Alin Iuga, Elena Dimitriu

1
 Alin Iuga, Elena Dimitriu RD National
Institute for Materials Physics
High efficiency ultrasonic siren
GOAL ULTRASONIC SIREN
Two PZT disks manufactured from ceramic with a
high lateral coupling coefficient are assembled
in an antiparalel bimorph. The radial mode is
thus converted into a lower flexural one and the
acoustic impedance of the disks is increased. In
order to increase further the acoustical coupling
with the air an aluminium extruded cone is
fastened to the center of the bimorf. The result
is a simple, robust, reliable, easy to handle,
insulated from corrosion siren which driven at
resonance with an alternative e.m.f. provides an
incredibly large ultrasonic output. This siren
can be used in intruder alarm devices, ultrasonic
telemeters, rat and dog deterrents, etc. The
PZT-type material used is MPT011, with
un-compensating valence substitutions, prepared
by the ceramic technique. The microstructure of
the sintered material at 1280oC was performed by
scanning electron microscopy (SEM) and by ? - 2?
X-ray diffraction. Dielectric and piezoelectric
properties were measured. The good planar
properties of the material enable to obtain
ceramic disks with a strong radial mode.
(1) The manufacture of the PZT bimorph
(2) Acoustic radiator
(3) The manufacture of the siren
Ultrasonic siren

• The bimorph disk and the conical radiator -
  assembled together using epoxy resin and an
  adequate holder.
• The device has a cylindrical symmetry and the
  center of the bimorph is used for fastening with
  the radiator.
• Electrical contacts with thin flexible wires
  have been realized on the exterior nickel
  electrodes by electrical soldering.
• The entire assemble is fastened into a holder
  using the lateral edge of the acoustical radiator
  using a rubber o-ring and assuring that the
  bimorf can oscillate freely and the frontal
  radiated acoustical energy can move unimpeded in
  the outer space.

• Manufacturing two PZT disks (12 mm diameter and
  1.7 mm thick) with nickel electrodes , poled in
  a hot silicon oil bath.
• Cleaning the disks
• Fastening together in an antiparalel geometry
  using conducting epoxy resin ? an antiparalel
  bimorph disk (12 mm diameter and 3.4 mm thick).

Extruded aluminium cone (150 ?m thickness)
radius 35 mm height 10 mm external edge
5 mm wide
The sketch of the siren. (1) the PZT antiparalel
bimorph (2) the conical acoustic radiator (3)
insulating o-ring.
ACOUSTIC FIELD DISTRIBUTION
The polar representation of the acoustic field
distribution at 30 cm from the transducer. A four
lobe field is produced due to the conical
acoustical radiator with very small rear
radiation. A very high acoustical output of 140.6
dB is measured at the main resonance i.e. at 43
kHz. The spectrum of the transducer is 2.6 kHz
wide with a relative bandwidth of 6 ?, i.e. an
acoustical Q number of 15.
FREQUENCY RESPONSE OF THE SIREN
MICROSTRUCTURE
The frequency response of the siren in dB. The
principal resonance due mainly to the bimorph can
be seen at 43 kHz. There are also secondary modes
due to the reflections in the acoustical radiator
PHYSICAL PROPERTIES OF THE MATERIAL
The polar distribution of the ultrasounds output
was measured. A four lobes acoustical field has
been found, occupying mainly the 180? in the
front of the transducer. Electrical impedance
measurements have pointed out as expected a
multimodal spectral configuration, which was due
to the reflections induced by the conical
radiator, which are occupying the region between
42 and 47 kHz. Nevertheless the 43 kHz resonance
due to the bimorph disk is the dominant one
SEM pattern of a sample of material MPT01
REFERENCES
1E.Dimitriu, P.Nicolau, V.Teodoru ,
Ultrasunetele - Utilizarea in industria
alimentara si biologie, Editura CERES,
Bucuresti, 1990 2 Berlincourt D.A., Curran
D.R. and Jaffe H. (1964). Piezoelectric and
piezomagnetic materials, Physical acoustics
principles and methods, Vol. I-part A, Warren P.
Mason, (Academic Press, London), pp.228-233.  3
Jaffe B., Cook W. R. Jaffe H. (1974),
Piezoelectric Ceramics, Acad. Press London and
N.Y.  4 Szilard J, Ultrasonic Testing, A.
Willey-Interscience Publication 1982  5 van
Randeraat J., Setterington R. E., Piezoelectric
Ceramics,(Philips Appl. Book), Mullard
Ltd.(1974)  6 Krautkrämer J., Krautkrämer H.,
Ultrasonic testing of materials, (1969),
(Springer Verlag, New-York), pp. 141-151
CONCLUSION
An ultrasonic siren with very high output can be
constructed in a simple way, using PZT disks with
a high planar coefficient. An antiparalel bimorph
made from such disks and equipped with a suitable
energy radiator constitutes a high efficiency
ultrasonic transducer with a well shaped
acoustical field and a broad band response, which
can be used in the making of animal deterrents,
intruder alarms, etc.
Sinteza, proprietatile si caracterizarea
nanomaterialelor cu aplicatii in sensori Sinaia,
ROMANIA, 2003