Use of ultrasound in metrology 2(1)

transcript

USE OF ULTRASOUND İN METROLOGY

Prepared By :

• Mustafa ERARSLAN• Serkan Ahmet ÇAM• Osman KAYA• Ferhat AYDIN• Ahmet KOYUNCU• Kadir YÜZER

Sound is a sequence of waves of pressure that propagates through compressible media such as air,water or solids.

During propagation, waves can be reflected, refracted, or attenuated by the medium.

PHYSİCS OF SOUND

The mechanical vibrations that can be interpreted as sound are able to travel through all forms of matter: gases, liquids, solids, and plasmas. The matter that supports the sound is called the medium. Sound cannot travel through a vacuum.

SOUND WAVE PROPERTIES AND CHARACTERISTICS

• Frequency, or its inverse, the period

• Wavelength• Wavenumber• Amplitude• Sound pressure• Sound intensity• Speed of sound• Direction • Polarization (Transverse Waves)

ULTRASOUND

Ultrasound is cyclic sound pressure with a frequency greater than the upper limit of human hearing. Ultrasound is thus not separated from "normal" (audible) sound based on differences in physical properties, only the fact that humans cannot hear it. Although this limit varies from person to person, it is approximately 20 kilohertz (20,000 hertz) in healthy, young adults. The production of ultrasound is used in many different fields, typically to penetrate a medium and measure the reflection signature or supply focused energy. The reflection signature can reveal details about the inner structure of the medium, a property also used by animals such as bats for hunting. The most well known application of ultrasound is its use in sonography to produce pictures of fetuses in the human womb. There are a vast number of other applications as well.

INFRASOUNDInfrasound is sound that is lower in frequency than

20 Hz (Hertz) or cycles per second, the "normal" limit of human hearing. Hearing becomes gradually less sensitive as frequency decreases, so for humans to perceive infrasound, the sound pressure must be sufficiently high. The ear is the primary organ for sensing infrasound, but at higher levels it is possible to feel infrasound vibrations in various parts of the body.

The study of such sound waves is sometimes referred to as infrasonics, covering sounds beneath 20 Hz down to 0.001 Hz. This frequency range is utilized for monitoring earthquakes, charting rock and petroleum formations below the earth, and also in ballistocardiography and seismocardiography to study the mechanics of the heart. Infrasound is characterized by an ability to cover long distances and get around obstacles with little dissipation.

ACOUSTICAcoustics is the interdisciplinary science that deals

with the study of all mechanical waves in gases, liquids, and solids including vibration, sound, ultrasound and infrasound. A scientist who works in the field of acoustics is an acoustician while someone working in the field of acoustics technology may be called an acoustical engineer. The application of acoustics can be seen in almost all aspects of modern society with the most obvious being the audio and noise control industries.

Hearing is one of the most crucial means of survival in the animal world, and speech is one of the most distinctive characteristics of human development and culture. So it is no surprise that the science of acoustics spreads across so many facets of our society—music, medicine, architecture, industrial production, warfare and more. Art, craft, science and technology have provoked one another to advance the whole, as in many other fields of knowledge.

MACH NUMBER

Mach number (Ma or M) is the speed of an object moving through air, or any other fluid substance, divided by the speed of sound as it is in that substance for its particular physical conditions, including those of temperature and pressure. It is commonly used to represent the speed of an object when it is traveling close to or above the speed of sound.

M = Mach NumberV = Relative velocity of the source to the mediuma = Speed of sound in the medium

For Subsonic ;

where:M = is Mach numberqc = is impact pressure (diffrence between total pressure and static pressure)p = is static pressure γ = is the ratio of specific heat of a gas at a constant pressure to heat at a constant volume (1.4 for air).

Regime Subsonic Transonic Sonic Supersonic HypersonicHigh-hypersonic

Mach <1.0 0.8–1.2 1.0 1.2–5.0 5.0–10.0 >10.0

CALCULATİNG MACH NUMBER

CALCULATİNG MACH NUMBER For Supersonic ;

For air Simplified Formula is ;

BASIC PRINCIPLES OF ULTRASONIC TESTING

Spectrum of sound

Frequency range Hz

Description Example

0 - 20 Infrasound Earth quake

20 - 20.000Audible sound

Speech, music

> 20.000 Ultrasound

gas liquid solidAtomic structures

•low density•weak bonding forces

•medium density•medium bonding forces

•high density •strong bonding forces•crystallographic structure

Wave propagation

AirWater

Steel, longSteel, trans

330 m/s

1480 m/s

3250 m/s

5920 m/s

Longitudinal waves propagate in all kind of materials.Transverse waves only propagate in solid bodies.

Due to the different type of oscillation, transverse wavestravel at lower speeds.

Sound velocity mainly depends on the density and E-modulus of the material.

Reflection and Transmission

• As soon as a sound wave comes to a change in material characteristics ,e.g. the surface of a workpiece, or an internal inclusion, wave propagation will change too:

Behaviour at an interface

Medium 1 Medium 2

Incoming wave Transmitted wave

Reflected wave

Interface

Reflection + Transmission: Perspex - Steel

Reflected wave

Perspex

1,00,87

Perspex Steel

Reflected wave

Amplitude of sound transmissions:

•Strong reflection•Double

transmission

•No reflection•Single

transmission

•Strong reflection with inverted phase•No transmission

Water - Steel Copper - Steel Air - Steel

Piezoelectric Effect

Piezoelectrical Crystal (Quartz)

Battery+

The crystal gets thicker, due to a distortion of the crystal lattice

The effect inverses with polarity change

Sound wave with

frequency f

An alternating voltage generates crystal oscillations at the frequency f

BASIC PRINCIPLES OF ULTRASONIC TESTINGReception of ultrasonic waves

A sound wave hitting a piezoelectric crystal, induces crystal vibration which then causes electrical voltages at the crystal surfaces.

Electrical energy

Piezoelectrical crystal

Ultrasonic wave

BLOCK DIAGRAM: ULTRASONIC INSTRUMENT

amplifier

work piece

horizontal sweep

pulser

screen

Sound reflection at a flaw

Flaw Sound travel path

Work piece

Plate testing

delaminationplate 0 2 4 6 8 10

IP = Initial pulseF = FlawBE = Backwall echo

0 2 4 6 8 10

Wall thickness measurement

Corrosion

Through transmission testing

0 2 4 6 8 10

Through transmission signal

surface = sound entry

backwall flaw

water delay

0 2 4 6 8 10 0 2 4 6 8 10

IE IEIP IP

BE BEF

Immersion testing

Weld inspection

0 20 40 60 80 100

a = s sinßa = s sinß

a' = a - xa' = a - x

d' = s cosßd' = s cosß

d = 2T - t'd = 2T - t'

Lack of fusion

Work piece with welding

ß = probe angles = sound patha = surface distancea‘ = reduced surface distanced‘= virtual depthd = actual depthT= material thickness

Straight beam inspection techniques:

Direct contact, single element probe

Direct contact, dual element probe

Fixed delay

Immersion testingThrough transmission

• Sonar stands for sound navigation and ranging.• Sonar uses a beam of sound waves and directs them

downward.• After the sound wave hits the bottom of the ocean

(ocean floor), or an object, it will bounce off and return back causing an echo.

• This is then recorded on a depth recorder on the ship.

• Some marine organisms use Echolocation, which is a form of sonar (dolphins, whales, porpoises).

SONAR (SOUND NAVIGATION AND RANGING)

TYPES OF SONAR SYSTEMSSYSTEMS

Active

• Deploys and receives its own signal

• Two categories echo ranging, and communication

• Allied Submarine Detection Investigation Committee ( ASDICS)

Passive

• Listening device• Detects underwater

sounds• Belongs to the Direct

Listening category

COMPONENTS OF A SONAR SYSTEM

Active

• Transducer (Emitter/Receiver)

• Indicator• Recorder• Computer System

Passive

• Transducer (Only Receiver)

• Indicator• Recorder• Computer System

MEDİCAL ULTRASONOGRAPHY

Diagnostic sonography (ultrasonography) is an ultrasound-based diagnostic imaging technique used for visualizing subcutaneous body structures including tendons, muscles, joints, vessels and internal organs for possible pathology or lesions. Obstetric sonography is commonly used during pregnancy and is widely recognized by the public.

In physics, the term "ultrasound" applies to all sound waves with a frequency above the audible range of human hearing, about 20,000 Hz. The frequencies used in diagnostic ultrasound are typically between 2 and 18 MHz.

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Use of ultrasound in metrology 2(1)

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