Re: questions (shear waves, air-coupled, lamb waves) contact transducer excite the signal in the plate???
: I suppose that the contact transducer creates Lamb waves. What is the difference between that the crystal of the contact tranducer works in shear or longitudinal mode for the created Lamb waves???
: No more questions for the moment. I apologise in some of the questions is too much evident or elemental but I am a few worried about them. Thanks a lot in advance to any kind of help, and sorry for my English.
: My e-mail is firstname.lastname@example.org
------The following are my answers:
1. Is possible to generate shear waves in a plate with air-coupled
The term Aircoupled transducer usually is reserved to a piezoelectric
crystal which transmits ultrasound through an impedance matching layer(s).
Since the transmission can be made in an angle, therefore shear wave can be
induced. However, any transmission through an interface can induce both
longitudinal and shear modes. Angulation issues needs to be taken into
account if you try to excite the shear mode only.
And pure longitudinal waves??
Pure longitudinal mode will produced when transmitting normal to a
structure (thru liquid or air coupling).
2. The theory that I have know about Lamb waves handle displacements in a
plane perpendicular to the plate, in other words plane strain. However a
contact transducer creates wave travelling in all directions all the plate.
How should I modify my theory to explain the shear and longitudinal Lamb
You need to include a geometric-spread factor to account for the contact
How a contact transducer excite the signal in the plate???
If a contact transducer is coupled to a plate and induces wave in an angle
there are frequencies which support the excitation of plate wave modes.
By theoretically driven the dispersion curves you can predict the necessary
angles and frequencies.
I suppose that the contact transducer creates Lamb waves. What is the
differencebetween that the crystal of the contact transducer works in
shear or longitudinal mode for the created Lamb waves???
Contract transducers can induce normal to the surface both pure shear and
pure longitudinal. The specific mode depends on the type of crystal that
excites the wave as well as the coupling material that you are using
(burned honey and other viscous pastes support shear mode). To induce
plate waves, the material thickness, the wave incidence angle and frequency
need to support plate waves as determined from the dispersion characteristics.