Elizabeth A. McLaughlin
George J. Kavarnos
Naval Undersea Warfare Ctr., New London Detachment, New London, CT 06320
A high-frequency projector was fabricated using solvent-cast piezoelectric
polyvinylidene trifluoroethylene P (VF[sub 2]/EF[sub 3]) copolymer film. It has
a higher electromechanical coupling factor, (k[sub T]~0.3) [Ohigashi and Koga,
Jpn. J. Appl. Phys. 21 (8), L455--457 (1982)], than P (VF[sub 2]) homopolymer
and it does not require stretching to align the polymer chains. 75% P(VF[sub
2]/EF[sub 3]) copolymer dissolved in methyl ethyl ketone was cast into a 200-to
300-(mu)m sheet, annealed at 130 (degrees)C, and slow cooled. A thin layer of
conductive metal was sputtered onto either side of the copolymer. The metalized
film was subsequently poled in a heated oil bath in the thickness direction.
The samples (6.5 cm[sup 2]) were tested with and without brass electrodes. The
brass brought the resonance frequency down to the 700-kHz range. Measured
parameters included coupling, quality factor, piezoelectric constant, and
transmit voltage response. The transducer was modeled using a modified Mason
equivalent circuit, which is similar to that demonstrated by Brown and Carlson
[IEEE Trans. Ultrason. Ferroelec. Freq. Control UFFC-36, 313--318 (1989)].
Measured and calculated parameters are compared with values obtained for
representative P(VF[sub 2]) homopolymer.