U.S. patent application number 15/060117 was filed with the patent office on 2016-06-30 for noise reduction in infrasound detection.
The applicant listed for this patent is University of Alaska Fairbanks. Invention is credited to Jeffrey L. Rothman.
Application Number | 20160187192 15/060117 |
Document ID | / |
Family ID | 51521282 |
Filed Date | 2016-06-30 |
United States Patent
Application |
20160187192 |
Kind Code |
A1 |
Rothman; Jeffrey L. |
June 30, 2016 |
NOISE REDUCTION IN INFRASOUND DETECTION
Abstract
Provided are methods, circuits and apparatuses for detecting
pressure variations. The circuit can comprise at least two pressure
sensors electrically coupled in parallel. At least one pressure
sensor can have a differential input and a differential output. The
circuit can also comprise a first switching mechanism electrically
coupled to the differential input of the at least one pressure
sensor. The first switching mechanism can be configured to
electrically couple a first current source to the at least one
pressure sensor according to a first reference signal. The circuit
can also comprise a second switching mechanism electrically coupled
to the differential output of the at least one pressure sensor. The
second switching mechanism can be configured to electrically couple
a second current source to the at least one pressure sensor
according to a second reference signal.
Inventors: |
Rothman; Jeffrey L.;
(Fairbanks, AK) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
University of Alaska Fairbanks |
Fairbanks |
AK |
US |
|
|
Family ID: |
51521282 |
Appl. No.: |
15/060117 |
Filed: |
March 3, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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14057704 |
Oct 18, 2013 |
9310246 |
|
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15060117 |
|
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61716324 |
Oct 19, 2012 |
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Current U.S.
Class: |
73/719 |
Current CPC
Class: |
G01V 1/36 20130101; G01V
1/28 20130101; G01H 17/00 20130101; G01V 1/36 20130101; G01H 11/06
20130101 |
International
Class: |
G01H 17/00 20060101
G01H017/00 |
Claims
1. A circuit for detecting pressure variations, comprising: at
least two pressure sensors electrically coupled in parallel,
wherein at least one of the pressure sensors comprises a
differential input and a differential output; a first switching
mechanism electrically coupled to the differential input of the at
least one pressure sensor, the first switching mechanism is
configured to electrically couple a first current source to the at
least one pressure sensor according to a first reference signal;
and a second switching mechanism electrically coupled to the
differential output of the at least one pressure sensor, the second
switching mechanism is configured to electrically couple a second
current source to the at least one pressure sensor according to a
second reference signal.
2. The circuit of claim 1, wherein the first switching mechanism is
configured to increase a signal-to-noise ratio of the at least one
pressure sensor by a predefined factor.
3. The circuit of claim 1, wherein the second switching mechanism
is configured to neutralize an alternating current offset voltage
of the at least one pressure sensor.
4. The circuit of claim 1, further comprising an amplifier
electrically coupled to the at least two pressure sensors, the
amplifier is configured to receive differential signals from the at
least one pressure sensor and provide a signal proportional to a
difference of voltages of the differential signals, wherein the
differential signals received by the amplifier are modified by
second switching mechanism.
5. The circuit of claim 4, wherein the second switching mechanism
is configured to provide feedback to null an offset directly at the
at least one pressure sensor, and wherein the amplifier is
optimized for high gain and low noise.
6. The circuit of claim 4, further comprising a bandpass filter
electrically coupled to the amplifier, wherein the bandpass filter
is configured to receive a signal from the amplifier and provide a
portion of the signal within a predefined frequency range.
7. The circuit of claim 6, further comprising a demodulator
electrically coupled to the bandpass filter, wherein the
demodulator is configured to receive an alternating current (AC)
signal from the bandpass filter and provide a direct current (DC)
signal.
8. The circuit of claim 1, wherein the at least two pressure
sensors have a front and a back, and wherein a back of a first
pressure sensor of the at least two pressure sensors faces a back
of a second pressure sensor of the at least two pressure
sensors.
9. The circuit of claim 1, further comprising a resistor
electrically coupled to the first switching mechanism, the resistor
is configured to provide a resistance that varies based on changes
in temperature.
10. The circuit of claim 1, wherein the at least two pressure
sensors comprise a set of resistors configured as a Wheatstone
bridge, at least one of the resistors of the set of resistors is
configured to provide a resistance that varies based on changes in
pressure upon the resistor, and wherein the first reference signal
and the second reference signal are phase locked.
11. The circuit of claim 1, wherein the at least two pressure
sensors are electrically coupled in parallel and in phase.
12. The circuit of claim 1, wherein the at least two pressure
sensors are connected pneumatically in parallel and in phase.
13. An apparatus for detecting pressure variations, comprising: a
sensing circuit, comprising, at least two pressure sensors
electrically coupled in parallel, wherein at least one of the
pressure sensors has a differential input and a differential
output, a first switching mechanism electrically coupled to the
differential input of the at least one pressure sensor, the first
switching mechanism is configured to electrically couple a first
current source to the at least one pressure sensor according to a
first reference signal, and a second switching mechanism
electrically coupled to the differential output of the at least one
pressure sensor, the second switching mechanism is configured to
electrically couple a second current source to the at least one
pressure sensor according to a second reference signal; a manifold
configured to receive a pressure and communicate the pressure to
the at least two pressure sensors; and a reference chamber
configured to provide a reference pressure to the at least two
pressure sensors.
14. The apparatus of claim 13, wherein the first switching
mechanism is configured to increase a signal-to-noise ratio of the
at least one pressure sensor by a predefined factor.
15. The apparatus of claim 13, wherein the second switching
mechanism is configured to neutralize an alternating current offset
voltage of the at least one pressure sensor.
16. The apparatus of claim 13, wherein the sensing circuit further
comprises an amplifier electrically coupled to the at least two
pressure sensors, the amplifier is configured to receive
differential signals from the at least one pressure sensor and
provide a signal proportional to a difference of voltages of the
differential signals, wherein the differential signals received by
the amplifier are modified by the second switching mechanism.
17. The apparatus of claim 13, wherein the at least two pressure
sensors are electrically coupled in parallel and in phase, and
wherein the at least two pressure sensors are connected
pneumatically in parallel and in phase.
18. A method for detecting pressure variations, comprising:
providing a power supply to at least two pressure sensors based on
a first reference signal, wherein the at least two pressure sensors
are electrically coupled in parallel; receiving a differential
signal from the at least two pressure sensors; neutralizing, based
on a second reference signal, an alternating current offset voltage
of the differential signal; and amplifying the neutralized
differential signal.
19. The method of claim 18, wherein amplifying the neutralized
differential signal comprises: receiving the neutralized
differential signal from the at least two pressure sensors; and
amplifying a difference between a voltage of a first signal of the
neutralized differential signal and a voltage of a second signal of
the neutralized differential signal.
20. The method of claim 18, wherein providing a power supply to the
at least two pressure sensors comprises increasing a
signal-to-noise ratio of the differential signal by a predefined
factor.
21. The method of claim 18, wherein neutralizing the alternating
current offset voltage of the differential signal comprises
alternating, based on the second reference signal, between
providing a current source to a first differential output of the at
least two pressure sensors and providing the current source to a
second differential input of the at least two pressure sensors.
22. The method of claim 18, wherein the at least two pressure
sensors have a front and a back, and wherein a back of a first
pressure sensor of the at least two pressure sensors faces a back
of a second pressure sensor of the at least two pressure
sensors.
23. The method of claim 18, wherein providing a power supply to the
at least two pressure sensors comprises alternating, based on the
first reference signal, between providing a current source to a
first differential input of the at least two pressure sensors and
providing the current source to a second differential input of the
at least two pressure sensors.
24. The method of claim 18, further comprising filtering the
amplified signal within a predefined frequency range.
25. The method of claim 24, wherein the filtered signal is an
alternating current (AC) signal, further comprising converting the
filtered signal to a direct current (DC) signal.
26. The method of claim 18, wherein providing a power supply to at
least two pressure sensors comprises providing a temperature
compensating power supply based on a resistor configured to change
resistance based on a change in temperature.
27. The method of claim 18, wherein the at least two pressure
sensors comprise a set of resistors configured as a Wheatstone
bridge, at least one of the resistors of the set of resistors is
configured to provide a resistance that varies based on changes in
pressure upon the resistor, and wherein the first reference signal
and the second reference signal are phase locked.
28. The method of claim 18, wherein neutralizing, based on a second
reference signal, an alternating current offset voltage of the
differential signal comprises providing feedback to null an offset
directly at the at least two pressure sensors, and wherein
amplifying the neutralized differential signal is optimized for
high gain and low noise.
29. The method of claim 18, wherein the at least two pressure
sensors are electrically coupled in parallel and in phase.
30. The method of claim 18, wherein the at least two pressure
sensors are connected pneumatically in parallel and in phase.
Description
CROSS REFERENCE TO RELATED PATENT APPLICATIONS
[0001] This application is a continuation of U.S. Nonprovisional
application Ser. No. 14/057,704 filed Oct. 18, 2013 which claims
priority to U.S. Provisional Application No. 61/716,324 filed Oct.
19, 2012, herein incorporated by reference in their entireties.
BACKGROUND
[0002] Infrasound occurs at frequencies below the range of human
hearing. These signals are of interest because of the signals'
ability to propagate long distances with very little attenuation,
making them useful for both scientific and military applications
(nuclear test ban treaty monitoring in particular). In the past,
infrasound microphones have been built with large diaphragms and
reference chambers to achieve the desired sensitivity. For many
applications, the size of these devices makes them impractical for
many applications. Thus, there is a need for sensing devices
reduced in size, weight and cost, which are more practical for a
wide range of new uses.
SUMMARY
[0003] It is to be understood that both the following general
description and the following detailed description are exemplary
and explanatory only and are not restrictive, as claimed. Provided
are methods, circuits and apparatuses for detecting pressure
variations, such as infrasound. In one aspect, exemplary circuits
can comprise at least two pressure sensors electrically coupled in
parallel. At least one of the pressure sensors can comprise a
differential input and a differential output. The circuit can also
comprise a first switching mechanism electrically coupled to the
differential input of the at least one pressure sensor. The first
switching mechanism can be configured to electrically couple a
first current source to the at least one pressure sensor according
to a first reference signal. The circuit can also comprise a second
switching mechanism electrically coupled to the differential output
of the at least one pressure sensor. The second switching mechanism
can be configured to electrically couple a second current source to
the at least one pressure sensor according to a second reference
signal.
[0004] In another aspect, exemplary apparatuses can comprise a
sensing circuit. The sensing circuit can comprise at least two
pressure sensors electrically coupled in parallel. At least one of
the pressure sensors can have a differential input and a
differential output. The sensing circuit can comprise a first
switching mechanism electrically coupled to the differential input
of the at least one pressure sensor. The first switching mechanism
can be configured to electrically couple a first current source to
the at least one pressure sensor according to a first reference
signal. The sensing circuit can comprise a second switching
mechanism electrically coupled to the differential output of the at
least one pressure sensor. The second switching mechanism can be
configured to electrically couple a second current source to the at
least one pressure sensor according to a second reference signal.
The apparatus can also comprise a manifold configured to receive a
pressure and communicate the pressure to the at least two pressure
sensors. The apparatus can also comprise a reference chamber
configured to provide a reference pressure to the at least two
pressure sensors. The apparatus can further comprise a housing
configured to enclose the at least two pressure sensors.
[0005] In yet another aspect, exemplary methods can comprise use of
a sensing device. The sensing device can comprise at least two
pressure sensors electrically coupled in parallel. At least one of
the pressure sensors can comprise a differential input and a
differential output. The sensing device can comprise a first
switching mechanism electrically coupled to the differential input
of the at least pressure sensor. The first switching mechanism can
be configured to electrically couple a first current source to the
pressure sensors according to a first reference signal. The sensing
device can comprise a second switching mechanism electrically
coupled to the differential output of the at least one pressure
sensor. The second switching mechanism can be configured to
electrically couple a second current source to the pressure sensors
according to a second reference signal. The method can also
comprise coupling the sensing device to a power source. The method
can further comprise collecting pressure measurements with the
sensing device.
[0006] In yet another aspect, exemplary methods can comprise
providing a power supply to at least two pressure sensors based on
a first reference signal. The at least two pressure sensors can be
electrically coupled in parallel. A differential signal can be
received from the at least two pressure sensors. An alternating
current offset voltage of the differential signal can be
neutralized based on a second reference signal. The neutralized
differential signal can be amplified.
[0007] Additional advantages will be set forth in part in the
description which follows or may be learned by practice. The
advantages will be realized and attained by means of the elements
and combinations particularly pointed out in the appended
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The accompanying drawings, which are incorporated in and
constitute a part of this specification, illustrate embodiments and
together with the description, serve to explain the principles of
the methods and systems:
[0009] FIG. 1 is a circuit diagram illustrating an exemplary
apparatus for detecting pressure variations;
[0010] FIG. 2 is a cross-section illustrating an exemplary
apparatus for detecting pressure variations;
[0011] FIG. 3 is a flowchart illustrating an exemplary method of
detecting pressure variations;
[0012] FIG. 4 is a block diagram illustrating an exemplary computer
in which the present methods can operate;
[0013] FIG. 5a is a circuit diagram illustrating an exemplary first
current source and switch;
[0014] FIG. 5b is a circuit diagram illustrating an exemplary pair
of piezo-resistive pressure sensors and switching mechanisms;
[0015] FIG. 5c is a circuit diagram illustrating an exemplary fixed
current source used in conjunction with the second current
source;
[0016] FIG. 5d is a circuit diagram illustrating an exemplary low
noise amplifier and portions of a bandpass filter;
[0017] FIG. 6a is a circuit diagram illustrating an exemplary
demodulator; portions of a bandpass filter, and portions of a
lowpass filter;
[0018] FIG. 6b is a circuit diagram illustrating an exemplary
amplifier and portions of a lowpass filter;
[0019] FIG. 6c is a circuit diagram illustrating an exemplary
inverting amplifier used to provide a differential output
signal;
[0020] FIG. 6d is a circuit diagram illustrating an exemplary
bandpass filter;
[0021] FIG. 7 is a circuit diagram illustrating an exemplary
voltage regulator;
[0022] FIG. 8 is a circuit diagram illustrating an exemplary
oscillator with primary and phase shifted outputs;
[0023] FIG. 9 is a circuit diagram illustrating an exemplary second
current source; and
[0024] FIG. 10 is a flowchart illustrating an exemplary method for
detecting pressure variations.
DETAILED DESCRIPTION
[0025] Before the present methods and systems are disclosed and
described, it is to be understood that the methods and systems are
not limited to specific methods, specific components, or to
particular implementations. It is also to be understood that the
terminology used herein is for the purpose of describing particular
embodiments only and is not intended to be limiting.
[0026] As used in the specification and the appended claims, the
singular forms "a," "an," and "the" include plural referents unless
the context clearly dictates otherwise. Ranges may be expressed
herein as from "about" one particular value, and/or to "about"
another particular value. When such a range is expressed, another
embodiment includes from the one particular value and/or to the
other particular value. Similarly, when values are expressed as
approximations, by use of the antecedent "about," it will be
understood that the particular value forms another embodiment. It
will be further understood that the endpoints of each of the ranges
are significant both in relation to the other endpoint, and
independently of the other endpoint.
[0027] "Optional" or "optionally" means that the subsequently
described event or circumstance may or may not occur, and that the
description includes instances where said event or circumstance
occurs and instances where it does not.
[0028] Throughout the description and claims of this specification,
the word "comprise" and variations of the word, such as
"comprising" and "comprises," means "including but not limited to,"
and is not intended to exclude, for example, other components,
integers or steps. "Exemplary" means "an example of" and is not
intended to convey an indication of a preferred or ideal
embodiment. "Such as" is not used in a restrictive sense, but for
explanatory purposes.
[0029] Disclosed are components that can be used to perform the
disclosed methods and systems. These and other components are
disclosed herein, and it is understood that when combinations,
subsets, interactions, groups, etc. of these components are
disclosed that while specific reference of each various individual
and collective combinations and permutation of these may not be
explicitly disclosed, each is specifically contemplated and
described herein, for all methods and systems. This applies to all
aspects of this application including, but not limited to, steps in
disclosed methods. Thus, if there are a variety of additional steps
that can be performed it is understood that each of these
additional steps can be performed with any specific embodiment or
combination of embodiments of the disclosed methods.
[0030] The present methods and systems may be understood more
readily by reference to the following detailed description of
preferred embodiments and the examples included therein and to the
Figures and their previous and following description.
[0031] As will be appreciated by one skilled in the art, the
methods and systems may take the form of an entirely hardware
embodiment, an entirely software embodiment, or an embodiment
combining software and hardware aspects. Furthermore, the methods
and systems may take the form of a computer program product on a
computer-readable storage medium having computer-readable program
instructions (e.g., computer software) embodied in the storage
medium. More particularly, the present methods and systems may take
the form of web-implemented computer software. Any suitable
computer-readable storage medium may be utilized including hard
disks, CD-ROMs, optical storage devices, or magnetic storage
devices.
[0032] Embodiments of the methods and systems are described below
with reference to block diagrams and flowchart illustrations of
methods, systems, apparatuses and computer program products. It
will be understood that each block of the block diagrams and
flowchart illustrations, and combinations of blocks in the block
diagrams and flowchart illustrations, respectively, can be
implemented by computer program instructions. These computer
program instructions may be loaded onto a general purpose computer,
special purpose computer, or other programmable data processing
apparatus to produce a machine, such that the instructions which
execute on the computer or other programmable data processing
apparatus create a means for implementing the functions specified
in the flowchart block or blocks.
[0033] These computer program instructions may also be stored in a
computer-readable memory that can direct a computer or other
programmable data processing apparatus to function in a particular
manner, such that the instructions stored in the computer-readable
memory produce an article of manufacture including
computer-readable instructions for implementing the function
specified in the flowchart block or blocks. The computer program
instructions may also be loaded onto a computer or other
programmable data processing apparatus to cause a series of
operational steps to be performed on the computer or other
programmable apparatus to produce a computer-implemented process
such that the instructions that execute on the computer or other
programmable apparatus provide steps for implementing the functions
specified in the flowchart block or blocks.
[0034] Accordingly, blocks of the block diagrams and flowchart
illustrations support combinations of means for performing the
specified functions, combinations of steps for performing the
specified functions and program instruction means for performing
the specified functions. It will also be understood that each block
of the block diagrams and flowchart illustrations, and combinations
of blocks in the block diagrams and flowchart illustrations, can be
implemented by special purpose hardware-based computer systems that
perform the specified functions or steps, or combinations of
special purpose hardware and computer instructions.
[0035] The present disclosure relates to methods, circuits, and
apparatuses for detecting pressure variations, such as infrasound.
Those skilled in the art will appreciate that present methods may
be used in systems that employ both digital and analog equipment.
One skilled in the art will appreciate that provided herein is a
functional description and that the respective functions can be
performed by software, hardware, or a combination of software and
hardware.
[0036] FIG. 1 is a circuit diagram of an exemplary apparatus 100
for detecting pressure variations, such as infrasound. In one
aspect, the apparatus 100 can comprise at least two pressure
sensors 102. The pressure sensors 102 can be electrically coupled
in parallel. The pressure sensors 102 can be commercially
available, miniature, piezoresistive, differential pressure
sensors. Each pressure sensor 102 can comprise a set of resistors
104 configured as a Wheatstone bridge, and at least one of the
resistors of the set of resistors 104 can be configured to provide
a resistance that varies based on changes in pressure upon the
resistor.
[0037] In one aspect, each pressure sensor 102 can have a
differential input 106 and 108 and a differential output 110 and
112. The differential output can comprise an inverting output 110
and a non-inverting output 112. The pressure sensors 102 can
generate a positive output voltage on the non-inverting output 112
(designated with the + sign) when pressure is applied to the
positive pressure input ports of the pressure sensors 102. In one
aspect, the resistors 104 are embedded in a silicon diaphragm, and
a hose barb is on either side of the diaphragm. If a positive
voltage is on differential input 106 and pressure is applied to the
positive pressure port, the differential output can be positive.
The inverting output 110 can behave similarly, but with opposite
polarity.
[0038] In one aspect, the pressure sensors 102 can be electrically
coupled to a power supply. For example, a DC voltage or current can
be used to drive piezoresistive sensors. Accordingly, the apparatus
100 can comprise a first current source 114. A DC amplifier can
then amplify the differential output voltage. It should be noted
that many amplifiers suffer from 1/f noise, a type of noise that
increases as the frequency drops. In one aspect, the problem of 1/f
noise can be addressed by the techniques described in the present
disclosure. To address this problem, at least in part, a phase
sensitive detector can be used. Additionally, the apparatus 100 can
comprise a first switching mechanism 116 and 118 electrically
coupled to the differential input 106 and 108 of at least one of
the pressure sensors 102. The first switching mechanism 116 and 118
can be configured to electrically couple the first current source
114 to the pressure sensors 102 according to a first reference
signal 120. For example, the first switching mechanism can comprise
one or more switches 116 and 118 configured to alternately inject
the first current source 114 (Ibr) into the top (e.g., differential
input 106) and bottom (e.g., differential input 108) of the
resistive bridges of the sensors 102. The first reference signal
120 can be a clock signal. In one aspect, the switches 116 and 118
can be controlled by a 1 KHz clock signal. In another aspect, the
first switching mechanism 116 and 118 can be configured to
eliminate large changes in the common mode voltage from the
pressure sensors 102 by alternating injecting current into the top
106 and bottom 108 of the pressure sensors 102.
[0039] In one aspect, the first switching mechanism 116 and 118 can
be configured to cause, at least in part, an AC signal to appear on
the differential output 110 and 112 of the pressure sensors 102
when pressure is applied to the pressure sensors 102. In one
aspect, the first switching mechanism 116 and 118 can be configured
to increase a signal-to-noise ratio of the pressure sensors 102 by
a predefined factor. This example configuration can reverse the
current through the pressure sensors 102 and can increase the
signal-to-noise ratio compared to using a single switch and simply
gating the drive current. For example, the signal-to-noise ratio
can be increased by driving the first current source 114 in
alternate directions through the pressure sensors 102 (e.g.,
thereby doubling the AC output signal amplitude with no increase in
power consumption).
[0040] In one aspect, the apparatus 100 can comprise a resistor
electrically coupled to the first switching mechanism 116 and 118.
The resistor can be configured to provide a resistance that varies
based on changes in temperature. The temperature compensating
resistor can be configured to cause the first current source 114 to
be configured as a temperature compensating drive current for the
resistive bridge (e.g., set of resistors 104). The first current
source 114 can be configured to vary with temperature to compensate
for the temperature coefficient of the pressure sensors 102.
Piezoresistive pressure sensors can be temperature sensitive and
can have large signal offsets. In this design, the first current
source 114 can change with temperature to precisely compensate for
changes in the sensor gain.
[0041] In one aspect, the apparatus 100 can comprise a second
switching mechanism 122 and 124 electrically coupled to the
differential output 110 and 112 of at least one of the pressure
sensors 102. The second switching mechanism can comprise one or
more switches 122 and 124. The second switching mechanism 122 and
124 can be configured to electrically couple a second current
source 126 to the pressure sensors 102 according to a second
reference signal 128. In one aspect, the second switching mechanism
122 and 124 can be configured to neutralize an alternating current
offset voltage of the pressure sensors 102. Since the pressure
sensor drive current (e.g. first current source 114) can alternate
direction, imbalances in the resistive legs of the pressure sensors
102 can cause an AC signal to appear on the differential output 110
and 112, and the amplitude of the AC signal can be proportional to
the degree of the imbalance. Accordingly, the offset can be removed
by servoing, or otherwise providing feedback to the sensor outputs
110 and 112 to zero the offset using a voltage controlled second
current source 126 (Itr). The high output impedance of the second
current source 126 can allow the second current source 126 to
correct the offset without affecting the temperature sensitivity of
the sensors 102. The second current source 126 can be injected into
alternating sides of the sensor bridges to null the AC output
signal. It should be noted that reducing the second current source
126 can reduce the amount of noise injected into the pressure
sensors 102. By selecting pressure sensors 102, during production,
such that the pressure sensors' 102 offsets cancel, the amount of
current from the second current source 126 can be reduced thereby
minimizing the noise contributed by the feedback process.
[0042] In one aspect, the first reference signal 120 can be the
same as the second reference signal 128. For example, the second
switching mechanism 122 and 124 can be controlled by the first
reference signal 120 and/or second reference signal 128, depending
on the polarity of the sensor offset. The second reference signal
128 can be in or out of phase with the first reference signal 120
depending on the polarity of the sensor offset. In one aspect, the
second reference signal 128 can be 180 degrees out of phase with
the first reference signal 120.
[0043] In one aspect, the apparatus 100 can comprise an amplifier
130 electrically coupled to the pressure sensors. The amplifier 130
can be configured to receive differential signals from at least one
pressure sensor 102 and provide a signal proportional to the
difference of the voltages of the differential signals. Since the
first switching mechanism 116 and 118 can be configured to
eliminate large changes in the common mode voltage, the common mode
rejection specification can be eased for the amplifier 130.
Additionally, the differential signals received by the amplifier
130 can be modified by the second switching mechanism 122 and 124.
For example, nulling directly at the sensor 102 caused by the
second switching mechanism 122 and 124 and second current source
126 can allow the amplifier 130 to have high gain and be optimized
for low noise.
[0044] In one aspect, the apparatus 100 can comprise a bandpass 132
electrically coupled to the amplifier 130. The bandpass filter 132
can be configured to receive a signal from the amplifier 130 and
provide a portion of the signal within a predefined frequency
range. For example, the bandpass filter 132 can be configured to
allow a 1 KHz output signal to pass through and, thus, can remove
1/f noise.
[0045] In one aspect, the apparatus 100 can comprise a demodulator
134 electrically coupled to the bandpass filter 132. The
demodulator 134 can be configured to receive an alternating current
(AC) signal from the bandpass filter 132 and provide a direct
current (DC) signal. For example, the demodulator 134 can full wave
rectify the signal using a phase delayed clock. The phase delayed
clock signal can be provided by a phase delay component 136
configured to receive a clock signal, such as the first reference
signal, and provide phase delayed signal.
[0046] In one aspect, the apparatus 100 can comprise a lowpass
filter 138. The lowpass filter 138 can be configured to remove high
frequency components from a received signal and produce a low noise
signal proportional to the applied pressure. Additionally, the
apparatus 100 can comprise other circuit components such as
amplifiers (e.g., amplifiers labeled as A2, A3, and A4), resistors,
capacitors, and the like to meet individual design
specifications.
[0047] FIG. 2 is a cross-section of an exemplary apparatus 200 for
detecting pressure variations, such as infrasound. The apparatus
200 can comprise some or all of the elements described above for
the apparatus 100. The apparatus 200 can comprise at least two
pressure sensors 102 configured in parallel. In one aspect, the
apparatus 200 can comprise a housing 202 configured to enclose the
pressure sensors 102. The pressure sensors 102 can be mounted on a
printed circuit board (PCB) 204. In one aspect, the apparatus 200
can comprise a transducer protector 206. The transducer protector,
can comprise a hydrophobic membrane 208. One or more of the at
least two pressure sensors 102 can comprise differential inputs.
The differential inputs can comprise a non-inverting input 210 and
an inverting output.
[0048] The non-inverting inputs 210 of the pressure sensors 102 can
be coupled (e.g., glued) into a manifold 212. The manifold 212 can
be configured to receive a pressure and communicate the pressure to
the pressure sensors 102. The pressure sensors 102 can be coupled
to the manifold 212 such that vibrational noise is cancelled. For
example, a pressure sensor 102 can have a front 211 and a back 213,
and the back of the pressure sensor 102 can face the back 213 of
another pressure sensor 102. Thus, the back 213 of the pressure
sensor 102 can be coupled to the manifold 212. The pressure sensors
102 can be connected together by a manifold 212 that applies
pressure to the positive differential inputs of both pressure
sensors 102. Physically the pressure sensors 102 can be mounted
back to back, such that the back to back configuration can cancel
spurious signals caused by vibrations. The pressure sensors 102 can
be configured back to back and in parallel to reduce thermally
induced Johnson noise (at the expense of power consumption). Noise
from the pressure sensors 102 can be reduced to arbitrarily low
levels by paralleling a large number of pressure sensors 102
together.
[0049] In one aspect, the apparatus 200 can comprise a reference
chamber 214. The reference chamber 214 can be within the housing
202. The reference chamber 214 can be configured to provide a
reference pressure to the pressure sensors 102. The hydrophobic
membrane 208 can prevent moisture from entering the reference
chamber 214, where moisture can damage the electronics. The
hydrophobic membrane 208 can be configured such that infrasound
signals can pass through the transducer protector 206 and can be
measured with respect to the pressure inside the reference chamber
214. In one aspect, the manifold 212 can comprise a vent hole 216.
The vent hole 216 in the manifold 212 can prevent the pressure
sensors 102 from being damaged by large changes in ambient
pressure. The time constant, created by the vent hole 216 and
reference volume, can be chosen to be long compared to the time
constant created by the auto-nulling circuit.
[0050] In one aspect, the apparatus 200 can comprise a face plate
218 and an o-ring 220. The face plate 218 and o-ring 220 can be
configured to close and seal the housing 202. In another aspect,
the apparatus 200 can comprise a housing without a reference
chamber. For example, if more durable pressure sensors are
available some protective measures will be unnecessary. The
inverting inputs can be sealed if the housing does not comprise a
reference chamber. Thus, the weight of the microphone can be
reduced even further. Additionally, in some implementations, with
use of feedback techniques to null offsets directly at the sensor,
the reference chamber can be eliminated.
[0051] FIG. 3 is a flowchart illustrating an exemplary method 300
of detecting pressure variations, such as infrasound. In step 302,
a sensing device can be coupled to a power source. The sensing
device can comprise some or all of the elements of the apparatuses
100 and 200 described above. In step 304, pressure measurements can
be collected with the sensing device. In step 306, the sensing
device can be electrically coupled to a computer system. For
example, the sensing device can be coupled directly to the computer
system or can be coupled through a wireless network. In step 308,
the pressure measurements can be stored in a digital media file. In
step 310, the measurements for one or more predefined events can be
analyzed. The predefined events can be represented by one or more
signal patterns within the measurements. Therefore, step 310 can be
performed by searching for one or more signal patterns within the
measurements.
[0052] In an exemplary aspect, the methods and systems can be
implemented on a computer 401 as illustrated in FIG. 4 and
described below. By way of example, the output 140 of the circuit
of FIG. 1 can be coupled to a computer as illustrated in FIG. 4.
Similarly, the methods and systems disclosed can utilize one or
more computers to perform one or more functions in one or more
locations. FIG. 4 is a block diagram illustrating an exemplary
operating environment for performing the disclosed methods. This
exemplary operating environment is only an example of an operating
environment and is not intended to suggest any limitation as to the
scope of use or functionality of operating environment
architecture. Neither should the operating environment be
interpreted as having any dependency or requirement relating to any
one or combination of components illustrated in the exemplary
operating environment.
[0053] The present methods and systems can be operational with
numerous other general purpose or special purpose computing system
environments or configurations. Examples of well-known computing
systems, environments, and/or configurations that can be suitable
for use with the systems and methods comprise, but are not limited
to, personal computers, server computers, laptop devices, and
multiprocessor systems. Additional examples comprise set top boxes,
programmable consumer electronics, network PCs, minicomputers,
mainframe computers, distributed computing environments that
comprise any of the above systems or devices, and the like.
[0054] The processing of the disclosed methods and systems can be
performed by software components. The disclosed systems and methods
can be described in the general context of computer-executable
instructions, such as program modules, being executed by one or
more computers or other devices. Generally, program modules
comprise computer code, routines, programs, objects, components,
data structures, etc. that perform particular tasks or implement
particular abstract data types. The disclosed methods can also be
practiced in grid-based and distributed computing environments
where tasks are performed by remote processing devices that are
linked through a communications network. In a distributed computing
environment, program modules can be located in both local and
remote computer storage media including memory storage devices.
[0055] Further, one skilled in the art will appreciate that the
systems and methods disclosed herein can be implemented via a
general-purpose computing device in the form of a computer 401. The
components of the computer 401 can comprise, but are not limited
to, one or more processors or processing units 403, a system memory
412, and a system bus 413 that couples various system components
including the processor 403 to the system memory 412. In the case
of multiple processing units 403, the system can utilize parallel
computing.
[0056] The system bus 413 represents one or more of several
possible types of bus structures, including a memory bus or memory
controller, a peripheral bus, an accelerated graphics port, and a
processor or local bus using any of a variety of bus architectures.
By way of example, such architectures can comprise an industry
Standard Architecture (ISA) bus, a Micro Channel Architecture (MCA)
bus, an Enhanced ISA (EISA) bus, a Video Electronics Standards
Association (VESA) local bus, an Accelerated Graphics Port (AGP)
bus, and a Peripheral Component Interconnects (PCI), a PCI-Express
bus, a Personal Computer Memory Card Industry Association (PCMCIA),
Universal Serial Bus (USB) and the like. The bus 413, and all buses
specified in this description can also be implemented over a wired
or wireless network connection and each of the subsystems,
including the processor 403, a mass storage device 404, an
operating system 405, sensing software 406, sensing data 407, a
network adapter 408, system memory 412, an Input/Output Interface
410, a display adapter 409, a display device 411, and a human
machine interface 402, can be contained within one or more remote
computing devices 414a,b,c at physically separate locations,
connected through buses of this form, in effect implementing a
fully distributed system.
[0057] The computer 401 typically comprises a variety of computer
readable media. Exemplary readable media can be any available media
that is accessible by the computer 401 and comprises, for example
and not meant to be limiting, both volatile and non-volatile media,
removable and non-removable media. The system memory 212 comprises
computer readable media in the form of volatile memory, such as
random access memory (RAM), and/or non-volatile memory, such as
read only memory (ROM). The system memory 412 typically contains
data such as sensing data 407 and/or program modules such as
operating system 405 and sensing software 406 that are immediately
accessible to and/or are presently operated on by the processing
unit 403.
[0058] In another aspect, the computer 401 can also comprise other
removable/non-removable, volatile/non-volatile computer storage
media. By way of example, FIG. 4 illustrates a mass storage device
404 which can provide non-volatile storage of computer code,
computer readable instructions, data structures, program modules,
and other data for the computer 401. For example and not meant to
be limiting, a mass storage device 404 can be a hard disk, a
removable magnetic disk, a removable optical disk, magnetic
cassettes or other magnetic storage devices, flash memory cards,
CD-ROM, digital versatile disks (DVD) or other optical storage,
random access memories (RAM), read only memories (ROM),
electrically erasable programmable read-only memory (EEPROM), and
the like.
[0059] Optionally, any number of program modules can be stored on
the mass storage device 404, including by way of example, an
operating system 405 and sensing software 406. Each of the
operating system 405 and sensing software 406 (or some combination
thereof) can comprise elements of the programming and the sensing
software 406. Sensing data 407 can also be stored on the mass
storage device 404. Sensing data 407 can be stored in any of one or
more databases known in the art. Examples of such databases
comprise, DB2.RTM., Microsoft.RTM. Access, Microsoft.RTM. SQL
Server, Oracle.RTM., mySQL, PostgreSQL, and the like. The databases
can be centralized or distributed across multiple systems.
[0060] In another aspect, the user can enter commands and
information into the computer 401 via an input device (not shown).
Examples of such input devices comprise, but are not limited to, a
keyboard, pointing device (e.g., a "mouse"), a microphone, a
joystick, a scanner, tactile input devices such as gloves, and
other body coverings, and the like These and other input devices
can be connected to the processing unit 403 via a human machine
interface 402 that is coupled to the system bus 413, but can be
connected by other interface and bus structures, such as a parallel
port, game port, an IEEE 1394 Port (also known as a Firewire port),
a serial port, or a universal serial bus (USB).
[0061] In yet another aspect, a display device 411 can also be
connected to the system bus 413 via an interface, such as a display
adapter 409. It is contemplated that the computer 401 can have more
than one display adapter 409 and the computer 401 can have more
than one display device 211. For example, a display device can be a
monitor, an LCD (Liquid Crystal Display), or a projector. In
addition to the display device 411, other output peripheral devices
can comprise components such as speakers (not shown) and a printer
(not shown) which can be connected to the computer 401 via
Input/Output Interface 410. Any step and/or result of the methods
can be output in any form to an output device. Such output can be
any form of visual representation, including, but not limited to,
textual, graphical, animation, audio, tactile, and the like. The
display 411 and computer 401 can be part of one device, or separate
devices.
[0062] The computer 401 can operate in a networked environment
using logical connections to one or more remote computing devices
414a,b,c. By way of example, a remote computing device can be a
personal computer, portable computer, smartphone, a server, a
router, a network computer, a peer device or other common network
node, and so on. Logical connections between the computer 401 and a
remote computing device 414a,b,c can be made via a network 415,
such as a local area network (LAN) and/or a general wide area
network (WAN). Such network connections can be through a network
adapter 408. A network adapter 408 can be implemented in both wired
and wireless environments. Such networking environments are
conventional and commonplace in dwellings, offices, enterprise-wide
computer networks, intranets, and the Internet.
[0063] For purposes of illustration, application programs and other
executable program components such as the operating system 405 are
illustrated herein as discrete blocks, although it is recognized
that such programs and components reside at various times in
different storage components of the computing device 401, and are
executed by the data processor(s) of the computer. An
implementation of sensing software 406 can be stored on or
transmitted across some form of computer readable media. Any of the
disclosed methods can be performed by computer readable
instructions embodied on computer readable media. Computer readable
media can be any available media that can be accessed by a
computer. By way of example and not meant to be limiting, computer
readable media can comprise "computer storage media" and
"communications media." "Computer storage media" comprise volatile
and non-volatile, removable and non-removable media implemented in
any methods or technology for storage of information such as
computer readable instructions, data structures, program modules,
or other data. Exemplary computer storage media comprises, but is
not limited to, RAM, ROM, EEPROM, flash memory or other memory
technology, CD-ROM, digital versatile disks (DVD) or other optical
storage, magnetic cassettes, magnetic tape, magnetic disk storage
or other magnetic storage devices, or any other medium which can be
used to store the desired information and which can be accessed by
a computer.
[0064] The methods and systems can employ artificial intelligence
techniques such as machine learning and iterative learning.
Examples of such techniques include, but are not limited to, expert
systems, case based reasoning. Bayesian networks, behavior based
AI, neural networks, fuzzy systems, evolutionary computation (e.g.
genetic algorithms), swarm intelligence (e.g. ant algorithms), and
hybrid intelligent systems (e.g. Expert inference rules generated
through a neural network or production rules from statistical
learning).
[0065] FIGS. 5-9 are circuit diagrams illustrating in greater
detail aspects of the circuit, apparatus, and device described in
the present disclosure. FIGS. 5a-5d are circuit diagrams
illustrating exemplary current sources, switches, pressure sensors,
and amplifiers. FIG. 5a is a circuit diagram illustrating an
exemplary first current source 114 and switch 116 as referenced in
FIG. 1. Circuit elements D2 and R7 can provide an adjustable
voltage that is referred to Vcc (+11V). Resistors R8-R10 and
capacitors C5 and C6 can function as a lowpass filter that reduces
noise from D2. Circuit elements U1G2, Q2, and R6 can function as a
current source whose current is determined by the voltage on pin 5
of U1G2. Switches U3G2 and U3G1 can be configured to alternately
inject current into the top of the pressure sensor (106 as
referenced in FIG. 1) then ground the top of the sensor. FIG. 5b is
a circuit diagram illustrating an exemplary pair of piezo-resistive
pressure sensors 102, switches 122 and 124, and switch 118 as
referenced in FIG. 1. Circuit elements S1 and S2 can implement the
pressure sensors 102. Circuit elements U5G1 and U5G2 can implement
switches 122 and 124, and circuit elements U4G1 and U4G2 can
implement switch 118. FIG. 5c is a circuit diagram illustrating an
exemplary fixed current source that can create a slight positive
offset on the output ports of the pressure sensor. In one aspect,
the circuit design can be identical to the one illustrated in FIG.
5a. The variable current source illustrated in FIG. 9 can servo the
sensor offset to zero by sinking the amount of current necessary
from node I.sub.tr to balance the sensor bridge. FIG. 5d is a
circuit diagram illustrating an exemplary low noise amplifier 130
and portions of the bandpass 132 filter as referenced in FIG. 1.
Transistor array U6, operational amplifiers ("op-amp") U7G2 and
U1G2, and related components can function as an ultra-low noise,
low power, differential amplifier. Op-amp U8G2, capacitor C17, and
resistors R30 and R31 can function as the highpass portion of
bandpass filter 132. Op-amp U7G1 and the voltage divider formed by
resistors R25 and R26 can provide a pseudo ground reference
voltage. FIGS. 6a-6d are circuit diagrams illustrating an exemplary
demodulator, lowpass filter, and output amplifiers. FIG. 6a is a
circuit diagram illustrating an exemplary demodulator 134 and
portions of a lowpass filter 138 as referenced in FIG. 1. The two
switches, op-amp U9G2 and related components can function as the
demodulator. The demodulator can operate by alternately connecting
the non-inverting input of U9G2 to pseudo-ground and then to the
amplifier input signal. This mode of operation can cause the
amplifier gain to switch between +1 and -1, thereby synchronously
full-wave rectifying the input signal. In one aspect, op-amp U11G1,
resistors R39 and R40, and capacitors C24 and C25 can constitute a
portion of lowpass filter 138 of FIG. 1. FIG. 6b is a circuit
diagram illustrating an exemplary amplifier A3 and a portion of
lowpass filter 138 as referenced in FIG. 1. In one aspect, op-amp
U11G2, resistors R41 and R42, and capacitors C27-C28 can function
as the remaining portion of lowpass filter 138. The remaining
components can form amplifier A3. FIG. 6c is a circuit diagram
illustrating an exemplary inverting amplifier used with U12G1 to
provide a differential output signal. FIG. 6d is a circuit diagram
illustrating an exemplary bandpass filter 132 as referenced in FIG.
1. For example, circuit element U9G1 and related components can
function as the lowpass portion of bandpassfilter 132 of FIG. 1.
FIG. 7 is a circuit diagram illustrating an exemplary voltage
regulator. FIG. 8 is a circuit diagram illustrating an exemplary
oscillator with primary and phase shifted outputs. FIG. 9 is a
circuit diagram illustrating an exemplary second current
source.
[0066] FIG. 10 is a flowchart illustrating an exemplary method 1000
for detecting pressure variations. At step 1002, a power supply can
be provided to at least two pressure sensors based on a first
reference signal. The at least two pressure sensors can be
electrically coupled in parallel. For example, the at least two
pressure sensors can be electrically coupled in parallel and in
phase. As another example, the at least two pressure sensors can be
connected pneumatically in parallel and in phase. In one aspect,
the at least two pressure sensors have a front and a back. For
example, a back of a first pressure sensor of the at least two
pressure sensors can face a back of a second pressure sensor of the
at least two pressure sensors. In one aspect, the at least two
pressure sensors can comprise (e.g., in each pressure sensor, in
one or more pressure sensors) a set of resistors configured as a
Wheatstone bridge. At least one of the resistors of the set of
resistors can be configured to provide a resistance that varies
based on changes in pressure upon the resistor.
[0067] In one aspect, providing a power supply to the at least two
pressure sensors can comprise increasing a signal-to-noise ratio of
the differential signal by a predefined factor. For example, the
signal-to-noise ratio can be increased by driving current in
alternate directions through the at least two pressure sensors
(e.g., thereby doubling or otherwise increasing the AC output
signal amplitude with no increase in power consumption). In another
aspect, providing a power supply to the at least two pressure
sensors can comprise alternating, based on the first reference
signal, between providing a current source to a first differential
input of the at least two pressure sensors and providing the
current source to a second differential input of the at least two
pressure sensors. In another aspect, providing a power supply to
the at least two pressure sensors can comprise providing a
temperature compensating power supply based on a resistor
configured to change resistance based on a change in temperature.
In another aspect, providing a power supply to the at least two
pressure sensors can comprise providing a temperature compensating
power supply based on a resistor configured to change resistance
based on a change in temperature.
[0068] At step 1004, a differential signal can be received from the
at least two pressure sensors. For example, the differential signal
comprise differential signals from each of (e.g., some or all of)
the at least two pressure sensors.
[0069] At step 1006, an alternating current offset voltage of the
differential signal can be neutralized based on a second reference
signal. In some configurations, the first reference signal and the
second reference signal can be the same signal. In one aspect,
neutralizing the alternating current offset voltage of the
differential signal can comprise alternating, based on the second
reference signal, between providing a current source to a first
differential output of the at least two pressure sensors and
providing the current source to a second differential input of the
at least two pressure sensors. In another aspect, neutralizing,
based on the second reference signal, an alternating current offset
voltage of the differential signal can comprise providing feedback
to null an offset directly at the at least two pressure
sensors.
[0070] At step 1008, the neutralized differential signal can be
amplified. For example, the neutralized differential signal can be
received (e.g., by an amplifier) from the at least two pressure
sensors. In one aspect, amplifying the neutralized differential
signal can comprise amplifying a difference between a voltage of a
first signal of the neutralized differential signal and a voltage
of a second signal of the neutralized differential signal. In one
aspect, amplifying the neutralized differential signal can be
optimized for high gain and low noise.
[0071] At step 1010, the amplified signal can be filtered within a
predefined frequency range. For example, the amplified signal can
be filtered by a bandpass filter. At step 1012, the filtered signal
can be converted to a direct current (DC) signal. For example, the
amplified signal (e.g., and the filtered signal) can be an
alternating current (AC) signal. In one aspect, the filtered signal
can be converted to a DC signal by a demodulator.
[0072] While the methods and systems have been described in
connection with preferred embodiments and specific examples, it is
not intended that the scope be limited to the particular
embodiments set forth, as the embodiments herein are intended in
all respects to be illustrative rather than restrictive.
[0073] Unless otherwise expressly stated, it is in no way intended
that any method set forth herein be construed as requiring that its
steps be performed in a specific order. Accordingly, where a method
claim does not actually recite an order to be followed by its steps
or it is not otherwise specifically stated in the claims or
descriptions that the steps are to be limited to a specific order,
it is no way intended that an order be inferred, in any respect.
This holds for any possible non-express basis for interpretation,
including: matters of logic with respect to arrangement of steps or
operational flow; plain meaning derived from grammatical
organization or punctuation; the number or type of embodiments
described in the specification.
[0074] Throughout this application, various publications are
referenced. The disclosures of these publications in their
entireties are hereby incorporated by reference into this
application in order to more fully describe the state of the art to
which the methods and systems pertain.
[0075] It will be apparent to those skilled in the art that various
modifications and variations can be made without departing from the
scope or spirit. Other embodiments will be apparent to those
skilled in the art from consideration of the specification and
practice disclosed herein. It is intended that the specification
and examples be considered as exemplary only, with a true scope and
spirit being indicated by the following claims.
* * * * *