Sonic Waveguide Arrangement Using Different Waveguides and Technique for Coupling the Waveguides Together

The utilization of sonic energy as part of a transducer for sensing temperature is known in the art. For example, one system which has been developed uses sonic energy which is varied in having a frequency over a predetermined range as an input to cause the vibratory element in a temperature sensor to vibrate such that energy transfer (or rejection) occurs at resonant frequency. This, in turn, varies with temperature at the sensor. Thus, the sonic energy can be used to monitor the temperature at the sensor. This, in turn, requires transmission of the input energy from its source to the temperature sensor and transmission of the output energy from the sensor to a suitable monitor. Sonic waveguides are presently available for accomplishing this and have been found to be satisfactory where the sonic energy is carried primarily over a linear path or where the path, if curved, is relatively short in length. However, where the path is a relatively long non-linear path, any given waveguide which is otherwise suitable for carrying sonic energy over a relatively long linear path with low transmission losses is not particularly suitable for carrying sonic energy over curved paths. On the other hand, flexible waveguides which may be used to carry sonic energy over a short curved path with relatively low transmission losses are not particularly suitable for carrying sonic energy over a long path.

In view of the foregoing, one object of the present invention is to provide a sonic waveguide arrangement which utilizes at least two different types of sonic waveguides, one which is especially suitable for carrying sonic energy over a relatively long linear path with minimum transmission losses and one which is especially suitable for carrying sonic energy over relatively short curved paths with minimum transmission losses.

Another specific object of the present invention is to provide an uncomplicated, economical and yet reliable technique for coupling together the two types of sonic waveguides referred to immediately above for passing sonic energy therebetween with minimum transmission losses at the junctures therebetween.

Still another specific object of the present invention is to provide the above-mentioned coupling technique in a way which results in a reliable mechanical joint between the waveguides and yet in a way which does not add much weight at the joint for otherwise damping the sonic energy passing therebetween.

The sonic waveguide arrangement and coupling technique disclosed herein will be described in more detail in conjunction with the drawing, wherein:

FIG. 1 is a diagrammatic illustration of an overall temperature sensing system including sonic waveguide arrangements designed in accordance with the present invention; and

FIG. 2 is a sectional view of one section of one of the sonic waveguide arrangements of FIG. 1, particularly illustrating a coupling technique of the present invention.

Turning first to FIG. 1, the temperature sensing system shown there is generally indicated by the reference numeral 10. This system includes conventional or otherwise readily provided means 12 for producing a source of sonic energy which controllably sweeps a predetermined range of frequencies. This energy is transmitted from source 12 to a temperature sensor 14 along a non-linear path by means of a first sonic waveguide arrangement 16 designed in accordance with the present invention. The energy from source 12 is used to cause the vibratory element in sensor 14 to vibrate at various frequencies (according to the sweep) including its resonant frequency, as discussed previously, and thereby provide a sonic energy output which is also temperature sensitive depending on the temperature at the sensor. The sonic energy at the output of sensor 14 is transmitted from the sensor along its own non-linear path by a second waveguide arrangement 16a to a suitable device 18 for monitoring the output energy and therefore the temperature at sensor 14. Device 18 may be readily provided and could be appropriately calibrated to provide a direct temperature readout, either in printed form or visually.

With the exception of waveguide arrangements 16 and 16a, the components making up overall temperature sensing system 10 including sonic energy source 12, sensor 14 and monitor 18 may be readily available in the prior art or may be readily provided by those with ordinary skill in the art. In any event, these latter components do not form part of the present invention. On the other hand, each of the sonic waveguide arrangements 16 and 16a does form part of the present invention along with the particular waveguide coupling technique utilized therewith, as will be described hereinafter.

As seen in FIG. 1, each waveguide arrangement 16 includes linear waveguides 20 and curved waveguides 22. Each waveguide 20 extends from one end thereof to its other end along a linear section of the path defined by the overall waveguide arrangement and each waveguide 22 extends from one end thereof to its other end along a curved section of the overall path. Some or all of the linear path sections may be relatively long. However, all of the curved paths are relatively short, for example, on the order of at most about four or five inches and define a relatively large radius of curvature, for example on the order of two to three inches. Arrangement 16a also includes linear waveguides 20 and a curved waveguide 22.

Referring to FIG. 2, attention is directed to the adjacent ends of two adjacent linear waveguides 20 and an intermediate curved waveguide 22. In the embodiment illustrated, each of the waveguides 20 consists essentially of a single rod of sonic energy transmitting material which is also a good electrical insulator, e.g. a dialectric, preferably polyester resin with glass fibers embedded therein. The reasons for using a dialetric material is that is most cases a high voltage is sustained between the sensor and the sending and receiving devices. Waveguide 22 in the embodiment illustrated is comprised of a plurality of flexible fibers, preferably quartz optical fibers, which are generally indicated at 24 and which are maintained in a flexible bundle by means of a circumferential jacket 26 constructed of, for example, TEFLON or like material. As seen in FIG. 2, the size of fiber bundle 24 (in cross-section) is greater than the size of individual rod 20 (in cross-section). As also seen in this figure, the opposite ends of jacket 26 terminate inwardly of their respective ends of fiber bundle 24, thereby exposing opposite end sections of the fiber bundle, indicated generally at 28.

In order to couple one end of the waveguides 20 to an associated end of waveguide 22, a coupling arrangement 30 is provided. Referring to the top lefthand end of waveguide 22 (as viewed in FIG. 2), one coupling arrangement 30 shown there includes an opening 32 extending centrally into end section 28 of fiber bundle 24. This opening serves to receive an end section 34 of the horizontal waveguide 20 shown in FIG. 2. End section 14 is bonded in place by suitable means such as epoxy cement generally indicated at 36. In order to reinforce each exposed end segment 28 of fiber bundle 24, suitable means such as a brass ferrule 38 may be positioned concentrically around the end segment, as also seen in FIG. 2, and maintained in place by suitable bonding means such as epoxy cement 40. The other end of waveguide 22 shown in FIG. 2 is coupled with its associated waveguide in the same manner.

The waveguides 20 and 22 and the way they are coupled together utilizing coupling arrangements 30 provide an overall waveguide arrangement which can define a relatively long non-linear path with minimum transmission losses. In an actual working embodiment, each of the waveguides 20 consists of a polyester rod having embedded glass fibers as described above. These rods and approximately 0.030 inch in diameter. Each of the waveguides 22 in the same actual embodiment include a bundle of 212 quartz optical waveguide fibers contained within the jacket and having exposed end sections reinforced by the brass ferrule described above. The outer diameter of the fiber bundle is approximately 0.060 inch. Each joint 30 in this embodiment is provided by boring a 0.035 inch hole into its associated end section 28. This hole is provided to a depth of one-half the length of the ferrule. Epoxy resin is used to hold the end section of each rod in place. This type of joint is simple, it adds little weight at the joint and therefore minimizes damping of the sonic vibration thereat and it is tight providing good transmission characteristics. Moreover it is mechanically sound.