Fiber optic transducer and method

A method and apparatus for detecting and measuring mechanical movement that is directly or indirectly representative of a physical phenomenon. The method and apparatus involve the use of at least one optical fiber that defines a region of bend having a curvature, the radius of which varies in direct relation with the particular mechanical movement that is induced by the physical phenomenon. Light is introduced into one extremity of the optical fiber and propagates through the fiber where the intensity of the light emitted or radiating from the opposite extremity of the fiber is measured. Differentiation between introduced light and emitted light determines the degree of perturbance caused by the region of bend and is thus representative of the physical phenomenon that alters the radius of curvature at the region of bend.

FIELD OF THE INVENTION 
This invention relates generally to detection and measurement of physical 
phenomenon and more particularly relates to a method and apparatus for 
detecting and measuring various physical phenomenon and more specifically 
to utilization of optical fiber material in conjunction with a method of 
detecting and measuring such physical phenomenon. 
BACKGROUND OF THE INVENTION 
Apparatus of various character has long been utilized for the purpose of 
detecting and measuring certain physical phenomenon. For example, in the 
measurement of mechanical movement, the character of the mechanical 
movement involved typically dictates the character of the equipment 
necessary for measurement of the same. In a case of mechanical structures 
which are subjected to internal pressure, strain gauges may be employed to 
measure the dimensional changes that are induced by the internal pressure. 
In the case of mechanical movement of more significant nature, mechanical 
devices such as micrometers are employed and electrical sensors may also 
be employed to detect such mechanical movement. 
Under certain circumstances it is desirable to measure the flow of fluid 
such as liquid through a conduit. In the past, this has been accomplished 
by providing certain types of flow meters such as turbine flow meters, 
vortex-shedding type flow meters as well as many other flow measurement 
devices. Most of the flow measurement devices develop either mechanical or 
electrical interference with the flowing fluid and in many cases such 
interference is quite undesirable. It is desirable to provide a system for 
detecting and measuring the flow of fluid through a conduit wherein the 
flow measurement device or system does not develop mechanical or 
electrical interference to fluid flow. 
In certain cases, it is necessary to measure the extent to which a 
mechanical object expands and contracts during the various phases of its 
activity. Many mechanical and electrical devices are provided for the 
purpose of measuring mechanical expansion and contraction of objects but, 
for the most part, such devices are complex, are of relatively expensive 
nature and, in many cases, lack the degree of accuracy that might be 
desired. Further, it may be desirable that the measuring device or system 
be such as to permit accurate measuring without the possibility of 
introducing any mechanical or electrical interference with the object 
being measured. Few, if any, known measuring devices have this desirable 
facility. 
SUMMARY OF THE INVENTION 
It is a primary feature of the present invention to provide a novel method 
and apparatus for detecting and measuring mechanical movement that is 
directly or indirectly representative of a physical phenomenon and which 
utilizes an optical fiber system for the purpose of accomplishing such 
measurement. 
It is also a feature of the present invention to provide a novel method and 
apparatus for detecting and measuring mechanical movement which is of 
electrical nature and yet does not require the use of wires, electrical 
currents or electromagnetic wave interference in or about the physical 
phenomenon being measured. 
It is another important feature of this invention to provide a novel method 
and apparatus for detecting and measuring mechanical movement which 
measurement can be conducted free of any danger of electrical shock, fire 
or explosion in the event the mechanical movement of interest involves 
combustible or explosive material. 
It is an even further feature of the present invention to provide a novel 
method and apparatus for detecting and measuring mechanical movement by 
means of an optical fiber system wherein the mechanical movement may be 
induced in response to various physical phenomenon such as the activity of 
a flowing fluid medium, the activity of increasing or decreasing pressure, 
expansion or contraction of a mechanical object as well as various other 
physical phenomenon. 
It is an even further feature of this invention to provide a novel method 
of detecting and measuring mechanical movement wherein such movement is 
converted by the perturbed total internal reflection of light waves 
passing through one or more optical fibers to an electrical phenomenon 
that can be observed. 
Other and further objects, advantages and features of the present invention 
will become apparent to one skilled in the art upon consideration of this 
entire disclosure, including this specification and the annexed drawings. 
The form of the invention, which will now be described in detail, 
illustrates the general principles of the invention, but it is to be 
understood that this detailed description is not to be taken as limiting 
the scope of the present invention. 
Briefly, the present invention relates to an optical fiber transducer 
system incorporating one or more optical fibers that are physically 
arranged in accordance with the particular physical phenomenon being 
detected and measured. In each case, the optical fiber or fibers is formed 
to define a region of bend wherein the radius of the curvature of the 
region of bend is of variable nature and wherein the curvature of the 
region of bend is caused to vary in accordance with the mechanical aspects 
of the physical phenomenon involved. Also in each case, the optical fiber 
system incorporates a light source for transmitting light into the optical 
fiber or fibers and a light sensitive measurement system having the 
capability of detecting and measuring the intensity of light waves being 
propagated through the optical fiber and being emitted at the end thereof 
opposite the light source. As the radius of curvature of the region of 
bend is decreased, perturbance of the light waves being emitted from the 
optical fiber also decreases, thereby causing light rays propagating 
through the optical fiber by total internal reflection to represent a 
decrease in the intensity of the emitted light signal. Through utilization 
of light sensitive electronic equipment, the intensity of the emitted 
light signal is detected and converted into an electrical signal that 
represents the character of bend or curvature in the region of bend at any 
point in time. By establishing the particular emitted light intensity that 
is determined by a particular radius of curvature in the region of bend, 
the optical fiber transducer can be simply and efficiently calibrated with 
respect to the physical phenomenon involved. Changes in the physical 
phenomenon which induce decrease or increase in the radius of curvature in 
the region of bend are thereby accurately represented in the form of an 
electrical signal that is converted from the detected light intensity 
being emitted from the optical fiber system. By appropriate observation of 
the receiver signal, the optical fiber system becomes a detector of 
physical motion, if that physical motion results in modifying the state of 
curvature of the region of bend in the optical fiber. 
By employing the optical fiber sensor system, a sensor is readily developed 
having the capability of converting the speed of flowing fluid into a 
light signal, the intensity of which is representative of the speed of the 
flowing fluid. A fluid flow meter is, therefore, capable of being 
developed simply by providing an optical fiber sytem having a region of 
bend and wherein the region of bend is altered in accordance with the 
speed of the flowing fluid medium. For example, a vortex shedding type 
flow meter may be provided incorporating a vortex sensitive element that 
is movable responsive to the vortices developed in the flowing fluid 
medium by an object positioned in the flow stream of a laminar flowing 
fluid. The optical fiber system may be interconnected physically with the 
movable vortex responsive element and, therefore, movement induced to the 
element by the vortices is converted efficiently into variation in the 
curvature of the optical fiber system in the region of bend. As the 
movable element oscillates within the flowing fluid responsive to the 
vortices, this oscillation is rendered by the optical fiber system to an 
electrical signal that is representative of the vortices and thus also 
representative of the velocity of the flowing fluid. 
In accordance with the present invention, a fluid pressure sensitive 
transducer may be provided which incorporates a variable volume chamber 
which may be evacuated and which is capable of expanding and contracting 
in response to fluid pressure. Expansion and contraction of the chamber 
may be converted efficiently into a simple mechanical movement and an 
electrical signal representative of this mechanical movement may be simply 
and efficiently provided by an optical fiber system that detects the 
mechanical movement. For example, the variable volume chamber may 
conveniently take the form of a bellows structure having an arm at the 
movable extremity thereof. As the bellows structure expands or contracts 
due to changes in internal pressure, the movable arm will change its 
position relative to the immovable base portion of the bellows structure, 
representing a simple mechanical movement. By interconnecting an optical 
fiber system to the movable and immovable portions of the bellows 
structure such that this relative movement will induce changes in 
curvature of the region of bend of the optical fiber, the optical fiber 
system will emit representative light intensities, have a value that 
represents fluid pressure. The pressure representative light signals are 
then converted into pressure representative electrical signals that may be 
further processed or utilized as appropriate to the various 
characteristics desired by the user. 
An optical fiber transducer may also be employed which detects and measures 
changes in the physical size of a mechanical object. A sensor may be 
employed which converts the changing spatial extent of the cross-sectional 
area of an entity into corresponding changes of light intensity. The 
changes in light intensity are then processed to define electrical signals 
that are representative of size and size changes that occur in the object 
being measured. This feature is efficiently accomplished by providing an 
optical fiber system incorporating one or more optical fibers that are 
formed in the nature of a figure "8" to define two loops by intermediate 
crossing of the fibers. The larger of the loops is positioned about the 
object to be measured while the smaller of the loops defines a region of 
bend. The combined cross-sectional area of the two loops of the figure "8" 
is caused to remain the same. As the larger loop is caused to expand and 
contract by cross-sectional dimensional changes of the object involved, 
the small loop defining the region of bend is caused to expand or contract 
in corresponding manner. The double looped optical fiber system is 
provided with light emitting and detecting apparatus as described above. 
As the object expands, causing expansion of the larger one of the loops, 
the smaller loop is caused to contract, thereby decreasing the radius of 
curvature in the region of bend. This causes a higher degree of 
perturbance, thereby resulting in diminished light wave reflection and 
decreased intensity of the light being emitted from the optical fiber 
system. Upon contraction of the object being measured, the larger of the 
two loops becomes diminished thereby causing expansion of the smaller one 
of the two loops. Expansion of the smaller loop thereby increases the 
radius of curvature in the region of bend and thereby causes a consequent 
increase in the intensity of light being emitted and detected by the light 
signal detector. 
BRIEF DESCRIPTION OF THE DRAWINGS 
So that the manner in which the above recited features, advantages and 
objects of the present invention are attained and can be understood in 
detail, more particular description of the invention, briefly summarized 
above, may be had by reference to the embodiments thereof which are 
illustrated in the appended drawings, which drawings form a part of this 
specification. 
It is to be noted, however, that the appended drawings illustrate only a 
typical embodiment of the invention and is, therefore, not to be 
considered limiting of its scope, for the invention may admit to other 
equally effective embodiments.

DETAIL DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The physical phenomenon which is utilized in all aspects of the fiber optic 
transducer system of this invention may be referred to as "perturbed total 
internal reflection". It is intended that the term "optical fiber" mean 
one or more optical fibers. An optical fiber is provided and is oriented 
such that a portion of the fiber defines a region of bend having a 
variable radius of curvature that changes responsive to the physical 
phenomenon that is involved. A light wave transmitter or light source is 
positioned at one extremity of the optical fiber and transmits light waves 
directly into the fiber by having the end of the fiber positioned in 
abutting or closely spaced relation with the light source of the light 
transmitter. A large fraction of the light rays which enter the 
transmitting end of the optical fiber will remain captured inside the 
fiber as the light waves propagate toward the opposite extremity of the 
optical fiber, which may be referred to as the light emitting extremity. 
An optical receiver is positioned at the light emitting extremity of the 
optical fiber and is adapted to measure or otherwise detect the intensity 
of the light waves being emitted at the emitting extremity of the optical 
fiber. From the standpoint of optical physics, as the light rays propagate 
through the optical fiber, the light waves remain inside the fiber by 
"total internal reflection". When the light waves arrive at the receiver 
positioned at the emitting extremity of the optical fiber, the light waves 
radiate out of the emitting extremity and are detected by the detection 
mechanism of the receiver. This process "the received signal" can be 
perturbed by bending the fiber. By the term "perturbed" is meant that some 
of the rays escape the inside of the fiber as they propagate along and 
inside the "region of bend" in the fiber. Under circumstances where the 
region of bend has a curvature that is excessively small or sharp for some 
of the light rays, those particular light waves leak out of the optical 
fiber and are lost. When the light waves leak out in this manner, the 
resulting light signal being emitted at the emitting extremity of the 
optical fiber is of less intensity than the light waves being introduced 
into the light transmitting extremity. By appropriate observation of the 
receiver signal, the optical fiber becomes a detector of physical motion, 
if that physical motion results in modifying the state of curvature (the 
region of bend) of the optical fiber. 
In accordance with the present invention, the optical fiber system of the 
transducer is positioned such that the optical fiber defines a region of 
bend having a present bend which may be in the shape of a "U" or may be of 
"O" shaped configuration. The mechanical linkage of suitable nature is 
then interconnected with the optical fiber in such a manner that movement 
of the mechanical linkage causes a consequent increase or decrease in the 
degree or radius of curvature in the region of bend of the fiber. By 
observation of the changes in intensity of the emitted light propagating 
through the optical fiber system, it will be observed that these changes 
in light intensity are representative of consequent changes in the 
physical phenomenon being detected. By appropriate calibration, an 
efficient transducer system may be simply and efficiently developed that 
allows detection of changes in the physical phenomenon involved wherein 
the changes can be monitored quite efficiently. 
Referring now to the drawings and first to FIG. 1, there is shown in 
optical fiber transducer system that is provided for the purpose of 
measuring dimensional changes in an object. The optical fiber transducer 
system is illustrated generally at 10 and incorporates a length of optical 
fiber 12 that is formed in such a manner as to define a large loop 14 and 
a small loop 16. The optical fiber 12 is formed so that an intermediate 
portion thereof crosses itself as shown at 18 so that the optical fiber is 
generally in the form of a figure "8". A constraint is provided as shown 
at 20 which is structurally interconnected with portions 22 and 24 of the 
optical fiber 12 so that portions 22 and 24 of the fiber are restrained in 
fixed relation with one another. This fixed relation causes the loops 14 
and 16 to encompass a specific combined cross-sectional dimension which 
does not vary regardless of the relative sizes of the loops. A loose 
constraining means 26 is provided to encompass the intersection 18 that is 
defined by the crossed portions of the optical fiber 12. The loose 
constraining means 26 functions only to maintain the intersecting portions 
of the optical fiber in close proximity to one another and yet allows the 
optical fibers to slide with respect to one another and to move through 
the opening defined by the loose constraining means. The loose 
constraining means 26 may conveniently take the form of a ring or grommet 
that is composed of any suitable material such as plastic, metal, glass, 
etc. 
A support structure 28 is provided which defines a structural support for a 
third constraining element 30 about which the small loop 16 of the optical 
fiber extends. The small loop 16 extends an opening 32 defined by the 
support structure 28 and then passes about the constraining element 30. 
The constraining element 30 has a diameter which represents the minimum 
possible diameter of the small loop 16. 
With the first constraining element 20 being in fixed relation with 
portions 22 and 24 of the optical fiber, it is apparent that expansion and 
contraction of the measured body B will cause a consequent expansion or 
contraction of the large loop 14, thereby causing consequent contraction 
or expansion of the small loop 16 defined by the optical fiber. The small 
loop 16 defines a region of bend which causes the light waves passing 
through the optical fiber to be perturbed, thus frustrating total internal 
reflection to at least some degree even at the largest dimension of the 
small loop 16. Any reduction in the radius of the region of bend that is 
caused by expansion of the body B, therefore, causes further perturbance 
of the light waves passing through the optical fiber thereby resulting in 
consequent frustration of total internal reflection in direct proportion 
to the mechanical expansion that has occurred. 
There is provided a light source 34 having a light emitting portion 36 
thereof positioned in abutting or closely spaced relation with the light 
emitting extremity 38 of the optical fiber. Light waves are thus 
introduced by the light source 34 into the optical fiber at an intensity 
that is determined by the intensity of the light source. The light waves 
propagate through the optical fiber 12 by the process referred to as total 
internal reflection and are emitted at an emitter extremity 40 of the 
optical fiber. A light detector is provided as shown at 42 having a light 
intensity detection portion 44 thereof positioned in abutting relation 
with the emitting extremity 40 of the optical fiber. The light detector 42 
may be of any suitable nature capable of detecting the intensity of the 
light emitted and converting the light intensity into an electrical signal 
that is directly representative of the light intensity. For example, the 
electrical signal may conveniently be in the form of an analog signal, the 
characteristics of which represent light intensity. 
Although the transducer system set forth in FIG. 1 may be utilized for 
measurement of expansion and contraction of various physical bodies, it 
has particular application in the medical field for the monitoring of 
patients. For example, the large loop 14 may be positioned in encompassing 
relation about the thorax of a patient under medical treatment and the 
dimensional changes of the thorax portion of the patient which occurs upon 
breathing may be efficiently monitored. The light detector apparatus 42 
may be arranged to provide a graphical chart representative not only of 
the breathing rate of the patient but of any volumetric changes in intake 
and expulsion of air that occur at various times during the period of 
monitoring. In another form suitable for medical monitoring, the 
transducer mechanism 10 may be conveniently utilized as a tumescence 
sensor that indicates certain medical characteristics of the patient upon 
detection of the physical changes that occur during tumescence. 
The first constraining element 22 may have the characteristics of 
adjustably clamping the portions 22 and 24 of the fiber in fixed relation. 
By loosening the clamp structure and shifting the fiber portions 22 or 24 
or both, the combined dimensional characteristics of the large and small 
loops may be modified. This feature may be effectively utilized for the 
purpose of calibrating and setting the response parameters of the large 
and small loops. It functions as a "0-set" control. Although the large and 
small loops 14 and 16 are defined by orienting the optical fiber 12 in the 
form of a figure "8" configuration, it is not intended to restrict the 
present invention to this particular optical fiber configuration. It is 
within the scope of this invention to orient the optical fiber into any 
suitable spatial configuration in order that the increase in diameter of 
the large loop will result in the consequent decrease of the diameter of 
the small loop. The small loop will always be the cause of the change in 
detected signal in the form of a change in light intensity because it will 
always be the loop of smallest diameter, defining the curvature of 
greatest perturbance. Under circumstances where other portions of the 
optical fiber are formed to define curved portions, as long as these 
curved portions are stabilized against movement, they will not effect the 
function or accuracy of the optical fiber transducer system. In other 
words, the transducer system may be zeroed, thus accommodating any 
perturbance that occurs by virtue of optical fiber bends that are not 
encompassed within the variable loops such as shown in FIG. 1. 
It may also be desirable to provide an optical fiber transducer system 
having the capability of responding to variations in fluid pressure. A 
pressure sensitive optical fiber transducer therefore may conveniently 
take the form illustrated generally at 50 in FIGS. 2 and 3. The optical 
fiber transducer at 50 may incorporate a substantially immovable base 
portion 52 such as might be mounted on any physical structure that is 
capable of providing stabilized support for the transducer. One or more 
upstanding posts 54 extend from the base structure 52 and are formed to 
receive a pivot element 56 in assembly therewith. A movable frame element 
58 is movable relative to the base structure 52 and incorporates one or 
more pivot arms 60 that are interconnected by the pivot pin 56 with the 
post structure 54. Thus, the frame structure 58 is pivotally 
interconnected with the base structure 52. Upper and lower optical fiber 
support elements 62 and 64 are supported respectively by the frame element 
58 and the base structure 52 and one or more optical fibers 66 are 
provided such that portions 68 and 70 thereof are secured in substantially 
immovable relation with respect to the support elements 62 and 64. The 
optical fiber 66 is also formed to define a region of bend 72 which is 
encompassed within broken lines as shown in FIG. 3 and which defines a 
variable radius of curvature which is identified by the radius arrow R. As 
portions 68 and 70 of the optical fibers 66 are subjected to relative 
movement, the radius R in the region of bend 72 either increases or 
decreases and thus causes a corresponding increase or decrease of 
perturbance which is detected by suitable electronic circuitry. 
A pressure containing bellows structure 74 is positioned in contact with 
internal surfaces 76 and 78 that are defind respectively by the frame 
element 58 and the base structure 52. If desired, end portions 80 and 82 
of the bellows 74 may be structurally interconnected in any suitable 
manner with the surfaces 76 and 78. The bellows 74 may be evacuated and 
arranged mechanically so as to control the linear physical motion of 
points A and B in space, in unison with the external pressure that is 
perceived by the bellows as pressure from a pressure source P is 
introduced to the bellows by means of a pressure conducting conduit 84. 
The physical distance between points A and B will control and effect the 
radius of bend of the optical fiber which has opposed portions 68 and 70 
thereof threaded through substantially parallel bores formed in the 
support elements 62 and 64. A light source 86 is provided having a light 
emitting portion 88 thereof positioned in abutting or closely spaced 
relation with the light receiving extremity 90 of the optical fiber 66. A 
light detector system 92 is provided having a light receiving portion 94 
thereof positioned in light receiving abutting relation with the light 
emitting extremity 96 of the optical fiber. Suitable electronic circuitry 
98 is interconnected with the light detector system and functions to 
process the light signals perceived by the light detector and render such 
signals to an electrical form which is then output to a suitable output 
conductor system 100. The output 100 of the electronic circuitry 98 may be 
interconnected with suitable recorder equipment in the event it is desired 
to display the output signals in a visually identifiable form. 
As the pressure of the pressure source P increases, the distance between 
points A and B decreases due to bellows contraction which causes the 
movable frame element 58 to move toward the base structure 52 about the 
pivot hinge 56. This mechanical movement causes the radius R of the region 
of bend to decrease which consequently causes the detected light emitted 
from the light emitting extremity 96 of the optical fiber and perceived by 
the light detector 92 to also decrease in intensity. This decrease in 
intensity, of course, is caused by an increase in perturbance as the 
curvature of the region of bend 72 is decreased. 
Since there is a linear relationship between pressure P and the intensity 
of light that is detected by the light detector 92, and a linear 
relationship between the detected light and the output electronic signal 
at the output 100, the result is the development of an electrical signal 
that is representative of the pressure of the pressure source. The 
transducer system identified in FIGS. 2 and 3 is, therefore, a pressure 
transducer incorporating an optical fiber transducer system. The 
transducer system does not invade the pressurized fluid system of the 
pressure souce P nor does it introduce any electrical signals into the 
system or develop electromagnetic activity that might interfere with 
optimum function of the pressure source system. The electrical aspects of 
the pressure transducer are remotely positioned with respect to the 
mechanical aspects of the transducer and are provided only to introduce 
light signals into the optical fiber system and to detect the intensity of 
light being emitted at the opposite end of the optical fiber system. 
Referring now to FIGS. 4 and 5, it is demonstrated that an optical fiber 
transducer system may be effectively employed for the purpose of detecting 
flow of a fluid medium flowing through a conduit. The optical fiber 
transducer system, which in this case may be referred to as an optical 
fiber flow detection transducer, is illustrated generally at 102 in FIGS. 
4 and 5. With egard to the function of the flow meter transducer, it is 
necessary to understand various characteristics of fluid flowing through a 
conduit system. Fluid flowing through a conduit, unless otherwise altered, 
tends to become laminar in nature. It is well known that under certain 
circumstances, the presence of an obstacle in a flow conduit will give 
rise to periodic vortices. For small Reynolds numbers, the downstream wake 
is laminar in nature, but at increasing Reynolds numbers, regular vortex 
paterns are formed. These paterns are known as Karman vortex streets. The 
frequency at which vortices are shed in a Karman vortex street is a 
function of flow rate. It is this phenomenon which is exploited to develop 
a flow meter of the vortex-shedding type. The vortex-shedding phenomenon 
is also exploited in the flow meter system set forth in FIGS. 4 and 5 
hereof. 
In a conduit 104, the directional fluid flow is indicated by means of a 
flow arrow at the left portion of FIG. 4. An obstacle 106 is positioned 
within the flow path and may be of any suitable configuration having the 
capability of developing desired vortices. One or more optical fibers 108, 
and collectively referred to in the singular, extend through the conduit 
104 into the conduit flow passage 110. The optical fiber 108 extends 
through protective sheath elements 112 through 118 with opposed pairs of 
the sheath elements being positioned on opposite sides of the obstruction 
element 106. The obstruction element 106 is arranged to secure portions of 
the optical fiber in such manner that a pair of loops 120 and 122 are 
formed. Each of the loops 120 and 122 are of substantially the same 
dimension and each of the loops is extended through respective apertures 
124 and 126 of a movable vortex responsive plate element 128. The optical 
fiber loops 120 and 122 are secured in substantially immovable relation 
with the plate element 128 such as by means of cement or by any other 
suitable means of retention. A reverse bent portion 130 of the optical 
fiber 108 is retained within a protective chamber 132 defined by a 
protective element 134 that is secured to the conduit 104. 
A light source 136 is provided having a light emitting surface portion 138 
thereof disposed in abutting or closely spaced relation with a light 
emitting extremity 140 of the optical fiber 108. A light detector 
mechanism 142 is arranged with a light receiving portion 144 thereof 
disposed in light receiving relation with a light radiating extremity 146 
of the optical fiber. 
The optical fiber loops 120 and 122 each define radii of curvature as shown 
at R in FIG. 4 which represent plural regions of bend in the optical 
fiber. As the vortex responsive plate element 128 moves upwardly or 
downwardly, its fixed relationship with the loops 120 and 122 causes the 
radii of curvature of the loops to change, thereby altering the total 
internal reflection capability of the optical fiber 108, Thus, the optical 
fiber emits light to the light detector 142 and this light is altered in 
intensity with alteration thereof being detected and converted into an 
appropriate electrical signal. As the vortices are shed within the flowing 
fluid from the obstruction 106, the vortices create stabilized fluidic 
oscillations within the flowing fluid medium with the signal frequency of 
the oscillations being proportional to the rate of flow within the conduit 
flow passage 110. The frequency of the vortices is converted into 
mechanical movement of the plate 128 thereby causing the plate 128 to 
oscillate at an induced frequency determined by the rate of flow within 
the flow passage 110. The intensity of light being emitted from extremity 
146 of the optical fiber therefore has a varying intensity with variations 
being representative of the fluidic oscillations induced to the movable 
plate 128. Thus, the light detector system provides a transducer output 
signal 148 that may be utilized in any convenient manner to display or 
record the particular flow rate being monitored at any given time. 
Although the fluid flow transducer 102 is illustrated with two optical 
fiber loops 120 and 122, it is not intended to limit the present invention 
to any particular number of optical fiber loops. It is intended only to 
illustrate that a flowing fluid medium yielding vortices that are 
responsive to the rate of flow may be employed to induce mechanical 
movement to a transducer structure that may be converted by an optical 
fiber system to appropriate signals for monitoring of the flow rate. This 
is accomplished efficiently without providing any electrical or 
electromagnetic interference with the flowing fluid system. In the event 
the flowing fluid medium should be of combustable character therefore, the 
rate of flow may be efficiently detected and monitored without any danger 
of explosion or fire. 
From the foregoing, it is apparent that I have developed an optical fiber 
transducer system that is effectively responsive to mechanical movement. 
Moreover, this mechanical movement can be induced directly or indirectly 
in a mechanical sense, may be induced by fluid pressure or vacuum 
conditions, may be induced electrically or by any other suitable means. 
There is provided, therefore, an optical fiber transducer system that is 
effectively adaptable for detection and the monitoring of a wide range of 
phenomenon having adaptation to a wide range of efficient uses. 
While there have been shown and described preferred embodiments in 
accordance with the invention, it will be appreciated that many changes 
and modifications may be made therein without, however, departing from the 
essential spirit thereof.