Bubble measuring instrument and method

• US 6,408,679 B1
• Filed: 02/04/2000
• Issued: 06/25/2002
• Est. Priority Date: 02/04/2000
• Status: Expired due to Fees

• Current Assignee: The United States of America As Represented By The Secretary of Agriculture
• Original Assignee: United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration
• Inventors: Magari, Patrick J., Kline-Schoder, Robert
• Primary Examiner(s): Williams, Hezron
• Assistant Examiner(s): WIGGINS, JOHN DAVID
• Application Number:
  US09/498,440
• Time in Patent Office: 872 Days
• Field of Search: 73/190.3, 73/191, 73/645.3, 73/647.9, 73/614.9, 73/617.1, 735/92, 736/02
• US Class Current: 73/19.03
• CPC Class Codes: A61B 8/08 Detecting organic movements or changes, e.g. tumours, cysts, swellings A61B8/02 - A61B8/06 take precedence
• CPC Class Codes: A61B 8/4209 by using holders, e.g. positioning frames
• CPC Class Codes: A61B 8/488 involving Doppler signals
• CPC Class Codes: G01N 2291/014 Resonance or resonant frequency
• CPC Class Codes: G01N 2291/02433 Gases in liquids, e.g. bubbles, foams
• CPC Class Codes: G01N 2291/0421 Longitudinal waves
• CPC Class Codes: G01N 29/036 by measuring frequency or resonance of acoustic waves
• CPC Class Codes: G01N 29/348 with frequency characteristics, e.g. single frequency signals, chirp signals measuring frequency of mechanical vibrations or acoustic waves in general G01H1/06, G01H3/04; measuring frequency or analysing frequency spectra G01R23/00
• CPC Class Codes: G01N 29/42 by frequency filtering or by tuning to resonant frequency
• CPC Class Codes: G01N 29/46 by spectral analysis, e.g. Fourier analysis or wavelet analysis spectral signal processing per se G06F17/14
• CPC Class Codes: G01S 7/52026 Extracting wanted echo signals Doppler systems G01S15/50; Doppler short range imaging systems G01S15/8979
• CPC Class Codes: G01S 7/52036 using analysis of echo signal for target characterisation
• CPC Class Codes: Y10S 128/916 Ultrasound 3-D imaging

Abstract

Method and apparatus are provided for a non-invasive bubble measuring instrument operable for detecting, distinguishing, and counting gaseous embolisms such as bubbles over a selectable range of bubble sizes of interest. A selected measurement volume in which bubbles may be detected is insonified by two distinct frequencies from a pump transducer and an image transducer, respectively. The image transducer frequency is much higher than the pump transducer frequency. The relatively low-frequency pump signal is used to excite bubbles to resonate at a frequency related to their diameter. The image transducer is operated in a pulse-echo mode at a controllable repetition rate that transmits bursts of high-frequency ultrasonic signal to the measurement volume in which bubbles may be detected and then receives the echo. From the echo or received signal, a beat signal related to the repetition rate may be extracted and used to indicate the presence or absence of a resonant bubble. In a preferred embodiment, software control maintains the beat signal at a preselected frequency while varying the pump transducer frequency to excite bubbles of different diameters to resonate depending on the range of bubble diameters selected for investigation.

Claims

1. A method for monitoring a selected volume of liquid for bubbles, said method comprising:

producing a first acoustic signal at a first frequency, said first frequency being a resonance frequency of a selected diameter of said bubbles and operable for resonating said bubbles of said selected diameter;

producing a second acoustic signal having a second frequency higher than said first frequency, producing said second acoustic signal in pulses such that said pulses are produced at a repetition frequency;

choosing said first frequency and said repetition frequency to produce a beat signal with a selected frequency; and

monitoring said beat signal at said selected frequency to detect said bubbles.

2. The method of claim 1, further comprising:

choosing said first frequency and said repetition frequency such that said repetition frequency is not equal to said first frequency divided by an integer.

3. The method of claim 1, further comprising;

varying said first frequency to monitor a range of bubble sizes.

4. The method of claim 3, further comprising:

controlling said repetition frequency to continually maintain said beat signal at said selected frequency as said first frequency varies.

5. The method of claim 1, further comprising:

varying said first frequency to monitor a range of bubble sizes, and

keeping said second frequency constant.

6. The method of claim 1, further comprising:

alternately producing said second acoustic signal and monitoring said beat signal with a single transducer.

7. The method of claim 1, further comprising:

filtering said beat signal with a highpass filter to eliminate signals below said selected frequency for detecting said beat signal.

8. The method of claim 1, further comprising:

filtering said beat signal with a lowpass filter to eliminate signals above said selected frequency for detecting said beat signal.

9. The method of claim 1, further comprising:

directing said first acoustic signal and said second acoustic signal at a position of said selected volume.

10. A method for monitoring a selected volume of liquid for bubbles, comprising:

producing a first acoustic signal at a first frequency, said first frequency being a resonance frequency of a selected diameter of said bubbles and operable for resonating said bubbles of said selected diameter;

varying said first frequency according to a range of bubble sizes to be detected;

directing said first acoustic signal at a position of said selected volume;

producing a second acoustic signal, said second acoustic signal having a higher frequency than said first frequency, maintaining said second frequency constant as said first frequency varies;

providing that said second acoustic signal pulses at a repetition frequency.

directing said second acoustic signal at said position of said selected volume; and

receiving a signal response from said selected volume.

11. The method of claim 10, further comprising:

choosing said first frequency and said repetition frequency such that said repetition frequency is not equal to said first frequency divided by an integer as said first frequency vanes.

12. The method of claim 10, further comprising:

detecting a beat signal related to a presence of a bubble in said selected volume;

controlling said repetition frequency to maintain said beat signal at a constant beat frequency as said first frequency varies.

13. The method of claim 10, further comprising:

selecting a rate for varying said first frequency, said rate being related to a time required for monitoring said range of bubble sizes to be detected.

14. The method of claim 13, wherein said selecting a frequency sweep increment such that said first frequency is incremented over time in steps through a range of frequencies related to said range of bubble sizes to be detected.

15. The method of claim 10, further comprising:

determining bubble size based on an instantaneous value noted for said first frequency.

16. A method for monitoring bubbles present in a liquid, comprising:

producing a first acoustic signal at a first frequency, said first frequency being a resonance frequency of a selected diameter of said bubbles and operable for resonating said bubbles of said selected diameter;

producing a second acoustic signal having a second frequency more than ten times greater than said first frequency;

pulsing said second acoustic signal at a repetition frequency that is lower than said first frequency; and

controlling said repetition frequency to prevent said repetition frequency being equal to said first frequency divided by an integer.

17. The method of claim 16, further comprising:

varying said first frequency for monitoring different bubble sizes.

18. The method of claim 16, further comprising:

monitoring a range of bubble sizes of interest by varying said first frequency over time through a range of frequencies related to said range of bubble sizes of interest.

19. The method of claim 16, further comprising:

maintaining said second frequency to be constant.

20. The method of claim 16, further comprising:

receiving a transducer signal, and

extracting a beat signal at a beat signal frequency from said transducer signal.

21. The method of claim 20, further comprising:

controlling said repetition frequency for controlling said beat signal frequency.

22. The method of claim 21, further comprising:

controlling said repetition frequency to keep said beat signal frequency substantially constant.

23. The method of claim 16, further comprising:

receiving a transducer signal, and

multiplying a predetermined reference signal at said second frequency times said transducer signal to produce a multiplier output signal.

24. The method of claim 23, further comprising;

sampling said multiplier output signal to produce a sampled signal.

25. The method of claim 24, further comprising;

filtering said sampled signal to produce a beat signal at a selected frequency.

26. The method of claim 25, further comprising:

measuring an amplitude of said beat signal to detect the presence of a bubble.