BACKGROUND

Acoustic emission sensors are used to monitor and report on the performance of valves and other pressurized devices while they are in service. The sensor operates by receiving sound waves from the valves and pipes in which the valves are installed and reporting on those sound waves. In particular, if there is a valve loss or leak, the turbulent flow from the loss or leak creates a different sound level than is produced during normal flow, and the sensor detects the different sound level.

Typically, the sensor is placed on the valve or pipe, and the output is amplified with a nearby amplifier. The output is normally recorded by a data acquisition system which may be nearby such as a personal digital assistant (PDA) device or more remote. If a PDA or other data capture device is not used, the readings may be recorded manually if the amplifier has a digital display. The sensor includes a piezoelectric transducer that detects mechanical energy carried by the acoustic wave and an acoustic couplant to ensure efficient transfer of the acoustic signal into the sensor. An exemplary sensor includes the MIDAS Meter, which is owned by the applicant.

The acoustic waves issuing from pressurized devices have relatively low signal-to-noise ratio and are difficult to measure. Therefore, despite the effectiveness of existing sensor systems, a need exists to improve the accuracy and robustness of measurements.

SUMMARY

According to a first aspect of the present invention there is provided a method of optimizing the transmission of acoustic waves from a test object to an acoustical sensor, the method comprising the steps of:

providing an acoustical sensor comprising a sensing interface, the sensor configured to receive sound waves emitted from a test object and generate a signal indicative of the sound waves; coupling the sensor to a surface of the test object, the test object having a first acoustical property; and

adjusting a pressure incident on the sensing interface such that a second acoustical property of the sensor approaches the first acoustical property.

Adjusting the pressure incident on the sensing interface may comprise compressing the sensing interface against the test object after coupling the sensor to the surface of the test object. There may be provided a housing for the acoustical sensor, the housing comprising an intervening material at a first end of the housing, wherein the step of adjusting the pressure incident on the sensing interface may comprise compressing the sensing interface against the intervening material prior to coupling the sensor to the surface of the test object.

The intervening material may define a disc shape.

The intervening material may define an annular shape. The intervening material may be metallic.

The method may further comprise disposing the intervening material against the test object. Disposing the intervening material against the test object may comprise compressing the intervening material against the test object.

The intervening material may have a third acoustical property and wherein compressing the intervening material may cause the third acoustical property to approach the first acoustical property. Adjusting the pressure may comprise decreasing the pressure incident on the sensing interface.

The sensor may comprise at least one layer of a piezoelectric material and at least one layer of a ceramic material.

The sensor may comprise at least one layer of a sapphire and at least one layer of a ceramic material. The ceramic material may be pre-stressed prior to layering.

The sensor may be frustoconically shaped.

Adjusting the pressure may comprise engaging a screw assembly.

The method may comprise:

providing a housing for the acoustical sensor, the housing having a first end in which the acoustical sensor is mounted, the housing defining one or more threads, and the acoustical sensor defining one more mating threads, and

engaging the mating threads of the acoustical sensor with the threads of the housing to mount the acoustical sensor within the housing.

The first end of the housing may comprise an intervening material and engaging the mating threads of the acoustical sensor and the threads of the housing in a first direction may compress the sensing interface against the intervening material and engaging the mating threads of the acoustical sensor and the threads of the housing in a second direction may decrease pressure incident the sensing interface from the intervening material, wherein the first direction is opposite the second direction.

The method may further comprise the steps of: providing a housing in which the acoustical sensor is mounted, the housing comprising a first end adjacent the sensing interface and a flexible skirt that extends from an outer surface of the housing toward the first end, the flexible skirt defining an interior concave portion in communication with a pump, and the first end being disposed within the interior concave portion;

disposing the flexible skirt against the test object such that the sensing interface is disposed adjacent the test object; and

engaging the pump to adjust the pressure between the skirt and the test object.

The step of engaging the pump may further adjust the pressure between the sensing interface and the test object.

The method may further comprise:

providing a housing in which the acoustical sensor is mounted, the housing comprising a first end adjacent the sensing interface, the first end comprising a magnetic material; and

disposing the first end against the test object such that the sensing interface is adjacent the test object, wherein the test object is a metallic material attractable to the magnetic material.

The magnetic material may be a permanent magnet.

The magnetic material may be an electro-magnet.

Adjusting the pressure may include urging the sensor toward the test object using one or more springs.

Coupling may include securing a housing containing the sensor to the test object. Securing may include at least one of strapping or magnetically attaching the housing to the test object.

Coupling may include securing an outer housing to the test object and securing an inner housing containing the sensor to the outer housing.

Adjusting the pressure may include urging the inner housing to move with respect to the outer housing. The method may further comprise the step of polishing one or more interfaces between the sensor and the test object.

The method may further comprise operating a feedback loop using the signal and the adjusting step.

According to a second aspect of the present invention there is provided an acoustical sensor comprising a sensing interface configured to receive sound waves emitted from a test object, wherein the pressure incident on the sensing interface is adjusted such that a first acoustical property of the sensing interface approaches a second acoustical property of a test object.

The sensing interface may comprise at least two different materials.

The materials may comprise at least one layer of a piezoelectric material and at least one layer of a ceramic material.

The materials may comprise at least one of a layer of a sapphire or a layer of a ceramic material or a piezoelectric material. The ceramic material may be pre-stressed prior to layering.

The sensing interface may be frustoconically shaped. The first acoustical property may be a first acoustical impedance of the sensing interface and the second acoustical property may be a second acoustical impedance of the test object.

According to a third aspect of the present invention there is provided an acoustical sensor housing assembly comprising:

a first end;

a second end opposite the first end;

a wall extending substantially between the first and second ends, the wall and the ends defining an interior portion; and

an acoustical sensor mounted adjacent the first end, the acoustical sensor comprising a sensing interface configured to receive sound waves emitted from a test object, wherein the pressure incident on the sensing interface is adjusted such that a first acoustical property of the sensing interface approaches a second acoustical property of a test object.

The acoustical sensor housing assembly may further comprise:

an amplifier for amplifying signals associated with sound waves received through the sensing interface;

a power control board for processing the signals;

a data logger for storing data and defining the signals; and a battery for providing electrical power to the amplifier, the power control board, and the data logger, wherein the amplifier, the power control board, the data logger, and the battery are disposed within the interior portion.

The acoustical sensor housing assembly may further comprise an intervening material disposed adjacent the first end of the housing, wherein the acoustical sensor is mounted such that the sensing interface substantially abuts the intervening material and the sensing interface is compressed against the intervening material.

The intervening material may define a disc shape. The intervening material may define an annular shape. The intervening material may be metallic.

The intervening material may have a third acoustic property that is substantially similar to the second acoustic property.

The first end may define a plurality of threads and the acoustical sensor may define a plurality of mating threads configured to engage the plurality of threads of the first end for securing the acoustical sensor within the housing assembly.

The pressure on the sensing interface may be increased by engaging the plurality of mating threads of the acoustical sensor with the plurality of threads in the first end in a first axial direction, and the pressure on the sensing interface may be decreased by engaging the plurality of mating threads of the acoustical sensor with the plurality of threads in the first end in a second axial direction, the first axial direction being opposite the second axial direction.

The acoustical sensor housing assembly may further comprise:

a flexible skirt that extends radially outwardly from an outer surface of the wall and axially toward the first end, the flexible skirt defining an interior concave portion in communication with a pump, and the first end being disposed within the interior concave portion, wherein the pump is operable to adjust the pressure between the skirt and the test object.

The pump may be further operable to adjust the pressure between the sensing interface and the test object.

The acoustical sensor housing assembly may further comprise:

a magnetic material adjacent the first end, wherein magnetic material is magnetically attracted to the test object. The magnetic material may be a permanent magnet. The magnetic material may be an electro-magnet.

The wall, the first end, and the second end may define an inner housing, the inner housing may further comprise a first annular flange extending from an outer surface of the inner housing, and the housing assembly may further comprise:

an outer housing disposed radially outwardly from the inner housing, the outer housing defining a groove on an interior surface of the outer housing configured to receive the first annular flange; and

one or more springs disposed between the groove and the first annular flange, wherein one or more springs may urge the first end of the inner housing toward the test object.

The outer housing may further define a second annular flange extending from an outer surface of the outer housing, and the outer housing may be configured to be strapped to the test object through the second annular flange.

The outer housing is affixed to the test object using an adhesive.

The wall, the first end, and the second end may define an inner housing, the inner housing may further comprise two or more lugs extending from an outer surface of the inner housing, and the housing assembly may further comprise:

an outer housing disposed radially outwardly from the inner housing, the outer housing defining a groove on an interior surface of the outer housing configured to receive the two or more lugs;

one or more springs disposed between each lug and the groove, wherein the one or more springs urge the first end of the inner housing toward the test object.

The acoustical sensor housing assembly may further comprise: an opening defined at the first end through which at least a portion of the acoustical sensor extends;

a bellows assembly disposed adjacent the opening, the bellows assembly comprising a proximate end and a distal end, the proximate end comprising an intermediate material disposed adjacent the sensing interface, the distal end being spaced axially from the proximate end and disposed axially inwardly of the opening of the housing, the bellows assembly further comprising annular shaped bellows extending axially inwardly from the proximate end in the direction of the distal end, such that an amount of fluid between the bellows and the housing can be removed or inserted to adjust the amount of pressure incident on the sensing interface by the intermediate material.

DETAILED DESCRIPTION

Implementations of the present disclosure now will be described more fully hereinafter. Indeed, these implementations can be embodied in many different forms and should not be construed as limited to the implementations set forth herein; rather, these implementations are provided so that this disclosure will satisfy applicable legal requirements. As used in the specification, and in the appended claims, the singular forms "a", "an", "the", include plural referents unless the context clearly dictates otherwise. The term "comprising" and variations thereof as used herein is used synonymously with the term "including" and variations thereof and are open, non-limiting terms.

As shown in FIG. 1, an acoustical sensor system 10 may include a housing 12, electronic hardware system 14 and a sensor 16. The acoustical sensor system 10 is configured for detection of acoustic vibrations emanating from valves, pipelines or other high-pressure containment devices. These acoustic vibrations may be correlated to important operational parameters of the valve or pipeline, such as leak detection. Advantageously, the system 10 may be configured to reduce attenuation of acoustic waves passing through boundaries between materials of the valve or pipeline and the sensor system 10 by the application of controlled compression forces across those boundaries. Generally, the system and methods are for modifying the acoustic properties of the transition from object to sensor sensing element such that a greater amount of signal is passed. This facilitates or enables a more sensitive, higher fidelity measurement to be taken.

These improvements may be had, for example, by matching the acoustic impedance of materials from the measured object through to the sensor. A smoother (or no) variation in acoustic impedance may be created between the object and the sensing element to soften or avoid any step changes. This eliminates or reduces the impact of reflected/transmitted boundaries where acoustic signal would be lost. Also, generation of a stress gradient across the object through to the sensing element may modify the acoustic impedance of intervening materials. Such forces, for example, may be generated by different mechanical means such as a bellows, lever, threads or differential pressure.

Returning again to FIG. 1, the electronic hardware system 14 includes an amplifier 18, battery pack 20, power control board 22 and data logger 24. Generally, these electronic components provide a consolidated system contained within the housing 12 for operation of the sensor 16, detection of the acoustic waves from the sensed object, processing or preprocessing of the data and storage of the data. Containment within the housing 12 has the advantage of protecting the sensor 16 and electronic hardware system 14 from harsh environments, such as a deep sea environment or explosive atmosphere.

The battery pack 20 is configured to supply power to the remaining electronic components including the sensor 16, amplifier 18, power control board 22 and data logger 24. The power control board 22 is configured to meter power amongst the systems to ensure robust and long operation. The amplifier 18 is connected to the sensor and applies a gain and/or filtration to signals coming from the sensor 16. (The signals detected by the sensor 16 are usually relatively low amplitude since they measure small leaks with relatively passive "listening" as opposed to the application of a sonar pulses.)

The data logger 24 is configured to receive and record data on sensed acoustic signals. It is a storage mechanism such as a hard drive or flash drive configured to receive, organize and save the data as part of a database. The electronic hardware system 14 components may also include centralized or distributed processing power. For example, the amplifier 18 may have signal processing algorithms that filter the recorded data prior to storage on the data logger 24. Also, the data logger 24 may have a processor configured to organize and retrieve data from the storage mechanism.

As shown in FIG. 2, the sensor 16 includes a sleeve 26, a retainer ring 28, a piezoelectric ring 30, leads 32 and ceramic disc 38. The sleeve 26 is an outer housing for the sensor 16 that has a cylindrical shape and is comprised of a relatively rigid material such as aluminum, steel or stainless steel. The sleeve 26 has a central opening in which are disposed the piezoelectric ring 30 and the leads 32. These components and other associated circuitry are held therein using potting compound, such as a resin.

One of the leads 32 extends from the piezoelectric ring to carry signals therefrom. The other lead attaches to a groundwire extending up along an inner surface of the sleeve 26. The leads 32 extend to and attach to a terminal plate 36 which itself is connected to an external communication line 34 that exits the potting compound and sleeve 26 for connection to, and communication with, the electronic hardware system 14.

The piezoelectric ring 20 is configured to convert the mechanical vibration energy into an electrical signal. Although crystals with piezoelectric properties are disclosed, other sensor materials (and devices such as MEMS fluid sensors) capable of mechanical to electrical conversion may be used. Additional variations are discussed below.

Abutted against the piezoelectric ring 20 is the ceramic disc 38. The ceramic disc 38 is configured to be relatively rigid so as to transmit vibration energy therethrough but also to protect the piezoelectric ring 20 against the environment.

The ceramic disc 38 is held against the piezoelectric ring 20 by the retainer ring 28.

The ceramic disc 38 also extends over the free edge of the sleeve 26 so that the sleeve is not making contact with the surface being sensed.

The retainer ring 28 includes an inner, annular flange that extends within an annular groove in an outer surface of the sleeve 26. An inner surface of the retainer ring 28 extends along a peripheral edge of the ceramic disc 38. The retainer ring 28 also is comprised of a material, such as a plastic, that is less rigid (generally) than the ceramic disc 38 and sleeve 26. In lieu of, or in addition to, the retainer ring 28, the ceramic disc 38 may be cemented or adhered to the end of the sleeve 26 and/or the piezoelectric ring 20. As will be described in more detail below, the boundary between the sensing face of the piezoelectric ring 20 and the ceramic disc 38 has an impact on the measured acoustic waves.

The sleeve 26 has defined near its sensing end a plurality of threads 40 that are configured to engage congruent threads on the housing 12.

Referring again to FIG. 1, the housing 12 includes a body 42, a first end cap 44, a second end cap 46 and a mounting flange 48. The body 42 is a rigid tubular structure having sufficient internal space to accommodate the electronic hardware system 14 and the sensor 16. Although shown as a self-contained system, valves or ports or other exits may be employed on the housing 12 for outside communication, power supply, etc. The body 42 is configured for the environments in which it will be used. For example, it may have sufficient rigidity and strength to withstand corrosive seawater at depths where pipelines, valves and other structures for measurement are found. Or, it may be configured for use in low pressure environments like the near vacuum of space.

The mounting flange 48 may, for example, be part of a flange configured to sleeve over the outer surface of the body 42 and to attach below the second end cap 46 with an interference fit. The mounting flange 48 is configured to attach to a clamping mechanism 50, as shown, for example, in FIG. 3. Other attachment handles could be employed also, like a set of lugs attached to opposite sides of the body 42.

The second end cap 46, as shown in FIGS. 1, 4 and 5, has an end plate 52, an inner wall structure 54 and an outer wall structure 56. The end plate 52 is a circular, planar structure configured to occlude the second open end of the cylindrical body 42. Extending from the end plate 52 at a right angle are the inner and outer wall structures 54, 56. The outer wall structure 56 has a cylindrical shape and extends from an outer periphery of the end plate 52 to form an outer surface of the second end cap 46.

The inner wall structure 54 is spaced a radial distance inward from the outer wall structure 56 to define an annular slot. The inner wall structure has a height that is less than a height of the outer wall structure 58. Annular grooves 58 are defined on an inner surface of the outer wall structure 56. The annular grooves 58 are sized and shaped to contain circular seals 60 that extend between the outer wall structure 56 and an outer, subjacent surface of the body 42.

When attached to the body 42, the free end of the body 42 is slipped into the annular slot between the inner and outer walls structures 54, 56. The free end of the outer wall structure 56 is abutted against the mounting flange 48.

The first end cap 44 includes the same end plate 52, inner walls structure 54, outer wall structure 56 and seals 60, as shown in FIGS. 1, 6 and 7. In addition, the first end cap 44 includes a sensor receptacle 62 that extending from a central location on the circular end plate 52.

The sensor receptacle 62 includes a receptacle wall structure 64 and an interface disc 66. The receptacle wall structure 64 has a cylindrical shape and defines a cylindrical sensor opening 68 configured to receive the sensor 16, as shown in FIG. 1. The sensor opening 68 has three internal diameters that decrease as they approach the interface disc 66. Defined on the middle diameter are threads configured to mate with the threads on the sleeve 26 of the sensor 16. The diameter closest to the interface disc 66 is the smallest and the largest diameter is in communication with the cavity of the body 42. This progression facilitates insertion and securing of the sensor 16 within the sensor receptacle 62.

The interface disc 66 extends between the edges of the receptacle wall structure 64 and is relatively thin at about 1 mm. The interface disc 66 is a balance between protection provided for the sensor 16 and reducing the intervening distance between the sensor and the object being sensed to reduce attenuation of the signal. This thickness could be varied based on expected signal strength and environmental conditions. For example, variations are selectable to ensure water pressure or other environmental factors can be withstood but without the generous factor of safety provided for the remainder of the housing 12.

The inventor(s) have determined factors for increasing transmission of the acoustic waves to the sensor 16 and piezoelectric ring 30 through boundaries between materials (and through the materials themselves), including: • reducing physical gaps to as small as possible to effectively allow frequencies of signal to ignore the gap;

• smoothing surfaces to allow for greater contact area; and

• using better matched materials and/or pressure to minimize step changes in acoustic impedance.

The piezoelectric transducers of prior art acoustical emissions sensors do not have the same acoustical properties as the pipes or valves through which the sound waves are traveling. Accordingly, the acoustical properties of the sound waves change through reflection and refraction as the signal encounters the boundary layer between the pipe or valve and the acoustic couplant and the boundary layer between the acoustic couplant and the piezoelectric transducer. For example, the amount of signal reflected at each boundary can be expressed by:

R = ((Z2-Z1)/(Z2+Z1)) ²

wherein Zl is the acoustic impedance of the first material and Z2 is the acoustic impedance of the second material. Thus, the sensor's ability to measure the sound waves being emitted from the valve or pipe is reduced at boundaries.

However, according to the equation above, as Z2 approaches the acoustic impedance of Zl, the reflected signal shrinks to zero.

The acoustical sensor system 10, such as the implementation described above, is configured to reduce transmission losses across boundaries by applying these and other principals.

The acoustical sensor system 10, for example, provides improvements in reducing the impact of the boundary layers between the pipe or valve and the acoustic couplant and between the acoustic couplant and the piezoelectric transducer.

During assembly of the acoustical sensor system 10, the sensor 16 is secured within the sensor receptacle 62 using a torque wrench or other securing device. The torque wrench is applied (60 Nm for AE sensors with conventional materials but much higher beyond 400Nm with stiff er components of the sensor) to the sensor 16 to advance the threads on the sleeve 26 along the threads of the receptacle wall structure 64. As the sensor 16 is advanced toward the interface disc 66, the intervening couplant is compressed to reduce the distance between the ceramic disc 38 and the interface disc 66. As the distance shrinks, the couplant becomes thinner and more compressed. The ceramic disc 38 and the interface disc 66 also become compressed, causing the acoustic impedance of these materials to rise to a value that is closer to the object being measured.

As a result, the boundaries between the piezoelectric ring 30 and the ceramic disc 38, and the ceramic disc 38 and the interface disc 66 cause less attenuation.

As shown in FIG. 3, the acoustical sensor system 10 may further include the clamping mechanism 50 that additionally applies pressure on the housing 12. In one implantation, the clamping mechanism is a "bucket" that forms an outer housing for the inner housing 12. The bucket 50 has an annular shape with an open first end 70 and an open second end 72. Extending around the second end 72 is a flange 74 that also has an annular shape that is configured to facilitate gripping and attachment to the pipe. The second end 72 also defines a groove 80 extending annularly around an inner surface of the bucket 50 within the thickness of the flange 74. One or more axially directed springs 76 are housed within the groove.

The bucket 50 may be permanently affixed to the pipeline or may be attached via straps that extend through its first end 70. The housing 12 is "stabbed" into the second end 72 of the bucket 50 and spring-loaded lugs 78 snap into the groove 80. Once in the groove, the lugs 78 are biased toward the first end 70 by the axially directed springs 76. In this manner, the interface disc 66 is compressed against the pipeline wall. This compression reduces the effective thickness of the boundary between the interface disc 66 and the pipeline wall. Also, the compression drives up the acoustic impedance of the intervening material of the interface disc 66. Matched impedance improves the transmission of the acoustic signal through the disc-pipe boundary.

As shown in FIGS. 8 and 9, the housing 12 may include a bellows style first end cap 44. The first end cap 44 includes a moving portion 82 that defines the sensor receptacle 62 and includes the interface disc 66. The moving portion 82 is connected to a fixed portion 84 by an annular bellows 86. The bellows 86 allows fluid within the housing 12 to be pumped out or in to adjust the amount of pressure exerted at the boundary between the ceramic and interface discs. This controlled clamping force may produce better transmission under dynamic circumstances such as vibration and thermal expansion or contractor. A snap ring 88 may also be included to limit an amount of travel of the moving portion 82 and fixed portion relative to each other.

As another implementation, instead of being part of the housing 12, the bellows end cap 44 may be employed as part of a clamping mechanism, exerting compression force on the outer surface of the interface disc.

As another implementation, the bellows 86 may be relatively stiff so that the bellows operates as a spring with or without fluid evacuation. This would hold a constant force on the boundary between the ceramic and interface discs.

Other options may improve transmission for the bellows (or other) implementations. For example, the surfaces of the interface disc 66 and the ceramic disc 38 may be polished to facilitate better face-to-face contact on the microscopic level. This also improves transmission. Further, the ceramic disc 38 may bonded to the interface disc 66 with an isolation layer adhesive for improved transmission. The adhesive selected balances a number of performance aspects.

1) Its gap filling capability may match the surface roughness of the ceramic and the interface disks.

2) The bond thickness may be a minimum to maximize the frequency which passes unaffected.

3) The acoustic impedance may be as high as possible once cured to

minimize the distortion of the frequencies that are affected.

4) The adhesive can have very low creep properties and these should extend to through bond creep. This will better allow for any clamping pressure applied during bonding to be sustained over time.

5) The adhesive may pass on shear wave as well as longitudinal or lamb wave acoustic signals.

6) These properties may be maintained through the temperature range of operation.

The bellows-style first end cap 44 is well-suited for use on the surface as opposed to the implementation of FIG. 1 which is more amenable to deep sea applications.

As shown in FIG. 10, the clamping mechanism 50 may include a skirt 90, a pump 92 and a valve 94. The skirt 90 may be constructed of a flexible or compliant material that has a bell or concave shape. The skirt 90 includes a fixed end 96 attached to the housing 12 at an annular interface, such as by an adhesive or fasteners. The flexible skirt 90 at its other end has a free peripheral edge 98. The flexible skirt 90 also may have an opening to receive a communication line 100.

The pump 92 may be a DC pump, for example, and is connected in fluid communication with the interior of the concave shape of the flexible skirt 90. The valve 94 is also connected in communication with the communication line 100. The valve 94 is positioned on the communication line 100 in line with the pump 92 opposite the flexible skirt 90.

The free peripheral edge 98 of the flexible skirt 90 is shaped to seal against the shape of the object being monitored. For example, it may have a planar seal or a saddle shape for a cylinder. Regardless, once sealed, the pump 92 is configured to remove a small amount of water or liquid (e.g., when in an underwater environment) to create a differential pressure. This differential pressure creates the clamping force, reducing gaps and increasing pressure on intervening layers to improve transmission. An advantage of the flexible skirt 90 is that a large force can be generated. Also, it is well-suited for one-handed use.

Also, a control algorithm can be used to operate the pump and/or valve to increase (by pumping) and reduce (by valve opening) the pressure applied by the skirt 90. This pressure could be adaptively adjusted or controlled based on the signal measured by the sensor 16 and electronic hardware system 14 to generate an optimized or maximized signal clarity and strength.

As shown in FIG. 1 1, the clamping mechanism 50 may include an annular permanent or electromagnetic magnet 114. The magnet 114 is attached at a second end to the housing 12 of the acoustical sensor system 10. It has the advantage of controllable clamping force, such as by controlling the electromagnetic energy. A disadvantage may be that its use is limited on non-magnetic materials such as aluminum or stainless steel. Magnetic attachment may also be well suited for dry land applications.

In another implementation, as shown in FIGS. 12-14 and 17, the clamping mechanism 50 may include one or more (or four) lever arms 102 that are positioned radially about an outer housing 110. These lever arms 102 may have a cam operation via upper arm portions 108 connected via pins to actuate lower arm portions 104 to drop down, and in, and grip a fixed base 106. The upper arm portions 108 can then be locked against an outer housing 110 of the clamping mechanism 50. Defined within the housing body 108 is a receptacle for holding the housing 12.

As shown in FIG. 17, the fixed base 106 defines an opening 120 allowing passage of the outer housing 110 of the clamping mechanism (and the sensor receptacle 62 held within the outer housing 110). The fixed base 106 is attached to the valve by strapping extending through strap openings 112. The strap openings 112 are tangential slots skived through a bottom portion 122 of the fixed base 106.

Retainer tabs 124 extend up to cover a portion of the strap openings 112 to help retain the straps from lateral sliding out of the strap openings.

The fixed base 106, as shown in FIGS. 12 and 17, includes a saddle shape on its bottom surface for abutting a cylindrical pipe or valve. The saddle shape is defined by shallow v-shaped cutouts 118 below the strap openings 112. The fixed base 106 also includes a top flange portion 126 that flares out from a neck and is configured to be gripped by the lower arm portions 108. The neck extends between the bottom and top portions and provides clearance for the ends of the lower arm portions 108.

As shown in FIG. 17, a bellows spring 128 may be positioned at an interface between the fixed base 106 and outer housing 110. The bellows spring has an annular shape with a central opening configured to allow passage of the sensor receptacle 62 of the housing 12.

As shown in FIGS. 13 and 17, the outer housing 110 includes a body 130 and a lid 132. The body 130 has a top portion 138 with a half-barrel shape and a bottom cylindrical portion 140 with a constant radius. Both portions define a central opening configured to receive the housing 12. The body 130 includes four pin mounts 134 spaced at equal 90 degree intervals about the circumference of the body 130. The pin mounts 134 are each positioned within a respective one of four spaced channels 136 extending axially along the outer surface of the top portion 138.

The body 130 also includes a communication line port 142. The port is a cylindrical opening extending through the wall of the body 130 between two of the pin mounts 134. The communication line port 138 is configured to allow passage therethrough of communication lines that connect to the electronic hardware system 14 and sensor 16 housed therein. The top portion 138 of the body 130 also defines four circumferentially spaced bolt openings 144.

The bottom portion 140 of the body 130 is configured to fit into the bellows spring 128 and into the central opening 120 of the fixed base 106. It has a smaller diameter than the top portion 138 of the body 130. The larger diameter of the top portion 138 is larger than the fixed base opening 120 so as to restrain the depth at which the bottom portion 140 can extend into the fixed base 106.

The lid 132 includes four circumferentially spaced ridge structures 146. The ridge structures each extend protectively about one of four bolt openings 144. The ridge structures 146 are spaced and positioned to extend radially outward over the channels 136. Also, the bolt openings in the lid 132 are positioned to align with the bolt openings 144 of the body 130. The aligned bolt openings 144 can then receive four bolts 148 to attach the lid 142 to the body 130.

Referring again to FIG. 17, the upper arm portions 108 include a pair of struts

150 that are configured to straddle the pin mounts 134. The pair of struts 150 include a pair of collinear top holes 152 and bottom holes 154. The bottom holes are configured to line up with the openings in the pin mounts 134 and receive a pin therethrough. This rotatably attaches the upper arm portions at the four

circumferentally spaced positions around the body 130.

The lower arm portions 104 each include a top end 156 with a width configured to extend between the struts 150 of the upper arm portions 108. The top end 156 includes a pin opening configured to line up with the top holes 152 of the upper arm portions 108. Also, the top end 156 includes a c-shaped inner clearance configured to extend over the pin and connection of the upper arm portions 108.

The lower arm portions 104 each also include a grip end 158 which is an L- shaped structure with a finger configured to point radially inward when the lever arms 102 are assembled to the body 130. These fingers are configured to extend around and engage the top flanged portion 126 of the fixed base 106.

During use, the housing 12 with the sensor 16 and electronic hardware system

14 is inserted into the opening of the body 130 of the outer housing 110. The lid 132 positioned over the open end of the body 130 and secured thereto using bolts 148. An internal ledge in the body 130 retains the housing 12 therein but allows extension of the sensor receptacle 62 past the end of the bottom portion 140 of the body.

The cylindrical bottom portion of the body 140 is inserted into the bellows spring 128 retained within the opening 120 in the fixed base 106. At this point, the lever arms 102 are in an unsecured position as shown in FIG. 13. In this position the upper arm portions 108 are tilted out rotating about the pin passing through the bottom holes and the pin mounts 134. The lower arm portions 104 have their grip ends 158 splayed outward and the top ends 156 rotated about the pin passing through the top holes 152 in the struts 150.

As insertion of the body 140 into the fixed base 106 continues, the bellows spring 128 is compressed and the sensor receptacle 62 passes through the central opening of the bellows spring. Further urging compresses the sensor receptacle 62 against the valve, pipe or other object being sensed. The flat tops of the upper arm portions 108 are pressed inwards until subjacent the ridge structures 146 on the lid 132. Relatively contemporaneously, the top end 156 of the lower arm is urged outward and the bottom, grip end 158 of the lower arm 104 moves inward to grip the flanged portion 126 of the fixed base. As the lever arms are locked tight, the body 130 is pushed toward the pipe or valve and the housing 12 nested therein is compressed against the pipe or valve. This compresses the interface disc 66 to better match its acoustic impedance to the valve material.

In another implementation, as shown in FIG. 15, the sensor 16 may be modified to improve its impedance match to adjacent materials including the sensed object. For example, the sensor 16 may include a sandwich of two sapphire material layers 116 on either side of a piezoelectric layer as the piezoelectric sensor. Sapphire has an acoustic impedance similar to that of steel. It also has a very similar thermal expansion coefficient, facilitating its use in large temperature ranges. Other piezoelectric materials may be used to better match acoustic impedance of a housing, couplant or the measured object.

Also, modification of the sensor 16 materials may allow increase of the applied pressure to generate the desired impedance gradient. For example, alternating layers of sensing material and ceramic may be used. Multiple alternating sensor layers could be tuned by predicting the delays and then filtering data to stack signals (predicting and eliminating the phase difference) from each layer of piezoelectric material. Further, different filtering techniques could be used to pick out the signal from each sensor layer despite the phase difference. Another advantage of multiple layers is increased sensitivity due to the multiple signals. The stack of layers may need to be calibrated at different compression pressures to generate characteristic curves that can be stored for filtering the signal. Also, the layers of the sensor 16 may be pre-stressed, such as by peripheral clamping, to remove the periodic aspect of the signal.

Compression of a piezoelectric stack shifts the frequency response up to have a more flat curve with a peak at resonant frequency. Clamping (and other methods used herein) may be used to shift the sensitivity range to fill up 60 to 600 kHz, with frequencies around 125 kHz and 300-350 kHz being particularly advantageous. Also, materials and stresses may be adapted to fill DC (macro events such as a valve opening or a blowout) through 1 MHz.

For material selection, the sensor may include an alumina electrical isolator having a good intermediate acoustic impedance (40.6) allowing for a smoother transition between the valve (46) and the PZT sensing element (33). The other materials, however, may be less tuned as materials and benefit more from

compression. For example, a silver epoxy glue between the piezoelectric disc and the alumina is 5.14 and the glycerine couplant is 2.34. Keeping the couplant(s) or adhesives as thin as possible (<40% of the wavelength of the maximum frequency of interest (~1 MHz)) avoids them becoming a dominant transmission / reflection boundary. For the silver epoxy and glycerine, for example, the thickness may be about 0.8 mm. A thickness of 0.4 mm may help to avoid filtering of shear wave information.

Other aspects of the system 10 may be the employment of light but strong materials for the housing 12, such as titanium and concomitant selection of structures/displacements for neutral buoyancy. Also, the housing 12 may have a pressure sensitive valve to release pressure that may have formed by a leak into the housing while underwater.

The intervening layers may also be shaped to change the pressure exerted on different axial layers. For example, as shown in FIG. 16, a sensor material 160 rests on a transition material 162 which is positioned against a valve body 164. The sensor material 160 has a relatively low acoustic impedance. The transition material 162 has a tapered shape, such as a rectangular pyramid shape or a frustoconical shape.

The shape of the transition material 162 may be tuned to the acoustic properties of the material. The transition section could vary cross section on a single axis for materials where acoustic impedance varies proportionally to the applied pressure, as shown for example in FIG. 18. FIG. 18 shows a truncated rectangular prism wherein, for example, the top has a surface area of 2 cm ² and the bottom has a surface area of 1 cm ² . The pressure then on the bottom interface is twice that of the top interface.

The transition section could vary in cross section on two axes for materials where acoustic impedance varies proportionally to the square of the applied pressure, as shown for example in FIG. 19. FIG. 19 shows a truncated cone where, for example, the top has a surface area of 2 cm ² and the bottom has a surface are of 0.5 cm ² . The pressure at the bottom interface is therefore four times that of the top interface.

A number of aspects of the systems, devices and methods have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. Accordingly, other aspects are within the scope of the following claims.

Reference Nos.

10 acoustical sensor system

12 housing

14 electronic hardware system

16 sensor

18 amplifier

20 battery pack

22 power control board

24 data logger

26 sleeve

28 retainer ring piezoelectric ring leads

communication line terminal plate ceramic disc

threads

body

first end cap

second end cap mounting flange clamping mechanism end plate

inner wall structure outer wall structure annular grooves seals

sensor receptacle receptacle wall structure interface disc sensor opening first bucket end second bucket end flange

springs

spring-loaded lugs groove

moving portion fixed portion

bellows

snap ring

skirt

pump valve

fixed end

free peripheral edge

communication line

lever arms

lower arm portions

fixed base

upper arm portions

outer housing

strap openings

magnet

sapphire layer

8 v-shaped cutouts

fixed base opening

2 bottom portion of fixed base retainer tabs

6 top flanged portion of fixed base8 bellows spring

0 body

2 lid

4 pin mounts

6 channels

8 top portion of body

0 bottom portion of body

2 communication line port4 bolt openings

6 ridge structures

8 bolts

0 struts

2 top holes

4 bottom holes

6 top end of lower arm grip end of lower arm sensing material transition material valve body