中美科学家联合设计出声场旋转器

留声机的原理介绍留声机（Phonograph）是一种早期的录音和播放音乐的机械装置。

它由美国发明家托马斯·爱迪生于1877年发明并获得了专利。

留声机使用了一种机械的方式来记录和播放声音，它是现代唱片机和录音机的前身。

以下将详细介绍留声机的原理。

留声机的核心原理是通过槽状的唱片将声音信息记录下来，并通过针尖读取唱片上的凹凸纹路完成音乐的播放。

首先，留声机工作的第一步是将声音转化为机械能。

这通过一个装置来实现，该装置由话筒（Microphone）和麦克风等组成。

当声音进入话筒时，话筒内的膜会随声音的振动而产生振动。

这个振动会转换为机械能，并被传递到一个称为振荡器的装置上。

接下来，振荡器会将机械能转换为电能。

当振荡器受到声音的振动时，它会产生变化的电流。

这个变化的电流会通过导线传送到机器的另一部分，即涡流法尧夫克环（Induction Coil），涡流法尧夫克环的作用是放大电流。

然后，涡流法尧夫克环会产生一种被称为震荡电流的特殊类型的变化电流。

接下来，这个震荡电流会通过连接到涡流法尧夫克环的导线传输到一个被称为焦层灯泡的光源上。

焦层灯泡上有一个碳化纸条，当电流通过时纸条会发光。

接下来是留声机最关键的部分：将声音记录在唱片上。

留声机的唱片是由一个特殊的材料制成，石墨或者类似材料。

这种材料比较硬，足以承受读取针下的压力，同时也允许机械振动传播到唱片上。

当电流通过焦层灯泡和导线进入唱片机的唱片时，机械部位中的细长针尖会跟随导线的震动而上下摆动。

针尖的下端与唱片接触，通过刻痕和凹凸纹路的方式将机械能转化为唱片上的凹凸形状。

接下来是播放的过程。

留声机上有一个转盘，唱片放在转盘上。

当开始旋转转盘时，针尖会沿着唱片的纹理移动，读取唱片上的凹凸形状。

针尖的振动通过声音盒传达到扬声器，扬声器会将机械能转化为声能，将声音放大并播放出来。

由于唱片上的凹凸纹路是由声音转化而成的，所以留声机可以将声音准确地还原出来。

音频混音中的旋转操作和声像定位随着科技的不断进步，音频混音技术也在不断发展。

其中，旋转操作和声像定位作为音频混音中的重要技术在音乐制作、电影制作以及场景再现等领域中扮演了重要角色。

本文将探讨音频混音中的旋转操作和声像定位的原理、应用和可能的发展方向。

一、旋转操作旋转操作是指通过调整声音的定位角度，使其在立体声或环绕声系统中更加立体且具有层次感。

通过旋转操作，音频制作人可以在空间中创造出各种立体声效果，以丰富听众的听觉体验。

1. 原理旋转操作的原理基于声音在空间中的传播速度和入耳时间差。

在立体声系统中，左右两个声道通过不同的声像定位将声音发送到听众的左右耳朵，以营造出真实、立体的听觉效果。

通过调整声音的定位角度，可以改变声音到达耳朵的时间差，从而使听众感受到声音的旋转和移动。

2. 应用旋转操作在音乐制作和电影制作中有着广泛的应用。

在音乐制作中，通过旋转操作可以制造出立体的合唱效果，增加音乐的层次感和韵律感。

在电影制作中，旋转操作可以使观众更好地感受到环境音效和人声的方向和移动，增强观影体验。

3. 发展方向随着虚拟现实（VR）和增强现实（AR）技术的兴起，旋转操作在这些领域中也有着广阔的应用前景。

通过结合VR和AR技术，可以实现更加立体和沉浸式的听觉体验，将听众完全融入音频环境中。

二、声像定位声像定位是指通过调整声音在空间中的位置和方向，使听众能够准确地感知声音的来源和位置。

声像定位在音频混音中扮演着重要的角色，通过合理的声像定位可以创造出丰富的听觉效果。

1. 原理声像定位的原理主要基于声音的水平和垂直立体声成像技术。

通过调整声音的音量平衡、延迟时间和频率响应等参数，可以实现声音在空间中的准确定位和方向感。

在声像定位中，声音的频率响应被广泛运用，低频声音较难感知来源，而高频声音则更容易指示声音的来源。

2. 应用声像定位在音频制作和电影制作中具有广泛的应用。

通过合理的声像定位，音频制作人可以使听众感受到演唱者或乐器的位置，营造出逼真的演唱或演奏效果。

自由能源装置实践手册作者：帕特里克·凯利译者：能量海序言先提供一点背景资料，以有助于您了解本书的性质。

我是个普通人，1980年，看了英国4频道电视台播放的《用水开车》节目后，开始对“自由能源”产生兴趣。

依我看，这部片子并不尽如人意。

它报道了许多非常令人关注的事例，但不够具体详细，让观众能对这一主题做进一步的探究。

尽管如此，我还是受益非浅，至少了解到这个世界上还有“自由能源”这回事。

这方面资料匮乏。

1986年，我在专利局购买了一些斯坦·梅耶的氢氧发生器专利的副本。

有点意思，但还是没有更多的补充。

网上查找，也没有实用一点的信息。

后来情况有了戏剧性改观，信息量是大大增加了。

但即使今天，要找到直接的、有用的和可实践的自由能源系统与技术，依然相当费劲。

大量信息都是些对人、事和发明描述模糊、概略的访谈以及无足轻重的文章，根本缺乏细节。

这些文章都是这样一种腔调：“有一种称之为‘公共汽车’的新发明，可以搭载乘客从某处到某处。

某日就有一辆这种‘新发明’出现在街上，涂成绿色和蓝色，颇为夺人眼球的。

司机是乔·布洛格。

他穿着一件手织毛衣，笑容可掬。

乔说，即便他的孩子也可以象他一样轻松驾驶一辆公共汽车。

乔希望最多再干六个月就退休，因为他准备去勘探金矿。

”尽管这类文章也挺不错，但我想要的还是诸如“有一种称作‘公共汽车’的新发明可用于搭载乘客，某日我们见到一辆，留下深刻印象。

它有45个乘客座位，车身由铝合金压制而成，车箱尺寸12×3米，四角各有一轮，一台约克镇博斯沃思引擎公司制造的5升柴油机，有助力转向系统、液压制动器和……”在许多的文章、科学著作和书籍里，作者用数字和方程式进行表述时，通常不对术语进行定义，使内容晦涩难懂，老实说，我无法理解。

我可不愿扎进数学方程式里，因而无法分享他们那些高层次的思维和分析。

尽管如此，我还是把这类文章挂在我的网站上，让那些具备这样的能力、可以很容易就理解它们的来访者使用。

金唇窃听物理原理
金唇窃听物理原理：谐振腔，电容耦合。

谐振腔：是指使高频电磁场在其内部持续振荡的金属空腔。

由于电磁场几乎全部集中于腔体内，没有辐射损耗，故电磁能量损失极小。

圆柱形谐振腔是常见的谐振腔样式。

在谐振腔内，电磁场可以在一系列频率下进行振荡，其频率大小与谐振腔的形状、几何尺寸及谐振的波型等因素相关。

电容耦合：又称电场耦合，是由于分布电容的存在而产生的一种信号由第一级向第二级传递的过程。

金唇窃听器的学术名称为谐振腔式麦克风，由谐振腔和电容式麦克风两部分组成。

金唇窃听器的外观类似一只蝌蚪，蝌蚪的头部既是一个谐振腔，又是电容式麦克风，腔体铜制镀银，腔体中心是一个可调节的蘑菇形圆盘平面，它与一层仅6.35微米厚的薄膜组合成一个电容器，薄膜能够接收声波的振动；蝌蚪的尾巴是一根天线，天线通过圆柱腔体侧面的绝缘孔进入腔体，与谐振腔电容耦合。

老式留声机的原理
首先，唱片盘位于留声机的顶部。

唱片是一个圆形平面，通常由乙烯
基或壳碟制成。

它的外缘有许多小坑，放置着音乐的信息。

唱片盘在留声
机上被固定住，通过电机驱动旋转。

接下来，为了使唱片能够旋转，留声机中有一个被称为转盘的组件。

它连接到电机，并通过马达的运转使得唱片旋转。

机械手臂是连接音头和转盘的部分。

机械手臂由可动和不可动部分组成。

可动部分连接到音头，而不可动部分连接到转盘。

机械手臂被设计成
S形状，以确保针能够准确地放置在唱片上。

音头是通过机械手臂将音乐信号转化为声音的关键组件。

音头的主要
部分是一个非常细小的针，也被称为音头针。

当唱片旋转时，针被放置于
唱片上的纹路中，针的振动会导致音槽内的信号被捕捉到。

当信号被捕获时，它将被传输到留声机的声音放大器中。

声音放大器
使用电子电路将音乐信号放大，并通过扬声器将它们转化为可以听到的声音。

留声机的声音放大器和扬声器的设计取决于制造商和型号，它们至关
重要地决定了音质的质量和清晰度。

总的来说，老式留声机的原理是通过电动马达的旋转让唱片旋转，机
械手臂将音头针放置在唱片上，音头针通过探测唱片上的纹路将音乐信号
转化为声音，声音放大器将信号放大，扬声器将其转化为可以听到的声音。

这种机械手动的播放方式质朴而独特，让人们可以享受到当时的音乐。

从美国微软世界上最安静的房间、德国的高铁声屏障、瑞士发明的手碟鼓、推演中国世界上创新的声学科技摘要：不论声音dB多少，低于20Hz人就听不见。

声屏障变形如漂浮的旗帜时，为NVH流体与固体耦合的自激振动。

识器才能知音，harshness在于心性与物性的交织。

亥姆霍兹衍射吸声体与共振吸声体无缝连接机理为二胡弦振动通过琴码及阻尼泛音触动膜振动、获共鸣腔。

非线性声学设施创新在于将一个乐队的音效用一个装置表现出来进行共振耗能。

关键词：非线性系统的“软” 心性与物性的交织共鸣腔为“魂” 交换共振理念1.微软世界上最安静的消音室、欧洲的高铁声屏障技术过时1.1微软消音室的吉尼斯世界纪录存疑微软的消音室，被吉尼斯世界纪录认可的世界上最安静的房间。

据其首席设计师Hundraj Gopal介绍，其内部均使用“吸音尖劈”，避免回声，使该消音室的音量达到了-20.3dB。

声音有多“高”指声波的“振幅”有多大，能使这个声音有多“响”。

人能听到的声音频率范围为20Hz～20000Hz。

吉尼斯验证的-20.3dB没有表示是声学技术数据还是仪表数字？来自哪个频率？就像新生儿要有父母的基本信息一样。

而且频段低于20Hz的次声波，不论dB多少，人都听不见，该世界之最没有危害环境与健康的次声波治理信息。

欧洲声学专家Philip Newell在《Recording Studio Design》（消音室设计手册）中指出：如今的消音技术即便吸收99.9%的能量，仅留下0.1%，仍然能够有一个30dB的衰减……；导致欧洲多家银行报道称有超过2万个项目贷款成为坏账。

1.2欧洲的高铁声屏障图1.1-1为德国K-F（科隆至法兰克福）线城际铁路声屏障全线拆除前的受力录像截图。

图1.1-2为我国公开发表的京津城际客运专线对声屏障上部长2m、厚20mm透明板、当列车车头和车尾经过时的分析。

图1.1-3为德国现役声屏障。

从NVH技术的角度分析，将德国K-F声屏障图1.1-1，以及京津城际客运专线声屏障图1.1-2顺时针旋转90°，如同无骨架随波逐流漂浮的一面旗帜。

桑斯坦的回音室效应桑斯坦的回音室效应是一种被广泛应用于音乐演奏、声学表演方面的现象，它指的是当声音在室内反射，形成“不断延伸的回声波”。

它最初出现在1859年由马丁·桑斯坦（Martin Sauers）第一次发现说，他还是一个年轻的美国医学生，他第一次发现这种独特的声音回声效应，从而发现和发展了左右声道的声音投影技术--双通道声音投影（Stereo Sound Projection）技术，也为日后的音频技术发展提供了基础。

这种回音室效应是由声音束（sound beam）反射，在反射过程中产生叠加效应，形成多次延伸的回声。

桑斯坦发现可以利用这种卷积（Convolution）叠加效应，使原声的独特性恢复到存在的状态，而不会衰减声音的品质。

他还继续发现，如果能够把这种叠加效应用到两个不同的音频信号上，那么会产生丰富的立体声效果，也就是双通道声音投影（Stereo Sound Projection）技术。

日后，由于技术的发展，左右声道的双通道声音投影（Stereo Sound Projection）技术成功应用在磁带录制和多音乐演奏中，也使音乐演出发生很大变化，能够营造出更加完美的远距离演出场景。

因此，桑斯坦的回声波叠加技术也受到了广泛的应用，被以下类似的技术所延伸：声影技术（Sound Cinematography），这是一种由一个音箱和一根线，可以生成3D环绕式的音效，来实现真实的3D环绕音效；同样地，桑斯坦的回声叠加技术也可用于房间内部比较狭窄的声乐演出场景，可以利用回音室效应帮助增强演出效果，如果使用空间控制（Spatial Control）技术，可以用它来控制声音的延迟和反射，以实现最佳的回声效果。

此外，桑斯坦的回音室效应最近也被广泛应用到有关声学的实验中，把它应用于声学表演（Acoustic Performance），这可以帮助人们更好地了解声音在室内空间中的传播，也可以研究声学知识。

用途：
古希腊的学者阿基米德曾豪情万丈地宣称：给我一个支点，我能撬动地球。

而现代的美国发明家特士拉更是“牛气”，他说：用一件共振器，我就能把地球一裂为二！可见共振作用有多大，当你敲击两面鼓中的其中一面时,另一面鼓上的小球也会不可思议地跳动起来，这种现象叫声音共振或共鸣。

构造：
共振鼓由支架、鼓、敲击鼓锤、共振小球等组成，如图。

原理：
对声音的共振共鸣现象,我国古代科学家沈括很早就进行了研究,并以一把古琴的若干根弦,调出相同的音调,使之出现明显的共振，这是世界上最早对共振现象作出的试验。

共振鼓产品用于演示声波传递并产生共振的原理。

当敲击两面鼓中的任一鼓面时，另一面鼓中心悬挂的小球就会跟着敲鼓的节奏跳起来，即物体振动发音时，会引起其它相邻近的同性物体共同振动。

如果两个物体的固有频率是成整数比，就会发生共振的现象。

震荡的强度是振幅的平方。

共振是指一个物理系统在其自然的振动频率（所谓的共振频率）下趋于从周围环境吸收更多能量的趋势。

18世纪中叶法国昂热市一座102米长的大桥上有一队士兵经过。

当他们在指挥官的口令下迈着整齐的步伐过桥时，桥梁突然断裂，造成226名官兵和行人丧生。

究其原因是共振造成的。

因为大队士兵迈正步走的频率正好与大桥的固有频率一致，使桥的振动加强，当它的振幅达到最大以至超过桥梁的抗压力时，桥就断了。

类似的事件还发生在俄国和美国等地。

鉴于成队士兵正步走过桥时容易造成桥的共振，所以后来各国都规定大队人马过桥，要便步通过。

使用方法：
实验时，只要用鼓锤轻轻的敲击一面鼓，另一鼓上的小球也会跟着跳动起来。

ULTRASONIC TESTINGOF STEEL CASTINGSbyJ . D . LavenderResearch Manager. Quality Assurance GroupSteel Castings Research & Trade AssociationSheff ield. EnglandTABLE OF CONTENTSPage Preface (2)Theory of Ultrasonic Flaw Detection (3)Calibration of the Ultrasonic Instrument (7)Calibration and Reference Blocks (7)Longitudinal Wave Probes (7)Transverse Wave Probes (10)Measurement of Steel Thickness (12)Formation of Casting Defects-Ultrasonic andRadiographic Correlation (13)Flaws from Inadequate Feeding. Macro-. Filamentary-.Micro-Shrinkage (13)Flaws from Hindered Contraction. Hot Tears. Cracks (14)Flaws from Gas and Entrapped Air. Airlocks. Gas Holes (19)Ultrasonic Attenuation - Carbon. Low Alloy and Austenitic Steels (22)Influence of Structure on Ultrasonic Attenuation (22)Measurement of Ultrasonic Attenuation (24)Sizing of Flaws and Acceptance Standards (27)Beamspread and Maximum Amplitude Techniques (27)Surface Flaws (30)Beamspread from Transverse Wave Probes (31)Production and Economics of an Ultrasonic Technique (33)References (36)© by Steel Founders' Society of America, 1976CAST METALS FEDERATION BUILDING20611 CENTER RIDGE ROADROCKY RIVER, OHIO 44116Printed in the United States of America1J. D. Lavender was educated at Ecclesfield Grammar School, Nr. Shef- field. He received the Associateship of the Institution of Metallurgistsin 1954 and became a Fellow in 1972. He is a member of the Instituteof Physics and of the British Institute of Nondestructive Testing. He was employed by Brown-Firth Research Laboratories from 1940 to 1946 on radiography of non-f errous and ferrous alloys, X-ray crystallography and metallography of low and high alloy steels.In 1954 he became foundry metallurgist with Firth-Vickers Stainless Steels in Sheffield, and in 1957 moved to the Steel Castings Research and Trade Association (S.C.R.A.T.A.) as a senior investigator of nondestructive testing. He was made section head in 1964 and research manager of quality assurance in 1972. Mr. Lavender has presented the S.C.RA.T.A. Exchange Lecture at the National Technical and Operating Conferenceof the Steel Founders’ Society of America in 1969 and 1975.PREFACEUltrasonic flaw detection is a method of non- destructive testing that is finding increasing ac- ceptance in the United States. This growth inthe application of ultrasonics is intimately tied to the field of fracture mechanics and the scientifi- cally based approaches to designing against fail- ure. Ultrasonic flaw detection, as opposed to the more widely used radiography, permits the in- spector to pinpoint accurately the location of the flaw and to determine its shape and size. These factors play an important role in fracture mechan- ics where the maximum safe stresses can be cal- culated for a given flaw size and location. Con- versely, for a given flaw type, size and operating stress field, the maximum flaw size that can be tolerated safely can be determined. Thus the unique ability of ultrasonic inspection to assess flaw location and flaw geometry is vital to engi- neering approaches of fracture-safe design.Further insight into the growth of nondestruc- tive testing is gained by a historical review of developments. Radiography was developed early and achieved industrial status when a set of radio- graphs called, “Gamma Ray Radiographic Stand- ards for Steam Pressure Service” was issued in 1938 by the Bureau of Engineering, U.S. Navy. Numerous ASTM specifications relative to radio- graphy in steel casting production have been is- sued since then. Ultrasonics, in contrast, received its first major boost towards industrial application for steel castings in Britain when a study on its use and development possibilities was undertaken in 1958. ASTM specification A-609, “Standard Specification for Longitudinal Beam Ultrasonic Inspection of Carbon & Low Alloy Steel Castings”was published in 1970. This specification wasfollowed in 1974 by the ASME Boiler & PressureVessel Code, Section V, T524.2, “Angle BeamExamination of Steel Castings.” Other specifica-tions of international importance are the West-inghouse Specification 600964, “Ultrasonic Testing of Steel Castings,” and the Central ElectricityGenerating Board United Kingdom Standard66011, “Turbine Castings (chromium, molyb-denum, vanadium steel) .”Increased acceptance and utilization of ultra- sonic inspection are to be expected for the future.These trends are apparent from the extensiveactivity going on now in the United States andabroad. Three standards, in addition to ASTMA-609, are currently considered. These are theBritish IS0 Standard-“Draft Proposal for anInternational Standard for the Ultrasonic Inspec-tion of Steel Castings,” the German standard-“Introduction of Ultrasonic Testing and Stand-ards and General Conditions of Delivery for Steel Castings,” and a new proposed ASTM specifica- tion which will be similar to Westinghouse Speci- fication 600964.This booklet is published to present basic in- formation on the nature of ultrasonic inspectionprinciples with specific guidelines on flaw detec-tion in steel castings. This information and thefavorable economic aspects of flaw detection byultrasonic means are presented for technical per- sonnel and managers of casting producers andparticularly the technical staff of casting userswho control the level to which ultrasonic inspec-tion will find acceptance in the future.P ETER F. WIESERResearch DirectorBy direction of theCarbon and Low AlloyTechnical Research CommitteeH. J. S HEPPARD, ChairmanA. G. LINLEY P. J. N EFFF. H. H OHNL. H. L O N G, J RA. J. W HITTLER. A. M ILLER2THEORY OF ULTRASONIC FLAW DETECTIONTHE CHARACTERISTICS OF SOUND WAVESSound is produced when a body vibrates and ispropagated only within a medium. Sound wavesare classified in terms of frequency, which is thenumber of vibrations per second or Hertz; thefrequency scale relating the sonic and ultrasonicranges is shown in Fig. 1.The basic formula, to which reference is madethroughout the whole study of ultrasonic examina-tion, is:The relationship between frequency and wave-length for the transmission of ultrasonic wavesin steel is given in Fig. 2.Sound waves must have a medium in which totravel and the velocities with which they aretransmitted through a particular medium dependson its elastic constants and on its density, as givenby the following formulae:Thin rod velocityLongitudinal wave velocityTransverse wave velocitywherec =wave velocity, mm/sE =Young’s modulus of elasticity, dynes/mm2G= shear modulus of elasticity, dynes/mm2ϕ =density, g/mm3σ=Poisson’s ratioValues of sound velocity, density and acousticimpedance of materials associated with ultrasonicexamination are given in Table I. The wavelengthsof longitudinal and transverse waves in steel aregiven in Table II.3COUPLANTSIn order to transmit ultrasonic energy efficient-ly into the specimen, the probe must be coupledto the casting surface by means of a liquid, e.g.glycerine, oil, grease, water.The reflected energy which arises when a longi-tudinal wave meets a boundary between two mediais a function of their relative acoustic impedances(ϕ1c1 and ϕ2c2 where ϕ=density and c=soundvelocity). The amount of energy reflected at aboundary is given by the formula (restricted tolongitudinal waves, normal to the boundary).Typical values of ϕ..c. are given in Table I. The useof values of ϕ.c. in this formula shows that at anair/steel interface, 100 % of the ultrasonic energyis reflected, while 88% is reflected at a water/steel interface.TYPES OF ULTRASONIC WAVESwith ultrasonic examination :There are two wave types normally associated(a) Longitudinal waves (Fig. 3).(b) Transverse waves (Fig. 4).The longitudinal waves are produced by a volt-age applied to a piezo-electric transducer. Themechanical vibrations produced are related to thisvoltage, and are propagated as ultrasonic waves.Transverse waves are normally obtained by in-itially producing longitudinal waves which arethen refracted in accordance with Snell's Law asthey pass from a Plexiglass wedge into the steel.The design of the Plexiglass wedge, which formspart of the probe, is such that the longitudinalwave does not enter the specimen. Fig. 5 showsthe conversions which occur when a longitudinalwave is transmitted from one isotropic medium(A) into a second isotropic medium (B).PRODUCTION OF ULTRASONIC WAVESare used to produce ultrasonic vibrations :There are two main types of transducers which(a) Naturally occurring, or artificially pro-duced anisotropic single crystals, e.g.quartz, lithium sulphate, Rochelle salt.(b) Ceramics, e.g. barium titanate, lead zir-conate.These transducers are frail and must thereforemechanical vibration, and a sturdy cover to pro-tect the whole device.This device is called a probe; several probesare illustrated in Figs. 6, 7 and 8.The above formula applies only to the far zone.The relationship between beam spread and fre-beam lies on the axis and decreases rapidly withincrease in angle from the probe axis; with fur-ther increase in angle, alternate maximum andminimum intensity values occur, which are calledside lobes, Fig. 10.be placed in a suitable housing which incorporatesa voltage lead, a suitable backing material to dampquency for 10, 15, and 23 mm diameter probes isgiven in Fig. 9. The maximum intensity of the4GEOMETRY OF THE ULTRASONIC BEAMIn order to use the probes for flaw detection, apulse of sound waves from the probe must betransmitted at regular intervals through thesteel ; the time intervals between successive pulsesmust be long in comparison with the time takenfor the echoes to return to the probe.The ultrasonic beam, which is produced as eachpulse of energy is supplied to the transducer, hasa certain geometry. This geometry, which coversthe beam spread and the near and far zones, isdependent on the ultrasonic frequency, the trans-ducer diameter and on the way in which the trans-ducer is damped.(a) Beam spreadThe solid angle of beam spread 2θ at 10% ofmaximum axial intensity is given bv the formula5The complex variations in sound intensity whichoccur close to the transducer cause interference effects. This interference is confined to the nearzone, in which the beam is essentially parallel.Note that the near zone is affected by the Plexi-glass block, shear and combined double probes.The near zone is defined by a distance N, beyondwhich the beam diverges:This relationship for a number of media is plottedin Figs. 11a and 11b. In the far zone, the intensityof the beam follows the inverse square law. A diagrammatic representation of the variationin intensity within the near and far zones is givenin Fig. 12; a transition zone separates these two zones.The interference and variation of intensitywithin the near zone makes flaw size estimation impossible and such measurements should onlybe made in the far zone: Claydon has carried outextensive work on this problem.6CALIBRATION OF THE ULTRASONIC INSTRUMENTCALIBRATION AND REFERENCE BLOCKS Ultrasonic instruments and their probe systems are not built to a universally recognized specifica- tion. In order to have a means of comparing the probe and instrument characteristics, it is ad- visable to use one or more reference blocks to calibrate the instrument (Fig. 13). This calibra- tion is particularly important under working con- ditions to ensure that the correct sensitivity levels are maintained. It may also be an advantage to prepare additional reference blocks of thickness, shape and surface finish appropriate to the needs of the operator.LONGITUDINAL WAVE PROBESThe first operation (Figs. 14a-d) is used forsteel thickness measurements between 0 and 200 mm and automatically sets the initial pulse at the zero point on the screen. It is necessary to re- calibrate each longitudinal wave probe for the zero point in a similar manner.1. Calibration of the time base in terms of steelthickness The probe is placed in position A on the test block and by controlled movement of the horizontal shift (or delay if no horizontal shift is provided) and the fine time base control, a series of echoes are obtained at the screen positions of 25, 50, 75 and 100 scale divisions (Fig. 14a). These move- ments of the two instrument controls automatical- ly set the zero point. If the echoes will not coin- cide with appropriate scale divisions, the time base is not linear and a graphical calibration should be prepared, or the supplier of the instrument ap- proached if the error is excessive.The following operations (Figs. 14b-14d) may require adjustment of the time base and other controls.For greater accuracy in the range of less than 10 mm, a 4-5 MH z probe should be used, because a higher frequency probe has a smaller dead zone. Place the probe in positions D and E, as shown in Figures 14d and 14e.782. Check on linearity of amplifierThe amplification is linear when the ratio ofthe height of any two consecutive echoes remains constant when the degree of sensitivity is altered(Fig. 14f). A quantitative value of amplifier lin-earity may be determined and reference shouldbe made to BS.4331: Part 1: 1968.In order to ensure that an apparatus has ade-quate penetrating power, operation 3 (a) shouldbe carried out.3. Assessment of-(a) Penetrating powerThe sensitivity control is set at a minimum andthe probe placed on the metallized surface of the Plexiglass block (Fig. 15a). The thickness of the Plexiglass is calculated to correspond to 50 mm of steel. A measure of the penetrating power canthen be obtained by slowly increasing the sensi-tivity control to a maximum and noting the num-ber of bottom echoes which appear. A low pene-trating power apparatus may only give 2-4 bot-tom echoes, a high penetrating power apparatus6 - 10 bottom echoes.(b) Relative sensitivityThe sensitivity control is initially set at a mini-mum and the probe moved until an echo fromthe 1.5 mm diameter hole is obtained on thescreen. The height of this echo at a given settingof the sensitivity control constitutes a relativemeasure of sensitivity (Fig. 15b).The dead zone, which is dependent on the instru- ment and probe characteristics, should be assessedfor each probe, since flaw indications cannot bereceived in this zone.4. Check of the dead zoneThe distance from the probe to the Plexiglassat positions D and E is 10 mm and 5 mm, respec- tively. The ability to see one or both of theseechoes is a measure of the dead zone (Figs.16a, b).95. Check on the resolving powersaid to have bad resolution. A quantitative valueof resolution may be determined and reference should be made to BS.4331:Part 1:1968.TRANSVERSE WAVE PROBESThe first three of the following operations are essential because the probe index and the beam spread must be found by practical measurement and not assumed to be correct from probe mark- ings and theoretical considerations. The resultscan then be used for the assessment and location of flaws.1. Determination of probe indexThe probe index is given on the probe ; in order to check that the position marked on the probeis correct, place the probe in position H (Fig. 18). Move the probe until maximum amplitude is re- ceived from the 100 mm curved surface. The cen- tral mark on the graduated scale will be the posi- tion at which the beam leaves the Plexiglass and enters the steel, i.e. the probe index.2. Determination of the angle of refractionMove the probe until maximum signal amplitude is obtained from the Plexiglass cylinder (Fig. 19). The reference block has calibrated scales engraved at 40-70° and the relevant angle of refraction marked on the probe should coincide with the cor- rect scale position. The probe index which has been previously determined should be marked onthe probe in order to obtain the correct results.3. Correction of the zero pointThe presence of the Plexiglass in the transverse wave probe causes a time lag between the moment at which the signal leaves the transducer and themoment it leaves the wedge. This time lag mustbe corrected for and the zero point set on the cathode ray screen. Obtain an echo at a maximum amplitude on the screen from 100 mm radius (Fig.20). Adjust the echo by movement of the hori- zontal shift and the fine time base control in order to obtain two echoes on the screen at 50 subdivi- sions and 100 subdivisions; the zero on the scale will then correspond to the moment the beam leaves the Plexiglass wedge.It is necessary to recalibrate each transverse wave probe for the zero point in a similar manner.A beam plot is used to verify the position ofthe beam in a cast section. It is used in conjunc- tion with a second Plexiglass slide on which a drawing is produced showing the geometric shape of the component. Flaw size, shape and position may be assessed using this method, and reference should be made to the Test Procedure. The above method may also be used to assess the beam spread from both single and combined double probes. A horizontal polar diagram is shown in Fig. 21.The scale on this part of the block is calibrated every 25 mm and the hole diameter is 1.5 mm. Obtain an echo on the screen by placing the probe at a suitable distance from the hole, e.g. for a 45° angle probe, the distance would be 25 mm. Rotate the probe from one side to the other and note the echo amplitude at various angles of probe posi- tion. A horizontal polar diagram can be plotted,as previously described. It is suggested that in order to plot a more accurate diagram, a similar check should be carried out at multiples of a given distance.4. Assessment of sensitivityObtain an echo at a convenient height on the screen by placing the probe 25 mm away fromthe 1.5 mm hole (Fig. 22). Move the probe back 50, 75 and 100 mm away from the hole and note the new echo amplitude. Note that to carry out a similar measurement using a 70° probe, the above figures, excepting the diameter of the hole, must be multiplied by 2.75. For a 60° probe the figures must be multiplied by 2.The sensitivity of the equipment can now be specified in terms of echo height and distancefrom the 1.5 mm hole.MEASUREMENT OF STEEL THICKNESS Ultrasonics, using longitudinal waves and con- ventional flaw detection equipment, can readily be used for thickness measurement. A frequency range of 2-5 MHz is recommended.The accuracy of the technique, which should be of the order of 2 - 5% steel thickness, depends on two main factors:(a) the surface roughness, and(b) whether or not the two surfaces are parallel. The value of 2 - 5% accuracy will fall off where steel thicknesses less than 6mm are to be meas- ured.The first technique which is described is theone recommended by the Procedure and may be used with any ultrasonic instrument provided the instrument is correctly calibrated.1. Direct calibration methodThis technique is widely used because of its simplicity, and depends on the time base linearity of the instrument. It consists of initially cali-brating the instrument on the A2 calibration block (Fig. 13), details of which are given in the pre- ceding pages under the heading, Calibration ofthe Time Base in Terms of Steel Thickness.Once this operation is complete, a check may be made by the use of the B.S.C.R.A. reference block, ignoring the echo from the drilled hole. A rule measurement in two directions on this block can be directly related to the position of each bottom echo on the graduated cathode ray screen.The next two techniques (2 and 3) are specific to certain types of equipment.2. The “resonance” methodIn this technique, a unit attached to the ultra- sonic equipment enables a pulse at a continuously variable repetition frequency to be transmittedinto the specimen. From the received signal, the thickness of material can be obtained.3. The use of a calibrated time markerThis technique depends on two factors, firstly,a linear time base on the instrument and, secondly, the sound velocity of the longitudinal wave in the material. Since this sound velocity is a variable factor, the method is not recommended, but is described in order to illustrate the use of the “time marker.”For a given material, the distance on the screen between the initial pulse and the reference echo, or between consecutive reference echoes, repre- sents the time interval for the pulse to travel the total distance from the transducer to the bottomof the material and back to the transducer. Cer- tain commercial instruments have a calibrated time marker circuit coupled to the time base, which enables accurate time measurements to be made.The thickness of the material is then calculated from the formula:s = v x ts = thickness, mmv = sound velocity, mm/sect = time interval, sece.g. number of bottom echoes = 6number of time markers = 20 Assume the marker time interval is 5 micro sec- onds (1 micro second = 10-6seconds).The total time for sound to travel 12 times the steel thickness is therefore 100 micro seconds. Time required totravel the thicknessof the materialVelocity of longi-tudinal wave = 5.85 106mm/sec*=100/12 micro seconds= 8.33 micro secondss = v x ts = (5.85x106) (8.33x10-6) mms = 48.7mm∴thickness ofmaterial = 48.7 mmReference is also made to ultrasonic thickness measuring devices, but direct reading methods using conventional flaw detection equipment is to be preferred.* In order to obtain correct results, this method requires accurate knowledge of the velocity of sound in the mate-rial undergoing testing.FORMATION OF CASTING DEFECTS ULTRASONIC AND RADIOGRAPHIC CORRELATIONThe use of non-destructive testing for the ex- amination of steel castings has increased consider- ably during the past few years. The most striking advance has been in the application of ultrasonic examination as a quality control technique in the steel foundry. Ultrasonic examination to assess the presence and nature of internal flaws in steel castings has many advantages over radiography, these including such factors as capital and run- ning costs, safety in operation, portability and,a most important point, ultrasonic examination is independent of section thickness. The Atlas of Some Steel Castings Flaws, therefore, places a particular emphasis on the use of ultrasonics for the detection of casting flaws. Its purpose is to illustrate and describe typical casting flaws and discuss how they may be detected by ultrasonics. In order to clarify the ultrasonic indications, ap- propriate radiographs, micro-sections, and dia- grams have been included.Ultrasonic examination requires an experienced operator to obtain the maximum economic bene- fits. It is essential that the operator be given every facility so that he can estimate the possible loca- tion of flaws before carrying out an examination, i.e. he should be provided with a drawing showing location of feeder heads, gating systems, etc. and should have all the information on the history of the casting.FLAWS DUE TO INADEQUATE FEEDING (SHRINKAGE FLAWS)1. Description of flawsShrinkage flaws are cavities formed during solidification, which occur as a result of liquid to solid contraction. The flaws are not normally as- sociated with gas but a high gas content will mag- nify their extent.Shrinkage flaws may occur in steel castings where there is a localized variation in section thickness ; they may, however, occur in parallel sections where penetration of the liquid feed metal is difficult. The shrinkage flaws which occur in steel castings may be considered as falling into three types, namely :(a) Macro-shrinkage(b) Filamentary shrinkage(c) Micro-shrinkage(a) Macro-shrinkageA large cavity formed during solidification is referred to as a macro-shrinkage flaw. The most common type of this flaw is piping, which occurs due to lack of sufficient feed metal. In good de- sign, piping is restricted to the feeder head. (b) Filamentary shrinkageThis is a coarse form of shrinkage but ofsmaller physical dimensions than a macro-shrink- age cavity. The cavities may often be extensive, branching and interconnected. Occasionally the flaw may be dendritic. Theoretically, filamentary shrinkage should occur along the center line of the section but this is not always the case and on some occasions it does extend to the casting surface. Extension to the casting surface may be facili- tated by the presence of pin or worm holes.(c) Micro-shrinkageThis is a very fine form of filamentary shrink- age due to shrinkage or gas evolution during solidification. The cavities occur either at thegrain boundaries, (intercrystalline shrinkage), or between the dendrite arms (interdendritic shrink- age).Typical locations at which shrinkage cavitiesare most likely to occur are illustrated in Fig.23. Localized changes of section thickness repre- sent hot spots which cannot be fed adequately in most cases. Shrinkage cavities will form, there- fore, unless special precautions are taken. In-scribing circles in the junction and in the adjacent sections, and determining the ratio of the circle diameters, provides a relative measure of the hot spot severity and hence susceptibility to shrinkage formation. If the technique is applied to L, T, V, and Y sections, it will be seen that crosses and acute angle junctions are to be avoided in favor of T and L junctions.2. Detection of flaws(a) Macro-shrinkageThe technique used for the detection of thisflaw is dependent on the casting section thickness. Where the section exceeds 3 inches a normal single probe is satisfactory, while for section thicknesses of less than 3 inches it is advisable to use a combined double probe. The presence of the flaw is shown by a complete loss in back wall echo, together with the appearance of a new flaw echo. The position of the flaw echo on the oscilloscope screen indicates the depth of the flaw below the surface. An angle probe should be used to confirm the results obtained from the scan using a normal probe.(b) Filamentary shrinkageThe presence of filamentary shrinkage is best detected with a combined double probe if the sec- tion thickness is less than 3 inches. The flaw echoes which are obtained reveal the extent ofthe flaw and also the flaw depth. It is suggested that an initial scan on expansive rough surfacesis best carried out with a large combined double probe (say 23 mm in diameter) ; final assessment and flaw depth measurement are achieved by a small diameter combined double probe (say 10 - 15 mm in diameter).(c) Micro-shrinkageA fine “grass” type of oscilloscope indication is typical of this flaw. The extent to which the flaw occurs may be assessed by a consideration of the number of back wall echoes which occur at any given frequency. Where it is difficult to obtainone or a number of back wall echoes at 4 - 5MHz due to random scattering of the ultrasonic beam, and since this could give the impression of a large cavity type of flaw, it is advisable to reduce the frequency to 1 - 2 MHz. This reduction in fre- quency will indicate that no large cavity does in fact exist if a back wall echo can be obtained.FLAWS ASSOCIATED WITH HINDERED CONTRACTION DURING COOLING1. Description of flaws(a) Hot tearsThese are cracks which are discontinuous and generally of a ragged form, resulting from stresses developed near the solidification tempera- ture when the metal is weak. The stresses arise when the contraction is restrained by a mold or core or by an already solid thinner section. Typical examples are illustrated in Fig, 24. Hot tears occur at or near to changes in section, e.g. re- entrant angles and joints between sections. They are not fully continuous and commonly exist in groups, often terminating at the surface of the casting.(b) Cracks or stress cracksThese are well defined and approximately straight cracks formed when the metal is com- pletely solid. They are revealed as clearly defined, smooth, dark lines.2. Detection of flaws(a) Hot tears and cracksThe location of a hot tear can rarely be deter- mined accurately using a normal probe because of the orientation of the flaw. The most satisfactory technique is the use of a transverse wave probe. Since the tears usually exist in groups, the extent is assessed by passing the beam underneath the flaw (Fig. 25). The location of a hot tear is found most easily by magnetic crack detection and its depth by the ultrasonic angle probe. A cold crack may be detected in a similar manner (Fig. 26).。