E-18
ElektroPhysik
and through thermal expansion and other effects, may
begin to adversely affect the accuracy of measurements.
9.3
Measuring Laminated Materials
Laminated materials are unique in that their density (and
therefore sound-velocity) may vary considerably from
one piece to another. Some laminated materials may
even exhibit noticeable changes in sound-velocity across
a single surface. The only way to reliably measure such
materials is by performing a calibration procedure on a
sample piece of known thickness. Ideally, this sample
material should be a part of the same piece being
measured, or at least from the same lamination batch.
By calibrating to each test piece individually, the effects
of variation of sound-velocity will be minimized.
An additional important consideration when measuring
laminates, is that any included air gaps or pockets will
cause an early reflection of the ultrasound beam.
This effect will be noticed as a sudden decrease in
thickness in an otherwise regular surface. While this
may impede accurate measurement of total material
thickness, it does provide the user with positive indication
of air gaps in the laminate.
Application Notes
