Inspection instrument with protective sheath for a harsh fluidic environment

Abstract

A protective sheath 110 for an ultrasonic transducer includes a thin region having a thickness that is near a low multiple of a quarter wavelength of an ultrasonic wave emitted or received by the transducer. A downhole tool or probe 100 includes a mandrel, a transducer array coupled to the mandrel, a first support 108 and the sheath 110 overlying the transducer array and underlying the first support at a first part edge of the support. A probe may include a chamber defined in part by the mandrel frame and sheath, and a pressure regulator 106 which in response to a pressure change in the environment outside the protective sheath equalises a pressure in the chamber with the outside pressure. The thin sheath thickness may typically be 50-1000 microns (1mm) for frequencies 3-5MHz. The transducer array may be rotationally symmetric on the mandrel.

Description

Technical Field

[0001] The disclosure pertains to the field of instruments used in a well or borehole, pipeline, water pipes, or other confined or inhospitable environments. Aspects of the disclosure relate to ultrasonic instruments including ultrasonic sensor arrays comprised of one or more piezoelectric transducers. BACKGROUND

[0002] In boreholes, wells, and fluid-carrying pipes, such as oil wells and water delivery infrastructure, there often arises a need to inspect the internal structure (e.g., pipe, fittings, valves) and surrounding material (e.g., ground) for integrity or anomalies (e.g., obstructions, voids). Various useful systems, devices, and methods based on ultrasonics are known ways to perform inspections often called non-destructive testing (NDT).

[0003] Ultrasonics is a specific branch of acoustics that deals with vibrational waves at or above the upper-frequency range of human hearing, e.g., 16 to 20 kHz or higher. Ultrasonics are used for imaging (e.g., sonar, non-destructive testing), and processing (e.g., cleaning, and welding).

[0004] Ultrasound is a form of energy, a vibration, that propagates through matter (e.g. solids, liquids, and gases) and may be emitted from, or detected by, piezoelectric transducers such as piezoelectric ceramic transducers. These circuit elements receive electrical signals and, in response, generate acoustic waves. The acoustic waves emitted by a transducer propagate through media refracting or reflecting on variations therein. The same, or a different, transducer receives the acoustic waves (e.g., acoustic reflections) which are converted to an electrical signal by the receiver transducer. The return signal is processed by an acoustic image processor, e.g., in real time. SUMMARY

[0005] An article of manufacture which, in use, protects an ultrasonic transducer. The article includes a protective sheath defining a central cavity extending along a first axis of the protective sheath, and a first edge connected to the protective sheath, defining a first passage to the central cavity. The article further includes a thin region defined in the protective sheath. The thin region is of a thickness that is near a low multiple of a quarter wavelength of an ultrasonic wave emitted, or received, by the ultrasonic transducer.

[0006] A machine including a mandrel, a rotationally symmetric transducer array coupled to the mandrel, and a first support coupled to the mandrel. The machine further includes a protective sheath overlying the rotationally symmetric transducer array and underlying the first support at the first part of the first support. The protective sheath includes a thin region of a thickness that is near a low multiple of a quarter wavelength of an ultrasonic wave generated, or received, by the rotationally symmetric transducer array. An instrument substantially as shown and described herein.

[0007] A machine including a frame, an ultrasonic transducer array coupled to the frame, and a sheath overlying the ultrasonic transducer array and coupled to the frame. The sheath includes a thin region of a thickness near a low multiple of a quarter wavelength of an ultrasonic wave generated, or received, by the ultrasonic transducer array. The machine further includes a chamber defined in part by the frame and the sheath, and a pressure regulator coupled to the frame. In response to a pressure change in an environment outside of the protective sheath the pressure regulator equalizes the pressure in the chamber with the pressure in the environment.

[0008] A kit for encapsulating an instrument substantial as shown and described herein.

[0009] This summary does not necessarily describe the entire scope of all aspects. Other aspects, features, and advantages will be apparent to those of ordinary skill in the art upon review of the following description of specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Systems, devices, articles, and methods are described in greater detail herein with reference to the following figures in which:

[0011] FIG. 1 is a technical diagram illustrating, in perspective view, a first instrument including a first protective sheath;

[0012] FIG. 2 is a technical diagram illustrating, in elevation view, the first instrument including the first protective sheath;

[0013] FIG. 3 is a technical diagram illustrating, in section view, a portion of the first instrument including the first protective sheath;

[0014] FIG. 4 is a technical diagram illustrating, in cross-section view, the portion of the first instrument including the first protective sheath;

[0015] FIG. 5 is a technical diagram illustrating, in perspective view, the first protective sheath;

[0016] FIG. 6 is a technical diagram illustrating, in perspective view, a second instrument including a second protective sheath;

[0017] FIG. 7 is a technical diagram illustrating, in elevation view, the second instrument including the second protective sheath;

[0018] FIG. 8 is a technical diagram illustrating, in section view, a portion of the second instrument including the second protective sheath;

[0019] FIG. 9 is a technical diagram illustrating, in cross-section view, the portion of the second instrument including the second protective sheath; and

[0020] FIG. 10 is a technical diagram illustrating, in perspective view, the second protective sheath.

[0021] FIG. 11 is a technical diagram illustrating, in perspective view, a third instrument including a third protective sheath;

[0022] FIG. 12 is a technical diagram illustrating, in elevation view, the third instrument including the third protective sheath;

[0023] FIG. 13 is a technical diagram illustrating, in section view, a portion of the third instrument including the third protective sheath;

[0024] FIG. 14 is a technical diagram illustrating, in cross-section view, the portion of the third instrument including the third protective sheath;

[0025] FIG. 15 is a technical diagram illustrating, in perspective view, the third protective sheath;

[0026] FIG. 16 is a technical diagram illustrating, in section view, a portion of a pressure regulator which in accordance with some embodiments, is included in the first, second, or third instrument;

[0027] FIG. 17 is a flow-diagram illustrating an implementation of a method of assembly of an instrument including a protective sheath;

[0028] FIG. 18 is a flow-diagram illustrating an implementation of a method of assembly (and / or manufacture) of an instrument including a protective sheath; and

[0029] FIG. 19 is a flow-diagram illustrating an implementation of a method of manufacture of a protective sheath.

[0030] In the drawings, the same reference numbers identify similar elements or acts. In the drawings, angle, size, and relative position of elements are not necessarily shown to scale. For example, some of these elements may be enlarged or positioned to improve drawing legibility. Further, the shapes of any elements as drawn, are not necessarily intended to convey any information regarding the actual shape of the particular elements and may have been solely selected for ease of illustration or recognition. DETAILED DESCRIPTION [0031 ] Most acoustic measurement encapsulation materials are not suitable for downhole, in-line inspection, or similar environments. The present disclosure includes a thermally stable, barophilic, chemically resilient, and acoustically transparent barrier between an instrument (e.g., transducer-carrying instrument, probe) and the surrounding environment.

[0032] Instruments down a borehole-like setting are desirable when they withstand temperatures of up to about 200 °C and pressures of up to about 200 Mega Pascals. Alternatively in aquatic settings, the environment can be just around 5 °C. Thus materials deal with the expansion, contraction, stress, and strain caused by these conditions. The materials are preferably thermally stable and barophilic or at least able to handle a change in pressure up to and including high pressures. Example pressures in water line inspection and other near-surface operations are 200 psi and downhole can be 8,000 psi or more.

[0033] Desirable materials should be chemically resistant in harsh operational environments such as those with high partial pressures of carbon dioxide (CO2), hydrogen sulfide (CH2S), or other dissolved gases; high concentrations of ions like chloride ions (Ch ), or the presence of other material like salts, metals, and elements, such as sulfur (S). Drilling muds can have harsh basicity of about 8.0 - 11.5 pH. Existing material was suspectable to infiltration and would react with measurable chemical or physical effects. For example, various rubber-like materials would blister making the material unsuitable for use in combination with an ultrasonic transducer.

[0034] Desirable materials desirably are acoustically transparent - that is, have suitable reflection, velocity, or attenuation for the wave generated, or received, by a given transducer. If the material reflects ultrasound, it is a mirror, not a lens. Material with inhomogeneous density interferes with ultrasonics and may be unsuitable much like looking through thick opaque glass.

[0035] Desirable material ideally should not only survive the above conditions but also function in a substantially stable manner for as long as possible (e.g. days or weeks in adverse conditions, months to years in standby utility).

[0036] Looking at the drawings in overview, note the following. A first instrument, e.g., probe, is described in relation to FIG. 1 through FIG. 4. A second instrument, e.g., probe, is described in relation to FIG. 6 through FIG. 9. A third instrument is described in relation to FIG. 11 through FIG. 14. The first instrument, second instrument, and third instrument each and respectively include a protective sheath. A first protective sheath is described in associated with, at least, FIG. 1 through FIG. 5, while a second protective sheath is described in associated with, at least, FIG. 6 through FIG. 10. A third protective sheath is described in associated with, at least, FIG. 11 through FIG. 15. Embodiments pressure regulators that may be used with the first, second, or third instrument is described in association with, at least, FIG. 16. FIG. 17, FIG. 18, and FIG. 19 are flow diagrams illustrating various implementations of methods of manufacture or assembly involving protective sheaths.

[0037] FIG. 1 shows, in perspective view, an instrument, tool, or probe 100 including a proximal end 102, a distal end 104, a pressure regulator 106, a distal outer housing or support 108, and a first protective sheath 110. The protective sheath 110 overlies a part of an ultrasonic imager 116 including a transducer array (not shown). The imager 116 as shown is protected by distal outer support 108, protective sheath 110, and a proximal outer housing, proximal outer cladding, or proximal outer support 112 which each may have a cylindrical shell shape (e.g., band, barrel, or collar). Imager 116 includes a plurality of transducers arranged in an array.

[0038] In some embodiments, an exposed part of the first protective sheath 110 sits shy of distal outer support 108, and proximal outer support 112. For example, the distal outer support 108, and proximal outer support 112 define a common surface of constant radius from the principal axis of probe 100 and the outer radius of first protective sheath 110 is less than the constant radius.

[0039] Protective sheath 110, in some embodiments, is a consumable article of manufacture, e.g., a wear part, comprising a web of material 150 in a continuous and connected arrangement to define a generally rotationally symmetric shape (e.g., band, bell, cap), which defines a central cavity, which sheath 110 overlies in the radial axis of probe 100. In some embodiments, protective sheath 110 has a general shape selected from the group consisting of: campanulate, that is, bell shape; cupola, that is dome shape; and cylindrical, like a cylindrical shell, e.g., band, barrel. In some embodiments, protective sheath 110 includes a first edge defining a first passage to the central cavity. In some embodiments, protective sheath 110 includes a second edge defining a second passage to the central cavity. For example, protective sheath 110 is a band. In some embodiments, protective sheath 110 has an elongated shape extending along the principal axis of probe 100 - e.g., the axis between proximal end 102 and distal end 104.

[0040] Probe 100 includes a body or a frame 114 located on the proximal side of proximal outer support 112. Frame 114 is coupled to a mandrel (not shown) extending along a portion of the principal axis of probe 100, and of proximal outer support 112. For example, frame 114 is connected to proximal outer support 112 by a threaded connection.

[0041] Probe 100 further includes an electronics bay 118 proximally disposed and coupled to frame 114. The electronics bay 118 includes suitable electronic components for probe 100, such as a power supply (e.g., battery, transformer, wire to external supply), a communication system, an image processor, an inertial measurement unit, and a data logger.

[0042] Electronics bay 118 includes suitable electronics that in response to control signals, e.g., generated by a microcontroller executing processor-executable instructions, transmit and receive ultrasound pulses, adjust the absolute or relative time of transmissions, modulate transmissions, convert digital signals into analog signals, or the reverse, record data, and process the received pulses. The electronics in electronics bay 118 can run in one or more modes including a plurality of modes at the same time such as B-mode (brightness mode) to obtain an image of the surrounding structures or D-mode (Doppler mode) to obtain information on fluid flow.

[0043] Pressure regulator 106 is fluidly coupled to the parts of probe 100 between frame 114 and the proximal side of pressure regulator 106 including imager 116 and parts of probe 100 underlying protective sheath 110. In some embodiments, pressure regulator 106 includes a cylinder with a fluid connection to the environment. Disposed in the cylinder is a piston in a sealed slip-fit engagement with the cylinder. On one side of the piston (e.g., imager side, proximal side) is a clean fluid (e.g., oil, mineral oil, synthetic oil) which surrounds one or more interior parts of the imager 116. In response to changing pressure of the environment the piston moves and equalizes the pressure in the clean fluid to that of the environment. In particular, in response to changing pressure in the environment, pressure regulator 106 reduces the pressure difference on either side of protective sheath 110. So in cooperative operation, pressure regulator 106, the clean fluid, and fluid in the environment minimize net forces on protective sheath 110, such as ballooning or crushing forces. Pressure regulator 106 is further described herein in relation to, at least, FIG. 16.

[0044] Turning to FIG. 2 which illustrates parts of probe 100 in elevation view from the near side of the view shown in FIG. 1. Distal outer support 108 includes a proximal end 120 that defines a first boundary for a clear area overlying protective sheath 110. Proximal outer support 112 includes a distal end 122 that defines a second boundary of the clear area overlying protective sheath 110. In some embodiments, distal outer support proximal end 120 is formed, for example, bevelled (shown), chamfered, inverse rounded, rounded, or stepped. In some embodiments, proximal outer support distal end 122 is formed. For example, end 120 or end 122 can be frustoconical. Section lines A-A’ and B-B’ define the views shown in FIG. 3 and FIG. 4.

[0045] Turning to FIG. 3 which illustrates imager 116 and parts of probe 100 in section view according to a cut indicated by line A-A’ shown in FIG. 2. Imager 116 includes a transducer array 130. Imager 116 is a radial imager transducer array 130 that emits signals in a plurality of directions at or near right angles to the principal axis of probe 100. In some embodiments, transducer array 130 has a cylindrical shell shape.

[0046] In some embodiments, transducer array 130 includes 32 to 2048 transducers arranged in an annular shape. The transducer array 130, more preferably includes 128 to 512 transducers. In some embodiments, transducer array 130 includes 384 transducers. The transducer array 130 operates in a frequency of 0.1 to 30 MHz, and more preferably 1 to 10 MHz. In some embodiments, transducer array 130 operates at 5 MHz. Transducer array 130 may include piezoelectric composites, such as lead zirconate titanate (PbZT), or compositions of bismuth scandium oxide and lead(ll) titanate such as 0.36BiSc03-0.64PbTi03. In some embodiments, the transducers are Piezoelectric Micromachined Ultrasonic Transducers (PMUT).

[0047] Probe 100 includes a mandrel 124 coupled to various parts of probe 100 including distal outer support 108, proximal outer support 112, frame 114, imager 116, and pressure regulator 106. In some embodiments, mandrel 124 couples frame 114 and pressure regulator 106.

[0048] In some embodiments, probe 100 includes one or more fluidic seals,for example, o-ring 126 and o-ring 128. In some embodiments, one or more fluidic seals are formed in a unitary body with protective sheath 110. As shown, o-ring 126 is in an interference fit with distal outer support 108 and protective sheath 110. In some embodiments, a part of protective sheath 110 which underlies o-ring 126 is forced against transducer array 130

[0049] Turning to FIG. 4 which illustrates imager 116 and parts of probe 100 in a crosssection view according to a cut indicated by line B-B’ shown in FIG. 2. Imager 116 includes a transducer array 130. In some embodiments, transducer array 130 includes a cylindrical shell shape which defines a central void, and imager 116 includes a mandrel 124 disposed in the central void. In some embodiments, as shown, a part of proximal outer support 112 overlies, in the radial direction, protective sheath 110 and protective sheath 110 overlies transducer array 130.

[0050] Turning to FIG. 5 which illustrates, in perspective view, protective sheath 110 which includes a web of material 150 in a continuous and connected arrangement to define a generally rotationally symmetric shape (e.g., cap, cylinder). The web 150 for protective sheath 110 defines a central cavity 152 that may extend along the principal axis of probe 100. Protective sheath 110 overlies central cavity 152 in the radial direction. In some embodiments, protective sheath 110 includes a first edge 154 defining a first passage (e.g., an opening) to the central cavity 152. In some embodiments, such as the one shown, protective sheath 110 includes a second edge 156 defining a second passage to the central cavity 152. Protective sheath 110 includes an outer surface 158 and an inner surface 160. [0051 ] Protective sheaths, such as protective sheath 110 include a material such as a fluoropolymer, thermoplastic polymer, or a fluoropolymer rubber or fluoroelastomer. The material is selected for its chemical and physical properties.

[0052] A suitable fluoropolymer for use in protective sheath 110 and imager 116 is FEP (fluorinated ethylene propylene), a copolymer of tetrafluoroethylene and hexafluoropropylene. FEP is flexible and chemically inert. It also has suitable acoustic properties, such that it does not interfere with acoustic waves from imager 116. FEP can be stretched mechanically and shrunk with heat to form against parts of imager 116 including transducer array 130. Commercially available tubes of FEP can have a stretched interior diameter of around fifty to one hundred millimeters or more. The stretched diameter may be ten to seventy percent more than the recovered diameter. In some embodiments, protective sheath 110 is stretched twenty percent over the recovered diameter and is at least 500 microns thick after heat has been applied to shrink it.

[0053] Protective sheaths, such as protective sheath 110 may include a membrane region 162 defined in the protective sheath 110. Membrane region 162 is of a thickness that is about a low multiple of a quarter wavelength of an ultrasonic wave. In some embodiments, membrane region 162 is of a thickness that is near a low odd multiple of a quarter wavelength of an ultrasonic wave. The thickness of membrane region 162 is characterized by a first difference between the thickness of membrane region 162, and the nearest odd multiple of a quarter wavelength of an ultrasonic wave. The wavelength is selected fora suitable imaging frequency and determined within the bulk of the material included in protective sheath 110. The thickness of the membrane region is characterized by a second difference consisting of the difference of the thickness to the nearest even multiple of the quarter wavelength. In some embodiments, the magnitude of the first difference for membrane region 162 is less than the magnitude for the second difference. In some embodiments, thickness of membrane region 162 in protective sheath 110 including FEP is two wavelengths (eight quarter wavelengths) of an ultrasonic wave. In some embodiments, membrane region 162 is of a thickness that is between two low multiples of a quarter wavelength of an ultrasonic wave. The thickness may be between about 50 pm and about 500 pm corresponding to an ultrasonic wave at 5 Mhz. The thickness may be between about 100 pm and about 1000 pm for 3 MHz. In some embodiments, membrane region 162 is of a thickness that is near a low odd multiple of a quarter wavelength of an ultrasonic wave. In some embodiments, membrane region is a thickness length selected from the group consisting of 65 pm, 195, pm, 326 pm, and 456 pm (0.003", 0.008", 0.013", or 0.018") corresponding to an ultrasonic wave at 5 MHz. In some embodiments, membrane region is a thickness length selected from the group consisting of 109 pm, 326, pm, 543 pm, and 760 pm (0.004", 0.013", 0.021", or 0.030") corresponding to an ultrasonic wave at 3 MHz.

[0054] A suitable fluoropolymer for use in protective sheath 110 and imager 116 is a fluoroelastomer. An example of a fluoroelastomer is a composition of hexafluoropropylene and vinylidene fluoride such as VITON® A-type fluoroelastomer. An example of VITON A is VITON A-331C available from Chemours Company of Wilmington, DE, US. In some implementations, protective sheath 110 comprises VITON A and is 356 pm (0.014") thick or about three times a quarter wavelength at 5 MHz or 500 pm (0.02") thick at 3 MHz. In some implementations, protective sheath 110 comprises VITON A and is 100 pm to 1 mm thick. In some embodiments, protective sheath 110 is injection molded.

[0055] The thickness of the membrane region 162 may approximately be a low multiple of a quarter wavelength of an ultrasonic wave. In some embodiments, the thickness of the membrane region 150 is near a low odd multiple, such as one, three, five, seven, and nine. In some embodiments, membrane region 162 extends completely around protective sheath 110. In some embodiments, membrane region 162 includes a plurality of thin areas. That is the membrane region 162 partially fenestrates protective sheath 110. In some embodiments, membrane region 162 extends along the principal axis of probe 100 overlying transducer array 130. In some embodiments, protective sheath 110 is rotationally symmetric with respect to the principal axis of probe 100.

[0056] FIG. 6 shows, in perspective view, a probe 200 including a proximal end 102, a distal end 104, a pressure regulator 106, a distal outer support 208, a second protective sheath 210, and a proximal outer support 212. The protective sheath 210 overlies part of an ultrasonic imager 216. Imager 216 is protected by protective sheath 210, and proximal outer support 212. Distal outer support 208 may protect imager 216. Protective sheath 210 is secured by distal outer support 208 and proximal outer support 212. Imager 216 includes a plurality of transducers arranged in an array, which in operation transmits and receives ultrasonic waves at a plurality of azimuthal angles and a narrower range of polar angles between the principal axis of probe 200 and right angles to the principal axis.

[0057] Probe 200 includes a frame 114 at the proximal side of proximal outer support 212 and is coupled to a mandrel (not shown) extending along a portion of the principal axis of probe 200, and pressure regulator 106. Probe 200 further includes electronics bay 118 proximally disposed and coupled to frame 114. Details of frame 114 and electronics bay 118 are discussed herein in relation to, at least, FIG. 1 and FIG. 2.

[0058] Turning to FIG. 7 which illustrates parts of probe 200 in an elevation view from the near side of the view shown in FIG. 6. Distal outer support 208 has a lesser diameter than proximal outer support 212 which lie on either side of protective sheath 210. In some embodiments, distal outer support 208 or proximal outer support 212 include formed ends. Section lines C-C’ and D-D’ define the views shown in FIG. 8 and FIG. 9.

[0059] Turning to FIG. 8 which illustrates imager 216 and parts of probe 200 in a section view according to a cut indicated by line C-C’ shown in FIG. 7. Imager 216 includes a transducer array 230 that emits signals in a plurality of directions, for example, 15, 30, 60, 180, 270, 350, and 360 degrees of the azimuthal directions. The azimuthal coverage may be one continuous sweep or a plurality of ranges in the azimuthal direction. The transducer array 230 emits at a plurality of polar angles between the principal axis of probe 200, for example, and right angles to the principal axis. In some embodiments, transducer array 230 is frustoconical in shape.

[0060] A frustoconical transducer array 230 includes a sloped outer surface 231. Transducer array 230 is associated with a plurality of principal rays with symmetry of revolution around the principal axis of probe 200 and aligned with the set of normal vectors to the sloped outer surface 231. That is, the plurality of principal rays corresponds to a fixed respective polar angle and changing azimuthal angles. Without loss of generality, the plurality of principal rays can be described with respect to a representative principal ray for a fixed azimuthal angle. For example, a representative principal ray in the plane of the drawing sheet. In some embodiments, the representative principal ray of transducer 230 is low-oblique - a polar angle selected from the range near right angle to the principal axis of probe 200 decreasing to 60 degrees off-axis. The representative principal ray of transducer 230 may be mid-oblique - a polar angle ranging from near 60 degrees to 45 degrees. In some embodiments, the representative principal ray of transducer 230 is high-oblique - a polar angle ranging from near 45 degrees to nearly aligned with the principal axis of probe 200. In some embodiments, imager 216, transducer array 230, protective sheath 210, and other components are mounted with a rear view.

[0061] In some embodiments, the representative principal ray of transducer 230 is high-oblique. In some embodiments, the representative principal ray has a polar angle near an angle selected from the group 45 degrees, 30 degrees, or 20 degrees. In some embodiments, the representative principal ray has a polar angle of between 19 and 21 degrees.

[0062] In some embodiments, transducer array 230 includes 32 to 2048 transducers. The transducer array 230, more preferably includes 128 to 512 transducers. In some embodiments, transducer array 230 includes 384 transducers. The transducer array 230 operates in a frequency of 0.1 to 30 MHz, and more preferably 1 to 10 MHz and still more preferably at around 5 MHz. Transducer array 230 may include piezoelectric composites, such as those described herein.

[0063] Probe 200 includes a mandrel 124 coupled to various parts of probe 100 including distal outer support 208, proximal outer support 212, frame 114, imager 216, and pressure regulator 106. In some embodiments, mandrel 124 couples frame 114 and pressure regulator 106.

[0064] In some embodiments, proximal outer support 212 overlies protective sheath 210 in an interference fit. Probe 200 may include one or more fluidic seals, such as, o-ring 226 and o-ring 228. A part of protective sheath 210 which underlies an o-ring, such as, o-ring 226, is forced against an underlying part of probe 200, e.g., body coupled to mandrel 124, or transducer array 230. A part of protective sheath 210 which overlies an o-ring, such as, o-ring 228, is forced against an overlying part of probe 200, e.g., proximal outer support 212.

[0065] In some embodiments, a protective sheath includes a lens, such as, lens 211. A lens is a body of different propagation velocity relative to an environment, the body includes one or more spatial invariant dimensions with respect to at least one axis of symmetry, and one or more changing dimensions with respect to variation of an angle from a fixed point, e.g., a focal point. Lens 211 is a positive lens as the lens thickness increases with off-angle propagation and the material of protective sheath 210 has a higher speed of sound relative to the environment.

[0066] Without loss of generality, lens 211 can be described for a fixed azimuthal angle, e.g., plane of drawing sheet. Lens 211 may have an aspherical concave shape, e.g., edge is described by a conic section. In some embodiments, lens 211 has a spherical concave shape. In some embodiments, lens 211 is has a concave shape and is characterized by an approximating spherical lens surface defined by a radius of curvature, denoted by ro, between 8 mm and 10 mm, for example, 8.8 mm. Lens 211, in some implementations, includes a central region 213 with a first thickness over a section parallel to and near the representative principal ray. For example, central region 213 is a nadir in line with the representative principal ray. Lens 211, in some implementations, includes an outer region 215 with a second thickness. The second thickness exceeds the first thickness by 4 mm to 6 mm, for example, by 4.5 mm.

[0067] Turning to FIG. 9 which illustrates imager 216 and parts of probe 200 in a crosssection view according to a cut indicated by line D-D’ shown in FIG. 7. Imager 216 includes a transducer array 230 having a rotationally symmetric shape defining a central void, and a mandrel 124 disposed in the central void. In some embodiments, as shown, a part of proximal outer support 212 overlies protective sheath 210. Protective sheath 210 overlies, in the radial direction, transducer array 230.

[0068] Turning to FIG. 10 which illustrates, in perspective view, protective sheath 210 which includes a web of material 250 in a continuous and connected arrangement to define a generally rotationally symmetric shape (e.g., band, barrel, cap, cylinder). Web 250 in protective sheath 210 defines a central cavity 252. Central cavity 252 may extend along the principal axis of probe 200. Protective sheath 210 overlies central cavity 252 in the radial axis. In some embodiments including the embodiment shown, protective sheath 210 includes a first edge 254 defining a first passage to the central cavity 252, and a second edge 256 defining a second passage to the central cavity 252. Protective sheath 210 includes an outer surface 258, and an inner surface 260.

[0069] Protective sheaths, such as protective sheath 210, include a material such as fluoropolymer, thermoplastic polymer, or fluoropolymer rubber or fluoroelastomer. The material is selected for its chemical and physical properties. A suitable thermoplastic polymer for use in protective sheath 210 is polyether ether ketone (PEEK). Prior uses of PEEK downhole have been made very thick for mechanical durability and tend to attenuate acoustic signals. The inventors have appreciated the value of creating a very thin PEEK sheath for acoustic signals, while providing means for supporting it mechanically at pressure.

[0070] Protective sheath 210 includes a central region 213 with a thickness that is within a range define by a pair of low multiple of a quarter wavelength of an ultrasonic wave. Protective sheath 210 may include a thickness of 100 pm to 1.2 mm (0.004" to 0.047") corresponding to an ultrasonic wave at 5 MHz. Protective sheath 210 may include a thickness of 200 pm to 2 mm (0.008" to 0.079") corresponding to an ultrasonic wave at 3 MHz. Protective sheath 210 includes a central region 213 with a thickness that is a low odd multiple of a quarter wavelength of an ultrasonic wave. In some embodiments, the thickness between outer surface 258 and inner surface 260 is near a length selected from the group consisting of 131 pm, 392, pm, 653 pm, 914 pm, or 1175 pm (0.005", 0.015", 0.026", 0.036", or 0.046") corresponding to an ultrasonic wave at 5 MHz. In some embodiments, the thickness between outer surface 258 and inner surface 260 is near a length selected from the group consisting of 218 pm, 653, pm, 1088 pm, 1523 pm, or 1958 pm (0.009", 0.026", 0.043", 0.060", or 0.077") corresponding to an ultrasonic wave at 3 MHz. The thickness between outer surface 258 and inner surface 260 of protective sheath 210 comprising PEEK seven quarter wavelengths of an ultrasonic wave.

[0071] The productive sheath 210 is characterized by a first difference between the thickness between outer surface 258 and inner surface 260 and the nearest odd multiple of the quarter wavelength. The thickness of the membrane region is characterized by a second difference consisting of the difference of the thickness and the nearest even multiple of the quarter wavelength. In some embodiments, for productive sheath 210 the magnitude of the first difference is less than the magnitude of the second difference.

[0072] Protective sheath 210 includes an outer region 215 which defines in part lens 211. Outer region 215 may have a thickness that is or is not a multiple of a quarter wavelength of an ultrasonic wave. In some embodiment, outer region 215 is 5.3 mm thick.

[0073] FIG. 11 shows, in perspective view, a probe 300 including a proximal end 102, a distal end 104, a pressure regulator 106, a proximal outer support 312, and a third protective sheath 310. The protective sheath 310 covers partofan ultrasonic imager 316 with principal rays generally inline with the principal axis of probe 300. In some embodiments, imager 316 includes a plurality of transducers arranged in an array, which in operation transmits and receives ultrasonic waves at a plurality of azimuthal angles and a plurality of polar angles at or near the principal axis of probe 300. Imager 316 is protected by protective sheath 310, proximal outer support 312, and other parts of probe 300. In some embodiments, protective sheath 310 is secured by proximal outer support 312 and at least one additional body described herein.

[0074] In some embodiments, probe 300 includes a reflector 320 that redirects ultrasonic waves from a plurality of transducers from polar angles generally inline with a principal axis of probe 300 to a plurality of polar angles extending radially outwards, or the reverse. Reflector 320 may include a multi-part collar that encloses a part of probe 300. In some embodiments, reflector 320 may have a radial extent less than that of proximal outer support 312.

[0075] Probe 300 includes a frame 114 at the proximal side of proximal outer support 312 and is coupled to a mandrel (not shown) extending along a portion of the principal axis of probe 300. Probe 300 further includes electronics bay 118 proximally disposed and coupled to frame 114. Details of frame 114 and electronics bay 118 are discussed herein in relation to, at least, FIG. 1 and FIG. 2.

[0076] Turning to FIG. 12 which illustrates parts of probe 300 in elevation view from the near side shown in FIG. 11. In some embodiments, reflector 320 is located adjacent the ultrasonic array 316 and redirects ultrasonic waves from a principal ray inline with the principal axis of probe 300 to a radial direction, or the reverse. Reflector 320 may be frustoconical and include a sloped surface 321. In some embodiments, a sloped surface 321 faces proximal end 102. In some embodiments, sloped surface 321 faces the distal end 104. Measuring for acute angles for ease of description, exemplary angles for reflector 320 include: 20 degrees, 30 degrees, and 45 degrees. In some embodiments, proximal outer support 312 includes a formed end. Section lines E-E’, F-F’, and G-G’ define the views shown in FIG. 13, FIG. 14, and FIG. 16.

[0077] Turning to FIG. 13 which illustrates imager 316 and parts of probe 300 in a section view according to a cut indicated by line E-E’ shown in FIG. 12. Imager 316 includes a transducer array 330 that emits signals over a plurality of polar angles approximately inline with the principal axis of probe 300, and over a plurality of azimuthal directions. The azimuthal coverage may be one continuous range or a plurality of ranges in the azimuthal direction as described herein.

[0078] Turning to FIG. 14 which illustrates imager 316 and parts of probe 300 in a crosssection view according to a cut indicated by line F-F’ shown in FIG. 12. Imager 316 includes a transducer array 330 having a rotationally symmetric shape, e.g., puck, cylindrical shell. In some embodiments including those shown, protective sheath 310 is inferior to transducer array 330 in the distal direction. In some embodiments, protective sheath 310 is superior to transducer array 330 in the distal direction.

[0079] Protective sheath 310 includes a region 313 placed beside the transducer array 330. Region 313 may be a continuous annular shape, e.g., washer shape. Region 313 has a thickness suitable for ultrasonic waves described herein. Ultrasonic waves emitted by transducer array 330 may pass through transducer array 330 at region 313 and reflect off surface 321. Transducer array 330 may receive ultrasonic waves reflected by surface 321 and travelling through region 313.

[0080] Reflector 320 may include a multi-part collar that encloses a part of probe 300. For example, reflector comprises a two-part collar joined by fasteners with a transverse orientation.

[0081] Imager 316 includes a distal support 308 (e.g., a barrel, collar) located inferior to protective sheath 310. In assembled form, and in some embodiments, distal support 308 and proximal outer support 312 are in an interference fit with protective sheath 310. One or more fluidic seals, e.g., o-rings can, be located between protective sheath 310 plus distal support 308 and proximal outer support 312. Distal support 308 is coupled to mandrel 124. In some embodiments, distal support 308 is connected to mandrel 124, e.g., interference fit.

[0082] Turning to FIG. 15 which illustrates, in a perspective view, protective sheath 310 which includes a web of material in a continuous and connected arrangement to define a generally rotationally symmetric shape (e.g.. cap, disk, washer). In some embodiments, protective sheath 310 includes a central cavity 352. Protective sheath 310 includes a first edge 354.

[0083] Protective sheaths, such as protective sheath 310 include a material such as a fluoropolymer, thermoplastic polymer, or a fluoropolymer rubber or fluoroelastomer. The material is selected for its chemical and physical properties. A suitable thermoplastic polymer for use in protective sheath 310 is polyether ether ketone (PEEK).

[0084] Protective sheath 310 includes an outer face 358 and an inner surface 360. In some embodiments, the thickness between outer face 358 and inner surface 360 is a valued between a pair of low multiples of a quarter wavelength of an ultrasonic wave. In some embodiments, the thickness between outer face 358 and inner surface 360 is a low odd multiple of a quarter wavelength of an ultrasonic wave. The thickness between outer face 358 and inner surface 360 may be between 100 pm and 1 mm (0.004" and 0.039") at 5 MHz. The thickness between outer face 358 and inner surface 360 may be between 200 pm and 2 mm (0.009" and 0.079") at 3 MHz. The thickness between outer face 358 and inner surface 360 may be between 100 pm and 1 mm (0.004" and 0.039") at 5 MHz. In some embodiments, the thickness between outer face 358 and inner surface 360 is near a length selected from the group consisting of 131 pm, 392, pm, 653 pm, or 914 pm (0.005", 0.015", 0.026", or 0.036") corresponding to an ultrasonic wave at 5 MHz. In some embodiments, the thickness between outer face 358 and inner surface 360 is near a length selected from the group consisting of 218 pm, 653 pm, 1088 pm, or 1523 pm (0.009", 0.026", 0.043", or 0.060") corresponding to an ultrasonic wave at 3 MHz. In some embodiments, the thickness between outer face 358 and inner surface 360 is nearer an odd multiple of a quarter wavelength of an ultrasonic wave as compared to an even multiple of a quarter wavelength of an ultrasonic wave. In an example where the protective sheath includes PEEK the thickness between outer face 358 and inner surface 360 is one quarter wavelength of an ultrasonic wave at 5 MHz.

[0085] In some embodiments, protective sheath 310 includes a peripheral part which, when assembled, overlies a part of transducer array 330 in the radial direction. In some embodiments, protective sheath 310 includes a first side 353 leading to the first edge 354. The first side 353 overlies a part of transducer array 330. In some embodiments, protective sheath 310 includes a central part which underlies a part of transducer array 330 in the radial direction. In some embodiments, protective sheath 310 includes a second side 355 leading to a second edge 356.

[0086] Turning to FIG. 16 which illustrates pressure regulator 106 in a section view according to a cut indicated by line G-G’ shown in FIG. 12. However, pressure regulator 106 can be coupled to probe 100 or probe 200. Pressure regulator 106 includes an outer housing, for example, a multipart outer housing including a barrel 402 and a nose cone 404. In some implementations, barrel 402 and nose cone 404 are threaded together. The interior of barrel 402 and / or nose cone 404 define a cylinder. For example, barrel 402 includes a cylinder wall 406 defining cylinder 408. Pressure regulator 106 includes a piston 410 in a sealed slip-fit engagement with the cylinder wall 406. In some embodiments, piston 410 encircles and is in a sealed slip-fit engagement with mandrel 124

[0087] In some embodiments, pressure regulator 106 includes a fluid connection between cylinder 408 and the environment. For example, cylinder 408 on the distal side of piston 410 is in fluid communication with the environment by passage 412.

[0088] Pressure regulator 106 is fluidly coupled to the parts of probe 100, probe 200, or probe 300 between frame 114 and the proximal side of pressure regulator 106.

[0089] In some embodiments, pressure regulator 106 is in fluid coupling with a void or chamber 409 defined within an imager such as imager 116, imager 216, or imager 316. In some embodiments, the chamber includes within, or encloses, a transducer array like transducer array 130, transducer array 230, or transducer array 330, described herein. The chamber may include a plurality of bodies within the housing and in the region of the sheath the chamber extends along a principal axis of the mandrel and is defined in radially extent by the protective sheath. Thereby the chamber encloses the transducer array. In some embodiments, the chamber is radially symmetric as defined by an inner side of the protective sheath.

[0090] In some embodiments, pressure regulator 106 includes a deformable body. In some embodiments, pressure regulator 106 includes a moveable body. In some embodiments, pressure regulator 106 includes a deformable body and a moveable body.

[0091] In some embodiments, pressure regulator 106 includes a deformable body separating the chamber from a void with a fluid connection to the environment. The deformable body may be a bladder, bellows, or diaphragm. In response to changing pressure of the environment, the deformable body moves and equalizes the pressure in the clean fluid in the chamber to that of the environment. In response to changing pressure in the environment pressure regulator 106 reduces the pressure difference on either side of a protective sheath, e.g., sheath 110. So in operation, pressure regulator 106 minimize net forces on the protective sheath, such as ballooning or crushing forces.

[0092] In some embodiments, pressure regulator 106 includes a moveable body separating the chamber from a void with a fluid connection the environment. In some embodiments, pressure regulator 106 includes a cylinder 408 with a fluid connection the environment, e.g., through passage 412. Disposed in cylinder 408 is piston 410 in a sealed slip-fit engagement. As shown, on the proximal side of the piston is a clean fluid (e.g., oil, mineral oil, synthetic oil) which surrounds interior parts of an imager, e.g., imager 316. In response to changing pressure of the environment the piston moves and equalizes the pressure in the clean fluid to that of the environment. In response to changing pressure in the environment pressure regulator 106 reduces the pressure difference on either side of the protective sheath, e.g., sheath 110. So in operation pressure regulator 106 minimize net forces on the protective sheath, such as ballooning or crushing forces.

[0093] In operation, pressure changes in the environment pass through the passage 412 and act on a distal side of the pressure regulator (e.g. piston baffle or diaphragm), which moves with respect to the chamber 409 until the chamber pressure and environment pressure are equal. The chamber may be fluid-filled, e.g. using mineral oil, and when pressurized by the pressure regulator will compress slightly. This chamber boundary includes the sheath itself, such that opposing sides of the thin sheath are exposed to the equal pressures.

[0094] In some embodiments, pressure regulator 106 includes a pressure relief valve used to limit the pressure difference between the pressure-equalized parts of pressure regulator 106 and a coupled imager. The pressure relief valve may be disposed in recess 414. The pressure relief valve may uni-directional with pressure regulator 106 including an inward relief valve to allow in fluid from the environment, or an outward relief valve to allow the clean fluid to escape from pressure regulator 106.

[0095] In some embodiments, probe 100 includes a chamber defined in radial extent by protective sheath 110 and pressure regulator 106 which are coupled to mandrel 124. In some embodiments, pressure regulator 106 includes a cylinder comprising a first passage to the environment and a second passage, a piston in a sliding interference fit with the cylinder and positioned between the first passage and the second passage. The pressure regulator is in a fluid connection with the chamber through the second passage. In response to a change in the pressure in the environment, the piston moves in the cylinder to equalize the pressure in the chamber with the pressure in the environment.

[0096] In some embodiments, a probe, such as probe 100, probe 200, or probe 300, may be coupled to a centralizer (not shown). The centralizer may be placed on the proximal end 102 or the distal end 104. A centralizer includes a plurality of biased vanes that are arranged with purposeful shape (e.g., trefoil or cruciform in cross-section) to exert outward forces on the surrounding walls. And in response to the net outward forces and resistance from the surroundings, the coupled probe is centered amongst the surroundings. The vanes may be unitary like a leaf spring on comprise multiple bars joined by a plurality of hinges and outwardly biased by at least one spring.

[0097] In some embodiments, a probe, such as probe 100, probe 200, or probe 300, may be coupled to a cable head at a proximal end, e.g., end 102. A cable head is a device used to couple a probe to a cable, line, string, or wireline - e.g., logging cable, amour wire, wire rope, string equipped with an electrical conductor. A cable head may provide both a mechanical coupling to mechanical armor of a wireline which provides tension to move the probe and an electrical coupling through conductors forming one or more circuits.

[0098] In some embodiments, a probe, such as probe 100, probe 200, or probe 300, includes, at distal end 104, a probe head (not shown) or a forward imager such as imager 316 without reflector 320. The probe head may be used to protect the probe. The forward imager may be used to observe obstruction or fluid flow. The forward imager may include one or more transducers.

[0099] Before turning to FIG. 17 the materials discussed herein at, at least FIG. 5, FIG. 10 and FIG. 15 may be summarized in the following table. Attenuation is measured in dB / cm, velocity in m / s, quarter wavelength in p.m for 5 MHz, impedance (MRayl), density (gr / cmA3). Material Attenuation Velocity X / 4 Impedance Density FEP 56.2 1302 65 2.76 0.47 PEEK 4.1 2611 131 3.50 1.32 VITON A 2.5 2000 100 3.7 1.85

[0100] Before turning to FIG. 17, the thicknesses of a protective sheath (e.g., sheath 110, sheath 210, and sheath 310) can be further characterized in terms of a duration of an ultrasonic pulse propagating through the protective sheath. An ultrasonic wave propagating through a thin protective sheath can experience constructive and destructive interference. For example, an ultrasonic wave emitted by, or received by, a transducer array, e.g., transducer array 130, thicknesses that are near an odd multiple are associated with constructive interference for propagation and destructive interference for reflection. The reverse is true for even quarter wavelength thicknesses. However, the interference effects are more pronounced when the pulse duration is long. For short-duration pulses there is less benefit and thinner media are preferred as there is less attenuation.

[0101] Thickness is a consideration in the direction of the ultrasonic wave. A low odd multiple of quarter wavelength is suitable for the thickness of a protective sheath when the wave propagates through a High-Medium-Low or Low-Medium-High sequence of acoustic impedance layers. For example, when a wave is emitted from the high-impedance ultrasonic transducer (e.g., transducer array 130), then a mid-impedance medium, such as protective sheath 110, and a lower impedance medium, typically a fluid, or vice versa for the returning wave. A thickness of a protective sheath that is a low even multiple of quarter wavelength (i.e. half-wavelength) is suitable to optimize propagation of a wave through a Low-Medium-Low sequence of acoustic impedance layers, e.g. a lower acoustic impedance medium, typically a fluid, then a mid-impedance medium, such as protective sheath 110, and a low-impedance medium. These effects are more pronounced with long pulse duration so the ultrasonic wave can interfere with itself.

[0102] In some embodiments, for long pulses (e.g., tens to hundreds of cycles or more) a protective sheath overlying transducer array (e.g., transducer array 130, transducer array 230, and transducer array 330) includes a region (e.g., membrane region 162, central region 213, a nadir, difference between outer face 358 and inner surface 360) with a thickness near a low odd multiple of a quarter wavelength, such as one, three, or five.

[0103] In some embodiments, for short pulses propagating through a protective sheath (e.g., sheath 110, sheath 210, and sheath 310) overlying transducer array (e.g., transducer array 130) includes a region (e.g., membrane region 162) with a thickness near a low multiple quarter wavelength, such as one, two, three, four, five, and six. In some embodiments, the thickness is near a very low multiple, such as one, two, or three.

[0104] Turning to FIG. 17 which illustrates an example method 500 for use with a flexible and stretchable protective sheath, such as a sheath including VITON. Various embodiments of flexible and stretchable protective sheaths are described herein including in relation to FIG. 1 through FIG. 5. For example, see various embodiments of protective sheath 110.

[0105] For method 500, as with other methods taught herein, the various acts may be performed in a different order than that illustrated and described. Additionally, the methods can omit some acts, combine acts, split an act, and / or employ additional acts. Method 500 may be performed by an assembler, e.g., a worker, processor controlled robot.

[0106] Method 500 begins at 502 when the assembler presents a flexible and stretchable protective sheath, and an imager, e.g., imager 116, for fitment.

[0107] At 504, optionally, the assembler stretches the protective sheath. At 506, the assembler places the protective sheath on the imager. The assembler stops stretching the sheath. Optionally the assembler can use one or more location marks on the protective sheath or imager to ensure a consistent placement of sheath with respect to: rotation, alignment, and proximal-distal extent. In some implementations, the assembler checks that a membrane region overlies a transducer array.

[0108] At 508 the assembler, optionally, inspects the protective sheath, e.g., visual inspection, electrical connection test.

[0109] Turning to FIG. 18 which illustrates an example method 600 for use with a flexible protective sheath that can be shrunk to fit, such as a sheath including FEP. Various embodiments of protective sheaths are described herein including protective sheath 110 and protective sheaths described in relation to FIG. 1 through FIG. 5. Method 600 may be performed by an assembler, e.g., a worker, processor-controlled robot.

[0110] Method 600 begins at 602 when the assembler presents a tube of heat shrink material, and an imager, e.g., imager 116. The tube of heat shrink material may have a cylindrical shape like the sheath shown in FIG. 5 or a reflected on itself like the sheath shown in FIG. 15.

[0111] At 604 the assembler trims the tube to length. At 606 the assembler places the tube of heat shrink material around the imager. For example, around the transducer array 130 shown in FIG. 3. The placement may be a loose fit (preferable), or an interference fit. Optionally the assembler can use one or more location marks on the tube or imager to ensure consistent placement.

[0112] At 608 the assembler heats the tube. In various implementations, the assembler submerges the tube and the imager in heated oil (e.g., mineral oil). For example, the clean fluid used in pressure regulator 106 described herein. Oil was found to reduce the number of air bubble trapped under the tube. With an FEP tube of about two-thousandths of an inch thick, the oil may be heated between 100 degrees and 130 degrees. Even though this is above the recommended setting temperature for commercial heat shrink tubes (i.e. 80°C), this serves to set the correct final thickness of the sheath, instead of having the tube re-shrink every time the tool is exposed to higher operating temperatures. The oil bath serves to ensure air is not trapped between the sheath and mandrel. While a thin film of oil will be trapped, oil is a good acoustic couplant and may simply mix into the pressure regulator oil when pressurized. A bathing time of about 30 minutes achieves an engagement fit, for example, shrinking about 15% down from the dimension of the loose fit.

[0113] At 610 the assembler, optionally, inspects the tube (protective sheath), e.g., visual inspection, electrical connection test.

[0114] Following method 500 or method 600, an assembler can fit a protective sheath, to an imager, e.g., imager 116, or imager 216. The assembler can follow instructions that respect the embodiments of the imager such as those shown in FIG. 1 through FIG 4. For example, assembling a probe with one or more supports that to define a sealed fit of a sheath, e.g., protective sheath 110. Examples of supports include distal outer support 108, and proximal outer support 112. One or more fluidic seals like o-rings may be included.

[0115] Turning to FIG. 19 which illustrates an example method 700 for use with rigid protective sheath that can be machined, such as a sheath including PEEK. Various embodiments of protective sheaths are described herein including protective sheath 210, protective sheath 310, and protective sheaths described in relation to FIG. 6 through FIG. 15. Method 700 may be performed by a manufacturer, e.g., a worker, processor-controlled milling machine.

[0116] Method 700 begins at 702 when the manufacturer presents a workpiece of plastic. A suitable plastic includes a thermoplastic polymer, such as, PEEK.

[0117] At 704 the manufacturer trims (e.g., cuts, mills, turn-down) the workpiece to size. At 706 the manufacturer places the workpiece in a vacuum fixture which is designed to hold the workpiece with uniform force across the workpiece. Traditional workpiece clamps and holders would normally crush or deform a sheath of this thinness.

[0118] At 708, the manufacturer forms the outer surface of a protective sheath on the workpiece. At 710, the manufacturer forms the inner surface of the protective sheath within the workpiece. In some implementations before 710, the manufacturer removes the workpiece from the fixture and attaches it to same fixture in a different orientation or a different fixture. At 712, the manufacturer, optionally, inspects the workpiece, e.g., visual inspection, surface roughness test.

[0119] Following method 700, an assembler can fit the workpiece, now a protective sheath, to an imager, e.g., imager216, imager316. The assembler can follow instructions that respect the embodiments of the imager such as those shown in FIG. 1 through FIG 4; FIG. 6 through FIG 9; and FIG. 11 through FIG 14. For example, assembling a probe with one or more supports that to define a sealed fit of a sheath, e.g., protective sheath , or protective sheath 310. Examples of supports include distal outer support 208, proximal outer support 212, distal outer support 308, and proximal outer support 312. One or more fluidic seals like o-rings may be included.

[0120] For methods taught herein, the various acts may be performed in a different order than that illustrated or described. Additionally, the methods can omit some acts, combine acts, split an act, and / or employ additional acts. For methods taught herein, the various acts may be performed by one or more circuits, for instance, one or more hardware processors. [0121 ] The word “a” or “an” when used in conjunction with the terms “comprise”, “include”, “comprising”, or “including” in the claims or the specification may mean “one”, “one or more”, “at least one”, and “a plurality” unless the content dictates otherwise. Similarly, the word “another” means “additional” or “at least a second” unless the content clearly dictates otherwise.

[0122] The terms “coupled”, “coupling” or “connected” as used herein can have several different meanings depending on the context in which these terms are used. For example, the terms coupled, coupling, or connected can have a mechanical or electrical connotation. For example, as used herein, the terms coupled, coupling, or connected can indicate that two elements or devices are directly connected to one another or connected to one another through one or more intermediate elements or devices via an electrical element, electrical signal or a mechanical element depending on the particular context. The term “and / or” herein when used in association with a list of items means any one or more of the items comprising that list.

[0123] As used herein, a reference to “about”, “approximately”, or “near” a number or to being “substantially” equal to a number means being within +1-10% of that number.

[0124] While the disclosure has been described in connection with specific embodiments, it is to be understood that the disclosure is not limited to these embodiments, and that alterations, modifications, and variations of these embodiments may be carried out by the skilled person without departing from the scope of the disclosure.

[0125] It is furthermore contemplated that any part of any aspect or embodiment discussed in this specification can be implemented or combined with any part of any other aspect or embodiment discussed in this specification.

Claims

1. A machine, comprising:a mandrel;a rotationally symmetric transducer array coupled to the mandrel;a first support coupled to the mandrel; anda protective sheath overlying the rotationally symmetric transducer array and underlying the first support at a first part of the first support, wherein the protective sheath includes a thin region of a thickness that is near a low multiple of a quarter wavelength of an ultrasonic wave generated, or received, by the rotationally symmetric transducer array.

2. The machine of claim 1 further comprising a second support coupled to the mandrel including a first part that overlies a second part of the rotationally symmetric transducer array.

3. The machine of claim 1, wherein the protective sheath comprises at least one of: fluorinated ethylene propylene (FEP), polyether ether ketone (PEEK), and VITON.

4. The machine of claim 1, wherein the thin region is near the low multiple selected from the group consisting of one, three, and five.

5. The machine of claim 1 further comprising:a chamber extending along a principal axis of the mandrel and defined in radially extent by the protective sheath; anda pressure regulator coupled to the mandrel and in fluid communication with the chamber, wherein in response to a pressure change in an environment outside of the protective sheath the pressure regulator equalizes a pressure in the chamber with the pressure in the environment.

6. The machine of claim 5, wherein the pressure regulator further includes:a cylinder comprising a first passage providing fluid communication to the environment and a second passage providing fluid communication to the chamber; anda piston in a sliding interference fit with the cylinder and positioned between the first passage and the second passage, wherein in response to a change in the pressure in the environment the piston moves in the cylinder to equalize the pressure in the chamber with the pressure in the environment.

7. The machine of claim 1, further comprising a reflector coupled to the mandrel and adjacent to the transducer array and positioned to reflect an ultrasonic wave from or to the rotationally symmetric transducer array.

8. A machine, comprising:a frame;an ultrasonic transducer array coupled to the frame;a protective sheath overlying the ultrasonic transducer array and coupled to the frame, wherein the sheath includes a thin region of a thickness near a low multiple of a quarter wavelength of an ultrasonic wave generated, or received, by the ultrasonic transducer array;a chamber defined in part by the frame and the sheath; anda pressure regulator coupled to the frame and in fluid communication with the chamber, wherein in response to a pressure change in an environment outside of the protective sheath the pressure regulator equalizes a pressure in the chamber with the pressure in the environment.

9. The machine of claim 8, wherein the pressure regulator further includes:a cylinder comprising a first passage in fluid communication with the environment and a second passage in fluid communication to the chamber; anda piston in a sliding interference fit with the cylinder and positioned between the first passage and the second passage.

10. The machine of claim 8 further comprising a reflector coupled to the frame and reflecting an ultrasonic wave from, or to, the ultrasonic transducer array.

11. The machine of claim 8, wherein the thin region is near a low odd multiple selected from the group consisting of one, three, and five.

12. The machine of claim 8, wherein the sheath comprises at least one of: fluorinated ethylene propylene (FEP), polyether ether ketone (PEEK), and VITON.

13. The machine of claim 8, wherein the ultrasonic transducer array emits or receives a principal ray in a direction selected from the group consisting of: low-oblique, midoblique, and high-oblique.

14. An article of manufacture, which in use protects an ultrasonic transducer, comprising:a protective sheath defining a central cavity extending along a first axis of the protective sheath;a first edge connected to the protective sheath defining a first passage to the central cavity; anda thin region defined in the protective sheath wherein the thin region is of a thickness that is near a low multiple of a quarter wavelength of an ultrasonic wave emitted, or received, by the ultrasonic transducer.

15. The article of manufacture of claim 14 further comprising a second edge connected to the protective sheath defining a second passage to the central cavity.

16. The article of manufacture of claim 14, wherein the protective sheath is rotationally symmetric with respect to the first axis.

17. The article of manufacture of claim 14, wherein the protective sheath comprises at least one of: fluorinated ethylene propylene (FEP), polyether ether ketone (PEEK), and VITON.

18. The article of manufacture of claim 14, wherein the thickness of the thin region is near a low odd multiple of a quarter wavelength of an ultrasonic wave emitted, or received, by the ultrasonic transducer, the low odd multiple is selected from the group consisting of one, three, and five.

19. The article of manufacture of claim 14, wherein the thickness of the thin region is near a low odd multiple of a quarter wavelength of an ultrasonic wave emitted, or received, by the ultrasonic transducer, the low odd multiple is selected from the group consisting of seven and nine.