Ultrasonic bubble detector

• US 3,974,681 A
• Filed: 10/23/1973
• Issued: 08/17/1976
• Est. Priority Date: 10/23/1973
• Status: Expired due to Term

• Current Assignee: Jerry Namery
• Original Assignee: Jerry Namery
• Inventors: Namery, Jerry
• Primary Examiner(s): Queisser, Richard C.
• Assistant Examiner(s): Kreitman, Stephen A.
• Application Number:
  US05/408,269
• Time in Patent Office: 1,029 Days
• Field of Search: 73/67 SR, 73/61 R, 73/24, 73/67.6, 73/67.7, 73/67.8 R, 73/19, 73/67.9, 73/53, 73/71.5 US, 73/104 A, 128/2 V, 128/2.05 Z, 128/2.05 R, 128/2.05 F, 310/8.2, 310/9.1
• US Class Current: 73/600
• CPC Class Codes: A61M 5/365 Air detectors A61M5/1684 takes precedence; in extracorporeal blood circuits A61M1/3626
• CPC Class Codes: G01N 2291/02433 Gases in liquids, e.g. bubbles, foams
• CPC Class Codes: G01N 2291/02836 Flow rate, liquid level
• CPC Class Codes: G01N 2291/0421 Longitudinal waves
• CPC Class Codes: G01N 2291/048 Transmission, i.e. analysed material between transmitter and receiver
• CPC Class Codes: G01N 29/032 by measuring attenuation of acoustic waves
• CPC Class Codes: Y10S 128/13 Infusion monitoring

Abstract

The mode of operation is by ultrasonic through-transmission, and the detector is preferably employed for detecting air bubbles in intravenous feeding tubes to prevent air embolism. Transmission of sound from the transmitter, via the sensor head, to the receiver of the detector is dependent upon the existence of a fluid within the tubing. Acoustic losses, operating frequency, and the distance between transmitter and receiver are optimized to permit constructive-interference of energy transmitted to and reflected from the receiver, resulting in a partial standing wave as in a resonant cavity. If an air bubble passes through the sensor head a large acoustic discontinuity occurs, causing ultrasound to scatter and reflect from its normal path. These losses allow little ultrasonic energy to couple to the receiver. The sensor head includes oppositely and spacedly disposed cylindrical sound pipe segments having facing tubing accommodating recesses, and respectively connecting to the transmitter and receiver. Sound pipe segments have a markedly higher refractive index in comparison with the feeding tubing and its liquid contents causing ultrasound energy to focus towards the center of the feeding tube, thereby yielding greatest sensitivity to transmittion losses through the fluid within the feeding tube.

Claims

1. An ultrasonic through-transmission bubble detector for use with a hollow, flexible tube for feeding liquid and comprising:

a first sound coupling element arranged on one side of the tube and having one end defining a concave lensing surface contacting the tube;

transducer means coupled to the other end of said first sound element;

means applying a signal to said transducer means for causing said transducer means to establish a collimated ultrasonic signal in the first sound element;

a second sound coupling element arranged on the opposite side of the tube to the first sound element to unidirectionally receive the ultrasonic signal transmitted through the tube and the liquid disposed in the internal space defined by the tube;

said second sound coupling element having one end defining a concave lensing surface contacting the tube;

said first and second element lensing surfaces extending about a major circumference of the tube but defining a gap between the facing element ends;

the total gap circumference being less than the lensing surface circumference;

said first and second sound coupling elements both being constructed of a material having a greater acoustic velocity than that of the liquid or tube to provide a first refractive index between the first sound coupling element and tube greater than unity at the lensing surface of the first element, and a second reciprocal refractive index between the tube and second sound coupling element at the lensing surface of the second element;

said lensing surfaces and said material in combination providing a lensing effect, respectively, whereby the beam pattern of the ultrasonic signal is converged inside the tube and collimating the ultrasonic signal with the minimum width of the beam pattern inside the tube being less than the inner diameter of the tube;

and means coupled from the second sound element for receiving the collimated ultrasonic signal including means for establishing an alarm condition.

2. The detector of claim 1 including first and second sound absorbent members having said first and second sound elements respectively imbedded therein.

3. The detector of claim 2 wherein each sound element includes a sound pipe.

4. The detector of claim 3 including means for securing the sound pipes against the tube.

5. The detector of claim 4 wherein the facing concave ends are arcuate for accommodating the tube.

6. The detector of claim 3 wherein each sound pipe has a length that is an integral number of half wavelengths of the material of which it is constructed.

7. The detector of claim 1 wherein the means applying the signal includes an oscillator circuit and the transducer means includes a transmitting transducer coupled to the first sound element.

8. The detector of claim 6 wherein the receiving means includes amplifier means, means for establishing a threshold level and comparator means coupled from the amplifier means and responsive to the received signal falling below the threshold level for enabling an alarm means.

9. The detector of claim 3 wherein the feed tube has a diameter that is an integral number of half wavelengths of the fluid flowing in the tube.

10. The detector of claim 3 wherein the total distance (L) between opposite ends of the sound pipes is equal to the diameter of the tube plus an integral number of half wavelengths of the material of which it is constructed.

11. A detector as set forth in claim 1 wherein the ends of the sound elements are substantially the same size as or larger than the diameter or like cross-dimension of the tube.

12. A detector as set forth in claim 1 wherein the concave ends are at least partially of a shape coincident with the shape of the tube.

13. A detector as set forth in claim 12 wherein the concave ends have an arcuate curvature to match a circular tube.

14. An ultrasonic through-transmission bubble detector for use with a hollow tube for feeding a liquid, said detector comprising;

a pair of sound conductors disposed on opposite sides of said tube, each said conductor having one end defining a concave leensing surface, means for maintaining said conductors lensing surfaces intimately in contact with said tube, means coupled to one of said sound conductors for establishing an ultrasonic signal in the one conductor, and means coupled from the other sound conductor for receiving the ultrasonic signal, the facing lensing surfaces of said conductors being arranged to surround a major circumference of the tube with a gap defined between the facing conductor ends when so intimately coupled to the tube and establish a standing wave pattern in the conductors and liquid in the tube, which standing wave pattern is interrupted upon passage of a bubble, said conductors both being constructed of a material having a greater acoustic velocity than that of the liquid or tube said lensing surface of the one conductor and said material in combination converges the ultrasonic signal toward the center of the tube and the lensing surface of the other conductor and said material in combination collimates the beam back to the other conductor, with the minimum width of the standing wave beam pattern inside the tube being less than the inner diameter of the tube.

15. The detector of claim 14 including a pair of sound absorbent members, one associated with each sound conductor at least partially for confining the signal to the sound conductors.

16. The detector of claim 14 wherein the total distance between opposite remote ends of the conductors is equal to the diameter of the tube plus an integral number of half wavelengths of the material of which it is constructed in order to sustain the standing wave pattern in the absence of a bubble.

17. The detector of claim 14 wherein each sound conductor has a higher index of refraction than the tube.

18. The detector of claim 17 wherein the incident wave from the one conductor is focused to a point at a distance of approximately 3R/2 from the point where the one conductor and tube join.

19. The detector of claim 14 wherein the lensing surfaces of both conductors extend about the tube over a total circumference greater than half the circumference of the tube.