Strain monitoring system and apparatus

• US 8,070,695 B2
• Filed: 01/08/2007
• Issued: 12/06/2011
• Est. Priority Date: 07/08/2004
• Status: Active Grant

• Current Assignee: Deborah Susan Munro
• Original Assignee: Deborah Schenberger
• Inventors: Gupta, Munish, Schenberger, Deborah, Lee, Eunice, Ramahi, Amjad
• Primary Examiner(s): HOEKSTRA, JEFFREY GERBEN
• Application Number:
  US11/620,973
• Publication Number:
  US 20070276294A1
• Time in Patent Office: 1,793 Days
• Field of Search: 600587-595, 73/11.5, 737/60, 737/63, 737/68, 737/74, 737/75, 737/77, 737/80
• US Class Current: 600/594
• CPC Class Codes: A61B 2090/064 for measuring force, pressure or mechanical tension
• CPC Class Codes: A61B 2560/0219 of externally powered implanted units
• CPC Class Codes: A61B 2562/0261 Strain gauges
• CPC Class Codes: A61B 2562/028 Microscale sensors, e.g. electromechanical sensors [MEMS]
• CPC Class Codes: A61B 5/0031 Implanted circuitry
• CPC Class Codes: A61B 5/0205 Simultaneously evaluating both cardiovascular conditions and different types of body conditions, e.g. heart and respiratory condition
• CPC Class Codes: A61B 5/024 Detecting, measuring or recording pulse rate or heart rate A61B5/0205, A61B5/021 take precedence
• CPC Class Codes: A61B 5/076 Permanent implantations telemetry using implanted circuitry A61B5/0031; implanted stimulators for therapy A61N1/3605, A61N1/362, A61N1/372
• CPC Class Codes: A61B 5/103 Detecting, measuring or recording devices for testing the shape, pattern, colour, size or movement of the body or parts thereof, for diagnostic purposes A61B5/08 takes precedence; measuring aids for tailors A41H1/00; measuring instruments specially adapted for dentistry A61C19/04
• CPC Class Codes: A61B 5/1036 Measuring load distribution, e.g. podologic studies
• CPC Class Codes: A61B 5/1126 using a particular sensing technique
• CPC Class Codes: A61B 5/14532 for measuring glucose, e.g. by tissue impedance measurement
• CPC Class Codes: A61B 5/14546 for measuring analytes not otherwise provided for, e.g. ions, cytochromes
• CPC Class Codes: A61B 5/4566 Evaluating the spine A61B5/4561 takes precedence
• CPC Class Codes: A61B 5/6846 specially adapted to be brought in contact with an internal body part, i.e. invasive
• CPC Class Codes: A61B 5/686 Permanently implanted devices, e.g. pacemakers, other stimulators, biochips A61B5/6861 takes precedence
• CPC Class Codes: A61B 90/06 Measuring instruments not otherwise provided for
• CPC Class Codes: A61B 90/98 using electromagnetic means, e.g. transponders
• CPC Class Codes: A61F 2/4455 for the fusion of spinal bodies, e.g. intervertebral fusion of adjacent spinal bodies, e.g. fusion cages intervertebral discs A61F2/442
• CPC Class Codes: A61F 2/4657 Measuring instruments used for implanting artificial joints for surgical instruments A61B90/06
• CPC Class Codes: A61F 2002/30668 : Means for transferring electromagnetic energy to implants
• CPC Class Codes: A61F 2250/0001 : Means for transferring electromagnetic energy to implants

Abstract

A system for monitoring strain as an indicator of biological conditions, such as spinal fusion, glucose levels, spinal loading, and heart rate. The system includes an inter-digitated capacitor sensor, and RF transmitter, and an associated antenna, all of which are microminiature or microscopic in size and can be implanted in a biological host such as a human or animal. An inductively coupled power supply is also employed to avoid the need for implantation of chemical batteries. Power is provided to the sensor and transmitter, and data is transmitted from the sensor, when an external receiving device, such as a handheld RF ID type receiver, is placed proximate the location of the implanted sensor, transmitter and inductively coupled power supply. The implanted sensor, transmitter and inductively coupled power supply can be left in place permanently or removed when desired.

Claims

1. An apparatus for sensing strain, comprising:

a sensor;

said sensor comprising an inter-digitated area variation capacitor;

wherein said sensor comprises a plurality of free-standing inter-digitated fingers;

and wherein lateral movement of the inter-digitated fingers produces a change in capacitance detected by said sensor;

a transmitter;

said transmitter coupled to said sensor; and

an antenna;

said antenna coupled to said transmitter;

wherein said sensor, said transmitter, and said antenna are adapted for implantation in a biological host; and

wherein said sensor, said transmitter, and said antenna are adapted for monitoring said change in capacitance to measure a characteristic of spinal fusion.

2. An apparatus as recited in claim 1:

wherein said sensor is adapted for mounting to a spinal plate or spinal rod and configured to produce a signal representative of strain in said spinal plate or spinal rod; and

wherein said transmitter is configured for transmitting said signal representative of strain.

3. An apparatus as recited in claim 2:

wherein said spinal plate or spinal rod has a central area;

wherein said spinal plate or spinal rod is reduced in width near said central area; and

wherein said sensor, said transmitter, and said antenna are affixed to said spinal plate or spinal rod proximate to where said spinal plate or said spinal rod is reduced in width.

4. An apparatus for sensing strain, comprising:

a sensor;

said sensor comprising an inter-digitated area variation capacitor;

wherein said sensor comprises a plurality of free-standing inter-digitated fingers;

and wherein lateral movement of the inter-digitated fingers produces a change in capacitance detected by said sensor;

a transmitter;

said transmitter coupled to said sensor; and

an antenna;

said antenna coupled to said transmitter;

wherein said sensor, said transmitter, and said antenna are adapted for implantation in a biological host; and

wherein said sensor is adapted for measuring spinal loading via said change in capacitance.

5. A system as recited in claim 4:

wherein said sensor is adapted for mounting to a spinal plate or spinal rod and configured to produce a signal representative of strain in said spinal plate or spinal rod; and

wherein said transmitter is configured for transmitting said signal representative of strain.

6. A system as recited in claim 5:

wherein said spinal plate or spinal rod has a central area;

wherein said spinal plate or spinal rod is reduced in width near said central area; and

wherein said sensor, said transmitter, and said antenna are affixed to said spinal plate or spinal rod proximate to where said spinal plate or spinal rod is reduced in width.

7. An apparatus for sensing strain, comprising:

a sensor;

said sensor comprising an inter-digitated area variation capacitor;

a transmitter;

said transmitter coupled to said sensor; and

an antenna;

said antenna coupled to said transmitter;

wherein said sensor, said transmitter, and said antenna are adapted for implantation in a biological host;

wherein said sensor is adapted for mounting to a spinal plate or spinal rod and configured to produce a signal representative of strain in said spinal plate or spinal rod;

wherein said transmitter is configured for transmitting said signal representative of strain;

wherein said inter-digitated area variation capacitor comprises a plurality of free-standing inter-digitated fingers; and

wherein lateral movement of the inter-digitated fingers produces a change in capacitance detected by said sensor.

8. An apparatus as recited in claim 7:

wherein said spinal plate or spinal rod has a central area;

wherein said spinal plate or spinal rod is reduced in width near said central area; and

wherein said sensor, said transmitter, and said antenna are affixed to said spinal plate or spinal rod proximate to where said spinal plate or spinal rod is reduced in width.

9. An apparatus as recited in claim 7, wherein said sensor is encapsulated in a housing such that the sensor is sealed from the environment within the biological host.

10. An apparatus as recited in claim 9, wherein said transmitter and said antenna form said housing for encapsulating said sensor.

11. An apparatus as recited in claim 7, wherein said sensor, said transmitter, and said antenna are adapted for permanent implantation in a biological host.

12. An apparatus as recited in claim 7, wherein said sensor has a sensitivity of 10⁻

14 F.

13. An apparatus as recited in claim 7, wherein lateral movement of the inter-digitated fingers and said change in capacitance are linearly related.

14. An apparatus as recited in claim 7, wherein said transmitter comprises a radio frequency transmitter.

15. An apparatus as recited in claim 7, wherein said transmitter comprises:

a voltage controlled oscillator; and

an RF power amplifier.

16. An apparatus as recited in claim 15, wherein said voltage controlled oscillator comprises a ring oscillator.

17. An apparatus as recited in claim 7, wherein said transmitter has an operating frequency of 100 GHz.

18. An apparatus as recited in claim 7, wherein said transmitter comprises a frequency modulation transmitter.

19. An apparatus as recited in claim 7, wherein said antenna comprises a microstrip antenna.

20. An apparatus as recited in claim 19, wherein said microstrip antenna comprises:

a conducting ground plane;

a low-loss dielectric substrate positioned on said ground plane; and

a thin metallic patch positioned on said dielectric substrate.

21. An apparatus as recited in claim 20:

wherein said substrate has a dielectric constant;

wherein said substrate includes a cavity; and

wherein said cavity reduces the dielectric constant of said substrate.

22. An apparatus as recited in claim 7, further comprising:

a power supply;

said power supply configured for inductive coupling to a power source;

said power supply coupled to said sensor and said transmitter;

wherein said power supply is adapted for implantation in a biological host.

23. An apparatus as recited in claim 22, wherein said power supply comprises:

an inductive coil;

a rectifier coupled to said inductive coil; and

a regular coupled to said rectifier.

24. An apparatus as recited in claim 7, further comprising a calibration circuit for calibrating said sensor by adjusting a baseline characteristic of said sensor.