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ABSORPTION

ABSORPTION

Description:

The component of ultrasonic wave attenuation resulting from conversion of ultrasonic energy into heat energy. absorption coefficient (linear) The fractional decrease in transmitted intensity per unit of absorber thickness. It is usually designated by the symbol µ or beta or alpha and is expressed in dB/m. It is sometimes referred to asattenuation. In literature, the absorption coefficient for longitudinal (compression) waves is usually listed. However the coefficient differs for transversal (shear) waves and is higher for these, especially in plastics.

Illustrations:

ABSORPTION

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ACCEPTANCE STANDARD

Description:

(1) A controlled specimen containing natural or artificial discontinuities that are well defined and, in size or extent, similar to the maximum acceptable in the product. (2) Also may refer to the document defining acceptable discontinuity size limits.
For automated testing the test part speed is an essential factor, hence the acceptance standard has to be tested dynamically. A test that will not accept any deviation in size will reject many perfectly good parts. In order to prevent this, the test itself must be tested.

Illustrations:

Specimen Example

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ACOUSTIC IMPEDANCE

Description:

Often used as the equivalent of characteristic acoustic impedance, a material property defined as the product of sound velocity and density of the material. The relative transmission and reflection at an interface are governed in part by the acoustic impedances of the materials on each side of the interface. The letter Z is used for the impedance and is expressed in [kg/s m²] = 1 Rayl. For water Z = 1.49 MRayls.

Illustrations:

Acoustic Impedance

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ACOUSTIC SHADOW

Description:

A region in a medium which cannot be reached by ultrasonic energy travelling in a given direction. Shadows are caused by geometry or the presence of intervening large discontinuities.

Illustrations:

Acoustic Shadow

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ACOUSTOGRAPHY

Description:

A relatively new option to model/assess ultrasonic transducer beams is a process called Acoustography. Acoustography is a full-field ultrasonic imaging process where a high resolution 2D Acousto-Optic (AO) sensor is employed to directly convert the ultrasound into a visual image in real time. Acoustic images can be formed in through transmission mode or in reflection mode where acoustic images can be formed using acoustic lens analogous to photography or video camera. The AO sensor converts ultrasound image directly into a visual image due to the inherent acousto-optic effect of a “mesophase” material contained in the sensor.

Illustrations:

Ultrasonic field of a 5MHz, 25mm diameter, disk-type unfocused transducer at various
distances from the radiating surface: (a) 1.65cm; (b) 3.0cm; (c) 6.75cm; and (d) 10.5cm

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ADVANCED DUAL ELEMENT PROBE TECHNOLOGY

Description:

Advanced Dual Elememt Probe Technology (ADEPT) and is a transmitter-reciever technique. In difference to the normal TR-technique, where transmitter and receiver are arranged in parallel with the same angle of incidence, the ADEPT elements are arranged in one row and transmitter and receiver have different angles of incidence

Illustrations:

Principle

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CALIBRATION BLOCK

Description:

A piece of material of specified composition, heat treatment, geometrical form and surface finished in such a way that the equipment can be assessed and calibrated. For contact transducers the calibration block should have properties and specifications as in calibration block EN 27963. The block contains side drilled holes and hemispheric holes of 3mm. For specific tests, methods such as Calibration block No.2 are available for ultrasonic examination of welds.

Illustrations:

Calibration Block

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