小型高灵敏度气介超声换能器的工艺控制

一、前言 以空气为辐射媒质的气介式超声换能器,以往大都采用圆管式、夹心式、弯曲式等几种形式。其中弯曲式换能器由于具有较低的辐射阻抗,容易向气体中辐射超声波,因而常被优先考虑使用。在弯曲式换能器中,由于结构方式及支撑条件的不同,灵敏度的差异相差甚大。结构简单,制作方便的换能器,一般灵敏度不高,而高灵敏度的换能器,则结构工艺、支撑条件不易控制及制作。本文叙述用于超声控制器的一种小型气介换能器,在使用频率为40千赫左右时,其灵敏度比其它形式的换能器都高,而结构合理、工艺简单。适当控制工艺条件,换能器一致性较好。 二、…     

气介式功率超声复合换能器的声辐射特性研究

本文对气介式功率超声复合换能器的辐射声场进行了理论计算并与实验结果进行了对比。该复合换能器由夹心式纵向振动半波长换能器及弯曲振动的薄圆盘组成。从理论上推出了弯曲振动辐射圆盘在不同边界条件下的辐射声场分布及其共振频率方程。理论分析结果表明,固定边界弯曲振动圆盘辐射声场的指向性最佳,并且指向性的理论计算结果与实验结果符合很好。     

测量超声换能器的简易消声室

一、引言 近十多年国内外气介超声检测技术发展迅速,如超声物位计、声开关、声报警装置等。因此,气介换能器的研究日益趋于重要。研究气介超声换能器需要消声室,以便用来测量在10～200千赫频率范围内各种超声换能器的灵敏度、频率响应特性和指向性。为此,我们建了一个简易消声室。 消声室建在一个原有房间内,其内部尺寸为3.8×2.8×2.8立方米,如图(一)所示。消声室外壳除地面外,其余表面均用2.5毫米厚的钢板拼焊而成,板面积重量约20公斤/米2,地面铺5厘米厚的疏孔聚氨基甲酸脂泡沫塑料,其容重约 25公斤/米2。其余五个表面(天花及壁面)均社有…     

功率超声换能器电声效率及辐射声功率的测量

在高频电功率计方法的基础上,本文提出了一种能够直接测量大功率压电超声换能器在实用状态下的辐射超声功率以及电声效率的新方法。与传统的高频电功率计法相比,本方法避免了介电以及机械损耗功率的测试,简化了测试步骤。     

弯曲振动气介式超声换能器的振动特性及辐射声场研究

本文对弯曲振动气介式超声换能器进行了研究，推出了夹心式换能器与弯曲圆板二者复合振子的机电等效电路及其总体频率方程，得出了其远场声压分布及指向性的解析表达式，并数值计算了换能器近场三维声压分布。     

两种超声清洗槽中的声场研究

本文对两种超声清洗槽中声场的均匀程度、超声频谱及换能器辐射阻抗进行了研究。一种是由夹心式换能器纵向振动通过清洗槽底向槽中辐射产生的声场,另一种是由夹心式换能器激发矩形薄板产生弯曲振动通过槽底向槽中辐射的声场。     

Ⅱ型大功率超声换能器的研制

本文研究了一种能在液体中辐射大功率的π型超声换能器。理论及实验表明,它频带较宽、功率容量大、辐射声场均匀,是超声应用中具有很大应用前景的辐射声源。     

一种超声手术刀推挽激励换能器的研究

设计了一种超声手术刀用的新型推挽激励换能器。它是在夹心式单晶堆压电超声换能器的经典构造基础上,把原先激励一组压电陶瓷晶片堆的方式,改为同时施加反相激励的前后两组晶堆。利用有限元方法,对该推挽激励换能器进行模态分析和频率响应分析。在相同大小的电压激励下,相对单晶堆换能器,推挽激励换能器可以获得更高的工作带宽和机电耦合系数,提高了换能器的电声转换效率。按照仿真结果加工推挽激励换能器,实现良好的动力学和电学特性,满足设计要求。     

超声换能器位置对碘化钾溶液碘释放影响的研究

本文用碘化钾溶液作为样品对双超声在同向,正交,相向辐射时溶液中碘释放进行了初步研究。结果表明;双频超声辐射效果比单频辐射好,同向超声辐射要比正交,相向效果好,它显示出声化学产额与换能器的位置有关,并对此现象予以分析解释。     

圆台型自聚焦超声压电换能器研究

对圆台型自聚焦超声压电换能器辐射声场分布进行了数值计算,分析了圆台换能器几何参数小端半径b、大端半径a以及高度h对轴向声场以及焦平面声场分布的影响。结果表明:圆台型自聚焦超声换能器轴向声场为振荡分布,声强平均值较高,存在一组最佳参数对应于最佳的聚焦效果,而径向声场分布比较均匀,焦平面有效半径小,受参数影响较小。     

The Research of Anti-Wear Properties of Organomolybdenum Compounds in the Engine Oils

A four-ball tester was used to evaluate the anti-wear performance of three kinds of organomolybdemun compounds in the engine oils, i. e., molybdenum dialkyldithiophosphate (MoDDP), molybdenum dialkyldithiocarbamate ( MoDTC), and sulphur and phosphorus freeorganomolybdeum (Molybdate). The results indicate that a low concentration of MoDDP doesn' t improve the anti-wear properties of the commercial engine oils, but a high concentration of MoDDP can obviously improve the anti-wear properties and the load-carrying capacity of the engine oils. MoDTC doesn' t improve the antiwear properties of the engine oils, but worsens the anti-wear properties of the oils. Signifi can timprove ment of frictional and wear characteristics is obtained with Molybdate added in the commercial engine oils and the formulated oils.     

Certification Becomes Important for the I Quality; and Safety Supervision of the Chinese Liquor Sector

The end of 2007, over 200 unit products of more than 80 Chinese firms have passed the quality grade certification for liquor products. These products involve distilled spirits, beer, wine, yellow wine, fruit syrup wine and others, and cover over 80% of the national top-branded liquor products.……     

Deposition and Coating Properties on CVD Tungsten

Surface characterization and microstructure studies are performed on chemical vapor deposited (CVD) tungsten coating. There is about 2 μm thickness diffusion layer of tungsten in the molybdenum substrate. The thermal shock test shows tungsten coating has good adhesion with molybdenum substrate, but the elements of oxygen and carbon in the tungsten coating have the bad affection to the adhesion. The result of high-temperature diffusion experiment is the diffusion rate from molybdenum substrate to tungsten coating is faster.     

Analysis of marine hydrobiont lipid extracts as possible cryoprotective agents

We studied a combined effect of the cryoprotectants both of lipid and carbohydrate origin at the presence of DMSO or without it on cell viability and the RNA synthesis in the embryonic mollusc and echinoderm cell cultures obtained at different developmental stages. Cryoprotective properties of exogenous lipids correlated with their thermotropic behavior. Lipid extracts from marine hydrobiontes, which thermal transitions are characterized by relatively small part of calorimetric thermogram area lying at temperatures above 0 °C (6–18%), were found to possess a considerable cryoprotective activity. The results are discussed in relation to the prediction of the cryoprotective activity of lipid extracts for marine animal cells. In addition, it was found that marine invertebrate cells can be cryopreserved without DMSO at the presence of trehalose and lipid extracts of some marine hydrobiontes.     

Low-Temperature Properties of Silver

Pure silver is used extensively in the preparation of high-temperature superconductor wires, tapes, films, and other configurations in which the silver not only shields the superconducting material from the surrounding materials, but also provides a degree of flexibility and strain relief, as well as stabilization and low-resistance electrical contact. Silver is relatively expensive, but at this stage of superconductor development, its unique combination of properties seems to offer the only reasonable means of achieving usable lengths of conductor. In this role, the low-temperature physical (electrical, thermal, magnetic, optical) and mechanical properties of the silver all become important. Here we present a collection of properties data extracted from the cryogenic literature and, to the extent possible, selected for reliability.     

Early ironwork in Biscay: Survey,excavation, experimentation and materials characterization. An integral study of the mountainside ironworks (ferrerías de monte or “haizeolak”)

ABSTRACT

The production of iron in Biscay (Basque Country, Spain) has been a hallmark of this territory of the North of the Iberian Peninsula throughout its history. The Archaeology team of the Basque Country Mining Museum has spent 13 years, so far, studying the origins of this activity through the evidences left at the old pre-hydraulic iron production workshops known as mountainside ironworks (ferrerías de monte) or haizeolak. It has catalogued 170 archaeometallurgical sites of this type in Biscay, and the archeological excavation of some of them has led to the knowledge of the different stages of the production process that took place in these workshops. The team has also experimentally reproduced the work carried out in a mountainside ironworks from the High Middle Ages, and it has currently started the characterization process of this type of activity through the study of the collected materials.     

Mechanism Study on the Wear of CrAlTiN Coated High-Speed Steel Twist Drills Under Dry Cutting Conditions

As demands about environment protection are growing up, dry cutting technology is getting more and more concerns from all over the world. Main works performed here are study on dry cutting performances and wear mechanisms of M2high-speed steel (HSS) twist drills with CrAlTiN multicomponent coatings, which was deposited using magnetron sputter ion plating system, in drilling 45 and 30CrMnSiA steel, and their comparisons to those in drilling the same steel but using monolayer CrN and commercial TiN coated drills. Drilling performances of drills are evaluated mainly through the measurements of width on outer corner flank land and the cutting forces. Results show that performances of CrAlTiN coated drills are better than those of monolayer CrN and TiN coated drills. In drilling 45 and 30CrMnSiA steel, the average tool life of the CrAlTiN coated drills are 17.2 and 11.8 times higher than those of the uncoated drills. Observing wear of the drill with scanning electronic microscope, results show that there is no crack or spallation of the CrAlTiN coatings in wear zones. Main mechanism of the wear here is adhesion.     

Study on Bond Ability of Arc-Spraying Coatings with Different Surface Pretreatment on Cast-Iron

Arc spraying coatings are widely used in various applications, but uncommon in cast iron substrate. Different surface pretreatment technology is tested on substrates of gray cast iron. Surface roughness and residual stress were measured by TR200 and X-ray diffraction analyzer. Influence of different surface pretreatment methods ( dry blasting and fusebond) on roughness and residual stress was analyzed. The arc-sprayed coatings of wire 3Cr13 (φ2mm) on gray cast iron substrate is studied. The microstructure and interface of bonding layer were observed by SEM. The bond strength was taken by tensile test. Results show that bond strength with grit blasting is higher than fuse-bond; it is feasible to make wire 3Cr13 coating with arc spraying on cast iron substrate roughened by grit blasting.     

Structural Characteristics of TiO2 Ceramic Coating by Micro-Plasma Oxidation

TiO2 ceramic coatings with thickness of 20 μm were formed on the surface of pure titanium by micro-plasma oxidation. Their micro-structures were investigated by by using X-ray diffraction and their surface images were detected by using scan electronic microscope. There were three kinds of TiO2 coatings, pure anatase type TiO2 phase, mixed phases consisted of rutile type TiO2 phase and anatase type TiO2 phase, pure rutile type TiO2 phase. The coating surface with the pure anatase type TiO2 phase is rough, while the coating surface with the pure rutile type TiO2phase is smooth. The upper coating surface with the mixed type TiO2 phases is anatase type TiO2 structure and the subsurface of the TiO2 coating is rutile type TiO2structure.     

Evaluation of fatigue life of steel using steel grain size

The insightful discussion of the relationship between the construction of metallographic and fatigue life and proposition of mathematical relationships describing this relationship was conducted in the paper. This paper presents a method for estimating the fatigue life, based on the construction of the microstructural material taking into account the grain size and the participation of ferrite and pearlite phase.