Self-powered sensor

• US 20080047355A1
• Filed: 08/24/2007
• Published: 02/28/2008
• Est. Priority Date: 08/24/2006
• Status: Active Grant

• Current Assignee: The Board of Trustees of Michigan State University (Michigan State University)
• Original Assignee: The Board of Trustees of Michigan State University (Michigan State University)
• Inventors: Elvin, Niell, Gore, Amit, Chakrabartty, Shantanu, Lajnef, Nizar
• Granted Patent: US 8,056,420 B2
• Time in Patent Office: Days
• US Class Current: 73/808
• CPC Class Codes: A61F 2/468 Testing instruments for artificial joints for testing non-implantable prostheses A61F2/76
• CPC Class Codes: A61F 2/488 Means for detecting or monitoring wear
• CPC Class Codes: A61F 2002/30087 piezoelectric
• CPC Class Codes: A61F 2002/3067 for data transfer
• CPC Class Codes: A61F 2250/0002 for data transfer
• CPC Class Codes: G01M 5/0033 by determining damage, crack or wear
• CPC Class Codes: G01M 5/0083 by measuring variation of impedance, e.g. resistance, capacitance, induction
• CPC Class Codes: G01M 5/0091 by using electromagnetic excitation or detection
• CPC Class Codes: G01N 2203/0073 Fatigue
• CPC Class Codes: G01N 2203/0623 using piezoelectric gauges
• CPC Class Codes: H10N 30/30 with mechanical input and electrical output, e.g. functioning as generators or sensors

Abstract

A self-powered sensor is provided for fatigue monitoring and other low power requirement applications. The self-powered sensor is comprised of: a piezoelectric transducer; a non-volatile memory comprised of at least one floating gate transistor; and a current reference circuit adapted to receive a voltage signal from the piezoelectric transducer and operable to output an injection current into the non-volatile memory. The current reference circuit may employ a floating gate transistor operating in a weak-inversion mode.

Claims

1. A self-powered sensor, comprising:

a piezoelectric transducer;

a non-volatile memory comprised of at least one floating gate transistor; and

a current reference circuit having a floating gate transistor operating in a weak-inversion mode, the current reference circuit adapted to receive a voltage signal from the piezoelectric transducer and operable to output an injection current into the non-volatile memory.

2. The self-powered sensor of claim 1 wherein the current reference circuit is arranged as a current mirror comprised of two transistors, where the floating gate transistor is coupled between gate nodes of the two transistors and source nodes of the two transistors.

3. The self-powered sensor of claim 1 wherein the non-volatile memory is comprised of an array of floating gate transistors

4. The self-powered sensor of claim 3 further comprises a driving circuit interposed between the reference current circuit and the array of floating gate transistors and operable to inject a charge onto different floating gate transistors of the array based on a magnitude of the voltage signal.

5. The self-powered of claim 4 wherein the driving circuit is comprised of a plurality of circuit branches, where each circuit branch electrically couples to a different floating gate transistor in the array of floating gate transistors.

6. The self-powered sensor of claim 5 wherein each circuit branch defines a different current threshold, whereby a charge is injected onto the floating gate transistor associated with a given circuit branch when the magnitude of the reference current exceeds the current threshold for the given circuit branch

7. The self-powered sensor of claim 1 further comprises a full wave rectifier interposed between the piezoelectric transducer and the current reference circuit.

8. The self-powered sensor of claim 1 wherein the piezoelectric transducer is operably coupled to a medical implant, such that total charge stored in the non-volatile memory is proportional to loading cycle applied to the medical implant.

9. The self-powered sensor of claim 1 wherein the piezoelectric transducer is comprised of a polyvinylidene fluoride material.

10. A self-powered sensor, comprising:

a current reference circuit adapted to receive a voltage signal and operable to output a reference current compensated for temperature variations;

an array of floating gate transistors which provides non-volatile storage; and

a driving circuit interposed between the current reference circuit and the array of floating gate transistors and operable to inject a charge into select transistors of the array of floating gate transistors based on a magnitude of the voltage signal.

11. The self-powered sensor of claim 10 wherein the current reference circuit having a floating gate transistor such that a magnitude of the reference current is determined by a charge injected onto the floating gate transistor.

12. The self-powered sensor of claim 10 wherein the current reference circuit is arranged as a current mirror comprised of two transistors, where the floating gate transistor is coupled between gate nodes of the two transistors and source nodes of the two transistors.

13. The self-powered of claim 10 wherein the driving circuit is comprised of a plurality of circuit branches, where each circuit branch electrically couples to a different floating gate transistor in the array of floating gate transistors.

14. The self-powered sensor of claim 13 wherein each circuit branch having a different voltage drop such that a charge is injected into the floating gate transistor coupled to a given circuit branch when the voltage signal exceeds the voltage drop of the given circuit branch.

15. The self-powered sensor of claim 10 wherein signals applied to gate nodes of the floating gate transistors in the array of floating gate transistors is derived from the voltage signal.

16. The self-powered sensor of claim 10 further comprises a capacitor coupled to gate nodes of each transistor in the array of floating gate transistors.

17. The self-powered sensor of claim 10 wherein the voltage signal is received from a piezoelectric transducer.

18. The self-powered sensor of claim 10 further comprises an array of read-out transistors coupled to the array of floating gate transistors and operable to measure charge stored in the array of floating gate transistors.

19. A self-powered sensor, comprising:

a piezoelectric transducer;

a non-volatile memory comprised of at least one floating gate transistor; and

a current reference circuit adapted to receive a voltage signal from the piezoelectric transducer and operable to output an injection current into the non-volatile memory, thereby recording output of the piezoelectric transducer.