Composite materials

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16 Νοε 2013 (πριν από 3 χρόνια και 11 μήνες)

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PHYSICISTS DEVELOP NEW CLASS OF COMPOSITE MATERIALS

WITH PHYSICAL
PROPERTIES NEVER BEFORE SEEN


1. Minneapolis, MN
-
Physicists at the University of California, San Diego have produced a new class of
composite materials with
unusual

physical properties that
scientists theorized might be possible, but
have never before been able to produce in nature.The remarkable
achievement
, detailed in a paper
that will appear in a forthcoming issue of Physical Review Letters, was announced at a meeting of the
American Phys
ical Society. The UCSD physicists said they expect their discovery to open up a new
subdiscipline within physics and produce an array of commercial applications for this material, on
which the university has applied for a patent.


2.Composite materials lik
e this are built on a totally new concept.


GAP A
-

they obey the laws of
physics, they are predicted to behave totally different from normal materials and should find interesting
applications. The unusual property of this new class of materials is esse
ntially its ability to reverse
many of the physical properties that govern the behavior of ordinary materials. One such property is
the Doppler effect, which makes a train whistle sound higher in pitch as it approaches and lower in
pitch as it recedes. Acc
ording to Maxwell's equations, which describe the relationship between
magnetic and electric fields, microwave radiation or light would show the opposite effect in this new
class of materials, shifting to lower frequencies as a source approaches and to hig
her frequencies as it
recedes.


3.


GAP B
-

, Maxwell's equations further suggest that lenses that would normally disperse
electromagnetic radiation would instead focus it within this composite material. This is because Snell's
law, which describes the an
gle of refraction caused by the change in velocity of light and other waves
through lenses, water and other types of ordinary material, is expected to be exactly opposite within
this composite.


4. If these effects turn out to be possible at optical freque
ncies, this material would have the crazy
property that a flashlight shining on a slab can
focus

the light at a point on the other side. There's no
way you can do that with just a sheet of ordinary material. Interestingly, the development of this new
class

of materials is entirely consistent with the laws of physics and was predicted as a possibility in
1968 by a Russian theorist, V.G. Veselago, but until now no one had the material, so it couldn't be
verified."


5. Underlying the reversal of the Doppler ef
fect, Snell's law, and Cerenkov radiation (radiation by
charged particles moving through a medium) is that this new material exhibits a reversal of one of the
"right
-
hand rules" of physics which describe a relationship between the electric and magnetic fie
lds
and the direction of their wave velocity.


6. The new materials are known by the UCSD team colloquially as "left
-
handed materials," after a term
coined by Veselago, because they reverse this relationship. What that means is physically
counterintuitive
-

pulses of electromagnetic radiation moving through the material in one direction are
composed of constituent waves moving in the opposite direction.


7. The UCSD physicists emphasized that while they believe their new class of composites will be
shown to

reverse Snell's law, the specific composite they produced will not do so at visible
-
light
frequencies.


GAP C
-
, it is now limited to transmitting microwave radiation at frequencies of 4 to 7
Gigahertz
-
a range somewhere between the operation of household

microwave ovens (3.3 Gigahertz)
and military radars (10 Gigahertz).


8.


GAP D
-

, the UCSD team will soon be attempting to verify that a composite constructed on similar
principles will be able to focus and disperse microwaves in exactly the opposite man
ner as normal
lenses. They did not do this experiment yet. But this is what the equations predict. Physicists will
understand that if the data presented in the UCSD team’s paper are correct, given Maxwell's
equations, then this will be the result."


9. The

composite constructed by the UCSD team was produced from a series of thin copper rings and
ordinary copper
wire

strung parallel to the rings. It is an example of a new class of materials scientists
call "metamaterials."
-

GAP E
-

it is composed of only c
opper wires and copper rings, the arrangement
has an effective magnetic response to microwaves that has never been demonstrated before.


10. The idea for the new composite came from David R. Smith, building on the work of John Pendry of
Imperial College, L
ondon. In 1996, Pendry described a way of using ordinary copper wires to create a
material with the property physicists call "negative electric permittivity." Electric permittivity
-
often
referred to as the "dielectric constant"
-
is the response of a materia
l to electromagnetic radiation. When
you take a material like plastic, glass or sapphire and you shine microwaves onto it, you can
characterize how the microwaves going through it will behave by a parameter called electric
permittivity. Most known material
s in nature have a positive electric permittivity. Pendry also recently
suggested a way of using copper rings to make a material with negative magnetic permeability at
microwave frequencies. Just about all of the magnetic materials in nature, those that
re
spond

to
magnetic rather than electric fields, have what physicists call a "positive magnetic permeability."


11. What's unusual about the new class of materials produced by the UCSD team is that it
simultaneously has a negative electric permittivity and a

negative magnetic permeability, a
combination of properties never before seen in a natural or man
-
made material. And the interesting
thing is that it's produced with no magnetic material. It's all done with copper.


12. The bottom line is that this materi
al
-

this metamaterial, at frequencies where both the permittivity
and permeability are negative, behaves according to a left
-
handed rule, rather than a right
-
handed
rule."



I. Decide which of the linking words below best fits the gaps of the text.


1.

GAP A



1)

While

2)

Unless

3)

However

4)

Despite

5)

Actually


2.

GAP B


1)

Similarly

2)

Because

3)

Inversely

4)

As

5)

Although


3.

GAP C


1)

Nevertheless

2)

Instead

3)

Likewise

4)

In addition

5)

As a result


4.

GAP D


1)

Last year

2)

Despite

3)

As explained above

4)

However

5)

Although


5.

GAP E


1)

However

2)

Accordingly

3)

Today

4)

Even thou
gh

5)

Unless



II. Decide which of the following best correspond to the ideas of the text


6.

The new class of composite metamaterials produced at the University of California, San Diego …


1)

do not follow any of the rules of physics whatsoever.

2)

have negative elec
tric permittivity and magnetic permeability.

3)

exhibit an extremely rare combination of properties only seen in some man
-
made materials at high
frequencies.

4)

have properties no physicists had ever bargained to see in materials.

5)

None of the above.


7.

The new cl
ass of composite materials …


1)

has largely inconsistent and completely unpredictable behaviour.

2)

exhibits a reversal of some of the laws of physics colloquially dubbed «

right
-
hand laws

».

3)

will force physicists to revise some of the basic laws of physics as
they fail to apply.

4)

was already developed by V. G. Veselago in the 1960s.

5)

None of the above.


8.

The new composite materials with reversed physical properties …


1)

go against all expectations.

2)

disprove every single law of conventional physics.

3)

were predicted by

Snell’s law and Maxwell’s equations.

4)

are being tested in series of USDC patented applications.

5)

None of the above.


9.

As can be inferred from the text, in so
-
called left
-
handed materials …


1)

electromagnetic radiation is due to particles moving through the me
dium from left to right.

2)

electromagnetic radiation taking place in one direction is caused by particles moving in the
opposite.

3)

electromagnetic radiation is unlikely to involve both magnitude and direction.

4)

electromagnetic radiation is only determined by i
ts direction.

5)

None of the above.


10.

The UCSD team leaders hope that the new class of composite materials will ….


1)

find scores of highly profitable applications.

2)

rec
ei
ve a patent.

3)

serve to develop more composites.

4)

open up new prospects for a new discipline t
hat will rival with


and perhaps replace

-

traditional
physics.

5)

All of the above.


11.

Due to the Doppler effect, …


1)

the further a train is the higher in pitch its whistle sounds.

2)

the sound of a train whistle becomes higher and higher in pitch as the train mo
ves away from the
listener.

3)

the closer the train is to a listener, the higher the pitch of its whistle.

4)

the closer a train approaches, the louder the sound of its whistle.

5)

None of the above.


12.

The reversal of Snell’s law characteristic of left
-
handed compos
ite materials …


1)

has been shown to occur all the time.

2)

has already been proved to occur at specific frequencies.

3)

can only be tested in microwave ovens.

4)

will be shown to occur but not at visible
-
light frequencies.

5)

None of the above.


13.

UCSD physicists hope ….


1)

to be able to construct microwave ovens operating at higher frequencies.

2)

to develop composites that will disprove Maxwell’s equations.

3)

to be able to show that Maxwell’s equations were correct.

4)

to demonstrate that new composites able to transmit microwave

radiation like glass can be
produced.

5)

None of the above.



III. Decide whether the following statements are True or False


14.

UCSD physicists have already conducted laboratory experiments showing that the new
composites are able to focus and disperse microwa
ves
exactly
as
conventional
lenses do.

15.

The UCSD team is working on composite lenses that would focus and disperse light in the
opposite way.

16.

Most natural and man
-
made materials known today have positive electric permittivity and
magnetic permeability.

17.

Unli
ke most known materials, the new composites produced by the UCSD team have negative
electric permittivity and positive magnetic permeability.

18.

The new metamaterials mentioned in the text are made up of rings and wires of magnetic copper.

19.

The starting point
of the UCSD team’s research on these new composites was the work of a
British physicist who showed how to use copper to create a material exhibiting negative electric
permittivity.

20.

Although V.G. Veselago theorized that it might be possible to develop a new

class of materials
with completely different physical properties, he failed to produce any of them.



IV. Find synonyms for the words below (underlined in the text)


21.

unusual


1) abnormal 2) uncommon 3) unwelcome 4)
customized

5)
dependa
ble



22.

achievement


1) breakthrough 2) research 3) property 4)
resilience

5)
requirement



23.

focus


1) disperse 2)
bring about

3) converge 4)
display

5)
distort


24.

wire


1) stud 2) beam 3)

girder 4) notch 5) thread


25)
respond


1) answer 2) respect 3) reply 4) react 5) behave



KEY


1)

1

2)

1

3)

2

4)

4

5)

4

6)

2

7)

2

8)

5

9)

2

10)

1

11)

3

12)

4

13)

5

14)

2

15)

2

16)

1

17)

2

18)

2

19)

1

20)

1

21)

2

22)

1

23)

3

24)

5

25)

4