A-scan
Conventional screen presentation in which the horizontal axis represents the transit time and the vertical axis represents the signal amplitude.
Acoustic Impedance
The resistance to acoustic propagation. Calculated as the product of the acoustic velocity and the specific gravity of the medium.
Acoustic Velocity
The velocity at which a mode propagates through a medium.
Amplifier
The component which amplifies the weak returning signal from the transducer to a voltage suitable for display on the screen of the UFD.
Amplitude
A representation of the relative acoustic sound pressure. Displayed as the vertical displacement in A-scan presentation.
Analogue
Any equipment which gives a continuous response proportional to the stimulus, as opposed to digital in which the response is stepwise.
Angle Probe
A probe which produces ultrasonic waves entering the test object at an angle to the normal (i.e. other than 90° to the surface).
Area Amplitude Blocks
Calibration blocks in which there are a series of flat-bottomed holes of varying diameter.
AS1065
The Australian standard for ultrasonic testing of carbon and low alloy steel forgings.
ASME
American Society of Mechanical Engineers. A code writing body which has produced a number of standards on ultrasonic testing.
ASTM
American Society for Testing and Materials. A code writing body which has produced a number of standards in ultrasonic testing.
ASTM A435
The standard specification for straight-beam ultrasonic examination of steel
plates.
ASTM A604
The test method for Macroetch Testing of consumable electrode remelted steel bars and billets.
Attenuation
The process by which acoustic pressure is reduced by a combination of scattering of ultrasound and heat dissipation.
Attenuation Coefficient
A quantitative measure of attenuation, expressed in decibels per millimetre (dB/mm).
Attenuator
US Term – A control that works in the opposite sense to gain, i.e. the higher the attenuation, the lower the amplification.
AVG Diagram
See DGS Diagram.
AWS
American Welding Society. A code writing body which has produced a number of standards on ultrasonic testing.
AWS D1.1
The American Welding Society code for welding of structural steel.
B-Scan
A means of presentation which approximates a cross section, and in which the horizontal axis represents length and the vertical dimension represents depth. Points are displayed which represent designated characteristics.
Back Reflection
See Backwall Reflection.
Backing Strip
A solid strip placed under a single V weld preparation to control the penetration of the weld joint.
Backwall Reflection
The reflection obtained from a boundary of the material normal to the beam axis.
Bandwidth
The range of frequencies that comprise a synthetic short pulse.
Beam
The ultrasonic wave envelope that includes a near zone in front of the probe and a far zone beyond the near zone.
Beam Axis
The line of highest acoustic pressure within the beam.
Beam Index
See Probe Index.
Beam Path
The physical distance between the beam entry point and a reflector.
Beam Profile
A stylised representation of the ultrasonic beam shape, generally determined experimentally.
Beam Spread
The angular divergence of the ultrasonic beam in the far zone.
C-Scan
A representation of the test object in plan, in which specific characteristics such as attenuation, thickness or the presence of reflectors are displayed.
Calibration
The process of adjusting the range, zero, amplification and other controls against traceable reflectors to allow quantitative measurements.
Calibration Block
A block used for calibrating ultrasonic flaw detector equipment.
Casting
The process of producing a solid metallic product by pouring the metal in liquid form into a mould.
Cathode Ray Oscilloscope
An electronic instrument which displays electrical signals in terms of their time (horizontal axis) and amplitude (vertical axis).
Cathode Ray Tube
An electronic device for displays found in cathode ray oscilloscopes and televisions.
Certification
The process of attesting the compliance of an individual’s qualifications and competence.
Characterisation
The process of giving a nature and possible cause to an ultrasonic reflector.
Code
A nationally recognised standard.
Compression Wave Probe
A probe that produces primarily compression waves. If the compression wave is angled, there will also be a shear wave produced.
Compression Waves
Wave propagation by alternate compression and decompression of the atoms of the medium.
Contact Testing
Ultrasonic testing in which the couplant is a thin film of liquid.
Corner Reflector
A reflector at which the ultrasonic beam makes reflections at two surfaces aligned at right angles and returns parallel to its incident direction.
Couplant
A liquid that permits transmission of sound energy from a probe to a test piece.
Crack
A physical separation of a material due to stress.
Creeping Waves
Ultrasonic waves generated when compression waves propagate almost parallel to a surface, with associated conversion to a shear wave at 33° (in steel).
Critical Angle
The angle of an incident wave that is refracted wave along the incident surface. At any higher incident angle, the wave is totally reflected back into the medium of the incident wave.
CRO
See Cathode Ray Oscilloscope.
Cross Talk
Ultrasonic energy travelling directly from the transmitter to the receiver of a twin crystal probe.
CRT
See Cathode Ray Tube.
Crystal
The structure of solid materials where the atoms are arranged in regular lattice patterns. A Crystalline material may exhibit the piezoelectric effect.
Curie Temperature
The temperature at which piezoelectric transducers lose their piezoelectric properties.
DAC
See Distance Amplitude Correction.
Damping
1. Electrical damping is the process of limiting the pulse duration of a transducer by mechanical means.
2. Acoustic damping is the process of using materials at an interface to encourage energy transmission into a high attenuation medium for the purpose of removing unwanted energy.
dB
The unit symbol for decibel. See Decibel.
Dead Zone
The area immediately in front of the probe in which the probe detects its own ringing as well as any unwanted reflections. The dead zone may prevent the detection of near surface reflectors.
Decibel
A logarithmic ratio of two amplitudes. dB=20log10A1/A2.
Defect
A discontinuity that makes an item unsuitable for its intended purpose.
DGS Diagram
Distance/Gain/Size is a relationship between beam path, signal amplitude and equivalent flat-bottomed hole diameter. Applied as an overlay screen or software, which allows direct estimation of equivalent reflector size.
Diffraction
The process of generation of a relatively low amplitude spherical wave from the tips of planar reflectors.
Digital
A means of displaying electrical signals in stepwise binary code, which allows mathematical analysis of the data.
See also Analogue.
Discontinuity
Any break in the homogeneity of a material.
Distance Amplitude Block
A block
Distance Amplitude Correction
Compensation for the effects of beam path and attenuation to allow direct comparison of reflectors over a range of beam path lengths.
Divergence
The angular spread of an ultrasonic beam in the far zone.
Dominant Frequency
The desired nominal frequency of a probe.
Dual Probe
See Twin Probe.
Dynamic Range
The useable range of an instrument.
EFBH
See Equivalent Flat Bottomed Hole.
Electrical Zero
The time (distance) at which the transmitter is energised.
EMAT
Electromagnetic Acoustic Transducer – a type of transducer that uses the Lorenz forces of an oscillating magnetic field of a coil to generate wave motion.
Energy Waves
Mechanical waves travelling in a medium.
Equivalent Flat Bottomed Hole
A flat bottomed whole whose diameter at a similar beam path in a similar material most closely provides reflection to a reference discontinuity under consideration.
Exit Point
See Probe Index.
Far Field
The area beyond the near zone of an ultrasonic beam in which the reflection from a backwall is inversely proportional to the beam path.
See also Near Field.
Far Zone
See Far Field.
Fatigue
The progressive propagation of a crack in a material due to cycling stresses below the static tensile strength, leading to ultimate failure.
First Critical Angle
The smallest angle of incidence to an interface at which the transmitted compression mode reaches a refracted angle of 90°, producing a creeping wave. Above the first critical angle, the compression mode is completely reflected back into the first medium.
Flaw
See Discontinuity.
Flaw Detector
See Ultrasonic Flaw Detector.
Focus
1. In Immersion, it is the use of an ultrasonic lens to focus the beam to a point.
2. In Twin Crystal Contact, it is the slight angled alignment of the transmitting and receiving crystal resulting in a depth of optimum reflection.
Forging
The process of forming a metal shape by mechanical deformation in the solid state at high temperature.
Fraunhofer Zone
See Far Zone.
Frequency
The rate of reversal of stress causing the generation of an ultrasonic wave. Expressed in Hertz.
Fresnel Diffraction Zone
See Near Zone.
FSH
See Full Screen Heigt.
Full Screen Height
Full vertical deflection to the maximum graticule marking. Also known as 100% FSH.
Fundamental Frequency
See Dominant Frequency.
Gain
The degree of amplification applied to ultrasonic signals. Measured in dB.
Gain in Hand
See Overall System Gain.
Gate
A selected range of transit time from which signals may be extracted for further processing.
Ghost Echo
An echo which occurs when a reflected echo returns to the receiver and is displayed after the following pulse has been transmitted, and therefore has no relationship to the later transmitted pulse.
Grass
Low amplitude signals due to scattered reflections from small inhomogenities in the material and/or equipment noise.
Graticule
An engraving on the CRO screen for quantitative measurement of amplitude or beam path.
Hash
US Term – see Grass.
Height (of discontinuity)
The vertical dimension of a discontinuity.
Hertz
A measure of frequency. One Hertz equals one cycle per second.
Horizontal Linearity
The relationship between the time base and the actual distances travelled by the ultrasonic beam should be linear.
Huygens’ Principle
The generation of a plane wave by the superposition of a large number of small spherical waves.
Hz
The unit symbol for Hertz. See Hertz.
IIW Block
See International Institute of Welding Block.
Immersion Testing
Testing by wholly or partially immersing the test object in water.
Impedance
1. Electrical impedance is the resistance of a circuit to the passage of alternating electrical current. Impedance is composed of resistance, capacitance and inductance.
2. Acoustic impedance – see Acoustic Impedance.
Impedance Matching
The use of an electrical component (generally an inductive coil) to match the electrical impedance of a flaw detector and probe.
Initial Pulse
See Transmission Pulse.
Interface
A boundary at which there is a change in acoustic impedance.
Interface Trigger
An enhancement in a flaw detector used for immersion testing which automatically sets the first water path echo as the zero point.
International Institute of Welding Block
An internationally recognised calibration block for ultrasonic equipment. Also called the V1 block.
Inverse Square Law
The amplitude/distance relationship f
ISO
International Standards Association.
Isobar
A line of equal pressure. Useful for defining the shape of ultrasonic beams.
Kidney Block
See V2 block.
Lamb Waves
A wave form generated and propagated in very thin materials.
Lamination
A central planar discontinuity in plates that have been made from ingots.
LSignificant Echo ast
The echo perceived when the centre of the ultrasonic beam passes over the tip of a planar reflector.
Linearity
1. Vertical linearity is the ability of an amplifier to faithfully represent the relative amplitude of ultrasonic signals.
2. Horizontal linearity is the ability of the X axis of the CRO to represent the relative beam path length across the range of the equipment.
Lobe
See Side Lobe.
Longitudinal Waves
See Compression Wavs.
LSE
See Last Significant Echo.
Main Bang
See Transmission Pulse.
Matching Coil
A coil used to match the electrical impedance of a probe and flaw detector.
Medium
Any solid, liquid or gas in which ultrasound is propagating.
Method
A specific discipline with nondestructive testing (e.g. Radiography, Ultrasonic, Eddy Current).
Mode
A means of sound propagation. Principle modes are compression, shear, surface and lamb waves.
Mode Conversion
The process of an incident beam splitting part of its energy to produce another mode by refraction or reflection when it strikes an interface.
Monitor
An electronic device f
See also Gate.
Multiple Echoes
The repeated reflection of an ultrasonic pulse between the surfaces or discontinuities in a test object.
Near Field
The area near the probe/transducer where the acoustic pressure fluctuates with distance.
See also Far Field.
Near Zone
See Near Field.
Noise
1. Electrical noise is the irregularity on the base line of the CRO due to electrical interference with the trace.
2. Material noise – see Grass.
OSG
See Overall System Gain.
Overall System Gain
The unused gain (amplification) when a probe UFD combination is being used at the required sensitivity.
Phase
The relationship between two waves. Waves that are aligned are said to be “in phase”. Waves that are opposing are said to be “out of phase”.
Piezoelectric Effect
The generation of a physical deformation as a result of the application of an electrical voltage and vice versa.
Planar
Having a shape predominantly in two dimensions.
Plate Waves
See Lamb Waves.
PoD
See Probability of Detection.
Porosity
Voids in a weld
PRF
See Pulse Repetition Frequency.
Primary Wave
The intended ultrasonic beam launched into the test object.
Probability of Detection
The likelihood that a discontinuity will be detected under operating test conditions.
Probe
Piezoelectric transducers mounted in a case, with suitable damping materials, electrical matching and coaxial connections.
Probe Index
The point where the centre of the ultrasonic beam emerges from an angle probe.
Procedure
A documented technique for undertaking a test.
Projection Distance
The h
Propagation
The movement of acoustic pressure through a medium at its characteristic velocity.
Pulse
A short burst of damped vibration.
Pulse Echo Technique
The process of sending a short transmitted pulse of energy, receiving the reflected pulse and recording the amplitude and transit time of the received pulse.
Pulse Envelope
The overall shape of the pulse, given by joining he peaks of the oscillation.
Pulse Length
The number of cycles in a damped pulse of energy.
Pulse Repetition Frequency
The frequency at which ultrasonic pulses are generated by the transmitter.
Q
See Quality Factor.
Qualification
1. Qualification process – demonstrating to be suitable for the purpose.
2. Qualification personal – a demonstrated level of knowledge and experience.
Quality Factor
The quality (purity of tone) of an energy pulse generated by an electrical circuit or probe.
Range
The maximum beam path displayed on the CRO.

Rayleigh Waves
See Surface Waves.
Recognition Envelope
The change in the reflected signal over time of a specific discontinuity type
Reference Block
A block which is non-standard and non-traceable, but contains a specific reflector or condition to aid interpretation.
Reference Sensitivity
The gain (amplification) at which a reference reflector is displayed on the CRO.
Reflection
The process of an ultrasonic wave interacting with an interface and producing a return wave.
Reflection Coefficient
The pressure of the reflected wave divided by the pressure of the incident wave at an interface.
Reflectivity
The ability of a discontinuity to generate a reflection that will be detected by the receiver. Reflectivity is influenced by size, orientation, texture and the relative acoustic impedances at the interface and the beam path travelled.
Refraction
The process of bending a wave at an interface due to a change in acousticvelocity.
Reject
US Term – see Suppression.
Resolution
The ability of a probe/UFD combination to produce separate echoes from adjacent reflectors.
Resonance
The establishment of a standing wave in a medium when the beam path is an exact multiple of half wavelengths.
Ringing
The continued oscillation of a transmitting crystal after initial stimulation.
Root
The zone in a weld where the first weld run is deposited.
S/N
See Signal to Noise Ratio.
Scanning
The process of seeking discontinuities by systematic movement of the probe over the test object such that the ultrasonic beam will interact with the discontinuities sought.
Search Unit
US Term – See Probe.
Second Critical Angle
The smallest angle of incidence to an interface at which the transmitted shear mode reaches a refracted angle of 90°, producing a surface wave. Above the second critical angle, the shear mode is completely reflected back into the first medium.
Secondary Wave
A mode converted wave split off from the primary wave after striking an interface.
Sensitivity
1. The ability to detect a required reflector.
2. Sensitivity eval‎uation is the sensitivity which discontinuities are recorded.
3. Scanning eval‎uation is the sensitivity at which the test object is scanned. Scanning sensitivity is generally a specified multiple of the eval‎uation sensitivity.
Shear Wave Probe
A probe which produces and receives angled shear waves.

Shear Waves
A mode of propagation in solid materials in which the direction of propagation is perpendicular to the particle displacement.
SHM
See Simple Harmonic Motion.
Side Lobe
A second wave at greater divergence than the primary wave due to additional constructive interference.
Signal to Noise Ratio
The ratio between the amplitude of relevant indications to non-relevant indications.
Simple Harmonic Motion
The sinusoidal motion that represents wave motion.
Single V
A weld preparation that permits welding from one side only of a weld.
6 dB Drop Technique
A technique f
Skip
To reflect an ultrasonic beam (generally shear) from the opposite wall. Allows the wave to approach a reflect
Skip Distance
The projection distance at which the beam skips from the walls. Half skip is the first point of reflection from the opposite wall. Full skip is the first point of reflection from the near wall.
Snell’s Law
The mathematical relationship between incident, reflected and refracted waves when ultrasound meets an interface.
Specification
A set of requirements agreed between a buyer and seller.
Specular Reflection
Mirr
Spurious Echo
An indication not directly associated with a discontinuity or boundary.
Spurious Indications
Ultrasonic indications that are not caused by discontinuities or obvious features reflecting the primary wave.
Squint Angle
The angle at which the beam of an angle probe deviates from its intended direction, as viewed in plan.
Standard
A nationally or internationally recognised document of requirements for a product or service.
Standing Waves
See Resonance.
Standoff
The distance between an ultrasonic probe and the test object. This is achieved by using solid standoff blocks for contact testing, or by water for immersi testing.
Standoff Distance
See Projection Distance.


Suppression
The application of non-linear attenuation to eliminate material noise.
Surface Waves
Waves generated at the second critical angle that propagate along a dry surface and interact with surface breaking discontinuities.
Sweep Generator
That part of the UFD which controls the horizontal movement of the trace across the CRO.
Tandem Technique
A technique in which separate remote transmitter and receiver probes are used to improve the probability of detection, usually for large planar reflectors.
Technique
A special application of a test method to achieve a particular result.
Test Object
The item being tested.
Through Transmission Technique
A technique in which the receiving probe is located opposite the transmitter and monitors the amplitude of the received signal.
Tickling
A technique for applying gentle pressure to the surface of a test object to determine whether certain reflections have occurred at the points of application.
Time Base
The horizontal axis of the CRO.
Time of Flight Diffraction
The use of a separate transmitter/receiver technique in which the receiver probe records the diffracted waves.
Timer
The circuit element in a UFD that controls the sequence of operations.
ToFD
See Time of Flight Diffraction.
Transducer
1. In general terms, it is a device for converting one form of energy to another form of energy.
2. US Term – see Probe.
Transfer Loss
The loss in sound pressure in the material under test (relative to the calibration block) due to its poorer surface condition.
Transmission
Sending out an ultrasonic wave.
Transmission Coefficient
The ratio between the pressure of the transmitted wave and the pressure of the incident wave at an interface.
Transmission Pulse
Self-detection of the transmitter ringing, and the display of a signal at the electrical zero.
Transverse Waves
See Shear Waves.
Tuning Coil
See Matching Coil.
20 dB Drop Technique
A technique for discontinuity measurement by measuring the point at which the 20dB isobar of the beam passes the edge of the discontinuity.
Twin Probe
Two transducers mounted in the one housing, with separate coaxial connector, thus allowing the separation of the transmission and reception function and minimising dead zone effects.
UFD
See Ultrasonic Flaw Detector.
Ultrasonic
Sound frequencies above the audible range for practical purposes in the frequency range 250kHz to 20MHz.
Ultrasonic Flaw Detector
An integrated instrument comprising a timer, pulse generator, amplifier and CRO plus other components and controls.
Ultrasonic Technician
A trained and experienced operator of ultrasonic equipment.
V1 Block
See IIW Block.
V2 Block
Miniature internationally recognised calibration block. It is also known as the Kidney Block.
Validation
The process of demonstrating that a proposed procedure or technique will successfully achieve its objective.
Velocity
See Acoustic Velocity.
Waveform
The representation of an ultrasonic pulse by a sinusoidal graph representing amplitude, pulse length and wavelength.
Wavelength
The physical distance between identical points on a waveform.
Wheel Probe
A liquid filled flexible wheel containing one or more piezoelectric transducers, which allows variable orientation of the incident beam.
Width (of a discontinuity)
The lateral dimension of a discontinuity in plan view.
Zero Probe
A compression probe that transmits sound normal to the test object.