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DESCRIPTION JPH08126094

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DESCRIPTION JPH08126094
[0001]
TECHNICAL FIELD The present invention relates to a transducer element used for a transducer
array such as a linear array, a phased array, and a two-dimensional array, and in particular, good
acoustic impedance matching with the human body, and The present invention relates to a
composite piezoelectric transducer element having good electrical impedance matching with an
imaging system.
[0002]
BACKGROUND OF THE INVENTION Acoustic transducers for medical ultrasound imaging are
made of piezoelectric materials. Various composite materials are made by combining the
piezoelectric ceramic and the passive polymer phase. These composites extend the range of
material properties obtained by conventional piezoceramics and polymers.
[0003]
In pulse / echo medical ultrasound imaging, a 1-3 complex geometry has been identified as the
most promising. See "Composite Piezoelectric Materials For Ultrasonic Imaging Transducers-A
Review" by W. A. Smith (1986 IEEE, CH 2358-0 / 86/0000/0249, pages 249-255). For example,
the 1-3 PZT rod / polymer composite structure 10 shown in FIG. 1 is a polymer matrix in which
thin, mutually parallel rods 12 of piezoelectric ceramic oriented perpendicular to the opposing
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plate surfaces 13, 14 are held together. It consists of 11 Metal electrodes are attached to the
plate surfaces 13 and 14. When a voltage pulse is applied to this plate (in the same direction "t"
as in the poling direction), the voltage pulse causes the plate to appear in the frequency band
near its fundamental thickness resonance. Thickness-mode oscillation is excited. The resulting
acoustic vibrations 15 are projected onto the soft tissue of the human body and scattered by the
boundaries of the organ and the structures within that organ. The echo that returns to the
transmitting transducer excites a thickness oscillation in the piezoelectric plate, thereby
producing an electronic signal that is used to form an image. By scanning the direction of the
interrogation beam and properly interpreting the echoes returned, the in-vivo image is provided
to the physician with substantial diagnostic values.
[0004]
Important parameters for a satisfactory piezoelectric material in this application include
sensitivity, acoustic and electrical impedance matching, low electrical and mechanical losses,
formability, thermal stability, and structural strength. In order to obtain good sensitivity, an
efficient conversion between electrical energy and mechanical energy must be performed by
means of piezoelectricity so that the electromechanical coupling is strong. The piezoelectrics
must be acoustically matched to the tissue so that sound waves in the transducer and in the
tissue couple well both on transmit and receive. The electrical impedance of each array element
must be compatible with the drive and receive electronics (usually 50 ohms). For an array
element of a given geometry, the electrical impedance is inversely proportional to the dielectric
constant of the piezoelectric material. Thus, the dielectric constant must be relatively large. In
short, good piezoelectric materials for medical ultrasound imaging have high electromechanical
coupling (kt close to 1), acoustic impedance close to that of tissue (Z close to 1.5 Mrayl), and
moderately large dielectrics It should have a rate (ε s 100 100), small electrical losses (tan δ ≦
0.10) and mechanical losses (Q m 10 10).
[0005]
The performance of composite piezoceramics varies with the volume ratio of piezoceramics for a
given ceramic and polymer. In general, a tradeoff is made between the reduction in acoustic
impedance as the volume fraction decreases and the enhancement of coupling. Nevertheless,
there are a wide range of ratios in which the coupling coefficients of composite piezoceramics
are higher and the acoustic impedance is lower compared to pure piezoceramic components. See
page 253 of Smith's reference.
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[0006]
Transducer arrays have been made from composites, as shown for example in FIG. In the
composite linear array 20, a rectangular ceramic rod 21 is embedded in a polymer matrix 22,
and metal electrodes 23, 24 are provided on the opposing major surfaces of the composite 27 so
as to be disposed adjacent to the body. A matching layer 25 is provided on one of the major
surfaces and the array element 26 is defined by the electrode pattern on the other major surface.
Alternatively, the composite can be machined to isolate the array elements to form the array. By
making the complex very flexible it is also possible that it can be formed into a curved shape for
focusing and steering of the beam.
[0007]
Another article by WASmith "New Opportunities in Ultrasonic Transducers Emerging From
Innovations in Piezoelectric Materials" (1992 SPIE International Ultrasonics Symposium (July 2122, 1992)) contains various piezoceramics (Table I). The material parameters for the) and
piezopolymer (Table II) materials are summarized. Smith also defined the relationship between
the triaxial coordinate system and the polar axis of the ceramic to define independent material
parameters (pages 2-3). These relationships determine the electromechanical coupling factors, ie,
k31, k33,. These electromechanical coupling factors measure the true strength of the
piezoelectric interaction if the elastic response and dielectric response of the medium are
normalized. For some of the main piezoelectric ceramic materials such as barium titanate, lead
zirconate titanate and modified lead titanate, and piezoelectric polymers such as polyvinylidene
difluoride and its copolymers with trifluoroethylene, with regard to the coupling coefficients
Known values and other important material parameters are listed.
[0008]
FIG. 3 is a schematic representation of three of the various types of composite piezoelectric
materials. The complex form is represented by the bonding pattern of the individual phases. For
example, 1-3 bond refers to a composite in which a piezoelectric phase is continuous or selfbonded in one dimension and a polymer phase is self-bonded in three dimensions. FIG. 3 (a)
shows a 1-3 PZT rod in a polymer structure 30 as described above with respect to FIGS. FIG. 3 (b)
shows a layered 2-2 structure 40 comprised of alternating layers of piezoceramic and polymer
with electrodes disposed on the top and bottom facing each other. FIG. 3 (c) shows a 3-3
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composite structure 50 comprised of a mixture of piezoceramic and polymer. Each of these
structures has advantages in a variety of applications. In general, a device structure with low Q is
desirable, which is best achieved by efficiently coupling the transducer acoustically to the
medium and electrically to the excitation and imaging electronics. To be achieved.
[0009]
The polymer in each of the composite structures of FIG. 3 serves to lower the acoustic impedance
to better match the medium. However, there are still problems in obtaining a good match of the
electrical impedance. In this regard, as shown in FIG. 4 (b), it has been proposed to form a
piezoceramics trip structure intermingled with a metal electrode, which is described in
“Performance of Multi-Layer” by R. Goldberg and S. Smith. It is quoted from "2-D Transducer
Arrays" (1993 Ultrasonic Symposium, 1051-10117-93-0000-1103, IEEE (1963), pages 11031106). For comparison, FIG. 4 (a) shows a single-layer ceramic element 60, and FIG. 4 (b) shows
a multilayer ceramic element 70 having the same overall dimensions. Arrows 61 and 71 in these
figures indicate the poling direction. The objective described in Goldberg et al. Is to utilize
multilayer ceramics to enhance both the transmit and receive sensitivities of two dimensional
array elements. The purpose in the transmit mode is to increase the acoustic output into human
tissue for a given power supply voltage. This object is achieved by matching the electrical
impedance of the power source and the transducer such that maximum power is transmitted.
Also, the purpose in the receive mode is to increase the receive voltage amplified and processed
by the ultrasound imaging system. The received voltage is increased by matching the impedance
of the transducer to the coaxial cable and imaging circuitry. In the case of a multilayer structure
70 such as Goldberg et al., The ceramic layers 72 (between the interdigitated electrodes 73) are
electrically connected in parallel, and the total capacitance is the sum of the capacitances of each
layer. Therefore, the capacitance CN of an N-layer transducer having an electrode area of A, a
layer thickness of t / N and a dielectric constant of ε is as follows.
[0010]
CN = NεA / (t / N) = N2Csingle where Csingle is a single layer transducer (such as element 60 of
FIG. 4 (a) having a single ceramic layer 62 between electrodes 63 and 64) It is a capacitance. As
described in the document by Goldberg et al., The open-circuit reception sensitivity is directly
proportional to the layer thickness t / N, so that increasing the number of layers will reduce the
open-circuit sensitivity. However, according to the author, the electrical load drive capability of
the multilayer ceramic structure compensates for the desensitization of the open circuit.
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[0011]
A multilayer ceramic structure such as Goldberg et al. Reduces the electrical impedance of the
array elements and improves power transfer with the imaging system, but does not solve the
acoustic matching problem. Furthermore, although a two-dimensional array is desirable when
providing elements along azimuth and elevation planes to provide dynamic control of the
ultrasound beam in both directions, the size of the array elements is small The higher the
electrical impedance, the worse the problem of insufficient sensitivity of the transducer. Thus,
both very good matching of the acoustic impedance to the medium to be observed and good
matching of the electrical impedance of the imaging system are effective, in particular for very
small transducers as required for phased arrays and two-dimensional matrix arrays. There is
nothing to offer in prior art systems.
[0012]
A two-dimensional array consists of small transducer elements distributed in two dimensions in a
square grid. One of the main problems in two-dimensional arrays is that the element size is so
small that the electrical impedance becomes very large. Even with current phased array devices,
the electrical impedance will be in the range of 200 ohms to over 1 k ohm depending on the
frequency and aperture of the device. In a two-dimensional array, each of the elements is
subdivided into 64 or more elements in the elevation direction. Thus, the impedance of each twodimensional array element is at least 64 times greater, which makes it difficult to couple
electrical energy from the 50 ohm imaging system to the transducer in general. The present
invention solves this electrical impedance problem and optimizes the acoustic impedance
matching for the human body.
[0013]
The object of the present invention is to provide a thin wafer of piezoceramics provided with
electrodes on the first and second main surfaces facing each other and polarized along the
thickness between the electrodes. To provide a composite structure.
[0014]
SUMMARY OF THE INVENTION The wafers in the present invention are separated by passive
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polymer layers.
One element comprises at least two electroded ceramic wafers and an intermediate passive
polymer layer. The piezoelectric wafer is electrically driven along the wafer thickness to generate
acoustic vibrations in the vertical direction (see FIG. 7). This vibration mode is called "31"
transverse mode. By increasing the electrode area on the main surface of the ceramic wafer and
making the wafer thickness relatively thin, the capacitance of each element is consequently
increased, and the electrical impedance is reduced correspondingly. The elements can also be
provided in a 2-2 or 3-1 composite structure. The number of wafers in a given device can be
selected to obtain the desired impedance match. In the case of linear arrays or phased arrays, it is
possible to provide hundreds of wafers in one strip. In the case of a two dimensional array, it is
possible to provide a plurality of such elements in a two dimensional square grid. Interspersing
the ceramic wafer with the polymer layer results in a low acoustic impedance composite
structure. Thus, both electrical and acoustic impedances will be optimized for small array
elements.
[0015]
Another aspect of the present invention is the various methods of making composite structures.
In the first method, a wafer of piezoelectric ceramic is provided with electrodes along its major
surface and polarized along its thickness. The wafers are stacked with spacers along one edge
depending on the desired application to form a stack of tens or hundreds of wafers. The stack is
then infused with an epoxy polymer matrix. The area containing the spacer is removed to provide
a composite structure. If the original surface electrode extends to the edge of the device, the
channels are cut at equal intervals along the edges of the composite structure and then the
channels are filled with polymer. End electrodes are respectively provided on the upper and
lower surfaces of the element, each of which is connected to a different one of the two sets of
surface electrodes. Alternatively, it is possible to first provide surface electrodes (for example by
applying masking) so that they do not extend to both edges, in which case the channel is not
necessary.
[0016]
Another alternative manufacturing method starts with a piezoceramic block and forms grooves
using diamond saw teeth to form a series of parallel piezoceramic wafers spaced from one
another. There is a way. The wafer is then provided with electrodes and the grooves are filled
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with epoxy. The lower piezoceramic layer is separated to form a composite structure. Again, the
channels are cut on the facing surface to form two sets of facing surface electrodes, and the
channels are filled with polymer to attach the end electrodes.
[0017]
The above and other advantages of the present invention will be described in more detail in the
following detailed description and the drawings.
[0018]
DETAILED DESCRIPTION OF THE INVENTION A block diagram of a phased array type pulse echo
ultrasound imaging system 100 is shown in FIG. 5 (a).
The system provides pulsed electrical stimulation (stimulus) to the transducer array 101, which
causes the transducer to deliver ultrasound waves 103. The ultrasound is delivered to a medium,
such as the human body, and will be at least partially reflected by an object (eg, the heart 115) in
the medium. The reflected wave (echo) is received by the transducer 101 and an electrical signal
104 representing the echo is generated by the transducer 101. The various characteristics (such
as amplitude and phase) of the electrical signal produced by the echo are then analyzed by the
signal processor of the imaging system to determine information (size, location, velocity, etc.)
about the object in the medium. The imaging system excites the transducer using beam steering,
phased array or other techniques known in the art and analyzes the electrical signal resulting
from the echo. See, for example, US Pat. No. 5,060,651, entitled "Ultrasonic Diagnostic
Apparatus."
[0019]
More specifically, FIG. 5 (a) shows microprocessor 108 which controls each of transmitter 107,
preamplifier 109, beamformer 106, and digital scan converter 111. ing. The echo signal 104
from the transducer array 101 is sent to a preamplifier 109 to be amplified and then sent in
series to a beamformer 106, a signal processor 105, an AD converter 110, and a digital scan
converter 111. The z component is sent to post processor 112 and the resulting z intensity is
displayed on CRT screen 114. Also, the xy components are sent via the xy raster 113 and
displayed on the CRT screen 114. Any number of different transmission and image processing
systems can be used.
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[0020]
FIG. 5 b is a simplified illustration of how one side of the transducer 120 is electrically coupled to
the imaging system 121 and the other side is acoustically coupled to the media (patient 122). .
The imaging system may comprise, for example, a power supply 123 having an electrical
impedance of approximately 50 ohms in series with a cable 124 having an impedance of 50
ohms. The maximum power transfer condition for the load (patient 122) occurs when the power
supply and cable impedance and the transducer impedance are substantially the same.
[0021]
In the receive mode (not shown), the incident sound pressure can be modeled as a voltage source
while the impedance of the transducer is the source impedance. The electrical load consists of
the shunt impedance of the cable and the input impedance of the preamplifier. The transducer
can effectively drive the cable load if the capacitance of the transducer is significantly greater
than the capacitance of the cable. The composite element of the present invention satisfies these
requirements.
[0022]
The capacitance of a given structure is determined by its configuration. For example, the
capacitance "C" of a parallel plate capacitor is: C = ε oKA / d where K is the relative permittivity,
ε o is the absolute permittivity of free space (8.85 × 10 -12 F / m ), A is the area facing the
parallel plates, d is the distance between the plates. In the case of a typical prior art transducer
element 200 used in a two dimensional array, as shown in FIG. 6, a parallel plate capacitor is a
suitable model. The transducer element 200 has a square cross section in which the two sides
201, 202 are each 250 μm, and the height between the opposing electrodes 203, 204 is about
500 μm. If such an element is formed of PZT ceramic with a relative dielectric constant of 3000,
then A = 250 × 250 μm 2, d = 500 μm, and the capacitance of the transducer is about 3.3 pF.
Thus, this prior art transducer has poor electrical alignment to a cable capacitance of 200 pF (ie,
the cable connecting the transducer to the preamplifier).
[0023]
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On the other hand, the first embodiment of the present invention uses a 2-2 composite structure,
and a plurality of wafer elements 210 (see FIG. 7) are sandwiched between polymer layers to
form a composite element. 230 (see FIG. 8) are formed. FIG. 7 shows a relatively thin PZT wafer
211 having a thickness t (in the x direction) and opposing major surfaces 212, 213 (in the yz
plane) each having a relatively large area A. ing. The opposing major surfaces 212, 213 are
formed with electrodes 214, 215 over most of their large surface area, and the wafer is polarized
across its thickness (in the x direction indicated by arrow 216). The resulting acoustic output
signal 217 will have z-direction. As a result, the capacitance of the wafer element becomes
relatively large. This is because the electrode area is wide and the thickness t is relatively thin.
Furthermore, when a plurality of these wafers are electrically connected in parallel, their
capacitances are summed, resulting in a large capacitance and a corresponding low electrical
impedance to match the imaging system Is improved. The relative size and number of wafer
elements can vary, and it is desirable to select the element thickness, area, and number so that an
impedance of about 50 ohms can be obtained for each element.
[0024]
FIG. 8 (a) is a perspective view of a composite 2-2 transducer 230 of the present invention, and
FIG. 8 (b) is a cross-sectional view thereof. A flat wafer or strip 235 of piezoelectric ceramic, such
as PZT, is sandwiched between a first electrode layer 240 on one side and a second electrode
layer 242 on the other side. The electrodes extend in the xy plane along the main surface of the
wafer. Each set of electrodes 240, 242 is connected to a different one of the end electrodes 241,
243 on opposite upper and lower surfaces of the composite transducer. Therefore, as shown in
FIG. 8A, the electrode 240 hanging down from above is connected to the end electrode 241 on
the upper surface, and the end thereof does not reach the end electrode 243 on the lower
surface. Similarly, the electrode 242 extending from the lower side is connected to the end
electrode 243 on the lower surface, and the end thereof does not reach the end electrode 241 on
the upper surface. A passive polymer layer 238 is inserted between each set of adjacent
electroded wafers 240/235/242 to improve the acoustic alignment with the human body.
[0025]
Wafer 235 is polarized in the x-direction along its thickness and is excited with an electrical
pulse along the same direction. In this manner, the k31 bond of the PZT material is used to drive
the wafer 235 to produce resonance along the z-direction.
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[0026]
Each combination 250 of electrode 240, wafer 235 and electrode 242 can be modeled as a
parallel plate capacitor. Further, the configurations of FIGS. 8A and 8B define a plurality of such
capacitors connected in parallel. Thus, the total capacitance of composite transducer 230 is the
sum of the individual capacitances of each combination 250. Since each combination 250
provides a relatively large electrode area and a relatively small inter-electrode distance t, the
capacitance of each combination 250 is relatively large.
[0027]
As mentioned above, the conventional transducer of FIG. 6 has a capacitance of about 3.3 pF. In
contrast, the composite transducer 230 of the present invention comprising a 50 μm wide PZT
wafer 235 sandwiched between electrodes 240 and 242 exhibits a capacitance of about 66 pF
for each combination 250. Furthermore, if the combination 250 is separated by a 25 μm thick
polymer layer 238, the three such combinations connected in parallel will fit in the same volume
as a conventional transducer element. Ultimately, transducer 230 exhibits a total capacitance of
approximately 198 pF.
[0028]
9 and 10 illustrate one of the methods for forming the composite transducer element 230. As
shown in FIG. The wafer 235 of PZT material is electroplated (or otherwise provided with
electrodes) on its opposite major surfaces 236, 237 (see FIG. 9 (a)). Each wafer can be, for
example, 50 μm thick. Because the wafer 235 is polarized (i.e., poled) along the thickness t, the
PZT exhibits piezoelectric properties. The electroded wafers are then stacked with the spacers
261 on the lower edge 260 to separate the major surfaces 236, 237 of adjacent wafers (see FIG.
9 (b)). Each spacer 261 can be, for example, 25 μm thick. The number of wafers stacked is
application dependent, but the stack 262 can include tens to hundreds of such wafers, if desired.
An epoxy matrix is then implanted throughout the stack 262 to form a polymer layer 238 that
fills the space between the ceramic wafers 235 (see FIG. 9 (c)). The lower portion 264 of the
stack, including the spacers, is cut away by diamond saw teeth, as shown in FIG. 10 (a). The
polymer filled layer 263 is cut to form the transverse portion (FIG. 10 (b)) of the transducer
element 230 of appropriate size. The transducer element 230 is then ground, for example with a
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dicing saw, to form channels 265, 266 at the ends of the electrodes 236, 237, respectively. These
channels are required to prevent the electrodes 236 and 237 from being electrically connected
when the electrodes are provided on the end faces 241 and 243 as described later. Such
channels can extend, for example, over 25 μm, as shown in FIG. 10 (c). Channels 265 and 266
are filled with polymer 238, and electrodes are provided on opposite cross sections 241 and 243
(see FIG. 10 (d)). The transducer elements 230 are then configured to form a two-dimensional
array using techniques known in the art (see FIG. 14).
[0029]
FIGS. 11 (a)-(d) illustrate another method for forming the composite transducer element 430, in
which case the range of the original electrode extends over the entire surface of the wafer. It is
not supposed to. As shown in FIG. 11 (a), the facing surface electrodes 402 and 403 of the
piezoceramic wafer 401 extend over almost the majority of the facing surface of the wafer, but
the ends thereof are the upper end surface 405 and the bottom facing each other The end face
406 has not been reached. In FIG. 11 (b), a plurality of such elements are spaced along one edge
by a series of spacers 412 and the area between the wafers is filled with polymer to form
polymer layer 411 in composite block 410. Is formed. As shown in FIG. 11C, the lower portion
413 including the spacer is cut off, and the upper portion 415 is lap-off to expose the opposing
pair of electrodes 402 and 403 of the central portion 414. In FIG. 11 (d), upper and lower
electrodes 421 and 422 are attached to the upper and lower parts of the composite transducer
element to form the final transducer element 430.
[0030]
FIGS. 12 and 13 illustrate another alternative method of manufacturing the composite transducer
element 330. The PZT block 300 is cut away, for example by a diamond saw, to form elongated
parallel channels 336 (see FIG. 12 (b)). The channels 336 separate extended rectangular
protrusions or wafers 337 that couple along one common edge 339. The upper surface of the
element including the side surface of each protrusion 337 is covered with electrodes 332 and
334, for example, by sputtering or vacuum evaporation (see FIG. 12 (c)). The resulting structure
302 is then coated and filled with a polymer to form a polymer layer 338, and the lower PZTonly portion 305 is removed (see FIG. 13 (a)). Again, the channels 365, 366 are machined to
remove both ends of the electrodes on the top and bottom surfaces (see FIG. 13 (b)) and the
channels are filled with polymer and the top of the resulting structure 330 End electrodes 341
and 343 are attached to the surface and the lower surface (see FIG. 13C).
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[0031]
In the preferred embodiment, transducer elements 230 (330 or 430) are arranged in a two
dimensional array 280 as shown in FIG. Each array element 251 comprises three piezoelectric
wafers 252 separated by a polymer layer 253. The individual elements 251 (separated by
scribed electrodes 254) are arranged in a 4 × 3 rectangular array.
[0032]
In a further alternative embodiment, a 1-3 composite structure is obtained which is designed to
be driven in the k31 transverse mode. Figures 15 (a), (b) illustrate a method for manufacturing
this alternative structure. FIG. 15 (a) shows a composite block 510 similar to block 410 of FIG.
11 (b). This block 510 comprises alternating layers of thin piezoceramic wafers 501 separated
along one edge by a spacer 502, and a polymer layer 503 between the piezoceramic wafers 501.
Counter electrodes 504 and 506 are provided on the facing surface of the piezo ceramic wafer
501. As shown in FIG. 15 (b), the lateral channels 511 are cut in the xz plane of the composite
block to form a series of elements 512 spaced parallel to one another. These channels 511 are
then filled with epoxy, and the steps similar to those shown in FIGS. 11 (c), (d): lapping the upper
surface, cutting the lower with spacers, and the upper and lower electrodes Follow the steps
including the placement of The resulting 1-3 composite block 520 is shown in FIGS. 16 (a) and
16 (b). The 1-3 composite block 520 includes a plurality of elements separated by the polymer
layer 522 and spaced apart from one another. Each element 521 comprises a plurality of thin
rectangular rods 524 having electrodes 525, 526 on opposite surfaces and separated by a thin
rectangular rod 527 of polymer.
[0033]
While several embodiments of the present invention have been described, various modifications
and improvements will readily occur to those skilled in the art. For example, the term
"piezoceramic" is meant to include various other piezoceramics such as relaxor ferroelectric or
electrostrictive materials such as lead magnesium niobate-lead titanate (PMT-PT) ing.
Accordingly, the foregoing description is by way of example only, and the present invention is
defined as set forth in the appended claims.
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[0034]
In the following, an exemplary embodiment is shown which consists of a combination of the
various components of the invention.
[0035]
A transducer comprising transducer elements having a 1.2-2 composite structure or a 1-3
composite structure and driven in the k31 transverse mode, the transducer elements comprising
a plurality of relatively thin spaced apart elements. Piezoceramic wafer having a relatively large
area of opposing major surfaces with electrodes and electrically connected in parallel with one
another, between the piezoceramic wafer and the electrodes of the adjacent wafer And a passive
polymer layer provided.
[0036]
【0036】2.
An array of transducer elements according to claim 1 above.
[0037]
【0037】3.
The transducer array according to claim 2, wherein the array is a two-dimensional array.
[0038]
【0038】4. A method for manufacturing a medical ultrasound transducer element having
an acoustic impedance that substantially matches an acoustic impedance of a human body and
an electrical impedance for efficient power transfer with an ultrasound imaging system, the
method comprising: k31 A 2-2 or 1-3 composite transducer element for driving in a transverse
mode, comprising a plurality of relatively thin piezo ceramic wafers spaced from one another
having opposite major surfaces of relatively large area A layer of a passive polymer selected to
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provide the transducer elements, provide electrodes on the main surface for electrically
connecting the wafers in parallel, and obtain an acoustic impedance substantially similar to that
of the body. Between the electrodes of the adjacent wafers to improve power transfer with the
imaging system. Yo electrical impedance to select the number of said spaced piezoceramic wafer
as transducer elements decreases is obtained, characterized in that it comprises the steps of, the
production method.
[0039]
【0039】5. A method of manufacturing a transducer, comprising a plurality of relatively
thin piezoceramic wafers spaced from one another, having relatively large areas of opposing
major surfaces, wherein opposing pairs of electrodes are said major surfaces. Forming a stack by
stacking the wafer with the electrode with a predetermined distance from the adjacent wafer
with the electrode, and filling the stack with a polymer. The gap is filled to form a composite
element, electrodes are provided on the opposing end surfaces of the composite element, one of
the end electrodes is connected to one of the opposing pair of electrodes, the end A method of
manufacturing a transducer, comprising the steps of: connecting the other of the partial
electrodes to the other of the opposing set of electrodes.
[0040]
【0040】6. Placing stack elements between the wafers along one edge of the stack in the
stacking step to form the predetermined spacing, and removing portions of the composite
element including the stack elements after the filling step; The manufacturing method of the
preceding clause 5.
[0041]
【0041】7. The opposing set of electrodes is provided on the entire opposing main
surface, and after the filling step, the opposing set of channels is cut at the opposing end of the
opposing set of electrodes. 6. A method according to claim 5, wherein the process is processed,
the channels are filled with polymer and end electrodes are provided.
[0042]
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【0042】8. One of the opposing sets of electrodes extends from a first end of the opposing
ends of the wafer by a predetermined distance not reaching the second end of the wafer, the
opposing The method according to claim 5, wherein the other of the pair of electrodes extends
from the second end by a predetermined distance not reaching the first end.
[0043]
【0043】9. The method of claim 5 further comprising the steps of: cutting a series of
laterally elongated channels spaced from one another into a stack and filling the channels with a
polymer to form an array of 1-3 composite elements .
[0044]
【0044】10. A method of manufacturing a transducer, comprising providing a block of
piezoceramic material having opposed upper and lower surfaces and four sides, cutting away a
series of spaced apart elongated rectangular channels extending through the upper surface of the
block. Forming a pair of elongated parallel rectangular protrusions extending from the lower
surface of the block, each protrusion having a relatively thin lateral thickness and an opposite
major surface of relatively large area The opposite major surfaces of the protrusion of the
piezoceramic material are provided with opposing pairs of electrodes, the channel is filled with a
polymer, and the piezoceramic portion adjacent to the lower surface of the block is removed to
provide a composite element And providing electrodes on opposite upper and lower surfaces of
the composite element, one of the end electrodes being in contact with one of the opposing pair
of electrodes on the main surface. And, the other of said end electrodes connected to the other
electrode forming a pair of opposing said main surface, characterized in that it comprises the
steps of method of manufacturing a transducer.
[0045]
Brief description of the drawings
[0046]
1 is a schematic diagram showing a conventional 1-3 rod / polymer composite structure.
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[0047]
2 is a schematic diagram showing a conventional linear array formed from the 1-3 rod polymer
composite transducer of FIG.
[0048]
FIGS. 3 (a)-(c) are schematic diagrams showing three conventional different composite structures,
ie, 1-3 rod, 2-2 layer composite structure and 3-3 block composite structure in polymer
structure, respectively. .
[0049]
FIG. 4 (a) shows a conventional single piezo ceramic element, and FIG. 4 (b) is a schematic view
showing an electrode alternating type piezo ceramic element.
[0050]
FIG. 5 (a) is a block diagram illustrating an ultrasound imaging system using a phased array, and
(b) is a schematic illustrating how the transducer is electrically coupled to the imaging system
and acoustically coupled to the patient. FIG.
[0051]
FIG. 62 is a schematic diagram showing a conventional square cross-section transducer element
used for the dimensional array, showing poor impedance matching.
[0052]
FIG. 7 is a schematic diagram showing a composite transducer element of the present invention
with greatly improved impedance matching.
[0053]
FIG. 8 (a) is a perspective view showing a 2-2 composite transducer structure according to the
present invention, and FIG. 8 (b) is a cross-sectional view thereof.
[0054]
FIGS. 9A to 9C are explanatory views showing a first manufacturing method according to the
present invention (1/2).
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[0055]
10 (a) to 10 (d) are explanatory views showing a first manufacturing method according to the
present invention (2/2).
[0056]
FIGS. 11A to 11D are explanatory views showing a second manufacturing method according to
the present invention.
[0057]
12 (a) to 12 (c) are explanatory views showing a third manufacturing method according to the
present invention (1/2).
[0058]
13 (a) to 13 (c) are explanatory views showing a third manufacturing method according to the
present invention (2/2).
[0059]
FIG. 14 is a plan view showing a 3 × 4 two-dimensional array of composite transducer elements
of the present invention.
[0060]
15 (a) and 15 (b) illustrate another method for fabricating an alternative 1-3 composite
transducer structure according to the present invention.
[0061]
FIGS. 16 (a) and 16 (b) illustrate alternative 1-3 compound transducer structures.
[0062]
Explanation of sign
[0063]
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230 Composite 2-2 transducer 235 wafer 240 first electrode layer 241, 243 end electrode 242
second electrode layer 238 passive polymer layer 240/235/242 wafer with electrode
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