Inventors: J. Zhang and R.E. Newnham
PSU Invention Disclosure No.
2000-2325
Licensing Contact: Matthew D. Smith
Flextensional
transducers are generally small compared to the wavelength of sound in the
usable frequency range, usually near their first resonance frequency. The resulting acoustic radiation pattern is
nearly omnidirectional resembling an acoustic monopole. The “double-driver” cymbal, a directional
class V flextensional tranducer like the Moonie and Cymbal transducers, maintains
the advantageous features of conventional cymbal transducers, including thin
profile, small size, simplicity, ease of fabrication and low cost, while
introducing a new mechanism to project sound in one direction. The double-driver cymbal transducer is
a promising candidate as directional
underwater sound projectors in conformable arrays mounted on underwater
vehicles.
Researchers
at Penn State University’s Materials Research Laboratory constructed a 3x3
double-driver element array, which demonstrated that under optimal conditions
the array can provide a directional beam pattern with a front-to-back ratio of
more than 20dB. In the dipole mode of
the double-driver cymbal, the Transmit Voltage Response (TVR) showed two maxima
in opposite directions (front and back), but the phase of the TVR output from
one lobe is opposite to that from the other.
When combined with the omnidirectional mode, this can be used to
generate a directivity pattern which has only one maximum. If the output from the dipole mode is added
to the output from a monopole of equal transmitting voltage response, the
resulting beam pattern is a cardioid curve with a single maximum.
The
finite element analysis code ATILA was used in modeling the performance of the
double-driver cymbal transducer, particularly the vibration modes and the
calculation of the TVR and beam pattern.
A nearly omnidirectional and a dipolar beam pattern were obtained for
the monopole and the dipole mode and are consistent with the ATILA
prediction. The driving voltages and
phases for the cardioid mode at 20kHz was not a perfect cardioid pattern
but shows a very directional beam shape.
When the driving amplitude and the phase was slightly adjusted, a nearly
perfect cardioid beam pattern was obtained.
The
researchers demonstrated that a directional beam pattern can be obtained from a
double-dipper transducer which is much smaller than a wavelength. With this method, a directional pattern can
be obtained at virtually any frequency.
However, the TVR amplitude and phases of the double-dipper fluctuates
dramatically with frequency. As a
consequence, the calculated voltage ratios (amplitude and phase) at different
frequencies are dramatically different, suggesting unique driving conditions at
each frequency or a narrow working bandwidth.
This may complicate the driving electronic circuits, if the
double-dipper is used over a wide frequency range.