Pendular unit with a monolithic inertial mass mounted on a piezoelectric beam, in particular for an energy harvester in a leadless autonomous cardiac capsule

1 . A pendular unit for a piezoelectric energy harvesting (PEH) module, the pendular unit comprising:

a lead zirconate titanate (PZT) transducer beam that is elastically deformable in bending and that extends in an axial direction between a clamped proximal end and a free distal end; and

an inertial mass mounted at the free distal end of the PZT transducer beam and mobile in a transverse direction,

the pendular unit being adapted to convert a mechanical energy produced by oscillations of the pendular unit under an effect of external stresses undergone by the PEH module into an oscillating electrical signal collected by surface electrodes of the PZT transducer beam,

wherein the inertial mass is a monolithic part including an axial slit forming a cavity, with two opposite longitudinal surfaces extending along a central axis of the inertial mass, the axial slit opening out on a proximal side of the inertial mass and receiving the free distal end of the PZT transducer beam,

and wherein the axial slit forming said cavity comprises:

on a proximal side, a clamping area in which the PZT transducer beam is secured between the two opposite longitudinal surfaces of the axial slit; and

on a distal side, a non-clamping area.

2 . The pendular unit of claim 1 , wherein, over a length of the clamping area, the two opposite longitudinal surfaces comprise flat and parallel symmetrical surfaces separated by a constant radial spacing.

3 . The pendular unit of claim 2 , wherein the two opposite longitudinal surfaces comprise surfaces that widen along a length of the non-clamping area.

4 . The pendular unit of claim 1 , wherein the two opposite longitudinal surfaces are symmetrical surfaces radially separated by an increasing radial spacing in a direction proximal to distal along at least part of a length of the axial slit in a longitudinal direction, in such a way as to produce a progressive clamping of the PZT transducer beam, with a maximum clamping force in the clamping area and a zero clamping force in the non-clamping area.

5 . The pendular unit of claim 1 , wherein, in a radial direction, the axial slit also opens out in at least one of a side of the inertial mass.

6 . The pendular unit of claim 1 , wherein at least one of the two opposite longitudinal surfaces comprise at least one non-return notch provided with an axial and/or radial stop adapted to block the PZT transducer beam in a position in the axial slit.

7 . The pendular unit of claim 6 , wherein the PZT transducer beam comprises, in an area located between the two opposite longitudinal surfaces of the axial slit, at least one cut adapted to cooperate with an axial and/or radial stop for mating a non-return notch of the inertial mass.

8 . The pendular unit of claim 1 , wherein, in the clamping area, a minimum value of a radial spacing between the two opposite longitudinal surfaces is equal to a thickness of the PZT transducer beam, to within a negative clearance, in such a way as to exert on the PZT transducer beam a pinching force between the two opposite longitudinal surfaces.

9 . The pendular unit of claim 8 , wherein a pinching force of the PZT transducer beam exerted by the two opposite longitudinal surfaces is between 0.5 and 2 N/mm 2 .

10 . The pendular unit of claim 1 , wherein the pendular unit is integrated to the PEH module, the PEH module comprising an elongated envelope tube containing the pendular unit.

11 . The pendular unit of claim 10 , wherein the PEH module is integrated to an autonomous device having a device body containing:

an electronic unit;

a power management circuit adapted to rectify and regulate the oscillating electric signal produced by the pendular unit of the PEH module to output a stabilized direct power voltage or current; and

an energy storage component for powering the electronic unit,

wherein said stabilized direct voltage or current provided by the power management circuit is used to power the electronic unit and/or to charge the energy storage component of the autonomous device.

12 . The pendular unit of claim 11 ,

wherein the autonomous device is an implantable autonomous capsule type active medical device comprising a capsule body with an element for its anchoring to a wall of a patient's organ,

and wherein the external stresses to which is subjected the pendular unit of the PEH module are stresses applied to the capsule body under an effect of movements of said wall and/or flow rate variations of a flow in a surrounding environment.

13 . A method for assembling a pendular unit for a piezoelectric energy harvesting (PEH) module, the pendular unit comprising a lead zirconate titanate (PZT) transducer beam that is elastically deformable in bending and an inertial mass mounted at a free distal end of the PZT transducer beam and mobile in a transverse direction,

the method comprising the following steps:

a) obtaining an inertial mass by forming an axial slit in a mass of a monolithic part, the axial slit extending along a central axis of the inertial mass from a proximal end, thus forming two opposite longitudinal surfaces,

the axial slit comprising successive cavities with different geometries, comprising: on a proximal side, a clamping area in which the PZT transducer beam is secured between the two opposite longitudinal surfaces of the axial slit; and on a distal side, a non-clamping area;

b) inserting into the axial slit the free distal end of the PZT transducer beam; and

c) securing the free distal end of the PZT transducer beam to the monolithic part between the two opposite longitudinal surfaces of the axial slit in the non-clamping area.

14 . The method of claim 13 , wherein, at step a), forming the axial slit in the monolithic part is performed using a material removal technique selected among wire electro-erosion or disk machining; or using an additive material deposition technique selected among stereolithography (SLA), selective laser sintering (SLS), or fused deposition modeling (FDM).

15 . The method of claim 13 , wherein, at step c), securing the free distal end of the PZT transducer beam to the monolithic part is performed using a technique selected among: temperature deformation of the PZT transducer beam or of the monolithic part before insertion in step b) then return to room temperature after insertion in step b); elastic deformation of the monolithic part to enlarge the axial slit before insertion in step b) then release after the insertion in step b); bonding; crimping; and/or welding of an added link part.