So good morning and welcome to the Wireless of Virginia
Tech seminar. It's been it's been a number of
weeks since we've had a regular seminar. We've been
having a number of faculty candidates come and visit and
talk to us. We may be seminar it out,
I don't know but thanks for coming this morning
to hear Amir Zaghloul who's going to talk with
us about metamaterials, meta surfaces and nanotechnology uh and
their applications to antennas, sensors and cognitive radar, not
cognitive radio. Apologies for that in the original announcement.
Um so Amir has been with Virginia Tech with
the ECE Department since 2001, which is
uh which is a couple years longer than I have.
He knocked on my door this morning and he
thought I didn't know who he was but I did.
Um so um he is currently a research professor
with the ECE Department of Virginia Tech and is also with
the U.S. Army Research Laboratory in Maryland.
Uh prior to joining Virginia Tech in 2001,
He was with Comsat Laboratories for 24 years,
performing and directing research and development uh work on
satellite communications and antennas. He's a life fellow of
the IEEE, as well as a fellow
of uh several other societies, the Applied Computational Electromagnetics Society,
the American Institute of Aeronautics and Astronautics uh
is also uh done a lot of service for the
community in the form of organizing conferences and doing editorial
work on journals and so on. So we're very
happy to have Amir with us here in Blacksburg
today. Although he's with Virginia tech, he's usually
in northern Virginia. So thanks. Thank you.
Thanks Alan for the introduction and for the opportunity.
Okay. Or the opportunity to come and give a
talk here in this series for wireless at Virginia Tech.
Uh when I thought about what to talk about,
I wanted actually two things to come out of
this, I'd like to talk about the quote-unquote
exciting work that's being done in the area of electromagnetics
and antennas which lots of people or many people
consider it to be an old technology that everything that
was to be done was done already. I'd like
to say that, no there are lots of exciting things
going on and I'd like to mention that to you,
especially to the young people who are probably interested
in lots of other areas. The other thing I'd
like to give you a little bit of introduction about
the army research where I spend all my time these
days as a member of one of the director
they're called sensors and electronic devices. And I'm doing
lots of research on antennas and on other related things
that are focused on army needs. Uh thinking about
like a good title to have here, I chose
almost every buzzword that I can throw into the title.
So I put meta materials, metal services,
nanotechnology, cognitive radar. And if I miss anything
let me know and I'm willing to throw it in
as well. [Inaudible] Plasmonic comes under metamaterials as
well, So, so we can we can have that
cover. Although when I talk about metamaterials the
only thing that I am uh I'm missing okay would
be the the uh photonics area and areas in the
frequency band that are beyond our rf and terahertz.
Uh my talk is going to include this outline
uh on how much time I have just to pace
myself. I think we have reserved the room until
12:15. Okay. Okay I'll be done by then.
Uh This is outline of the what I'm talking
about the three main things meta materials with definition applications
and stuff meta services on actually focusing on one type
of metal surface which the electromagnetic band gap services.
And then I'm going to talk about nanotechnology and also
I'm focusing on the carbon nanotube part of the nanotechnology.
We are doing work in other parts of nanotechnology
using graphene and other things. But I'm talking mainly
about the CNTS. So this is I
hope to cover all of this in the next hour,
but before we get there I'm going to have
to go to a commercial break with word from our
sponsor the army. Okay this is the ideal situation
that we hope all of us hope to have in
research work. I would like to have a combination
of or collaboration between academia, defense labs and industry
actually other kind of labs fall under industry but here
we are separating Defense labs for the Army, Navy
and Air Force and the like and the the combination
of all these things here is what we call here
transform transformative science and the main focus or the main
things that we are trying to use in this three
combination of course is the facilities which are plenty in
all the three are in the three circles here people,
smart people in all the three organizations and of
course the resources that everyone has to has to offer
uh and that will give us an efficient effective and
agile resource system. Okay. In the area that
we're talking about the antennas and electromagnetics and uh
the other words that I mentioned uh I think uh
it cannot be more helpful than this. Getting cooperation
cooperation between these 3 circles here. one of
the things in order to put that in more practice
or more practical way at the Army research lab.
Uh We came up with this idea. Um Of
course I was not part of we here but like
the A. R. L. Came up with
this idea of opens campus in the past what we
have been doing. We have been collaborating with academia
and giving contracts doing work and watching the results and
following everything that's being done there. But there was
always the restriction of having people from academia come and
spend some time at the research labs, there was
lots of that but all of these things came with
some restrictions. What is being done here will have
an area called open campus within the facilities at A.R.L.
Uh That is going to
be dedicated to people coming from outside and spending the
time there. And that is going to include it's
not going to be limited for us citizens anymore,
it's going to include foreign nationals which of course was
not the case before. So smart people who would
like to come and do work and whether being students
or faculty they can come and spend some time and
in that time they are going to collaborate with people
at the army line. Of course that will be
in a restricted area but you're going to have access
to lots of the facilities that we have in terms
of either computer stuff or lab area or something like
like that. So it's a campus like environment that
we're going to have there and you and it's going
to be access to everybody and it's going to be
an expansion of the collaboration that we already have.
I don't know what I do to stop this thing
from disappearing every females. Um This is of course
people will have access to the facilities that we have
which which I can say it's extremely uh We are
we are extremely well equipped with lots of good facilities
that we're using in our research. And the last
item here is that it's energetic with Maryland and DC
But also that includes Virginia. Uh
huh. Uh area because of the closeness then uh
there is some collaboration is going to be with local
small business and things like that. So I encourage
you to consider this as part of the research that
you would like to do. And there's a website
where you can actually apply to go to uh for
internship in the summer. I don't have it with
me now but if you email me I can send
you all the information if you are interested in coming
for the summer months to spend some time at the
A. R. L. Again that's being a
student or faculty. We both are wrong. Uh
The lab itself this is just the organization very sort
of high level organization chart here we have of course
the director of the labs and the labs includes six
directors vehicle technology human resource human research and engineering uh
sort of of ability, lethal Itty analysis, competition
and information sciences, sensors and electric devices. That's
where I reside. Weapons and material research and lots
of collaboration among the different directorates. Uh But the
work that are is of interest to the wireless group
here is going to fall in. Okay I guess
I cannot point to this thing here. It's going
to it falls into the The more to the three
on the right here. The lots of work in
wireless along with electro Magnetics and antennas radar and and
things of that nature. And very important the work
we are collaborating on with the materials people because when
you see in my presentation we are doing more work
with materials to improve the kind of devices and antennas
that we produced for the army. The seventh member
of this organization is the Army research Office. It
operates under the A. R. L. And
thats the one actually that catch the attention of academia
because that's where the money is. You get the
money from a roo a roo in contracts uh which
is part of A. R. L. Uh
sometimes we get to review some of the proposals that
are submitted there but we are working in the other
direct with and interact with the R. O.
On some of these uh contractual issues here. A
roo is situated in north Carolina as you may know
. Okay so now we go back to the technical
material here and I'm going to talk first about meta
materials and for those of you who don't know the
definition, what is meta materials. It is something
that is not natural, it is material that is
engineered. Okay. It doesn't doesn't happen in nature
and it is not like the simple composite materials like
when you have substrate for circuits and stuff. There
is material there and the substrate but that is a
simple composite material. The meta material includes more than
that material and includes some insertions that will give the
material properties that you cannot achieve in uh using any
of the natural or simple composite materials. The war
of the meta materials actually um is relatively recent.
Uh It came about maybe a few decades back,
two or three decades back. It was the word
was coined by a professor at University of texas at
Austin. Roger Roger Walser who coined the name metamaterials
. And after that he opened his own company called
metamaterials, inc but but but the word itself Includes
lots of work that was done even before that.
If you go back to the 60s or even before
that you will find that the concept of producing material
with certain characteristics was there But it was not named
meta materials until recently. Generally speaking, if you
look at the new absalon diagram that our quadrants that
I have here the right hand uh top corner here
positive, absolutely positive. Uh Is that something you
can control? Or? 11. Okay. So
uh okay, let me try to go faster than
over the slide before it does. Uh The the
right hand side is the right hand material which has
positive, absolutely positive immune. And that's what we
find in regular material. And in simple composite material
. Uh If we go negative on any of these
absolute arm, you we start generating these special meta
materials uh and then we can use the negative part
of absolute arm. You to give us certain characteristics
in the material. Also on the right side,
when we know that in free space. Absoluteal equal
to one. Or relative productivity is equal to one
and relative permeability is equal to one. If we
exceed that, we go with mu of equal 10
for instance, or absolute very, very high.
Then we call that also math a materials and that's
achieved by having certain inserts in the material. And
that's going to give us some properties that we cannot
achieve in the simple material. So meta material can
fall in any of these. And this actually,
by the way, the positive, the real part
of absolute. And and then you of course we
know absolute mu it's a complex number. So,
but but what we have here is the is the
real part. So this is the definition of the
meta material. And um they we use them as
just a simple tool set to redesign and tends to
make them smaller to make them high efficiency to make
them with higher gain and and all the other problems
that we want to have in them. Uh Also
to create some services that will give us certain properties
in reflection because we know that the simple material that
we have for reflection purposes is the simple ground plane
uh where you have, if you have an object
on the top of it, you create an image
and then in order to get a positive response from
the reflecting surface, you have to have your antenna
for instance, a quarter wavelength above the ground plane
. Uh When you use certain types of meta materials
or methods services will find that we don't have to
be that high above the ground plane. So we
can actually reduce the profile of the antenna or the
structure that we are doing. Also, we can
use the properties of the metal material to give us
impedance matching of the structure that we are building or
the antenna we are building. And that again goes
a long way in uh in improving the bandwidth,
increasing the bandwidth, reducing the sauce uh of the
antenna. We also use it to give us better
mutual coupling, reduce mutual coupling between elements and antennas
or electromagnetic structure. So those were some of the
design criteria that we can get out of the metamaterials
. These are some of the the meta material types
that were published but there are hundreds more than these
ones. The simple or the one of the basic
ones. The one on the top left. Um
What we have there is um uh if you look
at the small print on on these sheets, we
call that split ring resonator, which is actually um
There's my point here, I guess is uh the
in the small circles around this center block, the
one to the left and the bottom. This called
split ring resonator. Split ring resonator uh where you
have the ring resonates at a certain frequency and you
control the resonance by the dimensions and by the gap
okay between the sides of the of the ring and
there are different other different kinds and equivalent circuit of
that thing represented in these small circles. The one
to the top left again. Okay, gives us
the split ring resonator gives us negative are not negative
, but it controls the immune of the material and
you can get negative mule with certain dimensions of it
. However, it may be a narrow band behind
the split ring and you can see it in the
picture underneath it. There is a simple poles in
front of the rings and those give us the negative
absolute. So we can get negative, absolute and
negative mu out of these things and the negative absolute
concept actually came about back in 1963. Even before
we talked about any matter materials were uh walter.
Uh Rodman Wall Trotman. He actually introduced that back
in 1963. Rodman is well is more known with
for his Rotman lens, which we'll talk about in
a few minutes and these are other types. And
the one that's actually interesting if you look at the
bottom here, you have something that is surrounding another
object and its surrounding it to give it the property
of cloaking. So if you have electromagnetic field coming
hitting the object in the middle, as you can
see in. Okay, let me do this.
Okay. Uh If uh if you have the object
surrounded by some material as you see here. Okay
, this material which made out which is made out
of metal material. Okay, It's going to cause
the electric field when it comes to hit that object
to go through the object ends to the surrounding material
and come out as if there was nothing there.
So it's doing what we call clocking of the object
and and hiding it so that you don't see it
with the with the electromagnetic wave, of course,
the size of the cloaking material is much more than
the size of the material that you'd like to hide
. But of course the signal goes through and it
doesn't see neither of them. Ah Okay. Along
with the meta material, okay. Which has to
use a large number of inserts periodic or random or
whatever coordination. Uh We we wanted to be uh
you can produce meta material, antennas made out of
those things here. But after a while we came
to think that not everything we build is actually meta
material. In terms of being an antenna made of
metal material. Someone from Arizona Oregon. Szarkowski came
up with the expression that's called meta material inspired.
That means it is something some kind of antenna.
It's not, you cannot call it meta material,
but it uses some of the properties that we develop
in the meta material. So you can use single
cell. You can using you can use some other
metallic inclusions in order to use some antenna that does
not necessarily have a medium that has certain absolute and
new properties as in the meta material. So these
are the sorts of definitions of these things here at
A. R. L. Or at the D
. O. D. In general. Uh We
have our people have been working on different aspects of
meta materials as you can see here back down to
1967 all the way to today and uh and uh
oh oh this I'm sorry. Well that's a good
idea. Okay. Uh So there's some work that
was done outside era, like this piece here was
done by University of michigan. Uh There is uh
there is some other work that was done by by
other companies uh around here. Um This actually is
is my work is that I'm going to talk about
in a few minutes who are we demonstrated the negative
refractive index, both in simulation and in measurements.
And then after that we started building some other material
that has either negative absolute negative mu or high value
of mu. That is going to give us also
the reflection that we needed that will produce high gain
out of the out of the antenna. So this
is these are some examples here examples here of this
. This one here is a high new material that
we call it metaphor. Right? Again, this
a concept that lots of people working on including meta
material inc uh the meta materials inc the one that
uh walls or roger walls or is is running out
of texas. Uh This is also the same example
. We have a metaphor, right material that is
putting underneath this uh this printed antenna uh to improve
the performance of it, give it high gain and
uh and high efficiency are high uh basically high again
with very small, very low profile. So the
debt here is very small of the material under the
antenna. Uh Then we started thinking about why we
have to limit ourselves to the periodic materials. What
happens if we go to random materials and that's what
we have in this picture. We built a material
that's made out of unit selves that are not arranged
in a periodic structure but in random. And what
we are going to get out of that is uh
still we are working on that and uh we'll have
some results on that. Uh We had some results
but we'll have more results in the next hopefully short
time. Actually, there's a master's thesis that will
conclude end of this semester by one of the students
, john Hodge, who's going to talk about some
of these simulations that he did and that will be
followed by uh We are planning on doing some other
work on the analysis of that material. Regulars analysis
from the E. M. Point of view and
uh some uh uh more interesting simulation. Uh Okay
, so, so we are proceeding in this line
here to do lots of things. One thing we
are doing by the way in designing the antennas,
weather for meta materials or for others is that we
have to design the antennas institute. That means in
the presence of the environment that's going to be used
at for instance, if you have an antenna design
for use on a vehicle, then we have to
design the antenna with the vehicle body behind the antenna
to know exactly how the antenna is going to behave
. Okay, so that's the institute sort of analysis
is essential part of what we're doing for either analysis
of this or any other intent. Other things we
are doing is uh stack E B G. And
I'm going to talk about that in a minute and
and other things that uh we are doing within the
army lab of course some of that is again with
collaboration with other with universities and stuff. One example
here is a multi layer metal material and we are
starting from the individual cell and we are trying to
find what is the macro uh performance of a block
of metal material in analytical way. Of course we
can do simulation but the simulation takes lots of time
as we know. So we try to do some
analytical, develop analytical tools for that. And this
is being done by the University of Sienna in Italy
. And this again is the metaphor right thing.
These two here here we have an E. B
. G. With multiple dimensions to give us broadband
in addition to the stacked one that I showed you
in previous view graph this work here is actually we
have a PhD some deep already who's going to finish
hopefully by the end of this year. Uh And
his dissertation is mainly on the wideband electromagnetic band gap
structure which is considered to be some kind of metal
services. Uh So this again are the activities uh
the objective the accomplishments and the approaches we take to
analyze meta materials and build them and test them at
the army line. Uh This is something that we
did earlier. This is the one that I showed
you in that uh timeline where we used a an
element sell uh we call it capacitive lee loop uh
loaded loop. Okay. Which is this one which
is a little different than this littering resonator. Okay
. But if you put again probe in front of
it then this will give you the negative mule and
this one will give you the negative absalon. And
the combined structure is going to give you the negative
refractive index. Okay. And we proved that and
again this work also was a master's thesis topic that
was done a few years ago um uh by wang
that he did the simulation work and we did some
of the experimental work at the RL the experiment's simple
experiment experiment that we try to do to prove the
refractive index of the negative refractive index was simply like
this. We have a source and we have three
receivers on a circle centered here. If we don't
have material than the level of signal that we receive
here. Out of this mono paul is going to
be the same. Okay if we have a negative
refractive index then the signal is going to come hit
this medium, the negative refractive index medium and it's
going to bend this way as you can see here
Instead if this was positive material, it would refract
this way and again the facts again and then you
get reception somewhere here. But if you have the
negative are negative refractive index then it's going to bend
like this bend again as it gets out of the
medium and you can have higher level here okay than
what you get at these two points. So detecting
much higher level here than these two points is an
indication that we have a negative And in this material
this concept is called the Perfect lines and that was
introduced some time back. But what we did here
, we realize it and we proved that we can
actually do the measurements, the unit cell is like
this. It's a simple loop like this printed on
a piece of dielectric and on the other side of
the electric we have a poll or problem like this
to give us the negative negative. Also these dimensions
are for certain frequency. You adjust the dimensions to
get the frequency you want. But it's very,
very much as scalable to different frequencies. And this
is the set up. These are the pieces that
we built and this is the result with the materials
. The the signal from the source to the center
receiver is like this but to the edge receiver is
much lower. It's about maybe 10 or 15 db
lower because of the focusing that you get in this
direction here. Without the material, the to the
center and the edge are very close to each other
. The blue here is the s. shows a
good match in in either case. So that shows
the refractive index being negative and you have the focusing
as a result of this reflective index. These are
the measure data that that we did that show the
same thing as I showed you in the simulation results
. The next thing we did, we said that
we are not going to do that only in one
direction will do that in two directions. As you
see here. This is one direction and the the
orthogonal direction. The reason for that is that we
wanted the material to be icy trap to have the
negative performance negative refractive index uh with our psychotropic behavior
uh in in all directions. So we did that
and instead of one or the other directions which is
vertical or peril, which this one gives us a
coupling in the in the magnetic field in this direction
, this one couples the magnetic field in this direction
the cross Cll is going to couple in both directions
and give us the answer trophic behavior. And this
is the analysis that we did for the negative refractive
index calculation. And what you see here the blue
line is the case with the cross uh loops that
shows us isa tropic. That means the negative refractive
index is almost constant across the angle range from minus
From zero actually to hear up to 50. And
of course it's the same in the negative angle.
While the two other orientations are not ice a tropic
. They changed with angle. So here we indeed
achieve the reflective index that is Aissa tropic in all
directions. This is what we built. This is
the periodic structure. Okay. Of these loops.
And this is the random, the random, we
built individual cells and we throw them in the material
like you can see here the individual self for the
random looks like this. You have the printed CLL
and the printed probe. And we put that in
a body of raw cell material to give us a
absolutely equal one in the material here. And then
we cut it and shake it and put it in
the around the medium. Um This is some of
the properties that we can see that the random selves
are going to give us. Uh this is periodic
. Okay. And this periodic here shows that we
have a reflection represented by the red and transmission represented
by the blue. Okay, over a very narrow
band. So in this band the periodic material is
reflective in this part here is transmitted. Okay,
the layers of the material, if you have some
disordered cells, that means cells are not the same
size. But still you are trying to put them
on a periodic lattice. You get this kind of
response. You have some reflective and some transmitted and
different parts of the frequency band. If you do
it all random like this one here. This gives
us very interesting result because we have what's equivalent to
a band pass filter where you have through this band
, which is much broader than any of the bands
we had there. We have a very good transmission
coefficient. This is as to one and very high
reflection or high s 11 that means that within this
ban the material is acts like F. S.
S. Frequency selective service. But over a very
wide band so that we can achieve with the periodic
. Okay, uh against what we can achieve,
I'm sorry, with the random. Against what we
can achieve with the with the periodic Yes, your
random result, is that an average over a number
of different realizations are just one at one measure.
uh in this case it's only one when we do
the theoretical analysis. Okay, we are going to
do an average based on the theoretical analysis and see
how that is. But this is a case of
one run the same thing with the measurements. We
do it once and then we measured. So we
, when we do the averaging, we don't know
how wide sigma is going to be. If it's
going to be abroad, that means it's going to
have this wide band all the time or it's going
to be like fairly in a narrow number or a
small number of uh of sigma. Uh One of
the things actually I have in Houston who is going
to work on this thing from the theoretical point of
view and one of the things and actually I need
to run that by you very quickly is we would
like to use the theory of random medium Okay,
propagation through around the medium. In trying to analyze
this. There is a method of analyzing metamaterials,
periodic method materials that was done by Ishimaru at the
University of Washington. And we would like to follow
what he was doing in the propagation area to see
if we can also apply the theory of random media
market to this in order to simplify the analysis and
the simulation because the way we are doing it.
Now, the simulation is very time consuming. When
you use HFcs or any of the other methods,
it's very consuming, time consuming. But we hope
that when we do the theoretical analysis, that's going
to be uh more easy to handle than that.
Ah, okay. One of the applications that we
have for this is only because I'm giving this for
wireless activity. So I have to all this uh
one of the applications that we have for this meta
material in terms of improving the performance of an antenna
is take the very simple diaper, the whip antenna
, which of course you probably heard this expression many
, many times. You cannot beat the whip okay
. Which is the main antenna is being used for
on vehicles and army applications and all of that.
Of course, whip antenna on the vehicle means that
this is an important vehicle. Then then uh the
whoever wants to shoot is going to shoot that vehicle
first. So you'd like to reduce the profile or
the size of the antenna on the vehicle so that
it will not be easy to detect. And that's
a different subject. We're doing lots of work in
that area. But here, what we are doing
, we found out that this kind of loop structure
. Okay, in this plane here, if you
send a signal in this direction on the plane,
it is going to reflect back with this being high
new material when it is high new material. Okay
, you don't, it's going to act as if
it's a reflector but at very small distance with respect
to the default. So we have a die paul
here with very small distance to this material here and
that we found out that this is going to give
us not the omni directional pattern of the antenna,
but it's going to make the dipole directive in the
azimuth play. Okay, so I can produce directive
. P beam out of the dipole antenna in in
asthma. If I repeat this many times instead of
one thing like this one here, I put 12
pins around the die Paul. Then I can increase
again and reduce the size of the B. More
. So if you look at this table, you
will find that with no fins. That means The
default in free space gives you a gain of 2.2
DB. They should be D. B. I
. Uh When you have to fans like this one
here, this plane or You can get this kind
of gain 5.4 and then all the way to 12
. You can get 9.7 DB I out of a
disciple which of course is very good improvement. About
7.5 db improvement over the simple dipole. But of
course you get very narrow beam, which means that
if you have a diaper like this. Okay.
And you have the fence around it by rotating either
the fins or the die paul, you can have
actually scanning of the beam out of a simple dipole
. So this is a scanning die paul, which
you can get out of this using the meta material
structure around uh this, I'm sorry. Okay.
Uh This is the game. It doesn't show the
bandwidth. Uh No, it has actually fairly good
bandwidth. I don't have the number of the top
of my head now, but it's fairly good good
bandwidth. This here actually, this can give you
an idea. Uh this is over frequency band not
very wide here. 1.5- two GHz. The
top of the Where is the simple? The Die
Paul is the adopted one. So the dotted here
Is the simple dipole that gives you about 2.2 or
around two. Actually, here, it's this is
measured data by the way, is not simulated this
measure. But if you uh if you go to
the if you add the two, the two pens
around it, uh then you can yeah, you
can get of course when you have a simple die
pole, there's no backlog. It's going to be
omni directional, but if you add the defense,
then you're going to have front and back. So
this this is the front um This is the this
is the front. I'm sorry. Yeah, this
is the front simulated. And this is the front
measure. Okay, so you can see that we
have gained about 2-3 d be above. Uh the
simple deport at the same time. The back lobe
, which shows the directive Itty they have directed the
beam is is going to be shown by this here
. Okay, so if you take uh from here
to here, that's the front tobacco issue simulated from
the green to black. That's the front to back
ratio measure. And of course the die paul,
simple dipole doesn't have back. So it is,
it is constant in all directions, but this is
over frequency. Now this is the simulated radiation pattern
. Uh and actually we have measured but we have
measured for this one which is the two fins.
And as you can see, this is the disciple
in this direction and it's more directive here than in
the other direction. And uh in the in the
elevation plane, you still have the same pattern which
is peak and at 90 degrees and zero at 0
180 degrees. This one is the 12th in which
gives you higher again, uh the bandwidth is is
is a good question. But again, like when
you design for simple type all it has certain bandwidth
as well. Okay, another application for the negative
refractive index is going to be in the Rotman lines
and what we have here, we have this is
the, the old rotten ones starting from here and
going to here and then radiating in this direction.
So this is the beam surface, our beam array
and this is the receiving array and this is transmitting
array. If we use negative refractive index material between
these two services as I can show here in this
sketch, then I can actually bring this all the
way to here. And that is going to give
me through the optics of the lens, the same
performance as a lens that has this dimension. So
I'm reducing the size from this dimension to this dimension
here on the sides in order to prevent reflections of
the side of the lens. Usually in rotten lands
, we either put terminations on the side or put
absorbers uh in which both cases you do not,
of course the energy is lost over there. Using
meta material, we can use an ebc structure on
the sides that is going to prevent any surface were
from going there and it's going to be reflected and
add coherently with the radiation that's coming from this direction
here. And that's going to increase the amount of
energy that is transmitting from the beam array to the
to this. Our receiver right here. We haven't
built this one yet because it's going to depend on
using random material here and some fancy E B G
on the sides here. Okay, the next thing
and I have to move faster. The meta services
uh meta services actually is a general word for uh
any surface that gives you something different than the simple
reflection of the ground plane. If you have a
ground plane, you get a reflection of the surface
with 100 and 80 degree phase shift. The signal
going in and coming out has 100 and 80 degree
phase shift. That's why if you have an antenna
and you want the radiation to be strong above the
ground plane. Then you try to put the antenna
quarter wavelength Above the ground plate. So the signal
goes suffers under 80° comes back and then adds coherently
with your radiation. Uh The E. B.
G structure is something that is very thin or the
metal surface in general is service that's very thin and
gives you close to zero degree face reflection when you
get zero face degree his zero degree face reflection.
Then the signal is going to add coherently with very
small distance between the antenna and the surface. And
the meta surface can be uh sort of uh realized
with either high new value with this E. B
. G structure which gives you high impedance. The
structures are sometimes called in addition to metro surface,
high impedance surface or magnetic surface. Perfect magnetic conducting
artificial magnetic conductor AMC R E. B. G
is one of the structures that were devised to do
the same thing and they actually are the ones that
most commonly used. Uh So they are compact in
size and give you this kind of reflection phase versus
frequency. So the reflection phase is centered around zero
and we generally accept plus or minus 90 degree okay
of reflection phase of this service. And one of
the original forms of this CBgb was due to steven
piper out of U. C. L. A
. Back in in the 1999 along with other people
at U C. L. A. And this
is a mushroom structure where you have patches and then
connections to the ground plane like this. And that
does two things gives you the reflection phase that you
want and kills any surface with that propagates here.
So it reduces the mutual coupling between elements and I
can give you some other properties. The meta service
sometime also is used not just to kill the surface
where but to launch leaky way. Okay. And
that's a different structure that can be devised as well
. So this is the effect of the size of
the patches. Okay. And how it changes the
reflection phase profile so that you can shift the frequency
of uh the best performance of the body structure by
controlling the size of the patches. If you put
an antenna above this. And this is an example
by now cano back a few years ago. Uh
This is uh seniors antenna that you put it short
distance above the B. G. And then you
get the high performance. Uh So this is one
form of it, the squares another and there are
lots of lots of forms of E. B.
D. Now, what we did the BBg by
itself is a narrow band. So we decided that
we'd like to have it operating over broadband. So
we did two things again, that's the PhD that
sandy Paretti is doing uh the E B G here
is uh either progressive as you can see here.
We divide the surface into different regions with different dimensions
or we stack layers of E B G on the
top of the other. Uh to give us each
one is going to resonate a certain frequency. These
sketches actually are ugly sketches from the first time.
We envision this thing here, we have much better
uh ideas now than just doing it this way.
But again, they centered on changing the dimensions or
stacking them. And this is the irregular E B
G, the blue one. The red one is
the progressive and you can see you can have much
slower phase slope across frequency. That means that you
can get the pipeline plus or-90° over extremely wideband
ratio of 4-1 or even more than 4-1. This
one for the stack and again, uh this one
actually the red here is the uniform and the blue
is the stacked one. Uh Now the trick here
is how to also do the dB regime and change
the frequency dynamically, make it tunable. Okay.
And I have someone working on this and hopefully we'll
get some interesting designs out of that. Um and
then the student's name is chris Milligan, he is
devising some ways of producing its tunable mbg surface.
And this here is the old idea of using var
actor diodes and the idea here is that you change
the capacitance is and of course the conductance is which
are represented by these guys here are going to stay
fixed but by doing that, you are going to
move the face curve like you see here. So
this way you tune the BBg structure to resonate at
different frequencies. Uh this is another way of doing
it. This is to produce dual band E B
G. Okay, so you can produce again using
some kind of capacitive elements in order to control the
frequencies at which the two residences happened. You can
also use man's in order to do the tuning of
uh the E B. G structure and move the
frequency as you can see here. This is the
, the performance of of the, the structure here
at different frequencies. So you can do the dynamic
changes. Okay, uh I mean dynamically change the
phase to move the frequency of the B. G
. This is the progressive one uh and we got
a little bit smarter here and we still have different
dimensions of the patches that make the E B G
. And we have it on a single height.
Okay, this is still with pins but we can
also do the same thing without pains. We can
realize the capacitance and conductance of the BBg without depends
and this is a theoretical or uh study that we
are actually building this or in the process of building
this. Now we build it with a spiral like
this which we know is very wide band and we
have a very short distance above the structure. The
progressive or the white van de beek structure. Uh
This is the phase difference. Uh The face reflection
difference between uh the uniform which is the blue and
the progressive which is the red. And you can
see the red is shallower or lower in slope than
the blue. That thus it gives us wider bandwidth
. This is the radiation pattern of the different things
with the E. B. G. Or without
it over a very wide frequency band. And we
show that you can indeed get higher gain. Uh
This actually is the return loss showing that the spiral
without anything. And then the spiral with the E
. B. G. Structure uniform and progressive.
And here we should again and the red one which
gives us the highest gain is the one with the
progressive E. B. G. The Blue one
is the spiral in freeze bit. So increase the
gain because of the reflection that the uh is of
the reflected signal of the service that as coherently with
the radiated fields. And also we looked at the
X. R. Issue and it is getting is
giving us good results with that. Uh So the
the spire an antenna with progressive E. B.
G. It gives us higher gain and better both
side axle ratio. And of course you can put
the antenna very short height up of the progressive the
E. B. G structure. So you don't
have high profile and tennis or you're just the size
of it. Uh Now the adaptive meta surface or
adaptive E B. G. Because I can control
now the frequency at and the phase that I can
produce out of the surface. I can use that
as a new uh element in my tool set and
designing cognitive radar because in cognitive radar you would like
to control the reflection and the radar cross section of
the structure that you have so that when someone tries
to detect you or detect your range you can actually
send the wrong signal to the the signal that's coming
to the transmit and transmitter that's coming to you.
So by changing the phase the reflective phase then you
can use that your advantage in the overall process of
designing the cognitive radar Again, because of time I'm
going to go through this very quickly. This is
the concept of the cognitive radar as was published back
in 2006 by Salmon Hagen. Uh This is a
transmitter and then the environment is going to affect the
return and then the cognition here is that you adjust
things in your system based on the reflected signal that's
coming from the effect of the environment. So the
reflection phase is one of the things that you will
be able to control. Uh These are some of
the courts that Hagen had in his uh in his
paper and about how coming to radar can benefit from
playing with the environment so that you can you can
do the environment with the with the information that you
collect from it. The adaptive phase reflection phase is
the main idea that we have here with the with
this kind of service, the metal services. So
it's adaptive lee control the environment and then use the
false target uh information and radar jamming system. So
the idea here is that to produce the wrong information
for the jammers. Uh The idea of this service
can also be used in the digital radio frequency memory
which is there from the RFM which is another thing
that we are interested in in the dano in the
next two minutes. Let me do that very quickly
. We know the carbon nanotubes. They are single
wall multi wall and there are different structures for them
that will make them either conducting or semiconducting depending on
how you arrange this. And this is made out
of graphene rolled into these cylinders here and what we
did, we built patches out of the carbon nanotubes
uh and we looked at the patches, the performance
of them and we use try to use the patch
as gas sensors. Uh So gas sensor because some
of the elements in the patch are going to be
semiconducting and they are going to change residents frequency according
to the gas that's in the immediate neighborhood of the
patch. So we built this patch which is a
patch fed by a slot like this, which we
know and have all the equations. And then this
is the mesh patch that we built out of the
carbon nanotube. So the black one is the conductive
lines and the white ones or the light lines are
the ones using semiconducting carbon nanotubes that are going to
change the frequency according to the gas content. So
this patch can be used for communication through this and
through the gas gas sensor using this. So,
dual use kind of patch. This is the structure
of it. And this is the effect of the
meshing because now we have the patch made out of
um mesh which makes it work differently. This is
the pattern of that measure gas. Here is the
gas sensing that we did uh the analysis by changing
the amount of gas and in this case you are
talking about ammonia, we can change the resonance frequency
of the dielectric patch. Like this. So,
by detecting the frequency or by measuring the frequency,
then we'll know what kind of concentration we have.
This actually we did this uh sort of a little
bit more naively because the numbers we used in the
analysis 1000 up to 10,000 parts per million of ammonia
. That's not realistic number. These amounts are enough
to kill a whole town of course, would like
to detect very, very low level of ammonia.
So we found out that if you add perhaps to
the carbon nanotube, then you can get Responses of
about 50 parts per million or even loss. The
other thing in the patch, it has polarization selectivity
because the patch is made out of lines arranged this
way. So it's going to reduce it better.
If the radiation in the direction of the lines then
it's orthogonal. And we measured the some of the
patches that have different levels of thickness and stuff.
And these are the results for the co and across
performance. Uh So I guess this in conclusion we
have all these are kind of elements in the toolbox
that we can use to improve the antenna, reduce
the size of it, make it low profile and
using it for some applications like sensors and cognitive reader
and lots of others. But the main thing is
reduce the size of the antenna and the profile as
much as you can without affecting the performance of.
Thank you. Yeah. Yeah. Ok. Any
question? I think I used a little bit more
than my time. But if you have any questions
Yes. Gary is the use of synthetic material.
The primary focus of came around. Mhm. In
other words that you've forgotten everything. Yeah. Ordinary
. Yeah. No, no, no, no
, of course not. Well actually, these three
topics I talked about today along with other techniques we
are using to reduce the size of the antenna.
Okay, I can I can talk in detail for
a whole day. Okay. But the other methods
uh for instance, one other thing we are doing
okay, we are building a spherical disciples. They
don't have anything to do with math materials but they
are mainly basically they are depending on trying to have
a very good matching of dai pole made out of
a sphere that is going to give you the same
resonance and the same performance as along with Anton.
Okay, that's that's one thing uh there are lots
of other types of antennas that that that we developed
beside this one. So this is only one sort
of avenue in what we are doing but we have
electrically small antennas Antanas uh um uh This is 44°
in. What is that philadelphia? Okay. Um
the other other antennas of different different kinds, we
do lots of work on things like the rotten lines
and other antennas. But the key thing is the
antennas that are going to be carried on a vehicle
with very low profile and with very high performance.
So that's the one of the main goals that we
that we have. Yeah, other questions. Thank
you. Okay, I'm still not going to answer
this. Mhm. Okay, thank you very much 973 01:06:16.690 --> A:middle L:90% . No