ABSTRACT
An ultrasonic wave propagates through a material as a
series of mechanical deformations as small volume ele-
ments are first displaced from their resting position then
return elastically.[1] Propagation therefore depends on the
amount of material in each volume element (i.e., density)
and the strength of the internal elasticity (i.e., modulus).
The deformations most commonly used in food sensing
occur parallel to the direction of wave propagation (i.e.,
longitudinal waves sensitive to the bulk modulus of the
material, Fig. 1) but can also occur normal to the direction
of propagation (i.e., shear waves sensitive to the shear
modulus, Fig. 1). (Other types of waves containing differ-
ent combinations of shear and longitudinal deformation or
waves trapped in surfaces are also possible but these are
very rarely used in food characterization.[1])
