PULSED ECHO PROPAGATION DEVICE AND METHOD FOR MEASURING A PARAMETER

• US 20100327848A1
• Filed: 03/26/2010
• Published: 12/30/2010
• Est. Priority Date: 06/30/2009
• Status: Active Grant

• Current Assignee: OrthoSensor, Inc (Stryker Corporation)
• Original Assignee: OrthoSensor, Inc (Stryker Corporation)
• Inventors: Stein, Marc T.
• Granted Patent: US 8,421,479 B2
• Time in Patent Office: Days
• US Class Current: 324/76.12
• CPC Class Codes: A61B 5/4509 Bone density determination
• CPC Class Codes: A61B 5/4528 Joints A61B5/4533, A61B5/4538 take 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 5/6878 Bone
• CPC Class Codes: A61B 5/7239 using differentiation including higher order derivatives
• CPC Class Codes: A61B 8/15 Transmission-tomography

Abstract

At least one embodiment is directed to a sensor for measuring a parameter. A signal path of the system comprises an amplifier (612), a sensor element, and an amplifier (620). The sensor element comprises a transducer (4) at a first location of a waveguide (5), and a reflective surface (30) at a second location of the waveguide (5). A parameter such as force or pressure applied to the sensor element can change the length of waveguide (5). A pulsed energy wave is emitted by the transducer (4) into the waveguide (5) at the first location. The transducer (4) is responsive to pulsed energy waves reflected from reflective surface (30) to the second location. The transit time of each pulsed energy wave is measured. The transit time corresponds to the pressure or force applied to the sensor element.

Claims

1. A low power measurement system for measuring a parameter comprising:

a medium where the parameter to be measured affects the medium;

a transducer coupled to the medium at a first location where the transducer emits a pulsed energy wave into the medium in response to a pulse; and

a reflective surface coupled to the medium at a second location where the pulsed energy wave propagates through the medium to the second location and where reflective surface reflects the pulsed energy wave back to the first location; and

a pulsed system including;

an edge detect circuit for detecting an edge of the signal from transducer; and

a first pulse circuit for generating a pulse to initiate a subsequent measurement sequence in response to a detected edge by the edge detect circuit where a transit time of the pulsed energy wave is measured and the transit time or change in transit time corresponds to the parameter.

2. The system of claim 1 where the medium is a waveguide for containing and directing the pulsed energy wave.

3. The system of claim 2 where the waveguide comprises polyethylene and where the waveguide is cylindrical

4. The system of claim 1 further including an amplifier having an input coupled to an output of the first pulse circuit and an output coupled to the transducer.

5. The system of claim 4 where the amplifier includes circuitry to dampen a wave shape for optimal transmission and reception in accordance with a matched network.

6. The system of claim 5 further including a second pulse circuit for providing one or more pulses to the transducer to initiate a sensing process where the second pulse circuit is decoupled from the first transducer when the edge detect circuit detects an edge of a first pulsed energy wave corresponding to the first of the one or more pulses provided by the second pulse circuit.

7. The system of claim 6 where the first pulse circuit is coupled to the input of the amplifier to provide the pulse to initiate the next measurement sequence when the second pulse circuit is decoupled from the first transducer.

8. The system of claim 7 where the pulsed system modulates a time period of pulsed energy waves as a function of changes in distance or velocity through the medium of the one or more pulsed energy wave propagating structures, or a combination of changes in distance and velocity, caused by changes in the one or more pulsed energy wave propagating structures.

9. The system of claim 1 where the pulsed energy wave is a damped ringing waveform and where the edge detect circuit detects a leading edge of the signal from the second transducer and where upon detecting the leading edge of the signal, the edge detect circuit is disabled from edge detecting for a predetermined period of time.

10. The system of claim 1 where the transit time is the sum of the pulsed energy wave propagating time from the first location to the second location and the pulsed energy wave propagating time from the second location to the first location of the medium.

11. The system of claim 10 further comprising a digital block for digitizing the frequency of operation of the pulsed system where the frequency corresponds to a time period of one or more pulsed energy waves.

12. The system of claim 1, where the system operates to measure changes in transit time due to changes in the length of the medium such that the physical length change under load are in proportion to the applied force.

13. A low power method of measuring a parameter comprising the steps of:

emitting a pulsed energy wave at a first location of a medium where the medium is subject to the parameter being measured and where the pulsed energy wave is generated in response to a pulse;

reflecting the pulsed energy wave at a second location in the medium;

generating a signal corresponding to the pulsed energy wave reflected from the second location and received at the first location of the medium;

detecting an edge of the signal;

measuring a transit time of the pulsed energy wave;

correlating the transit time to the parameter being measured; and

generating a pulse upon detecting the edge of the signal to initiate the emission of a pulsed energy wave into the medium for a subsequent measurement of the parameter.

14. The method of claim 13 further including a step of initiating sensing by emitting one or more pulsed energy waves into the medium in response to one or more pulses.

15. The method of claim 14 further including a step of maintaining an integer number of pulsed energy waves propagating in the medium where each pulsed energy wave has a time period and where the time periods of pulsed energy waves changes in response to changes in the parameter applied to the medium.

16. The method of claim 14 further including the steps of:

measuring the transit time or time period of each pulsed energy wave; and

correlating the transit time or time period to the parameter being measured.

20. The method of claim 13 further including the steps of:

forming the medium of polymer having a predetermined height and cross-sectional area;

coupling a piezoelectric transducer to the first location of the medium; and

coupling a reflecting surface to the medium at a second location where a pressure or force is applied to either the first location, the second location, or both to produce a change in length of the medium thereby producing a corresponding transit time or time period of a pulsed energy wave therethrough.

17. A method of measuring a parameter comprising the steps of:

maintaining more than one discontinuous pulsed energy wave in a medium subjected to the parameter being measured;

measuring a transit time of the pulsed energy wave emitted into the medium at a first location to a second location and reflected from the second location back to the first location; and

relating the transit time to the parameter being measured.

18. The method of claim 17 further including the steps of:

initiating measurement by emitting one or more pulsed energy waves into the medium in response to one or more pulses from a first pulse circuit;

detecting a first pulsed energy wave of the one or more pulsed energy waves reflected back to the first location; and

preventing the pulse circuit from providing further pulses.

19. The method of claim 18 further including the steps of:

generating a pulse from a second pulse circuit upon detecting the first pulsed energy wave; and

emitting a pulsed energy wave into the medium at the first location response to the pulse to continue transit time measurements.