US3604441A

US3604441A - Proportional acoustic transducer

Info

Publication number: US3604441A
Authority: US
Inventors: Donald O Rockwell Jr; Kenji Toda
Original assignee: US Department of Army
Current assignee: US Department of Army
Priority date: 1969-10-15
Filing date: 1969-10-15
Publication date: 1971-09-14
Anticipated expiration: 1988-09-14

Abstract

A proportional acoustic transducer and fluid demodulator. Proportionality of fluid output to acoustic input is achieved by causing a power jet to attach to a semicircular sidewall and directing acoustic signals at the power jet. The angle of deflection of the power jet provides a measure of the amplitude of frequency of the acoustic signal. Sensitivity of the system is greatest when the frequency of the acoustic input is close to the fundamental frequency of the settling chamber from which the power jet is derived.

Description

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[72] in ento Donald Rockwell, J 3,212,515 10/1965 Zisfein et a]. 137/8 1.5 Bethesda; 3,233,621 2/1966 Manion 137/8 1 .5 Kenji Toda, Rockville, both of, Md. 3,295,543 l/ 1967 Zalmanzon... 137/8 1.5 [21] Appl. NO. 866,675 3,509,897 5/1970 Abler l37/81.5 [22] Filed Oct. 15, 1969 3,511,255 5/1970 Bauer 137/8 1.5

[45] Patented Sept. 14, 1971 [73] Assignee The United States of America as represented by the Secretary of the Army Primary Examiner-Samuel Scott Attorneys-l-larry M. Saragovitz, Edward J. Kelly, Herbert Berl and .l. D. Edgerton [54] PROPORTIONAL ACOUSTIC TRANSDUCER 10 Claims, 1 Drawing Fig.

[52] 1.8. CI ABSTRACT: A roportional acoustic transducer and fluid 1337/815 demodulator. Proportionality of fluid output to acoustic input f Cl F156 1/08 is achieved by causing a power jet to attach to a semicircular [50] Field of Search 137/81.5, id ll d di i acoustic signals at the power jet. The

13 angle of deflection of the power jet provides a measure of the amplitude of frequency of the acoustic signal. Sensitivity of [56] I References Cited the system is greatest when the frequency of the acoustic input U IT STATES PATENTS is close to the fundamental frequency of the settling chamber 3,171,422 3/1965 Evans 137/8l.5 from which the power jet is derived.

SOURCE PRoPoRTroNAL ACOUSTIC TRANSDUCER RIGHTS OF THE GOVERNMENT The invention described herein may be manufactured, used, and licensed by or for the United States Government for governmental purposes without the payment to me of any royalty thereon.

BACKGROUND OF THE INVENTION This invention relates to proportional acoustic transducers, and more particularly to a flueric transducer in which the angle of deflection of a power stream is a measure of the amplitude or frequency of an acoustic input signal.

Pure fluid acoustical transducers are known in the prior art. One such transducer is disclosed in U.S. Pat. No. 3,413,996 issued Dec. 3,1968 to Fine, in which an acoustic signal is used to control the power stream of a fluid amplifier. In Fines system an acoustic signal is applied to a control nozzle of a proportional fluid amplifier and the deflection of the power stream is used as a measure of the acoustic input signal. While this system is satisfactory for its purpose, its range of operation is severely limited. This is because the deflection of the power stream is confined between two output channels, and because deflection is achieved solely by fluid interaction without the aid of wall attachment.

It is, therefore, a primary object of this invention to provide a transducer which is a measure of the amplitude or frequency of an acoustic signal.

It is another object to provide an acoustic transducer wherein deflection of a power stream is achieved by the combined effects of wall attachment and fluid interaction.

Another object is to achieve high sensitivity and gain.

Still another object is to provide a demodulator capable of recognizing amplitude and frequency modulated acoustic signals.

SUMMARY OF INVENTION Briefly, in accordance with this invention, an acoustic signal is used to vary the deflection of a power jet in a fluid amplifier. Large deflection is achieved by providing a semicircular wall to which a power jet attaches upon emergence from a power nozzle. In the absence of any external signals the power jet will remain attached to the semicircular wall to form an arc of attachment which subtends a predetermined angle along the semicircular wall. At the point of detachment from the wall the power jet continues in a tangential path to one of a plurality of outputs. When an acoustic signal is applied to the power jet at a point slightly-above the power nozzle, detachment of the power jet from the semicircular wall occurs sooner, so that the arc of attachment and the subtended angle are smaller. Again, the power jet continues in a tangential direction to another one of the plurality of outputs. By measuring the angle of deflection of the power jet in the absence of an input signal and comparing this angle with the angle of deflection when an acoustic signal is applied to the power jet, the amplitude or frequency of the input acoustic signal can be determined.

BRIEF DESCRIPTION OF THE DRAWING The specific nature of the invention as well as other objects, aspects, uses, and advantages thereof, will clearly appear from the following description and from the accompanying drawing in which:

The FIGURE is a plan view of one embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Considering the FIGURE, power nozzle issues a stream of power fluid which, upon its emergence, attaches to sidewall 11 of semicircular block 12. The point of attachment will of course depend upon the number of factors including the orientation of the block with respect to the power nozzle and the velocity of the issuing stream. Once attachment has ocand continue in a straight path toward one of the outputs such as output 19. Again the precise point of detachment will depend upon the geometry of the system and the velocity of the fluid stream. The arc of attachment subtends'an angle B which may be as much as or more.

When acoustic signal 15 is directed at the power stream, the effect will be to disturb the stream and cause it to detach from sidewall 1 l of semicircular block 12 at some earlier point such as 14, thereby defining a smaller arc of attachment which subtends a smaller angle at. Once detached, the power stream will again continue in a tangential path and will exit from a different output channel 20 which is separated from output channel 19 by one or more splitters 18. Thus it is seen that in the absence of an acoustic signal the power stream is deflected through a first angle of deflection (which is equal to B as measured from the vertical) and in the presence of an acoustic signal the angle of deflection is reduced to a smaller angle of deflection (equal to a as measured from the vertical). The precise mechanism by which an input signal causes the power fluid to detach from the curved sidewall is not fully understood. It is believed that certain disturbances are created in the ambient region 25 which produces a force tending to pull the fluid stream away fromthe curved sidewall. While the mechanism of detachment cannot be fully explained, the resulting effect is fully discernable and, in fact, it has been found that a change in output deflection of as much as 90 can be achieved with relatively small changes in the amplitude or frequency of the input signal. The system thus has very high sensitivity and gain.

Input signal 15 is applied to the power stream by means of an input channel 16 which directs the signal from an external source 17. External source 17 may, for example, be a loud speaker, an electrically vibrated diaphragm, a piezoelectric crystal, or any other electrical or acoustic source. The use of an input channel 16 is merely exemplary, and it has been found that the input signal may be directed at the fluid stream without such a channel. That is, the acoustic signal may be applied over a much wider area than shown in the FIGURE, the signal being directed generally toward the power stream.

Power fluid may be supplied directly from a regulated power source, or it may be derived from settling chamber 22 as shown in the FIGURE. Thus fluid may be applied through input Channel 23 to fill settling chamber 22 and to issue from power nozzle 10 as a power fluid. Depending upon the dimensions of settling chamber 22, the chamber will have a certain fundamental frequency. This fundamental frequency is important in determining the most sensitive operating frequency of the system.

By applying an acoustic signal 15 which is set to the fundamental frequency of the settling chamber 22 or to one of its harmonic frequencies it is found that the power stream can be deflected through a maximum angle in response to variations of the amplitude of signal 15. In other words, sensitivity and gain are greatest at this frequency. The same effect is achieved when the system is responding to variations in frequency of the acoustic signal. Thus, by maintaining the amplitude of the acoustic signal constant and varying only its frequency within the range of the fundamental frequency of the settling chamber the greatest angle of change of the power stream will be realized.

As a consequence of the sensitivity of the system to particular frequencies it follows that the system can be made nonresponsive or insensitive to certain other frequencies. This leads to a particular useful application of the system as a demodulator. That is, by utilizing a carrier signal of a frequency to which the power fluid would be nonresponsive and modulating this carrier signal with a frequency which is within the range of responsive frequencies, the power fluid will be responsive only to variations in the modulating frequency, the

carrier signal having no effect upon the deflection of the power fluid. Because the angle of the deflection of the power fluid can be made both amplitude and frequency responsive, the system can of course be used as a demodulator for AM or FM signals.

An example of an operative embodiment of the invention would be one in which the fundamental frequency of the cavity is 1,092 Hz., the area of the power nozzle exit is l 6.08 mm? and the radius ofthe semicircular block is between 0.3 inches and 3.0 inches. These figures are of course merely exemplary as numerous modifications are within the skill of the art. The FIGURE shows an aspirator channel 21 which provides fluid communication between the output of nozzle 10 and ambient. The size of this aspirator channel is not critical and, in fact, the system has been shown to operate equally well without the aspirator channel. That is, block 12 may be located directly adjacent the output nozzle 10. 1

Although not shown in the FIGURE, it will be appreciated that each of the output channels 19 will be provided with a measuring means to determine whether or not there is flow in that channel. The means to measure the flow may be provided with a threshold detector so that a small amount of residual flow will not be counted. This is because the power fluid has a tendency to expand over a wide area as the distance between the point of detachment and the output channel increases.

By comparing the angle of deflection in the absence of an acoustic signal with that angle when an acoustic signal is applied it is possible to calibrate the output signal in terms of the input amplitude or frequency. The output may of course be converted into an electronic or mechanical readout if desired.

Having described our invention we wish it to be understood that we do not desire to be limited to the exact details of construction shown and described, for obvious modifications will occur to a person skilled in the art.

I claim as my invention: 1. A proportional acoustic transducer comprising: a. a source of power fluid; b. a curved sidewall for causing said power fluid to attach thereto and to produce a first angle ofdeflection; an acoustic signal directed at said power fluid to create a force tending to pull said fluid away from said curved sidewall and thereby to deflect the fluid to produce a second angle of deflection; and d. means to compare the first angle of deflection with the second angle of deflection, whereby an output signal is obtained which is a measure of said acoustic signal.

2. The transducer of claim 1 wherein said means to compare comprises a plurality of output channels separated by a plurality of splitters.

3. The transducer of claim 1 wherein said curved sidewall comprises part of a semicircular block.

4. The transducer of claim 1 wherein said means todirect an acoustic signal comprises a conduit having an open end directed at the power fluid as it emerges from a power nozzle.

5. The transducer of claim 1 wherein said acoustic signal comprises a carrier signal of a frequency to which said power fluid is nonresponsive and a modulating signal to which said power fluid is responsive, whereby said transducer functions to demodulate said acoustic signal.

6. The transducer of claim 1 wherein said source of power fluid comprises a settling chamber having a source of fluid supply.

7. The transducer of claim 6 wherein said settling charnber has a fundamental frequency and said acoustic signal has a constant frequency equal to said fundamental frequency or one of its harmonics, whereby said fluid stream is deflected through its maximum angle in response to variations in amplitude of said acoustic signal.

8. The transducer of claim 6 wherein said settling chamber has a fundamental frequency and the frequency of said acoustic signal is varied within a range of harmonics of said fundamental frequency.

9. A method of providing a fluid output signal which is a measure ofan acoustic input signal comprising;

a. providing a source 0 power fluid;

b. causing said fluid to attach to a curved sidewall;

' c. measuring the deflection of said fluid caused by said sidewall;

d. directing an acoustic signal at said fluid in the region of said sidewall of such frequency as to create a force tending to pull said fluid away from said sidewall;

e. measuring the new deflection of said fluid; and

f. comparing the deflection of said fluid in the absence of an acoustic signal with the deflection caused by the presence of an acoustic signal.

10. The method of claim 9 wherein said acoustic signal is a modulated signal and the step of comparing further comprises the step of producing a demodulated output signal.

Claims

1. A proportional acoustic transducer comprising: a. a source of power fluid; b. a curved sidewall for causing said power fluid to attach thereto and to produce a first angle of deflection; an acoustic signal directed at said power fluid to create a force tending to pull said fluid away from said curved sidewall and thereby to deflect the fluid to produce a second angle of deflection; and d. means to compare the first angle of deflection with the second angle of deflection, whereby an output signal is obtained which is a measure of said acoustic signal.

4. The transducer of claim 1 wherein said means to direct an acoustic signal comprises a conduit having an open end directed at the power fluid as it emerges from a power nozzle.

7. The transducer of claim 6 wherein said settling chamber has a fundamental frequency and said acoustic signal has a constant frequency equal to said fundamental frequency or one of its harmonics, whereby said fluid stream is deflected through its maximum angle in response to variations in amplitude of said acoustic signal.

9. A method of providing a fluid output signal which is a measure of an acoustic input signal comprising; a. providing a source of power fluid; b. causing said fluid to attach to a curved sidewall; c. measuring the deflection of said fluid caused by said sidewall; d. directing an acoustic signal at said fluid in the region of said sidewall of such frequency as to create a force tending to pull said fluid away from said sidewall; e. measuring the new deflection of said fluid; and f. comparing the deflection of said fluid in the absence of an acoustic signal with the deflection caused by the presence of an acoustic signal.