I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

1 

I 

I 

I 

OHIO 

:m 

Measurement of the Properties of Lossy Materials 

Inside a Finite Conducting Cylinder 

A. Dominek, A. Park and R. Caldecott 

The Ohio State University 

ElectroScience laboratory 

Department of Electrical Engineering 

Columbus, Ohio 43212 

(uASA-CX-1626t4) HbASUBEMEZI CF THE Ba 13-2 c 402 

ELOPEEIXES OF LCdSP HIIEYIALS IbSlCE A 

IILrXtIK CCIDUClIEG CYLlEDEB SrPiannual Report (Chio State Llr.ir.) 34 E CSCL 2oc Unclas 

63/70 0134774 

Semi-Annual Report No. 719300-1 

Grant No. NAG3-784 

March 1988 

National Aeronautics and Space Administration 

Lewis Research Center 

21000 Brookpark Rd. 

Cleveland, OH 44135 
NOTICES 

When Government drawings, specifications, or other data are 

used for any purpose other than in connection with a definitely 

related Government procurement operation, the United States 

Government thereby incurs no responsi bil ity nor any ob1 igation 

whatsoever, and the fact that the Government may have formulated, 

furnished, or in any way supplied the said drawings, specifications, 

or other data, is not to be regarded by implication or otherwise as 

in any manner licensing the holder or any other person or corporation, 

or conveying any rights or permission to manufacture, use, or sell 

any patented invention that may in any way be related thereto. 

I 

I 

I 

1 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 
I 

I 

1 

1 

I 

1 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

L Availability 8imtemont 19. Socurity C1a.r (This Rome) 

Uncl ass i f i ed 

8icl ass1 f led 

20. urity Clop qhis Pago) 

io272 -101 

REPOfilT DOCUMENTATION 1. REPORT NO. 2. 

PAGE 

21. NO Of Pages 

28 

22. Price 

8. Title ond Subtitle 

MEASUREMENT OF THE PROPERTIES OF LOSSY MATERIALS 

INSIDE A FINITE CONDUCTING CYLINDER 

A. Dominek, A. Park and R. Caldecott 

The Ohio State University 

ElectroScience Laboratory 

1320 Kinnear Road 

Columbus, Ohio 43212 

V. Authoifs) 

P. Perfonming Oaaniration Name end Address 

12. Sponyoring Ormaniratlon Name and Address 

Na t ii o na 1 Aeronaut i cs and Space Admi n i strati on 

Lewis Research Center 

Cleveland, Ohio 44135 

' 21c100 Brookpark Road 

15. Suppltrmontay Notes 

3. RecipBent's Accession No 

5. Rcporl Date 

March 1988 

6. 

a. Performing Orianization Rept. No. 

719300- 1 

10. ProjectlTasklWork Unit No. 

11. ContracW3 or Crant(G) No 

(c) NAG3-784 

13. Type of Reporl 6 Period Covered 

Semi -Annual 

14. 

i6. Abstract (Limit: 200 words) 

Broadband, swept frequency measurement techniques were investigated for 

the evaluation of the electrical performance of thin, high temperature 

material coatings. Reflection and transmission measurements using a HP8510B 

Network Analyzer were developed for an existing high temperature test rig at 

NASA Lewis Research Center. Reflection measurements will be the initial 

approach used due to fixture simplicity even though surface wave transmission 

measurements would be more sensitive. The minimal goal is to monitor the 

electrical change of the material's performance as a function of temperature. 

If possible, the materials constitutive parameter, E and u will be found. 

17. Documant Anolyslr 0. b..crl@on 

b. Idontlfi.n/O#n.Endod Tormr 
I 

I 

I 

1 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

Contents 

List of Figures 

1 Introduction 

2 Material Evaluation 

iv 

1 

3 

3 Measurement Hardware 6 

4 Measurement Techniques 8 

I Reflection Measurement .................... 11 

I1 Transmission Measurement .................. 13 

6 Conclusions 27 

PRECEDING PAGE BLANK NOT FILMED 

... 

111 
List of Figures 

3.1 Proposed hardware configuration for the HP-8510B Network 

Analyzer. ............................ 7 

4.1 Illustration of test fixture for reflection and transmission 

measurements. ......................... 9 

4.2 Illustration of a high temperature probe connection to a test 

plate. .............................. 10 

4.3 Test fixture at the ElectroScience Laboratory for measurement concept evaluation at room temperature. ....... 11 

4.4 The measured reflected signal using a probe feed with no 

material treatment on the metal test sample support plate. 15 

4.5 The measured reflected signal using a probe feed with material treatment on the metal test sample support plate. ... 16 

4.6 The measured, time gated reflected signal at the probe aperture with no material treatment on the metal test sample 

support plate. .......................... 17 

4.7 The measured, time gated reflected signal at the probe aperture with material treatment on the metal test sample support plate.. ........................... 18 

terial treatment on the metal test sample support plate. .. 4.8 The measured reflected signal using a horn feed with no ma19 

4.9 The measured reflected signal using a horn feed with material 

treatment on the metal test sample support plate. ..... 20 

4.10 The measured, time gated reflected signal from the metal 

test sample support with no material treatment using the 

AEL horn. ........................... 21 

iv 

I 

I 

I 

I 

I 

1 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 
I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

1 

1 

I 

I 

4.11 The measured, time gated reflected signal from the metal 

test sample support with material treatment using the AEL 

horn.. .............................. 22 

4.12 The measured surface wave signal on the metal test sample 

support with no material treatment and a 3” probe spacing. 23 

4.13 The measured surface wave signal on the metal test sample 

support with no material treatment and a 6” probe spacing. 24 

4.14 The measured, time gated surface wave signal on the metal 

test sample support with no material treatment. Probe spacing: 3” solid, 6” dashed. .................... 25 

4.15 The measured, time gated surface wave signal on the metal 

test sample support with material treatment. Probe spacing: 

3” solid, 6” dashed. ...................... 26 

V 
I 

I 

I 

I 

I 

I 

I 

I 

I 

U 

I 

I 

I 

I 

I 

I 

8 

I 

I 

Chapter 1 

Introduction 

Modern material treatments on metallic structures have to perform and 

survive in a variety of environments. One practical environment has hot 

flowing gases heating the material treatment. NASA Lewis Research Center presently operates a test rig to evaluate the mechanical survivability 

of a material coated metal plate in a confined region. The confined region 

consists of a circular pipe with hot jet gases being directed at a coated plate 

in its interior. The material so far has been evaluated mechanically through 

repeated heat cycles. The highest temperature of interest is approximately 

1800" F. It would be reasonable that the electrical properties of the material change during the heat cycles, especially when such high temperatures 

are of interest. An effort is underway to develop measurement techniques 

centered around the present test rig at NASA Lewis Research Center to 

monitor the electrical characteristics of material coatings on metal plates. 

The ElectroScience Laboratory (ESL) has developed a variety of techniques applicable for such measurements using time domain technology. 

The use of time domain techniques is essential for the above task since 

electromagnetic energy in a closed region will be multiply reflected and 

most certainly corrupt any measurement unless range gating techniques 

are applied. The basis is to use these techniques to isolate the mechanisms 

associated with the material of interest from all other mechanisms and 

1 
thus be able to better interpret the measured data in terms of the material 

properties. 

The goal has been to develop these measurements at the ESL in the 

absence of the hot flowing gases and then to assist in the development of 

a hardened system as needed. It is envisioned that the hardened system 

will measure the desired electrical characteristics in the absence of the hot 

air flow and repeat the appropriate measurements in the presence of the 

hot air flow at the various temperatures of interest. It would be desirable 

to measure the absolute value of these electrical properties but this is not 

practical due to the lack of the required absolute calibration references. The 

minimum achievable goal has been to measure any changes in the electrical 

(consequently mechanical) properties of the lossy materials. 

However, the major effort in this program has been concerned with the 

design, development, construction and testing of the required apparatus. 

This report discusses the practical electromagnetic measurement techniques 

that have been evaluated. 

2 

I 

1 

I 

1 

I 

I 

I 

I 

1 

I 

I 

I 

I 

I 

I 

I 

1 

I 

I 
Chapter 2 

Material Evaluation 

The electrical performance of a material treatment on a conducting surface 

can be evaluated by either monitoring the reflected signal from the surface 

or the surface wave through the material. Ideally, the monitoring is best accomplished if the material parameters, er and p,, can be determined. This 

can be accomplished if the performed measurements are adequately calibrated and there is an analytical model for the measured quantity including 

the dependency of the material parameters. Two alternative approaches in 

monitoring the material performance are to characterize the relative energy 

of the reflected field from a material treated plate or the relative attenuation 

of a surface wave. 

There are two traditional measurements possible being, reflection and 

. transmission from a material interface or through the material, respectively. 

In any measurement, it is always desirable to have the sensing fields interact 

sufficiently with the material. The material test sample is a thin coating 

over a metal surface which can limit the sensitivity for a reflection measurement. A transmission measurement can permit greater material interaction 

but its sensitivity can be limited in adequately exciting surface waves. 

The determination of material complex parameters, e, and pp, requires 

four independent equations involving these parameters. Traditionally, this 

has entailed reflection and transmission measurements at each frequency 

3 
of interest with each measurement supplying two independent values (real 

and imaginary). When the parameters are not highly frequency dependent, 

a reflection or transmission measurement will suffice. The most obvious 

practice is to perform two measurements at slightly different frequencies. 

Another approach is to integrate the measured values, M(w), around the 

frequency of interest w, such as 

to provide two other indepedent values from the real and imaginary parts 

of M. The shifted cosine function performs a simple weighted average 

process resulting in a noise reduction of the measured signal. Such an 

integration can provide another independent relationship when the material 

parameters are functionally different such as is the case for a coated planar 

metal surface. The reflected wave for a plane wave normally incident upon 

the coating is given by 

jqr sin( kt) - cos( kt) 

jqr sin(&) + cos(kt) R(f, t, er, pr ) = 

where f is the frequency, t is the coating thickness, the relative material 

wave impedance qr = fi and the material wave number IC = 27r f @. 

This approach would be convenient since then only one measurement 

type would be required. A major drawback in actually determining the 

electrical parameters with the test rig is providing an adequate reference to 

calibrate the measurements discussed in the next chapter. The HP-8510B 

can be calibrated before a heat cycle test of a material sample but the 

system as a whole can drift during the test due to thermal expansion of the 

test rig. 

Another aspect in determining the material parameters is having a rigorous reflection or transmission model. Only the reflection technique has a 

I 

I 

I 

1 

I 

I 

1 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

1 

4 
simple analytical model involving the complex material parameters, E? and 

Pr - 

An alternate approach to monitor the electrical performance of the material treatment is calculating the energy of the reflected or transmitted 

signal. This calculation is simply equal to the sum of the squared signal 

samples in the time domain. 

The third approach to monitor the electrical performance of the material 

treatment requires one or two transmission measurements using probes. 

The surface wave has a functional form given by 

where A is some constant, 7 = a + jp is the sum of the attenuation constant and the phase constant, and d is the distance between the probes. A 

relative measure of the loss in a material during a test could be acquired 

since 7 is dependent upon e and p. However, this measure would not be 

applicable between different material samples due to the dependence that A 

would have. This limitation can be eliminated by taking two measurements 

with different probe distances. The propagation constant can be obtained 

by taking the ratio of two transmission measurements where the probe separation distances are different for each measurement assuming everything 

else is constant. The propagation constant is given by 

where d1,2 are the probe separation distances, and M1,z are the measured 

transmission values. This 7 is still relative and a measurement of a material 

with a known 7 would have to be performed to scale the measured 7. The 

material’s parameters could also be found with a calibrated 7 but there 

would be better success with a reflection measurement. 

5 
Chapter 3 

Measurement Hardware 

All the measurements and initial data processing will be performed using 

the HP-8510B Network Analyzer [l]. This instrument has the capability to 

perform the necessary swept frequency reflection and transmission between 

2 and 18 GHz. Although the instrument is already heavily automated, an 

external HP-300 series PC will be used as a controller for the HP-8510B 

to initiate a desired measurement sequence, perform any signal processing 

and for data storage. The HP-8510B is a unique instrument, for it can 

perform a variety of useful processing techniques on the acquired data. An 

essential feat ure is the frequency to time domain transformation capability. 

This permits the exclusion of undesired reflected and transmitted signals in 

the measurement to recover the frequency response of the desired quantity. 

This time domain concept will be demonstrated in the following section. 

The hardware configuration for the HP-8510B will not be in the standard mode. The configuration is illustrated in Figure 3.1 as proposed by 

Jim Cusick of NASA Lewis. This hardware layout was primarily dictated 

by the operating conditions in the test rig room and to have the basic 

analyzer portion of the HP-8510B available for other applications during 

inactive periods of the test. 

6 

I 

I 

I 

1 

I 

I 

1 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 
HP 9836 

computer 

Special Signal 

Cable 

HP 8510B 

Network 

500 BNC Cable 

488 Bus 

750 BNC Cable 

HPIB Serial 

HP 37204A 

Extender 

2-18 GHZ Horn II TEST CELL 

Frequency 

Converter 

I 1 'I 

HP 37204A 

Extender 

Bus 

a Figure 3.1: Proposed hardware configuration for the HP-8510B Network 

Analyzer. 

7 
Chapter 4 

Measurement Techniques 

There are a variety of measurements possible to sense changes in the electrical characteristics of a material using reflection and transmission concepts. 

The main difficulty of performing such measurements in the desired high 

temperature environment is to supply a RF signal for the illumination or 

excitation of a wave in the test rig. Figure 4.1 illustrates a modified section 

of the existing test rig to incorporate the means to electrically monitor a 

test sample of material. A test section based upon the drawing in Figure 

4.1 has been designed at W.L. Tanksley and ASSOC., Inc [2]. As shown in 

Figure 4.1, an electromagnetic horn is used as one means to illuminate the 

test sample. This is a wide band horn (2-18 GHe) manufactured by AEL 

[3]. The horn proved to be functional at elevated temperatures before it 

failed at approximately 900" F. during a reflection measurement. The ac- 

' tual test rig section incorporates air and water cooling to maintain the base 

of the horn below 200" F.. 

Other methods of illuminating a test sample by means of a slotted coaxial line or waveguide proved not to couple or radiate well, to be too narrow 

banded and to be thermally too unstable. However, a high temperature 

cable was found to deliver a high temperature region with RF in the 2-18 

GHz band. This cable, manufactured by ERD[4], would survive these elevated temperatures and provide reasonable electrical performance. The 

8 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

1 

1 

I 

I 

I 

I 
8 

8 

I 

1 

I 

I 

I 

I 

I 

I 

I 

I 

I 

1 

1 

I 

I 

1 

I 

cable construction uses a silicon dioxide powder to support the inner conductor which forces the cable to be hermetically sealed since the powder 

is hygroscopic. This cable has an application in the transmission measurements to be discussed later. Figure 4.2 illustrates a proposed probe 

assembly for such transmission measurements. The cable would actually 

form part of the probe which would penetrate the material sample. 

COWRESSION PITTING FOR RF cmrn (.141' OD) 

OFFSET BLOCK .25* CLcmANcE Horns 

(NOT IN CONTRACT) 

0 Figure 4.1: Illustration of test fixture for reflection and transmission measurements. 

Figure 4.3 shows the test fixture with the HP-8510B Network Analyzer 

which has been used to evaluate the potential measurement techniques. 

The test fixture has comparable physical dimensions to the actual section 

being built for the test rig. It has an appendage similar to the one shown 

in Figure 4.1 for the AEL horn. The test fixture also has a sample holder 

similar in size and location as will the actual test rig section. All known 

relevant aspects of the geometry and conditions were simulated to develop 

9 
Sup lied Plate 

an8Stand Off 

Fit 

Figure 4.2: Illustration of a high temperature probe connection to a test 

plate. 

the measurement technique and software to perform the measurements. 

The capability of performing automated measurements between 2 and 18 

GHz to monitor the electrical performance of material treatments was the 

main design criterion for development of these measurement approaches. 

The measurements using the HP-8510B Network Analyzer has to be 

calibrated for material parameter determination. The calibration process 

requires two steps for absolute measurement values. The first calibration 

would involve the HP-8510B Network Analyzer using a short or a through 

reference for a reflection or transmission measurement, respectively. This 

calibration is sufficient if relative measurements are going to be obtained. 

The second calibration would involve the measurement of a known sample 

to scale the material measurements. The reflection measurement has the 

10 

1 

I 

I 

1 

I 

I 

I 

I 

I 

I 

1 

I 

1 

1 

I 

I 

I 

I 

I 
I 

1 

I 

I 

1 

simplest reference of using the time gated return from an untreated metal 

test sample. 

The actual material coating to be evaluated will be approximately 40 

mils thick on a one foot square test plate. The test plate was simulated 

asi shown in Figure 4.3. The material treatment used in the measurements 

was Standard Emerson and Cuming’s rubber loaded radar absorber SF-9 

material (50 mils thick). 

1 

1 

I 

I 

li 

I 

Figure 4.3: Test fixture at the ElectroScience Laboratory for measurement 

concept evaluation at room temperature. 

I Reflection Measurement 

A reflection measurement of a coated metal plate can be performed by two 

approaches for this geometry. One approach is to use the broadband AEL 

horn in the appendage in the new test rig section. The other approach is 

:ORIGINAL PAGE IS 

POOR QUALITY 

11 
to use a probe such as the one shown in Figure 4.2. Using the horn as 

the radiating element has two significant advantages over the probe. One 

advantage is a much better impedance match is possible over the 2-18 GHa 

band which relates to having a better signal to noise ratio. The other 

advantage is a potentially better calibration scheme exists if a horn is used. 

An untreated plate can be used to calibrate the reflected signal when a horn 

is used. 

Figures 4.4 and 4.5 show the frequency and time domain responses for 

the measured reflected signal using a probe assembly without and with 

the Emerson and Cuming’s material, respectively. The time domain gated 

response due to just the reflected signal at the probe aperture is shown 

in Figures 4.6 and 4.7. The probe was constructed from semi-rigid cable 

and inserted into a .141” diameter drilled hole which tightly held the cable. 

The inner conductor waa permitted to extend .0625” above the test plate 

sample with the outer conductor flush to the illuminated side of the metal 

support plate. The reflected signal is sensitive to the aperture environment 

as seen in the figures. The measurement sensitivity is poor for the lower 

portion of the spectrum but improves to a useful range as the aperture 

becomes electrically large. Another disadvantage for this technique is a 

good calibration reference and a simple analytical model is not readily 

available and more difficult than for the following reflection measurement 

technique. 

A more realistic approach is to make a reflection measurement using a 

horn. Figures 4.8 and 4.9 show the frequency and time domain responses for 

the measured reflected signal using a horn without and with the Emerson 

and Cuming’s material. The time domain gated response due to just the 

reflected signal at the material interface is shown in Figures 4.10 and 4.11. 

A 70 percent reduction of the reflected signal 

material in the time domain representation. A 

12 

is shown for the measured 

good figure of merit for the 

1 

1 

1 

1 

I 

I 

I 

I 

1 

I 

I 

I 

I 

I 

I 

1 

I 

I 

I 
I 

I 

1 

1 

I 

I 

I 

I 

1 

I 

1 

I 

1 

1 

8 

I 

I 

I 

I 

material’s performance would be the sum of the squared time domain data. 

A calibration reference for this approach would simply be an untreated 

metal test sample. This calibration measurement would be performed at 

the start of a heat test. It is unknown at this time how accurate the 

reference would be during the operation of the NASA Lewis test rig due to 

the temperature dependence of the physical dimensions which the reference 

would be sensitive to. 

I1 Transmission Measurement 

A transmission measurement of a coated metal plate can be performed by 

two approaches for this geometry. One approach would be to transmit 

and receive a RF signal through the material using both the AEL horn 

and the probe assembly. The other would be to use at least two probes 

to excite and receive a surface wave along the coated metal surface. The 

latter approach has the advantage of being more sensitive to the material 

parameters than the former approach because of greater field-to-material 

interaction. The major drawback in either transmission measurement is 

coupling efficiency of the cable’s aperture. The aperture of the coaxial cable 

will not radiate efficiently until its effective probe height is approaching 

one quarter wavelength and its effective probe diameter is approximately 

I one-half wavelength which occurs above 18 GHe. The aperture size can 

be increased by using open ended waveguides which have been tested and 

perform well but are narrow banded and are not physically desirable for 

high temperature applications. 

The transmission measurement results for the two surface probes separated 3 and 6 inches apart in the metal test plate are shown in Figures 4.12 

and 4.13. Figure 4.14 illustrates the frequency response of time domain 

gated signals for the dominant surface wave. These curves demonstrate the 

13 
poor coupling due to the small aperture size. Figure 4.15 shows the time 

gated signals for the dominant surface wave when Emerson and Cuming’s 

material is placed on the test sample support with the probe separation 

distances of 3 and 6 inches. The received signal for the two separation 

distances almost has a constant offset over the entire frequency band with 

and without a material coating. Maintaining the same constant offset in 

the received signal. with the material coating as without indicates the measurement values were still in the dynamic range of the HP 8510B. 

14 

1 

1 

I 

1 

I 

I 

I 

I 

I 

I 

1 

1 

I 

I 

I 

I 

I 

I 

I 
e 

8 

I 

1.5 

w 

3 

I0 1.0- 

- 

g 0.5- 

U 

I 

0 

TIME DOMAIN I 

- 

? 

- 

- i I- I I I - 

w 

0 

3 

Iz 

(3 

U 

I 

- 

1.5 

1.0 

0.5 

0 

TIME DOMAIN I 

- 

? 

- 

- - 

- i I- I I I - 

-I 

lo0. 

-IO 

* --20 

=) -30 

m 

0 

W 

0 

I2 

(3 

u -40 

I 

-50 

- 

I 3 5 7 9 

TIME IN NANOSECONDS 

FREOUENCY DOMAIN 

- 

- 

- 

- - 

- - 

- - 

- - 

I I I I I I I I I 

Figure 4.4: The measured reflected signal using a probe feed with no material treatment on the metal test sample support plate. 

15 
1.5 

TIME DOMAIN 

~~ 

1 

1 

I 

I 

I 

I 

I 

I 

I 

$ 0.5- 

a 

I 

- 

I I I I 

-I I 3 5 7 9 0 

lo- FREQUENCY DOMAIN 

0. 

1 

- 

TIME IN NANOSECONDS 

-IO 

rn 

n 

- *-20 

3-30- 

W 

P 

c 

z 

c3 

a -40 

I 

- 

-50 

- 

- 

- 

- - 

- - 

I I I I I I I I I 

2 IO 18 

Figure 4.5: The measured reflected signal using tl probe feed with material 

treatment on the metal test sample support plate. 

16 
IO 

'0 

-IO 

m 

* --20 

= -3c 

0 

w 

0 

Iz 

(3 

a -4a 

I 

- 5c 

- 

- 

- 

- 

I I I I I I I I I 

TIME IN NANOSECONDS 

9 FREOUENCY DOMAIN 

- 

Figure 4.6: The measured, time gated reflected signal at the probe aperture 

with no material treatment on the metal test sample support plate. 

17 
1.5 

TIME DOMAIN 

W 

3 

I0 1.0- 

5 0.5- 

I 

- 

- 

- 

I I I I 

1 

Figure 4.7: The measured, time gated reflected signal at the probe aperture 

with material treatment on the metal test sample support plate. 

lo0 

-IO 

f -20 

3 -30 

m 

0 

W 

D 

c 

z 

13 

a -40 

I 

-50 

- 

18 

FREOUENCY DOMAIN 

- 

- 

- - 

- 

- - 

- - 

- - 

I I I I i I I I I 

IO 18 2 

1 

a 

1 

1 

1 

1 

1 

I 

1 

1 

I 

1 

I 

1 

1 

I 

I 

I 

I 
0.15 

I 

W 0 0.1 HORN MISMATCH 

3 

t- - 

0.05 REFLECTED SIGNAL 

a 

I 

0 

- 

TIME IN NANOSECONDS 

1 FREQUENCY DOMAIN 

-IO 

-20 

W 

0 

2 -30 c 

z 

W 

a -40 

I 

m 

0 

- 

-50 - 

I I I I I I I I I 

2 IO 18 

FREQUENCY IN OH2 

Figure 4.8: The measured reflected signal using a horn feed with no material 

treatment on the metal test sample support plate. 

19 
0.1 5 

TIME DOMAIN 1 

- ; 0.1 - -HORN MISMATCH 

I- - 

- 

REFLECTED SIGNAL $0.05 - 

U 

I 

- I 4A-I- - I 

FREOUENCY DOMAIN 

I 

-10 

* --20 

w 

0 

3 -30 Iz 

(3 

a -40 

I 

m 

a 

- 

-50 - 

_1 I I I I I I I I I 

2 IO I8 

FREQUENCY IN OH2 

Figure 4.9: The measured reflected signal using a horn feed with material 

treatment on the metal test sample support plate. 

1 

1 

1 

1 

I 

I 

I 

I 

1 

1 

I 

1 

I 

1 

I 

1 

I 

I 

I 

20 
0.15 

TIME DOMAIN 

E 0.05 

a 

I 

Or 

- - 

I I I I - 

TIME IN NANOSECONDS 

lor FREOUENCY DOMAIN 

Q- 

- 

- 

-IO - 

- 

z 

c3 

a -40 

I 

-50 

Figure 4.10: The measured, time gated reflected signal from the metal test 

sample support with no material treatment using the AEL horn. 

- - 

- - 

I I I I I I I I I 

21 
0.15 

TIME DOMAIN 

t 5 0.05 

a 

I 

I 

I I 

3 P 7 9 01 

-1 I 

lo- FREQUENCY DOMAIN 

1 

0- 

- 

-IO - 

- 

- 

9-30 - 

- 

TIME IN NANOSECONDS 

-40 - 

- 

-50 - 

- 

I I I I 

c 

a 

z 

Figure 4.11: The measured, time gated reflected signal from the metal test 

sample support with material treatment using the AEL horn. 

I 

I 

I 

1 

1 

1 

22 
TIME DOMAIN 1 

TIME IN NANOSECONDS 

FREQUENCY IN GHt 

Figure 4.12: The measured surface wave signal on the metal test sample 

support with no material treatment and a 3” probe spacing. 

23 
.006 

TIME DOMAIN DIRECT SURFACE WAVE RETURN 

- 

I- - 

TIME IN NANOSECONDS 

FREQUENCY IN GHr 

Figure 4.13: The measured surface wave signal on the metal test sample 

support with no material treatment and a 6” probe spacing. 

24 

I 

I 

I 

1 

1 

I 

I 

1 

1 

1 

1 

1 

1 

1 

1 

1 

I 

I 

I 
-40 

QI -50’ 0 

I: 

__ -60 

- 

-90 

-I00 

- - 

I I I I I I t I I 

Figure 4.14: The measured, time gated surface wave signal on the metal 

test sample support with no material treatment. Probe spacing: 3” solid, 

6” dashed . 

25 
-50 

0 

5 -60- 

W 

m 

Figure 4.15: The measured, time gated surface wave signal on the metal 

test sample support with material treatment. Probe spacing: 3” solid, 6” 

dashed. 

- - 

FREOUENCY DOMAIN 

- - 

- 

- 

26 

0 

= -?O- M 

t 

3 -00- 

I 

b ---- I 

\ 

-90 - \ ”-\- 

- IO0 I I I 1 I I I I I 

-- \ 

--- 
Chapter 5 

Conclusions 

Sensing the material changes can ,e achieved with either reflection or transmission measurements. Even though a transmission measurement would 

be more sensitive to the material parameters since the surface wave would 

have a longer path length than a reflected signal through a thin coating, 

it has been decided to place more emphasis on the reflection measurement 

approach due to the physical difficulty of using surface probes and maintaining a long usable probe life. The reflection measurement approach has 

the most likely chance of finding the material's parameters during the heat 

cycle test based upon the physical constraints of the two measurement approches. Acquiring the actual material parameters would be thwarted by 

not being able to supply a sufficiently stable calibration. This will not be 

known until the actual heat tests are performed. If the parameters can not 

be determined to characterize the electrical performance of the material, 

then at least the reflected signal can be monitored on a relative basis. The 

relative figure of merit can be either the frequency spectrum of the reflected 

signal or equivalently, the energy of the reflected signal in the time domain. 

The programming of the HP computer is presently underway to perform 

the desired measurements and store the data. 

27 
Bibliography 

[l] Hewlett-Packard Co., Palo Alto, CA. 

[2] John Combs, Tanksley Engineering, Cleveland, OH. 

[3] American Electronic Laboratories, Inc., 305 Richardson Road, Lansdale, PA 19446. 

[4] Electronic Resources Division, Whittaker Corporation, 1955 North Surveyor Ave., Simi Valley, CA 93063. 

[5] E.K. Walton and M.L. Mittal, “Estimation of the Electromagnetic Properties of Dielectric Material Layers,” Journal of Wave-Material Interaction, Vol. 2, No. 2, January 1987. 

28 

I 

1 

I 

1 

1 

I 

I 

I 

1 

I 

1 

1 

1 

1 

I 

I 

1 

I 

I