonance (transient regime) prior to the forcing frequency response (steady state regime). The PTF value of the system is the difference between the phases deduced from the transient and the steady state regimes. Good agreement, to within 7°, was obtained between KLM simulations and measurements on two transducers in a 1-8 MHz frequency range. The reproducibility of the method was ±10°, with a systematic error of 2° at 1 MHz increasing to 16° at 8 MHz. This work demonstrates that the PTF of a transducer can be measured in a simple laboratory setting.     

Estimation of the sound pressure field of a baffled uniform elliptically shaped transducer

In this paper an alternative approach to estimate the sound field of an elliptically shaped transducer in an infinite baffle is described. The method is based on a singular value decomposition of a propagating matrix which is computed through a division of the vibrating surface into a finite number of small circular piston sources flush-mounted on the elliptical surface. This decomposition is combined with the volume velocity vector on the discretized surface to obtain the sound pressure field. Numerical examples for both on-axis sound pressure and directivity are presented for the uniform elliptical piston transducer and they are in good agreement with the results given by other methods.     

Ordering sequences by permutation transducers

To extend a natural concept of equivalence of sequences to two-sided infinite sequences, the notion of permutation transducer is introduced. Requiring the underlying automaton to be deterministic in two directions, it provides the means to rewrite bi-infinite sequences. The first steps in studying the ensuing hierarchy of equivalence classes of bi-infinite sequences are taken, by describing the classes of ultimately periodic two-sided infinite sequences. It is important to make a distinction between unpointed and pointed sequences, that is, whether or not sequences are considered equivalent up to shifts. While one-sided ultimately periodic sequences form a single equivalence class under ordinary transductions, which is shown to split into two under permutation transductions, in the two-sided case there are three unpointed and seven pointed equivalence classes under permutation transduction.     

激光荧光肺癌诊断图象处理系统滤光片的研制

本文论述用于激光荧光肺癌诊断图象处理系统滤光片的膜系设计,制备这套滤光片所采取的工艺措施,最后给出研制的结果。