Shock resistant accelerometer for implantable medical device

An implantable stimulator comprising a pulse generator, an accelerometer assembly mounted within the stimulator for providing a signal indicative of a patient's level of activity, and control means responsive to said accelerometer signal for controlling operation of said pulse generator, the accelerometer assembly comprising:

• at least one of an upper housing member and a lower housing member, the upper member having at least one downwardly facing bottom surface, the lower member having at least one upwardly facing top surface;
• a sheet of piezoelectric material disposed generally within an imaginary plane defined by two major substantially horizontal orthogonal axes, the sheet having upper and lower surfaces, the sheet having formed therein a beam disposed along an imaginary longitudinal axis extending between the first and second ends, laterally extending outer members being formed in the sheet and adjacent at least the first end, the second end of the beam being deflectable along an imaginary vertical axis oriented substantially perpendicular to the plane;
• at least portions of the lower or upper surfaces of the first end of the sheet and optionally at least portions of the upper or lower surfaces of the laterally extending outer members of the sheet being attached to at least one of the upper surface of the lower housing member and the lower surface of the upper housing member, and
• at least one stop disposed on at least one of the upper surface of the beam and the lower surface of the beam, the stop limiting the vertical range of motion through which the beam may deflect along the imaginary vertical axis to prevent failure, breakage or fracturing of the beam.

An implantable stimulator comprising a pulse generator, an accelerometer assembly mounted within the stimulator for providing a signal indicative of a patient's level of activity, and control means responsive to said accelerometer signal for controlling operation of said pulse generator, the accelerometer assembly comprising:

• at least one of an upper housing member and a lower housing member, the upper member having at least one downwardly facing bottom surface, the lower member having at least one upwardly facing top surface, the downwardly facing bottom surface and upwardly facing top surface defining at least portions of an internal cavity;
• a sheet of piezoelectric material disposed generally within an imaginary plane defined by two major substantially horizontal orthogonal axes, the sheet having upper and lower surfaces, the sheet having formed therein a beam disposed along an imaginary longitudinal axis extending between the first and second ends, laterally extending outer members being formed in the sheet and adjacent at least the first end, the second end of the beam being deflectable along an imaginary vertical axis oriented substantially perpendicular to the plane;
• at least portions of the lower or upper surfaces of the first end of the sheet and optionally at least portions of the upper or lower surfaces of the laterally extending outer members of the sheet being attached to at least one of the upper surface of the lower housing member and the lower surface of the upper housing member, and
• a stop comprising a visco-elastic damping fluid or gel disposed within the internal cavity, the stop limiting the vertical range of motion through which the beam may deflect along the imaginary vertical axis to prevent failure, breakage or fracturing of the beam.

A method of making an implantable stimulator comprising a pulse generator, an accelerometer assembly mounted within the stimulator for providing a signal indicative of a patient's level of activity, and control means responsive to the accelerometer signal for controlling operation of said pulse generator, the accelerometer assembly comprising at least one of an upper housing member and a lower housing member, the upper member having at least one downwardly facing bottom surface, the lower member having at least one upwardly facing top surface;

• a sheet of piezoelectric material disposed generally within an imaginary plane defined by two major substantially horizontal orthogonal axes, the sheet having upper and lower surfaces, the sheet having formed therein a beam disposed along an imaginary longitudinal axis extending between the first and second ends, laterally extending outer members being formed in the sheet and adjacent at least the first end, the second end of the beam being deflectable along an imaginary vertical axis oriented substantially perpendicular to the plane;
• at least portions of the lower or upper surfaces of the first end of the sheet and optionally at least portions of the upper or lower surfaces of the laterally extending outer members of the sheet being attached to at least one of the upper surface of the lower housing member and the lower surface of the upper housing member, and at least one stop disposed at a location above or below the second end of the beam, the stop limiting the vertical range of motion through which the beam may deflect along the imaginary vertical axis to prevent failure, breakage or fracturing of the beam, the method comprising the steps of:
• (a) providing at least one of the upper housing member and the lower housing member;
• (b) providing the sheet of piezoelectric material;
• (c) forming the beam by cutting first and second notches in the sheet, the notches defining the lateral edges of the beam separating the beam from the laterally extending outer members;
• (d) attaching at least portions of the lower or upper surfaces of the first end of the sheet and optionally at least portions of the upper or lower surfaces of the laterally extending outer members of the sheet to at least one of the upper surface of the lower housing member and the lower surface of the upper housing member, and
• (e) providing at least one stop at a location above or below the second end of the beam, the stop limiting the vertical range of motion through which the beam may deflect along the imaginary vertical axis to prevent failure or fracturing of the beam.