NASA CASE NO.

PRINT FIG. 1

NOTICE

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LAR 14591-1

The invention disclosed in tt_is document resulted from research in aeronautical and

space activities performed under programs of the National Aeronautics and Space

Administration. The invention is owned by NASA and is, therefore, available for

licensing in accordance with the NASA Patent Licensing Regulation (14 Code of

Federal Regulations 1245.2).

To encourage commercial utilization of NASA-owned inventions, it is NASA policy to

grant licenses to commercial concerns. Although NASA encourages nonexclusive

licensing to promote competition and achieve the widest possible utilization, NASA

will provide the necessary incentive to the licensee to achieve early practical

application of the invention.

Address inquiries and all applications for license for this invention to NASA Patent

Counsel, Langley Research Center, Code 143, Hampton, Virginia 23681-0001.

Serial No." 07/957,014

08-31/92 LaRC

(NASA-Case-LAR-14591-1) MULTIPLE N9]-19493

LAYER DIELECTRICS, HOT FILM

SENSORS, AND METHODS OF PRODUCING

SAME Patent Application (NASA) Unclas

13 p

G3/35 0149911
NASA Case No. LAR 14591-1 

MULTIPLFJ LAYER DIELECTRICS, HOT FILM SENSORS, AND 

METHODS OF PRODUCING SAME 

AWARDS ABSTRACT 

The detection of the transition between laminar and turbulent flow is important in 

aerodynamics research and it is often desired to detect transition over a wide range of 

temperatures, e.g., 150°F to -300°F. There is currently no sensor which can obtain data over 

these temperature extremes. Also, the formation of a dielectric over an electrically conducting 

layer for use of a wide range of temperatures is desirable. 

The invention is a method of forming metal designs such as hot film sensors on a 

composite surface according to the present invention. The outer composite layer is an epoxy 

resin which is shaped to a desired surface on an underlying metal layer. The epoxy resin is 

bombarded with an ion beam for a brief period and then a fused silica layer is simultaneously 

vapor deposited thereon via an electron beam. The fused silica and epoxy resin form a dielectric 

over the metal layer. A sensor design mask is then positioned over the newly deposited fused 

silica. The exposed portion of the fused silica layer is then bombarded with an ion beam for a 

brief period of time and then a metal layer is simultaneously vapor deposited thereon via an 

electron beam. Thin film leads leading to a data acquisition system are then connected to the 

metal sensor and fused silica layer in a similar manner. All operations employing the ion beam 

and electron beam were conducted in a vacuum environment. 

Novel features of the present invention include its use of a fused silica layer to stabilize 

the resin for further deposition of metal layers. 

Inventors: Sang Q. Tran 

Address: 106 Susan Newton Drive 

Yorktown VA 23693 

ss: - 

Michael T. Oliver 

Route 3, Box 822 

Employer: NASA LaRC 

Initial Evaluator: Alan W. Frizzell 

Benjamin M. Copeland, Jr. 

13246 Lawns Court 

Smitbfield, VA 23430 

ss: - 

Serial No.: 07/937,014 

Filed: 08-3 1-92 
LAR 14591-1 -1 - PATENT APPLICATION

MULTIPLE LAYER DIELECTRICS, HOT FILM SENSORS,

AND METHOD OF PRODUCING SAME

5

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Ori.qln of the Invention

The invention described herein was made by employees of the United

States Government and may be manufactured and used by or for the

Government for governmental purposes without the payment of any royalties

thereon or therefor.

Back.qround of the Invention

o Technical Field of the Invention

15 The present invention relates generally to bonding metal to composites

and more particularly to a method of applying a metal design such as a hot film

sensor onto a composite surface exposed to cryogenic as well as elevated

temperatures.

20 2. Discussion of the Related Art

The detection of the transition between laminar and turbulent flow is very

important in aerodynamic research. A conventional sensor exposed to an

airflow comprises leads connected to a constant temperature anemometer

25 circuit, whereby the changing voltage requirements of the circuit are indicative

of the flow transition. Current test proposals require applying the sensors to

models made of a composite material without damage to or significant alteration

of the model surface. In addition, the sensors must be able to detect transition

while experiencing cryogenic temperatures of approximately -300°F. Operating

30 conditions of up to approximately 150°F are also experienced. A single sensor
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LAR 14591-1 -2- PATENT APPLICATION

capable of proper attachment and sensing between those two extremes is

especially desirable. Also the resulting sensor should not exceed a critical

roughness height specification to avoid flow disturbances.

There is currently no known technique for attaching the sensors to

composite models that meets these requirement. Proposed alternatives to hot

film sensors include various flow visualization techniques, infrared

thermography, fluxuation surface pressures, and the use of pressure

transducers to determine fluctuating surface pressures. These techniques are

intrusive, incompatible with a cryogenic environment, or hampered by poor

resolution.

Objects of the Invention

It is accordingly an object of the present invention to provide a method

15 of applying hot film sensors onto a composite surface.

It is another object of the present invention to provide a method of

applying hot film sensors onto a composite surface without any damage to or

significant alteration of the surface of the model surface.

It is a further object of the present invention to provide a method of

20 applying a hot film sensor to a composite surface which can endure cryogenic

conditions.

it is another object of the present invention to provide a method of

applying a hot film sensor to a composite surface which can endure elevated

temperatures of up to 150°C.

25 It is a further object of the present invention to provide a method of

applying a hot film sensor to a composite which can endure both cryogenic and

elevated temperatures.

It is another object of the present invention to accomplish the foregoing

objects without interfering with the air flow with excessively thick sensors.
5

LAR 14591-1 -3- PATENT APPLICATION

It is a further object of the present invention to accomplish the foregoing

objects in a simple, straightforward manner.

Additional objects and advantages of the present invention are apparent

from the specification and drawings which follow.

Summary of the Invention

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20

The foregoing and additional objects are achieved by a method of

forming metal designs such as sensors on a composite surface according to the

present invention. The outer composite layer is an epoxy resin which is shaped

to a desired surface. The epoxy resin is bombarded with an ion beam for a

brief period and then a fused silica layer is simultaneously vapor deposited

thereon via an electron beam. A sensor design mask is then positioned over

the newly deposited fused silica. The exposed portion of the fused silica layer

is then bombarded with an ion beam for a brief period of time and then a metal

layer is vapor simultaneously deposited thereon via an electron beam. Thin film

leads leading to a data acquisition system are then connected to the metal

sensor and fused silica layer in a similar manner. All operations employing the

ion beam and electron beam were conducted in a vacuum environment.

Brief Description of the Drawin.qs

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30

FIG. 1 is an exposed side view of a sensor formed on an epoxy resin

surface according to the present invention;

FIGS. 2(a)-(i) are respective graphs for nine sensors formed in an epoxy

resin surface according to the present invention, plotting resistance versus

temperatures from room temperature to 150°F; and

FIGS. 3(a)-(i) are graphs for the same nine sensors depicted respectively

in FIGS. 2(a)-(i), plotting resistance versus temperatures from room

temperature to -300°F.
LAR 14591-1 -4- PATENT APPLICATION

Detailed Description of the Invention

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3O

The present invention is directed toward a method of non-invasively

applying metal designs such as hot film sensors onto an outer surface for

operation in cryogenic and elevated temperatures. Referring now to FIG. 1, a

composite model 10 is shown comprising an inner stainless steel hull 12, an

intermediate fiberglass layer 14, and an outer epoxy resin layer 16. The resin

layer may be any suitable resin such as a bisphenoI-A based epoxy resin

diluted with butyl glycidyl ether commercially available from Shell Chemical

Company under the trademark EPON Resin 815@. The epoxy resin is

malleable and permits formation of the desired airfoil surface geometry.

The epoxy resin composite model is first placed in a vacuum chamber.

The chamber is evacuated to a pressure of below 2x10-5 Torr. Next, the

model is bombarded with an ion beam source for approximately three minutes.

The ion beam source employed is a high current/low energy type. It is set to

generate an ion beam current of approximately 625mA with an ion energy in

the range of 90eV. While the model is bombarded by the ion beam, the

electron beam is turned on so that fused silica (SiO2) layer 18 is simultaneously

evaporated onto the composite model surface via vapor deposition. Fused

silica layer 18 serves as a surface stabilization for the subsequent deposition

steps. The typical thickness of the fused silica layer is in the range of 5,000A

to 10,000A. The ion source is used to clean the composite model surface as

well as reduce the stresses inherent in newly deposited materials, especially

metallic materials.

After the fused silica is applied, the model is then removed from the

vacuum environment in preparation for the next step. A metal mask is masked

down over the newly deposited fused silica layer 18. The mask is used to form

the desire sensor patterns and dimensions, as is known in the art. The model

is then placed back in the vacuum chamber and the ion beam source is once
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LAR 14591-1 -5- PATENT APPLICATION

again activated with the same operating parameters as above so that the

exposed fused silica surface under the mask can be cleaned similarly to the

previous step. While the ion beam source is on, the electron beam is activated

so that the chosen metal is vapor deposited through the mask to form the metal

sensor. The resulting metal layer 20 can be any conventionally used metal

such as nickel, platinum or palladium. The thickness of the chosen metal is

varied according to the particular intended application. In one particular

embodiment used in the tests described below, the metal layer was nickel and

the thickness was approximately 2,500A.

After the metal sensor was formed, the model is removed from the

vacuum chamber so that the metal mask can be removed and a predetermined

lead pattern for the particular sensor is positioned on the fused silica 18 to

expose a portion thereon. The model is placed back in the chamber for the

upcoming thin film lead deposition step. The ion beam source, using the same

operating parameters as described in previous steps, is turned on again in

order to clean the exposed silica surface. The electron beam is then

concurrently turned on to vapor deposited a selected metal to form the thin film

leads 22. This metal can be any suitable electric conductor such as copper,

gold and aluminum. In the particular embodiment discussed below, the leads

22 were copper and had a thickness of approximately 5000 A.

The resulting sensor and other like sensors are connected to a known

anemometer system to detect flow transition under various conditions. The

epoxy resin composite and fused silica serve to electrically insulate the metal

model from the sensors, i.e., to form a dielectric on the metal model.

The sensor according to the present invention is thus firmly attached to

a model having an outer coating of epoxy resin. No significant surface

roughness results, thereby avoiding degradation of aerodynamic effects. Also,

no messy and thickness increasing glue is required. In addition, the dielectric

sensor can be applied to two- or three-dimensional surfaces. Most importantly,
LAR 14591-1 -6- PATENT APPLICATION

the sensor is firmly applied to the epoxy resin surface and remains so applied

over a wide range of temperatures, e.g., -300°F to 150°F, as evidenced below.

FIGS. 2(a)-(i) respectively show the resistances of nine sensors

fabricated according to the present invention plotted at room temperature

5 (78.5°F), 100°F, 125°F, and 150°F. Each sensor was operated at a 1.4

overheat ratio at the peak temperature. As shown, each sensor exhibited

proportional, approximately linear relationship between the measured resistance

and the temperature. The resistances of the sensors accordingly are suitable

indicators of temperature in the tested range of room temperature (78.5°F) up

10 to 150°F.

FIGS. 3(a)-(i) respectively show the resistance of the same nine sensors

as FIGS. 2(a)-(i) plotted at room temperature (84.5°F), 0°F, -50°F, -100°F,

150°F, -200°F, -250°F, and -300°F. Once again, all of the sensors were

operated at a 1.4 overheat ratio at the peak temperature. As shown, each

15 sensor continued to exhibit a proportional, approximately linear relationship

between the measured resistance and the temperature. The resistance of the

sensors are suitable indicators of temperature in the tested range of room

temperature (84.5°F) down to -300°F. The total effective range of the sensors

fabricated according to the present invention is thus -300°F to 150°F.

20 Sensors fabricated according to the present invention were also used to

detect boundary layer transition in the 0.3-M Cryogenic Tunnel located at NASA

Langley Research Center, Hampton, Virginia. The sensors were operated

continuously for a few days at temperatures down to 100K and pressures up

to 45 psia, marking the first successful transition detection in a cryogenic tunnel

25 operated near its operational temperature.

The present invention is described with reference to a specific example

of forming a sensor. It is understood that it is not limited to the example, but

applies to applications wherein a metal design is formed on an epoxy resin

substrate which overlies an electrically conducting layer, especially wherein the

30 resulting structure is exposed to wide temperature variations.
LAR 14591-1 -7- PATENT APPLICATION

Many improvements, modifications and substitutions will be apparent to

the skilled artisan without departing from the spirit and scope of the present

invention as described herein and defined in the following claims.
LAR 14591-1 PATENT APPLICATION

MULTIPLE LAYER DIELECTRICS, HOT FILM SENSORS, AND

METHODS OF PRODUCING SAME

5

10

15

Abstract of the Disclosure

The invention is a method of forming metal designs such as hot film

sensors on a composite surface according to the present invention. The outer

composite layer is an epoxy resin which is shaped to a desired surface on an

underlying metal layer. The epoxy resin is bombarded with an ion beam for a

brief period and then a fused silica layer is simultaneously vapor deposited

thereon via an electron beam. The fused silica and epoxy resin form a

dielectric over the metal layer. A sensor design mask is then positioned over

the newly deposited fused silica. The exposed portion of the fused silica layer

is then bombarded with an ion beam for a brief period of time and then a metal

layer is simultaneously vapor deposited thereon via an electron beam. Thin film

leads leading to a data acquisition system are then connected to the metal

sensor and fused silica layer in a similar manner. All operations employing the

ion beam and electron beam were conducted in a vacuum environment.
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