Pulsed echo propagation device and method for measuring a parameter

• US 8,421,479 B2
• Filed: 03/26/2010
• Issued: 04/16/2013
• Est. Priority Date: 06/30/2009
• Status: Expired due to Fees

• Current Assignee: OrthoSensor, Inc (Stryker Corporation)
• Original Assignee: Navisense
• Inventors: Stein, Marc
• Primary Examiner(s): TANG, MINH NHUT
• Application Number:
  US12/748,088
• Publication Number:
  US 20100327848A1
• Time in Patent Office: 1,117 Days
• Field of Search: None
• US Class Current: 324/642
• 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 the 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 a signal from the transducer; and

a first pulse circuit far 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 where the system includes an amplifier having an input coupled to an output of the edge detect circuit and an output coupled to the transducer.

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 where the amplifier includes circuitry to dampen a wave shape for optimal transmission and reception in accordance with a matched network.

5. The system of claim 4 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 transducer when the edge detect circuit detects an edge of a first pulsed energy wave.

6. The system of claim 5 where the first pulse circuit is coupled to the input of the transducer to provide the-pulse to initiate the next measurement sequence-when the second pulse circuit is decoupled from the first transducer.

7. The system of claim 6 where the pulsed system modulates a time period of pulsed energy waves as a function of changes in distance or velocity through the medium.

8. The system of claim 1 where each pulsed energy wave is a damped ringing waveform where the edge detect circuit detects a leading edge of each pulsed energy wave and where upon detecting, the leading edge of each pulsed energy wave, the edge detect circuit is configured to be disabled from edge detecting for a predetermined period of time.

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

10. The system of claim 9 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.

11. The system of claim 1 where a force applied to the medium produces a proportional change in length of the medium.

12. The system at claim 1 where the medium comprises bone.

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

maintaining at least one pulsed energy wave in a medium subjected to the parameter being measured comprising the steps of;

detecting a first pulsed energy wave of the at least one pulsed energy waves reflected back to a first location with an edge detect circuit;

preventing a first pulse circuit from providing further pulses;

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 first location in response to each detected pulsed energy wave reflected back to the first location;

initiating measurement by providing a fixed integer number of pulsed energy waves to the medium from the second pulse circuit;

measuring a transit time of each pulsed energy wave with a timer where the transit time comprises each pulsed energy wave traversing the medium to the second location, being reflected by a reflector at a second location and traversing the medium to the first location; and

relating the transit time to the parameter being measured.

14. 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.