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JP2009069153

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DESCRIPTION JP2009069153
The disadvantages of the known ultrasound sensors are at least partially avoided. A thin and
relatively soft solid intermediate layer is provided between an ultrasonic transducer and an
ultrasonic window of a casing, and the surface of the ultrasonic window in contact with the solid
intermediate layer has a predetermined roughness. Force is applied to the ultrasonic transducer,
the material of the solid intermediate layer and the ultrasonic window, the predetermined
roughness of the surface of the ultrasonic window, and the force, the solid intermediate layer is
at least plastic The deformations are mutually adjusted so as to be in intimate contact with the
ultrasonic window of the casing. [Selected figure] Figure 1
Ultrasonic sensor
[0001]
The present invention relates to an ultrasonic sensor, in particular to an ultrasonic flow meter,
comprising a casing and an ultrasonic transducer arranged in the casing. An ultrasound signal
can be generated and / or detected by the ultrasound transducer, and an ultrasound signal can
be transmitted and / or received from the ultrasound transducer through the ultrasound window
of the casing.
[0002]
The ultrasound sensors mentioned at the outset are previously known and are used, for example,
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in the field of ultrasound flow meter method technology. In the present invention, the use of the
ultrasonic sensor in the field is not important, but the teaching of the present invention described
below can be applied to many different ultrasonic sensors.
[0003]
In the case of the ultrasound sensors in question here, the best possible connection between the
ultrasound transducer and the ultrasound window of the housing is of crucial importance. The
“as good as possible” connection is transmitted from the ultrasonic transducer, on the one
hand by the surface of the ultrasonic transducer and on the other hand by the contact surface
formed by the surface of the ultrasonic window as large as possible. It means that the ultrasound
signal to be transmitted, or the ultrasound signal to be received by the ultrasonic transducer, can
propagate through the aforementioned contact surfaces as unobtrusively as possible. The
acoustic coupling between the ultrasonic transducer and the ultrasonic window is limited if the
contact surface is not well formed and an air pocket is present between the ultrasonic transducer
and the ultrasonic window Be done. Because at the interface with air the ultrasound signal is
substantially reflected and thus may not be transmitted from the ultrasound transducer to the
ultrasound window and vice versa from the ultrasound window to the ultrasound transducer It is.
[0004]
It is known from the prior art, for example, to use an adhesive to bond the ultrasound transducer
and the ultrasound window to one another. In this case, the known adhesives used often have
little stability to the influence of heat, and in particular are vaporized under the influence of heat,
as a result of which inside the adhesive It is a problem that air pockets with undesired air
interfaces occur, which have the negative effect as described above with respect to the
transmission capability of the ultrasound signal. Furthermore, it is also disadvantageous that the
ultrasonic transducer may be completely peeled off from the ultrasonic window or casing due to
the reduced stability of the adhesive due to the heating effect. Furthermore, since the adhesive
loses its function even at very low temperatures, such as so-called low temperature applications,
ultrasonic sensors to which ultrasonic transducers are attached frequently have a limited
temperature range, for example from about -40 ° C. It has been found that it can only be used in
the temperature range of + 150 ° C.
[0005]
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It is likewise known from the prior art that a wet bond between the ultrasonic transducer and the
ultrasonic window of the casing can be established using, for example, an oil-based liquid. With
regard to such wet bonding and for high temperature applications and low temperature
applications, substantially the same as in the case of bonding with the aforementioned adhesive
applies. The liquid used is not stable at high temperatures, for example it vaporizes and loses its
ability to mediate contact at very low temperatures.
[0006]
For example, from Patent Document 1, the ultrasonic transducer is thermally separated by the
ultrasonic waveguide, and thus the connection point between the ultrasonic transducer and the
ultrasonic waveguide is also thermally separated. It is known that the sensor can also be used for
high temperature applications and low temperature applications. However, the use of ultrasound
waveguides raises the problem that additional signal propagation times have to be taken into
account in ultrasound sensors, which lead to additional inaccuracies of the measurement.
Particularly in low temperature applications, unwanted heat may be applied to the measurement
medium via the ultrasound waveguide, which may result in changes in the medium that have a
significant effect on the measurement. For example, when contacting with liquid nitrogen having
a boiling point of about -196 ° C at atmospheric pressure, bubbles are generated very rapidly at
the end of the ultrasonic window or the end facing the medium of the ultrasonic waveguide. This
again reduces the transmission of the ultrasound signal significantly. DE 100 21 117 C1
[0007]
The object of the present invention is to at least partially avoid the disadvantages of the known
ultrasound sensors as described above.
[0008]
The problem is that a thin and relatively soft solid intermediate layer is provided between the
ultrasonic transducer and the ultrasonic window of the casing, and the surface of the ultrasonic
window in contact with the solid intermediate layer has a predetermined roughness. Force is
applied to the ultrasonic transducer, the material of the solid intermediate layer and the
ultrasonic window, the predetermined roughness of the surface of the ultrasonic window, and the
force, the solid intermediate layer is at least plastic The deformation is solved by being mutually
adjusted to be in intimate contact with the ultrasonic window of the casing.
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[0009]
The thin, relatively soft solid intermediate layer is fixed as a medium that mediates between the
ultrasonic transducer and the surface of the ultrasonic window inside the casing simply by the
application of force to the ultrasonic transducer. If a suitable material is selected for the
intermediate layer, the known temperature sensitivity of the adhesive connection or liquid
connection between the ultrasonic transducer and the surface of the ultrasonic window is
reduced.
However, this measure alone does not guarantee that the contact area generated between the
solid interlayer and the surface of the ultrasound window is as large as practically possible and
thus particularly well suited for ultrasound transmission.
This is because the interface between the remaining solid and air, ie, the transition from the solid
interlayer to the air or the surface from the surface of the ultrasonic window to the air, is as
small as possible.
[0010]
According to the knowledge known from the prior art on the formation of a contact surface
between two interfaces consisting of different materials with different material properties
(Young's modulus, hardness) and geometrical surface properties (roughness) For example, the
tendency to form a contact surface between such materials can be represented, for example, by
the plastic property value ψ. The plastic property value ψ can be defined, for example, by the
following equation according to a known model for the contact between rough surfaces.
[0011]
In the above definition of the plastic property value E, E is Young's modulus, K is a hardness
constant depending on Poisson's ratio of a soft material, R is a radius of curvature of the uneven
portion of the surface, and σs is the uneven surface. Represents the standard deviation of a part.
A more detailed description of the above relationship may be found, for example, in Kogut, L., et
al. Et al. "An improved elastic-plastic model for the contact of rough surfaces" 3rd Aimeter
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International Tribology Conference, 2002.
[0012]
The plastic property value ψ is represented by the first term solely dependent on the size of the
material, ie the parameters E, K and H, and the second term dependent on the characteristic
index of the geometrical surface, ie σs and R Ru. The combination of a surface formed by a
material having a predetermined material property index and having a predetermined geometric
surface property into one contact surface is applied when a predetermined force is applied to
press the two surfaces together. Represents the ratio of the contact surface obtained between
these two surfaces.
[0013]
In surface combinations having a small plasticity value ψ, the contact surface obtained when the
forces pressing the surfaces against one another are increased greatly, whereas in the surface
combination having a relatively large plasticity value ψ. There is only a slight increase in the
actual contact surface between the surfaces when the force pushing the surfaces together is
likewise increased. With respect to values of plastic property values above 8, the contact between
the surfaces is completely plastic and does not depend on this plastic property value.
[0014]
According to the above relationship, it is possible to select between the two surfaces, ie in the
present invention between the surface of the solid interlayer and the surface of the ultrasonic
window, that is to say, freely predetermined for these surfaces, In order to achieve as large a
contact surface as possible when applying a constant force, the plastic property values must be
adjusted as small as possible. By selecting on the one hand a material having the lowest possible
Young's modulus and on the other the highest possible hardness, as well as the lowest possible
roughness of the surface, ie the lowest possible roughness of the surface irregularities The
standard deviation and the radius of curvature of the surface asperities as possible should be
adjusted by choosing the material. That is, in the case of the case considered here, the surface of
the ultrasonic window inside the casing should be as flat as possible, and the material of the solid
interlayer should have as low elasticity as possible. It does not.
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[0015]
However, according to the teachings of the present invention, the surface of the ultrasonic
window inside the casing does not have as little roughness as possible, but is larger if it has a
predetermined preset roughness. It has been found that a good ability for ultrasound
transmission between the contact surface and thus the solid interlayer and the ultrasound
window can be realized. In the usual case, this roughness, i.e. the presence of predetermined
irregularities on the surface of the ultrasonic window made of a harder material than a thin,
relatively soft solid interlayer, made the surface of the ultrasonic window sharp. The asperities
generate a stress in the solid intermediate layer when a predetermined force is applied, and this
stress exceeds the yield point of the relatively soft solid intermediate layer. The solid interlayer is
also in intimate contact with the ultrasonic window of the casing, at least by plastic deformation.
[0016]
The force that can be maximally applied to the ultrasound transducer is defined by the stability
of the ultrasound transducer material. That is, due to the maximum force applied to the
ultrasonic transducer, inside the ultrasonic transducer, it is necessary to generate only a stress
below the fracture limit of the material used for the ultrasonic transducer. Ultrasonic transducers
are usually manufactured from piezoelectric crystals. The surface of the ultrasonic window is
roughened in certain materials for solid interlayers and generally relatively hard ultrasonic
windows, this roughness having minimal values as taught in the prior art Instead of having a
relatively large value according to the invention, this value results in a relatively large contact
surface between the solid interlayer and the ultrasonic window.
[0017]
Taking into account all these peripheral conditions, the plasticity characteristic value ψ of the
contact surface between the ultrasonic transducer and the ultrasonic window of the casing in an
advantageous embodiment of the invention lies in the interval [0-8]. That is, the plastic
characteristic value ψ is in a region where the contact surface obtained between the two
surfaces further changes with the change of the plastic characteristic value 際 when a
predetermined force is applied.
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[0018]
According to another advantageous embodiment of the invention, the plasticity value ψ between
the ultrasonic transducer and the ultrasonic window of the casing is as small as possible, which is
particularly small on the surface of the ultrasonic window. Roughness is achieved, in particular
by a slight standard deviation of the irregularities of the surface of the ultrasonic window and /
or on account of the large radius of curvature. However, the roughness can not be reduced
arbitrarily. This is because, according to the invention, a predetermined minimum roughness has
to be maintained in order to guarantee a maximum contact surface and thus a good ultrasound
transmission.
[0019]
According to another advantageous embodiment of the invention, the contact surface between
the solid intermediate layer and the ultrasonic window of the casing is based on the plastic
deformation of the solid intermediate layer which is achieved by applying a predetermined force.
It is as large as possible, particularly preferably the largest. Here, instead of achieving a contact
surface that is larger than would be conceivable in the configuration of the surface according to
the prior art ("flat as possible" constant surface, "soft as possible" counterpart material), two
surfaces An optimal configuration of the contact surfaces between is achieved.
[0020]
According to another particularly advantageous embodiment of the invention, the solid
intermediate layer is composed of a material which remains in the agglomerated “solid” state,
for example in the temperature range of −200 ° C. to + 300 ° C. This temperature zone is
between the ultrasound transducer and the ultrasound window of the casing and corresponds to
the temperature zone at which the known interlayer of adhesive or liquid ceases to function for
the transmission of ultrasound signals. In this connection, it has proved particularly
advantageous if the solid intermediate layer consists of a metal or metal alloy, in particular silver,
gold or platinum. Overall, gold is particularly suitable for achieving a good contact surface for
transmitting ultrasound signals.
[0021]
According to another advantageous embodiment of the invention, the solid interlayer is thinner
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than 1/10 of the wavelength of the ultrasound signal to be transmitted in the propagation
direction of the ultrasound signal, whereby the energy loss is reduced Very little due to the
transmission of ultrasound signals through, and generally less important for signal transmission.
[0022]
In particular, there are various possibilities for constructing and developing the ultrasound
sensor according to the invention.
This is described in the dependent claims and in the following description of the preferred
embodiments with reference to the drawings.
[0023]
The sole figure shows an ultrasonic sensor 1 according to the invention with a casing 2 and an
ultrasonic transducer 3 arranged in this casing 2. An ultrasound signal can be generated and / or
detected by the ultrasound transducer 3, and the ultrasound signal from the ultrasound
transducer 3 can be transmitted and / or received through the ultrasound window 4 of the casing
2. Can. The ultrasound window 4 of the casing 2 is simply a region of the casing 2 which
transmits ultrasound signals to the medium (not shown) in contact with the casing 2. The
ultrasound window does not have to be configured in a special way in accordance with the
material or geometrically; for example, in the example shown, this ultrasound window is used as
an ultrasound transducer 3 and a casing 2 It can be easily configured in a geometrical connection
between the media in contact with the. In the illustrated ultrasonic sensor 1, a thin and relatively
soft solid intermediate layer 5 is provided between the ultrasonic transducer 3 and the ultrasonic
window 4 of the casing 2. Since the surface of the ultrasonic window 4 in contact with the solid
intermediate layer 5 has a predetermined roughness, and a force is applied to the ultrasonic
transducer 3, the ultrasonic transducer 3 is a solid intermediate The layer 5 is pressed against
the ultrasound window 4 inside the casing.
[0024]
The material used for the ultrasonic window 4 and the solid intermediate layer 5, the
predetermined roughness of the surface of the ultrasonic window 4, and the force applied to the
ultrasonic transducer 3 are such that the solid intermediate layer 5 is at least plastic They are
mutually adjusted so as to be in close contact with the ultrasonic window 4 of the casing 2 also
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by deformation.
[0025]
Unlike the dry connection between the ultrasound transducer 3 and the ultrasound window 4
known from the prior art, the roughness of the surface of the ultrasound window 4 is not
configured as small as possible, When a predetermined force is applied to the ultrasonic
transducer 3, the predetermined roughness is to ensure that the solid intermediate layer 5 is in
close contact with the ultrasonic window 4 of the casing 2 also by at least a plastic deformation.
A contact surface is provided between the ultrasound transducer 3 and the ultrasound window 4
that is larger than in the case where the surface of the ultrasound window 4 of the casing 2 is as
flat as possible. .
This is because in order to generate mechanical stress above the yield point of the material
constituting the solid intermediate layer 5 inside the solid intermediate layer 5 when a
predetermined force is applied. It is due to the fact that the desired roughness of the surface of 4
is necessary.
[0026]
In the illustrated ultrasonic sensor 1, the above-mentioned plastic characteristic value ψ of the
contact surface between the ultrasonic transducer 3 and the ultrasonic window 4 of the casing 2
is approximately 1 and thus in the interval [0-8] .
[0027]
That is, in the illustrated embodiment, the standard deviation .sigma.s of the uneven portion on
the surface of the ultrasonic transducer 3 is made as small as possible, so that the distance
between the ultrasonic transducer 3 and the ultrasonic window 4 of the casing 2 is reduced. The
plastic property value ψ of the contact surface of the contact is designed to be as small as
possible, which means that the heights of the asperities are very close to each other in value and
deviate from each other only in a small range. There is.
Here, in another embodiment not shown, the curvature radius R of the asperities of the surface of
the ultrasonic window 4 is made as large as possible to achieve the smallest possible plastic
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property value ψ. At this time, the surface asperities as a whole should not be reduced in
roughness to such an extent that the solid intermediate layer 5 is no longer in a state of
deforming to plasticity.
[0028]
The material for the thin and relatively soft solid intermediate layer 5, the roughness of the
surface of the ultrasonic window 4 and the force with which the ultrasonic transducer 3 is
pressed against the solid intermediate layer 5 are illustrated by this force In the example, it must
be considered that the ultrasonic transducer 3 which is a piezoelectric crystal is not broken.
Furthermore, although the lowest possible plastic characteristic value ψ between the ultrasonic
transducer 3 and the ultrasonic window 4 of the housing 2 is advantageous, the plastic
deformation of the soft solid intermediate layer 5 is particularly weak. It has to be taken into
account that on a visual scale the surface roughness of the ultrasound window 4 must not be
reduced to such an extent that it is no longer possible.
[0029]
In the illustrated embodiment, the solid intermediate layer 5 is made of gold, so that the solid
intermediate layer 5 remains in the aggregated state “solid” in a temperature range of, for
example, −200 ° C. to + 300 ° C. Is guaranteed. Gold, as is known, remains in this aggregated
state well above 300 ° C. Thus, the illustrated configuration of the ultrasonic sensor 1 achieves
that a contact surface larger than the contact surface of the known configuration is formed
between the ultrasonic transducer 3 and the surface of the ultrasonic window 4. . Furthermore,
the disadvantages of the known glued or liquid connection layers can be avoided, as well as the
disadvantages of measurement accuracy that are inevitably linked to the use of ultrasound
waveguides. it can.
[0030]
Furthermore, in the embodiment illustrated, the solid interlayer 5 is thinner than 1/10 of the
wavelength of the ultrasonic signal to be transmitted in the propagation direction of the
ultrasonic signal, whereby the energy loss of the ultrasonic signal to be transmitted Is guaranteed
to be very low.
[0031]
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In the illustrated ultrasonic sensor 1, the force applied to the ultrasonic transducer 3 is formed
by the spring element 6.
In the present invention, this spring element 6 is composed of a plurality of disc springs. This
measure also achieves the intended tolerance for the thermal expansion of the entire device. In
this illustrated embodiment, the spring element 6 is pre-loadable. That is, it can be screwed into
the casing 2 of the ultrasonic sensor 1 and can be preloaded by the screw element 7 that
pressurizes the spring element 6.
[0032]
1 shows an ultrasound sensor according to the invention.
Explanation of sign
[0033]
1 ultrasonic sensor, 2 casing, 3 ultrasonic transducer, 4 ultrasonic window, 5 solid interlayer, 6
spring element, 7 screw element
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