U.S. patent application number 14/688134 was filed with the patent office on 2015-08-06 for energy harvester device for autonomous intracorporeal capsule.
This patent application is currently assigned to SORIN CRM SAS. The applicant listed for this patent is SORIN CRM SAS. Invention is credited to Martin Deterre, Elie Lefeuvre.
Application Number | 20150217123 14/688134 |
Document ID | / |
Family ID | 45937123 |
Filed Date | 2015-08-06 |
United States Patent
Application |
20150217123 |
Kind Code |
A1 |
Deterre; Martin ; et
al. |
August 6, 2015 |
ENERGY HARVESTER DEVICE FOR AUTONOMOUS INTRACORPOREAL CAPSULE
Abstract
An energy harvester device for an autonomous intracorporeal
leadless capsule comprises a surface formed on the outside of the
body of the capsule that is deformable under the effect of pressure
variations in the environment surrounding the capsule. A first
capacitor electrode coupling to the deformable surface with the
interposition of a damping element forming high-pass filter with
respect to pressure variations in the surrounding medium, and a
second capacitor electrode mounting on a support connected to the
body. The movement of the deformable surface produces a
modification of surfaces in vis-a-vis of the two electrodes and/or
of the dielectric gap which separates them, with a variation of the
capacity of said capacitor. The capacitor is preloaded when its
capacity is maximum, and unloaded by transferring energy into
storage circuit when this capacity decreases from a reduction in
surfaces in vis-a-vis and/or of an increase of the dielectric
gap.
Inventors: |
Deterre; Martin; (Paris,
FR) ; Lefeuvre; Elie; (Montreuil, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SORIN CRM SAS |
Clamart |
|
FR |
|
|
Assignee: |
SORIN CRM SAS
Clamart
FR
|
Family ID: |
45937123 |
Appl. No.: |
14/688134 |
Filed: |
April 16, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13464795 |
May 4, 2012 |
9014818 |
|
|
14688134 |
|
|
|
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Current U.S.
Class: |
607/7 |
Current CPC
Class: |
A61N 1/3756 20130101;
A61N 1/3785 20130101; A61N 1/3975 20130101 |
International
Class: |
A61N 1/39 20060101
A61N001/39 |
Foreign Application Data
Date |
Code |
Application Number |
May 4, 2011 |
FR |
1153790 |
Claims
1. An autonomous intracorporeal leadless capsule, comprising: a
circuit; an energy harvesting device with at least one movable
surface for powering the circuit; a capsule body having a
deformable element directly exposed to an environment exterior of
the capsule body, the circuit and the energy harvesting device
within the capsule body; and a mechanical high-pass filter
positioned within the capsule body, wherein the mechanical
high-pass filter comprises a piston having a rod, the rod extending
from the piston out of a chamber and coupling to the at least one
movable surface of the energy harvesting device.
2. The capsule of claim 1, wherein the mechanical high-pass filter
facilitates movement of the piston during high frequency
displacements of the deformable element such that the movement of
the piston is transferred to the at least one movable surface.
3. The capsule of claim 1, wherein the mechanical high-pass filter
prevents the movement of the piston during low frequency
displacements of the deformable element such that the piston does
not move.
4. The capsule of claim 1, wherein the chamber is fixed to and
movable with the deformable element with respect to at least one of
the capsule body and the piston.
5. The capsule of claim 1, wherein the chamber is filled with a
fluid, the piston separating the chamber into a first volume and a
second volume.
6. The capsule of claim 5, wherein the piston and an inner surface
of the chamber are separated by a calibrated clearance.
7. The capsule of claim 6, wherein the calibrated clearance
provides a passageway for the fluid to flow between the first
volume and the second volume.
8. The capsule of claim 6, wherein the calibrated clearance is
sized to restore a pressure equilibrium within the chamber such
that low frequency displacements of the deformable element are not
transferred to the at least one movable surface.
9. A method for powering an autonomous intracorporeal leadless
capsule, comprising: receiving a low frequency pressure variation
at an external surface of a deformable member on the capsule, the
deformable member displacing in response to the low frequency
pressure variation; using a high pass mechanical filter to prevent
displacement of a movable member of an energy harvesting device
within the capsule responsive to the displacement of the deformable
member due to the low frequency pressure variation; receiving a
high frequency pressure variation at the external surface of the
deformable member on the capsule, the deformable member displacing
in response to the high frequency pressure variation; using the
high pass mechanical filter to facilitate the displacement of the
movable member of the energy harvesting device responsive to the
displacement of the deformable member due to the high frequency
pressure variation; and generating energy with the energy
harvesting device responsive to the displacement the movable member
of the energy harvesting device.
10. The method of claim 9, wherein the high pass mechanical filter
comprises a piston coupled to the movable member of the energy
harvesting device.
11. The method of claim 10, wherein the displacement of the
deformable member due to the high frequency pressure variation
causes a displacement of the piston, causing the movable member of
the energy harvesting device to displace.
12. The method of claim 10, wherein the piston is enclosed within a
fluid-filled chamber that is movable with the deformable
member.
13. The method of claim 12, wherein the piston and an inner surface
of the fluid-filled chamber are separated by a calibrated
clearance.
14. The method of claim 13, wherein the calibrated clearance
provides a passageway for a fluid to flow between a first volume
and a second volume of the fluid-filled chamber.
15. The method of claim 13, wherein the calibrated clearance is
sized to restore a pressure equilibrium within the fluid-filled
chamber such that the low frequency pressure variation does not
displace the piston.
16. An autonomous intracorporeal leadless capsule, comprising: a
circuit; an energy harvesting device including a capacitor
configured to facilitate powering the circuit, the capacitor
comprising opposing capacitor electrodes separated by a dielectric
gap; a capsule body having a deformable element directly exposed to
an environment exterior of the capsule body, the circuit and the
energy harvesting device within the capsule body; and a mechanical
high-pass filter positioned within the capsule body, wherein the
mechanical high-pass filter comprises a piston having a rod, the
rod extending from the piston out of a fluid-filled chamber and
coupling to one of the opposing capacitor electrodes of the
capacitor.
17. The capsule of claim 16, wherein the opposing capacitor
electrodes are movably suspended relative to the capsule body such
that relative movement of the opposing capacitor electrodes
generates power for powering the circuit.
18. The capsule of claim 16, wherein the mechanical high-pass
filter is configured to mechanically couple the deformable element
and the opposing capacitor electrodes during high frequency
displacements of the deformable element to generate power for
powering the circuit.
19. The capsule of claim 16, wherein the mechanical high-pass
filter is configured to mechanically decouple the deformable
element and the opposing capacitor electrodes during low frequency
displacements of the deformable element.
20. The capsule of claim 16, wherein the piston and an inner
surface of the fluid-filled chamber are separated by a calibrated
clearance, wherein the calibrated clearance is sized to restore a
pressure equilibrium between a first volume and a second volume
within the fluid-filled chamber such that low frequency
displacements of the deformable element are not transferred to the
one of the opposing capacitor electrodes of the capacitor by the
piston.
Description
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 13/464,795, filed May 4, 2012, which claims the benefit of and
priority to French Application No. 11/53790, filed May 4, 2011,
both of which are hereby incorporated by reference herein in their
entireties.
TECHNICAL FIELD
[0002] The present invention relates to the field of "medical
devices" as defined by the Jun. 14, 1993 directive 93/42/CE of the
European Communities, and more particularly to the "active
implantable medical devices" as defined by the of Jun. 20, 1990
directive 90/385/CEE of the European Communities. Such devices in
particular include implantable medical devices that continuously
monitor a patient's cardiac rhythm and deliver if necessary to the
heart electrical pulses for cardiac stimulation, resynchronization,
cardioversion and/or defibrillation in case of a rhythm disorder
detected by the device. Such devices also include neurological
devices, cochlear implants, etc., as well as devices for pH
measurement or devices for intracorporeal impedance measurement
(such as the measure of the transpulmonary impedance or of the
intracardiac impedance). The invention relates even more
particularly to those devices that implement autonomous implanted
capsules and are free from any physical connection to a main
implanted device (for example, the can of a stimulation pulse
generator).
BACKGROUND
[0003] Autonomous implanted capsules are referred to as "leadless
capsules" to distinguish them from the electrodes or sensors placed
at the distal end of a lead, which lead is traversed throughout its
length by one or more electrical conductors connecting by galvanic
conduction the electrode or the sensor to a generator connected at
the opposite, proximal end, of the lead.
[0004] Such leadless capsules are, for example, described in U.S.
Patent Pub. No. 2007/0088397 A1 and WO 2007/047681 A2 (Nanostim,
Inc.) and U.S. Patent Pub. No. 2006/0136004 A1 (EBR Systems,
Inc.).
[0005] These leadless capsules can be epicardial capsules, which
are typically fixed to the outer wall of the heart, or endocardial
capsules, which are typically fixed to the inside wall of a
ventricular or atrial cavity, by means of a protruding anchoring
helical screw, axially extending from the body of the capsule and
designed to penetrate the heart tissue by screwing to the
implantation site.
[0006] In one embodiment, a leadless capsule includes
detection/stimulation circuitry to collect depolarization
potentials of the myocardium and/or to apply pacing pulses to the
site where the leadless capsule is located. The leadless capsule
then includes an appropriate electrode, which can be included in an
active part of the anchoring screw.
[0007] It can also incorporate one or more sensors for locally
measuring the value of a parameter such as the oxygen level in the
blood, the endocardial cardiac pressure, the acceleration of the
heart wall, the acceleration of the patient as an indicator of
activity, etc. Of course, the leadless capsules incorporate
transmitter/receiver means for wireless communication, for the
remote exchange of data.
[0008] The present invention is nevertheless not limited to a
particular type of leadless capsule, and is equally applicable to
any type of leadless capsule, regardless of its functional
purpose.
[0009] Whatever the technique implemented, the signal processing
inside the leadless capsule and the remote transmission of data
into or out of the leadless capsule requires a non-negligible
energy supply as compared to the energy resources a leadless
capsule can store. However, due to its autonomous nature, the
leadless capsule can only use its own resources, such as an energy
harvester circuit (responsive to the movement of the leadless
capsule), associated with an integrated small buffer battery. The
management of the available energy is thus a crucial point for the
development of autonomous leadless capsules and their capabilities,
especially their ability to have an integrated self-power supply
system.
[0010] Various techniques of energy harvesting have been proposed,
adapted to leadless autonomous implants. U.S. Patent Pub. No.
2006/0217776 A1, U.S. Pat. No. 3,456,134 A and WO 2007/149462 A2
describe systems using piezoelectric transducers directly
transforming into electrical energy the movement of a mass
resulting from the acceleration of the patient's organs or body.
However, given the relatively low excitation frequencies (below 10
Hz), the excursions of the movements are relatively large, which
does not allow a for significant miniaturization. In addition,
since these excitations do not have stable specific frequencies,
the piezoelectric generator cannot operate in a resonant mode, and
thereby loses much of its effectiveness.
[0011] Other devices have been proposed to transform pressure
changes occurring within the body into electricity, including
changes in blood pressure or those resulting from the movements of
the patient's diaphragm during breathing. This transformation is
effected by means of a magnetic microgenerator, functioning as an
alternator or as a dynamo, by variations in magnetic flux induced
in a coil. Reference is made to U.S. Patent Pub. No. 2005/0256549
A1, GB 2350302 A, U.S. Patent Pub. Nos. 2008/0262562 A1 and
2007/0276444 A1. Due to the presence of moving parts, however, the
complexity of the design of the mechanical and electrical parts and
their relatively large volume effectively limit, the
miniaturization and the overall reliability of such a generator.
Moreover and most importantly, such a generator is inherently
sensitive to external magnetic fields and is not compatible with
the magnetic resonance imaging systems (MRI) because of the very
high static magnetic fields generated by these systems, typically
in the order of 0.5 to 3 T or more.
[0012] It also has been proposed to use an electrostatic transducer
made of electrodes modeling a capacitor, for example, with a set of
combs and interdigitated-counter combs. One of the electrodes is
secured to a support fixed on the body of the case, the other being
coupled to an oscillating mass called "seismic mass". This mass is
set in motion by movement of the entire system including the
transducer, and it carries with it one of the electrodes of the
transducer, which thus move relative to the other by a variation of
the dielectric gap and/or of the facing surfaces of the two
electrodes. If the capacitor is initially pre-loaded with an energy
charge, or if the structure includes electrets (or electrets films)
to maintain a continuous load, the capacity variation causes an
energy increase in this capacitor that can be extracted by an
electronic circuit and then stored in a buffer battery. The
mechanical energy collected by the oscillating mass can thus almost
entirely be converted into electrical energy in a single cycle.
This technique is described, for example, by F. Peano and T.
Tambosso, Design and Optimization of a MEMS Electret-Based
Capacitive Energy Scavenger, Journal of Microelectromechanical
Systems, 14 (3), 429-435, 2005, or S. Meninger et al.
Vibration-to-Electric Energy Conversion, IEEE Transactions on Very
Large Scale Integration (VLSI) Systems, vol. 9, no. 1, pp. 64-76,
2001. This type of transducer has the same drawbacks, however, as
the piezoelectric transducers because of limitations imposed by the
oscillating mass, both in terms of miniaturization (the seismic
mass is relatively large) and efficiency with respect to the
driving movements. Indeed, the relatively low excitation
frequencies (below 10 Hz) involve relatively large excursions
and/or a relatively high mass of the oscillating element, which
does not allow a significant miniaturization.
[0013] Another known energy harvester system, without an
oscillating weight, is disclosed by U.S. Patent Pub. No.
2009/021292A1. This document discloses an energy harvesting power
system incorporated into an implantable capsule in which the
housing body has a deformable element resulting from changes in
pressure of the surrounding environment. The deformation of this
element is transmitted to an electrostatic transducer directly
converting the mechanical energy of deformation into electrical
energy, which is then delivered to a power management and storage
module powering the device with energy. Note that such a system
does not need to be resonant or to contain magnetic elements.
However, the system described utilizes pressure variations that
result at least partly from mechanical forces applied to the
capsule, under the effect of contact forces with the surrounding
tissues or deformation thereof. Thus, in the case of a system that
is fully submerged in a body fluid (for example such an energy
harvesting system used in an intracardiac capsule blood pressure
changes during rapid changes in the systole-diastole cycle), the
slow variations of atmospheric pressure disrupt the operation of
the energy harvesting system: indeed, as the capsule is strictly
waterproof, its interior volume is initially at the pressure
defined during manufacturing and the equilibrium point at rest of
the deformable element is offset compared to the nominal rest
position if the atmospheric pressure varies.
SUMMARY
[0014] It is therefore an object of the present invention is to
provide an improved power generator for an implantable autonomous
leadless capsule.
[0015] It is another object to provide an energy harvesting circuit
that ensures that changes in a patient's systole-diastole cardiac
cycle are fully transmitted to the electrodes around the same
nominal rest point.
[0016] Broadly, the present invention relates to an autonomous
intracorporeal leadless capsule of a type similar to that described
in the aforementioned U.S. Patent Pub. No. 2009/021292 A1,
including a body and, within the body, electronic circuits and a
power supply including:
[0017] an energy harvester transducer, for converting an external
physical stress applied to the capsule to an electrical quantity,
this transducer comprising: [0018] a first capacitor electrode,
coupled with a movable actuator receiving said external physical
stress, the movable element of actuation of the transducer being
substantially free of an oscillating weight and comprising a
deformable surface, formed on the exterior of the capsule body and
being alternately deformed in one direction and in the other under
the effect of pressure variations in the surroundings of the
capsule; and [0019] a second capacitor electrode, mounted on a
support connected to a region of the body other than the movable
actuator, the two electrodes having facing surfaces separated by a
dielectric gap together defining a capacitor (C), and said physical
stress producing a consequential modification of said facing
surfaces and/or of said dielectric gap with correlative variation
of the capacity of said capacitor; and
[0020] a storage and power management circuit, powered by the
energy harvester transducer as a result of a decrease of the
distance between the facing surfaces and/or of an increase the
dielectric gap of the capacitor.
[0021] Both electrodes have facing surfaces separated by a
dielectric together defining a capacitor, and the deformation of
the deformable surface produces a corresponding modification of
said facing surfaces and/or of said dielectric gap with correlative
variation of the capacity of the capacitor. In addition, the
management module includes a means for preloading a charge on the
capacitor when its capacity is maximum, and of unloading the
capacitor by transferring its energy changes to a storage device
when this capacity decreases as a result of a decrease of the
distance between the facing surfaces and/or of an increase of the
dielectric gap of the capacitor.
[0022] Preferably, the deformable surface is coupled to the first
electrode with the interposition of a damping element forming a
mechanical high-pass filter with respect to pressure variations in
the medium surrounding the capsule.
[0023] In one embodiment, the deformable surface has a rigid
surface coupled to the first electrode and an elastically
deformable structure, such as a bellows or other organ, for
connecting the rigid surface to the body, or to a membrane coupled
to the first electrode in a region of greater deformation of the
latter.
[0024] In one embodiment, the first and second capacitor electrodes
are advantageously made in the form of combs and interdigitated
counter-combs, and the first capacitor electrode can be coupled to
the body of the capsule by an elastically deformable support
forming a guiding spring.
[0025] The leadless capsule may further comprise means for
preloading the capacitor when its capacity is maximum, and for
unloading it by transferring its stored energy to a storage device,
e.g., a suitable battery or other device, when that capacity
decreases as a result of a decrease in space between the facing
surfaces and/or of an increase in the dielectric gap of the
capacitor.
[0026] Advantageously, the present invention provides for improved
miniaturization: compatibility with the extremely small volume (a
few cubic millimeters) of a leadless implant;
[0027] Advantageously, the present invention provides for improved
reliability: guaranteed secured operation over several years of
lifetime of the implant;
[0028] Advantageously, the present invention provides for improved
insensitivity to magnetic phenomena, including MRI compatibility
which is now required for implanted devices;
[0029] Advantageously, the present invention provides for improved
biocompatibility: absence of external elements that can cause
inflammatory reactions.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] Further features, characteristics and advantages of the
present invention will become apparent to a person of ordinary
skill in the art from the following detailed description of
preferred embodiments of the present invention, made with reference
to the drawings annexed, in which like reference characters refer
to like elements, and in which:
[0031] FIG. 1 schematically illustrates a set of medical devices
including leadless capsules, implanted within the body of a
patient;
[0032] FIG. 2 is a functional block diagram showing the various
components of a leadless capsule;
[0033] FIGS. 3 and 4 illustrate respectively two embodiments of a
body of leadless capsule of the present invention;
[0034] FIGS. 5a and 5b are schematic sectional views of a first
embodiment of an electrostatically energy harvesting leadless
capsule of the present invention;
[0035] FIG. 6 is a plan view taken along line VI-VI of FIG. 5a, of
the first embodiment of the electrostatically energy harvesting
leadless capsule;
[0036] FIG. 7 is a load/voltage diagram illustrating two methods to
operate the energy harvesting circuit, at constant load or at
constant voltage, respectively;
[0037] FIG. 8 is a schematic representation of an energy harvester
circuit with constant voltage;
[0038] FIG. 9 is a schematic representation of an energy harvester
circuit at constant load;
[0039] FIG. 10 illustrates a second embodiment of an
electrostatically energy harvesting leadless capsule of the present
invention, for energy harvesting in both directions of movement of
the movable electrode;
[0040] FIG. 11 illustrates a third embodiment of an
electrostatically energy harvesting leadless capsule, of the
present invention using a stack of structures such as that
illustrated in FIG. 5a for the first embodiment;
[0041] FIG. 12 illustrates a fourth embodiment of an
electrostatically energy harvesting leadless capsule, wherein the
deformable element is a flexible membrane;
[0042] FIG. 13 illustrates a fifth embodiment of an
electrostatically energy harvesting leadless capsule, using a
bellows for connecting the movable element to the body of the
capsule;
[0043] FIG. 14 illustrates an embodiment of a leadless capsule
according to the present invention, applicable to the various
embodiments described above, that eliminate the effects of the slow
variations of pressure;
[0044] FIG. 15 illustrates an embodiment of an electrostatically
energy harvesting leadless capsule, using photolithographic
technology to produce fixed combs and movable counter-combs
suspended by guiding springs; and
[0045] FIGS. 16 and 17 illustrate two alternative embodiments of
the capacitor structure, particularly adapted to the use of
armatures carrying electrets.
DETAILED DESCRIPTION
[0046] With reference to the drawing FIGS. 1-17, various examples
of preferred embodiments of an electrostatically energy harvesting
capsule will be described.
[0047] With reference to FIG. 1, a set of medical devices implanted
in the body of a patient is shown. This set is equipped with a
device 10 such as an implantable
defibrillator/pacemaker/resynchronizer, a subcutaneous
defibrillator or a long-term recorder. Device 10 is deemed the
master device of a network comprising a plurality of slave devices
12 to 18, which may include intracardiac 12 or epicardial 14
leadless capsules located directly on the patient's heart, other
devices 16 such as myopotential sensors or neurological stimulation
devices, and optionally an external device 18 disposed on armlets
and provided with electrodes in galvanic contact with the skin.
[0048] Main device 10 also can be used as a gateway to the outside
world to communicate via telemetry with a compatible external
device 20 such as a programmer or a device for remote transmission
of data.
[0049] With reference to FIG. 2, an internal circuit of the
implanted autonomous leadless capsules 12 to 16 is illustrated. The
leadless capsule contains, for example, a pair of electrodes 22, 24
connected to a pacing pulse generator circuit 26 (e.g., for an
active leadless capsule incorporating this function) and/or a
detection circuit 28 for the collection of depolarization
potentials collected between the electrodes 22 and 24. A central
circuit 30 includes all the electronics required to control the
various functions of the capsule, the storage the collected
signals, etc. It comprises a microcontroller and an oscillator
generating the clock signals needed for the operation of the
microcontroller and for the communication. It may also contain an
analog/digital converter and a digital storage memory. The capsule
may also be provided with a sensor 32 such as, for example, an
acceleration sensor, a pressure sensor, a hemodynamic sensor, a
temperature sensor, and an oxygen saturation sensor. The leadless
capsule also include an energy harvester circuit 34 powering all
circuits via an energy management circuit 36. The electrodes 22 and
24 are also connected to a pulse transmission/reception circuit 38
used for wireless communication with the master device or the other
leadless capsules.
[0050] The present invention more particularly relates to the
energy harvester circuit 34 which, typically, uses the pressure
variations of the surrounding environment, including the cyclic
variations of blood pressure, to move an electrode of a capacitor
element relatively to another electrode positioned vis-a-vis (i.e.,
facing) one another. The energy harvesting is obtained by the
variation of capacity of the capacitor resulting from the relative
displacement of the two electrodes, which causes a change in the
spacing between their facing surfaces and/or a variation of the
dielectric gap that separates them.
[0051] To take into account these deformations, preferably the
capsule is provided in the form of a body 40, as shown in FIGS. 3
and 4, with one or more deformable elements 42 operating at the
rhythm caused by the changes in the pressure of the fluid in which
the capsule is immersed (typically, the variations of blood
pressure, in the case of a cardiac capsule). Deformable element 42
includes a rigid surface 44 which is effected by the pressure
exerted, and is connected to the rest of the body by a deformable
bellows 46, which moves in response to the effect of the external
forces to which rigid surface 44 is exposed.
[0052] With reference to the embodiment illustrated in FIG. 3, this
surface/bellows assembly 44, 46 is disposed on an axial end face of
the capsule 40, which has a generally cylindrical shape. Dimensions
are typically about 6 mm in diameter for a length of 20 mm, and
provides a very small volume of about 0.5 cm.sup.3.
[0053] With reference to the embodiment illustrated in the FIG. 4,
two deformable sets 42 are arranged on side faces of the body 40 of
the leadless capsule. Rigid surfaces 44 are connected to block 40
by bellows 46, with surfaces 44 arranged parallel to each other and
to the main axis of the capsule. In this embodiment the energy
harvesting system is split; it also frees the two axial ends of the
capsule, which can be important, particularly to place an anchoring
screw system with no obstacles to this configuration due to the
energy harvesting system.
[0054] In one embodiment, the body 40 and its deformable element 42
are advantageously made in a monobloc form, for example, of
evaporated titanium or electrodeposited on a soluble stylet.
[0055] With reference to FIGS. 5a, 5b and 6, a first embodiment of
an electrostatically energy harvesting capsule will be described
here to illustrate the principle of the electrostatic transducer
with a variable capacitor.
[0056] In this first embodiment, deformable element 42 includes a
planar rigid surface 44 coupled to body 40 of the capsule by an
elastic element 48, preferably formed of peripheral ripples around
rigid surface 44. Rigid surface 44, which is movable under the
effects of the pressure variations of the surrounding environment,
is connected to a series of first capacitor electrodes 50 via the
coupling element 52, which is simply shown here as a rod. As can be
seen particularly in FIG. 4, electrodes 50 are preferably
configured in the form of combs made, for example, by conventional
photogravure (photolithography). The device also comprises second
electrodes 54, for example, made in the form of counter-combs
interdigitated with the combs of electrodes 50 (cf. FIG. 6),
connected to the body 40 by a peripheral support 56. The assembly
formed by electrodes 50, 54 is enclosed in a sealed volume 58
formed by body 40 closed by deformable member 42.
[0057] This provides a transducer that can be modelled by a
variable capacitor comprising:
[0058] A first suspended electrode, incorporated by the combs 50
which are mechanically and electrically gathered by arms 60 and
central support 62 connected to movable surface 44;
[0059] A second fixed electrode, constituted by the counter-combs
54 mechanically and electrically gathered together by the fixed
arms 64 themselves attached to the body 40 via the annular support
56; and
[0060] A dielectric gap, defined between the two electrodes.
[0061] With the combs and the interdigitated counter-combs, as
illustrated FIG. 6, in the case of a depression of deformable
element 42, the air gap and the overlap in the plane of the combs
remain constant, but the vertical overlap changes during the
movement. The capacity is maximum when the two structures (combs
and counter-combs) are vertically at the same level, and is minimal
(close to zero) when the movable structure (suspended combs 50)
have moved by a distance equal to their thickness (as shown in FIG.
5b), having thus rendered almost null the facing surfaces of the
combs with the counter-combs.
[0062] Concretely, when external pressure is exerted on movable
surface 44, for example, during the systole in the case of a
leadless capsule immersed in a blood medium, the pressure variation
produces a depression of surface 44 towards the inside the leadless
capsule, as shown in FIG. 5b. Combs 50 of the movable electrode
then move away from fixed combs 54 of the fixed capacitor electrode
and produce a variation in the capacity of the capacitor, in this
case a decrease in that capacity because of the decrease of the
facing surfaces of the stationary and movable electrodes and of the
increase in the dielectric gap between these surfaces.
[0063] If the capacitor had previously been preloaded, the decrease
in the capacity of the capacitor produces an energy excess which
may be discharged by appropriate circuits to a storage device, and
thus allows, at each systolic cycle, to recover an amount of energy
that is eventually sufficient to ensure continuous operation of the
electronic circuits of the leadless capsule without any additional
energy contribution.
[0064] The preload of the capacitor can be performed by specific
circuits, described below with reference to FIGS. 7-9.
[0065] In one embodiment, the preload can be achieved by annexed
piezoelectric elements, which during the initial pressure
variations deform and generate a voltage precharging the capacitor
during its start-up, according to a technique notably described by
Khbeis & al., Design of a Hybrid Ambient Low Frequency, Low
Intensity Vibration Energy Scavenger, the Sixth International
Workshop on Micro and Nanotechnology for Power Generation and
Energy Conversion Applications, Berkeley, 2006, or in FR 2896635
A1.
[0066] In yet another embodiment, the preload can be avoided by
having an electret structure on one side of the capacitor, these
electrets generating the required electric field. This particular
technique is described in the cited article Peano Tambosso
discussed above, or by Sakane & al., The Development of a
High-Performance Perfluorinated Polymer Electret and Its
Application to Micro Power Generation, Journal of Micromechanics
and Microengineering, Vol. 18, pp. 1-6, 2008.
[0067] With reference to FIGS. 7-9, an embodiment of a method to
harvest the energy through the change in the capacity of the
capacitor is illustrated. Two techniques for recovery, respectively
at constant voltage and constant load, will now be described. The
diagram in FIG. 7 illustrates two charge/voltage characteristics
for a full charge/discharge cycle of the variable capacitor. The
characteristic I corresponds to a cycle following the path ACDA at
constant voltage. The capacitor is initially charged to the maximum
voltage V.sub.max (segment AC), while the capacity is maximum
(C=C.sub.max). This load is operated in a sufficiently short time
(typically less than a microsecond) for this capacity to be
considered constant. During the movement of the movable element,
the capacity is reduced from C.sub.max to C.sub.min, the voltage
being held constant (by hypothesis) and maintained at Vmax, the
characteristic follows the segment CD.
[0068] During this phase, the energy stored in the capacitor is
transferred to the storage device. The residual charge Q.sub.0 is
then harvested by following the DA segment, with C=C.sub.min. The
total harvested energy is the area of the cycle I,
1/2(C.sub.max-C.sub.min)V.sub.max.sup.2.
[0069] In the case of a conversion at constant load (characteristic
II following the path ABDA), the capacitor is initially charged to
a starting voltage V.sub.st, with a maximum capacity C=C.sub.max
(segment AB).
[0070] The circuit is then left open (constant load Q.sub.0) during
the movement of the electrodes of the capacitor, which decreases
the capacity from its maximum value C.sub.max to its minimum value
C.sub.min (segment BD), the voltage increasing to its maximum value
V.sub.max for satisfying the equation Q=CV. The load is then
returned (segment AD), in the same method as before. The total
harvested energy is equal to the area of the cycle II,
1/2(C.sub.max-C.sub.min)V.sub.stV.sub.max. This value is, for the
same maximum voltage V.sub.max, lower than that of the solution at
constant voltage (characteristic I); however, this solution may
provide additional benefits, including the ability to operate with
a low initial voltage. It is also possible to provide an additional
capacitor, connected in parallel with the variable capacitor C, to
increase the energy and thus reach closer performance to the
solution at constant voltage.
[0071] FIG. 8 schematically illustrates an exemplary circuit for
energy harvesting at constant voltage. This circuit configuration
is in itself known, and for details one can refer, for example, to
E. Torres and G. Rincon-Mora, Electrostatic Energy-Harvesting and
Battery-Charging CMOS System Prototype, IEEE Transactions on
Circuits and Systems I: Regular Papers, Vol. 56, No. 9, 1938-1948,
September 2009.
[0072] Essentially, the four switches S1 to S4 are initially open
and the circuit monitors the voltage across the capacitor C for
detecting when it becomes maximum. At that moment, the preload
phase is triggered, starting first of all by loading the inductance
L (S1 and S3 closed, S2 and S4 open), then by discharging this
inductance L in the capacitor C (S1 and S3 open, S2 and S4 closed),
all in a very short time with respect to the variation of capacity
of the capacitor C. The switches are then opened, and the diode D
fixes the voltage across C, by discharging the capacitor into a
storage device, preferably a battery BAT, thus loading it.
[0073] FIG. 9 illustrates a circuit diagram of an energy harvesting
circuit at constant load. This circuit is also known, and more
details can be found in the aforementioned article of S. Meninger
et al. Vibration-to-Electric Energy Conversion, IEEE Transactions
on Very Large Scale Integration (VLSI) Systems, vol. 9, no. 1, p.
64-76, 2001.
[0074] Essentially, the voltage across the capacitors C and Cp (an
additional capacitor Cp is optionally added in parallel to C to
increase the produced energy) is initially zero. When the control
circuit detects the maximum capacity of the capacitor C, S1 opens
and S2 closes, loading the inductance L, then immediately after S1
closes and S2 opens, which transfers energy from L to capacitors C
and Cp. Then the two IQ switches S1 and S2 open and the capacity of
capacitor C declines as a result of mechanical forces, to the
minimum value C.sub.min. At that moment, S1 is closed and S2
remains open, which loads the inductance L from the energy
accumulated in the capacitors C and Cp. As soon as the voltage at
the terminations of the latter is equal to zero, S1 opens and S2
closes, which allows transferring the collected energy from the
inductor L to the storage device, preferably battery BAT.
[0075] FIG. 10 illustrates a second embodiment of an
electrostatically energy harvesting leadless capsule, wherein the
electrode formed by the movable comb 50 is, at rest, positioned
between two fixed superimposed counter-combs 54, so that the
movable comb 50 comes next to one or the other of the counter-combs
54 along the direction of movement of the membrane. This allows
harvesting the energy when the membrane moves in either direction,
for example, during both phases of systole and diastole in the case
wherein the leadless capsule is surrounded by a blood medium.
[0076] FIG. 11 illustrates a third embodiment of an
electrostatically energy harvesting leadless capsule, wherein the
transducer is a multilayer structure as described with reference to
FIGS. 5 and 6, to increase the electrode surface by the further
multiplication of the combs/counter-combs sets, which maximizes the
difference between minimum capacity C.sub.min and maximum capacity
C.sub.max.
[0077] FIG. 12 illustrates a fourth embodiment of an
electrostatically energy harvesting leadless capsule, wherein
deformable element 42 is made of a flexible membrane 66, fixed to
housing 40 of the leadless capsule at its periphery and bearing in
its center the part 52 for connection to movable electrode 50.
[0078] FIG. 13 illustrates a fifth embodiment of an
electrostatically energy harvesting leadless capsule, wherein
deformable element 42 is made of a rigid movable element 44
extending from one edge to the other of housing 40, connected to
housing 40 by an elastic element 46 in the form of bellows instead
of peripheral ripples 48 as illustrated in the embodiments of FIGS.
10 and 11. This configuration advantageously allows in particular
increasing both the travel of movable member 44, and therefore that
of the movable electrode, and the surface of rigid movable member
44 over which the external pressure is applied, with correlative
increase of the force exerted at the center of this element.
[0079] FIG. 14 shows an improvement of the present invention, which
is equally applicable to the various embodiments described above.
This embodiment is configured to overcome one of the problems of
harvesting of the forces exerted by changes in blood pressure,
which is the change in atmospheric pressure. Indeed, the inside of
the leadless capsule is sealed and therefore strictly at constant
pressure (adjusted at the factory during manufacture). If the
atmospheric pressure varies, the equilibrium at rest of the
deformable element is offset relative to the nominal position at
rest.
[0080] The proposed solution of the embodiment illustrated in FIG.
14 is to replace the rigid coupling between deformable element 42
and the movable electrode by a coupling incorporating a mechanical
high-pass filter 68 interposed between the deformable element
submitted to the external pressure and the electrostatic movable
structure. This filter, for example, includes a piston 70 having a
rod 52 connected to the movable electrode, with piston 70 moving in
a fluid 72 such as air or other gas enclosed in a sealed enclosure
74. In this way, the slow movements of deformable member 42 due to
changes in atmospheric pressure are not transferred to the
suspended movable electrode, the fluid being able to flow from
either side of piston 70 through, by example, microstructured
holes, or by a calibrated clearance 76, so as to restore the
pressure equilibrium. However, during rapid changes in the
systole-diastole cardiac cycle, these pressure changes are fully
transmitted to the suspended electrode, which can fully play the
role assigned to it.
[0081] FIG. 15 illustrates an embodiment in the monolithic form of
the structure combs/counter-combs produced by conventional
photolithography techniques. Indeed, one of the difficulties of
designing interdigitated structures of combs and counter-combs is
to obtain a dielectric gap as small as possible, to maximize the
capacity, while maintaining sufficient tolerance to prevent the
combs to come in contact, to avoid they are unstable under the
influence of the implemented electrostatic forces if the transverse
stiffness of the fingers is too low, and that a breakdown between
the electrodes happens if the electric field is too intense.
[0082] The device presented in the various embodiments described
above (which are not in themselves limited), with a variable
overlap out of plane, advantageously allows realization by
conventional, in themselves known, microfabrication to manufacture
electrostatic comb devices.
[0083] The combs 50 and counter-combs 54 can thus be simultaneously
manufactured on a single slice of a typical substrate of silicon,
heavily doped to be conductive. The separation of the combs to form
the dielectric gap can be realized by deep etching of silicon using
a technique such as DRIE (Deep Reactive Ion Etching), allowing for
example to obtain gaps of less than 10 microns on a slice thickness
of the order of 300 to 500 microns. With gaps as low as 10 .mu.m,
for the gap between the combs remains constant and to avoid that
the latter do not come to contact, alignment and assembly of two
independent structures of combs is difficult. To overcome this
difficulty, the structure can be performed on a slice of SOI
(Silicon On Insulator) the substrate of which is structured so as
to form, as shown in FIG. 15, the combs and counter-combs 50, 54
and their common supporting elements 60, 64, and wherein the upper
layer (active) of the slice is structured so as to form very broad
and thin springs 78 between each of the supports 64 of the movable
structure and the peripheral ring 80 connected to the body 40 of
the capsule.
[0084] These springs, because of their configuration, present an
important rigidity in the plane containing the suspended movable
structure of the combs 50, and greatly limit the transverse
displacements, typically at less than 1 .mu.m. These elements
ensure therefore, in addition a function of elastic support in the
axial direction, a guiding and centering function in the transverse
plane, thus guaranteeing a substantially constant dielectric gap.
Because of the very small thickness of the springs 78, they are
very flexible in the vertical direction (axial), which therefore
allows deformable member 42 of the leadless capsule and the
suspended electrode constituted of combs 50 to axially move without
difficulty and without adding significant stiffness.
[0085] FIGS. 16 and 17 illustrate two alternative embodiments of
the capacitor structure, adapted to the use of reinforcement
electret armatures having an electret film 57, as described in the
aforementioned articles of Peano & al. and Sakane & al. In
this case, the electrodes are advantageously configured with
overlap in the plane (FIG. 16) or with a variable dielectric gap
(FIG. 17). The rest of the structure of the transducer is identical
to what has been described, according to various embodiments
illustrated and described with reference to FIGS. 5 and 10-14.
[0086] One skilled in the art will appreciate the present invention
may be practiced by other than the embodiments described herein,
which are provided for purposed of illustration and not of
limitation.
* * * * *