Note: Descriptions are shown in the official language in which they were submitted.
Patent Application
ACTIVE ACOUSTIC PRESSURE MAPPING SYSTEM
Technical Field
15 [0004] The present invention relates to a sensitive surface and, more
particularly, to a
surface that is sensitive to contact pressure and position of an object.
Background
[0005] Touch screens that are most widely used today are based on
capacitive
surfaces, which require a matrix of semiconductor-based detection elements.
While they
20 address most of the current consumer electronics market, they are
limited in many respects.
Among other limitations, scalability of capacitive touch screen is limited by
the high number
of semiconductors required. In addition, capacitive touch screens usually
require costly
manufacturing environment and costly material. Typically, capacitive-based
solutions are
inadequate for pressure determination.
25 [0006] Outside the consumer electronics market, other types of
surfaces dedicated to
pressure mapping are also used. For instance, a pressure mat can be used in
conjunction
with cameras to analyze behaviors of small animals (e.g., pain-related
postural deficits). The
pressure mat has a matrix of pressure detection cells. Each cell is connected
to a
management unit and delivers a pressure measurement. Among other limitations,
the
30 pressure mat is difficult to maintain in working condition (e.g.,
fragile surface ill-adapted to
animals) and presents scalability issues (e.g., required number of cells for
an appropriate
density, required number of input ports for the management unit, etc.).
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[0007] The present invention addresses at least some of the
aforementioned
problems.
Summary
[0008] A first aspect of the present invention is directed to a method
for determining
that a pressure field is applied on a structure. The method comprises
generating a plurality of
acoustic waves within the structure using at least one wave generator and
taking a plurality
of measurements of the plurality of acoustic waves using at least one wave
sensor. The
method also comprises determining that a pressure field is applied to a
surface of the
structure by processing the plurality of measurements. The acoustic waves are
scattered
due, for instance, to the presence of the pressure field. The wave generator
and the wave
sensor may, for instance, be piezoelectric elements. The piezoelectric
elements may
alternate between acting as the wave generator and acting as the wave sensor.
[0009] The structure may be a thin structure made of rigid or flexible
material, planar
or curved and may allow the acoustic wave to be propagated therein. The
acoustic waves
may be propagated as guided waves.
[0010] Processing the measurements may further comprise obtaining a
differential
value between the measurements and comparing the differential value to a
threshold.
[0011] Determining that the pressure field applied may further
comprise processing
the measurements using a model of acoustic wave propagation within the
structure. The
model may, for instance, comprise propagation speed of the plurality of
acoustic waves
within the structure. In addition, if the at least one wave generator and the
at least one wave
sensor are at known coordinates on the structure, the model may be determined
by
processing the measurements before storing the model in a memory. The model
may be
determined by performing a free-calibration while the structure is free of
external pressure
and/or by performing a loaded-calibration while an object of known
characteristics is placed
at a known location on the structure. The model may also be based on
theoretical or
experimental results.
[0012] The method may further comprise providing a model and
determining that the
pressure field is applied to the structure at a location on the surface by
processing the
measurements from one or more wave sensors. The method may then also further
comprise
determining an amplitude of the pressure field at the location on the surface
by processing
the measurements.
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[0013] If, optionally, more than one wave sensor is provided, the
method may further
comprise providing a model comprising at least propagation speed of the
plurality of acoustic
waves within the structure and determining that the pressure field is applied
to the structure
at a location on the surface by processing the measurements from different
wave sensors.
The method may then also further comprise determining an amplitude of the
pressure field at
the location on the surface by processing the measurements from the different
wave
sensors. Optionally, correlating the measurements with the model retrieved
from memory
may further be performed in order to provide a mapping of the pressure field
on the surface
of the structure.
[0014] The method may further comprise determining that at least one object
applies
the pressure field on the structure. It may further be determined that the
object applies the
pressure field on the structure at more than one determined locations with an
associated
number of determined amplitudes. The object may be one or more fingers and the
determined locations and determined amplitudes may allow for fingerprint
determination.
[0015] The location may be determined within a predictable location
tolerancing and
the amplitude is determined within a predictable amplitude tolerancing.
[0016] The method may further comprise approximating, from the
determination, a
position of the at least one object in three dimension.
[0017] Optionally, the method may comprise obtaining a series of
determinations
over time. The series of determinations may be used as an input to an
electronic device. It
may also be determined that at least one animal applies the pressure field on
the structure.
The series of determinations may then be used to evaluate behaviors of the
animal. The
animal may be a mammal such as a rodent or a human.
[0018] A second aspect of the present invention is directed to an
apparatus
comprising a structure on which a pressure field is applied, a wave generator
and a wave
sensor. The wave generator is for generating a plurality of acoustic waves
within the
structure. The wave sensor is for taking a plurality of measurements of the
plurality of
acoustic waves. The apparatus further comprises a processing module for
determining that a
pressure field is applied to a surface of the structure by processing at least
two of the
plurality of measurements. The wave generator and the wave sensor can be
piezoelectric
elements. Each of the piezoelectric elements may further alternate between
acting as the
wave generator and acting as the wave sensor.
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[0019] Processing the measurements by the processing module may
further
comprise obtaining a differential value between the measurements and comparing
the
differential value to a threshold.
[0020] Determining by the processing module that the pressure field is
applied may
.. further comprise processing the measurements using a model of acoustic wave
propagation
within the structure stored in a memory module of the apparatus. The model may
comprise
propagation speed of the plurality of acoustic waves within the structure. The
model may be
based on a theoretical model or experimental results.
[0021] The apparatus may also comprise a plurality of wave generators
and a
plurality of wave sensors. Each wave generator and each wave sensor may be at
known
coordinates on the structure. In such an example, the processing module may
further
determine the model by processing the measurements and storing the model in
the memory
module. The processing module further may determine the model by performing a
free-
calibration while the structure is free of external pressure. The processing
module may
further provide the model by performing a loaded-calibration while an object
of known
characteristics is placed at a known location on the structure.
[0022] The processing module may further provide a model and determine
that the
pressure field is applied to the structure at a location on the surface by
processing the
plurality of measurements from different wave sensors from the plurality of
wave sensors.
[0023] If the apparatus comprises a plurality of wave sensors, the
processing module
may further provide a model comprising at least propagation speed of the
plurality of acoustic
waves within the structure and determine that the pressure field is applied to
the structure at
a location on the surface by processing the plurality of measurements from
different wave
sensors from the plurality of wave sensors. The model is either based on a
theoretical
approach or on experimental results. The processing module may further
determine an
amplitude of the pressure field at the location on the surface by processing
the
measurements from the different wave sensors. For instance, the processing
module may
correlate the measurements against the model retrieved from memory and provide
a
mapping of the pressure field on the surface of the structure from the
correlated
measurements. The processing module may determine that at least one object
applies the
pressure field on the structure. The object that applies the pressure field on
the structure may
be at more than one determined locations, the pressure field being of an
associated number
of determined amplitudes. The object may be one or more fingers and the
determined
locations and determined amplitudes allow for fingerprint determination. The
location may be
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determined by the processing module within a predictable location tolerancing
and the
amplitude is determined within a predictable amplitude tolerancing. The
processing module
may further approximate, from the determination, a position of the at least
one object in three
dimensions.
[0024] The processing module may further obtain a series of determinations
over
time. The series of determinations may be used as an input to an electronic
device. The
processing module may further determine that at least one animal applies the
pressure field
on the structure and use the series of determinations to evaluate behaviors of
the animal.
The animal may be a mammal such as a rodent or a human.
Brief description of the drawings
[0025] Further features and exemplary advantages of the present
invention will
become apparent from the following detailed description, taken in conjunction
with the
appended drawings, in which:
[0026] Figure 1 is a schematic diagram representing exemplary
interactions of
acoustic waves in the presence of a local pressure field, in accordance with
the teachings of
the present invention;
[0027] Figures 2A and 2B, referred to together as Figure 2, present
graphs illustrating
an evolution of the phase velocity for AO mode (2A) and SO mode (2B) in a
surface under a
pressure, in accordance with the teachings of the present invention;
[0028] Figure 3 is a graph illustrating an evolution of a reflection
coefficients in an
exemplary 0.25 mm thick polycarbonate structure associated with SO mode at 100
kHz with
respect to the local pressure for different lengths of application dx, in
accordance with the
teachings of the present invention;
[0029] Figure 4 is a visual representation of an exemplary prototype
used for
development in accordance with the teachings of the present invention;
[0030] Figure 5 is an exemplary imaging result obtained from the
exemplary
prototype using a 1 kg mass over a 6mm x 6mm area in accordance with the
teachings of the
present invention;
[0031] Figure 6 is a perspective view of an exemplary apparatus in
accordance with
the teachings of the present invention;
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[0032] Figure 7 is a modular representation of an exemplary controller
unit in
accordance with the teachings of the present invention; and
[0033] Figure 8 is a flow chart of an exemplary method for determining
that a
pressure field is applied on a structure in accordance with the teachings of
the present
invention.
Detailed description
[0034] The present invention proposes a method and an apparatus for
determining
that a pressure field is applied on a structure. The method and apparatus may
also be used
for determining the position and the strength of the pressure field applied to
the structure. A
plurality of acoustic waves are generated within the structure using at least
one wave
generator and a plurality of measurements of the plurality of acoustic waves
is taken using at
least one wave sensor. A pressure field applied to a surface of the structure
is determined by
processing at least two of the plurality of measurements. It is thought that
the measurements
correspond to reflections and echoes of the acoustic waves within the
structure, as affected
by a given pressure or pressure field. As such, the acoustic waves are
scattered due, for
instance, to the presence of the pressure field. The wave generator and the
wave sensor
may, for instance, be piezoelectric elements. The piezoelectric elements may
alternate
between acting as the wave generator and acting as the wave sensor. Other
examples of
wave generators and wave sensors include ultrasonic wedges and air-coupled
ultrasonic
transducers.
[0035] The structure may be a thin structure made of rigid or flexible
material, planar
or curved and may allow the acoustic wave to be propagated therein. The
acoustic waves
may be propagated as guided waves.
[0036] Processing the measurements may further comprise obtaining a
differential
value between the measurements and comparing the differential value to a
threshold.
[0037] Determining that the pressure field is applied may further
comprise processing
the measurements using a model of acoustic wave propagation within the
structure. The
model may, for instance, comprise propagation speed of the plurality of
acoustic waves
within the structure. In addition, if the at least one wave generator and the
at least one wave
sensor are at known coordinates on the structure, the model may be determined
by
processing the measurements before storing the model in a memory. The model
may be
determined by performing a free-calibration while the structure is free of
external pressure
and/or by performing a loaded-calibration while an object of known
characteristics is placed
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at a known location on the structure. The model may be based on theoretical or
empirical
approaches.
[0038] A model may determine that the pressure field is applied to the
structure at a
location on the surface by processing the measurements from different wave
sensors. An
amplitude of the pressure field at the location on the surface may further be
determined by
processing the measurements of the scattered wave due to the local pressure
field.
Optionally, correlating the measurements with the model retrieved from memory
may further
be performed in order to provide a mapping of the pressure field on the
surface of the
structure.
[0039] If, optionally, more than one wave sensor is provided, a model
comprising at
least propagation speed of the plurality of acoustic waves within the
structure may be
providing and it may determine that the pressure field is applied to the
structure at a location
on the surface by processing the measurements from different wave sensors. An
amplitude
of the pressure field at the location on the surface may further be determined
by processing
the measurements from the different wave sensors. Optionally, correlating the
measurements against the model retrieved from memory may further be performed
in order
to provide a mapping of the pressure field on the surface of the structure.
[0040] It may further be determined that at least one object applies
the pressure field
on the structure. It may further be determined that the object applies the
pressure field on the
structure at more than one determined locations with an associated number of
determined
amplitudes. The object may be one or more finger and the determined locations
and
determined amplitudes may allow for fingerprint determination. The location
may be
determined within a predictable location tolerancing and the amplitude is
determined within a
predictable amplitude tolerancing. From the determination, a position of the
at least one
object in three dimension may be approximately provided.
[0041] A series of determinations may be obtained over time. The
series of
determinations may be used as an input to an electronic device. It may also be
determined
that at least one animal applies the pressure field on the structure. The
series of
determinations may then be used to evaluate animal behavior. The animal may be
a
mammal such as a rodent or a human.
[0042] The present invention relates to a method and an apparatus that
can be used
for determining the spatiotemporal distribution of at least one pressure level
applied on a
surface of a structure. As will be detailed herein, some structures allow for
acoustic waves to
be propagated therein. In some structures, the acoustic waves will be
propagated as guided
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waves. For instance, thin structures usually allow for ultrasonic acoustic
waves to be
propagated as guided waves. Reflection and dispersion of the guided waves can
then be
modeled within the structure. It has been determined that a pressure field
applied to the
modeled structure at one or more specific locations predictably affect the
reflection and
dispersion of the acoustic waves. As such, based on the model, it is possible
to determine
applied pressure and amplitude of at least one applied pressure. Curved or
irregular
structures (e.g., those structures that can be modeled) would also be suitable
in the context
of the present invention. Various parameters are known to affect the precision
of the
determination of location and amplitude. Some parameters can be set in order
to obtain an
expected precision (e.g., depending on the expected use of the determination).
[0043] The present invention is based on the interaction of acoustic
waves in the
presence of a local pressure field. Reference is now made to the drawings in
which Figure 1
shows a schematic diagram representing exemplary interactions of acoustic
waves (I) in the
presence of a local pressure field (P), in accordance with the teachings of
the present
invention. The current state of the research performed suggests that the local
contact of an
object on a structure is responsible for three different effects.
[0044] Firstly, it appears that the object creates a reaction force
into the host
structure, such that a local deformation is observed. However, the local
change of thickness
is not seen as important (few microns), even on a very flexible structure. In
this case, the
current research suggests that the propagation of waves is not impaired by
this phenomenon
and no local reflection is induced.
[0045] Secondly, another effect of local added object is that part of
the energy
appears to be transmitted into the object, responsible for a loss of
transmitted energy. This
effect can be observed when a perfect contact is ensured between the host
structure and the
added object and when the acoustic impedances of both structures are similar.
However, for
sensitive surfaces, such as touch-screens or pressure mapping solutions, the
sensed object
is expected to be a tissue with associated low acoustic impedance compared to
metallic or
polymer structures. Thus, in the context of the present invention, it appears
that this effect
can be neglected when considering the interaction of an acoustic wave with a
local added
mass.
[0046] Thirdly, an added mass M applied at the surface of a thin
structure appears to
create a local change of surface stress, such that the propagation of acoustic
waves, and
especially guided waves (for instance AO and SO modes), is locally modified.
The added
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mass M applied over a surface S can be described as a local change of boundary
stresses
(equations are not necessary since it is an approximation).
[0047] This local change of boundary condition at the contact appears
to induce a
change of propagation characteristics. Indeed, in the absence of added mass,
the dispersion
relation is obtained by considering the traction free boundary conditions at
the upper and
lower surfaces of the plate while in the presence of added mass M distributed
over a surface
S, the resulting pressure P is responsible for a local change of the stress
field at the upper
boundary, while the other boundary remains free of stress, leading to a new
dispersion
relation (local change of phase and group velocities at the contact) as
presented in Figure 2.
[0048] In that case, the mode shapes associated with propagating modes
(antisymmetric AO and symmetric SO) are strongly modified and surface waves
are mostly
observed in the contact region. This local change of propagating modes induces
reflection of
acoustic waves in the medium that may be estimated theoretically and is
related to:
[0049] Material properties (Young's modulus, density and Poisson's
ratio),
[0050] Thickness of the host structure,
[0051] Frequency of incident field,
[0052] Mode of the incident wave (symmetric, antisymmetric, Shear-
Horizontal,
Surface wave),
[0053] Surface of contact of the mass,
[0054] Added pressure.
[0055] As an example, Figure 3 represents the evolution of the
reflection coefficient
associated with SO mode at 100 kHz with respect to the added pressure for a
0.25 mm thick
polycarbonate structure for various pressure application lengths. In Figure 3,
it appears that
no reflections are observed below 3 Pa no matter the contact length. Moreover,
above 100
Pa, the reflection of SO mode is total (reflection coefficient of 1), defining
a range of
detectable pressure levels. Those minimal and maximal pressure values define
the pressure
sensitivity range, depending on the desired application and are related to the
material
properties and thickness only.
[0056] Some parameters of interest that have been determined during
prototype
design will now be discussed. The interaction of a pressure wave with a local
pressure has
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been discussed hereinabove. For detection and evaluation of pressure field,
the reflection
coefficient at the contact may be mapped using an imaging algorithm (e.g.,
EUSR, Excitelet,
etc). Sensitivity to an applied pressure or pressure field will be determined
by parameters of
the host structure and propagation characteristics therewithin. More
specifically, depending
on the application, requirements can be defined:
[0057] Pressure sensitivity: A given application likely provides a
requirement of
sensitivity within a given range of pressure. Thus, minimal and maximal
pressures are to be
defined. It appears that those parameters are related to the material
thickness and properties
(Young's modulus, density and Poisson's ratio). In the case of touch screen
applications, for
.. instance, pressure levels from 10 to 10 000 Pa have been identified, such
that thin structures
(below 1mm) with Young's modulus above 5GPa can be employed.
[0058] Imaging precision: According to the research conducted, the
mode and
frequency of an acoustic wave will determine if imaging of the pressure field
is possible.
Indeed, the frequency and mode selection determines the wavelength A of the
generated
wave. The imaging precision is related to this wavelength and imaging spot
surfaces are of
the order of A2. For touch screen application, for instance, a wavelength of
approximately
5mm could be used. The choice of mode, frequency and piezoceramic size are
derived from
this value after selecting the material properties. Moreover, the precision of
imaging contour
is related to the number of wave generators and sensors used in the
application. The
precision of imaging contour may also be related to the number of units and
the quality of the
signal processing algorithm.
[0059] Signal to noise ratio (SNR): For proper imaging for real-time
application,
reflected signals must be measured with high SNR. The amplitude of the
reflected signal is
affected by the actuator energy sent (e.g., the wave generator energy) into
the host structure,
the propagation distance between emitter, reflector and sensor, the sensor
sensitivity and
wave attenuation which is related to mode, frequency and material damping. For
large
applications (above .5m), it has been determined that AO mode on metallic
structures can be
employed due to its low attenuation coefficient. For smaller applications, it
appears that
polymers with low damping coefficients should be employed. Piezoceramic
characteristics
(material, size and thickness) influence the actuator and sensor
characteristics. Commonly,
circular piezoceramics of 2 mm to 10 mm diameter and 0.5mm thickness are used.
[0060] Real-time application: Depending on the refresh rate of the
application
(number NI of images per second), the acquisition parameters can be derived.
Indeed, the
averaging A and acquisition time T can be determined using the relation: NI =
1 / A*T. The
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number N of transducer units, the sampling rate Fs and size of grid for
imaging are
determined by the limitations of the processing unit. For portable application
(FPGA
integration, for instance), 8 units processed at 10 MHz can be used for
imaging over a grid of
100x100 pixels.
[0061] In the course of the research work performed, an exemplary prototype
has
been developed for determination of pressure field for touch screen
application over a large
surface. The sensitive part is composed of the 0.25 mm thick stainless steel
plate. The plate
dimensions are 500 x 500 mm and it is instrumented with 8 piezoceramics (4
actuators and 4
sensors) of 10 mm diameter and 0.25 mm thickness located at the periphery. In
the context
of the present prototype, an absorbing layer (viscoelastic tape) is added at
the edges in order
to prevent reflections from the boundaries. Figure 4 is a visual
representation of an
exemplary prototype used for development in accordance with the teachings of
the present
invention.
[0062] The signal generation, acquisition and processing can be
performed by a
dedicated platform (NI PXI 7962) and analysis is performed using Matlab
application. For
embedded solution, implementation on a Field Programmable Gate Arrays (FPGA)
card can
be envisaged. Figure 5 shows an exemplary imaging result obtained from the
exemplary
prototype of Figure 4 using a 1 kg mass over a 6mm x 6mm area.
[0063] An exemplary flow chart will now be described with particular
reference to the
exemplary prototype of Figure 4. Each unit (actuator / sensor / processing)
acts
independently of the other. However for imaging of the whole structure, the
measured signals
from each unit are used in order to determine the location and intensity of
the receiver. Thus,
the steps of the exemplary flowchart are performed for each time step between
two
consecutive pressure mapping results.
[0064] 1. Signal generation
N cycles burst (typically N= 5.5)
Central frequency (typically f= 300 kHz)
[0065] 2. Signal acquisition
Averaging (typically 10 to 100)
Recording length (typically 1 ms)
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Sampling frequency (typically 10 MHz)
[0066] 3. Signal processing
- denoising (band pass filtering)
- reference subtraction
[0067] 4. Imaging
- Grid of imaging points (typically 100 x 100)
- Processing algorithm (EUSR, Excitelet)
- Number of units (typically 4 to 8)
[0068] 5. Feature extraction
Maximum detection
Pressure determination
- Tracking
[0069] As mentioned previously, in the context of the present
invention, it has been
found that generating the waves in the structure was best achieved by using a
piezoelectric
.. element, acting as a generator, at the periphery of the structure of
interest. A plurality of
piezoelectric elements, acting as piezoelectric sensors, then measure the
response of the
structure to the waves. It has also been determined that by using a plurality
of piezoelectric
elements, they could be used, in turn, as the wave generator and piezoelectric
sensors. For
instance, the piezoelectric elements (or piezoelectric ceramics) may be
permanently fixed to
the structure (e.g., glued or eventually built in). The response of the
structure to the waves is
collected as a plurality of signals. As mentioned above, it is thought that
the signals
correspond to reflections and echoes of the waves within the structure, as
affected by a
given pressure or pressure field. However, an important exemplary advantage
with regard to
the industrial applicability of the solution is that the plurality of signals
collected allow to
predictably represent location and amplitude of at least one pressure applied
to the structure.
[0070] Based on the model derived from the structure, a determination
can then be
made on an eventual pressure applied to the surface. For example, it has been
found that
using an imaging tool such as Embedded Ultrasonic Structural Radar (EUSR)
and/or
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Excitelet (as mentioned in the referenced document), allows for determining a
signature of
the collected signals and to plot a two-dimensional map of the structure.
[0071] Figure 6 shows a perspective view of an exemplary apparatus 100
in
accordance with the teachings of the present invention. A structure 110 is
provided with a
plurality of transducers 132-146 thereon. The transducer 140 is illustrated in
a different
shade to illustrate that it functions as an ultrasonic wave generator while
the other
transducers 132-138, 142-146 function as wave sensors. The transducers are
shown
connected to an exemplary data bus 150, which connects the transducers to a
controller unit
120_ Skilled person will understand that only one generator is shown, but that
a plurality of
generators may be used in order to increase precision to a desired level.
Still in order to
increase precision, the transducers 132-146 may exchange their role as
generator and
sensors.
[0072] It is noticed that, under the effect of a pressure applied by
an object (not
shown) on the structure 110, the wave pattern changes and can be measured by
the
transducers 132-146 then acting as wave sensors. In the context of the example
of Figure 6,
the measurements can be passed on to the controller unit 120 where it can be
processed to
identify a position in the plane and to determine pressure data with respect
to the
measurements. For additional precision, processing may be improved with the
use of three
or more sensors.
[0073] Mapping tools such Embedded Ultrasonic Structural Radar (EUSR)
and/or
Excitelet may then be used to establish a spatial mapping of locations and
amplitudes of the
applied pressure. Interpretation of the results obtained by these imaging
algorithms is
enhanced by knowledge of the mechanical properties of the structure 110.
Calibration may
be required in order to precisely identify the properties and material of the
structure 110 may
need to be changed to achieve desired results.
[0074] Figure 7 shows a modular representation of the exemplary
controller unit 120
in accordance with the teachings of the present invention. The controller unit
120 comprises
a data acquisition module 210 for obtaining the measurements from the
transducers 132-
138, 140-146 and a wave generation module for controlling the transducer 140.
As
mentioned above, the wave generation module 220 may further use more than one
of the
transducers 132-146 as wave sensors and/or more than one of the transducers
132-146 as
wave generator(s). The wave generation module 220 may further control the
transducers
132-146 so that they exchange their role as generator and sensors (e.g. please
provide
range of frequency).
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[0075] Thus, by applying an electrical signal pulse having a center
frequency (e.g.,
typically in the order of several hundred kilohertz as a burst), it becomes
possible to generate
a wave propagating in a guided manner, within the structure, over the time and
space.
Generated waves are attenuated differently in different materials.
Viscoelastic material (e.g.
elastomers) tend to attenuate waves rapidly while, conversely, large
propagation distances
can be reached in the case of low viscoelastic materials (e.g. Corning's
Gorilla Glass 2,
metals and amorphous polymers).
[0076] The location of sources of reflection (e.g., position of object
on the structure
110) may be obtained by processing of measurements. The transducers 132-146
(e.g.,
piezoelectric ceramics) may be distributed over the structure 110 or its
periphery (sparse
array) or condensed in order to achieve an antenna (compact array).
[0077] In order to derive a map of the pressure amplitude on the
structure 110, an
imaging tool can be used (such Embedded Ultrasonic Structural Radar (EUSR) or
Excitelet).
EUSR is based on the estimate of the position of a reflector using time data
spread (Time-of-
Flight), which ignores the dispersive nature of waves propagating. The result
is a rapid but
imprecise determination. Excitelet is based on the correlation of measured
reflections with
synthetic signals from the theoretical propagation or experimental
measurements (e.g.
model) of the waves. The Excitelet can detect defects in thin structures and
it appears
advantageous to use this approach in this case, at least for applications
requiring higher
precision. A mix of both techniques may also be used (e.g., depending on an
application
running on an electronic product which has the structure 110 as an input
device). For
instance, in tests performed in a research context with two identical objects,
EUSR shows
the extent of pressure areas but the relative intensity of each differs while
Excitelet shows the
two pressure zones with the same intensity (with less than 10% error).
[0078] In the context of the research performed, it appears that the size
of the area to
be inspected is limited by the spread of waves. Indeed, any material has a
coefficient
representing the rate viscoelastic damping mechanical waves therein. Also, the
material and
the frequencies of waves generated should be chosen carefully in view of the
desired
application to ensure that the echo can be spread without limitation, other
than the
deformation, to the sensors. The expected sizes for this type of application
can range from a
few centimeters (e.g., graphic palettes) to more than one meter (e.g., medical
and oversized
touch screen).
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[0079] If robustness to external stress is a criteria, the material
should then have a
strong resistance to external shocks. This is characterized by a large yield
(of the order of
several hundreds of MPa).
[0080] To obtain better imaging results, is appears that waves
generated are to be as
little dispersive as possible and a limited number of modes propagation should
be respected.
These parameters can be adjusted by controlling the size of piezoelectric
ceramics, their
positioning, the frequencies of electrical signals sent and the
characteristics of the
propagation medium (thickness and materials).
[0081] The quality of the results obtained by the imaging algorithms
is improved by
knowledge of mechanical properties of the propagation. The accuracy of the
pressure
mapping depends on the imaging algorithm implemented and the desired response
time. At
the present stage of development, the use of Field Programmable Gate Arrays
(FPGA) have
allowed using the Excitelet algorithm with a 100 x 100 grid and achieve 25
frames per
second.
[0082] More specifically, in the example of the prototype achieving real-
time
performance (e.g., 25 frames per second), processing is performed by a high-
speed FPGA in
coordination with LabVIEW. The imaging algorithm (e.g., EUSR, Excitelet, etc.)
is
implemented on the dedicated FPGA, which then performs data acquisition
operations and
image processing. In the present example, an electronic signal conditioning
has also been
developed to adapt the impedance of the sensor and pre-amplify the signals. It
is expected
that dedicated solutions will keep improving on those results and provide
diverse real-time
ranges of sensitivity and size.
[0083] Figure 8 shows a flow chart of an exemplary method for
determining that a
pressure field is applied on a structure in accordance with the teachings of
the present
invention. The method comprises generating a plurality of acoustic waves
within the structure
using at least one wave generator 810 and taking a plurality of measurements
of the plurality
of acoustic waves using at least one wave sensor 820. The method also
comprises
determining that a pressure field is applied to a surface of the structure by
processing the
plurality of measurements 830. The acoustic waves are scattered due, for
instance, to the
presence of the pressure field. The wave generator and the wave sensor may,
for instance,
be piezoelectric elements. The piezoelectric elements may alternate between
acting as the
wave generator and acting as the wave sensor.
[0084] To demonstrate functional and economical viability of the
present invention,
new prototypes that are more compact are under research. The treatment of
signals is of
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specific interest. A larger number of sensors are expected in the new
prototypes. A structure
of lm x 1m is under development for specific application to the medical field.
Requirements
in terms of detectability and measurement accuracy will also be determined
with respect to
data required by the partners in the medical field.
[0065] In the context of the present invention, a processor module may
represent a
single processor with one or more processor cores or an array of processors,
each
comprising one or more processor cores. A memory module may comprise various
types of
memory (different standardized or kinds of Random Access Memory (RAM) modules,
memory cards, Read-Only Memory (ROM) modules, programmable ROM, etc.). A
storage
devices module may represent one or more logical or physical as well as local
or remote
hard disk drive (HDD) (or an array thereof). The storage devices module may
further
represent a local or remote database made accessible to a network node by a
standardized
or proprietary interface. A network interface module represents at least one
physical interface
that can be used to communicate with other network nodes. For the sake of
simplicity, the
following example related to the network node will refer to a repository to
represent the
various means that can be used to store records. The network interface module
may be
made visible to the other modules of the network node through one or more
logical
interfaces. The actual stacks of protocols used by the physical network
interface(s) and/or
logical network interface(s) of the network interface module do not affect the
teachings of the
present invention. The variants of processor module, memory module, network
interface
module and storage devices module usable in the context of the present
invention will be
readily apparent to persons skilled in the art. Likewise, even though explicit
mentions of the
memory module and/or the processor module are not made throughout the
description of the
present examples, persons skilled in the art will readily recognize that such
modules are
used in conjunction with other modules of the network node to perform routine
as well as
innovative steps related to the present invention.
[0086] A method is generally conceived to be a self-consistent
sequence of steps
leading to a desired result. These steps require physical manipulations of
physical quantities.
Usually, though not necessarily, these quantities take the form of electrical
or magnetic
signals capable of being stored, transferred, combined, compared, and
otherwise
manipulated. It is convenient at times, principally for reasons of common
usage, to refer to
these signals as bits, values, parameters, items, elements, objects, symbols,
characters,
terms, numbers, or the like. It should be noted, however, that all of these
terms and similar
terms are to be associated with the appropriate physical quantities and are
merely
convenient labels applied to these quantities. The description of the present
invention has
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been presented for purposes of illustration but is not intended to be
exhaustive or limited to
the disclosed embodiments. Many modifications and variations will be apparent
to those of
ordinary skill in the art. The embodiments were chosen to explain the
principles of the
invention and its practical applications and to enable others of ordinary
skill in the art to
understand the invention in order to implement various embodiments with
various
modifications as might be suited to other contemplated uses.
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