RF absorbent
 

Anybody have any info the material used on the stealth aircraft to absorb
radar signals?

Standard stuff is a flexible plastic with powdered ferrite to match air, but
attenuate for no reflection, usually too heavy.
Stealth I think used a carbon material that matched air but had loss, also
in little hex patterns to keep the number of reflections high, more loss.
But they would not let us get that close to it 10 foot.
--Dwezil Smith

"Frank Alforo" wrote in message
...
Anybody have any info the material used on the stealth aircraft to absorb
radar signals?

Frank Alforo wrote:
Anybody have any info the material used on the stealth aircraft to absorb
radar signals?

I heard the first thing they ever tried was horsehair.
--
73, Cecil http://www.qsl.net/w5dxp



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"Frank Alforo" wrote in message
...
Anybody have any info the material used on the stealth aircraft to absorb
radar signals?



The 297 hits on Google for "radar absorbent material" was information
overload? The 3,730 hits for "RF anechoic material" frightened you? And the
70,100 hits for "stealth aircraft design" sent you scurrying here to see if
we had anything for you?

At least it's nice to see you doing your homework before Sunday night.

Ed
wb6wsn

A major portion of 'stealth design' is to deflect the radar signal in
directions away from the transmitter [i.e. deflect the echo]. Hence, the
many flat panels on the F-117.

A secondary feature of the design is absorbent material.

A third feature is the hex filter designs in the windows/turbine
aperture etc [allow rf in but keep it from getting out].

But, your basic absorbing material is found in numerous graphite epoxies
whose composition is classified.

You may find useful information on basics by checking out 'space cloth'.
Space cloth is used for radar dummy loads and is available in Zo that
provide VSWRs from 5:1 to 1:1. At 1:1 there is no reflection.

Frank Alforo wrote:

Anybody have any info the material used on the stealth aircraft to absorb
radar signals?

Dave wrote:

A major portion of 'stealth design' is to deflect the radar signal in
directions away from the transmitter [i.e. deflect the echo]. Hence, the
many flat panels on the F-117.

A secondary feature of the design is absorbent material.

A third feature is the hex filter designs in the windows/turbine
aperture etc [allow rf in but keep it from getting out].

But, your basic absorbing material is found in numerous graphite epoxies
whose composition is classified.

You may find useful information on basics by checking out 'space cloth'.
Space cloth is used for radar dummy loads and is available in Zo that
provide VSWRs from 5:1 to 1:1. At 1:1 there is no reflection.

I read somewhere that the absorbant material had an impedance of 377 ohm per
square. J Kraus showed that space cloth of this impedance reflects 30
percent of the incident wave.
Is space cloth still manufactured? A google search turned up zero hits.

Tnx es 73, Frank

"Ed Price" wrote in message
news:CAw9c.15750$Q45.10237@fed1read02...

"Frank Alforo" wrote in message
...
Anybody have any info the material used on the stealth aircraft to
absorb
radar signals?

The 297 hits on Google for "radar absorbent material" was information
overload? The 3,730 hits for "RF anechoic material" frightened you? And
the
70,100 hits for "stealth aircraft design" sent you scurrying here to see
if
we had anything for you?

At least it's nice to see you doing your homework before Sunday night.

Ed
wb6wsn

Tnx for the tip, Ed. Your point is well taken. But it seems to me that the
same can be said for the great majority of the posts seen here. Perhaps we
need a moderator to keep irksome and inane posts from cluttering up the
newsgroup and provoking the ire of the members who visit here.

Frank :)

Frank Alforo wrote:

SNIP

I read somewhere that the absorbant material had an impedance of 377 ohm per
square. J Kraus showed that space cloth of this impedance reflects 30
percent of the incident wave.
Is space cloth still manufactured? A google search turned up zero hits.

Tnx es 73, Frank


I last purchased 'space cloth' [122 ohm/square] in 1990. I don't know if
it's still manufactured.

W1MCE

"Frank Alforo" wrote in message
...

"Ed Price" wrote in message
news:CAw9c.15750$Q45.10237@fed1read02...

"Frank Alforo" wrote in message
...
Anybody have any info the material used on the stealth aircraft to
absorb
radar signals?

The 297 hits on Google for "radar absorbent material" was information
overload? The 3,730 hits for "RF anechoic material" frightened you? And
the
70,100 hits for "stealth aircraft design" sent you scurrying here to see
if
we had anything for you?

At least it's nice to see you doing your homework before Sunday night.

Ed
wb6wsn

Tnx for the tip, Ed. Your point is well taken. But it seems to me that the
same can be said for the great majority of the posts seen here. Perhaps we
need a moderator to keep irksome and inane posts from cluttering up the
newsgroup and provoking the ire of the members who visit here.

Frank :)


Naah, an official moderator isn't needed. Besides, he'd get burned out too
fast anyway.

BTW, absorbent material is NOT 377 ohms per square. The traditional
absorbent material is decidedly low-tech, consisting of open-cell urethane
foam with carbon particles dispersed along the cell walls. The grungy way to
make this is to cast a monster billet of foam, maybe 10' long by 4' by 4'.
The billet is then squashed flat in a press, and submerged in a solution of
carbon particles (lampblack; and seems I heard of that being made by
scraping the soot of a propane flame off of a copper block), water and
ethylene glycol (for wetting). The billet is allowed to expand, soaking up
the solution, and then drips dry. It's just like a huge kitchen sponge.
Particles of carbon are then left disperesed, almost painted, on the cell
walls. Then, after some more oven drying, they cut the billet, with a hot
wire, into those fancy pyramidal shapes. Then, some latex spray paint for
that high-tech blue or white look. And then they sell them to you for $175
per 24" square!

If you think of a plane wave propagating along, it has a 377 ohm wave
impedance over a unit area of wavefront. As the wave encounters the tips of
the pyramidal cones, a bit of the wave begins to encounter a slightly lower
impedance. As the wave propagates further, the impedance over the unit area
decreases. The wave begins to lose energy to ohmic heating of the lower and
lower impedance medium. Finally, at the base of the cones, the wave is
trying to propagate in a much lower than 377 ohm medium, and it's giving up
energy rapidly to warm the carbon particles. (With enough energy lost, it
might even melt the foam or ignite it.)

The tapered shape is used so as to present a gradual change in impedance.
The thing to avoid is any sudden change in impedance, which would result in
a reflection. There is much debate on optimizing the shape; right pyramids,
truncated pyramids, rotated sections of the pyramid, cones; some have
advantages in certain applications. The particles creating the loading can
be adjusted; sometimes ferrite particles are used with, or in place of, the
carbon.

(Before urethane foam was used, early researchers did use horse-hair. Maybe
one of them had some auto upholstery experience to draw on.)

All stealth is a combination of absorbing what you can, reflecting what you
can't (in more benign directions), trapping energy in labyrinths and
avoiding resonant structures (like exposed weapons or long panel seams,
etc). Another approach is to use multi-layer 'sandwiches" to create ohase
cancellation to a wave, but this is really difficult to optimize for more
than one frequency.

Ed
wb6wsn

I think someone would be in a lot of trouble if you find the recipe for
a specific stealth aircraft on the Internet. The "spacecloth" mentioned
in another post could be similar to Echosorb, a popular microwave RF
absorbent material that is available in sheet form. It ranges from a
1/16" thick pliable rubber to thicker, multilayer foam that looks like
the black antistatic foam used to ship IC's and other semiconductors.

Frank Alforo wrote:
Anybody have any info the material used on the stealth aircraft to absorb
radar signals?

On Mon, 29 Mar 2004 07:08:02 GMT, Mike wrote:
Echosorb, a popular microwave RF
absorbent material that is available in sheet form. It ranges from a
1/16" thick pliable rubber to thicker, multilayer foam that looks like
the black antistatic foam used to ship IC's and other semiconductors.

Hi Mike,

It is also quite heavy which would be inappropriate for aviation
applications. I played with this stuff a dozen years ago when one of
my buddies got a speeding ticket in his 'Vette. He asked me to design
a stealth bra for his ride - it didn't seem to be practical for any of
several reasons.

73's
Richard Clark, KB7QHC

Richard Clark wrote:
It is also quite heavy which would be inappropriate for aviation
applications. I played with this stuff a dozen years ago when one of
my buddies got a speeding ticket in his 'Vette. He asked me to design
a stealth bra for his ride - it didn't seem to be practical for any of
several reasons.

Why didn't he just put aluminum foil on his hubcaps like everyone else? :-)
--
73, Cecil http://www.qsl.net/w5dxp



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On Mon, 29 Mar 2004 12:14:27 -0600, Cecil Moore
wrote:
Why didn't he just put aluminum foil on his hubcaps like everyone else? :-)

Do they sell Vettes with steel wheels and hubcaps in Texas?
Do you wear your Levis tucked in your boots or outside them?

Richard Clark wrote:
Do you wear your Levis tucked in your boots or outside them?

I'm not allowed to wear boots. I don't own any cows.
--
73, Cecil http://www.qsl.net/w5dxp



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"Richard Clark" wrote
Mike wrote:
Echosorb, a popular microwave RF
absorbent material that is available in sheet form. It ranges from a
1/16" thick pliable rubber to thicker, multilayer foam that looks like
the black antistatic foam used to ship IC's and other semiconductors.

Hi Mike,

It is also quite heavy which would be inappropriate for aviation
applications. I played with this stuff a dozen years ago when one of
my buddies got a speeding ticket in his 'Vette. He asked me to design
a stealth bra for his ride - it didn't seem to be practical for any of
several reasons.

I was going to paint a whole-car with the RAM-paint used on my submarine
masts. Until I saw the price. Cheaper to pay the tickets ;-)

Jack

The 297 hits on Google for "radar absorbent material" was information
overload? The 3,730 hits for "RF anechoic material" frightened you? And
the
70,100 hits for "stealth aircraft design" sent you scurrying here to see
if
we had anything for you?

At least it's nice to see you doing your homework before Sunday night.

Ed
wb6wsn


Wow. Good thing Frank is a seasoned ham; had he been a newbie you would
have just chased him from ham radio. Congratulations, Elmer!

Al W6LX

Frank Alforo wrote:
"J. Kraus shower that space cloth of this impedance reflects 30 percent
of the incident wave."

There must be an impedance discontinuity. Not 377 ohms?

Kraus said sheets of space cloth backed by a reflecting plate are
sandwiched between plastic layers. Kraus has an appendix "D" on
absorbers.

Searching on "Salisbury screens" got me 4578 hits.

Best regards, Richard Harrison, KB5WZI

"Al Lorona" wrote in message
...

The 297 hits on Google for "radar absorbent material" was information
overload? The 3,730 hits for "RF anechoic material" frightened you? And
the
70,100 hits for "stealth aircraft design" sent you scurrying here to see
if
we had anything for you?

At least it's nice to see you doing your homework before Sunday night.

Ed
wb6wsn


Wow. Good thing Frank is a seasoned ham; had he been a newbie you would
have just chased him from ham radio. Congratulations, Elmer!

Al W6LX




Don't be an apologist for people who ask stupid or ill-phrased questions.
Don't pander to the lowest level. I provided a reply which I thought was
appropriate to the question. It was slightly sarcastic, though, by Usenet
standards, reasonably civilized. It provided three direct lines of search
for what was a very nebulous and obvious query. At no point did I attack the
poster, demean his mentality, question his civilization, or impugn the
length of his manhood.

Further, I hope your self-worth is well seasoned, or at least insulated, as
you don't seem to understand the difference between Usenet and Ham Radio.
Cranking off a dumb query on Usenet is equivalent to tuning up on a repeater
or net frequency. It's a bad use of electrons, and you can expect to be
chastised.

Perhaps I shouldn't be so harsh with you, as you can't seem to follow the
thread. If you were, you would have noticed that I provided considerable
background on RF absorbent material in a subsequent post.

Now, do YOU have anything informative to add to the subject, or are you just
trolling for sympathy? BTW, in addition to being in the dictionary,
"sympathy" yields about 3,700,000 hits on Google. Now there's a project for
your dotage.

Ed
wb6wsn

Ed wrote,

Don't be an apologist for people who ask stupid or ill-phrased questions.
Don't pander to the lowest level. I provided a reply which I thought was
appropriate to the question. It was slightly sarcastic, though, by Usenet
standards, reasonably civilized. It provided three direct lines of search
for what was a very nebulous and obvious query. At no point did I attack the
poster, demean his mentality, question his civilization, or impugn the
length of his manhood.

Further, I hope your self-worth is well seasoned, or at least insulated, as
you don't seem to understand the difference between Usenet and Ham Radio.
Cranking off a dumb query on Usenet is equivalent to tuning up on a repeater
or net frequency. It's a bad use of electrons, and you can expect to be
chastised.

Perhaps I shouldn't be so harsh with you, as you can't seem to follow the
thread. If you were, you would have noticed that I provided considerable
background on RF absorbent material in a subsequent post.

Now, do YOU have anything informative to add to the subject, or are you just
trolling for sympathy? BTW, in addition to being in the dictionary,
"sympathy" yields about 3,700,000 hits on Google. Now there's a project for
your dotage.

Ed
wb6wsn


Aha! Another pompous, sarcastic, smug, overbearing, insufferable post from
a
gentleman whose acumen is as nebulous as his reply is asinine. You should
get a job at a community college, Ed. College students are inured to your
particular brand of snide, demeaning discourse, since many teachers use
it as a technique for avoiding having to answer questions requiring knowledge
those teachers don't possess.
73,
Tom Donaly, KA6RUH

"Tdonaly" wrote in message
...
Ed wrote,

Don't be an apologist for people who ask stupid or ill-phrased questions.
Don't pander to the lowest level. I provided a reply which I thought was
appropriate to the question. It was slightly sarcastic, though, by Usenet
standards, reasonably civilized. It provided three direct lines of search
for what was a very nebulous and obvious query. At no point did I attack
the
poster, demean his mentality, question his civilization, or impugn the
length of his manhood.

Further, I hope your self-worth is well seasoned, or at least insulated,
as
you don't seem to understand the difference between Usenet and Ham Radio.
Cranking off a dumb query on Usenet is equivalent to tuning up on a
repeater
or net frequency. It's a bad use of electrons, and you can expect to be
chastised.

Perhaps I shouldn't be so harsh with you, as you can't seem to follow the
thread. If you were, you would have noticed that I provided considerable
background on RF absorbent material in a subsequent post.

Now, do YOU have anything informative to add to the subject, or are you
just
trolling for sympathy? BTW, in addition to being in the dictionary,
"sympathy" yields about 3,700,000 hits on Google. Now there's a project
for
your dotage.

Ed
wb6wsn


Aha! Another pompous, sarcastic, smug, overbearing, insufferable post
from
a
gentleman whose acumen is as nebulous as his reply is asinine. You should
get a job at a community college, Ed. College students are inured to your
particular brand of snide, demeaning discourse, since many teachers use
it as a technique for avoiding having to answer questions requiring
knowledge
those teachers don't possess.
73,
Tom Donaly, KA6RUH



Thomas obviously has problems with higher education, as his most potent
insult is to suggest that I teach at a community college. Oh, the horror!

Whatsa matter Tommy, did I hit a button on you? Some jackass community
college teacher give you a low grade, and it ruined your life? Nothing left
for you but trolling Usenet?

So here's my challenge to you, Tommy Twerp. Either add something useful
about RF absorbent materials, or go fellate an operating 5U4!

Ed
wb6wsn

Ed wrote, assuming his usual air of superiority,

Thomas obviously has problems with higher education, as his most potent
insult is to suggest that I teach at a community college. Oh, the horror!

Whatsa matter Tommy, did I hit a button on you? Some jackass community
college teacher give you a low grade, and it ruined your life? Nothing left
for you but trolling Usenet?

So here's my challenge to you, Tommy Twerp. Either add something useful
about RF absorbent materials, or go fellate an operating 5U4!

Ed
wb6wsn


Behind the man, the child. I must have pressed the right button.
73,
Tom Donaly, KA6RUH

"Tdonaly" wrote in message
...
Ed wrote, assuming his usual air of superiority,

Thomas obviously has problems with higher education, as his most potent
insult is to suggest that I teach at a community college. Oh, the horror!

Whatsa matter Tommy, did I hit a button on you? Some jackass community
college teacher give you a low grade, and it ruined your life? Nothing
left
for you but trolling Usenet?

So here's my challenge to you, Tommy Twerp. Either add something useful
about RF absorbent materials, or go fellate an operating 5U4!

Ed
wb6wsn


Behind the man, the child. I must have pressed the right button.
73,
Tom Donaly, KA6RUH



Yes, you are pressing the correct button. Unfortunately, your meds are not
being dispensed commensurate with your previous conditioning.

This is far too easy, and since you STILL have nothing to add on the topic,
I will refrain from further comment.

Best Regards for a speedy recovery, OM!

Ed
wb6wsn