Method and apparatus for acoustically measuring the volume of an object

• US 4,640,130 A
• Filed: 10/29/1984
• Issued: 02/03/1987
• Est. Priority Date: 10/29/1984
• Status: Expired due to Fees

• Current Assignee: Baylor College of Medicine (Baylor College)
• Original Assignee: Baylor College of Medicine (Baylor College)
• Inventors: Winter, Dean C., Garza, Cutberto, Deskins, William G., Sheng, Hwai-Ping
• Primary Examiner(s): Birmiel, Howard A.
• Application Number:
  US06/665,800
• Time in Patent Office: 827 Days
• Field of Search: 73/579, 73/149
• US Class Current: 73/579
• CPC Class Codes: A61B 5/1073 Measuring volume, e.g. of limbs
• CPC Class Codes: G01B 17/00 Measuring arrangements characterised by the use of infrasonic, sonic or ultrasonic vibrations
• CPC Class Codes: G01H 13/00 Measuring resonant frequency

Abstract

A non-invasive method and apparatus for measuring the volume of an object such as an infant using the principle of the Helmholtz resonator. A container having a cavity therein containing gas and having an opening is subjected to a variable frequency loud speaker. The resonance frequency of the cavity is proportional to the volume of the cavity. By placing an object to be measured in the cavity, the change in the resonance frequency of the cavity before and after the object is placed is an indication of the volume of the object. The loudspeaker is mechanically uncoupled from the opening, the volume of the cavity is large enough compared to the object to be measured so the object will not change the shape of the cavity, and the temperature inside the cavity is maintained substantially constant during the measurements. Various lung measurements may be taken by determining the volume of air inhaled or exhaled from the lungs of an animal.

Claims

1. An apparatus for measuring the volume of an object comprising:

a container adapted to receive the object to be measured and having gas therein, said container having an opening;

variable frequency means positioned for producing periodic pressure fluctuations at the mouth of the opening;

means for measuring the resonance frequency in the container; and

wherein said pressure fluctuation producing means is mechanically uncoupled from the opening so that a uniform and normal pressure wavefront impinges on the opening.

2. An apparatus for measuring the volume of an object comprising:

a container adapted to receive the object to be measured and having gas therein, said container having an opening;

variable frequency means positioned for producing periodic pressure fluctuations at the mouth of the opening;

means for measuring the resonance frequency in the container; and

wherein said pressure fluctuation producing means is separated from the opening a distance sufficient to avoid acoustical reflections between the container and the pressure fluctuation producing means.

3. An apparatus for measuring the volume of an object comprising,

a container having a cavity therein containing gas, said container having a single opening, said container being substantially symmetrical and having an openable and closable portion for inserting the object to be measured into the cavity,

the volume of said cavity being large enough compared to the volume of the object to be measured whereby the object will not significantly change the shape of the cavity,

a variable frequency sound producing loudspeaker positioned to direct sound waves into the opening, but the loudspeaker is mechanically uncoupled from the opening, and

means for measuring the resonance frequency in the cavity.

4. The apparatus of claim 3 wherein the volume of the cavity is at least eight times the volume of the object to be measured.

5. The apparatus of claim 3 including,

feedback means between the resonance frequency measuring means and the loudspeaker for operating the loudspeaker at the resonance

6. A method of determining the volume of air inhaled or exhaled from the lungs of an animal comprising,

placing the animal into a cavity of a container having an opening to which is applied sound waves pressure fluctuations,

changing the frequency of the pressure fluctuations to provide resonance frequency in the cavity as the volume of air in the lungs of the animal changes;

and

measuring the resonance frequencies as the volume of air in the lungs changes; and

comparing the difference in the measured resonance frequencies which is an indication of the volume changes in the lungs.

7. The method of claim 6 wherein the tidal volume of the lungs are measured.

8. A method for determining the volume of an animal comprising,

measuring the resonant frequency of the cavity having a gas therein, when empty, of a container having an opening to which is applied pressure fluctuations, the cavity having at least eight times larger volumes than the animal to be measured, the pressure fluctuations being produced by means which are mechanically spaced from the opening so that a uniform and normal pressure wavefront impinges on the opening,

placing the animal to be measured into the cavity, and again measuring the resonant frequency of the gas in the cavity with the animal in the cavity, and

comparing the difference between the first and second measurements which is an indication of the volume of the animal.