Note: Descriptions are shown in the official language in which they were submitted.
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Ultrasonic transducers method for fixin~ ~lltrasonic trans-
ducers and high output power ultrasonic transducers
The present invention relates to ultrasonic transducers and more
precisely to an ultrasonic transducer for such high power, as
well as to a method for mounting such ultrasonic transducers.
The use of ultrasonics to solve various technical problems has
very rapidly increased during the last decades. Among the
applications are e.g. technologies for space research, aviation,
communication, marine applications, applications in the auto-
motive and other industries, laboratory and medical applications,
gas lighters, nebulizers and alarm systems. The electromechanical
transducers most commonly used in said connections are using
piezoelectrical materials, which convert mechanical energy into
electrical energy or vice versa. The material can in addition be
polarized to change dimension merely horizontally, vertically or
radially depending upon which the desired effect is. Piezoelec-
trical properties exist naturally in certain crystalline
materials and can be made to exist in certain other polycristal-
line materials.
The most commonly used piezoelectrical materials for the
manufacture of ultrasonic transducers are based upon piezoelec-
trical ceramics manufactured from either leadzircontitanate (PZT)
or leadtitanate (PT). The ceramic material composition and the
manufacturing process can be adapted to fit the application in
order to achieve e.g. high power or high sensitivity. The ceramic
materials are delivered in the shape one prefers to use them,
e.g. in the form of circular discs or rings, square discs, tubes,
spherical elements etc. They can also be delivered in various
thicknesses depending upon what result one wishes to achieve.
The ceramic elements can either be glued directly onto the
structure one wishes to transmit the ultrasound to, or be used
for the manufacture of ultrasonic transducers, which in turn are
applied onto this structure. For the transmission of high power
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ultrasonic transducers are used where the ceramic part has been
precompressed by way of exposing it to a permanent compression
caused by that two metal parts with the ceramic between them are
compressed by means of one or several bolts which have been
tightened using a torque so large that the desired pressure onto
the ceramic part occurs. This design is generally referred to as
a "sandwich transducer".
The invention as well as the background thereo~ are more closely
described in the following with reference to the attached
drawings, in which
Figs. 1 and 2 are examples of sandwich transducers,
Fig. 3 is an example of a mounting of two ultrasonic
transducers,
Fig. 4 is a partially broken longitll~i n~l section through
an ultrasonic transducer also showing the mounting thereof
to a structure,
Fig. 5 is a cross-section through an alternative embodiment
of an ultrasonic transducer , and
Fig. 6 is a longitll~i n~l section through a ~urther em-
bodiment of an ultrasonic transducer.
Figs. 1 and 2 show examples of sandwich transducers in different
projections. The ceramic rings 3 are placed between the top metal
part 1 and the bottom metal part 2, which have been tightened by
means of the bolt 6, which in this case has been applied through
a hole drilled through the bottom metal part and into a drilled
and tapped hole in the top metal part whereafter it has been
tightened by means of an applied torque which has been calculated
so that the desired pressure is applied onto the ceramic rings.
Between the rings is a contact shim with a solder tag 4 used ~or
the connection to live and a corresponding shim with solder tag
5 between the ceramic ring and the metal part used for the
connection to neutral. When mounting the finished ultrasonic
transducers, these are glued onto the wall or bottom of e.g. a
tank used for ultrasonic cleaning. The reason why the bottom
metal part 2 in Fig. 2 has a conical shape is, that the contact
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surface is larger, and thus can transmit more ultrasonic energy
into the tank. Fig. 3 shows a mounting of two ultrasonic
transducers built up by that the bottom metal part 2 is an
aluminium plate common to both transducers which in turn is then
glued onto the bottom or walls of the tank as per above. In this
connection the bolts used for applying pressure onto the ceramic
rings are brought through two holes from the bottom side of the
common bottom plate and through the ceramic rings into the
drilled and tapped holes in the top metal part and tightened with
a calculated torque to arrive at the desired pressure onto the
ceramic rings.
The above mentioned design principle leaves us with three
different problem areas:
1. The structure of the transducer means that in certain
industrial applications the entire installation will have to be
encapsulated, so that there is no risk that a short circuit
occurs because of the presence of water or other liquids since
the solder tags as well as the ceramic rings themselves are
directly exposed to the ambient surroundings. This could in turn
mean that one, due to that risk of condensation in closed
chambers can occur, must install a continuous air purging using
moisture free instrument air. In a large number of the industrial
installations one has to expect that machine clean-ups are
carried out using high pressure wash appliance which puts
additional demand on the installation. The transducer design
therefore does not meet the demands one has to put on a trans-
ducer for industrial applications.
2. The way of mounting the transducers, where they are glued,
most often using epoxy glue reinforced with an aluminium mesh
onto the surface one wants to transfer the ultrasonic energy
from, creates large mounting difficulties when the fixing is done
in narrow areas and where the fixing has to be done from below.
Since the transducers are glued onto the surface, a faulty
transducer cannot easily be exchanged since the glue joint is
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very strong and can only be made to come off adding considerable
heat to it which degrades the epoxy. The necessary water tight
encapsulation as per 1. above is many times difficult to carry
out on already existing equipment. The glue joint reduces the
heat transfer from the transducers and in addition cuts down the
efficiency of ultrasonic transmission into the liquid.
3. To dimension the transducers gets to be very complicated.
In order to have the entire transducer to resonate at the desired
frequency, one has to consider the influence of the lengths of
the first metal section, the other metal section and the ceramic
section as well as of speeds of sound, the cross section areas
and the densities of these sections. The transmission of the
ultrasonic wave and dissipation of heat from the first metal
section to the other metal section and further on into the liquid
is only done by means of the bolt which clamps the two sections
together and then only by means of the pressure from the bolt
head and the other metal section, which further reduces the
efficiency and contributes to raise the transducer temperature.
The above mentioned three problems constitute major limitations
for the possibilities to carry out an installation in a large
number of industrial applications. It has therefore been regarded
necessary to redesign the transducers and the way of mounting
them in order to meet the following specifications:
1. The transducer must be designed so that it is submersible
and is sealed so that it in itself is completely gas and liquid
tight and is to be mounted in such a way that it can be subjected
to high pressure cleaning without any risk of damage and
breakdown.
2. The transducer must be designed in such a way that it
consists of only one single metal housing with encapsulated
piezoelectrical elements so that one gets only one resonating
unit and thus avoids the necessity to fit the dimensions of each
single resonating element to be in common resonans with all the
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others at the same time and without any phase displacement of the
frequency between the different elements.
3. The efficiency for generating and transmitting of ultrasonic
energy must be as high as possible and offer more ultrasonic
transmission e~ect per contact surfac than does the present
transducer technology.
4. The transducer must be designed and mounted in such a way
that the cooling of the transducer is so good that the increase
of transducer temperature is as little as possible.
5. The method of mounting the transducer must be based upon
direct metal to metal contact electrically as well as accous-
tically and offer possibilities to a service based upon modular
exchange of transducers.
6. Transducers and method of mounting them must be adapted to
one another in such a way that the distribution of ultrasonic
energy into the liquid is as large as possible and so that no
harmful concentrations of ultrasonic energy, so called "hot
spots" will occur but that the ultrasonic energy will function
in the same way and with the same concentration in the entire
volume of the liquid.
TRANSDUCER DESIGN AND METHOD OF TRAN~U~'~ MOUNTING
The transducer and the method of mounting the same must be
individually designed in a way that they together function as one
single unit in order to meet the above mentioned specifications.
The transducer must have metal to metal contact between the
different transducer elements and for external mounting they are
fixed together with metal to metal contact into a fixing ring
which in turn has been welded onto the surface which constitutes
the base of the transducer installation.
Fig. 4 shows an example of a cross section side-view of such a
structure. The transducer consists of a core 1 located inside a
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bottom vessel 2 with two circular piezoelectric ceramic discs 3
with a contact shim with a solder tag 4 between them for cable
connection to the generator live connector via the milled and
drilled hole 5 through the core. By securing total metal-ceramic
contact when pressure is applied to the ceramic discs which are
silver coated, the connection to the generator common can be
accomplished via the metal parts of the transducer. The bottom
vessel 2 is threaded in the bottom part in order to allow for
screwing same into the threaded mounting ring 6 when fixing the
transducer during the mounting. The bottom vessel 2 is also
threaded at the top end to allow for screwing same into a
threaded connector part 7 to allow for connecting several
transducers together and for securing protected cable connections
of the entire transducer assembly. A hole 5 has been drilled
through the transducer core from the location of the solder tag
of the contacts shim to the top center of the transducer core to
allow for cable connection to the generator and thereafter one
arranges total electrical insulation between the cable core and
the transducer metal parts.
After cabeling and insulation the drilled hole is filled with
epoxy or a similar type of sealing material in such a way that
a complete sealing is achieved. The dimensions of the core 1
outside and the bottom vessel 2 inside diameters are selected
such to each other that they can be regarded as one single metal
part after one has been fixing them together by shrinking,
welding or by another suitable fixing method.
After one has fixed the piezoelectric discs 3 with the contact
shim with cable connection between them to the bottom part of the
core 1, the cable is brought through the drilled hole 5 in the
core 1 with insulated cable connection and cable, the core 1 is
chilled by exposing it to e.g. liquid nitrogene. The core 1 is
then positioned inside the bottom vessel 2 in a hydraulic press,
where the two parts are pressed together with a pressure so high,
that the desired precompression of the ceramic will occur. This
can be controlled by means of a load cell mounted in the
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hydraulic press. As a safety precausion, the electrical voltage
emitted by the piezoelectric ceramics 3 when exposed to a
pressure is measured. Should it divert substantially from what
is normal, it is probably due to that the ceramic discs 3 do not
meet specifications and the manufacture o~ this transducer is
abandoned. When the core 1 and the bottom vessel 2 have been
shrunk together, they will be fixed together maintaining the same
pressure by means o~ welding, pins, screws or the like, so that
the desired pressure against the ceramic discs 3 will be
maintained after that the transducer has been removed from the
hydraulic press. After the transducer has been Lel~lo~ed from the
hydraulic press, the drilled hole 5 is filled from the bottom of
the hole with a suitable sealing material e.g. epoxy. Since the
transducer parts have been ~ixed together under a predetermined
pressure, constant and repeatable transducer properties per
tranducer type is secured.
When mounting the transducer, the mounting ring 6 is first welded
onto the plate wall through which one desires to transmit the
ultrasound into the liquid. Into the bottom of the cup formed
that way, one applies an adhesive with a high content of a metal,
e.g. colloidal silver. This is done to secure a very good metal
to metal contact between the transducer and the plate despite the
uneven surface of a product such as a welded stainless steel
container. After that, the transducer is screwed into the
mounting ring using a torque which secures that this contact is
achieved and the connector part screwed onto the top part of the
bottom vessel, the transducer cable will be connected to the high
tension cable. All cable parts, both supply cable and transducer
cables are enclosed within protecting pipes with sealed pipe
connections and the transducer installation is completed. After
that, all transducers for the installation are installed in the
same way and the entire system installation is ready with
completely sealed transducers and all cable connections protected
by pipes dimensioned so that the entire installation can be
exposed to high pressure cleaning without risk of damage.
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If one wishes to manufacture a submersible unit made up by
several transducers, they are connected in the same way via a
connector pipe and with cables protected by pipes as per above.
The connector pipe 7 showed in Fig. 4, has been shown in a T-
shaped form for connection of one single transducer but can as
well be manufactured for connecting several transducers to it.
If e.g. one has four transducer connections per connector pipe,
one can have a submersible unit which emits ultrasonic energy in
all four directions, which can be a great advantage e.g. in an
installation into a tank with large diameter and height.
Submersible transducers will preferably be manufactured out of
acid-proof materials, whereas transducers for external mounting
generally will be manufactured out of dural, since this material
transfers heat away from the transducer much better than does
acid-proof materials. Transducers for external mounting in
corrosive environment will of course also be manufactured out of
acid-proof materials.
Another solution to the transducer design is shown in Fig. 5,
where one as the piezoelectric element has used a piezoelectric
ceramic pipe 1 coated in- and outside with silver. This pipe has
been precompressed by positioning it between an inside pipe 2 and
an outside pipe 3, where the diameters 4 and 5 have been
dimensioned in such a way that one by cooling the inner pipe 3
and heating the outer pipe 2 arrives at a desired precompression
onto the ceramic pipe 1, after that the temperatures of the
elements have arrived at ambient or operation temperature. In
such a way one can, by mounting several ceramic segments between
long inner and outer pipes before the shrink compression is done,
build together long transducer units where one can arrive at very
high output power per transducer unit.
Fig. 6 shows a length section of such a structure where a number
of ceramic rings 1 with radial polarization have been positioned
between an outer pipe 2 and an inner pipe 3. Each transducer end
wall 4 which preferably is manufactured out of stainless steel,
can be manufactured to make sure that the end connections are
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completely water and gas tight by means of welding, O-ring seals
or the like. This manufacturing method thus allows for the
manufacture of completely gas and water tight transducers very
well suited as submersible ultrasonic units. Only two electrical
connection points with connectors 6 and 7 are used on the inner
pipe 3 and the outer pipe 2 and the emission will be radially
outwards for submersible units. If the polarity is shifted, the
ultrasonic power will be transmitted radially inwards to be used
for e.g. deaeration, sterilization, homogenization and improved
reactivity between different substances in a liquid pumped
through the open area 8 inside the inner pipe. If the transducer
unit is intended to be used for radiation outwards, the open area
8 inside the inner pipe will have to be used for the circulation
of a cooling medium since the energy added to the inner pipe via
the ceramic pipe will cause a temperature increase of pipe and
ceramic and will have to be transferred away since it should
otherwise increase the temperature of these parts to an unaccep-
table level.
Since the transducer unit is manufactured in the form of a
cylindrical bar, the ultrasonic energy for submersible units will
be emitted radially outwards, which means that the ultrasonic
energy will be evenly distributed within the surrounding liquid.
Point 6 of the transducer specification where this need has been
identified has therefore been met in an ideal way. It offers
possibilities to work with very high output power. If one uses
ceramic rings with an outside diameter of 76 mm and with a wall
thickness of 6,35 mm, a submersible unit could emit 10 kW and
maybe up to 20 kW per meter transducer unit. For transducer units
with transmission radially inwards, one reaches very high
ultrasonic effect into the liquid pumped through the pipe even
at very high rate of flow. This opens up completely new possibi-
lities for the use of ultrasonic energy in industrial processes.
These levels of output power are completely impossible to achieve
using the present ultrasonic transducers as per Fig. 1-3, which
are normally limited to max 200 W and it therefore constitutes
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a completely new thinking within the ultrasonic ~ield of
technology.
The above mentioned transducer structure is not limited to com-
pletely round profiles but can of course be used for all shapes
of profiles, elliptical, quadrangular, hexagonal etc. where the
ceramic part has a hole inside it so that by shrinking can
achieve a precompression of the ceramic, so that it can be used
for high power output installations. Several areas of application
have been mentioned on page 1 of this document but the technology
which has been described in this patent will make many other
applica~ion areas possible. The expert in the matter can find
many other areas of application for this high power technology
but these are intended to be within the scope of this invention.
