Ultrasonic Glossary

Glossary of Ultrasonic Terms.

AccuracyIs the maximum error between expected and actual position following a move. It can be linear or axial, and it includes the effects of backlash and hysteresis.
Acoustic ImpedanceProduct of density and velocity of sound in a particular material. The amount of reflection of a sound beam is determined by the difference in the impedances of the two tissues.
Acoustic Impedance (Z)The product of velocity of sound in a material and density of the material. It is changes in acoustic impedance that reflect and refract ultrasonic energy. The metric unit is “kilograms per second per square meter.”
Acoustic PowerQuantity of energy generated by the transducer, expressed in watts. Also transmit power.
Acoustic ScatteringReflections from small objects that are the size of the wavelength or smaller.
Acoustic ShadowLoss of echo signals from distal structures due to attenuation of overlying structures.
Acoustic VelocityThe speed of sound through a medium as determined by the stiffness and density of the medium. Also: speed of sound; propagation speed; sound velocity.
AliasingA technical artifact occurring when the frequency change is so large that it exceeds the sampling view and pulse repetition frequency. The frequency display wraps around so that the signal is seen at both the top and bottom of the image.
AmplitudeIs the vertical height of the indication on an A-Scan display measured from the lowest to the highest point on the indication.
Amplitude mode (A-mode)A one-dimensional image displaying the amplitude strength of the returning echo signals along the vertical axis and the time (the distance from the transducer) along the horizontal axis.
AnechoicRefers to a structure that returns no echoes. This could be a simple cyst or cystic structure? such as the gall bladder, urinary bladder, or chambers of the heart. Also, sonolucent, echo-free, echolucent, transonic.
A-ScanA method of data presentation on a display screen utilizing a horizontal base line, which indicates elapsed time reading from left to right. A vertical deflection in the base line indicates reflected signal amplitude.
AttenuationLoss of ultrasonic intensity as it passes through a material.
Axial ResolutionDepth resolution; ability to separate two objects lying in tandem along the axis of the beam.
AzimuthalThe dimension perpendicular to the image slice, the thickness of the slice of anatomy.
Back ReflectionIndication of the echo from the far boundary of the material under test.
BacklashIs the amount of play (lost motion) between a set of moveable parts.
Band-PassFrequencies within the acceptable limits of a filter. The term is commonly used as an adjective, as in “band-pass filter,” to denote a filter that passes a range of frequencies unaltered while rejecting frequencies outside the range.
BandwidthThe frequency range represented in a pulse from the transducer; quality factor.
BoosterA mechanical transformer used to increase or decrease the amplitude of the horn.
B-ScanAn ultrasonic presentation of a cross-sectional view or image of the material under test.
CalibrationThe process of comparing an instrument or system with a standard to determine accuracy or produce a scale.
CertificationWith respect to NDT personnel and AWS D1.1, certification is a “written statement of qualification” from the employer of the NDT technician. The employer’s written practice will document the requirements for acquiring the certification.
CineloopThe system memory stores the most recent sequence of images in a series of frames before the freeze button is pressed allowing a continuous loop of images to be reviewed.
Color Flow DopplerOperating mode in which a two-dimensional image is generated that portrays moving reflectors in color simultaneously with B-mode images.
ComplexRefers to a structure that is heterogeneous and may contain both cystic (fluid-filled) and solid components.
CompressionRegions of high pressure and density as sound travels through a medium.
Compressional WaveThose waves in which the particle motion of the atoms of the material is essentially in the same direction as the wave propagation. Also known as longitudinal wave.
CouplantAny material, usually a liquid or semi-liquid, used between the face of the transducer and the test surface to permit or improve transmission of the ultrasonic vibration from the transducer to the material under test.
CrystalThe active transducer component that actually generates and receives ultrasonic energy by converting electrical impulses into sound waves and vice versa.
C-ScanAn ultrasonic data presentation, which provides a plain view image of the area selected by a data gate set in the A-Scan. The image can be a representation of the amplitude variations or the depth relationship of the indications detected by the data gate.
CycleOne complete set of recurrent values of a periodic quantity comprises a cycle. In other words, any one set of variations starting at one condition and returning once to the same condition is a cycle.
CysticA sac or pouch with a definite wall that contains fluid or semisolid material
Damping ControlA control, which varies the duration of the ring of the transducer.
Data GateAn electronic or software means of selecting a segment of the time range for monitoring or further processing.
dB (Decibel)The fundamental unit of sound intensity. A logarithmic function of the ratio of the obtained amplitude to the reference amplitude.
Decibel (db)A unit used to express the intensity of amplitude of sound waves; does not specify voltage.
DensityConcentration of matter (mass per unit volume).
Doppler ShiftThe perceived frequency change that occurs dependent upon whether the source and listener are moving toward or away from one another.
Dynamic RangeThe ratio of maximum to minimum size of reflection area that can be adequately distinguished on the A-Scan display at a constant gain control.
EchoIndication of reflected energy.
EchogenicCapable of producing echoes. Correlate with the terms hyperechoic, hypoechoic and anechoic which refer to the quantity of echoes produced.
EcholucentWithout internal echoes; anechoic.
EchopenicFew echoes within a structure; less echogenic. Echo-poor.
Edge EnhancementAn electronic postprocessing function which makes contours of structures within the image more distinct and clear.
Electronic FocusingEach crystal element within a group is pulsed separately to focus the beam at a particular area of interest.
EnhancementBecause sound traveling through a fluid-filled structure is barely attenuated, the structures distal to a cystic lesion appear to have more echoes than neighboring areas. Also called through transmission.
Far field weldRefers to a weld where the distance between the contact surface of the horn and the weld joint is more than 1/4 inch. Ultrasonic energy is transmitted through the upper portion of the part to the joint surface.
Far GainControl that affects the strength of the distant echoes in the image.
Fast Fourier TransformAn iterative computer algorithm to perform the Fourier transform of digitized waveforms rapidly. A set of mathematical formulas used to convert a time function to a function in the frequency domain (Fourier analysis) and back (Fourier synthesis). The function is expressed as a convergent trigonometric series, similar to that first formulated by French mathematician Jean-Baptiste- Joseph, Baron Fourier (1768 to 1830). The Fourier transform is used extensively in signal processing to design filters and remove coherent noise. Many filtering operations are performed in the frequency domain.
FillerAn inert substance added to a resin to modify its physical properties.
Focal ZoneThe depth of the sound beam where resolution is the highest.
Focused BeamConverging energy of the sound beam at a specific distance.
FocusingThe act of narrowing the beam to a small width at a set depth.
FootprintShape of the transducer that is in contact with the patient.
Frame rateRate at which the image is refreshed in a real-time system display.
FrequencyThe number of cycles per second of a wave (i.e. sound wave), measured in cycles per second, or hertz.
Full Screen HeightThe highest point on an A-Scan display used for evaluation and recording purposes, designated as 100%.
Gain ControlA control, which varies the amplification of the ultrasonic system. Also considered the sensitivity control. Units are in decibels.
Gray ScaleDisplay mode in which echo intensity is recorded as degrees of brightness or shades of gray.
HertzUnit for wave frequency (cycles per second); pulse repetition frequency (pulses per second); frame rate (frames per second).
Hertz (Hz)A unit of frequency equivalent to the “cycle-per-second” (cps). One Hertz (1 Hz) equals 1 cps.
HeterogeneousRefers to an uneven echo pattern or reflections of varying echodensities.
HomogeneousRefers to an even echo pattern or reflections that are relative and uniform in composition.
HornAn acoustical tool that transfers mechanical vibrations from the transducer and booster to the parts to be assembled.
HyperechoicA relative term that refers to the echoes returned from a structure. Hyperechoic refers to a lesion or tumor which produces a stronger echo than surrounding structures or tissues.
HypoechoicRefers to structures that contain fewer or weaker echoes than surrounding tissues.
InterfaceThe boundary between two materials, which are in contact with each other.
IsoechoicRefers to a lesion or tumor which produces an echo of the same strength as that of the surrounding structures or tissues.
Kilohertz1000 hertz or 103 cycles/s
Kilohertz (KHz)A unit of frequency equivalent to one thousand “cycles-per-second” (cps). One Kilohertz (1 KHz) equals 1,000 cps.
Lateral ResolutionAbility to separate two objects that are positioned perpendicular to the axis of the ultrasound beam. Related to beam width.
Linear ArrayMany small electronically coordinated transducers producing a rectangular image.
Longitudinal Wave(Also known as a compression wave or “straight beam”) Wave propagation in which the particles of the medium in which a wave is traveling are disturbed or move in the same direction as the sound energy, e.g., sound moves left to right, particles move left to right. The wave is composed of compressions, where the particles are closer together than normal, and rarefactions, where the particles are farther apart than normal.
Megahertz (MHz)A unit of frequency equivalent to one million “cycles-per-second” (cps). One Megahertz (1 MHz) equals 1,000,000 cps.
Modulus of Elasticity(Young’s Modulus). A measure of the stiffness of a material, the MOE is the ratio of stress to strain in the elastic region of strain. It is measured in the same units as stress, that is, psi in English units or megapascals in the metric system. Steel has a modulus of elasticity of approximately 29,000,000 psi or approximately 200,000 megapascals.
Near field weldRefers to a weld where the contact surface of the horn is 1/4 inch or less away from the joint surface. It is important that the horn fits the exact contour of the part to be welded.
Near GainThe amplification of echoes returning from the near field.
Nodal pointThe point or points in a booster or horn where little or no linear motion occurs.
NoiseArtifactual echoes resulting from too much gain rather than echoes from true anatomic structures.
Overall Gain ControlSingle gain control that increases amplification at all depths.
PersistenceThe accumulation of echo information over a specified period of time.
Phased ArrayElectronically steered system where many small transducers are electronically coordinated to produce a focus wave front.
PiezoelectricHaving to do with systems driven by the effect of certain crystals, such as lead- zirconate-titanate, and other materials, which expand and contract in an alternating (charged) electrical field.
Piezo-Electric CeramicA material made of crystalline substance, which creates charges of electricity by the application of pressure and vice versa.
Piezoelectric EffectElectric current created by pressure forces. Certain types of ceramic materials can convert pressure to electricity and vice versa. Transducer elements utilize this phenomenon, which is also referred to as piezoelectricity.
Power DopplerThe presentation of two-dimensional Doppler information by color-encoding the strength of the Doppler shifts. Power Doppler is free of aliasing and angle dependence and is more sensitive? to slow flow and flow in small or deep vessels.
ProbeA sensing element used in non-destructive testing and measuring. Also known as transducer.
Pulse Repetition Frequency (PRF)The number of times per second that a transmit-receive cycle occurs.
Pulse-EchoA technique in which an ultrasonic transducer, in transmit mode, emits a high- frequency acoustic pulse towards the sample wall, where it is reflected back to the same transducer operating in receive mode. The measurement consists of the amplitude of the received signal, the time between emission and reception, and sometimes the full waveform received.
Pulse-echo PrincipalSending pulses of ultrasound into the body so that they react with tissue and return reflections.
ReflectionThe phenomenon by which a wave strikes a boundary and changes the direction of its propagation.
RefractionThe change in the direction of propagation of a sound wave resulting fro the passage of that wave from one medium to another medium having different acoustic properties. The change in velocity is accomplished by change in angular direction of propagation.
RepeatabilityIs a measure of how close a positioning system can return to a given starting point. To eliminate the effects of backlash and hysteresis, the actuator must approach the target position from the same direction, at the same speed and deceleration rate, and under the same load conditions.
ResolutionThe ability to clearly distinguish signals obtained from two reflective surfaces with a minimum difference in either depth, or spatially.
Resonant FrequencyThe frequency at which a piezo-electric ceramic will vibrate most efficiently i.e. will produce the highest output with the least amount of voltage applied.
ReverberationThe phenomenon of multiple back-and-forth reflections created by two strong reflectors that causes the echoes to be misplaced in the display thereby representing a false image; ring-down effect.
RingingAnalogous to the ringing of a bell, it is the rise and decay time before and after the transducer reaches maximum amplitude. Expressed as the mechanical Q of the transducer, which is the number of cycles it takes to get up to 90% of maximum amplitude, or down to 10% above zero amplitude.
ScanningThe moving of the transducer along a test surface to obtain complete testing of the entire volume of the material being tested.
ScatteringRedirection of ultrasound from a reflector which is small compared to the wave length of the beam. This occurs with rough surfaces or heterogeneous substances such as a solid organ.
SensitivityThe measure of the ability of the ultrasonic equipment to detect discontinuities.
ShadowingFailure of the sound beam to pass through an object.
Shear Wave (Also known as transverse wave or “angle beam”). Wave propagation in which the particles of the medium in which a wave is traveling are disturbed or move in a direction perpendicular (or “normal) to the direction of travel of the sound energy, e.g., sound moves left to right, particles move up and down or in and out.
Slice thicknessElevational resolution. The size of the beam perpendicular to the image plane.
SonodenseA structure that transmits sound poorly.
Spatial ResolutionHow closely positioned two reflectors can be to one another and still be identified as separate reflectors on an image display.
SpeckleInterference effects of the scattered sound from the distribution of scatterers in the tissue that is not related to the scattering properties of tissue (echo texture). Produces granular appearance.
Specular ReflectorsReflections from surfaces, which are smooth, compared to the wavelength of sound thereby creating a bright echo on the monitor.
StakingThe melting and forming of a plastic stud to retain or lock another material (often dissimilar) in place.
StiffnessResistance of a material to compression. Hardness.
SwagingUsed to capture another component of an assembly by melting and reforming a ridge of plastic around the component. The ridge locks the second component in place without welding the two materials together.
Temporal ResolutionThe ability of a display to distinguish closely spaced events in time and to present rapidly moving structures correctly. Improves with frame rate.
TextureThe echo pattern within an organ.
Thermoplastic resinsMaterial that can be repeatedly softened and reshaped with heat and pressure. They are ideal for ultrasonic welding.
Thermoset resinsMaterial that cannot be melted or reformed. Hard and brittle, they are not suitable for ultrasonic welding.
Through Transmission TestingA test procedure in which the ultrasonic vibrations are emitted by one transducer and received by another at the opposite surface of the material being tested.
Time Gain Compensation (TGC)or Depth Gain Compensation. Control that compensates for the loss (attenuation) of the sound beam as it passes through tissue.
Time-of- FlightTechnique for calculating the distance to a target by using the timing of the return echo from target utilizing the speed of sound in the medium between the two reference points.
TransducerIn ultrasonic testing, a device containing a piezo-electric material used for introducing vibrations into the material to be tested and receiving the vibrations reflecting from the material. The active element of the transducer is defined as the effective transmitting area.
UltrasonicA term referring to acoustic vibration frequencies greater than about 20,000 hertz.
Ultrasonic AbsorptionThe damping of ultrasonic waves as they pass through a medium. See attenuation coefficient.
Ultrasonic Simulation (UTSIM)A user interface integrating a CAD model representing a part under inspection and an ultrasound beam model.
Ultrasonic SpectroscopyAnalysis of the frequency content of an acoustic wave. Generally performed mathematically using a fast Fourier transform.
Ultrasonic SpectrumUsually, the frequency range from 20,000 to 107 hertz. But may extend much higher in special applications.
Ultrasonic TestingThe transmission of high frequency sound waves into a material to detect imperfections or to locate changes in material properties.
Ultrasonic VibrationsVibrational waves of a frequency above the hearing range of the normal human ear are referred to as ultrasonic, and the term therefore includes all those waves of a frequency of more than approximately 20,000 cycles per second. Also known as ultrasonic waves.
Ultrasonic WavesSound waves too high in frequency for humans to hear.
Ultrasonic WeldingAn assembly process in which parts are joined by the local application of pressure and high-frequency vibratory energy.
Ultrasonically Sound MaterialA material having no discontinuities which cause discernible ultrasonic indications at the required test sensitivity level.
UltrasoundA test using ultrasonic waves to create an image of the inside of an object.
Velocity (V)The speed at which the sound wave travels through the test material.
Water PathThe distance from the transducer to the test surface in immersion testing.
Wave TrainA succession of ultrasonic waves arising from the same source, having the same characteristics, and propagating along the same path.
WaveformThe shape of a wave, typically shown as a graph of amplitude (or other quantity of interest) versus time.
WavelengthFor a longitudinal wave, the distance from the start of one compression or rarefaction to the start of the next compression or rarefaction. For a shear wave, the distance between successive peaks in the perpendicular motion of the particles of the medium. Wavelength is defined as V/f . V = Material Velocity, f = Transducer Frequency.