U.S. patent application number 12/464655 was filed with the patent office on 2009-11-19 for medical device with liquid filled housing.
This patent application is currently assigned to CARDIAC PACEMAKERS, INC.. Invention is credited to Douglas J. Brandner, Scott Dahl, Kevin J. Ely, William J. Linder, John H. Tangren.
Application Number | 20090287263 12/464655 |
Document ID | / |
Family ID | 41316884 |
Filed Date | 2009-11-19 |
United States Patent
Application |
20090287263 |
Kind Code |
A1 |
Dahl; Scott ; et
al. |
November 19, 2009 |
MEDICAL DEVICE WITH LIQUID FILLED HOUSING
Abstract
Embodiments of the invention are related to medical devices
filled with a liquid composition, amongst other things. In an
embodiment, the invention includes a hermetically sealed housing
defining an interior volume, a component module disposed within the
interior volume, the component module comprising a circuit board,
the component module displacing a portion of the interior volume. A
liquid composition can be disposed within the housing, the liquid
composition filling at least 80% of the interior volume not
displaced by the component module. Other embodiments are also
included herein.
Inventors: |
Dahl; Scott; (Minneapolis,
MN) ; Tangren; John H.; (Lino Lakes, MN) ;
Ely; Kevin J.; (Youngsville, NC) ; Brandner; Douglas
J.; (New Brighton, MN) ; Linder; William J.;
(Golden Valley, MN) |
Correspondence
Address: |
PAULY, DEVRIES SMITH & DEFFNER, L.L.C.
PLAZA VII- SUITE 3000, 45 SOUTH SEVENTH STREET
MINNEAPOLIS
MN
55402-1630
US
|
Assignee: |
CARDIAC PACEMAKERS, INC.
St. Paul
MN
|
Family ID: |
41316884 |
Appl. No.: |
12/464655 |
Filed: |
May 12, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61053157 |
May 14, 2008 |
|
|
|
Current U.S.
Class: |
607/2 |
Current CPC
Class: |
A61N 1/37512 20170801;
A61N 1/3968 20130101; A61N 1/375 20130101; A61N 1/362 20130101 |
Class at
Publication: |
607/2 |
International
Class: |
A61N 1/36 20060101
A61N001/36 |
Claims
1. An implantable medical device comprising: a hermetically sealed
housing defining an interior volume; a component module disposed
within the interior volume, the component module comprising a
circuit board, the component module displacing a portion of the
interior volume; and a liquid composition disposed within the
housing, the liquid composition filling at least 80% of the
interior volume not displaced by the component module.
2. The implantable medical device of claim 1, wherein the pressure
within the interior volume is greater than 760 mmHg.
3. The implantable medical device of claim 1, wherein the pressure
within the interior volume is greater than 800 mmHg.
4. The implantable medical device of claim 1, the biocompatible
liquid composition comprising a liquid at temperatures between -50
degrees Celsius and 150 degrees Celsius and at pressures between
about 380 mm Hg and 2280 mm Hg.
5. The implantable medical device of claim 1, the device comprising
between about 1 ml and 3 ml of the liquid composition.
6. The implantable medical device of claim 1, wherein the liquid
composition is biocompatible.
7. The implantable medical device of claim 1, the liquid
composition comprising a material selected from the group
consisting of fluorocarbons, hydrofluoroethers, silicone oils,
mineral oils, and esters.
8. The implantable medical device of claim 1, the liquid
composition comprising a perfluorocarbon.
9. The implantable medical device of claim 1, the liquid
composition comprising a material selected from the group
consisting of perfluorodecalin and 1-bromoperfluorooctane.
10. The implantable medical device of claim 1, the liquid
composition comprising a liquid material with a dielectric strength
of greater than about 0.5 kV/mm.
11. The implantable medical device of claim 1, the liquid
composition comprising a liquid material with a dielectric strength
of greater than about 5 kV/mm.
12. The implantable medical device of claim 1, the liquid
composition comprising a liquid materials with a kinematic
viscosity of less than about 1000 cSt at 25 degrees Celsius.
13. The implantable medical device of claim 1, the liquid
composition comprising a liquid material with a coefficient of
thermal expansion of less than about 0.01 per degree Celsius.
14. The implantable medical device of claim 1, the liquid
composition filling at least 95% of the interior volume not
displaced by the component module.
15. The implantable medical device of claim 1, the liquid
composition filling at least 99% of the interior volume not
displaced by the component module.
16. The implantable medical device of claim 1, the housing
comprising an electrically conductive material.
17. The implantable medical device of claim 16, the electrically
conductive material comprising titanium.
18. The implantable medical device of claim 1, the electronics
module configured to generate an electrical stimulation pulse.
19. The implantable medical device of claim 1, further comprising
an electrical conductor in electrical communication with the
component module, the hermetically sealed housing comprising a
housing wall, the electrical conductor passing across the housing
wall.
20. An implantable medical device comprising: a hermetically sealed
housing defining an interior volume, the pressure within the
interior volume greater than 760 mm Hg; an electronics module
disposed within the housing, the electronics module displacing a
portion of the interior volume, the difference between the interior
volume and the portion displaced by the electronics module
comprising a residual volume; and a liquid composition disposed
within the housing, the liquid composition filling at least 90% of
the residual volume.
21. An implantable medical device comprising: a header module; a
hermetically sealed housing defining an interior volume, the
pressure within the interior volume greater than 760 mm Hg, the
housing coupled to the header module; an electronics module
disposed within the housing, the electronics module displacing a
portion of the interior volume; an electrical conductor providing
electrical communication between the electronic module and the
header module; and a liquid composition disposed within the
housing, the liquid composition filling at least 90% of a residual
volume of the housing.
Description
[0001] This application claims the benefit of U.S. Provisional
Application No. 61/053,157, filed May 14, 2008, the content of
which is herein incorporated by reference.
TECHNICAL FIELD
[0002] This disclosure relates generally to medical devices and,
more particularly, to medical devices including a liquid filled
housing, amongst other things.
BACKGROUND OF THE INVENTION
[0003] Some medical devices include a housing that holds and
protects electronic components. By way of example, implantable
cardiac rhythm management (CRM) devices such as pacemakers and
implantable cardioverter defibrillators frequently include a
housing that hermetically seals off an interior volume. Components,
such as electronic components, used to generate and control
electrical stimulation pulses are then disposed within the
hermetically sealed interior volume of the housing.
[0004] Frequently, there is some amount of the volume of the
housing that remains unused after the device components are placed
within the housing. This space can be referred as the "residual
volume" or the "free interior volume". In some circumstances, this
residual volume has simply been filled with ambient air. In other
circumstances, the residual volume of housings has been filled with
a non-reactive gas such as pure nitrogen. In still other
circumstances, the residual volume of housings has been filled with
a solid such as an epoxy.
SUMMARY OF THE INVENTION
[0005] Embodiments of the invention are related to medical devices
filled with a liquid composition, amongst other things. In an
embodiment, the invention includes a hermetically sealed housing
defining an interior volume, a component module within the housing,
and a liquid composition disposed within the residual volume of the
housing. Embodiments herein can be used in a variety of
applications including, but not limited to, implantable medical
devices generally, but more specifically, cardiac rhythm management
devices, such as pacemakers, cardiac resynchronization therapy
(CRT) devices, remodeling control therapy (RCT) devices,
cardioverter/defibrillators, and
pacemaker-cardioverter/defibrillators.
[0006] This summary is an overview of some of the teachings of the
present application and is not intended to be an exclusive or
exhaustive treatment of the present subject matter. Further details
are found in the detailed description and appended claims. Other
aspects will be apparent to persons skilled in the art upon reading
and understanding the following detailed description and viewing
the drawings that form a part thereof, each of which is not to be
taken in a limiting sense. The scope of the present invention is
defined by the appended claims and their legal equivalents.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] The invention may be more completely understood in
connection with the following drawings, in which:
[0008] FIG. 1 is a schematic view of a device in accordance with an
embodiment disposed within a subject.
[0009] FIG. 2 is a schematic view of an exemplary medical device in
accordance with an embodiment.
[0010] FIG. 3 is a schematic cross-sectional view of an exemplary
medical device in accordance with an embodiment.
[0011] FIG. 4 is a schematic view of components of an exemplary
medical device in accordance with an embodiment.
[0012] FIG. 5 is a schematic cross-sectional view of an exemplary
medical device including a sensor.
[0013] While the invention is susceptible to various modifications
and alternative forms, specifics thereof have been shown by way of
example and drawings, and will be described in detail. It should be
understood, however, that the invention is not limited to the
particular embodiments described. On the contrary, the intention is
to cover modifications, equivalents, and alternatives falling
within the spirit and scope of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0014] Frequently, there is some volumetric amount of a medical
device housing that remains unused after the device components are
placed within the housing. This unused volume can be referred to as
a "residual volume" or "free interior volume". In some instances in
the past, this residual volume has simply been filled with ambient
air. However, ambient air contains components such as oxygen that
can contribute to the degradation of some materials. In other
circumstances, the residual volume of housings was filled with a
non-reactive gas such as pure nitrogen. In still other
circumstances, the residual volume of housings was filled with a
solid such as an epoxy. However, a solid can undesirably serve to
concentrate stresses inside the housing in certain areas,
potentially leading to decreased service life. Furthermore, an
epoxy filling can make it very difficult to deconstruct the device
for purposes of failure analysis.
[0015] Embodiments of the present invention can include medical
devices where the residual volume is filled with a liquid
composition. In contrast to approaches described above such as
filling the residual volume with air, nitrogen, or epoxy, filling
the residual volume with a liquid in accordance with embodiments
herein can offer various advantages.
[0016] In some embodiments the liquid can serve to evenly
distribute pressure throughout the interior volume, thereby
minimizing stresses on individual components. As such, medical
devices in accordance with various embodiments herein can exhibit
enhanced durability with respect to forces stemming from pressure
changes, shock, vibration, and the like. This is a particularly
important benefit in the context of implantable medical devices
implanted subpectorally because of the applied forces associated
with muscle contraction and breathing.
[0017] In some embodiments the liquid filling the residual volume
can serve to evenly disperse thermal energy originating inside or
outside of the housing. Also, the thermal mass of liquids is
generally substantially higher than that of gases on a volumetric
basis. As such, the use of a liquid filling in comparison to a gas
filling can effectively provide a heat sink within the medical
device in order to safely absorb and then dissipate any thermal
energy that may exist or form within the housing of the medical
device.
[0018] In some embodiments the use of a liquid filling in
comparison to a gas filling can serve to minimize the presence of
water vapor which may otherwise contribute to the deterioration of
electronic components.
[0019] In some embodiments the use of a liquid filling can serve to
enhance longevity of the device because of the lubricious
properties of the liquid. When the internal components of a device
are bathed in a liquid, the surfaces of the components are less
susceptible to any type of frictional wear which may otherwise
occur. This is because the liquid effectively makes the surface of
such components more lubricious.
[0020] In some embodiments the use of a liquid filling in the
residual space can facilitate the use of communication techniques
that rely on propagation of a pressure wave such as ultrasonic
communication techniques. As such in some embodiments, the medical
device can include a housing, electronic components disposed within
the housing including an ultrasonic emitter and receiver, and a
liquid filling the residual space within the housing. In some
embodiments the use of a liquid filling can facilitate the
transmission of sound, allowing for more efficient sound
transmission.
[0021] In some embodiments the liquid for filling the residual
volume can be selected so as to have a relatively high dielectric
strength. As such, the liquid can be highly resistant to dielectric
breakdown. Such embodiments can offer increased protection against
internal electrical arcing.
[0022] In some embodiments the interior volume of the medical
device housing can be configured to have a slight positive pressure
with respect to the local in vivo environment. This can enhance the
rigidity of the medical device housing. In addition, as the liquid
can be substantially incompressible, filling the residual volume
can serve to preserve any spacing gap in between the wall of the
housing and the electronic components contained therein.
[0023] Referring now to FIG. 1, a schematic view is shown of an
implantable medical system 100 in accordance with an embodiment
disposed within the body 50 of a subject. The implantable medical
system 100 includes a pulse generator 101 and one or more leads
106. Depending on the configuration, the leads 106 can provide
electrical and/or optical communication between the distal ends of
the leads 106 and the pulse generator 101. In FIG. 1, the distal
ends of the leads 106 are located in the subject's heart 52.
However, it will be appreciated that the distal ends of the leads
106 could be disposed in other locations.
[0024] In various embodiments, the implantable medical device 100
can include a cardiac rhythm management device, such as a
pacemaker, a cardiac resynchronization therapy (CRT) device, a
remodeling control therapy (RCT) device, a
cardioverter/defibrillator, or a
pacemaker-cardioverter/defibrillator. In some embodiments, the
implantable medical device 100 can include a neurological
stimulation device. It will be appreciated that embodiments of the
invention can also be used in conjunction with implantable medical
devices that lack pulse generators, but include a housing, such as
monitoring devices and drug delivery devices.
[0025] Referring now to FIG. 2, an enlarged schematic view of the
device 100 of FIG. 1 is shown. The pulse generator 101 can include
a housing 102 that serves to hold and protect various components of
the device, such as a component module or an electronics module.
The housing 102 is coupled to a header module 104. The header
module 104 can include ports to receive the proximal ends 108 of
the leads 106. The header module can be made from various materials
such as polymers. The distal ends 110 of the leads 106 can include
electrodes 112 that can interface with tissue of the subject's
heart 52. However, it will be appreciated that in some embodiments
electrodes can be included at locations other than the distal ends
of the leads.
[0026] Referring now to FIG. 3, a cross-sectional schematic view is
shown of a housing 102 is shown as taken along line 3-3' of FIG. 2.
The housing 102 can include a housing wall 150. The housing wall
150 can be made of various materials including metals, polymers,
and ceramics. In some embodiments, the housing wall 150 can be
substantially rigid. In other embodiments, the housing wall 150 can
be flexible. In a particular embodiment, the housing wall 150 is
titanium. The housing wall 150 can define an interior volume 151.
Various device components can be disposed within the interior
volume 151. For example, a circuit board 154 can be disposed within
the interior volume 151. Various electronic components 156, 158,
160, 162, 164, 166, 168 can be mounted on the circuit board 154
within the housing 102. The electronic components can include
various items for operation of the device including
microprocessors, batteries, capacitors, telemetry modules,
amplifiers, transducers, converters, filters, various types of
integrated circuit chips (IC chips), and the like. Taken together,
the components (other than the liquid composition) within the
interior volume can be referred to as a component module. The
residual volume 153 is the portion of the interior volume 151 not
occupied by the component module.
[0027] A liquid composition 152 can be disposed within the residual
volume 153. In some embodiments, the liquid composition can
substantially fill the residual volume 153. In some embodiments,
the liquid composition 152 can fill at least 80% of the residual
volume 153. In some embodiments, the liquid composition 152 can
fill at least 90% of the residual volume 153. In some embodiments,
the liquid composition 152 can fill at least 95% of the residual
volume 153. In some embodiments, the liquid composition 152 can
fill at least 99% of the residual volume 153.
[0028] It will be appreciated that the total volume of the liquid
composition used with embodiments herein can vary based on the size
of the housing, the percentage of residual volume within the
housing with respect to total volume, the degree to which the
residual volume is filled, and the like. However, in some
embodiments the volume of the liquid composition 152 is between
about 0.1 ml to 30 ml. In some embodiments, the volume of the
liquid composition 152 is between about 1.0 ml and about 3.0 ml.
Aspects of exemplary liquid compositions are described in greater
detail below.
[0029] The housing 102 can be hermetically sealed. The pressure
within the housing 102 can be configured to be at atmospheric
pressure (such as equal to 760 mmHg), greater than atmospheric
pressure (such as greater than 760 mm Hg), or less than atmospheric
pressure (such as less than 760 mm Hg). While not intending to be
bound by theory, there can be advantages to configuring the
pressure within the housing 102 to be greater than atmospheric
pressure. For example, configuring the pressure within the housing
102 can, in effect, enhance the rigidity of the housing 102. As
such, where the interior of the housing 102 is at a pressure
greater than 760 mm Hg, the housing 102 would be expected to
exhibit less flexion in response to normal pressure changes within
the body than an otherwise identical housing wherein the interior
pressure is at 760 mm Hg. In some embodiments, the pressure within
the housing 102 can be greater than 780 mm Hg. In some embodiments,
the pressure within the housing 102 can be greater than 800 mm Hg.
In some embodiments, the pressure within the housing 102 can be
greater than the ambient pressure at the site in the body in which
housing 102 is to be implanted.
[0030] It will be appreciated that various components of a device
system can be housed within a housing. Referring now to FIG. 4,
some components of an exemplary implantable device system 400 are
schematically illustrated. The implantable medical system 400 can
include a housing or housing 420 coupled to one or more stimulation
leads 430 and 428. Components within the housing 420 can be
referred to as a "component module" or an "electronics module".
Components within the housing can include a microprocessor 448 (or
processor) that communicates with a memory 446 via a bidirectional
data bus. The memory 446 typically includes ROM or RAM for program
storage and RAM for data storage. The microprocessor 448 can be
configured to execute various operations such as processing of
signals and execution of methods as described herein. A telemetry
interface 464 is also provided for communicating with an external
unit, such as a programmer device or a patient management
system.
[0031] The components can include ventricular sensing and pacing
channels including sensing amplifier 452, output circuit 454, and a
ventricular channel interface 450 which communicates
bidirectionally with a port of microprocessor 448. It will be
appreciated that in some embodiments some of the components shown
in FIG. 4 may be omitted. Further, in some embodiments, additional
elements may be included. By way of example, various embodiments
can include a power supply, such as a battery, though not shown in
FIG. 4. In addition, various embodiments can include a circuit
board (such as that shown in FIG. 3) for purposes of mounting
various electronic components.
[0032] The ventricular sensing and pacing channel can be in
communication with stimulation lead 430 and electrode 434. The
device can include atrial sensing and pacing channels including
sensing amplifier 458, output circuit 460, and an atrial channel
interface 456 which communicates bidirectionally with a port of
microprocessor 448. The atrial sensing and pacing channel can be in
communication with stimulation lead 428 and electrode 432. For each
channel, the same lead and electrode can be used for both sensing
and pacing. The channel interfaces 450 and 456 can include
analog-to-digital converters for digitizing sensing signal inputs
from the sensing amplifiers and registers which can be written to
by the microprocessor in order to output pulses, change the pacing
pulse amplitude, and adjust the gain and threshold values for the
sensing amplifiers. A shock pulse generator 474 can also be
interfaced to the microprocessor for delivering defibrillation
shocks to the heart via a separate pair of electrodes 476, 478. In
some embodiments, electrodes 476 and 478 can be disposed along
stimulation lead 430 and stimulation lead 428 respectively.
[0033] It will be appreciated that in some embodiments, devices and
systems herein can include sensors. By way of example, as part of
the component module of a device, a sensor can be included. The
sensor can be disposed within the housing of the device. Referring
now to FIG. 5, a schematic cross-sectional view of an exemplary
medical device 500 including a sensor 564 is shown. The device 500
can include a housing wall 550. The housing wall 550 can define an
interior volume 551. Various device components can be disposed
within the interior volume 551. For example, a circuit board 554
can be disposed within the interior volume 551. Various electronic
components (such as 562) can be mounted on the circuit board 554 on
the inside of the housing wall 550. In this embodiment, the sensor
564 is mounted on the circuit board. However, it will be
appreciated that the sensor 564 could also be within the interior
volume, but separate from the circuit board 554. The sensor can be,
for example, an acoustic sensor, an accelerometer (such as a
fluid-filled accelerometer), a temperature sensor, a pressure
sensor, or the like.
[0034] In some embodiments, the sensor can be part of a switch
element, such as a pressure sensitive switch. In such embodiments,
the device can be configured to initiate various actions based on
switching of the pressure sensitive switch.
Exemplary Liquid Compositions
[0035] Embodiments herein can include a housing filled with a
liquid composition. The liquid composition can be substantially
inert. In some embodiments, the liquid composition can prevent
oxidation of electronic components within the housing. In some
embodiments, the liquid compositions can be biocompatible.
[0036] The liquid composition can have a dielectric strength
sufficient to prevent arcing between electronic components within
the housing. In some embodiments, the dielectric strength of the
liquid composition is greater than about 0.5 kV/mm. In some
embodiments, the dielectric strength of the liquid composition is
greater than about 1.0 kV/mm. In some embodiments, the dielectric
strength of the liquid composition is greater than about 5.0
kV/mm.
[0037] In some embodiments, the liquid composition has a kinematic
viscosity sufficiently low so that the housing can be filled
effectively through an aperture or port. In some embodiments, the
liquid composition 213 can have a kinematic viscosity of less than
about 20,000 cSt at 25 degrees Celsius. In some embodiments, the
liquid composition 213 can have a kinematic viscosity of less than
about 10,000 cSt at 25 degrees Celsius. In some embodiments, the
liquid composition 213 can have a kinematic viscosity of less than
about 1000 cSt at 25 degrees Celsius.
[0038] It will be appreciated that the device may be exposed to a
variety of different temperatures such as during shipping and
storage prior to implantation. The liquid composition can have a
thermal expansion coefficient that is relatively small to prevent
large pressure changes within the housing. The liquid composition
can have a thermal expansion coefficient of less than about 0.1 per
degree Celsius. The liquid composition can have a thermal expansion
coefficient of less than about 0.01 per degree Celsius. In some
embodiments, the liquid composition can have a thermal expansion
coefficient of less than about 0.001 per degree Celsius.
[0039] Exemplary liquid compositions can be in a liquid state at
temperatures between about -50 degrees Celsius and 150 degrees
Celsius and at pressures between 380 mm Hg (0.5 ATM) and 2280 mm Hg
(3.0 ATM). Exemplary liquid compositions can be in a liquid state
at temperatures of about 37 degrees Celsius and at pressures
between about 720 mm Hg and 800 mm Hg.
[0040] In some embodiments, liquid compositions herein can be
selected that remain a liquid long term. For example, liquid
compositions can be used that remain a liquid for the duration of
the medical device. In some embodiments, the liquid is selected so
that it can reversibly change from one physical state of matter to
another. For example, in some embodiments the liquid can be
selected so that it is in a flowable liquid state during a filling
operation of the device, then changes to a solid form, then can be
converted back to a liquid through the application of heat,
electricity, pressure, or the like.
[0041] Exemplary liquid compositions can include halogen
substituted organic compounds such as fluorocarbons (including
perfluorocarbons) and hydrofluoroethers, silicone oils
(polysiloxane liquids), mineral oils, and esters. Specific examples
can include, but are not limited to, perfluorodecalin,
perfluorooctylbromide, perfluorotripropylamine,
perfluorotripentylamine, and 1-bromoperfluoroctane. Exemplary
liquid compositions are commercially available and sold under the
trade names FLUOROMED.RTM., FLUORINERT.TM., NOVEC.RTM., NUSIL.RTM.,
and SILIKON.RTM..
Example Fill Methods
[0042] Various methods can be used to fill the residual volume of a
hermetically sealed housing. In some embodiments, an aperture or
hole is formed in the housing in order to allow the insertion of a
liquid composition. The hole location(s) for each device can be
selected to avoid potential contact with internal electronic
components and to facilitate removal of any air bubbles. In other
embodiments, the liquid can be in place before the housing is fully
formed. By way of example, the component module can be disposed
within a bath of the liquid composition and then the housing can be
welded in place around the component module within the bath.
[0043] In embodiments where an aperture or apertures are formed in
the housing, the liquid composition can be introduced into the
interior volume by submersing the housing in the liquid
composition. In some embodiments, a syringe or similar instrument
can be used to inject the liquid composition into the housing.
[0044] In embodiments where an aperture or apertures are formed in
the housing, the apertures can be plugged or sealed after the
liquid composition is inserted. As an example, the apertures or
holes can be sealed by welding a small titanium sphere over them.
In another example, a titanium patch can be laser welded over the
aperture(s).
[0045] The present invention may be better understood with
reference to the following examples. These examples are intended to
be representative of specific embodiments of the invention, and are
not intended as limiting the scope of the invention.
EXAMPLES
Example 1
Device HALT (Highly Accelerated Life Test) Testing Performance
[0046] CRM devices with titanium housings (RENEWAL DS, Boston
Scientific Corporation, Natick, Mass.) were obtained and used for
HALT testing. Holes (1.58 mm) were milled in the titanium housings.
A liquid composition (perfluorodecalin, FLUOROMED APF-140HP) was
inserted into the housing through the holes. Specifically, the
device were immersed in the liquid composition. A syringe was also
used to insert the liquid composition. The housings were then
sealed by welding a titanium sphere over the hole or by welding a
titanium patch over the hole.
[0047] The liquid composition-filled devices were then tested in a
HALT testing chamber. The conditions were .about.80.degree. C. and
vibration of 60 G.sub.rms. The test duration was between 8 and 14
hours. The objective was to assess and compare the durability of
the liquid filled devices in comparison with similar gas filled
devices in response to vibration forces.
[0048] Data for the liquid filled devices was then compared with
previous HALT testing of gas filled CRM devices. The gas filled
devices were tested with a slightly different procedure than the
liquid filled devices. Instead of a constant temperature and
vibration level, the gas filled devices were tested using a series
of step changes in temperature and vibration levels.
[0049] Time to failure data for the devices tested in this study
are provided in Table 1, below. The data was analyzed using
RELIASOFT.RTM. Weibull++.RTM. v.6 software program. Since only one
of the liquid filled devices experienced a failure, the Weibull
distribution was calculated using the assumption that the
Beta-value of the liquid filled devices is the same as the
Beta-value for the gas filled devices. In addition, a MLE (Maximum
Likelihood Estimation) analysis method was selected because of the
relatively large number of suspended data points.
TABLE-US-00001 TABLE 1 HALT testing conditions and results Testing
Conditions Time to Temp Vibration Duration Failure Device Fill
.degree. C. G (rms) (Hours) (Hours) RENEWAL DS Liquid 80 60 8 No
Failure H175 RENEWAL DS Liquid 80 60 14 No Failure H175 RENEWAL DS
Liquid 80 60 14 10.5 H195 RENEWAL DS Gas 80 60 12 3 H175 RENEWAL DS
Gas 80 60 12 No Failure H175 RENEWAL DS Gas 80 60 12 No Failure
H177 RENEWAL DS* Gas 80 60 4 1-4 *represents data for a plurality
of device models
[0050] The data show that the time to failure for liquid filled
devices is approximately six times greater than the time to failure
for the gas filled devices. The improved performance was attributed
to a viscous damping effect minimizing damage from shock and
vibration.
[0051] It should be noted that, as used in this specification and
the appended claims, the singular forms "a," "an," and "the"
include plural referents unless the content clearly dictates
otherwise. It should also be noted that the term "or" is generally
employed in its sense including "and/or" unless the content clearly
dictates otherwise.
[0052] It should also be noted that, as used in this specification
and the appended claims, the phrase "configured" describes a
system, apparatus, or other structure that is constructed or
configured to perform a particular task or adopt a particular
configuration. The phrase "configured" can be used interchangeably
with other similar phrases such as "arranged", "arranged and
configured", "constructed and arranged", "constructed",
"manufactured and arranged", and the like.
[0053] All publications and patent applications in this
specification are indicative of the level of ordinary skill in the
art to which this invention pertains. All publications and patent
applications are herein incorporated by reference to the same
extent as if each individual publication or patent application was
specifically and individually indicated by reference.
[0054] This application is intended to cover adaptations or
variations of the present subject matter. It is to be understood
that the above description is intended to be illustrative, and not
restrictive. The scope of the present subject matter should be
determined with reference to the appended claims, along with the
full scope of equivalents to which such claims are entitled.
* * * * *