U.S. patent application number 15/235266 was filed with the patent office on 2017-05-11 for high intensity ultrasound transducers and methods and devices for manufacturing high intensity ultrasound transducers.
The applicant listed for this patent is St. Jude Medical, Atrial Fibrillation Division, Inc.. Invention is credited to Chris Bagley, John E. Crowe, John P. Goetz, Derek Hillstrom, Michael Holzbaur, Stephen A. Morse, Jonathan L. Podmore, Steve Schellenberg, John W. Sliwa.
Application Number | 20170133994 15/235266 |
Document ID | / |
Family ID | 37087658 |
Filed Date | 2017-05-11 |
United States Patent
Application |
20170133994 |
Kind Code |
A1 |
Sliwa; John W. ; et
al. |
May 11, 2017 |
High intensity ultrasound transducers and methods and devices for
manufacturing high intensity ultrasound transducers
Abstract
A method of manufacturing an ultrasound transducer is provided.
The ultrasound transducer is activated and the activity across the
transducer is measured to determine whether the activity at any
area does not meet an acceptance criteria. The transducer is then
modified so that the area meets the acceptance criteria. The
transducer may be modified with a laser which removes material from
the area which does not meet the acceptance criteria.
Inventors: |
Sliwa; John W.; (San Jose,
CA) ; Podmore; Jonathan L.; (San Carlos, CA) ;
Bagley; Chris; (Santa Clara, CA) ; Crowe; John
E.; (Menlo Park, CA) ; Holzbaur; Michael;
(Clemmons, NC) ; Hillstrom; Derek; (Union City,
CA) ; Schellenberg; Steve; (Aptos, CA) ;
Goetz; John P.; (Aptos, CA) ; Morse; Stephen A.;
(Menlo Park, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
St. Jude Medical, Atrial Fibrillation Division, Inc. |
St. Paul |
MN |
US |
|
|
Family ID: |
37087658 |
Appl. No.: |
15/235266 |
Filed: |
August 12, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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11104294 |
Apr 11, 2005 |
9445211 |
|
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15235266 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B23K 2101/36 20180801;
G01N 29/245 20130101; Y10T 29/49004 20150115; H04R 31/00 20130101;
H03H 2003/0407 20130101; H03H 2003/045 20130101; H03H 3/02
20130101; Y10T 29/42 20150115; Y10T 29/49005 20150115; H03H 3/08
20130101; B23K 26/351 20151001; B06B 1/06 20130101; H03H 3/04
20130101 |
International
Class: |
H03H 3/04 20060101
H03H003/04; B23K 26/351 20060101 B23K026/351; G01N 29/24 20060101
G01N029/24 |
Claims
1. A system for modifying an ultrasound transducer, the system
comprising: a sensor which detects an activity level across an area
of an ultrasound transducer, the sensor comparing the level of
activity to a desired level of activity; and a modifying apparatus
which is adapted to modify the ultrasound transducer to modify the
level of activity at a location which does not meet an acceptance
criteria.
2. The system of claim 1, wherein the sensor detects at least one
of an acoustic activity and a temperature.
3. The system of claim 1, further comprising: a memory component
which receives the activity level across the area of the ultrasound
transducer to create a map of the activity; and the modifying
apparatus being coupled to the memory component to receive the
map.
4. The system of claim 1, wherein the modifying apparatus removes
material from the ultrasound transducer.
5. The system of claim 1, wherein: the sensor detects the activity
level on a first side of the ultrasound transducer; and the
modifying apparatus modifies a second side of the transducer
opposite the first side.
6. The system of claim 1, wherein the modifying apparatus is a
laser.
7. The system of claim 1, wherein the modifying apparatus is
configured to alter poling on a part of the transducer.
8. The system of claim 7, wherein the modifying apparatus is
configured to depole the part of the transducer.
9. The system of claim 1, wherein the modifying apparatus is
adapted to remove material from the transducer.
10. The system of claim 1, wherein the modifying apparatus is
adapted to change the shape of the ultrasound transducer to modify
the activity level at the area which does not meet the acceptance
criteria.
11. The system of claim 1, wherein the sensor indirectly detects
the activity of the transducer.
12. The system of claim 1, wherein the sensor detects electrical
impulses from the transducer resulting from directing acoustic
energy at the transducer.
13. An acoustic test and yield-improvement system capable of
mapping and correcting out-of-spec acoustic activity, the system
comprising: an imaging device which can measure activity of a
transducer; a modification apparatus capable of modifying a level
of activity at a location of the transducer having out-of-spec
acoustic activity; wherein the imaging device provides spatial
locational information to the modification apparatus such that the
out-of-spec location identified during an activation can be brought
in to specification by the modification apparatus.
14. The system of claim 13, wherein the activation is at a power
level substantially reduced from a full-power design limit of the
transducer.
15. The system of claim 13, wherein the activation of the
transducer is in contact with at least one of water, a workpiece,
an acoustic standoff and a phantom.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. application Ser.
No. 11/104,294, filed 11 Apr. 2005 (the '294 application), now U.S.
Pat. No. ______. The '294 application is hereby incorporated by
reference as though fully set forth herein.
BACKGROUND
[0002] The present invention is directed to ultrasound transducers
and their methods of manufacture and use.
[0003] In some applications of ultrasound transducers, such as
high-intensity ultrasound therapeutic devices, the ultrasound
transducers may have to meet certain criteria regarding the
distribution of activity across the ultrasound transducer. For
example, it may be desirable to provide acoustic or thermal
uniformity across the proximate ultrasound transducer face as well
as in the distal transducer's focal region. One reason for
requiring acoustic or thermal uniformity proximately at the
transducer face is that some of these devices also provide therapy
in the nearfield and may have to avoid localized hot spots which
can lead to overheating of nearfield tissue portions. Another
reason to provide acoustic and thermal nearfield uniformity is that
some ultrasound devices may utilize water-filled contact members
which can undergo undesirable localized boiling if hot spots are
present. Such considerations are in addition to the normal
expectation of acoustic uniformity at the distal focus-which would
lead to thermal-heating uniformity at that distal focus. As
practitioners of the acoustic arts know, acoustic output
nonuniformities on the proximate transducer face will also cause
nonuniformities at the focus. Various examples of such devices are
found in U.S. Pat. Nos. 6,840,936 and 6,805,129 which are hereby
incorporated by reference
[0004] The present invention is also directed to methods and
devices for manufacturing ultrasound transducers and to methods for
modifying the characteristics of an ultrasound transducer. The
acceptance criteria regarding the distribution of activity across
the ultrasound transducer nearfield, farfield or focal region
typically require that some transducers be rejected. The present
invention provides devices and methods for modifying transducers
which might otherwise be rejected or might perform less than
optimally. The present invention also allows for a substantial
speedup in the process of determining whether such uniformity is
acceptable or is a candidate for our additional and optional
inventive uniformity-correction methods.
SUMMARY
[0005] The present invention provides methods and devices for
modifying an ultrasound transducer. In accordance with a method of
the present invention, an ultrasound transducer is activated and
then the activity across the transducer is measured to determine
whether any parts of the transducer do not meet an acceptable
activity level. For example, if the activity level exceeds a
threshold level, the transducer is then modified to reduce the
activity level at the portion which exceeds the acceptance
criteria. The present invention may also be used to modify a
transducer having unacceptable low activity but is particularly
useful in modifying areas of unacceptably high activity. Most
frequently the activity is acoustic activity whose presence, as
explained below, can be monitored using thermographic
activity-monitoring or imaging means or using hydrophone or
Schlieren imaging means.
[0006] The transducer may be modified in a number of different ways
to favorably change or alter the distribution of activity across
the transducer such as by removing material from the transducer.
The material may be removed from an acoustically active material or
from an acoustically inactive or passive material such as an
electrode or matching layer. Material may be removed with a laser,
a mechanical abrasion device or any other suitable material removal
device including those which use erosion, etching, abrasion or
ablation. The transducer may also be modified by changing the
dimensions of the transducer, by selective poling/depoling of a
piezomaterial or by even adding material to the transducer. The
transducer may be retested after such modification and modified
again if necessary. It should be understood that any or all of
these modification measures are undertaken in response to a
uniformity test indicating an undesirable uniformity different from
an expected desired uniformity. Thus our invention is fundamentally
different than any method used to create fixed predefined activity
patterns in a transducer such as by patterning a transducer
electrode during manufacturing with a fixed mask in order to
achieve well-known acoustic apodization profiles. Such measures
have nothing to do with responding to an undesired and varying
nonuniformity appearing in random locations as does our
invention.
[0007] The present invention is also directed to a system for
modifying an ultrasound transducer. The system includes a sensor
for sensing the activity across the ultrasound transducer and a
modifying apparatus for modifying the transducer. A memory element
may also be used to temporarily or permanently save at least one
partial map of the activity across the transducer. It will be
understood by the reader that a nonuniformity "across" the
transducer may contribute to undesired nonuniform performance in
the proximal transducer-face and/or distal transducer-focus
regions. In either or both cases the invention provides beneficial
modification capabilities.
DESCRIPTION OF DRAWINGS
[0008] FIG. 1 is a perspective view of an ultrasound transducer
showing its layers and focal geometry.
[0009] FIG. 2 is a view of the transducer with a schematic view of
a therapy apparatus.
[0010] FIG. 3A shows a medical device using a number of ultrasound
transducers.
[0011] FIG. 3B shows a membrane in contact with tissue being
treated.
[0012] FIG. 4 shows a map of activity across the transducer.
[0013] FIG. 5 shows a system for modifying an ultrasound transducer
in accordance with the present invention.
[0014] FIGS. 6A-6F are cross-sections of the ultrasound transducer
after various embodiments of the inventive modifications are
carried out.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0015] Referring to FIGS. 1 and 2, an ultrasound transducer 2 is
shown. The ultrasound transducer 2 generally has a piezoelectric
layer 8 and one or more acoustic matching layers 8A. Typically, the
piezoelectric layer 8 is positioned between an active or "hot"
electrode 4 and a passive or "ground" electrode 6. The
piezoelectric layer 8 may be made of any suitable piezoelectric
material such as lead-zirconate-titanate (PZT), lead metaniobate,
lithium-niobate or polyvinyldifluoride (PVDF) compounds as is
known. Of course, any other suitable material may be used including
those made of piezoceramics, piezopolymers, electrostrictive
materials and magnetostrictive materials. The piezoelectric layer
8, matching layer 8A, and electrodes 4, 6 may be laminated or
bonded in any suitable manner such as by known epoxy lamination.
Electrodes 4, 6 may be provided in any suitable manner such as by
depositing or laminating a metal film or foil on or to the
piezomaterial and matching layer. In some cases the matching layer
8a will comprise electrically conductive material and it may then
itself also serve as the electrode 6.
[0016] The active transducer electrode 4 has an associated
electrical lead 10 coupled to a power source 12 for driving the
ultrasound transducer 2 in a conventional manner. The ultrasound
transducer 2 of FIGS. 1 and 2 is cylindrically curved so that the
ultrasound energy is focused and, in particular, cylindrically
focused along a linear focal-line segment LS. The focal length of
the ultrasound energy is essentially the radius of curvature R of
the ultrasound transducer 2. The present invention may be
particularly useful in modifying transducers 2 having a focal
length less than 12 mm and even less than 10 mm. The present
invention is particularly useful in that one may modify the
transducer proximal-face uniformity thereby improving both the
nearfield treatment uniformity as well as the distal focal-line
treatment uniformity. For example, if the transducer 2 were a HIFU
lesion-making transducer having a focal radius of 8 or 10 mm one
could modify the transducer 2 uniformity using the invention such
that the HIFU treatment uniformity is improved both in the
nearfield and in the farfield. In that manner a uniform tissue
lesion can be formed everywhere between the distal focal line LS
and the proximal tissue surface transducer-face.
[0017] FIG. 2 schematically shows the transducer 2 of FIG. 1
mounted to a transducer housing 3. An electrical pulser subsystem
31, a group of logic, sensors and software 32 and a graphical user
interface 33 are connected to each other and to the transducer 2 by
wires, cables or data buses 34. In this particular transducer
application the transducer 2 is air-backed as shown. This is a
common measure for HIFU transducers in order not to generate large
amounts of waste heat. The "pulser" 31 typically delivers
continuous wave (CW) pulses or pulse trains at an operating
frequency of 1-10 megahertz for the most common HIFU applications.
The graphical user interface keeps the user informed of delivered
power levels and temperatures etc. while the logic/sensors/software
portion typically includes interlocks, system control software and
patient information inputs. It will be noted in both FIGS. 1 and 2
that the driven "hot" lead 10 connected to the energy source 12
applies the excitation energization across the piezomaterial
thickness in reference to an opposed ground electrode.
[0018] The ultrasound transducer 2 may be mounted to a medical
device 16 as shown in FIGS. 3A and 3B which is used to ablate
myocardial tissue in the manner described in the patents
incorporated herein by reference. A number of ultrasound
transducers 2 are mounted on a body 18 and the body is able to form
a closed loop around a structure such as the heart. Of course, the
present invention may be used in any suitable procedure and,
furthermore, the ultrasound transducer 2 is merely one example of
an ultrasound transducer 2 to which the present application may be
applied. Referring to FIG. 3B, the ultrasound transducer 2 may have
a fluid filled membrane 20 which acts as the contact surface to the
tissue and may also provide cooling. The fluid, such as saline, is
delivered to the membrane 20 and may either circulate in a closed
loop and/or may weep out holes 22 in the bottom of the membrane 20
as described in the patents which have been incorporated herein by
reference. As mentioned above, the present invention is directed to
modifying the characteristics of the ultrasound transducer 2 such
as the elimination of local hot spots which may cause overheating
of the nearfield tissue or excessive heating or boiling of the
nearfield juxtaposed fluid. Localized boiling can cause obvious
problems including reduction, redirection or reflection of
propagating ultrasound energy and subsequent undesired nonoptimal
treatment to tissue. Further, any nonuniformity on the transducer
face may result in a nonuniformity at the focal line(s) LS and
certainly, at-least, in nonuniformities in the acoustic beam
between the transducer face and the distal focal line(s) LS.
[0019] Depending on the particular device being manufactured, the
acceptance criteria for the activity level across the ultrasound
transducer 2 proximal face may vary depending on the nearfield,
focal and farfield uniformity requirements. For example, it may be
desirable to have uniform acoustic energy or heat generation take
place in nearby proximal tissue. The "activity" across the
transducer face 2 is a direct or indirect measure of an acoustic
parameter such as acoustic intensity output, acoustic-receive
sensitivity or acoustically output-derived waste-heat (which
correlates with acoustic output). Note here that the modification
may be applied to transducer energy output as for delivering a HIFU
therapy or may be applied to a transducer energy input as for an
acoustic receive-mode uniformity. Thus the invention is applicable
to both outgoing and incoming energy uniformities. Of course, it
may also be desired to have a controlled non-uniform distribution
of output energy (or receive-sensitivity) activity across the
ultrasound transducer as opposed to a uniform activity. In any
event the invention can correct unexpected deviations from any
desired uniformity pattern. The acceptance criteria may be an
absolute set level of activity or may simply comprise a relative
comparison of one part of the transducer with another part of the
transducer or to the transducer as a whole. Furthermore, the
transducer 2 may be activated at a power which is lower than would
be expected during operation so that the threshold criteria could,
in fact, be a lower level of activity than expected during actual
use. Low power testing may be used so long as the acceptance
criteria is relevant for the power used during testing. Thus, the
acceptance criteria may be much different than the desired
full-power operating limits of the ultrasound transducer but
usefully predictive.
[0020] The ultrasound transducer 2 is tested by activating the
transducer 2 and sensing a parameter related to the transducer
activity across all or part of the ultrasound transducer
2--typically in the nearfield, as that is where any corrective
modifications can be physically made as will be discussed.
Referring to FIG. 4, a map 24 of the activity across the ultrasound
transducer 2 output face (as seen from the exposed matching layer
8a surface) is shown. The map 24 may be an "indirect" thermal map
of acoustically-derived waste-heat or a "direct" map of acoustic
activity such as an acoustic intensity. The map 24 shown in FIG. 4
has a high activity area HA which does not meet the acceptance
criteria or threshold level of activity. As discussed above, the
high activity area HA might produce localized boiling or excessive
heating of the tissue in the near of farfields. As can be
appreciated, the map 24 of FIG. 4 may also depict acoustic activity
across the ultrasound transducer with the HA being an area where
high acoustic activity is measured. Furthermore, the map 24 may be
a steady-state map or a transient state map. The map may include
lines of activity or temperature such as isotherms as shown or may
comprise an array of values. Transient isotherms of temperature are
particularly telling of acoustic output nonuniformities. Typically,
the transient delay involved is a characteristic of the structure
and comprises a thermal diffusion time constant measured in
milliseconds to seconds. Short transient mapping allows for
inspection at very low total inputted (pulsed) power such that the
transducer optionally need not be coupled to the patient or to
water during such testing.
[0021] The term "activating" as used herein in reference to the
transducer may mean applying an activation excitation energy or
field such that acoustic energy is produced by the transducer. As
used herein, "activity" may mean any characteristic of the acoustic
energy produced by the transducer measured directly or indirectly
as described herein. "Activating" the transducer may also mean
using the transducer to receive acoustic energy which is transduced
into electrical impulses. The "activity" of the transducer in this
case would be the electrical impulses. Thus, the transducer may be
"activated" to transduce an excitation energy or field into
acoustic energy or may be "activated" to transduce acoustic energy
into electrical impulses.
[0022] The map 24 of the activity of the ultrasound transducer 2
may be created directly or indirectly in any suitable manner. For
example, the map 24 may be acquired by progressive or rastered
hydrophone scanning using known single or arrayed hydrophones,
using Schlieren-imaging, or using actual ablation of a tissue or
other thermal-witness or acoustic-witness phantom such as known
albumin-containing phantoms. The thermal map 24 may be acquired by
thermography or by the heating of a juxtaposed exposure phantom. Of
course, other measures of the activity across the ultrasound
transducer 2 may be used to determine whether higher than
acceptable activity exists when the transducer 2 is activated. The
term "map" as used herein may have one, two or even three
dimensions. The map 24 of FIG. 4 may be a transient pulsed
temperature map which is two-dimensional (three dimensional if you
account for the curved surface being imaged using thermography).
The map 24 could be one dimensional when measured along the focal
line of FIG. 1 or could be a three dimensional map when using 3D
Schlieren imaging. The term "map" may, of course, also simply be a
listing of numerical values related to the activity corresponding
to a particular area or location on the transducer 2. The term
"area of the transducer" as used herein may also have one, two or
three dimensions in keeping with the term "map" as defined herein
since the map of the area across the transducer may have one, two
or three dimensions.
[0023] It is understood that the use of a saved or stored map 24
may not strictly be necessary since one could progressively image
or sense the activity across the transducer 2 and simultaneously
modify the transducer as described herein in a piecemeal manner.
However, in preferred embodiments at-least a partial map is
obtained before any modification is carried out since the map
allows for corrections to be made to normalized criteria as well as
to absolute criteria. Thus, inspection typically involves at-least
a partial map of activity being sampled along a 1 D or 2D line or
surface. This line or surface may be sampled proximal to the
transducer face or distally near or at the transducer focus or at
any other region of the beam. The line or surface may have any
orientation with respect to the transducer and may comprise one or
more such lines or surfaces thereby forming a surface or volume of
sampling. In FIG. 4 we show a thermal map of the transducer face
itself as fired into air using a very short CW pulse such that peak
heating within the milliseconds to few-seconds timeframe is on the
order of 1 to 50 degrees C. The `map" may also comprise a
mathematically processed set of data-such as an averaged map taken
over several separate heating events. Thus, the activity of the
transducer 2 may be determined directly or indirectly in a number
of different manners without departing from the scope of the
invention. In all cases deviations being looked for are deviations
from an intended map-even if the intended map is a usefully
"shaped" nonuniform map.
[0024] Referring to FIG. 5, the ultrasound transducer 2 may be
tested and modified with a system 39 which includes a modifying
apparatus 40. The apparatus 40 may modify the transducer 2
immediately after evaluating the activity across the ultrasound
transducer 2 or may use the map 24 as discussed above to do so at a
later point in time. To this end, the system 39 may include an
activity sensor 42 which detects the level of activity across the
transducer 2 preferably in a high speed serial or even more
preferably in a rapid parallel manner. The sensor 42 may be an
acoustic sensor, a thermal sensor or another type of sensor which
detects the activity level across the transducer 2. The system 39
may simultaneously or sequentially acquire the acoustic or thermal
map 24 and then perform modification of the transducer 2 to improve
or correct that map without requiring transfer of the transducer 2
to another test apparatus. Of course, the distribution of activity
across the ultrasound transducer 2 may be saved as the map 24 so
that the ultrasound transducer 2 may be moved from the sensor 42 to
a separate modifying device 40. (40 not shown as being separate in
FIG. 5). The system 39 may also include a memory element 46, which
may be part of the modifying device 40 or sensor 42, which saves
the map 24 of activity created by the sensor 42 for use by the
modifying apparatus 40. The system 39 may also receive a number of
maps 24 of different regions of the transducer 2 or may receive a
number of maps 24 related to different parameters. It is also
understood that the transducer 2 may be directly measured in the
manner described herein or another suitable manner. The activity
across the transducer 2 may also be detected indirectly by sensing
activity in ultrasound beam in any suitable manner including some
of those described herein related to detecting acoustic activity.
Memory means, such as 46, may not only store inspection maps but
may also store the desired (perfect part) maps to which tested
parts are compared. As is known in the arts of product inspection,
the desired maps may include acceptance tolerances of an absolute
or comparative nature.
[0025] The modifying apparatus 40 may be used to modify the
distribution of activity across the ultrasound transducer 2 in any
suitable manner at one or more locations. We note that in FIG. 5
the modifying apparatus operates upon the exposed backside of the
piezomaterial/electrode 8/4. This is because in this example we
wish to directly modify the acoustics producing member (the
electroded PZT) in order to modify output. FIG. 5 illustrates that
mapping is taking place from the frontside or matching-layer 8a
side. More or less, the acoustic nonuniformities in the piezolayer
8 appear as hotspots on the overlying matching layer 8a outer
surface-particularly for short pulse times and thermally insulative
and attenuative matching layer materials. We include in the scope
of the invention practicing both mapping and modification from the
same side-such as from the backside electrode 4 side as well as
from or on opposite sides. The advantage of this is that the
thermal contrast of hot spots is maximal here where you are not
"looking through" a matching layer.
[0026] The modifying device 40 may be an excimer laser 43 which is
used to destroy or otherwise modify part of an area of high
activity. UV lasers and excimer lasers may be used since they are
capable of nonthermal removal of thin films without underlying
thermal substrate damage. Use of such an excimer laser 43 would
allow for the selective removal of electrode material from an
optically exposed electrode 4 without damaging the underlying
piezoelectric layer 8. By removing an electrode portion the
energization bias is no longer applied to the PZT in the removed
region. Another method of modifying the ultrasound transducer is to
remove electrode or acoustic-component material with the modifying
apparatus 40 being a microabrasive device which mechanically
removes material. If the transducer 2 is curved as shown in FIGS.
1, 2 and 5 the transducer 2 and/or the laser 43 may be manipulated
so that the beam impacts the electrode at a desired illumination
angle such as 90 degrees. One may optically or thermally optimize
one or both of the electrodes 4, 6 to have appropriate absorbance
or reflectivity in addition to having the required electrical and
metallurgical properties to accept solder or other connections as
necessary for the particular application and materials being used.
One may also optimize a material making up the piezocomponent 8 or
matching layer(s) 8a such that it is easily and controllably
modified by modification tool 40.
[0027] Referring to FIG. 5, the high activity area HA is easily
modified by removing or damaging a portion of electrode 4 opposite
the overactive region HA. The portion of the electrode 4 (or
electrode 6 if it is accessible to modification) that is modified
may be at the high activity area HA as shown in FIG. 5 or may be
near or around the high activity area so long as the result is to
lower the activity in the high activity area HA. The mapping and
modifying apparatus 39 may include an image acquisition and
processing device 51 which acquires and processes the inspection
map 24 relative to a desired map. The apparatus 39 may also include
powering, logic and control device 52 and a transducer power
application supply 53. Still another device 54 may be used to
perform needed motion or alignment of the transducer relative to
the modifying apparatus and/or inspection means 42. A user
interface provided by a workstation or terminal 55 is used to
control the devices and provide information to the user. The test
results may also be saved in a database 46. The various components
are coupled together with bus and cable connections 34 and uploaded
to a network. The description of the mapping and modifying
apparatus 39 is merely one example of an apparatus which may be
used to modify the transducer 2 and it can be appreciated that
numerous other devices may be used to modify transducers without
departing from the scope of the present invention. More explicitly
we note that some or all of the systems 39 functions or memory may
be network-resident in that, for example, a network provides most
or all required storage of desired and measured activity maps for
example. In another variation the mapping and modification
apparatus 39 may be able to hold several transducers 2 which can
sequentially or simultaneously at-least one of be mapped or
modified without transfer of the transducers under test. An
excellent example of this would be a system 39 wherein a
thermographic imager 43 maps an entire tray of 50 transducers.
Another variation would be where virtual instruments, such as
software, allow for a conventional PC to operate one or more test
and modification tools.
[0028] The ultrasound transducer 2 may be modified in a number of
different ways but what they all have in common is that an acoustic
activity parameter relating to the transducers function or acoustic
beam will be beneficially directly or indirectly modified at least
one physical location. This location is typically on or at the
transducer but could also be, for example, in an acoustic standoff
material that spaces the transducer from the workpiece or patient
and through or across which acoustic energy is transmitted or
received. The ground electrode 6 or the active electrode 4 may be
altered at areas of activity not meeting the acceptance criteria,
such as regions of unacceptably high activity, using the laser 43
or the like-give modification access. In one embodiment, for
example, the activity sensor 42 performs an image-wise thermography
test and electrode material is removed as necessary such as with
the laser 43 in order to reduce the acoustic (and thermal) hotspot.
The thermography test may be conducted on one side, such as the
output matching-layer frontside or active side of the transducer 2,
while the material is removed from the other side of the transducer
2 as shown in FIG. 5. This dual-side approach allows plenty of room
for the mapping and modification apparatus and any motions they
need to undergo.
[0029] We note that in FIG. 5 if one were to employ thermographic
imaging 42 and utilize a galvanometer-scannable modification laser
43 it would be possible to carry out the entire mapping and
modification sequence with minimal or no movement of the major
parts of the apparatus or of the workpiece. Mapping may be
accomplished using minimal or no mapping-required movement and that
modification will be done using lasers and minimal motions, if any,
to retain desired laser focusing and directing. "Motion" refers to
relative motion which may include moving one or more of the various
portions of the apparatus and/or the transducer. Thermographic
imaging cameras are routinely available as from FLIR Systems of
Boston, Mass. Their S-series and Phoenix.TM. models offer high
frame rates of up to hundreds of frames per second and high
sensitivity.
[0030] Referring to FIGS. 6A to 6F, various techniques for altering
the activity across a transducer 2 are shown. FIGS. 6A-6F show
localized alteration of the transducer 2, such as at or near the
high activity area HA, however, it is understood that the localized
alteration may take place at one or more discrete locations.
Furthermore, the present invention is useful in modifying the
transducer 2 prior to adding the matching layers 8A. Of course, the
transducer 2 may also be modified after adding the matching
layer(s) 8A.
[0031] Beginning with FIG. 6a we see a transducer 2 having the
typical hot electrode 4 ground electrode 6, and intermediate
piezomaterial such as PZT 8. This figure depicts the hotspot HA
being modified by removing a portion of the hot excitation
electrode 4 generally opposite the hot spot. The missing electrode
4 portion results in the region HA receiving less of a pulsed
energization and thus results in reducing the local acoustic power.
It should be obvious that the larger the area of removed electrode
4, the larger the region which is reduced in acoustic output
intensity. The piezomaterial 8 of FIG. 6a has a uniform poling P1
which is depicted as not being altered by the electrode removal
modification. This can be accomplished, as previously described, by
using a nonthermal excimer laser to etch the electrode away
locally.
[0032] Moving now to FIG. 6b we see another transducer 2. This
transducer hotspot HA has been modified. Similarly to that of FIG.
6a however note that the poling of the piezomaterial 8 beneath the
etched electrode region has been reduced to P2 from its original
higher level P1. This is what would happen if a thermal-based laser
such as a Nd-YAG or C02 laser is used. Such thermal-based lasers
inevitable heat the PZT not only through the electrode but once the
PZT is exposed. From an acoustics point of view the transducer of
FIG. 6b not only has a missing modified electrode portion but the
PZT in that selected region is also selectively depoled or reduced
in poling level by heating toward the known Curie temperature of
paiticular PZT formulations. The acoustic difference between the
modified structures of FIGS. 6a and 6b is that in the FIG. 6a
structure, since the PZT in the HA area is still poled, one can
have fringing electrical fields from remaining adjacent electrode
still firing the PZT to some degree. In the case of FIG. 6b because
the poling in the region HA has been reduced, possibly to zero, the
fringing fields are unable to excite the PZT in the region of HA.
This difference is small in the overall spectrum of transducer 2
unless one has a significant number or area of modified
regions.
[0033] Moving now to FIG. 6c we see the case wherein a
thermally-based laser has heated the electrode in the HA region
which, in turn or in parallel, heats the underlying PZT in the HA
region. In this case the heating is insufficient to ablate the
electrode but is high enough to locally depole the PZT to reduced
poling P2 in the region HA.
[0034] FIG. 6d shows a transducer 2 for the case wherein a laser
ablates and removes the electrode at region HA and provides modest
nonzero heating to the PZT however that heating is below the Curie
temperature so the poling remains at the original P 1 level.
[0035] FIG. 6e shows a transducer 2 wherein in the general HA
hotspot region we have deposited a small mass of material on the
electrode 6e. Adding mass will provide a mass-loading downshift of
the local frequency spectra. This spectral contribution change will
be superimposed on the overall transducer 2 spectrum. Thus such
mass-loading may be implemented in order to beneficially affect not
only the local spectral contribution but the overall integrated
spectrum.
[0036] FIG. 6f shows a transducer wherein mass has been removed
from the electrode in a hotspot region HA. The mass removal has two
effects. The first is a frequency upshift opposite that of FIG. 6e.
The second is that the electrode becomes more resistive in the HA
region thus delivering a slightly lower voltage pulse. Included in
the scope of the invention is the case wherein the modification
means, such as a thermal laser, heats an electrode and either
increases or decreases its local resistivity in order to affect the
applied local voltage pulse.
[0037] We have repeatedly referred to HA as a hotspot as an
illustrative deviation from a desired activity level at that
location. We emphasize now that the deviation being mapped and
modified can be any deviation of any one or more acoustic or
electro-acoustic parameters which affect the acoustic performance
in transmit or receive operation. We emphasized as illustrative
examples electrode removal and PZT depoling. Other variables that
are known to be influenced by such localized electrode and/or
piezomaterial modifications include PZT Kt and capacitance as well
as crystallographic stiffnesses and coupling coefficients. We also
show our transducer as a monolithic transducer 2. The scope of the
invention also covers the cases where the transducer is of a
composite or multi-element nature. The activity being modified may
be any acoustic or electroacoustic activity such as an acoustic
intensity, an acoustic frequency spectrum, an acoustic coupling
coefficient, a degree or state of poling, an electroacoustic loss
factor or coupling coefficient, a phase of an acoustic wave, a mass
or dimension of an acoustic component which affects mass-loading, a
resonant behavior or a degree of narrow or broad bandedness for
example. Any one or more passive or active materials that is part
of the transducer or is in the acoustic path forwards or backwards
may be so modified. It will also be realized from figures such as
FIGS. 6b and 6c that the PZT properties are actually rendered
nonuniform in the thickness dimension despite the fact that the
example modification means address the materials from only one
face.
[0038] Thus, it can be appreciated that the modification of
activity across the transducer 2 may be accomplished in a number of
different ways. Of course, various methods and devices described
herein may be used together to modify the characteristics of the
transducer.
[0039] After modification of the transducer 2, the transducer 2 may
be retested to determine whether any areas still do not meet the
threshold criteria and/or to validate the modification(s) made. If
parts of the ultrasound transducer 2 still do not meet the maximum
deviation criteria the ultrasound transducer 2 may be modified
further and retested as necessary. After modification of the
ultrasound transducer 2, parts of the ultrasound transducer 2 may
be selectively repaired or restored after being modified. An
example of this would be wherein an electrode was locally removed
in order to locally depole the PZT but the manufacturer desires to
replace the missing electrode simply to chemically protect the
depoled PZT in that modified region.
[0040] It will be understood that one may optionally conduct
mapping and modification operations in parallel on a given
transducer--and perhaps even two or more of mapping, modification,
and remap validation. Such decisions will preferably be limited
only by the physical interference of the mapping and modification
hardware.
[0041] It will also be understood that we have shown in our
examples the transducer under test being fired at a low power in
air. One may also choose to fire the transducer into water or into
a phantom. In such a case one could map from the PZT exposed
backside using thermography or from the transducer frontside using
hydrophones or Schlieren imaging, for example, and modify in-place
or after moving to a separate station. Certain acoustic behaviors
and thermal behaviors, particularly if they are of a nonlinear
nature, may best be seen using full power testing. Thus the
invention is not limited to testing at low power and inferring high
power behavior.
[0042] We have mentioned that the invention may be applied to
transducers coupled to acoustic standoffs or spacers widely known
to the acoustic arts. Such standoffs are frequently used to
implement skin cooling, to implement disposable standoff sanitary
skin-contact schemes, or to move the acoustic focus back toward the
skin surface. The modification means of the invention may be used,
for example, to modify the passive acoustic attenuation of the
standoff material to reduce hotspots at the focal region-even if
the focal hotspot is caused by a hotspot on the transducer face its
negative consequence can be modified by a downstream prefocal
propagation modification.
[0043] The present invention has been described in connection with
various preferred embodiments, however, it is understood that
various modifications may be made without departing from the scope
of the invention. Furthermore, the present invention may be applied
to a wide variety of acoustic producing devices including
piezoacoustic, magnetoacoustic, electroacoustic, thermoacoustic,
optoacoustic and micromechanical ones and is not limited to those
discussed, described or suggested herein.
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