U.S. patent application number 10/842880 was filed with the patent office on 2006-05-11 for method and apparatus for echolocation.
Invention is credited to Robert Hickling.
Application Number | 20060098533 10/842880 |
Document ID | / |
Family ID | 36316181 |
Filed Date | 2006-05-11 |
United States Patent
Application |
20060098533 |
Kind Code |
A1 |
Hickling; Robert |
May 11, 2006 |
METHOD AND APPARATUS FOR ECHOLOCATION
Abstract
Method and apparatus for application of echolocation to robot
guidance and assisting the blind. The method is based on the
echolocation of bats. It combines a source of pulsed ultrasound
(100) with a recently-developed acoustic vector probe (AVP) (200)
into an echolocation instrument (1000), together with a
data-acquisition system (300), a digital signal processor (400) and
an output device (500). The source emits pulses of ultrasound of
about 35 kHz over a beam angle of approximately 100 degrees and the
AVP detects backscattered pulses from a discrete distribution of
acoustic highlights on surrounding objects. The ultrasonic sound
pressures of the backscattered pulses are heterodyned down to lower
frequencies so that the signal processor can make an accurate
determination of the sound-intensity vector for each pulse. The
sound-intensity vector points in the direction of the highlight
from which the backscattered pulse originates while the round-trip
time of flight of the pulse determines the distance to the
highlight. In this way the positions of the highlights on
surrounding objects can be determined. The distribution of such
highlights changes when the echolocation instrument moves relative
to surrounding objects, generating a sequence of highlight
distributions that can be stored in the memory of the processor and
combined to provide a more complete representation of surrounding
objects.
Inventors: |
Hickling; Robert;
(Huntington Woods, MI) |
Correspondence
Address: |
REISING, ETHINGTON, BARNES, KISSELLE, P.C.
P O BOX 4390
TROY
MI
48099-4390
US
|
Family ID: |
36316181 |
Appl. No.: |
10/842880 |
Filed: |
May 10, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10396541 |
Mar 25, 2003 |
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10842880 |
May 10, 2004 |
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10658076 |
Sep 9, 2003 |
6862252 |
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10842880 |
May 10, 2004 |
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10746763 |
Dec 26, 2003 |
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10842880 |
May 10, 2004 |
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Current U.S.
Class: |
367/87 ;
367/99 |
Current CPC
Class: |
G01S 15/42 20130101 |
Class at
Publication: |
367/087 ;
367/099 |
International
Class: |
G01S 15/00 20060101
G01S015/00 |
Claims
1-12. (canceled)
13. An apparatus for robot guidance and for assisting the blind,
based on the echolocation abilities of bats, comprising: a source
of pulsed ultrasound; an acoustic vector probe; said vector probe
including four microphones supported by a frame at vertices of a
regular tetrahedron; two of said microphones facing a same of first
direction and another two of said microphones facing a same
opposite direction; said probe connected to a data acquisition
system; said data-acquisition system providing input to a digital
signal processor; said processor controlling the source of pulsed
ultrasound; and said processor connected to a device for outputting
data.
14. The apparatus as defined in claim 13 wherein said source of
pulsed ultrasound and said acoustic vector probe are combined into
an echolocation instrument, said vector probe and said source of
pulsed ultrasound structurally connected together and pointing in
the same direction.
15. The apparatus as defined in claim 14 wherein said source of
pulsed ultrasound has a beam approximately 100 degrees wide and
wherein said acoustic vector probe detects backscattered pulses
from a discrete distribution of acoustic highlights on surrounding
objects.
16. The apparatus as defined in claim 14 wherein the sound
pressures of said backscattered pulses measured by the four
microphones of said acoustic vector probe are heterodyned to lower
frequencies by said digital signal processor to enable said
processor to make an accurate determination of the sound-intensity
vector for each of said backscattered pulses.
17. The apparatus as defined in claim 16 wherein said
sound-intensity vector for each of said backscattered pulses
determines the directions of the acoustic highlights from which
said backscattered pulses originate.
Description
[0001] THIS APPLICATION IS A CONTINUATION-IN-PART OF U.S. patent
application ENTITLED "ACOUSTIC MEASUREMENT METHOD AND APPARATUS"
Ser. No. 10/396,541, FILED Mar. 25, 2003, ALSO OF
CONTINUATION-IN-PART ENTITLED "METHOD AND APPARATUS FOR ACOUSTIC
DETECTION OF BURIED OBJECTS" Ser. No. 10/658,076, FILED Sep. 9,
2003 AND ALSO OF CONTINUATION-IN-PART ENTITLED "SOUND SOURCE
LOCATION AND QUANTIFICATION USING ARRAYS OF VECTOR PROBES" Ser. No.
10/746,763, FILED Dec. 26, 2003, ALL THREE SUBMITTED BY ROBERT
HICKLING, THE PRESENT INVENTOR.
TECHNICAL FIELD
[0002] This invention relates to an echolocation instrument for
robot guidance and for aiding the blind that combines a recently
developed acoustic vector probe (AVP) and a source of pulsed
ultrasound.
BACKGROUND OF THE INVENTION
Acoustic Vector Probes
[0003] Recently a patent application was filed for a new acoustic
instrument, the acoustic vector probe (AVP). [0004] 1. R. Hickling
2003, "Acoustic Measurement Method and Apparatus", patent
application to the United States Patent and Trademark Office, Ser.
No. 10/396541, Filing Date Mar. 25, 2003. The technical information
contained in this application is hereby incorporated herein by
reference.
[0005] An AVP consists of a tetrahedral arrangement of four small
microphones less than 6 mm in size that simultaneously measures at
a point in air the three fundamental quantities of acoustics,
namely the sound-intensity and sound-velocity vectors, and sound
pressure. Sound intensity is the time average of sound power flow
per unit area. The time dependence of sound intensity is determined
by taking a series of averages over short intervals. AVPs are more
accurate, more compact and less expensive than previous instruments
for measuring sound intensity. A calibration procedure described by
Hickling (Ref.1) ensures the probe is accurate and
omnidirectional.
[0006] The sound-intensity vector determines the direction of a
sound source. Because it is expressed as a fast Fourier transform
(FFT), it also provides information about the frequency
characteristics of the source, enabling the AVP to distinguish one
source from another. Sources can also be distinguished by how they
occur in time.
[0007] The microphones that are used in AVPs can be of the electret
type such as the Knowles FG series or the Primo EM123 which respond
to ultrasonic frequencies up to about 40 kHz. Also the frequency
range of the calibrating microphone, such as the Bruel and Kjaer
4135, extends to about 100 kHz. However measurement with an AVP is
presently limited to the audible frequency range below about 15
kHz, because the measurement calculations for the AVP are based on
finite-difference approximations that are valid only when the
wavelength of sound exceeds the spacing d between microphones, i.
e. according to the relation kd<1 where k=2.pi./wavelength.
[0008] Subsequently two continuations-in-part (CIPs) were submitted
describing the use of arrays of AVPs [0009] 2. R. Hickling, 2003,
"Method and Apparatus for Acoustic Detection of Buried Objects",
patent application to the United States Patent and Trademark
Office, Ser. No. 10/658,076, Filing Date Sep. 9, 2003. [0010] 3. R.
Hickling, 2003, "Sound Source Location and Quantification using
Arrays of Vector Probes", patent application to the United States
Patent and Trademark Office, Ser. No. 10/746,763, Filing Date Dec.
26, 2003. The technical information contained in these CIPs is
hereby incorporated herein by reference. They describe how arrays
of AVPs can be used for a variety of applications. They also
indicate how modern digital signal processing permits simultaneous
measurement at all the AVPs in the array. Review of Echolocation
and Use of Ultrasonics
[0011] Echolocation (perceiving objects using acoustic echoes) is a
well-known concept, particularly for underwater detection and
machine perception. The most advanced form of echolocation in air
appears to be that of bats whose remarkable abilities have been
described by [0012] 4. D. R. Griffin, 1958, "Listening in the Dark,
The Acoustic Orientation of Bats and Man", Yale University Press,
New Haven. and by [0013] 5. J. A. Simmons, 1997, "Bats and
Echolocation", Chapt. 151, 1819-1822, "Encyclopedia of Acoustics",
(M. J. Crocker, Ed.) John Wiley and Sons. Use of echolocation by
the blind is discussed by Griffin. A clicking or tapping device is
used to generate audible sound pulses and the ears detect the
resulting echoes from nearby objects. In general bats use
ultrasound which is sound above the frequency range of human
hearing. This enables them to detect small objects such as insects
and generally to operate at frequencies above background noise,
both natural and man-made. The signals emitted by bats have
directional characteristics, as described by [0014] 6. D. J.
Hartley and R. A. Suthers, 1989, "The sound emission pattern of the
echolocating bat, Eptesicus fuscus", J. Acoust. Soc. Amer. 85,
1348-1351. A more easily understood version of the data in this
paper is presented by [0015] 7. J. A. Simmons, 2002,
"Directionality of biosonar broadcasts and reception by the ears",
Tutorial Lecture, Acoustical Society of America, Pittsburgh, Pa.,
Jun. 2, 2002. The horizontal cross-section of the beam of the
emitted signals is regular in shape and generally too wide to
distinguish individual objects. For example for frequencies around
35 kHz the beam is roughly 100 degrees wide. Obviously bats cannot
distinguish individual objects with so wide a beam. Instead they
have to depend on their hearing system to achieve the resolution
needed for echolocation.
[0016] Ultrasound is used in devices, such as range finders in
cameras, distance measuring systems and depth gages. Generally the
same transducer is both the source and receiver. The transducer
emits a pulse and waits to receive the echo before emitting another
pulse. Perhaps the most widely known system of this kind is
manufactured by the Polaroid Corporation of Wayland, Mass. for
range finding by a camera. This has been used extensively in
research studies, for example by [0017] 8. D. Lee, 1996, "The
Map-Building and Exploration Strategies of a Simple Sonar Equipped
Mobile Robot" Cambridge University Press. This book illustrates
signal processing methods associated with use of the Polaroid
sensor. In addition ultrasonic sensing systems for industry are
manufactured by The Ultrasonic Arrays Company of Woodinville, Wash.
where the source and receiver are again generally the same
transducer.
[0018] The use of the same transducer as a source and receiver has
disadvantages. There is a time constraint because the transducer
has to wait to receive the echo before emitting another signal.
Also it can only receive echoes from ahead of the transducer. With
the echolocation system of bats, on the other hand, the source and
receiver are separate. A bat can emit ultrasonic signals whenever
it wants and can hear echoes and other sounds from many directions.
In this way it is able to echolocate successfully.
[0019] It is not easy for humans, whose dominant sense is vision,
to relate to echolocation. Vision operates passively, because
objects are perceived only when illuminated by natural or
artificial light. Echolocation, on the other hand, is active,
objects being perceived when sound emitted by a source operates in
conjunction with a receiver. Also there is a major difference
between reflected light and reflected sound. Usually light is
scattered in all directions from all points on a surface, so that
every point on the surface can be seen by the eye. On the other
hand, sound is usually backscattered by mirror-like highlights
where these highlights are the only parts of a surface that can be
perceived at any one time. A complex surface generally will have
more highlights and will reveal more of itself. Additional
information is obtained when the source/receiver and the reflecting
surface are in relative motion, so that the highlights move over
the surface. The bat's motion through the air is therefore a major
part of it's ability to echolocate. To return a detectable echo, an
object must be larger than the wavelength of the incident sound.
The strength of an echo is generally determined by the radius of
curvature at the location of a highlight on a surface.
[0020] Distance to a reflecting object is determined by the
round-trip time of flight of an acoustic signal, i. e. the time
taken for sound to travel from the source to the object and back to
the receiver. Multiplying the time of flight by the speed of sound
and dividing by two gives the distance. Two methods have been used
to measure time of flight. The most common method uses sound pulses
or bursts of sound. Time of flight is the interval of time between
the departure of the outgoing pulse from the source and the return
of the corresponding echo to the receiver. A feature of the pulse,
such as the leading edge or its maximum amplitude, is used as a
time marker. This method is used in devices, such as range finders
in cameras, and depth gages.
[0021] The second, less common method uses frequency modulation.
Here the outgoing sound generally consists of a continuous signal
with a saw-tooth frequency modulation, whose frequency sweep is
related to the distance between the source and the reflecting
object. Because the source transmits a continuous signal, a
separate receiver is required. The echoes have a corresponding
saw-tooth frequency modulation, delayed relative to the outgoing
signal by the round-trip travel of the sound. The received signal
is then heterodyned or mixed with the outgoing signal. This
generates a trace of pressure amplitude versus time, or time
response (based on frequency differences), which determines the
distances of various reflecting surfaces from the source/receiver.
The method has been is described by [0022] 9. R. C. Heyser,
"Acoustical Measurements by Time Delay Spectrometry" U.S. Pat. No.
4,279,019, July, 1981. A similar method was developed as an aid to
the blind by [0023] 10. L. Kay, 2000, "Auditory perception of
objects by blind persons, using a bioacoustic high resolution air
sonar", Journ. Acoust. Soc. Amer., 107(6), 3266-3276. The device
has earphones and is worn on the head.
[0024] Bats use frequency-modulated pulses, the frequency generally
decreasing from the beginning to the end of the pulse. Distance to
an object is determined by the time of flight of the pulses.
Frequency modulation of the echoes compared to the frequency
modulation of the outgoing pulsed signals provides additional
information. Echoes using frequency modulated pulses were studied
by [0025] 11. R. Hickling and R. W. Means, 1968, "Scattering of
Frequency-Modulated Pulses by Spherical Elastic Shells in Water,"
Journ Acoust. Soc. Amer., 44, 5, 1246-1252.
[0026] Incident sound can generate a vibrational response in an
object, as shown, for example, by [0027] 12. R. Hickling, 1962,
"Analysis of echoes from a solid elastic sphere in water", Journ.
Acoust. Soc. Amer., 34, 1582-1592. This gives the echo a quality
determined by the internal structure of the reflecting object and
is probably used by bats. The effect is relatively weak for solid
objects in air, compared to solid objects in water. Bat
Detectors
[0028] The ultrasonic signals of bats can be changed to audible
frequencies by using an electronic process called heterodyning or
mixing. This is a standard procedure in radio technology, as
described for example in [0029] 13. D. B. Rutledge, 1999, "The
Electronics of Radio", Cambridge University Press. Griffin was the
first to apply heterodyning to bat signals to make them audible to
the human ear and the method has been used extensively since
then.
BACKGROUND OF THE INVENTION--OBJECTS AND ADVANTAGES
[0030] What is needed and desired is an echolocation instrument for
robot guidance and assisting the blind that [0031] (a) simulates
the capabilities of bats by combining an AVP with a source of
pulsed ultrasound. [0032] (b) heterodynes ultrasonic measurements
by the AVP down to lower frequencies so that the measurement
calculations of the AVP can be applied to determine sound-intensity
vectors accurately and hence the direction of echoes. [0033] (c)
locates the position of echo highlights on the surfaces of objects
by combining the time-of-flight of the ultrasonic pulses and the
direction of travel of the echoes. [0034] (d) uses the positions of
highlights to locate and identify objects. [0035] (e) significantly
increases highlight information when the echolocation instrument is
in motion. [0036] (f) determines additional information from the
Doppler shift of the echo highlights.
SUMMARY OF THE INVENTION
[0037] The present invention includes and utilizes an echolocation
system for robot guidance and assisting the blind. It is modeled on
the echolocation abilities of bats. It combines into one instrument
a source of pulsed ultrasound and a recently developed acoustic
vector probe (AVP). This instrument is used in conjunction with a
data acquisition system, a signal processor and an output device.
The source emits pulses of ultrasound over a beam width of about
100 degrees and the AVP detects backscattered pulses from a
discrete distribution of acoustic highlights on surrounding
objects. The ultrasonic sound pressures of the backscattered pulses
is measured at each of the four microphones of the AVP, which are
then heterodyned in the digital signal processor down to lower
frequencies so that the processor can make an accurate
determination of the sound-intensity vector for each pulse. The
sound-intensity vector points in the direction of the highlight
from which a pulse originates while the time of flight of the pulse
determines the distance of the highlight from the echolocation
instrument. By combining distance and direction, the position of
the highlight is located in space. At any instant in time the
distribution of echo highlights provides an instantaneous
impression of surrounding objects. As the echolocation instrument
moves relative to the surrounding objects, a sequence of such
impressions can be stored in processor memory and assembled to
provide a more complete representation of the surroundings. Also
Doppler shifting can provide additional information about the
movement of the highlights.
BRIEF DESCRIPTION OF THE DRAWINGS
[0038] In the drawings:
[0039] FIG. 1 is a block diagram of an echolocating system with a
source of pulsed ultrasound operating in conjunction with an
acoustic vector probe (AVP).
[0040] FIG. 2 is a perspective view of an AVP forming a part of the
invention.
[0041] FIG. 3 is a cubic lattice diagram showing the geometry of
the tetrahedral arrangement of microphones in the AVP and the
relation of the microphones to the system of Cartesian coordinates
used in determining the sound-intensity vector at the origin M and
the directions of the highlights.
[0042] FIG. 4 is a pictorial representation of an echolocating
instrument consisting of an AVP combined with a source of pulsed
ultrasound.
[0043] FIG. 5 illustrates how highlights on the surface of an
object return backscattered pulses to the AVP and how the AVP
determines the direction of the highlight from which each pulse
originates.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0044] FIG. 1 is a block diagram showing the different components
of the invention. A source of pulsed ultrasound 100 is combined
with an acoustic vector probe (AVP) 200 to form an echolocation
instrument 1000 linked to a data acquisition system 300, a digital
signal processor 400 and a display unit 500. The processor controls
the source 100 and the data acquisition system 300. Backscattered
echoes to the pulses from the source 100 are returned by an object
250 to the probe 200.
[0045] FIGS. 2 and 3 illustrate the structure and function of the
AVP 200 in determining the sound-intensity vector. AVP 200 includes
a fixture 42 being an annular member formed as a ring with a
central opening 46. Protruding from the ring are four support tubes
for the microphones parallel to the axis of the ring, two on one
side of the ring pointing in one direction and two on the reverse
side pointing in the opposite direction. These tubes are spaced
around the ring at ninety degree intervals at openings in the ring
at 48, 50, 52 and 54, and centered on an annular centerline 56
having a diameter d. The pair of tubes 58 on one side of the ring
is attached to the ring coincident with diametrically opposite
openings 48 and 50, and the pair of tubes 60 on the reverse side of
the ring is attached to the ring coincident with diametrically
opposite openings 52 and 54. The outer ends of the support tubes
58, 60 are each a distance d/(2 {square root over (2)}) from the
central base plane 64 of the ring and a distance d/ {square root
over (2)} from each other. Within the ends of the two support tubes
58 are located microphones 1, 2 and within the ends of the support
tubes 60 are located microphones 3 and 4. Microphones 1 through 4
are located at the vertices of an imaginary regular tetrahedron.
The advantages of the structure in FIG. 2 are: (a) the microphones
are symmetric on the two opposite sides of the base ring so that
they detect sound equally from both directions; (b) the measurement
point M is well defined; (c) the procedure for normalizing and
calibrating can be applied easily. Since the dimensions of the
probe are required to be less than the wavelengths being measured,
the effect of diffraction will be insignificant.
[0046] In FIG. 3, the geometric placement of the four microphones
in the tetrahedral arrangement is shown inserted within an
imaginary cubic lattice 70 having 6 faces with midpoints 12, 13,
14, 23, 24, 34. Lines through the midpoints of the opposite faces
of the lattice pass through an origin M, which is the measurement
point, and form X, Y and Z axes of the cubic lattice 64. The lines
between the microphones form diagonals (not shown) across the faces
of the cubic lattice, which also represent the edges of the regular
tetrahedron and pass through the midpoints 12, 13, 14, 23, 24 and
34 with a length of the dimension d. These lines form hypotenuse
lines for the respective faces of the cubic lattice 64 so that the
edges of the sides of the lattice have dimension d/ {square root
over (2)}.
[0047] At the microphones 1, 2, 3 and 4 at the vertices of the
regular tetrahedron in FIG. 2, the corresponding sound pressures
p1, p2, p3 and p4 are measured and digitized. In order to determine
the sound-intensity vector accurately, the AVP 200 has to satisfy
the condition kd/2<1 (1) where k=2.pi./wavelength. Because of
their relatively short wavelength, the ultrasonic pulses emitted by
the source 100 do not satisfy this condition and it is necessary to
apply a heterodyning procedure to the measured sound pressures to
convert them from ultrasound to sound in the audible frequency
range satisfying Equation (1). The discrete Fourier transforms
(DFTs) of the heterodyned sound pressures are then computed,
normalized and calibrated using the transfer-function procedure
described by Hickling in Ref.1, providing the modified transforms
Fp1(f), Fp2(f), Fp3(f) and Fp4(f) at the discrete points f=f.sub.i,
i=1,.n. For simplicity, the frequency dependence (f) will be
dropped. Finite difference approximations (derived from Taylor
series expansions) are then used to obtain the DFTs of the sound
pressures at the six midpoints of the edges of the regular
tetrahedron at 12, 13, 14, 23, 24 and 34 in FIG. 3, giving
respectively Fp12=(Fp1+Fp2)/2 Fp13=(Fp1+Fp3)/2 Fp14=(Fp1+Fp4)/2
Fp23=(Fp2+Fp3)/2 Fp24=(Fp2+Fp4)/2 Fp34=(Fp3+Fp4)/2. (2) These
approximations are accurate to the second order, i. e. order
(kd).sup.2/4, provided Equation (1) is satisfied.
[0048] The components of the sound-intensity vector at the
measurement point M are determined from the sound pressure DFTs in
Equation (1), using the cross-spectral formulation for sound
intensity described by Hickling (Ref 1). The components are FIX=-Im
CS[Fp24, Fp13]/(.rho.2.pi.f(d/ {square root over (2)})) FIY=-Im
CS[Fp23, Fp14]/(.rho.2.pi.f(d/ {square root over (2)})) FIZ=-Im
CS[Fp12, Fp34]/(.rho.2.pi.f(d/ {square root over (2)})) (3) where
Im is the imaginary part and CS is the cross spectrum of the sound
pressures at the midpoints of the opposite edges of the imaginary
regular tetrahedron in FIG. 3, and .rho. is the density of the
fluid medium, which is approximately 1.3 kg/m.sup.3 for air. The
amplitude of the sound-intensity vector is given by FIA=
[FIX.sup.2+FIY.sup.2+FIZ.sup.2] (4) Sound intensity is expressed in
SI units of watts per meter squared per second.
[0049] FIG. 4 shows a source of pulsed ultrasound 100 is combined
with an AVP 200 to form an echolocation instrument 1000. Typically
the source and the AVP have similar dimensions. The axis of the
source is in the same direction of the z-axis in FIG. 3. If
necessary the echolocation instrument 1000 can be rotated about a
vertical or other axis to simulate the movement of a bat's
head.
[0050] FIG. 5 illustrates how the backscattered pulses are returned
to the echolocation instrument 1000 from the echo highlights 150 on
the surface of an object 250 at locations 1, 2, 3 and 4.
Backscattering occurs where a part of the surface of the object is
perpendicular to the direction from the echolocation instrument. In
FIG. 5 backscattered pulses from the highlights at 1, 2, 3 and 4
are received by the AVP in a sequence shown in the lower part of
the figure, according to the distance of the highlight from the
AVP. The AVP then determines the sound-intensity vector for each
backscattered pulse which indicates the direction 350 of the
highlight originating the pulse. Combining this directional
information with the round-trip time of flight of the pulse
determines where a highlight occurs on the surface of the object.
The distribution of highlights at any one instant provides a first
impression that can help to locate and possibly identify an object.
When the echolocation instrument 1000 moves it can track the
corresponding movement of highlight distributions over surrounding
objects. The sequence of distributions can be stored in the memory
of the digital signal processor 400 and can be used to obtain a
more complete representation of the objects. Additional information
can be obtained using the Doppler shift of the highlights.
[0051] More than one echolocation instrument can be used for any
application. Among possible applications is the detection of
obstacles in the blind spots of moving vehicles.
[0052] While the invention has been described by reference to
certain preferred embodiments, it should be understood that
numerous changes could be made within the spirit and scope of the
inventive concepts described. Accordingly it is intended that the
invention not be limited to the disclosed embodiments, but that it
have the full scope permitted by the language of the following
claims.
* * * * *