Note: Descriptions are shown in the official language in which they were submitted.
5~;~ 83 P 3n7s llS
BACKGROUND OF THE INVE~TION
This invention is related to an ultrasonic transducer with a sur~ort
body, an emitting layer constructed of a material of rel~tively high dielectric
constant, a first ~/~ adaptation layer facing the cnitting layer and a second
/4 adap-tation layer facing a load.
In medical ultrasonic diagnostics and in non-destructive material
tes~ing, ultrasonic broadband transducers are used. In particular, in medical
applications, where a coupling must be effected between tissue and an acoustic
transducer with a minimum of loss, an improvement of the electromechanical and
acoustic properties of these transducer systems is required.
An ultrasonic transducer is known whose ceramic transducer is adapt-
ed to a load medium comprised of tissue or water by two ~/~ ada~tation layers.
This transducer system contains a backing layer of epoxy resin having an acoustic
impedance of 3 X 106 Pas/msa ceramic transducer, a first ~/4 adaptation layer of
glass having an acoustic impedance of 10 X 106 Pas/m and a second ~ adaptation
layer of polyacryl or of epoxy resin having an acoustic impedance of 3 X 106
Pas/m. The ceramic transducer is applied on a backing. The glass plate serving
as a first adaptation layer is applied with an adhesive of very low viscosity,
so that bonding layers in the range of about 2 micron are obtained. The epoxy
resin, as tlle second adaptation layer, is poured directly on the first adaptation
layer ("Exl~erirnental Studies for the Construction of Ultrasonic Broadband Trans-
ducers, " Biomedizinische Technik, Vol. 27, No. 7 to 8, 1')82, pages 182 to 185).
By this double ~/~ adaptation one achieves only an irnprovement of the sensitivity
and of the bandwidth of the ceramic emitting layer. The bandwidth of this ultra-
sonic transducer is about 60 to 70% of the center frequency.
In addition, an ultrasonic transducer is known which contains an
emitting layer of a material with a relatively high dielectric constant and high
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acoustic impedance and a receiving layer of a material with a
relatively low dielectric constant and low acoustic impedance,
which are connected face-to-face ln a hybrid fashion. I'he emitting
layer consists for example of lead-zirconate-titanate PZT or lead
metaniobate Pb(NO3)~ The receiving layer, on the other hand,
consists of a piezoelectric plastic foil with an acoustic impedance
of about 3 X 106 Pas/m, for example polyvinyli~enefluoride PVDF or
polycarbonate or polyvinyl chloride PVC. The receiving layer
serves at the same time as the adaptation layer for transmitting
purposes (German patent 29 14 031). The receiving layer used as
the adaptation layer for adaptation to body tissues, however,
can be formed only as a singly ~/4 layer. Here, however, the
adaptation layer for transmittlng is not a single ~/4 adaptation.
For single ~/4 adaptation there results from known deviation
theories an adaptation layer with an acoustic impedance of about
7 X 106 Pas/m.
SUMMARY OF THE INVENTION
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It is an object of the invention to provide an ultrasonic
transducer with an effective br~adband transmitter and a sensitive
~ and broadband receiver.
It is another object of the invention to provide a
transducer with a ceramic oscillator material for an emmitting
layer which is adaptable to tissue or water and which provides
a broadband response.
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Thus, in accordance with a broad aspect of the invention,
there is provided an ultrasonic transducer of the type having a
support body, an emitting layer of material having a relatively
high dieleetric eonstant and high acoustic impedanee, a first
~/4 adaptation layer facing said emitting layer, and a seeond ~/4
adaptation layer faeing toward a load, wherein the improvement
eomprises a receiving layer, said secona ~/4 adaptation layer
being provided at the same time as said receiving layer and said
first ~/4 adaptation layer being provided to also function as a
backing for said receiving layer.
Due to the fact that the second ~/4 adaptation layer
funetions at the same time as a reeeiving layer and that the first
~/4 adaptation layer serves at the same time as a baeking for the
reeeiving layer, one obtains an ultrasonic transducer whose
emitting layer is adapted to a load with low reflection
charaeteristies and with a reeeiving layer whieh is exceedingly
sensitive and broadbanded.
In an especially advantageous embodiment of the ultra-
sonie transdueer, the reeeiving layer comprises a staek of thin
~ piezoeleetrie plastie foils
~25Z~
electrically connected in series. Through this design of the receiving layer it
is easier to polarize the individual piezoelectric ~plastic foils because o:f their
small thickness.
In another advantageous embodiment of the ultrasonic transducer, the
receiving layer consists of an active and a passive piezolelectric plastic foil,
the active piezoelectric plastic foil being disposed on the first adaptation
layer, and the passive piezoelectric plastic foil being turned toward the load.
The thickness of the passive piezoelectric plastic foil is a multiple of the
thickness of the active piezoelectric plastic foil. Through this design of the
receiving layer one obtains a broadband, sensitive ultrasonic transducer of rel-
atively high capacitance and a correspondingly low internal impedance.
Other features and advantages of the invention will be apparent from
the following description of the preferred embodiments, and from the claims.
For a full understanding of the present invention, reference should
now be made to the following detailed description of the preferred embodiments
of the invention and to the accompanying drawings.
BRIEF DESCRIPTION OF '~E DRAWINGS
Figure 1 shows an ultrasonic transducer according to the invention.
Figure 2 shows a further embodiment of the invention.
~O Figure 3 illustrates a still further embodiment of the invention.
DETAILED DESCRIPTION
The invention will now be described with reference to Figure 1. An
ultrasonic transducer which contains a support body 2, an emitting layer 4, and
two ~/4 adaptation layers. The second ~/4 adaptation layer is provided at the
same time as a receiving layer 6. The first ~/~ adaptation layer 8 faces toward
the emitting layer ~ and functions at the same time as backing for the receiving
layer 6. All layers may be joined together, ~r~ploying h,vbrid techniques, pre-
ferably over a large area. At a given resonance frequcncy the thicknesses of theadaptation layers measure a quarter wavclength in each instance. At a resonance
frequency of for instance 10 Mllz, the thickness of the adaptation layers is forexample, 55 microns and at a resonance frequency of for instance 2 ~1Hz, the
thickness of the adaptation layers is for example, 275 microns. For emitting
layer 4 it is advantageous to use a material with a relatively high dielectric
constant and high acoustic impedance, for example a piezoelectric material. It
is preferred that an emitting layer 4 of lead-zirconate-titanate PZT or lead
metaniobate Pb~NO3) be used. The two adaptation layers have the task to adapt
different acoustic impedances to one another and achieve low reflection. }lere
one must adapt the emitting layer of lead-zirconate-titanate PZT having an acous-
tic impedance of approximately 30 X 106 Pas/m to a load of for example, tissue
or water, having an acoustic impedance of 1.5 X 106 Pas/m. To obtain optimum
low-reflection coupling there is known from pertinent theory a multi-step trans-formation with two A/4 adaptation layers, through which an input reflection fac-tor is approximated according to the Tschebyscheff formula. From this there
results for the first ~/4 adaptation layer 8 an acoustic impedance of about
14 X lO Pas/m and for the second ~/4 adaptation layer an acoustic impedance of
about 4 X 106 Pas/m. The first adaptation layer 8 may be co~prised of, for ex-
ample, porcelain, preferably quartz glass, in particular a glass-like substance
(Macor). For the second adaptation layer polyvinly chloride PVC, in particular
polvvulylidene flouride PVDF may be used.
So that the second adaptation layer will function, at the same time,
as the receiving layer 6, the polyvinlidene fluoride PVDF layer must be polar-
ized and provided with electric terminals which are not shown in Figure 1.
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lhrough this design one obtains a broadband and sensitive ultrasonic
transducer which, in particular because of its low-reflection coupling between
tissue and ultrasonic transducer which is very useful in the field of medicine.
In the particularly advantageous form of realization which is shown in
Figure 2, the receiving layer 6 consists of a stack of thin piezoelectric plastic
foils 10 electrically connected in series. These piezoelectric plastic foils 10
are each polarized in the same direction, and the thickness of the stack is one
quarter wavelength at a predetermined resonance frequency. Up to a frequency of
for example 4 MHz the stack may appropr~tely consist for example of 25 micron
thick plastic foils 10, while for higher frequencies the stack may be composed of
plastic foils 10 with a micron thickness of 9 microns for example. As material
for the piezoelectric plastic foils of the receiving layer 6 polyvinyl chloride
PVC, in particular polyvinylideile fllloride PVDF, may be used.
Due to this realization of the reciving layer 6, which comprises thin
piezoelectric plastic foils which is 9 to 25 micro~ls thick, very good polarization
is achieved.
In a further embodiment according to Figure 3, the receiving layer 6
consists of an active piezoelectric plastic foil 12 and a thicker passive piezo-
electric plastic foil 14. The thickness of the passive piezoelectric plastic
20 foil 14 of the receiving layer 6 is a multiple, for example 2 to lS times, of the
thickness of the active piezoelectric plastic foil 12 of the receiving layer 6.
The active piezoelectric plastic foil 12, which is for example 25 micron thick, is
arranged on the first ~/4 adaptation layer 8, and the passive piezoelectric p]as-
tic foil 14 faces toward the load. Also in the form of realization one used as
material for the piezoelectric plastlc foils of the receiving layer 6 for example
polyvinylchloride PVC, in particular polyvinylidene fluoride PVDF. Both the active
~2~25~
and the passive piezoelectric plastic foils 12 and 1~ consist of the same mater-
ial, the active piezoelectric plastic foil 12 being polarized.
Through this design of the receiving layer 6 one obtains a broad-
band and sensitive ultrasonic transducer with relatively great capacitance and
correspondingly low internal impedance with a relatively small spatial dimensions.
There has thus been shown and described a novel ultrasound trans-
ducer which fulfills all the objects and advantages sought therefor. ~lany
changes, modifications, variations and other uses and applications of the subject
invention will, however, become apparent to those skilled in the art after con-
sidering this specification and the accompanying drawings which disclose pre-
ferred embodiments thereof. All such changes, modifications, variations and
other uses and applications which do not depart from the spirit and scope of the
invention are deemed to be covered by the invention which is limited only by the
claims which follow.
