JPH0827199B2 - Sensor decals and how to make sensors - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to sensors used to sense conditions, and more particularly to thin film sensor structures that are easy to fabricate and use.

[0002]

BACKGROUND OF THE INVENTION It is often desirable to measure the condition of materials and the environment on the surfaces of structures and other articles during testing and use. This information is measured by sensors mounted on or near this surface. This data correlates with the performance of the structure and is used both to assess current performance as well as to predict future performance.

For example, the surface temperature of structures operating at high temperatures is one factor in determining the life of a structure. Surface temperature can be measured in a number of ways, one of which is a thermocouple. A thermocouple is a bimetal pair formed of two kinds of metals, and their contact produces a potential related to temperature. The measured potential is easily converted to the temperature at the contact point. Thermocouples are usually
It is created by welding two metal wires together and placing a welded bead on the surface whose temperature is to be measured. Thermocouples can also be made by deposition methods such as sputtering two metals directly onto the surface so that the required bimetal contacts can be made.

Thermocouples, by determining the electrical potential,
Determine the temperature variables of the environment. Other environmental variables such as the composition of the surface of the medium having the structure inside can also be measured by electrochemical techniques. Other types of sensors, such as strain gauges and crack opening gauges, can also be used to measure the physical properties of the structure itself.

Although sensors that measure various properties of the surface of an article are known, their use often has certain drawbacks. The presence of the sensor itself can affect the condition. For example, when attaching a wire-welded thermocouple to a surface, its presence
The environmental flow pattern at the surface changes, which can result in changes in temperature. It may also be inconvenient to mount the sensor on a surface that is in an inaccessible location. The sensor may not be able to be easily retained on the surface for extended periods of use.

These problems are especially acute when the structure to be measured is operated in extreme environments. In aircraft gas turbine engines, the hot section components are operated at temperatures of about 2000 ° F. and above in a high velocity, highly corrosive combustion gas stream. Measuring surface temperature and component deformation during use is important in developing better materials and structures, and also during use to predict the imminent onset of failure. It is not easy to provide a sensor on the surface of some of these parts, and even if it is provided, the life is often short.

There is a need for improved methods of measuring test specimens, structures and other articles using sensors that measure surface deformation, temperature and other properties. The present invention meets this need and provides further associated advantages.

[0008]

SUMMARY OF THE INVENTION The present invention is a sensor structure suitable for use in a wide variety of thin film sensors mounted on a surface to monitor various engineering conditions of the surface, methods of manufacture and methods of application. I will provide a. The method of the present invention allows the sensor to be very thin so that it does not project too far from the surface. The sensor element can be made in a single-layer structure or a multi-layer structure, and if necessary, surrounding layers such as an insulator layer and a protective layer can be provided. The sensor can be made inexpensively and is easy to apply on the surface.

According to the present invention, a sensor decal (transfer)
However, it has a thin film measuring unit and a release layer to which the thin film measuring unit is coupled. The release layer includes means for releasing the thin film measurement unit from the release layer when in contact with the solvent. More specifically, the sensor
The decal includes a release layer containing a material that can be softened by a solvent. A tie layer is in contact with the release layer and a thin film sensor element is integrally formed with the tie layer.

The inventive approach to the construction and use of engineering sensors utilizes the techniques of making and applying decals, which are widely known for use in decorative and identification applications. The sensor is made as a multi-layered decal structure and then applied in the usual manner of a decorative decal. This approach allows the sensor to be conveniently made in any shape and size, while facilitating its application to flat or curved surfaces.

That is, according to the present invention, a method of making a sensor comprises a thin film measuring unit comprising a thin film measuring unit bound to a release layer by a solvent softenable substance.
Use decals. The method involves contacting a sensor decal with a solvent to separate the thin film measurement unit from a release layer, applying the thin film measurement unit to a substrate, and drying the thin film measurement unit to remove the solvent. Typically,
After applying the measuring unit, the thin film measuring unit is fired to effectively and permanently fix the unit to the surface of the substrate to be measured.

The sensor can be made in any convenient manner, but is typically manufactured using conventional decal silk screening or sputtering. A number of thin layers are silk screened and / or sputtered on top of each other in a pattern that can create the desired thin sensor structure. For example, a glass, ceramic or polymer tie layer is deposited on the paper release layer. An insulator layer, optionally a ceramic layer, is optionally deposited on the tie layer. Release papers typically contain a water-soluble substance. In some cases, metal screening is deposited by silk screening, sputtering or other methods to form thermocouples, strain gauges or other sensors. Optionally, an insulating layer is provided by silk screening on the metal trace. It is preferred to deposit a support layer on top of this structure. Create a large number of sensors simultaneously as a large sheet,
The cost of making each sensor is low, as it can be separated from this sheet if desired.

The decal is dipped in a solvent, which may be warm water, to soften (and typically dissolve) any material that may be softened by the solvent and slide the decal onto the surface. By doing so, this preferred sensor measurement unit is applied to the surface on which the measurement is to be performed. The excess solvent, such as water, is removed with a cage and the sensor and structure are dried to remove residual solvent. The tie layer helps hold the decal in place. In most cases, decal sensors are relatively small in size and easy to apply. However, a large sensor can be manufactured and applied by this method.

In most applications, the thin film measurement unit is heated to an elevated temperature to consolidate and effectively permanently bond the thin film measurement unit to the substrate. During this heating step, the tie layer may decompose. This consolidation is usually done prior to actual testing or use, but may be part of the initial heating cycle of the structure. The measuring leads are attached to the sensor at a sufficient distance from the measuring point so that the presence of the leads does not interfere with the measurement.

This sensor decal system is an inexpensive and versatile system for making, applying and using thin film surface sensors for materials and structures. The sensor elements can be shaped into any desired pattern, either of one type of material or of several types of materials, so that many different types of sensor elements can be created.

[0016]

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a sensor decal for engineering applications, and methods of making and using the same. The sensor decal provides a thin film sensor that can be easily applied to a surface. After connecting the appropriate external electrical leads, the sensor senses the condition of the material or environment on the surface of the substrate to which the sensor is applied. The sensed signal is
External circuitry and / or calibration equipment translates to the material or environmental conditions displayed in the usual way.

The present invention will be mainly described in the case of a preferred thin film temperature sensor or thermocouple. Thin film strain gauges and crack opening gauges are also shown. The present invention is not limited to these applications and can also be used in connection with other types of thin film sensors. FIG. 1 shows a thin film sensor decal 20. The sensor decal 20 includes a thin film sensor element thermocouple 22 attached to and embedded within the base 24.

FIG. 2 shows the structure of the sensor decal 20 in more detail. Thermocouple 22 is formed by joining two traces 26 and 28 made of different metals at seam 30 (FIG. 1). The seam 30 is sometimes called a “bead” by analogy with a common thermocouple. Traces 26 and 28 are made of metal pairs known to those skilled in the art as being suitable for making thermocouples. For example, without intending to be limited to this, one trace may be pure tungsten and the other may be rhodium with a tungsten-3% content. One trace may be iron and the other may be constantan.
One trace may be copper and the other may be constantan. One trace is platinum and the other is platinum-10%
May be rhodium. One trace is platinum,
The other may be platinum-13% rhodium. One trace may be chromel and the other may be alumel. Many such metal pairs are used to construct common thermocouples, and their electromotive potentials are
It is calibrated to the temperature of the seam 30. The choice of metal pair used is related to the temperature range and measurement conditions experienced by and measured by the thermocouple. In general, the present invention may be practiced with any of the many known pairs of thermocouple metals known in the art, or with thermocouple metals that may be discovered hereafter. You may implement.

Traces 26 and 28 overlie insulator layer 32. The insulator layer 32 is preferably made of a good heat insulating material such as aluminum oxide. Insulator layer 32 overlies bonding layer 33, which is ultimately used to bond the thermocouple assembly to the substrate. Preferred tie layer 33
Is a glass, ceramic or polymer capable of softening and melting at temperatures slightly above the maximum planned operating temperature of the substrate / thermocouple combination. A wide variety of such materials are known in the art. For example, if the temperature of use is relatively low, ambient or up to several hundred degrees, the layer 33 is a thermoplastic polymer having a softening temperature slightly above the planned temperature using a thermocouple. It is usually selected to. At intermediate temperatures of use, that is, from a few hundred degrees to about 2000 degrees Fahrenheit, glass is generally used. At higher temperatures, ceramic can be used for layer 33. Such temperature limits are not absolute, and the appropriate material can be selected based on maximum operating temperature and conditions. Essentially any kind of material for such a tie layer can be deposited as layer 33 by the manufacturing methods described below.

In some cases, the insulator layer 32 and the bonding layer 3
The actions of 3 can be combined in a single layer. Such a single layer, referred to herein as the tie layer 33, bonds the thermocouple 22 to the surface and insulates the thermocouple from the surface. FIG. 2 shows the general case where both layers 32 and 33 are present, and FIG. 5 shows two layers 3
2 and 33 are combined (and the combination is referred to as layer 33).

Insulator layer 32 is deposited on release layer 34. The release layer 34 has an integral layer 36 of organic material that softens when exposed to a solvent. (A "layer" 36 of solvent softenable material may be on the surface of the release layer 34, as shown, or such that solvent softenable material completely impregnates the release layer 34. Release layer 3
4 may be spread throughout. ) Release layer 34
Is preferably paper. “Solvent” is broadly understood and as used herein includes water, organic solvents, or other substances that selectively soften layer 36 when exposed. The "solvent" may completely dissolve the organic substance, but it is not necessary. Layer 36 is preferably a water soluble organic material. This is because in most applications of interest to the present invention, water can be removed from the structure after the sensor decal has been applied to the substrate by heating without damaging the substrate. Such paper release layer materials are well known in the art of making decals and are widely available commercially.

Another insulating layer 38 overlies the thermocouple 22. The insulator layer 38 may have the same composition as the insulator layer 32 or the bonding layer 33. One example of a material that can be used for the insulator layer 38 is a ceramic oxide such as aluminum oxide, but other materials can also be used. Insulator layer 38 helps achieve thermal stability, but
It can be omitted depending on the application.

A support layer 40 overlies the insulator layer 38. The support layer 40 is preferably an organic material that provides strength and flexibility to the finished sensor decal 20. The insulator layer 38 is provided with vias 42 (FIG. 1) in the shape of openings. Vias 42 provide access to the ends of traces 26 and 28 so that external leads 44 can be attached. (The support layer 40 is removed before attaching the leads.) Leads 44 are traces 26 and 28 by conventional methods.
It is attached to the end of, but electrically and physically,
It is selected so as not to interfere with the operation of the thermocouple 22. Although shown as relatively short in the drawings, traces 26 and 28 may be very long so that the location connecting outer lead 44 is well away from seam 30.

A preferred method of making and applying the sensor decal 20 is shown in FIG. As shown at step 50, the tie layer 33 is deposited on the solvent-acting release paper 34 by any suitable method. Tie layer 3
If 3 is plastic, the tie layer 33 can be deposited by the conventional doctor blade method. If the bonding layer 33 is glass or ceramic,
It is preferably applied by silk screen printing (as shown in Figure 3). This method, which is well known for other applications, involves placing a fine-meshed fabric on a support and removing a slurry of fine particles of glass or ceramic in a carrier liquid such as water. Apply over this fabric. If the tie layer 33 is to be patterned into a particular shape, a mask material is used in the fabric to define the desired pattern. In either case, a slurry of fine particles of glass or ceramic is applied through the fabric and through the fabric to the release paper 34. This fabric and the mask, if used, are then removed, the slurry is dried and the release paper 34
Leave a layer of glass or ceramic particles on top.

If there is an insulator layer 32, then insulator layer 32 is deposited on bonding layer 33, as shown in step 52. Insulator layer 32 is deposited by any suitable method. As mentioned previously, silk screen printing with a mask is preferred. Traces 26 and 28 are either directly on insulator layer 32 if insulator layer 32 is present, or directly if insulator layer is not present, as shown in step 54 of FIG. And is deposited on the bonding layer 33. If each trace 26 and 28 has a different composition, as in a thermocouple, first deposit one trace 26 and then the other trace 28,
The traces 26 and 28 are physically overlapped at the seam 30. Traces 26 and 28 can be deposited by any method that can be used. The traces 26 and 28 can be applied by silk screen printing as described above, but in this case a separate mask is used to define the shape of each trace. The material for the traces is provided as a slurry of metal powder in a carrier liquid and applied on top of the insulator layer 32 or the bonding layer 33 via the respective mask and fabric. Remove the dough and mask, dry the slurry,
Leave traces 26 and 28.

Traces 26 and 28 can be applied in other ways. For example, silk screen printing has difficulty forming traces thinner than about 0.001 inch thick. If it is desired to form thinner traces, the traces may be deposited by sputtering or any other suitable method.

Insulator layer 38 is placed over traces 26 and 28, and exposed portions of insulator layer 32 and tie layer 33, if required for thermal stability, as shown in step 56 of FIG. Applied by any suitable method. Silk screen printing as described above is preferred. Support layer 40 is applied over insulator layer 38 by any suitable method, as indicated by step 58 in FIG. The support layer 40 is preferably an organic material and can be applied by conventional silk screening or doctor blade methods.

Tie layer 33, and (if provided)
The structure in which the insulator layer 32, the traces 26 and 28, and the insulator layer 38 (if provided) are deposited is referred to as a measurement unit 70. Upon completion of these manufacturing steps, the measuring unit 70 is held between the support layer 40 and the solvent-acting release paper 34. An important advantage of this manufacturing method is that very large numbers of sensor decals can be made with much less effort and expense than it takes to make one sensor decal. In most cases, to make a large number of sensor decals 20 in the shape of one large sheet, even if it takes extra effort to make an appropriately large area mask and to use extra material, It requires very little effort. Since such costs are relatively small, it is preferable to make a large sheet of sensor decals 20 and cut individual sensor decals from the sheet when the sensor decals are needed.

FIG. 3 also illustrates the method of applying and processing the completed sensor decal 20 at a time after the sensor decal has been created. This application will be described for the case of the substrate shown as turbine disc 72 in FIG. To apply the sensor decal 20, the sensor decal is placed 60 in a container of solvent for the release layer 34. The organic material in the release layer 34, shown as layer 36, is preferably water soluble and the solvent is warm water.
The water softens the organic matter in the release layer 34, and the step 60 of FIG.
The release layer 34 can be removed from the thin film measurement unit 70, as shown in FIG.

As shown in step 62 of FIG. 3, the thin film measurement unit 70 is slid off the release paper 34 and slipped onto the surface 74 of the turbine disk 72, in this case the substrate to be measured. Excess solvent (ie water) is mechanically removed using a cage or the like. At this point, the lead wire 44 is not attached. This method of applying a thin film measurement unit is much simpler than the traditional method,
It will be appreciated that it has much more general usage. The thin film measurement unit can be easily applied to a flat surface or a curved surface. The thickness of the thin film measurement unit is
Only a few thousandths of an inch and does not interfere with the gas flow pattern on the surface. If the thin film measuring unit is applied incorrectly or the thin film measuring unit does not work, another one can be easily applied. Due to the low cost of each sensor decal, redundant units can be used on a daily basis. In contrast, one conventional approach is to weld a thermocouple to the surface, which interferes with the gas flow pattern and adversely affects the heat treatment of the substrate below the weld. In other conventional methods, individual sensors are directly deposited on the surface of the substrate by sputtering or the like. This method involves subjecting the surface to other treatments and cannot be used on areas that are not accessible by direct sight, or on many curved surfaces. In another conventional method, a thin film thermocouple is deposited on a sheet such as Kapton, which is then bonded to the surface of the substrate using an adhesive. The results were painful and it was uncertain whether the thermocouple was bonded to the substrate. Kapton cannot be used at high temperatures and this method has limited generality. In all such conventional methods, whether the thermocouple is in good contact with the surface to be measured to obtain a good temperature value is problematic, and the skill of the person applying the thermocouple is problematic. Depended heavily on. In contrast to this, the method of the invention is very reproducible both in terms of the quality of the measuring unit and in terms of ease of application and reproducibility. The inventive method is technically and economically superior to these conventional methods.

Thus, the thin film measuring unit 70 is applied to the surface to be measured. As mentioned previously, the preferred method of forming at least some layers of the measurement unit 70 is with a slurry of particles.
It is necessary to consolidate these slurries into a single layer. It is also necessary to bond the measuring unit 70 to the surface 74. These purposes are to consolidate such layers to bring the insulator layer 32 to the surface 74, as shown in step 64 of FIG.
This is achieved by baking (baking) the substrate and the applied measuring unit 70 at a temperature high enough to bond to the substrate.

In the usual case, this firing operation applies the measuring unit 70 before the final heat treatment of the article to which the measuring unit is applied, and then with the article together with the measuring unit 7.
0 is also subjected to the heat treatment.
Therefore, the use of the measuring unit does not interfere with the normal manufacturing procedure of the article. With the procedure thus planned in mind, the material of tie layer 33 is selected such that tie layer 33 fuses to the surface of the article at a temperature below the maximum heat treatment temperature of the article. The insulator layers 32 and 38 are sintered,
They have been chosen in terms of their thermal and electrical stability so that optimum properties are achieved through fusion or consolidation by melting. The support layer 40 is no longer needed and typically burns out during the heat treatment and firing processes. When operating at lower temperatures, the support layer 40 may remain but does not adversely affect the operation of the device.

FIG. 5 shows an exemplary measuring unit 70 without the separate insulation layer 32 (support layer 40 already removed). Bonding layer 33 is bonded to surface 74 of substrate 72 of the article. Elements 26, 28, 33 and 38
Are connected to each other and are completely consolidated. After firing is complete, the lead wire 44 is applied, preferably by spot welding, as shown in step 66 of FIG. The lead wire 44 extends to an external measuring device such as a potentiometer in the case of the thermocouple 22.

The sensor decals of the present invention, and their methods of manufacture and application, are flexible. It is also easy to create sensor devices other than thermocouples (one or more)
It is common to only need different masks to apply the metal traces. 6-8 show some examples of other sensors. 6 shows a thin film strain gauge 76, FIG. 7 shows a thin film crack opening gauge 78, and FIG. 8 shows an optical strain measuring grid 80. Each of these sensors 76, 78 and 80 is typically made using only a single composition of metal for the traces rather than the two compositions required for thermocouples. The sensor 80 has no external leads,
It differs from the sensors 22, 76 and 78. This is a grating that is placed on top of the surface and is optically observed. Other more complex sensors can be made. For example, a multi-layer sensor can be easily deposited by the silk screen printing method.

The present invention has provided important advances in the field of thin film sensors. The decal sensor can be easily manufactured and applied, with the decal sensor providing reproducible results. Although the present invention has been described with respect to particular embodiments and examples, those skilled in the art will be able to make various modifications and changes within the scope of the invention as defined by the claims. Easy to understand.

[Brief description of drawings]

FIG. 1 is a perspective view of a thin film thermocouple sensor made in accordance with the present invention.

2 is a cross-sectional view of the sensor of FIG. 1 taken along line 2-2.

FIG. 3 is a flow chart of making and applying a thin film sensor.

FIG. 4 is a perspective view of a disc structure to which a decal sensor is applied.

5 is a cross-sectional view of the disc structure of FIG. 4 taken along line 5-5.

FIG. 6 is a perspective view of a thin film strain gauge sensor.

FIG. 7 is a perspective view of a thin film crack sensor.

FIG. 8 is a perspective view of a thin film grating.

[Explanation of symbols]

 20 Sensor Decal 22 Thermocouple 26, 28 Trace 32, 38 Insulator Layer 33 Bonding Layer 34 Release Layer 36 Softening Material Layer 40 Support Layer 42 Via 44 Lead Wire 70 Thin Film Measuring Unit 72 Turbine Disk 74 Surface 76, 78, 80 sensor

 ─────────────────────────────────────────────────── ———————————————————————————————— 72 Inventor Douglas Marshall Carlson Barrett Road, West Chester, Ohio, United States, 6601

Claims (18)

[Claims] 1. A thin film measuring unit, and a release layer to which the thin film measuring unit is coupled,
An engineering sensor decal comprising a release layer including means for releasing the thin film measurement unit from the release layer when contacted with a solvent. 2. The sensor decal according to claim 1, wherein the release layer is formed of paper, and the releasing means is an organic material that can be softened by a solvent in the release paper. 3. The sensor decal according to claim 2, wherein the organic material softens in water. 4. The sensor decal according to claim 1, wherein the thin film measurement unit includes a bonding layer in contact with the release layer. 5. The bonding layer comprises ceramic, glass, and
The sensor decal according to claim 4 formed of a material selected from the group consisting of a polymeric material and. 6. The sensor decal according to claim 1, wherein the thin film measurement unit includes a sensor element. 7. The sensor decal according to claim 6, wherein the thin film measurement unit further comprises at least one thin film insulator layer adjacent to the sensor element. 8. The sensor decal according to claim 6, wherein the sensor element is a thermocouple. 9. The sensor decal according to claim 8, wherein the sensor element is a strain gauge. 10. The sensor decal according to claim 8, wherein the sensor element is a crack opening gauge. 11. The sensor decal according to claim 1, wherein the measurement unit includes a support layer remote from the release layer. 12. A release layer comprising a substance that can be softened by a solvent, a bonding layer in contact with the release layer, and a thin film sensor element formed integrally with the bonding layer. Sensor decal. 13. The sensor decal according to claim 12, further comprising a first insulator layer between the tie layer and the sensor element. 14. The sensor according to claim 12, further comprising a second insulator layer overlying the sensor element.
Decal. 15. The sensor decal according to claim 12, further comprising a support layer overlying the sensor element. 16. The release layer is made of paper,
The sensor decal according to claim 12, wherein the solvent-softenable substance is softened in water. 17. A step of supplying a sensor decal including a thin film measurement unit bonded to a release layer by a substance softenable by a solvent, the thin film measurement by contacting the sensor decal with a solvent. A method of making a sensor comprising: separating a unit from the release layer; applying the thin film measurement unit to a substrate; and drying the thin film measurement unit to remove the solvent. 18. The method of claim 17, further comprising the step of heating the thin film measurement unit and the substrate to bake the measurement unit onto the substrate after the drying step.