Browse Prior Art Database

Wideband Transducer for the Detection of Surface Displacement with High Spacial Resolution

IP.com Disclosure Number: IPCOM000111393D
Original Publication Date: 1994-Feb-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 2 page(s) / 92K

Publishing Venue

IBM

Related People

Baier, W: AUTHOR [+3]

Abstract

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.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Wideband Transducer for the Detection of Surface Displacement with
High Spacial Resolution

      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.

      The 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.

      The Figure shows  a piezoelectric polymer film on the knife
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.

      The transducer generates an electrical signal from  the surface
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...