SELF-POWERED SENSOR

• US 20090120200A1
• Filed: 11/19/2008
• Published: 05/14/2009
• 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: Chakrabartty, Shantanu
• Granted Patent: US 7,757,565 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: G01L 5/0052 measuring forces due to impact G01L5/0061, G01L5/14 take precedence; impact testing of structures G01M7/08; impact testing of material G01N3/00
• CPC Class Codes: G01M 5/00 Investigating the elasticity of structures, e.g. deflection of bridges or air-craft wings G01M9/00 takes precedence
• CPC Class Codes: G01N 2203/0073 Fatigue
• CPC Class Codes: G01N 2203/0623 using piezoelectric gauges
• CPC Class Codes: G01N 2291/02827 Elastic parameters, strength or force
• CPC Class Codes: G01N 29/043 in the interior, e.g. by shear waves
• CPC Class Codes: G01N 29/2481 Wireless probes, e.g. with transponders or radio links
• CPC Class Codes: H02N 2/18 producing electrical output from mechanical input, e.g. generators for measurement devices G01

Abstract

A self-powered sensor is provided for strain-rate 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; a current reference circuit adapted to receive a voltage signal from the piezoelectric transducer and operable to output a reference current into the non-volatile memory; an impact-monitoring circuit having a triggering circuit and a switch; the triggering circuit adapted to receive the voltage signal from the piezoelectric transducer and operable to control the switch based on the rate of change of the voltage signal.

Claims

1. A self-powered sensor comprising:

a piezoelectric transducer;

a non-volatile memory

a reference circuit, the reference circuit adapted to receive a voltage signal having rate of change from the piezoelectric transducer and operable to output the reference current into the memory;

an impact rate monitoring circuit including a switch and a triggering circuit;

the switch interposed between the reference circuit and the memory; and

the triggering circuit adapted to receive the voltage signal from the piezoelectric transducer and operable to control the switch based on the rate of change of the voltage signal.

2. The self-powered sensor of claim 1 wherein the triggering circuit is operable to close the switch when the rate of change of the voltage signal exceeds a predefined threshold.

3. The self-powered sensor of claim 1 wherein the triggering circuit includes a high-pass filter sensitive to the rate of change of the voltage signal.

4. The self-powered sensor of claim 3 wherein the triggering circuit further comprises an amplifier interposed between the high-pass filter and the switch.

5. The self-powered sensor of claim 4 wherein the amplifier is configured as a comparator and is operable to drive the switch when the high-pass filter determines that the voltage signal has exceeded the predefined threshold.

6. The self-powered sensor of claim 1 wherein the piezoelectric transducer is operable to power the self-powered sensor.

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

8. The self-powered sensor of claim 7 wherein the reference circuit is operable to inject a charge onto different floating gate transistors of the array based on the rate of change of the voltage signal.

9. The self-powered sensor of claim 8 wherein the impact monitoring circuit is comprised of a plurality of channel circuits, where each channel circuit is operable to inject a charge into different floating gate transistors of the array based on the rate of change of the voltage signal.

10. The self-powered sensor of claim 9 wherein each circuit branch defines a different voltage rate threshold, whereby charge is injected into the floating gate transistor associated with a given channel circuit when the magnitude of the reference current exceeds the voltage change rate threshold for a given channel circuit.

11. The self-powered sensor of claim 1 further comprising a startup circuit interposed between the piezoelectric transducer and the current reference circuit.

12. The self-powered sensor of claim 11 wherein the startup circuit is operable to receive a voltage signal and to cause the reference circuit to generate a stable reference current.

13. The self-powered sensor of claim 9 wherein each channel circuit is further comprised of a current copier operable to receive the reference circuit and to supply the triggering circuit and the switch with the reference current.

14. The self-powered sensor of claim 1 wherein the piezoelectric transducer is operably coupled to a medical implant, such that the voltage signal is generated by the piezoelectric transducer when the piezoelectric transducer experiences a change in strain.

15. The self-powered sensor of claim 14 wherein the total charge stored the non-volatile memory corresponds to the amount of time the rate of strain exceeds a predefined threshold.

16. A self-powered sensor comprising:

a piezoelectric transducer operable to produce a voltage signal corresponding to a change of rate of strain exerted on the piezoelectric transducer;

a startup circuit operable to receive the voltage signal produced by the piezoelectric transducer and to supply a current to a reference circuit;

the reference circuit operable to receive a current from the startup circuit, to generate a stable reference current and to mirror and supply the reference current to an impact monitoring circuit;

the impact monitoring circuit comprising a plurality of impact monitoring channel circuits, each impact monitoring channel circuit sensitive to a predefined frequency corresponding to a rate of change in the voltage signal;

each impact monitoring channel circuit operable to supply the reference current to a corresponding floating gate injector when the impact monitor channel circuit senses a frequency exceeding the predetermined frequency threshold; and

each floating gate injector operable to inject charge into a floating gate transistor while the frequency of the voltage signal exceeds the predefined frequency threshold.

17. The self-powered sensor of claim 16 wherein each impact monitoring channel circuit further comprises a triggering circuit and a switch, the triggering circuit operable to drive the switch when the frequency of the voltage signal exceeds the predefined frequency threshold.

18. The self-powered sensor of claim 17 wherein the triggering circuit further comprises a high-pass filter operable to detect a frequency of the voltage signal that exceeds the predefined frequency threshold and operable to bias the gate of a common-source amplifier, the common-source amplifier operable to drive the switch when the gate of the common-source amplifier is biased.

19. The self-powered sensor of 18 wherein the impact monitoring channel circuit further comprises a first current copier and a second current copier;

the first current copier operable to receive the reference current and to supply the reference current to the common source amplifier;

the second current copier operable to receive the reference current and to supply the reference current to the floating gate injector.

20. The self-powered sensor of 18 further comprising a plurality of voltage nodes, each node corresponding to a impact rate channel circuit and each node having a charge corresponding to the charged stored in a capacitor in the floating gate capacitor.

21. A self-powered device for gathering statistics on strain rate comprising:

a transducer operable to generate a voltage signal in response to mechanical stress;

a reference circuit operable to receive said voltage signal and generate a stable reference current;

an impact monitoring circuit operable to receive the voltage signal and the reference current when the frequency of the voltage signal exceeds a predetermined threshold; and

the impact monitoring circuit operable to inject a charge into a non-volatile memory when the frequency of the voltage signal exceeds said predetermined threshold.

22. The self-powered device of claim 21 wherein the impact rate monitoring circuit further comprises a triggering circuit operable to determine when the frequency of the voltage signal exceeds the predetermined threshold and to inject charge into said memory when the voltage signal exceeds the predetermined threshold.

23. The self-powered device of claim 22 wherein the triggering circuit further comprises a high pass-filter operable to receive the voltage signal and to bias the gate of a common source amplifier when said the frequency of the voltage signal exceeds a predetermined threshold.

24. The self-powered device of claim 23 wherein the triggering circuit further comprises a switch that is driven by the common-source amplifier when the voltage signal exceeds a predetermined threshold and operable to allow the reference current to flow to the memory when said switch is closed.

25. The self-powered device of claim 21 wherein said device is operable to interface with an RFID chip, whereby statistics relating to strain may be uploaded by a user.

26. A self-powered sensor comprised of:

a piezoelectric transducer operable to generate a voltage signal;

a non-volatile memory operable to store statistics of strain rate and strain level;

a means for injecting a charge into said memory when a rate of strain exceeds a predetermined threshold;

a means for injecting a charge into said memory when a level of strain exceeds a predetermined threshold

27. A device for measuring the rate of strain applied to a tamperproof cap comprising:

a piezoelectric film sized to fit on a tamperproof cap and operable to generate a voltage signal corresponding to the rate of strain applied to the tamperproof cap;

a reference circuit operable to receive the voltage signal from said film and operable to generate a reference current;

a impact monitoring circuit operable to receive the voltage signal and the reference current and to inject charge into a non-volatile memory when said the frequency of said voltage signal exceeds a predetermined threshold.