Wideband Transducer for the Detection of Surface Displacement with High Spacial Resolution
Original Publication Date: 1994-Feb-01
Included in the Prior Art Database: 2005-Mar-26
Baier, W: AUTHOR [+2]
Disclosed is a device for measuring time dependent surface displacements, caused, for example, by the propagation of bulk or surface acoustic waves or acoustic pulses, with high spatial and temporal resolution.
Wideband Transducer for the Detection of Surface
High Spacial Resolution
a device for measuring time
displacements, caused, for example, by the propagation of bulk or
surface acoustic waves or acoustic pulses, with high spatial and
transducer consists of a thin electret film that is in
mechanical contact with the sample under study, a backing material to
press the electret against the sample at a well defined location, an
electric pick-up for the signal induced on the electrodes, and a
conductive enclosure for electric shielding. The spatial
resolution of the sensor is accomplished by shaping the backing
material in such a form that the electret touches the sample only in
the desired area. For a point transducer the backing material is
shaped like a needle, for a line transducer like a knife edge,
etc.. The temporal resolution of the transducer is then determined
by the transit time of acoustic waves across the contact area and
the time required to convert the mechanical deformation of the
electret into an electric signal.
shows a piezoelectric polymer film on
edge of a metal rod. The polymer film has a conducting material
deposited as an electrode on one side of the film. This electrode is
in electrical contact with the grounded metal housing that is
used for electrical shielding. The other side of the polymer film is
contacted by a conducting rod which is inside an isolating collar to
prevent electrical contact between grounded housing and signal
carrying components. A metal spring connects the conducting rod to a
coaxial connector and establishes the appropriate pressure for
acoustic coupling of the electret foil to the sample under study. A
suitable preamplifier can be incorporated in the housing.
transducer generates an electrical signal from
displacement of the sample by deforation of the piezofilm.
Poly(vinylidene fluoride) (PVDF) and PVDF-Trifluoroethylene
copolymers are used since they are soft, pliable and of high
piezoelectric activity. The side of the piezoelectric material that
contacts the sample has to be coated with a thin conductive film.
This film is in electrical contact with the ground...