A - Scan		The response of the ultrasonic system display to the transmitter pulse (sometimes called main bang).
Amplitude		Acoustic center line of a search unit’s beam pattern ac defined by the locus of points of maximum sound pressure in the far field, and its extension into the near field
Angle Beam		Base to peak height of a signal produced from A- Wave
C - Scan		Particle motion of the material is essentially in the same direction as the wave propagation.
B - Scan presintation		Electroacoustical device for converting electrical energy into acoustical energy
Back Reflection		Region of the ultrasonic beam adjacent to the transducer (Fresnel zone)
Back Surface		The distance in the material from the surface of the test object to the depth at which a reflector can first be resolved
Beam Axis		The end of a reference block opposite of the entry surface
Beam Spread		Signal bouncing back from the far boundary of the part
Critical Angle		The spreading or bending of waves as they pass through an aperture or around the edge of a barrier
Crystal		Angle of incidence or refraction
Dead Zone		Incident angle of the ultrasonic beam beyond which a specific refracted wave no longer exists.
Diffraction		The piezoelectric element in an ultrasonic search unit.
Impeadance		Horizontal base line that indicates distance
Initial Pulse		Particle motion is perpendicular to the direction of propagation.
Far Field		Plan view
Near Field		Mathematical quantity used in computation of reflection characteristics at boundaries
Longitudinal Wave		Zone of the beam where equal reflectors give exponentially decreasing amplitudes with increasing dis- tance
Resolution		Presentation of Cross section view, Length, Reflectors and their relative position
Sensitivity		Divergence of the ultrasonic beam as the sound travels through a medium
Shear Wave		A measure of the smallest ultrasonic signal
Transducer		Separate indications from discontinuities having nearly the same range and lateral position