U.S. patent application number 12/112779 was filed with the patent office on 2012-09-27 for meta materials integration, detection and spectral analysis.
This patent application is currently assigned to SECURITY LOGIC AG. Invention is credited to Noel Axelrod, Amir Lichtenstein, Eran Ofek.
Application Number | 20120241616 12/112779 |
Document ID | / |
Family ID | 46800696 |
Filed Date | 2012-09-27 |
United States Patent
Application |
20120241616 |
Kind Code |
A1 |
Axelrod; Noel ; et
al. |
September 27, 2012 |
META MATERIALS INTEGRATION, DETECTION AND SPECTRAL ANALYSIS
Abstract
A detector and modulator of electromagnetic radiation is
3-dimensional structure made of substantially 2 dimensional high
impedance metamaterial surfaces stacked one above the other with a
dielectric layer in between and located above a conducting ground
plane. Each 2 dimension surface may be formed by an open continuous
conductive trace, such as metallic wire or a printed circuit line,
which is cast or plated on or into a 2-D periodic arrangement of an
element that belongs to the Hilbert space filling curves.
Inventors: |
Axelrod; Noel; (Jerusalem,
IL) ; Lichtenstein; Amir; (Tel Aviv, IL) ;
Ofek; Eran; (Modi'in, IL) |
Assignee: |
SECURITY LOGIC AG
Zug
CH
|
Family ID: |
46800696 |
Appl. No.: |
12/112779 |
Filed: |
April 30, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60914787 |
Apr 30, 2007 |
|
|
|
60914798 |
Apr 30, 2007 |
|
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Current U.S.
Class: |
250/336.1 |
Current CPC
Class: |
H01Q 15/0086
20130101 |
Class at
Publication: |
250/336.1 |
International
Class: |
G01J 1/42 20060101
G01J001/42 |
Claims
1-4. (canceled)
5. A circuit for detecting electromagnetic radiation which
comprises: a) A detector comprising a continuous conductive 2-D
Hilbert space filling curve having at least a first and second
terminal for receiving electromagnetic radiation of a predetermined
first frequency, b) a ground plane separated from the detector by a
dielectric layer, the ground plane being connected to at least one
terminal of said detector, c) a mixer having at least two input
terminals and an output terminal, at least one input terminal
connected to the other terminal of the detector not connected to
said ground plane of said detector, said mixer being further in
signal communication with d) a local oscillator having an output
connected to the other input of said mixer, e) a low pass filter
connected to the output terminal of said mixer, wherein said local
oscillator operative to be tuned to a frequency (f.sub.o) which is
close to the first frequency of the detector, whereby the output
from the circuit includes a power spectrum of signal and phase
information about the electromagnetic radiation received at said
detector.
6. A circuit for detecting electromagnetic radiation according to
claim 5 and further comprising an amplifier connected to receive
and amplify the output of said low pass filter.
7. A circuit for detecting electromagnetic radiation according to
claim 5 wherein said dielectric layer is air.
8. A circuit for detecting electromagnetic radiation according to
claim 5 wherein the continuous conductive 2-D Hilbert space filling
curve is at least one of a Peano curve and a Z-curve.
9-12. (canceled)
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims priority to the U.S.
provisional patent applications having application Ser. Nos.
60/914,787 (for "Meta Materials Based Phase Discrimination
Analysis") and 60/914,798 (for "Pulse Compression and Expansion In
Meta Materials"), both of which were filed on Apr. 30, 2007, and
are now both incorporated herein by reference.
BACKGROUND OF INVENTION
[0002] This invention relates generally to the fields of
metamaterials, spectral analysis and electromagnetic radiation
detection, and more specifically to the use of metamaterials for
the detection and spectral analysis of electromagnetic
radiation.
[0003] Another aspect of the invention relates generally to the
fields of metamaterials and wave analysis, and more specifically to
phase discrimination analysis on a monochromatic waveform utilizing
metamaterials.
[0004] Still a further aspect of the invention relates generally to
the fields of metamaterials and wave analysis, and more
specifically to expanding or compressing electromagnetic radiation
pulses using metamaterials.
[0005] An integral part of systems in the area of both material
detection and "see through walls" systems, as well as other systems
used for detection, are the detector elements. In different
embodiments of these systems, the detector elements can have
differing requirements. Some of the requirements can include the
following.
[0006] Operating in the gigahertz to terahertz (GHz-THz) frequency
ranges.
[0007] Performing processing on the detected information in the
GHz-THz frequency ranges (In current systems it is extremely
difficult to perform processing in the GHz-THz frequency ranges due
to computational power limitations. Current methods for
auto-correlation analysis were shown to be efficient at frequencies
of up to 20-30GHz.)
[0008] Having a small enough size to be portable. This can allow a
system that includes the detector elements to be installed in the
field with relative ease.
[0009] Sensitivity is another important aspect of the detector
requirements. The detector elements may have requirements to be
sensitive enough to detect even low-energy signals which are of
interest to the overall system.
[0010] Accordingly, at least some of the objections of the present
invention are to overcome the deficiencies and limitations in the
prior art noted above.
SUMMARY OF INVENTION
[0011] In one embodiment of the invention a detector for
electromagnetic radiation, comprises a plurality of metamaterials
layers for receiving electromagnetic radiation of a predetermined
frequency,a dielectric layer separating each meta-material layer, a
ground plane separated from at least one of the metamaterial layers
by another dielectric layer, wherein the metamaterial is a
continuous conductive 2-D Hilbert space filling curve having at
least two terminals.
[0012] In another embodiment a circuit for detecting
electromagnetic radiation comprises; a detector comprising a
continuous conductive 2-D Hilbert space filling curve having at
least a first and second for receiving electromagnetic radiation of
a predetermined first frequency, as well as a ground plane
separated from the detector plane layers by a dielectric layer, the
ground plane being connected to at least one terminal of said
detector, a dielectric layer separating each meta-material layer, a
mixer having at least two input terminals and an output terminal,
at least one input terminal connected to with another terminal of
the detector not connected to said ground plane of said detector,
said mixer being further in signal communication with a local
oscillator having an output connected to the other input of said
mixer, a low pass filter connected at an input terminal to the
output terminal of said mixer, wherein said local oscillator
operative to be tuned to a frequency (f o) which is close to the
first frequency of the detector, whereby the output from the
circuit includes the power spectrum of the signal and phase
information about the electromagnetic radiation received at said
detector, and preferably includes an amplifier connected to receive
and amplify the output of said low pass filter.
[0013] In a still further embodiment of the invention there is
provided a method of pulse width modulation of electromagnetic
radiation comprising providing a composition of matter comprising;
plurality of metamaterials layers, each layer for receiving
electromagnetic radiation of a predetermined frequency, a
dielectric layer separating each meta-material layer, wherein the
metamaterial is a continuous conductive 2-D Hilbert space filling
curve having at least two terminals, and then exposing the
composition of matter to an electromagnetic signal to be modulated
followed by acquiring the electromagnetic radiation signal after at
least one of transmission, absorption or reflection by the
composition of matter.
[0014] The above and other objects, effects, features, and
advantages of the present invention will become more apparent from
the following description of the embodiments thereof taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] Aspects of the present invention are more particularly
described below with reference to the following figures, which
illustrate exemplary embodiments of the present invention.
[0016] Figure A-C is an illustrate an embodiment of Peano space
filling curves at three different scales;
[0017] FIG. 2 is an illustration of another embodiment of space
filling Z curves at four different scales;
[0018] FIG. 3A is an exploded perspective view of an embodiment of
a detector using three Peano layers or slices of increasing
iteration order; while FIG. 3B is a cross-sectional elevation of
the detector
[0019] FIG. 4 is an illustration of an embodiment of an analysis
circuit for each detector slice.
[0020] FIG. 5 illustrates a chirp-down linear frequency modulated
waveform;
[0021] FIG. 6 illustrates a chirp-up linear frequency modulated
waveform; and
[0022] FIGS. 7A and 7B illustrate the magnitude and phase of the
reflection coefficient from a Peano surface above a conducting
ground plane.
DETAILED DESCRIPTION
[0023] Referring to FIGS. 1 through 7, wherein like reference
numerals refer to like components in the various views, there is
illustrated therein a new and improved Meta Materials Integration,
Detection and Spectral Analysis, generally denominated 100
herein.
[0024] Metamaterials are basic materials with artificial molecular
structure, designed to intentionally alter the basic material
properties including the electromagnetic properties of the
material. Some examples of metamaterials are terahertz (THz) and
optical-magnetic structures, as well as lenses for microwave
frequencies with a shorter focal length than conventional lenses
but having the same radius of curvature.
[0025] The following publications are incorporated herein by
reference: 1. Yen T. J. et al., "Terahertz Magnetic Response from
Artificial Materials," Science, 2004, vol. 303, pp. 1494-1496; 2.
Grigorenko A. N et al., "Nanofabricated Media with Negative
Permeability at Visible Frequencies," Nature, 2005, vol. 438, pp.
335-338; 3. Parrazoli e. G., et al., "Performance of a Negative
Index of refraction Lens," Applied Physics Letters, Am. lost. of
Physics, 2004, vol. 84, no. 17, pp. 3232-3234; 4. Notomi M.,
"Theory of Light Propagation in Strongly Modulated Photonic
Crystals," Physical Rev. B, Am. Physical Soc., 2000, vol. 62, no.
16, pp. 10 696-10 705; 5. Eleftheriades G. V., et al., "Planar
Negative Refractive Index Media Using Periodically L-C Loaded
Transmission Lines," IEEE Trans. Microwave Theory & Techniques,
2002, vol. 50, no. 12, pp. 2702-2712; 6. Alu A. and Engheta N.,
"Optical Nanotransmission Lines," 1. Opt. Soc. Am. B, 2006, vol.
23, no. 3, pp. 571-583; 7. Zhu J, et al., "Peano Antennas," IEEE
Antennas & Wireless Propag. Letters, 2004, vol. 3, pp. 71-74.
8. P. Vodo et al., "Microwave photonic crystal with tailor-made
negative refractive index," Applied Physics Letters, Vol. 85,
Number 10, 6 Sep. 2004; and. 9. Moussa, S. Foteinopoulou, C. M.
Soukoulis, "Delay-time investigation of electromagnetic waves
through homogenous medium and photonic crystal left handed
materials," Applied Physics Letters, Vol. 85, Number 7, 16 Aug.
2004.
[0026] Metamaterials are formed from repeating structural elements
known to have strong response to electromagnetic fields. So long as
the size and the spacing of the elements are much smaller than the
electromagnetic radiation of interest, the incident radiation
cannot distinguish between features and treats the material as a
homogeneous composite. There are several approaches to obtain
metamaterials, including photonic crystals, split ring resonators,
transmission lines and their optical analogs.
[0027] Herein we describe a first embodiment of the invention as a
3-dimensional structure made of high impedance metamaterial
surfaces stacked one above the other with a dielectric layer (such
as air for example) in between and located above a conducting
ground plane. Each surface is formed by an open continuous
conductive trace, such as metallic wire or a printed circuit line,
which is cast or plated on or into a 2-D periodic arrangement of an
element that belongs to the Hilbert space filling curves. The
repeating arrangement may be a Peano-Gosper curve (shown in FIG.
1), a Z-curve (shown in FIG. 2), or similar periodic arrangement.
As the iteration order of the curve increases, the step order
increases for the iterative filling of the 2-dimensional region.
FIG. 1 shows the Peano-Gosper curve at three different iteration
orders. FIG. 2 shows the Z-curve at four different iteration
orders.
[0028] The curves pass through every point in the two dimensional
space in which they are contained, without intersecting themselves.
Physically this means that more "lines" can be compacted into the
same surface area. From an electromagnetic point of view, these
curves provide resonant structures of a very small footprint.
Though small in its footprint, the structure can resonate at a
wavelength much longer than its footprint. The following discussion
will look at an embodiment using the Peano-Gosper curves, but
similar periodic arrangements, including those discussed above, can
be used.
[0029] When a Peano-Gosper high impedance surface made of thin
metallic wire is placed in free space and is excited by normally
incident electromagnetic radiation of varying frequencies, current
is induced which reaches resonance on some frequencies. When the
maximum value of the current is evaluated as a function of the
excitation frequency, it is found that as the iteration order
increases the resonance frequency decreases, meaning the electrical
footprint of the surface changes according to its space filling
arrangement.
[0030] Stacking surfaces of increasing order one beneath the other
creates a structure that selects a very narrow bandwidth and
resonates to it while being of a dimension smaller then the
wavelength, thus overcoming the photonic crystals main
disadvantage. An arrangement comprising multiple layers of Peano
curves can be used.
[0031] The following section describes the structure, composition
and operational principle of this metamaterial as a detector.
According to Mc-Vay et. al., these space filling curves have a
specific response in the gigahertz (GHz) frequency range. This
structure allows us to obtain a specific response with a single
frequency of the incoming electromagnetic radiation while the other
components of the electromagnetic radiation pass through this
structure without any interaction (no absorption etc). The
interaction of electromagnetic waves with the conducting Peano
curves induces electrical currents that could be easily
measured.
[0032] The Peano curves are usually comprised of wires in specific
patterns. The following calculations will help describe the
operational principle in more detail. The power spectrum P(.omega.)
is related to the signal waveform s(t) as follows:
P ( .omega. ) = .intg. - .infin. .infin. s ( t ) - .omega. t t 2 (
1 ) ##EQU00001##
[0033] Assuming a 100% conversion of electromagnetic energy into
electrical current at the resonance frequency, the current power in
watts can be calculated from the following equation:
P(f.sub.0).DELTA.f (2)
[0034] where f.sub.o is the resonant frequency and .DELTA.f is the
difference in the width of the resonance curve. If R is the entire
electrical resistance of the entire structure, then the amplitude
of the current could be calculated from the following equation:
I 2 2 R = P ( f 0 ) .DELTA. f ( 3 ) ##EQU00002##
[0035] When changing the scale of the structure (i.e. keeping the
same layout of the original structure, but changing the size of the
elements respectively), we are also changing the resonance
frequency of the structure.
[0036] To perform a spectral analysis on an incoming waveform, the
bandwidth B of the signal can be divided into separate frequency
slices. The number of frequency slices N can be chosen to be:
N = B .DELTA. f ( 4 ) ##EQU00003##
[0037] When taking N layers of Peano curves, where each layer has a
different iteration order or scale which matches a specific
frequency, this structure can fill the signal bandwidth where each
layer corresponds to a specific frequency slice.
[0038] At each specific layer, there is an interaction with the
electromagnetic radiation only at the resonant frequency of that
specific layer. Also, there is no interaction between other
frequency components of the electromagnetic radiation and that
specific layer. This type of metamaterial is completely absorbent
for specific frequencies and completely transparent to others.
[0039] The detector can be arranged as multi-layered Peano curves,
where the distance between each layer should be enough to prevent
current induction between each separate layer. FIG. 3 illustrates a
possible arrangement for the detector. FIG. 3 shows a detector with
three layers, but it should be noted that embodiments can contain
many more layers depending on the amount of slices desired and also
depending on the bandwidth. Each layer has two terminals at
opposite ends, each representing a different electrical pole.
[0040] Each layer has a different iteration order or scale, but the
total physical size of each layer is substantially the same. The
layers of the detector can be stacked from highest to lowest order
iteration or lowest to highest order iteration depending on the
application for the detector. Each layer has resonance at the
frequency of the incoming radiation.
[0041] Each slice of the detector is connected to a circuit that
enables the measurement of both signal amplitude and phase. FIG. 4
illustrates an embodiment of a circuit 40. The circuit 40 includes
one of the metamaterial slices 42, a mixer 44, a local oscillator
46, a low pass filter (LPF) 48 and an amplifier 50. Each
metamaterial slice 42 has two terminals, one is connected to ground
and the other is connected to the mixer 44 for that slice. The
metamaterial slice 42 can be a Peano curve (shown in Figure I), a
Z-curve (shown in FIG. 2), or similar periodic arrangement.
[0042] The circuit illustrated in FIG. 4 obtains the signal (f 1)
from the metamaterial slice 42, and this signal is fed into the
mixer 44 which has another input connected to the local oscillator
46. The local oscillator 46 is tuned to a frequency (f o) which is
close to the frequency of interest (the frequency to which the
metamaterial slice 42 reacts). The output of the mixer 44 is the
combination of both frequencies, which is fed into the low pass
filter 48.
[0043] If the difference between the frequencies is small enough
(i.e. the frequencies are close to one another) then the frequency
difference is the output of the LPF 48 which is then fed into the
amplifier 50 for future processing. The output from the circuit
includes the power spectrum of the signal and phase information
about the signal. The output from a circuit is the amplitude and
phase of the signal at the resonance frequency of the circuit. The
output from all of the circuits covering a bandwidth B from the
start frequency f.sub.1 to the end frequency f.sub.2 will
constitute the power spectrum of the signal.
[0044] The output of the detector is the power spectrum of the
incoming pulse. The sensitivity of the detector will be determined
by several factors, for example:
[0045] Impedance of the metamaterial "slice";
[0046] Electrical resistance of the structure; and
[0047] Resonance width.
[0048] The detector described above can provide a solution for
detection and analysis in the Terahertz range, since currently, THz
detectors either require cryogenic temperatures (which increase the
cost, complexity and limits possible uses for the detector) or are
based on an electro-optic effect which is much less efficient. This
detector is much smaller, can operate in room temperature and is
therefore much less expensive and much easier to maintain and
operate than present day THz detectors. These factors, coupled with
the fact that it does not require the electro-optic effect, makes
this detector a solution for THz detection. This detector is much
smaller, can operate in room temperature and is therefore much less
expensive and much easier to maintain and operate than present day
THz detectors. These factors, coupled with the fact that it does
not require the electro-optic effect, makes this detector a
solution for THz detection.
[0049] In an analogous manner to equation 1, The electromagnetic
density of the incoming signal at the detector is given by:
S ( .omega. ) = 1 2 Y E ( .omega. ) 2 ( 5 ) ##EQU00004##
[0050] where Y is the free space impedance of approximately 3770.
and E(.omega.) are the Fourier components of the incoming signal.
Assuming a 100% conversion of electromagnetic energy into
electrical current at the resonance frequency, the current power in
watts can be calculated from the following equation, which is a
modified form of equation 2 above:
P=AS(f.sub.0).DELTA.f (6)
[0051] where A is the Peano curve footprint (area), f.sub.0 is the
resonant frequency and .DELTA.f is the width of the resonance
curve. If R is the entire electrical resistance of the entire
structure, then the amplitude of the current could be calculated
from the following equation (which is a modified form of equation 3
above):
I 2 2 R = AP ( f 0 ) .DELTA. f ( 7 ) ##EQU00005##
[0052] When changing the scale of the structure (i.e. keeping the
same layout of the original structure, but changing the size of the
elements respectively), we are also changing the resonance
frequency of the structure.
[0053] The proposed method enables an analysis of the spectrum
component of the signal without a digital FFT implementation. This
ability can be helpful for high-frequency RF signals in the
hundreds of MHz frequency range and up to the THz frequency
range.
[0054] Metamaterial based structures such as those described above
can be used in a method of wave phase discrimination to enable
analysis of monochromatic waves (single frequency waveforms). By
obtaining a signal and various time-delayed replicas of this same
signal, phase decomposition of the signal can be derived.
Metamaterial organized in multilayered grids, such as the multiple
layer Peano-Gosper curves shown in FIG. 3, can be used as
three-dimensional receptors for wave discrimination. FIG. 3 shows
three layers, but it should be noted that embodiments can contain
many more layers depending on the amount of slices desired. Each
layer has a different iteration order or scale, but the total
physical size of each layer is substantially the same. The multiple
layers are positioned at various depths in order to absorb specific
phases of the incoming signal.
[0055] Successive layers of the three-dimensional receptors are
graduated to permit variable depth-of-interception of the incoming
waves, allowing discrimination between concurrently received,
varying wavelengths. Absorbed energy levels vary according to the
depth at which the waves are intercepted by the metamaterial
structure, thus exposing the wave frequency and phase shift. This
is enabled by the graduated distance between layers of the three
dimensional structure of the metamaterial receptor grid.
[0056] The wave phase interception delay can be calculated from the
following equation:
.DELTA..PHI. = 2 .pi. f c d ( 8 ) ##EQU00006##
[0057] where f is the frequency of the incoming wave, d is the
depth of the slice from the front surface of the device and c is
the speed of light. This structure can be used for signal
auto-correlation analysis where the original signal and the delayed
replica of the signal are needed.
[0058] In another aspect of the invention, Metamaterial based
structures can be used for pulse width manipulation, i.e. to widen
or shorten the width of a specific incoming or outgoing pulse from
a device. This can be done as part of a detector or part of a
transmitter.
[0059] Meta Materials experience a strong dispersion effect near
the absorption bands. FIG. 7 describes changes in the reflection
coefficient as a function of the frequency. From the figure, it can
be seen that at a frequency 0.65 GHz there is a change in the
magnitude of the reflection coefficient which will therefore cause
a strong dispersion effect to the signal.
[0060] Pulse compression is defined as changing the width of a
pulse. Metamaterials, such as Peano curves, can be used for
expanding or compressing electromagnetic radiation pulses. This
idea is based on the fact that metamaterials have a property of
being highly dispersed, i.e. the group velocity of the wave depends
on the frequency. The dispersion coefficient is defined as:
D v = v ( 1 v ) ##EQU00007##
[0061] where .nu. is the group velocity. The dispersion
coefficient, D.sub..nu.' is a measure of pulse time broadening per
unit spectral width per unit propagation distance (s/m*Hz). If
D.sub..nu.>0, these materials are considered as normal
dispersive materials. In the opposite case, where D.sub..nu.<0,
these materials are considered as anomalous dispersive
materials.
[0062] In normal dispersive materials, the travel time for the
higher frequency components is longer than the travel time of the
lower frequency components. In anomalous dispersive materials, this
behavior is opposite, the higher frequency components have a
shorter travel time and the lower frequency components have a
longer travel time.
[0063] Metamaterials, such as Peano curves, exhibit both normal and
anomalous dispersion, depending on the frequency band. By
manipulating the order of the Peano curves, we build a three
dimensional structure which operates as a medium which will provide
the desired dispersion coefficient. The desired dispersion
coefficient is a function of the relevant frequency band, the
material from which the Peano curves are comprised of, and the
dimensions of the structure. In the relevant frequency band, it is
desired that the dispersion coefficient will be a negative or
positive constant.
[0064] The following example utilizes this proposed structure and
concept for pulse compression of the signal. The incoming signal is
a linear frequency modulated signal which is widely used in the
field of RF (radiofrequency) communications. Frequency and phase
modulated waveforms are used to achieve much wider operating
bandwidth.
[0065] Linear Frequency Modulation CLFM) is commonly used in radar
detection. In this case, the frequency is swept linearly across the
pulse-width, either upward or downward. The signal bandwidth is
proportional to the sweep bandwidth, and is independent on the
pulse-width. The pulse-width is T and the bandwidth B.
[0066] The LFM up-chirp instantaneous phase can be expressed
by:
.psi. ( t ) = 2 .pi. ( f 0 t + .mu. 2 t 2 ) - T 2 .ltoreq. t
.ltoreq. T 2 ( 9 ) ##EQU00008##
[0067] where fo is the transmitter antenna center frequency, and
.mu.=B/T is the LFM coefficient. Thus, the instantaneous frequency
is
f ( t ) = 1 2 .pi. .differential. .differential. t .psi. ( t ) = f
0 + .mu. t - T 2 .ltoreq. t .ltoreq. T 2 ( 10 ) ##EQU00009##
[0068] An example of compressing an incoming pulse is given for the
chirp-down linear frequency modulated waveform illustrated in FIG.
5, and the chirp-up linear frequency modulated waveform illustrated
in FIG. 6.
[0069] When a chirp-down LFM signal, illustrated in FIG. 5, enters
into a normal dispersive medium, the high frequency components of
the signal, which are at the "beginning" of the signal, propagate
within the medium at a much slower rate than the lower frequency
components. The dispersion coefficient of the material could be
chosen in such a manner, that the time delay of the signal between
the highest and lowest frequencies will be substantially equal to
the pulse width. In such a case, all of the signal frequencies exit
the metamaterial at approximately the same time and the pulse
duration is very close to 0 (in the Pico-second range)--i.e. a very
short pulse.
[0070] In the opposite case, where a chirp-up LFM signal,
illustrated in FIG. 6, enters into an anomalous dispersive medium,
the low frequency components of the signal, which are at the
"beginning" of the signal, propagate within the medium at a much
slower rate than the higher frequency components. The dispersion
coefficient of the material can be chosen in such a manner that the
time delay of the signal between the lowest and the highest
frequencies is substantially equal to the pulse width. In such a
case, all of the signal frequencies exit the metamaterial at
approximately the same time and the pulse duration is very short
pulse (similar to the above case, in the Pico-second range).
[0071] The opposite is also true, a short pulse can be expanded.
When a short pulse enters into a normal dispersive medium, the low
frequency components of the signal propagate at a much faster rate
within the medium than the higher frequency components; which forms
a signal similar to a chirp-down LFM signal (FIG. 5), and
effectively widens the pulse.
[0072] When a short pulse enters into an anomalous dispersive
medium, the high frequency components of the signal propagate at a
much faster rate within the medium than the lower frequency
components, which forms a signal similar to a chirp-up LFM signal
(FIG. 6), again, effectively widening the pulse (assuming that the
dispersive coefficient is constant).
[0073] An example includes an embodiment used in a system for
sending and/or receiving very narrow pulses (at the pico-second
range). The system could use a regular transmitter which transmits
much wider pulses than desired, enabling use of a standard
inexpensive transmitter. Either at the transmitter end, or at the
detector, the system could utilize an embodiment of the present
invention to narrow the pulse to the desired pulse width. The
energy of the signal remains the same. However, the power of the
signal, which is the energy divided by the width of the signal, can
become much higher than that of the original signal
[0074] Exemplary embodiments of the present invention have been
shown by way of example in the drawings and are herein described in
detail; however the present invention is susceptible to various
modifications and alternative forms. It should be understood that
there is no intent to limit the system to the particular forms
disclosed, but on the contrary, the intention is to address all
modifications, equivalents, and alternatives falling within the
spirit and scope of the system as defined herein that would occur
to one skilled in the art.
[0075] Exemplary embodiments of the present invention have been
shown by way of example in the drawings and are herein described in
detail; however the present invention is susceptible to various
modifications and alternative forms. It should be understood that
there is no intent to limit the system to the particular forms
disclosed, but on the contrary, the intention is to address all
modifications, equivalents, and alternatives falling within the
spirit and scope of the system as defined herein that would occur
to one skilled in the art.
[0076] While the invention has been described in connection with a
preferred embodiment, it is not intended to limit the scope of the
invention to the particular form set forth, but on the contrary, it
is intended to cover such alternatives, modifications, and
equivalents as may be within the spirit and scope of the invention
as defined by the appended claims.
* * * * *