U.S. patent application number 15/145659 was filed with the patent office on 2016-08-25 for device for measuring wind speed.
The applicant listed for this patent is EPSILINE. Invention is credited to Christophe Lepaysan, Raphael Teysseyre.
Application Number | 20160245839 15/145659 |
Document ID | / |
Family ID | 41820141 |
Filed Date | 2016-08-25 |
United States Patent
Application |
20160245839 |
Kind Code |
A1 |
Lepaysan; Christophe ; et
al. |
August 25, 2016 |
DEVICE FOR MEASURING WIND SPEED
Abstract
A device comprises: an emitting element for emitting a laser
beam, referred to as an emitted beam; a focusing element for
focusing the emitted beam at a predetermined focal distance (D); a
receiving element for receiving the emitted beam after being
reflected by a particle in the air (18), referred to as a reflected
beam; a transmitting element for transmitting the signal of
interference occurring between the emitted beam and the reflected
beam to a signal processor in order to deduce the speed of the
particle therefrom. The emitting element includes a laser diode and
the receiving element is combined with the laser diode by
self-mixing. The focal distance is between 5 cm and 2 m.
Inventors: |
Lepaysan; Christophe;
(Toulouse, FR) ; Teysseyre; Raphael; (Toulouse,
FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
EPSILINE |
Toulouse |
|
FR |
|
|
Family ID: |
41820141 |
Appl. No.: |
15/145659 |
Filed: |
May 3, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13499619 |
Jun 13, 2012 |
9354315 |
|
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PCT/FR2010/052149 |
Oct 11, 2010 |
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15145659 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01N 2015/1075 20130101;
G01N 2015/1454 20130101; G01P 5/26 20130101; G01N 2015/0046
20130101; G01N 15/0205 20130101; G01N 2015/1447 20130101; G01N
15/1429 20130101; G01N 2015/1486 20130101; G01F 1/663 20130101;
G01S 17/58 20130101 |
International
Class: |
G01P 5/26 20060101
G01P005/26 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 9, 2009 |
FR |
0957080 |
Claims
1. A wind speed measurement device, comprising: a first laser diode
configured to emit a laser beam, referred to as the emitted beam,
focusing means for focusing the emitted beam at a predetermined
focal distance between 5 centimeters and 2 meters, receiving means
for receiving a reflected beam produced by an air particle
reflecting the emitted beam, the receiving means being associated
with the first laser diode by self-mixing and configured to provide
an interference signal corresponding to an interference occurring
between the emitted beam and the reflected beam by the self-mixing;
and transmission means for transmitting the interference signal to
a signal processing means, in order to deduce a speed of the
particle, the signal processing means being configured to select a
portion of the interference signal, the portion having an amplitude
or a power exceeding a threshold corresponding to an amplitude or a
power of a signal obtained by a measurement in a windless
location.
2. The wind speed measurement device according to claim 1, wherein
the laser diode is a diode configured to emit in single
longitudinal mode.
3. The wind speed measurement device according to claim 1, wherein
the signal processing means is configured to select the portion of
the interference signal after prior processing of the interference
signal.
4. The wind speed measurement device according to claim 1, wherein
the transmission means is electronic and comprises a transmission
board.
5. The wind speed measurement device according to claim 4, wherein
the transmission means comprises electronic amplification means for
amplifying the interference signal electronically.
6. The wind speed measurement device according to claim 1, wherein
the signal processing means comprises detecting means for detecting
a peak, recording means for recording the interference signal
within an interval of time around the peak, and applying means for
applying a Fourier transform to the interference signal.
7. The wind speed measurement device according to claim 6, wherein
the time interval during which the interference signal is recorded
is between 50 and 300 microseconds around the peak.
8. The wind speed measurement device according to claim 1, wherein
the laser diode has a power between 0 and 50 milliwatts.
9. The wind speed measurement device according to claim 1,
comprising a photovoltaic device configured to provide power based
on photovoltaic energy.
10. The wind speed measurement device according to claim 1,
comprising second and third laser diodes which are configured to
emit, along with the first laser diode, three non-coplanar laser
beams.
11. The wind speed measurement of claim 1, wherein the receiving
means include: an optical cavity configured to receive the
reflected beam and produce the interference by self-mixing the
emitted beam with the reflected beam; and a photodiode to provide
the interference signal corresponding to the interference produced
by the self-mixing.
12. The wind speed measurement device according to claim 1, wherein
the signal processing means is configured to deduce the speed of
the particle based on the portion of the interference signal having
an amplitude or a power exceeding the threshold corresponding to
the amplitude or the power of the signal obtained by the
measurement in the windless location and not based on any portions
of the interference signal that do not have an amplitude or a power
exceeding the threshold corresponding to the amplitude or the power
of the signal obtained by the measurement in the windless location.
Description
BACKGROUND
[0001] 1. Technical Field
[0002] The invention relates to the field of wind measurement,
particularly when using laser light.
[0003] 2. Description of the Related Art
[0004] A prior art anemometer using a LIDAR (Light Detection And
Ranging) system is known, particularly from document WO
2009/046717. This device emits a laser beam, focused by an optical
system at a focal distance of several dozen meters, targeting a
measurement volume in which particles in the air are blown about by
the wind. These particles reflect the light received, emitting a
beam in the direction of the optical system, referred to as the
reflected beam. The LIDAR receives the beam reflected by the
particles, and then processes the interference occurring between
the emitted beam and the reflected beam in order to deduce the
speed of the particles, as the frequency shift between the emitted
beam and the reflected beam is dependent on this speed due to the
Doppler effect.
[0005] Such a device for emitting laser beams is particularly
costly to make.
BRIEF SUMMARY
[0006] One aim of the invention is to propose a wind speed
measurement device that is less costly.
[0007] For this purpose, an object of the invention is a wind speed
measurement device, comprising:
[0008] a means for emitting a laser beam, referred to as the
emitted beam,
[0009] a means for focusing the emitted beam at a predetermined
focal distance,
[0010] a means for receiving the emitted beam after it is reflected
by a particle in the air, referred to as the reflected beam,
[0011] a means for transmitting the signal for the interference
occurring between the emitted beam and the reflected beam to a
signal processing means, in order to deduce the speed of the
particle,
[0012] wherein the emitting means comprises a laser diode and the
receiving means is associated with the laser diode by self-mixing,
the focal distance being between 5 cm (centimeters) and 2 m
(meters).
[0013] By using a laser diode, a much more economical device for
measuring the wind speed is obtained. In addition, the receiving of
the reflected beam is achieved by self-mixing, which is
particularly attractive. Self-mixing is also known as intra-cavity
optical feedback, and corresponds to a device in which the
reflected beam re-enters the same cavity as the beam emitted by the
laser diode. Generally, the means for receiving the reflected beam
comprises a photodiode, arranged just behind the laser diode, and
the interference is created directly inside the laser cavity then
received by the photodiode. The receiving means associated with the
laser diode by the self-mixing provides optical amplification of
the interference signal. The use of self-mixing is advantageous,
because a laser diode and a photodiode are inexpensive, and they do
not require a separate detector placed in a location other than
that of the laser and receiving only the reflected beam after this
reflected beam has been redirected by an interferometer. A
photodiode placed just behind the diode is therefore used, and
there is no need for management of the alignment issues related to
an interferometer. The device is also particularly compact, because
the reflected beam returns to the cavity of the laser diode. This
is very different from the case of an interferometer which reflects
the received beam, for example at an angle of 90.degree. relative
to the emitted beam, which requires placing the detector at a
certain distance from the laser and therefore takes up space. Thus
the proposed device can have the approximate volume of a cube with
1 cm edges, and of a cube with 10 to 20 cm edges if the signal
processing means is included in the device, while a device equipped
with a LIDAR generally has the approximate volume of a cube with 50
cm edges and weighs about 50 kg (kilograms).
[0014] One will note that the particles reflecting the light from
the device are particles located in the air, often called airborne
particles. These particles generally have a diameter of between 0.1
.mu.m (micrometers) and 10 .mu.m. The scattering occurring when the
emitted beam is reflected is Mie scattering, which applies at the
particle scale, in contrast to Rayleigh scattering which applies at
the molecular scale. The particles can, for example, be particles
containing carbon or ions.
[0015] The density of these particles in the air is very low and it
is therefore difficult to obtain a continuous signal for analyzing
the interference. Generally, the longer the focal distance, the
better the measurement, because the presence of the device has
little effect on the air movement.
[0016] Also, while anemometers comprising a laser generally focus
at a distance of several dozen meters, the inventor had the idea of
focusing at a shorter distance and observed that, for a focal
distance of between 5 cm and 2 m, a sufficiently periodic signal of
sufficient intensity is obtained for processing in order to provide
the wind speed. Note that this signal is occasional, however.
[0017] By providing a focal distance of between 5 cm and 2 m, an
appropriate use of the self-mixing phenomenon to measure the wind
speed is made. By focusing at a shorter distance, more light is
collected after it is reflected by the particle. Thus the power of
the received signal can be greater than that generated by the noise
from the laser diode and the device yields satisfactory results.
Also, a focal distance greater than 5 cm is used so that air
movement in the focus area is not affected by the presence of the
device.
[0018] Note that the means of focusing the emitted beam focuses the
towards a predetermined focus volume. This volume is sufficiently
large for a signal to be reflected by one or more particles at
least every few seconds, and sufficiently small for the light from
the laser beam to be sufficiently concentrated. The device is
adapted to process a beam reflected by particles having a diameter
of between 0.1 and 10 .mu.m, for example a particle containing
carbon or an ion.
[0019] The device may additionally comprise one of more of the
following features.
[0020] The signal transmission means is electronic. It comprises a
transmission board containing a printed circuit onto which
electronic components are welded, in order to act as an interface
between the receiving means of the device and the signal processing
means. Note that this transmission board is configured in a
specific manner, to be able to transmit a processable signal for
the interference occurring between the emitted beam and the
reflected beam. In particular, the board is configured to emit
relatively low noise, given that the signal reflected by the
particles is intermittent and relatively weak.
[0021] The signal transmission means comprises an electronic
amplification means, to provide electronic amplification of the
interference signal. This amplification is particularly useful
because the signal is intermittent and relatively weak.
[0022] The laser diode is a diode emitting in single longitudinal
mode. The signal is therefore easier to process than when the diode
has a higher power and is multimode. The laser diode can be a
Fabry-Perot diode, for example.
[0023] The signal processing means is configured to select a
portion of the received signal, namely the portion having an
amplitude or power exceeding a threshold corresponding to the
amplitude or power of a signal obtained by measuring in a windless
location. It is particularly useful to select only a portion of the
received signal. The interference signal generated by a particle is
occasional and it is therefore advantageous to select only the
portion of the signal that has a certain amplitude or power,
corresponding to the actual interference. Instead of using the
entire received signal with no pre-selection, we propose processing
only the portion of the signal corresponding to a peak and only
deducing the wind speed from that portion. One will note that it is
possible for the selection by the signal processing means to occur
after pre-processing the received signal. For example, a Fourier
transform can first be applied to the received signal, then the
selection can be made on the signal resulting from this transform.
Such a selection can consist of selecting the portion of the
transform having an amplitude or power greater than a threshold
corresponding to the amplitude or power of the Fourier transform of
a signal obtained when measuring in a windless location.
[0024] The signal processing means comprises a means for detecting
a peak, a means for recording the signal within an interval of time
around this peak, and a means for applying a Fourier transform to
this signal. As the signal is occasional, applying a Fourier
transform to the entire signal is more difficult to implement. By
only applying the transform to a given portion of the signal, the
results are particularly satisfactory for determining the wind
speed.
[0025] The time interval during which the signal is recorded is
between 50 and 300 .mu.s (microseconds) around the peak.
[0026] The Fourier transform is done over a range of frequencies of
between 0 and 1 GHz.
[0027] The wavelength of the light emitted by the laser diode is
about 780 nm (nanometers). Other wavelengths can be considered,
however.
[0028] The power of the laser diode is between 0 and 50 mW
(milliwatts), preferably between 0 and 30 mW.
[0029] The Fourier transform is done over an interval of time of
less than 200 .mu.s (microseconds).
[0030] The device is powered by photovoltaic energy. The above
device requires little energy, only a few watts (W), and therefore
a photovoltaic cell can be used to operate this device, for example
a cell providing 10 W of power. This is a particularly attractive
type of power source, as the anemometer is placed outside and
therefore has access to solar energy, and there is no need to
install cabling to supply energy to the device. Note that the power
source is not necessarily part of the device. Also, the device may
be powered by other means, such as a battery for example.
[0031] The signal processing means is capable of providing the
number of particles in the air, in addition to the particle speed.
The amount of air pollution can be quantified in this manner, for
example.
[0032] The device comprises three laser diodes, arranged in a
manner that emits three non-coplanar laser beams. A very precise
measurement of the wind speed in three dimensions is thus obtained,
due to the fact that each laser diode allows obtaining the wind
component in one direction, and the three directions are not
coplanar. In other words, as a laser diode allows measuring the
speed in one direction, the wind speed can be measured in one
direction (one diode), in a plane (two diodes), or in three
dimensions (three diodes).
[0033] The device comprises the processing means for processing the
signal from the interference occurring between the emitted beam and
the reflected beam. In this case, the processing means is part of
the device.
[0034] Another object of the invention is a wind speed measurement
system, comprising the device described above and the processing
means for processing the signal from the interference occurring
between the emitted beam and the reflected beam. In this case, the
processing means is at a distance from the device.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0035] The invention will be better understood from reading the
following description, provided solely as an example, with
references to the attached drawings in which:
[0036] FIG. 1 is a schematic representation of an example of a wind
speed measurement device; and
[0037] FIG. 2 is a diagram illustrating an example of the particle
size distribution for the air particles reflecting the laser
light.
DETAILED DESCRIPTION
[0038] A wind speed measurement device 10 is represented in FIG.
1.
[0039] This device 10 comprises a laser beam emission means 12. The
means 12 comprises a laser diode, for example a Fabry-Perot diode,
emitting in single longitudinal mode, at a wavelength of 785 nm in
this example. Other wavelengths can be used. In this example, the
power of the laser diode 12 is between 0 and 30 mW. This laser
diode 12 comprises an optical cavity 14 for amplifying the emitted
laser light. The device 10 also comprises a focusing means 16, able
to focus the beam emitted by the photodiode 12 towards a focus
space 18. The focus volume 18, or effective volume, is at a
distance D from the focusing means 16, this distance D
corresponding to the focal distance of the device. The focal
distance D is between 5 cm and 2 m.
[0040] The device 10 also comprises a means 20 for receiving a
reflected beam. More specifically, this means 20 is configured to
receive a beam emitted by the diode 12, after this beam is
reflected by a particle in the air located in the focus volume 18,
for example a particle composed of carbon or an ion. As can be seen
in FIG. 2, the particle size in this example is in tenths of a
.mu.m, between 0.1 and 5 .mu.m.
[0041] The receiving means 20 comprises a photodiode, arranged just
behind the laser diode 12, and is associated with the laser diode
12 by self-mixing, meaning that the reflected beam travels back
into the optical cavity 14 so that interference occurs between the
emitted beam and the reflected beam.
[0042] The device 10 also comprises a transmission means 2 which
transmits the interference signal to a processing means 24 for this
signal, to enable deducing the speed of the particle or particles
that reflected the emitted beam. The transmission means 22 is
electronic. It comprises an electronic amplification means which
amplifies the interference signal electronically. The transmission
means consists for example of a transmission board, comprising a
printed circuit onto which electronic components are welded,
including operational amplifiers. The signal processing means 24 is
configured to apply one or more Fourier transforms to the received
signal in order to provide information concerning the wind speed.
In this example, the means 24 is distanced from the device 10, but
it could just as well be integrated with the device 10.
[0043] More specifically, the signal processing means 24 is
configured to select a portion of the signal received by the
transmission means 22, this portion corresponding to the portion of
the signal having an amplitude or power greater than a
predetermined threshold. This predetermined threshold corresponds
to the amplitude or power of the signal received by the
transmission means 22 after measuring in a windless location. In
other words, this predetermined threshold is characteristic of the
average noise of the device 10. This noise is then eliminated from
the received signal when wind measurements are being calculated.
The signal processing means 24 also comprises a peak detection
means and a recording means for recording the received signal. This
recording means is configured to record the signal over an interval
of time around the detected peak. This time interval is between 50
and 300 .mu.s around the peak, for example 90 .mu.s, meaning that
it starts 45 .mu.s before the detected peak and stops 45 .mu.s
after the detected peak. In fact, a particle traveling into the
beam produces a temporary sinusoidal signal of a duration
determined by the interaction time between the particle and the
beam. This duration is generally between 50 .mu.s and 300
.mu.s.
[0044] The signal processing means 24 comprises a means for
applying one or more Fourier transforms to the recorded signal. The
Fourier transform is done over a range of frequencies of between 0
and 1 GHz, for a time interval of less than 200 .mu.s.
[0045] The signal processing means 24 is also capable, in this
example, of providing the number of particles in the air, which
allows deducing the air pollution in the vicinity of the focus
volume 18.
[0046] The device 10 additionally comprises a power source 26,
which may be in the form of a photovoltaic cell or any other type
of power supply which allows the laser diode 12 to operate.
[0047] The operation of the device 10 will now be described.
[0048] In order to measure the wind speed, the laser diode 12 emits
a beam, referred to as the emitted beam, which exits the cavity 14,
travels into the optical system 16, and is then focused towards the
focus volume 18. Air circulates in this focus volume 18, and
therefore particles do as well. The focus volume 18 has sufficient
dimensions to guarantee that at least one particle is inside this
volume at intermittent times, for example at least every second,
and is capable of reflecting the emitted laser beam. After
reflection by at least one of the particles, the reflected beam
travels back through the optical system 16, traverses the cavity
14, and is received by the photodiode 20. Interference can
therefore occur, in the optical cavity 14, between the beam emitted
by the diode 12 and the beam reflected by the particle. Also, the
photodiode 20 receives an interference signal which is then
transmitted to the processing means 24 by the transmission means
22. Note that the signal is electronically amplified before being
transmitted to the processing means 24. The means 24 processes this
received signal to deduce the speed of the particle or particles
that reflected the beam. Because of the effect of the wind, a
particle located within the volume 18 is moving relative to the
receiver 20, so that the frequency of the reflected beam is shifted
relative to the frequency of the emitted beam, due to the Doppler
effect. Also, the frequency shift can be deduced from the
interference signal, and therefore the component of the particle
speed relative to the receiver 20 in direction X.
[0049] More specifically, using the interference signal, first a
portion is selected by eliminating the portion of the received
signal having an amplitude or power less than the threshold
corresponding to the noise of the device 10, determined by
measurement in a windless location. Then a peak is detected in the
selected signal and the signal is recorded for an interval of time
consisting for example of 45 .mu.s before the peak to 45 .mu.s
after the peak. Next, one or more Fourier transforms are applied to
this signal over an interval of time of less than 200 .mu.s. The
frequency shift between the emitted beam and the reflected beam can
be deduced from this Fourier transform, and therefore the speed
component in direction X.
[0050] This is a wind speed measurement device 10 which is
inexpensive and requires very little space. In addition, the device
10 is easy to use because there is no need for alignment with an
interferometer.
[0051] The invention is not limited to the embodiments described
above.
[0052] In particular, in order to obtain better precision in the
wind speed measurement, the device 10 can comprise three laser
diodes 12, each emitting in a non-coplanar direction.
[0053] In the described example, the processing means 24 is placed
at a distance from the device 10. However, the processing means 24
could easily be part of the device 10, for example as an electronic
chip integrated with the device 10, configured to transmit
information to a recorder that is remote from the device 10.
* * * * *