U.S. patent application number 11/484973 was filed with the patent office on 2006-11-23 for method and apparatus for remote measurement of vibration and properties of objects.
This patent application is currently assigned to The Trustees of the Stevens Institute of Technology. Invention is credited to Dimitri Donskoy, Nikolay Sedunov, Edward A. Whittaker.
Application Number | 20060260407 11/484973 |
Document ID | / |
Family ID | 36643939 |
Filed Date | 2006-11-23 |
United States Patent
Application |
20060260407 |
Kind Code |
A1 |
Donskoy; Dimitri ; et
al. |
November 23, 2006 |
Method and apparatus for remote measurement of vibration and
properties of objects
Abstract
A method and apparatus is provided which employs phase or
amplitude modulated electromagnetic probing waves (in optical or
microwave frequency ranges or both) emitted toward a vibrating
object. The optical and/or microwave probing signals remotely
irradiate an object of interest. The object reflects and/or
scatters the probing wave toward to a receiver. The
reflected/scattered modulated signal is received with a remote
sensor (receiver). Vibration causes additional phase modulation to
the probing wave. At the receiving end, the signal is demodulated
to extract and analyze the vibration waveform. The present
invention can be utilized for nondestructive testing, monitoring of
technological processes, structural integrity, noise and vibration
control, mine detection, etc.
Inventors: |
Donskoy; Dimitri; (Hoboken,
NJ) ; Sedunov; Nikolay; (Hoboken, NJ) ;
Whittaker; Edward A.; (Hoboken, NJ) |
Correspondence
Address: |
MCCARTER & ENGLISH, LLP
FOUR GATEWAY CENTER
100 MULBERRY STREET
NEWARK
NJ
07102
US
|
Assignee: |
The Trustees of the Stevens
Institute of Technology
|
Family ID: |
36643939 |
Appl. No.: |
11/484973 |
Filed: |
July 11, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10069696 |
Jun 13, 2002 |
7073384 |
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PCT/US00/23057 |
Aug 23, 2000 |
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11484973 |
Jul 11, 2006 |
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60150224 |
Aug 23, 1999 |
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Current U.S.
Class: |
73/657 |
Current CPC
Class: |
G01N 29/2412 20130101;
G01N 29/30 20130101; G01N 2291/015 20130101; G01N 2291/044
20130101 |
Class at
Publication: |
073/657 |
International
Class: |
G01B 9/02 20060101
G01B009/02 |
Claims
1. An electromagnetic wave vibrometer apparatus comprising: a
signal generator for generating an optical signal; an amplitude
modulator for amplitude modulating the optical signal with a
microwave frequency electromagnetic signal to produce an amplitude
modulated optical signal; a first transmitter for transmitting the
amplitude modulated optical signal at a vibrating object; a first
receiver for receiving a reflected amplitude modulated optical
signal from the vibrating object; a demodulator for demodulating
the reflected amplitude modulated optical signal to produce a
demodulated signal; and a signal processor for extracting and
analyzing a vibration waveform from the demodulated signal.
2-5. (canceled)
6. The apparatus of claim 1, wherein the optical signal is
modulated by the same frequency as the microwave frequency
electromagnetic signal.
7. The apparatus of claim 1 wherein the signal generator further
comprises a laser signal source.
8. The apparatus of claim 1 wherein the signal generator further
comprises an LED signal source.
9. The apparatus of claim 1 further comprising a second vibration
receiver mounted with the first receiver for compensation for
unwanted background or coupled vibration.
10. The apparatus of claim 9 further comprising a second vibration
transmitter mounted with the first receiver for calibration of the
apparatus to determine an angle of reflection.
11. An apparatus for remotely measuring properties of an object
comprising: a signal generator for generating an optical signal; an
amplitude modulator for amplitude modulating the optical signal
with a microwave frequency electromagnetic signal to produce an
amplitude modulated optical signal; a first transmitter for
transmitting the amplitude modulated optical signal at an object;
means for vibrating the object to modulate the amplitude modulated
optical signal transmitted at the object; a first receiver for
receiving a reflected amplitude modulated optical signal from the
object; a demodulator for demodulating the reflected amplitude
modulated optical signal using the modulating signal to produce a
demodulated signal; and a signal processor for extracting and
analyzing a vibration waveform from the demodulated signal.
12-15. (canceled)
16. The apparatus of claim 11 wherein the signal is modulated by
the same frequency as the microwave frequency electromagnetic
signal.
17. The apparatus of claim 11 wherein the signal generator further
comprises a laser signal source.
18. The apparatus of claim 11 wherein the signal generator further
comprises an LED signal source.
19. The apparatus of claim 11 further comprising a second vibration
receiver mounted with the first receiver for compensation for
unwanted background or coupled vibration.
20. The apparatus of claim 19 further comprising a second vibration
transmitter mounted with the first receiver for calibration of the
apparatus to determine an angle of reflection.
21. A method of remotely measuring vibration comprising: generating
an optical signal; amplitude modulating the optical signal with a
microwave frequency electromagnetic signal to produce an amplitude
modulated optical signal; transmitting the amplitude modulated
optical signal at a vibrating object; receiving a reflected
amplitude modulated optical signal from the vibrating object;
demodulating the reflected amplitude modulated signal using the
microwave frequency electromagnetic signal; and analyzing the
demodulated signal.
22-25. (canceled)
26. The apparatus of claim 21, further comprising modulating the
optical signal at the same frequency as the microwave frequency
electromagnetic signal.
27. The method of claim 21 further comprising generating the
optical signal using a laser or a low coherent laser diode.
28. The method of claim 21 further comprising generating the
optical signal using an LED.
29. The method of claim 21 further comprising compensating for
vibration errors by determining vibration displacements of the
transmitter and receiver.
30. The method of claim 30 further comprising compensating for
unwanted background or coupled vibration using a second vibration
receiver mounted with the first receiver.
31. The method of claim 30 further comprising calibrating the
vibrometer to determine an angle of reflection using a second
vibration transmitter mounted with the first receiver.
32. A method for remotely determining properties of an object
comprising: amplitude modulating an optical signal with a microwave
frequency electromagnetic signal to produce an amplitude modulated
optical signal; transmitting the amplitude modulated optical signal
at an object; vibrating the object; receiving reflected amplitude
modulated optical signals from the vibrating object; and processing
the reflected amplitude modulated optical signals to extract
information about the properties of the object.
33-36. (canceled)
37. The method of claim 32 further comprising modulating the
optical signal at the same frequency as the microwave frequency
electromagnetic signal.
38. The method of claim 32 further comprising generating the
optical signal using a laser or a low coherent laser diode.
39. The method of claim 32 further comprising generating the
optical signal using an LED.
40. The method of claim 32 further comprising splitting the
amplitude modulated optical signal into first and second signals
and transmitting the second signal to a demodulator for comparing
the second signal with the received reflected amplitude modulated
optical signal.
41. The method of claim 32 further comprising compensating for
vibration errors by determining vibration displacements of the
transmitter and receiver.
42. The method of claim 41 further comprising compensating for
unwanted background or coupled vibration by providing a second
vibration receiver mounted with the first receiver.
43. The method of claim 42 further comprising calibrating the
vibrometer to determine an angle of reflection by providing a
second vibration transmitter mounted with the first receiver.
44. The apparatus of claim 1, wherein the amplitude modulated
optical signal is modulated in the GHz range.
45. The apparatus of claim 11, wherein the amplitude modulated
optical signal is modulated in the GHz range.
46. The method of claim 21, wherein the step of amplitude
modulating the optical signal comprises amplitude modulating the
optical signal in the GHz range.
47. The apparatus of claim 1, wherein the optical signal is
non-coherent.
48. The apparatus of claim 11, wherein the optical signal is
non-coherent.
49. The method of claim 21, wherein the step of generating the
optical signal comprises comprising generating a non-coherent
optical signal.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of Invention
[0002] The present invention generally relates to a method and
apparatus for nondestructive testing, monitoring of technological
processes, determining structural integrity, noise and vibration
control, and mine detection. More specifically, the present
invention relates to a phase-amplitude modulated electromagnetic
wave (PAM-EW) vibrometer.
[0003] 2. Related Art
[0004] Existing remote vibrometers are generally based on coherent
laser generated signals. These devices, known as laser-doppler
vibrometers, require precision and expensive optical elements
(acousto-optic modulators, gas lasers, mirrors, beam splitters,
etc.) A very precise, very coherent source is required, i.e. very
stable phase characteristics. Fine adjustments are necessary to
achieve a desirable effect. As a result, the laser-doppler
vibrometers are quite expensive and delicate instruments are best
suited for laboratory use.
[0005] Another serious drawback of the conventional remote sensing
devices is their high sensitivity to unwanted vibration of the
transmitting/receiving assembly (TRA). In fact, vibrometers measure
only relative velocity/displacement between the vibrating object
and the TRA. Since the sensitivity of the conventional
laser-doppler vibrometers is very high it is very difficult to
isolate the TRA from such small vibrations especially under field
conditions. In addition to this, conventional vibrometers are
susceptible to so-called cosine error. That is, if the incident
electromagnetic wave is not precisely perpendicular to the
irradiated surface, an error proportional to the cosine of the
angle between the line of radiation and a normal to the surface is
introduced.
[0006] Efforts of others in this area include U.S. Pat. No.
5,883,715, to Steinlechner et al., entitled Laser Vibrometer for
Vibration Measurements; U.S. Pat. No. 5,897,494, to Flock, et al.,
entitled Vibrometer; U.S. Pat. No. 5,495,767, to Wang, et al.,
entitled Laser Vibrometer; and U.S. Pat. No. 4,768,381, to
Sugimoto, entitled Optical Vibrometer.
[0007] None of these efforts of others teaches or suggests all of
the elements of the present invention, nor do they disclose all of
the advantages of the present invention.
OBJECTS AND SUMMARY OF THE INVENTION
[0008] It is a primary object of the present invention to provide a
phase-amplitude modulated electromagnetic wave (PAM-EW)
vibrometer.
[0009] It is an additional object of the present invention to
provide a method and apparatus for measuring vibration of a
vibrating object which uses a modulated electromagnetic probing
wave, wherein the vibration of the vibrating object additionally
modulates the modulated probing wave.
[0010] It is another object of the present invention to provide a
vibrometer which uses an optical source which is not necessarily
coherent, for example, an LED source.
[0011] It is even an additional object of the present invention to
provide an additional set of acoustic transmitters/receivers
attached directly to the electromagnetic wave transducer assembly
to enhance performance.
[0012] These and other objects of the present invention are
achieved by a method and apparatus which employs phase or amplitude
modulated electromagnetic probing waves (in optical or microwave
frequency ranges or both) emitted toward a vibrating object. The
optical and/or microwave probing signals remotely irradiate an
object of interest. The object reflects and/or scatters the probing
wave toward to a receiver. The reflected/scattered modulated signal
is received with a remote sensor (receiver). Vibration causes
additional phase modulation to the probing wave. At the receiving
end, the signal is demodulated to extract and analyze vibration
waveform. The invention also employs an innovative method and
algorithm for enhanced performance of the vibrometer by using an
additional set of acoustic transmitters/receivers attached directly
to the electromagnetic wave transducer assembly. This additional
set and corresponding data processing algorithm allow for
compensation of the unwanted background (or coupled) vibration of
the vibrometer and for calibrated measurements of the displacement
of the vibrating object irradiated under an arbitrary angle. The
method and apparatus of the present invention can be utilized for
nondestructive testing, monitoring of technological processes,
structural integrity, noise and vibration control, mine detection,
etc.
[0013] The present invention can be used in connection with
existing methods and apparatuses for detecting land mines and
detecting defects in structures. Such existing methods and
apparatuses include U.S. Pat. No. 5,974,881, dated Nov. 2, 1999 to
Donskoy, et al. and pending U.S. application Ser. No. 09/239,133,
filed Jan. 28, 1999 by Donskoy, et al., the entire disclosures of
which are expressly incorporated herein by reference.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] Other important objects and features of the present
invention will be apparent from the following Detailed Description
of the Invention taken in connection with the accompanying drawings
in which:
[0015] FIG. 1 is a schematic view of the method and apparatus of
the present invention.
[0016] FIG. 2 is a schematic view of the method and apparatus for
compensating for errors arising from unwanted vibration of the
transmitting/receiving assembly (TRA).
[0017] FIG. 3a is a schematic view of an experimental set-up of the
method and apparatus of the present invention.
[0018] FIG. 3b is a graph of the results of the experiment shown in
FIG. 3a.
[0019] FIG. 4 is a schematic of a microwave vibrometer embodiment
of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0020] The present invention relates to a method and apparatus
which employs phase or amplitude modulated electromagnetic probing
waves (in optical or microwave frequency ranges) emitted toward a
vibrating object. This is shown schematically in FIG. 1. The
apparatus is generally indicated at 10. A signal is generated by
the signal generator 12, and then modulated by the modulating
device 14 which receives a modulating signal from the modulating
generator 16. Preferably, the signal is amplitude modulated. The
optical or microwave probing signals 20 are transmitted by
transmitter 18 and remotely irradiate an object 8 of interest. The
object 8 reflects and/or scatters the probing wave 20 toward to a
receiver 22, where it is received. Vibration of object 8 causes
additional phase modulation to the probing wave 20, based on the
fact that object 8 is vibrating, which becomes amplitude/phase
modulated signal 24. At the receiving end, the signal 24 is
demodulated by demodulation device 26, according to signal
processing system 28, to extract and analyze vibration
waveform.
[0021] The present invention can be used regardless of coherency of
the emitting radiation, thus eliminating need in precision and
expensive optical elements. A laser, or even a light emitting diode
(LED) can be used as the source. The intensity is modulated at a
very high frequency, for example in the GHz range. This results in
significant cost reduction of the vibrometer.
[0022] The use of microwave radiation brings additional
capabilities for the remote sensing, allowing for measurements of
internal vibrations of the object due to penetrating capabilities
of microwave radiation. The frequency of the microwave radiation
can be the same as the modulating frequency of the optical signal,
thus allowing for a shared use of electronic circuitry for both
received microwave and optical signals.
[0023] The present invention also employs an innovative method and
algorithm for enhanced performance of the vibrometer by using an
additional set of acoustic transmitters/receivers attached directly
to the electromagnetic wave transducer assembly. This additional
set and corresponding data processing algorithm allow for
compensation of the unwanted background, or coupled, vibration of
the vibrometer and for calibrated measurements of the displacement
of the vibrating object irradiated under an arbitrary angle.
[0024] Referring to FIG. 2, the method and algorithm for
compensating for cosine and transmitter/receiving assembly (TRA) 30
vibration errors, is shown. A 3D accelerometer 32 (or any motion
sensor) and a CW (continuous wave) source 34 of vibration at
frequency f.sub.0, are attached to the TRA 30. The 3D sensor 32
measures three components of the TRA vibration displacements: x(t),
y(t), and z(t). The output of the TRA 30 is proportional to the
variation in the length, L(t), between the TRA 30 and the surface
of the tested object 8. L(t) can be defined using FIG. 2 geometry.
For simplicity only the XZ-plate dependent (2D case) is considered:
L(t)=.xi.(t)/cos .THETA..sub.xz+x(t)sin .THETA..sub.xz/cos
.THETA..sub.xz+z(t) (1) where .xi.(t) is the normal displacement of
the vibrating object, and .THETA..sub.xz is the angle between the
normal to the surface of the object 8 and z-axes of the TRA 30.
Here x(t) and z(t) are unwanted components of the output signal.
The signal z(t) can be easily compensated (subtracted) since it is
directly measured with the 3D sensor 32. However to compensate for
x(t), the angle .THETA..sub.xz must be determined. This can be done
using a CW vibration source 34, which causes the TRA 30 to vibrate
at a fixed frequency f.sub.0 with amplitude A.sub.ox. Taking this
vibration into account, Eq. (1) can be re-written as:
L(t)-z(t)=[.xi.(t)/sin .THETA..sub.xz+x(t)+A.sub.ox
cos(2.pi.f.sub.0t)]tan .THETA..sub.x2. (2)
[0025] By choosing the applied vibration large enough that
A.sub.ox>>[.xi.(t)/sin .THETA..sub.xz+x(t)], the output
signal at the known frequency f.sub.0 can be used to evaluate
unknown angle .THETA..sub.xz: L(t)-z(t)|.sub.f=f0.apprxeq.A.sub.0x
tan .THETA..sub.xz. (3)
[0026] Thus, formula (3) can be used to evaluate the angle
.THETA..sub.xz and knowing x(t) and z(t), which are measured with
the 3D sensor 32, the true displacement .xi.(t) can be determined
using formula (1).
[0027] This algorithm can be easily extended for the 3D case, in
which a vibrating source generates x and y components of vibration
and the 3D sensor also measures the y component of the TRA
vibration.
[0028] The apparatus of the present invention comprises an optical
or microwave transmitter, corresponding receiver, and electronics
including power supplies, signal generators, amplifiers,
modulators, demodulators, acquisition and processing units.
[0029] FIG. 3a is a schematic view of an experimental setup of the
present invention. A laser diode 40 is used as the source of light.
One suitable laser diode is the Sharp LT-023, having a wavelength
of 790 nm and 2 mW of power. Any other suitable light source can be
used. Coherency of the light source is not too important, and
accordingly, even and LED could be used. The laser diode 40 is
powered by current source 42 which supplies current to drive the
laser 40. The current goes through a bias tee 44 which is an
electronic scheme which allows for the modulation of the current
supplied to the laser diode 40. The current is modulated by the
signal from signal generator 46, at for example 250 kHz. However,
for better results in practice, the modulating signal is in the GHz
range, i.e. a few GHz or higher, because the device is more
sensitive at higher frequencies. The intensity of the laser signal
is thereby amplitude modulated.
[0030] The modulated signal 48 is then sent at the object 50. The
signal 48 is reflected or scattered by the object 50, and the
reflected signal 54 is received by photodetector 52. In the
experimental setup shown, the vibrating object 50 comprises a
shaker and an accelerometer to make actual measurements of the
vibration for comparison to experimental results. The reflected
signal 54 received by the photodetector 52 is proportional to
intensity. The amplitude modulated signal 48 is additionally
modulated in phase by the vibration of the object 50 such that
reflected signal 54 is amplitude and phase modulated. The reflected
signal 54 is then amplified by amplifier 56 and fed to mixer 58
which also receives a signal from the signal generator 46. The
mixer 58 mixes these signals, the phase modulated signal and the
reference signal to demodulate the reflected signal, which is sent
to the spectral analyzer 60.
[0031] FIG. 3b graphically shows the frequency response of the
vibrating object measured by the laser of the present invention and
as measured directly by the accelerometer. As can be seen, the
present invention measures the vibration in accordance with
measurements taken directly of a vibrating object. As the
modulating frequency is increased, the results become more
accurate.
[0032] FIG. 4 is a schematic of a microwave vibrometer embodiment
of the present invention. An oscillator or signal generator 60
generates a signal at, for example, 2.45 GHz. The signal is split
by power splitter 62. Part of the signal goes to mixer 76 where it
will later be used. The other part of the signal is sent to
amplifier 64 where it is amplified and then to circulator 66 and
then to antenna 68 which sends signal 70 to vibrating surface 72
where it is reflected, scattered and modulated. Modulated signal 74
is also received by the antenna 68 and sent back to the circulator
66 which decouples the signal. This signal is then sent to
amplifier 76 and then to mixer 82 which is part of a heterodyne
scheme including second oscillator 78 which sends a signal at an
intermediate frequency, for example 2.56 GHz, through power
splitter 80 to mixer 82. In this way, the reference signal and the
reflected signal are not mixed directly, but rather each is mixed
with an intermediate frequency, which provides advantages in terms
of signal to noise ratio. The signal leaving the mixer 82 is the
difference of 2.56 GHz and 2.45 GHz which is the intermediate
frequency (IF) of 110 MHz. This signal is sent to low pass filter
84 and then to amplifier 86 and then to I&Q demodulator 88.
Mixer 76 receives signals from both oscillators 60 and 78 through
power splitters 62 and 80 respectively, and sends them to low pass
filter 90 and then through amplifier 92 to I&Q demodulator 88.
I&Q demodulator 88 functions essentially as a mixer which
demodulates the signal into real and imaginary parts which
correspond to amplitude and phase. These signals are sent through
preamplifiers 94, bandpass filters 96 and amplifiers 98.
[0033] The present invention can be used as a remote sensing device
used for various applications, including, but not limited to,
nondestructive testing, characterization and monitoring of
mechanical structures and civil structures (bridges, storage tanks,
etc), air- and car-frames, pipes, pressure vessels, weldments,
engines, etc.
[0034] Accordingly, the present invention provides a method and
apparatus that relates to an electromagnetic wave vibrometer which
generates an electromagnetic signal and transmits the signal at a
vibrating object. A receiver for receiving a reflected or scattered
phase modulated signal from the vibrating object is provided and
feeds the signal to a demodulator for demodulating the received
signal and a signal processor for analyzing the vibration waveform.
Additionally, a method and apparatus is provided for remotely
measuring properties of an object including a signal generator for
generating an electromagnetic signal and transmitting a signal at
an object. A means for vibrating the object is provided. The
vibrating object phase modulates the transmitted signal. A receiver
picks up the reflected and scattered phase modulated signal and a
demodulator demodulates the received signal and a signal processor
analyzes the vibration waveform. Similarly, the present invention
relates to methods for remotely measuring vibration and remotely
determining properties of an object.
[0035] Having thus described the invention in detail, it is to be
understood that the foregoing description is not intended to limit
the spirit and scope thereof. What is desired to be protected by
Letters Patent is set forth in the appended claims.
* * * * *