Patent Description:
Ultrasound imaging probes continue to enjoy widespread use in the medical field. By way of example, ultrasound probes are utilized for a wide variety of external, laparoscopic, endoscopic and intravascular imaging applications. The ultrasound images provided by imaging probes may, for example, be used for diagnostic purposes. The probes typically include a plurality of parallel piezoelectric transducer elements arranged along a longitudinal axis, with each element interconnected to a pair of electrodes. An electronic circuit excites the transducer elements causing them to emit ultrasonic energy. The transducer elements then convert the received ultrasonic energy into electrical signals, which may then be processed and used to generate images. Typically, the transducers include an active layer of a piezoelectric material with an acoustic face from which acoustic signals are emitted. An acoustic attenuation member is also generally disposed on the back surface of the active layer to dampen undesirable acoustic signals (e.g., signals that may emanate from and be reflected back to the rear face of the transducer), which would otherwise interfere with the acoustic signals received at the acoustic face. Unfortunately, due to the increased complexity of most probe designs, power consumption is increased, which in turn leads to an increase in the amount of heat that is produced by the probe. This increased production of heat can be a problem due to the fact most acoustic attenuation members are not highly heat sensitive. Over time, this can ultimately lead to a malfunction of the camera sensor. <CIT> discloses thermally conductive backing materials for ultrasound probes and systems.

As such, a need exists for an improved ultrasonic probe having a higher degree of heat sensitivity.

In accordance with one embodiment of the present invention, an ultrasonic probe is disclosed that comprises an ultrasonic transducer that includes an array of transducer elements capable of converting electrical energy to ultrasonic acoustic energy for emission towards a region of interest and an attenuation material that is capable of inhibiting the return of the ultrasonic acoustic energy back towards the ultrasonic transducer after emission towards the region of interest. The attenuation material comprises a polymer composition that includes a liquid crystalline polymer and a thermally conductive particulate material. The thermally conductive particulate material is present in the polymer composition in an amount of from about <NUM> to about <NUM> parts per <NUM> parts of the liquid crystalline polymer. The liquid crystalline polymer has a melting temperature of about <NUM> or more and a melt viscosity of about <NUM> Pa-s or less as determined at a temperature of <NUM> above the melting temperature and shear rate of <NUM>-<NUM> in accordance with ISO Test No. <NUM>:<NUM>, and the polymer composition also has a through-plane conductivity of about <NUM> W/m-K or more.

Other features and aspects of the present invention are set forth in greater detail below.

A full and enabling disclosure of the present invention, including the best mode thereof to one skilled in the art, is set forth more particularly in the remainder of the specification, including reference to the accompanying figures, in which:.

Generally speaking, the present invention is directed to an ultrasonic probe that contains an ultrasonic transducer and an attenuation material that is capable of attenuating acoustic energy incident upon the material, such as energy having a frequency between <NUM> and <NUM>. The attenuation material includes a polymer composition, which contains a liquid crystalline polymer and thermally conductive particulate material. By selectively controlling the nature of the components in the polymer composition and their relative concentration, the resulting composition is capable of serving as an effective acoustic attenuation material, but also exhibit good thermal properties that allow for heat transfer so that "hot spots" can be quickly eliminated and the overall temperature of the part can be lowered during use. More particularly, the composition exhibits a through-plane thermal conductivity of about <NUM> W/m-K or more, in some embodiments about <NUM> W/m-K or more, in some embodiments about <NUM> W/m-K or more, in some embodiments from about <NUM> to about <NUM> W/m-K, in some embodiments from about <NUM> to about <NUM> W/m-k, and in some embodiments, from about <NUM> to about <NUM> W/m-K, as determined in accordance with ASTM E <NUM>-<NUM>.

Various embodiments of the present invention will now be described in more detail.

As indicated above, the liquid crystalline polymer employed in the polymer matrix has a melting temperature within a carefully controlled range of from about <NUM> to about <NUM>, in some embodiments from about <NUM> to about <NUM>, in some embodiments from about <NUM> to about <NUM>, and in some embodiments, from about <NUM> to about <NUM>. One particularly suitable liquid crystalline polymer contains the following repeating units (<NUM>) to (<NUM>):
<CHM>
<CHM>
<CHM>
wherein,.

In certain embodiments, the repeating units (<NUM>) may be derived from <NUM>-hydroxybenzoic acid ("HBA") (l is <NUM>), the repeating units (<NUM>) may be derived from hydroquinone ("HQ") (m is <NUM>), and/or the repeating units (<NUM>) may be derived from isophthalic acid ("IA") (q is <NUM>).

By selectively controlling the nature and relative proportion of the repeating units (<NUM>)-(<NUM>), the present inventors have discovered the resulting polymer may not only achieve a melting temperature within the range noted above, but also still achieve a significant degree of chain entanglement such that the polymer exhibits good melt strength, which enables it to be readily employed in the ultrasonic probe of the present invention. For example, the repeating units (<NUM>) may constitute from about <NUM> mole% to about <NUM> mole%, in some embodiments from about <NUM> mole% to about <NUM> mole%, and in some embodiments, from about <NUM> mole% to about <NUM> mole% of the polymer. Likewise, the repeating units (<NUM>) and (<NUM>) may each constitute from about <NUM> mole% to about <NUM> mole%, in some embodiments from about <NUM> mole% to about <NUM> mole%, and in some embodiments, from about <NUM> mole% to about <NUM> mole% of the polymer. Regardless of the exact molar amount employed, the molar ratio of repeating units (<NUM>) to the repeating units (<NUM>) may be selectively controlled so that it is from about <NUM> to about <NUM>, in some embodiments from about <NUM> to about <NUM>, and in some embodiments, from about <NUM> to about <NUM>. In some cases, the repeating units (<NUM>) are used in a molar amount greater than the repeating units (<NUM>) such that the molar ratio is greater than <NUM>.

Of course, it should be understood that other repeating units may also be employed in the polymer. <CHM>
<CHM>
wherein,.

In certain embodiments, the repeating units (<NUM>) may be derived from <NUM>,<NUM>'-biphenol ("BP") (n and o are <NUM>) and/or the repeating units (<NUM>) may be derived from terephthalic acid ("TA") (p is <NUM>).

The repeating units (<NUM>) and (<NUM>) may each constitute from about <NUM> mole% to about <NUM> mole%, in some embodiments from about <NUM> mole% to about <NUM> mole%, and in some embodiments, from about <NUM> mole% to about <NUM> mole% of the polymer. Regardless of the exact molar amount employed, the molar ratio of repeating units (<NUM>) to the repeating units (<NUM>) may be selectively controlled so that it is from about <NUM> to about <NUM>, in some embodiments from about <NUM> to about <NUM>, and in some embodiments, from about <NUM> to about <NUM>. In some cases, the repeating units (<NUM>) are used in a molar amount greater than the repeating units (<NUM>) such that the molar ratio is greater than <NUM>.

Still other repeating units may also be employed in the polymer. For example, other aromatic hydroxycarboxylic repeating units may also be employed that are derived from aromatic hydroxycarboxylic acids other than HBA, such as, <NUM>-hydroxy-<NUM>'-biphenylcarboxylic acid; <NUM>-hydroxy-<NUM>-naphthoic acid ("HNA"); <NUM>-hydroxy-<NUM>-naphthoic acid; <NUM>-hydroxy-<NUM>-naphthoic acid; <NUM>-hydroxy-<NUM>-naphthoic acid; <NUM>'-hydroxyphenyl-<NUM>-benzoic acid; <NUM>'-hydroxyphenyl-<NUM>-benzoic acid; <NUM>'-hydroxyphenyl-<NUM>-benzoic acid, etc., as well as alkyl, alkoxy, aryl and halogen substituents thereof, and combination thereof. Likewise, other aromatic dicarboxylic repeating units may be employed that are derived from aromatic dicarboxylic acids other than TA and IA, such as <NUM>,<NUM>-naphthalenedicarboxylic acid ("NDA"), diphenyl ether-<NUM>,<NUM>'-dicarboxylic acid, <NUM> ,<NUM>-naphthalenedicarboxylic acid, <NUM>,<NUM>-naphthalenedicarboxylic acid, <NUM>,<NUM>'-dicarboxybiphenyl, bis(<NUM>-carboxyphenyl)ether, bis(<NUM>-carboxyphenyl)butane, bis(<NUM>-carboxyphenyl)ethane, bis(<NUM>-carboxyphenyl)ether, bis(<NUM>-carboxyphenyl)ethane, etc., as well as alkyl, alkoxy, aryl and halogen substituents thereof, and combinations thereof. Aromatic diol repeating units may also be employed that are derived from aromatic diols other than HQ and BP, such as resorcinol, <NUM>,<NUM>-dihydroxynaphthalene, <NUM>,<NUM>-dihydroxynaphthalene, <NUM>,<NUM>-dihydroxynaphthalene, <NUM>,<NUM>'-dihydroxybiphenyl (or <NUM>,<NUM>'-biphenol), <NUM>,<NUM>'-dihydroxybiphenyl, <NUM>,<NUM>'-dihydroxybiphenyl, <NUM>,<NUM>'-dihydroxybiphenyl ether, bis(<NUM>-hydroxyphenyl)ethane, etc., as well as alkyl, alkoxy, aryl and halogen substituents thereof, and combinations thereof. Repeating units may also be employed, such as those derived from aromatic amides (e.g., acetaminophen ("APAP")) and/or aromatic amines (e.g., <NUM>-aminophenol ("AP"), <NUM>-aminophenol, <NUM>,<NUM>-phenylenediamine, <NUM>,<NUM>-phenylenediamine, etc.). It should also be understood that various other monomeric repeating units may be incorporated into the polymer. For instance, in certain embodiments, the polymer may contain one or more repeating units derived from non-aromatic monomers, such as aliphatic or cycloaliphatic hydroxycarboxylic acids, dicarboxylic acids (e.g., cyclohexane dicarboxylic acid), diols, amides, amines, etc. Of course, in other embodiments, the polymer may be "wholly aromatic" in that it lacks repeating units derived from non-aromatic (e.g., aliphatic or cycloaliphatic) monomers.

Although not necessarily required, it may be desired that the liquid crystalline polymer contains a low content of repeating units derived from naphthenic hydroxycarboxylic acids and naphthenic dicarboxylic acids, such as NDA, HNA, or combinations thereof. That is, the total amount of repeating units derived from naphthenic hydroxycarboxylic and/or dicarboxylic acids (e.g., NDA, HNA, or a combination of HNA and NDA) is typically less than about <NUM> mol. %, in some embodiments less than about <NUM> mol. %, and in some embodiments, less than about <NUM> mol. % of the polymer. The liquid crystalline polymer may also contain a low content of repeating units derived from aromatic amides and aromatic amines, such as APAP, AP, or combinations thereof. That is, the total amount of repeating units derived from aromatic amides and/or amines (e.g., APAP, AP, or a combination of APAP and AP) is typically less than about <NUM> mol. %, in some embodiments less than about <NUM> mol. %, and in some embodiments, less than about <NUM> mol. % of the polymer. In particular embodiments, the polymer contains <NUM> mol. % of naphthenic hydroxycarboxylic acids (e.g., HNA), <NUM> mol. % of naphthenic dicarboxylic acids (e.g., NDA), <NUM> mol. % of aromatic amides (e.g., APAP), and/or <NUM> mol. % of aromatic amines (e.g., AP). In fact, the liquid crystalline polymer may be formed entirely from the repeating units (<NUM>)-(<NUM>) if so desired such that the total molar percentage of the repeating units (<NUM>)-(<NUM>) equals <NUM>%.

The liquid crystalline polymer may be synthesized in a melt polymerization process. The process may involve initially introducing the monomer(s) used to form the repeating units (e.g., HBA, IA, HQ, TA, and/or BP) into a reactor vessel to initiate a polycondensation reaction. The particular conditions and steps employed in such reactions are well known, and may be described in more detail in <CIT> to Calundann; <CIT> to Linstid, III, et al. ; <CIT> to Linstid, III, et al. ; <CIT> to Shepherd, et al. ; and <CIT> to Waggoner. The vessel employed for the reaction is not especially limited, although it is typically desired to employ one that is commonly used in reactions of high viscosity fluids. Examples of such a reaction vessel may include a stirring tank-type apparatus that has an agitator with a variably-shaped stirring blade, such as an anchor type, multistage type, spiral-ribbon type, screw shaft type, etc., or a modified shape thereof. Further examples of such a reaction vessel may include a mixing apparatus commonly used in resin kneading, such as a kneader, a roll mill, a Banbury mixer, etc..

If desired, the reaction may proceed through the acetylation of the monomers as known the art. This may be accomplished by adding an acetylating agent (e.g., acetic anhydride) to the monomers. Acetylation is generally initiated at temperatures of about <NUM>. During the initial stage of the acetylation, reflux may be employed to maintain vapor phase temperature below the point at which acetic acid byproduct and anhydride begin to distill. Temperatures during acetylation typically range from between <NUM> to <NUM>, and in some embodiments, from about <NUM> to about <NUM>. If reflux is used, the vapor phase temperature typically exceeds the boiling point of acetic acid, but remains low enough to retain residual acetic anhydride. For example, acetic anhydride vaporizes at temperatures of about <NUM>. Thus, providing the reactor with a vapor phase reflux at a temperature of from about <NUM> to about <NUM> is particularly desirable. To ensure substantially complete reaction, an excess amount of acetic anhydride may be employed. The amount of excess anhydride will vary depending upon the particular acetylation conditions employed, including the presence or absence of reflux. The use of an excess of from about <NUM> to about <NUM> mole percent of acetic anhydride, based on the total moles of reactant hydroxyl groups present is not uncommon.

Acetylation may occur in in a separate reactor vessel, or it may occur in situ within the polymerization reactor vessel. When separate reactor vessels are employed, one or more of the monomers may be introduced to the acetylation reactor and subsequently transferred to the polymerization reactor. Likewise, one or more of the monomers may also be directly introduced to the reactor vessel without undergoing pre-acetylation.

In addition to the monomers and optional acetylating agents, other components may also be included within the reaction mixture to help facilitate polymerization. For instance, a catalyst may be optionally employed, such as metal salt catalysts (e.g., magnesium acetate, tin(I) acetate, tetrabutyl titanate, lead acetate, sodium acetate, potassium acetate, etc.) and organic compound catalysts (e.g., N-methylimidazole). Such catalysts are typically used in amounts of from about <NUM> to about <NUM> parts per million based on the total weight of the recurring unit precursors. When separate reactors are employed, it is typically desired to apply the catalyst to the acetylation reactor rather than the polymerization reactor, although this is by no means a requirement.

The reaction mixture is generally heated to an elevated temperature within the polymerization reactor vessel to initiate melt polycondensation of the reactants. Polycondensation may occur, for instance, within a temperature range of from about <NUM> to about <NUM>. For instance, one suitable technique for forming the polymer may include charging precursor monomers and acetic anhydride into the reactor, heating the mixture to a temperature of from about <NUM> to about <NUM> to acetylize the monomers (e.g., forming acetoxy), and then increasing the temperature to a temperature of from about <NUM> to about <NUM> to carry out melt polycondensation. As the final polymerization temperatures are approached, volatile byproducts of the reaction (e.g., acetic acid) may also be removed so that the desired molecular weight may be readily achieved. The reaction mixture is generally subjected to agitation during polymerization to ensure good heat and mass transfer, and in turn, good material homogeneity. The rotational velocity of the agitator may vary during the course of the reaction, but typically ranges from about <NUM> to about <NUM> revolutions per minute ("rpm"), and in some embodiments, from about <NUM> to about <NUM> rpm. To build molecular weight in the melt, the polymerization reaction may also be conducted under vacuum, the application of which facilitates the removal of volatiles formed during the final stages of polycondensation. The vacuum may be created by the application of a suctional pressure, such as within the range of from about <NUM> to about <NUM> pounds per square inch ("psi"), and in some embodiments, from about <NUM> to about <NUM> psi, wherein <NUM> psi = <NUM>,<NUM> kPa.

Following melt polymerization, the molten polymer may be discharged from the reactor, typically through an extrusion orifice fitted with a die of desired configuration, cooled, and collected. Commonly, the melt is discharged through a perforated die to form strands that are taken up in a water bath, pelletized and dried. The resin may also be in the form of a strand, granule, or powder.

Regardless of the particular method employed, the resulting polymer may have a relatively low melt viscosity, such as from about <NUM> to about <NUM> Pa-s, in some embodiments from about <NUM> to about <NUM> Pa-s, and in some embodiments, from about <NUM> to about <NUM> Pa-s, determined at a shear rate of <NUM> seconds-<NUM>. Melt viscosity may be determined in accordance with ISO Test No. <NUM>:<NUM> at about <NUM> higher than the melting temperature of the polymer (e.g., at <NUM> for a polymer with a melting temperature of <NUM>).

To help achieve the desired thermal properties, the polymer composition also contains a thermally conductive particulate material. The particulate material typically has an average size (e.g., diameter) of about <NUM> to about <NUM>,<NUM> micrometers, in some embodiments from about <NUM> to about <NUM>,<NUM> micrometers, in some embodiments from about <NUM> to about <NUM>,<NUM> micrometers, and in some embodiments, from about <NUM> to about <NUM>,<NUM> micrometers, such as determined using laser diffraction techniques in accordance with ISO <NUM>:<NUM> (e.g., with a Horiba LA-<NUM> particle size distribution analyzer). The thermally conductive particulate material may also have a narrow size distribution. That is, at least about <NUM>% by volume of the particles, in some embodiments at least about <NUM>% by volume of the particles, and in some embodiments, at least about <NUM>% by volume of the particles may have a size within the ranges noted above. In certain embodiments, the particulate material may have a "flake" shape in that it has a relatively high aspect ratio (e.g., average length or diameter divided by average thickness), such as about <NUM>:<NUM> or more, in some embodiments about <NUM>:<NUM> or more, and in some embodiments, from about <NUM>:<NUM> to about <NUM>:<NUM>. The average thickness may, for instance, be about <NUM> micrometers or less, in some embodiments from about <NUM> micrometers to about <NUM> micrometers, and in some embodiments, from about <NUM> micrometers to about <NUM> micrometers. The specific surface area of the material may also be relatively high, such as about <NUM><NUM>/g or more, in some embodiments about <NUM><NUM>/g or more, and in some embodiments, from about <NUM> to about <NUM><NUM>/g. The specific surface area can be determined according to standard methods such as by the physical gas adsorption method (B. method) with nitrogen as the adsorption gas, as is generally known in the art and described by <NPL>). The particulate material may also have a powder tap density of from about <NUM> to about <NUM>/cm<NUM>, in some embodiments from about <NUM> to about <NUM>/cm<NUM>, and in some embodiments, from about <NUM> to about <NUM>/cm<NUM>, such as determined in accordance with ASTM B527-<NUM>.

Further, the thermally conductive particulate material may have a high intrinsic thermal conductivity, such as about <NUM> W/m-K or more, in some embodiments about <NUM> W/m-K or more, and in some embodiments, about <NUM> W/m-K or more. Examples of such materials may include, for instance, boron nitride (BN), aluminum nitride (AIN), magnesium silicon nitride (MgSiN<NUM>), graphite (e.g., expanded graphite), silicon carbide (SiC), carbon nanotubes, carbon black, metal oxides (e.g., zinc oxide, magnesium oxide, beryllium oxide, zirconium oxide, yttrium oxide, etc.), metallic powders (e.g., aluminum, copper, bronze, brass, etc.), etc., as well as combinations thereof. Graphite is particularly suitable for use in the polymer composition of the present invention. In fact, in certain embodiments, graphite may constitute a majority of the thermally conductive particulate material employed in the polymer composition, such as about <NUM> wt. % or more, in some embodiments, about <NUM> wt. % or more, and in some embodiments, from about <NUM> wt. % to <NUM> wt. % of the thermally conductive particulate material.

The thermally conductive particulate material is employed in the polymer composition in an amount of from about <NUM> to about <NUM> parts, preferably in some embodiments from about <NUM> to about <NUM> parts, and further preferably in some embodiments, from about <NUM> to about <NUM> parts by weight per <NUM> parts of the liquid crystalline polymer. For example, the thermally conductive particulate material may constitute from about <NUM> wt. % to about <NUM> wt. %, in some embodiments from about <NUM> wt. % to about <NUM> wt. %, and in some embodiments, from about <NUM> wt. % to about <NUM> wt. % of the polymer composition. Liquid crystalline polymers may likewise constitute from about <NUM> wt. % to about <NUM> wt. %, in some embodiments from about <NUM> wt. % to about <NUM> wt. %, and in some embodiments, from about <NUM> wt. % to about <NUM> wt. % of the polymer composition.

A wide variety of other components can also be included in the polymer composition, such as flow modifiers, lubricants, pigments, antioxidants, stabilizers, surfactants, waxes, flame retardants, anti-drip additives, nucleating agents (e.g., boron nitride), inorganic particle fillers (e.g., talc, mica, etc.), inorganic fibrous fillers (e.g., glass fibers), and other materials added to enhance properties and processability, and other materials added to enhance properties and processability. Lubricants, for example, may be employed in the polymer composition that are capable of withstanding the processing conditions of the liquid crystalline polymer without substantial decomposition. Examples of such lubricants include fatty acids esters, the salts thereof, esters, fatty acid amides, organic phosphate esters, and hydrocarbon waxes of the type commonly used as lubricants in the processing of engineering plastic materials, including mixtures thereof. Suitable fatty acids typically have a backbone carbon chain of from about <NUM> to about <NUM> carbon atoms, such as myristic acid, palmitic acid, stearic acid, arachic acid, montanic acid, octadecinic acid, parinric acid, and so forth. Suitable esters include fatty acid esters, fatty alcohol esters, wax esters, glycerol esters, glycol esters and complex esters. Fatty acid amides include fatty primary amides, fatty secondary amides, methylene and ethylene bisamides and alkanolamides such as, for example, palmitic acid amide, stearic acid amide, oleic acid amide, N,N'-ethylenebisstearamide and so forth. Also suitable are the metal salts of fatty acids such as calcium stearate, zinc stearate, magnesium stearate, and so forth; hydrocarbon waxes, including paraffin waxes, polyolefin and oxidized polyolefin waxes, and microcrystalline waxes. Particularly suitable lubricants are acids, salts, or amides of stearic acid, such as pentaerythritol tetrastearate, calcium stearate, or N,N'-ethylenebisstearamide. When employed, the lubricant(s) typically constitute from about <NUM> wt. % to about <NUM> wt. %, and in some embodiments, from about <NUM> wt. % to about <NUM> wt. % (by weight) of the polymer composition.

The components of the polymer composition (e.g., liquid crystalline polymer(s), thermally conductive particulate material(s), etc.) may be melt processed or blended together. The components may be supplied separately or in combination to an extruder that includes at least one screw rotatably mounted and received within a barrel (e.g., cylindrical barrel) and may define a feed section and a melting section located downstream from the feed section along the length of the screw. The extruder may be a single screw or twin screw extruder. The speed of the screw may be selected to achieve the desired residence time, shear rate, melt processing temperature, etc. For example, the screw speed may range from about <NUM> to about <NUM> revolutions per minute ("rpm"), in some embodiments from about <NUM> to about <NUM> rpm, and in some embodiments, from about <NUM> to about <NUM> rpm. The apparent shear rate during melt blending may also range from about <NUM> seconds-<NUM> to about <NUM>,<NUM> seconds-<NUM>, in some embodiments from about <NUM> seconds-<NUM> to about <NUM> seconds-<NUM>, and in some embodiments, from about <NUM> seconds-<NUM> to about <NUM> seconds-<NUM>. The apparent shear rate is equal to 4Q/πR<NUM>, where Q is the volumetric flow rate ("m<NUM>/s") of the polymer melt and R is the radius ("m") of the capillary (e.g., extruder die) through which the melted polymer flows.

Regardless of the particular manner in which it is formed, the resulting polymer composition can possess excellent thermal properties. For example, the melt viscosity of the polymer composition may be low enough so that it can readily flow into the cavity of a mold having small dimensions. In one particular embodiment, the polymer composition may have a melt viscosity of about <NUM> Pa-s or less, in some embodiments from about <NUM> to about <NUM> Pa-s, in some embodiments from about <NUM> to about <NUM> Pa-s, in some embodiments from about <NUM> to about <NUM> Pa-s, and in some embodiments, from about <NUM> to about <NUM> Pa-s, determined at a shear rate of <NUM> seconds-<NUM>. Melt viscosity may be determined in accordance with ISO Test No. <NUM>:<NUM> at a temperature that is <NUM> higher than the melting temperature of the composition (e.g., about <NUM>).

Of course in addition to those noted above, the polymer composition may also exhibit other good strength properties. For example, the composition may exhibit a Charpy unnotched impact strength of about <NUM> kJ/m<NUM>, in some embodiments from about <NUM> to about <NUM> kJ/m<NUM>, and in some embodiments, from about <NUM> to about <NUM> kJ/m<NUM>, measured at <NUM> according to ISO Test No. <NUM>-<NUM>:<NUM> (technically equivalent to ASTM D256-10e1). The composition may also exhibit a tensile strength of from about <NUM> to about <NUM> MPa, in some embodiments from about <NUM> to about <NUM> MPa, and in some embodiments, from about <NUM> to about <NUM> MPa; tensile break strain of about <NUM>% or more, in some embodiments from about <NUM>% to about <NUM>%, and in some embodiments, from about <NUM>% to about <NUM>%; and/or tensile modulus of from about <NUM>,<NUM> MPa to about <NUM>,<NUM> MPa, in some embodiments from about <NUM>,<NUM> MPa to about <NUM>,<NUM> MPa, and in some embodiments, from about <NUM>,<NUM> MPa to about <NUM>,<NUM> MPa. The tensile properties may be determined in accordance with ISO Test No. <NUM>:<NUM> (technically equivalent to ASTM D638-<NUM>) at <NUM>. The composition may also exhibit a flexural strength of from about <NUM> to about <NUM> MPa, in some embodiments from about <NUM> to about <NUM> MPa, and in some embodiments, from about <NUM> to about <NUM> MPa and/or a flexural break strain of about <NUM>% or more, in some embodiments from about <NUM>% to about <NUM>%, and in some embodiments, from about <NUM>% to about <NUM>%. The flexural properties may be determined in accordance with ISO Test No. <NUM>:<NUM> (technically equivalent to ASTM D790-<NUM>) at <NUM>. The composition may also exhibit a deflection temperature under load (DTUL) of about <NUM> or more, and in some embodiments, from about <NUM> to about <NUM>, as measured according to ASTM D648-<NUM> (technically equivalent to ISO Test No. <NUM>-<NUM>:<NUM>) at a specified load of <NUM> MPa.

As indicated above, the polymer composition of the present invention is employed in at least a portion of an ultrasonic transducer probe. The probe may be used to generate two-dimensional and/or three-dimensional imaging, may be a linear, convex (curved), phased (sector), single, or TV-type probe. Generally speaking, the ultrasonic probe contains at least one ultrasonic transducer that includes an array of transducer elements capable of converting electrical energy to ultrasonic acoustic energy for emission towards a region of interest. The probe also contains an attenuation material that is capable of inhibiting the return of the ultrasonic acoustic energy back towards the ultrasonic transducer after emission towards the region of interest.

The particular configuration of the probe may vary as is known to those skilled in the art. Referring to <FIG>, for example, one embodiment of an ultrasonic probe <NUM> is shown that includes at least one ultrasonic transducer <NUM>. The ultrasonic transducer <NUM> may be a mechanically active layer operable to convert electrical energy to mechanical (e.g., acoustic) energy and/or convert mechanical energy into electrical energy. For example, the ultrasonic transducer <NUM> may be operable to convert electrical signals from the ultrasound imaging apparatus <NUM> into ultrasonic acoustic energy. Furthermore, the ultrasonic transducer <NUM> may be operable to convert received ultrasonic acoustic energy into electrical signals. The ultrasonic transducer <NUM> may contain at least one ground electrode <NUM> and at least one signal electrode <NUM>. The signal electrode <NUM> and the ground electrode <NUM> may be electrically interconnected to the ultrasound imaging apparatus <NUM> by at least one signal connection <NUM> (e.g., at least one signal wire) and at least one ground connection <NUM> (e.g., at least one ground wire), respectively. The ultrasonic transducer <NUM> may also contain an array of individual transducer elements (not shown) that may each be electrically connected to the ultrasound imaging apparatus <NUM> via a signal connection and a ground connection. The array may be a one-dimensional array that includes a single row of individual transducer elements, or a multi-dimensional array (e.g., two-dimensional) that includes individual transducer elements arranged, for example, in multiple columns and multiple rows. Ground connections of the entire array may be aggregated and be electrically connected to the ultrasound imaging apparatus <NUM> through a single ground connection.

To generate an ultrasound image, the ultrasound imaging apparatus <NUM> may send electrical signals to the ultrasonic transducer <NUM>, which in turn may convert the electrical energy to ultrasonic acoustic energy <NUM> for emission towards a region of interest <NUM>. The region of interest <NUM> may be an internal structure of a patient, such as an organ. The structure within the region of interest <NUM> may reflect a portion of the acoustic energy <NUM> back toward the ultrasonic transducer <NUM>. The reflected acoustic energy <NUM> may be converted to electrical signals by the ultrasonic transducer <NUM>, which may be sent to the ultrasound imaging apparatus <NUM> where the signals may be processed and an image of the region of interest <NUM> may be generated. The process of converting the electrical signals from the ultrasound imaging apparatus <NUM> into ultrasonic acoustic energy <NUM> may also produce additional acoustic energy <NUM> directed in directions other than toward the region of interest <NUM>. This additional acoustic energy <NUM> may reflect off of various structures, such as the housing <NUM> of the ultrasound probe <NUM>, and return to the ultrasonic transducer <NUM> where it may be converted to electrical signals. The electrical signals from the reflected additional acoustic energy <NUM> may interfere with the electrical signals from the reflected acoustic energy <NUM>. Such interference may result in image quality degradation.

Thus, to reduce interference from the reflected additional acoustic energy <NUM>, an acoustic attenuation material <NUM> may be included in the ultrasound probe <NUM>. The acoustic attenuation material <NUM> may be interconnected to the ultrasonic transducer <NUM> along a surface of the ultrasonic transducer <NUM> opposite from the surface of the ultrasonic transducer <NUM> facing the region of interest <NUM> (e.g., a back surface of the ultrasonic transducer <NUM>). The acoustic attenuation material <NUM> may prevent a substantial amount of the additional acoustic energy <NUM> from returning to the back surface of the ultrasonic transducer <NUM>. The acoustic attenuation material <NUM> may also reduce the amount of acoustic energy reaching the back surface of the ultrasonic transducer <NUM> from other sources. In this regard, the acoustic attenuation material <NUM> may provide for reduced interference and enhanced image quality. In embodiments where the acoustic attenuation material <NUM> is connected directly to the ultrasonic transducer <NUM>, the signal connection <NUM> may pass through the acoustic attenuation material <NUM>.

The acoustic attenuation material <NUM> may also be positioned in other locations within the ultrasound probe <NUM> to attenuate acoustic energy within the ultrasound probe <NUM>. For example, an amount of acoustic attenuation material <NUM> may be placed against the housing <NUM> or even form all or a part of the housing <NUM> to dampen (e.g., absorb) acoustic energy that may otherwise reflect off of an inner surface of the housing <NUM> and reduce image quality. Although illustrated as lining one entire side of the inside of the housing <NUM> in <FIG>, it should also be understood that the acoustic attenuation material <NUM> may be placed along any surface or portion thereof of the housing <NUM> where it may be beneficial to attenuate acoustic energy. The acoustic attenuation material <NUM> may also be located adjacent to other structures within the ultrasound probe <NUM> (e.g., circuit boards) to attenuate acoustic energy that could otherwise reflect off of those other structures.

<FIG> illustrates a perspective view of one particular embodiment of an ultrasound probe assembly <NUM>. The probe assembly <NUM> includes a housing <NUM> and a cable <NUM>. The cable <NUM> is interconnected to an ultrasound imaging apparatus (not shown). Generally, the probe assembly <NUM> includes a plurality of ultrasonic transducers contained within the housing <NUM> and operable to transmit ultrasonic energy through a probe assembly face <NUM> along one end of the probe assembly <NUM>. The ultrasonic energy, in the form of acoustic waves, may be directed through the outer surface of a patient and into the internal structure of the patient. The acoustic waves may interact with and reflect off of various internal features. These reflections may then be detected by the probe assembly <NUM> and displayed as images of the internal structure of the patient by the ultrasound imaging apparatus.

The probe assembly <NUM> may be operable to scan an imaging volume <NUM>. This may be accomplished by mounting a one-dimensional transducer array on a movable member. Generally, one-dimensional transducer arrays include a single row containing a plurality of transducer elements along a longitudinal axis <NUM>. Through electronic control, a beam of acoustic energy may be swept along the longitudinal axis <NUM>. Some of the acoustic energy is reflected back to the transducer array where it is converted by the transducer array from acoustic energy to electrical signals. These electrical signals may then be converted into a two-dimensional image of the area swept by the acoustic energy. The probe assembly <NUM> may contain a one-dimensional transducer array that may be mechanically swept (e.g., rotated) along an elevation axis <NUM>. Thus, through a combination of electronic sweeping along a longitudinal axis <NUM> and mechanical sweeping of the transducer array along an elevation axis <NUM>, a beam of acoustic energy may be swept through the imaging volume <NUM>. Energy reflected back to the transducer array may be converted into a three-dimensional image of the imaging volume <NUM>.

The transducer array in probe assembly <NUM> may also be a two-dimensional array that may be mechanically swept (e.g., rotated) along an elevation axis <NUM>. The dimension of the array perpendicular to the axis of rotation (e.g., the elevation axis <NUM>) may be utilized to further control the transmitted acoustic energy. For example, transducers along the elevation axis <NUM> may be used to shape the acoustic energy to reduce side lobes and improve focus along the elevation axis <NUM>.

Turning to <FIG>, a cross-sectional schematic view of a one-dimensional ultrasonic transducer system <NUM> is presented. The ultrasonic transducer system <NUM> has a longitudinal axis <NUM> and an elevation axis <NUM>, which, for example, are similar to the longitudinal axis <NUM> and elevation axis <NUM>, respectively, of the probe assembly of <FIG>. The ultrasonic transducer system <NUM> may be operable to transmit and/or receive ultrasonic signals.

Generally, as known to those skilled in the art, a transducer <NUM> (comprising an active layer such as piezoelectric layer <NUM> and any optional matching layer attached thereto described below) may be divided into a predetermined number of discrete sections (for example, sections 1309a through 1309n, where n represents the predetermined number of discreet sections) along the longitudinal axis <NUM>. Each of these discrete sections may be a transducer element (e.g., discrete section <NUM> a may be a transducer element). The discrete sections may be electrically interconnected so that two or more of the discrete sections operate as a single transducer element (e.g., discrete sections <NUM> a and <NUM> b may be electrically interconnected and function as a single transducer element). A backing <NUM> may also be present.

<FIG> shows the ultrasonic transducer system <NUM> as being straight along the longitudinal axis <NUM>. The ultrasonic transducer system <NUM> may be curved along the longitudinal axis <NUM>. This curvature may, for example, be achieved by placing individual planar transducer elements at angles to each other along the longitudinal axis <NUM>. <FIG> also shows the individual transducer elements of the ultrasonic transducer system <NUM> as planar along the elevation axis <NUM>. In an alternative configuration, the individual transducer elements of the ultrasonic transducer system <NUM> may be curved along the elevation axis <NUM>.

The transducer <NUM> may include a piezoelectric layer <NUM>. The piezoelectric layer <NUM> may include a layer of piezoelectric material <NUM>, a first electrode layer <NUM> and a second electrode layer <NUM>. The layer of piezoelectric material <NUM> may include a ceramic-based material (e.g., lead zirconate titanate (PZT)). The first electrode layer <NUM> and second electrode layer <NUM> may include one or more layers of electrically conductive material. The portion of the first electrode layer <NUM> connected to each individual transducer element may serve as the signal electrode for that individual transducer element. Similarly, the portion of the second electrode layer <NUM> connected to each individual transducer element may serve as the ground electrode for that individual transducer element.

Generally, the signal electrodes and ground electrodes are arranged as illustrated in <FIG> with the ground electrode on the side of the piezoelectric material <NUM> that faces the region to be imaged. The position of the signal and ground electrodes may be reversed. In such embodiments, it may be necessary to provide an additional grounding layer to shield the signal layer. The ground electrodes may be individual electrodes as illustrated in <FIG> or may be one continuous layer of grounding material situated over each of the individual transducer elements. The individual transducer element electrodes may be interconnected to electronic circuitry, which may provide for acoustic wave generation and sensing.

Optional acoustic matching layers may be interconnected to the piezoelectric layer <NUM>. The ultrasonic transducer system <NUM> of <FIG> shows a first optional matching layer <NUM> and a second optional matching layer <NUM> interconnected to the piezoelectric layer <NUM>. The presence and number of optional matching layers may vary from the configuration illustrated in <FIG>. The transducer <NUM> comprises the piezoelectric layer <NUM>, along with any optional matching layers attached thereto.

The piezoelectric layer <NUM> may be a mechanically active layer operable to convert electrical energy to mechanical energy and mechanical energy into electrical energy. As previously described, the piezoelectric layer <NUM> may include a layer of PZT material sandwiched between ground and signal electrodes. A variety of components and materials able to generate acoustic signals may be substituted for at least a portion of the piezoelectric layer <NUM>. Such components and materials include ceramic materials, ferroelectric materials, composite materials, capacitor micromachined ultrasound transducers (CMUTs), piezoelectric micromachined ultrasound transducers (PMUTs), and any combination thereof. Regardless of the specific components, electromechanical principle of operation or materials, the mechanically active layer may comprise a means of converting electrical energy to mechanical energy and mechanical energy into electrical energy, which has an acoustic face <NUM> and a plurality of transducer elements that may be controlled individually. Generally, any system known to those skilled in the art for generating ultrasonic acoustic signals that may be used for imaging purposes may be utilized in the mechanically active layer.

Each individual discrete section may be separated from neighboring discrete sections by kerfs (e.g., kerf <NUM> between discrete sections <NUM> c and <NUM> d) produced during the dicing of the transducer <NUM>. The kerfs may be filled with a filler material. Additionally, one or more acoustic lenses may be interconnected to the acoustic face <NUM>.

As the piezoelectric layer <NUM> emits acoustic energy, some acoustic energy will pass into the backing <NUM>. Since such acoustic energy is not directed to the imaging volume <NUM>, it is desirable that this acoustic energy be attenuated. Attenuating this acoustic energy helps to reduce the amount of acoustic energy being reflected back into the piezoelectric layer <NUM> through the back side of the piezoelectric layer <NUM>. Such reflected acoustic energy may interfere with the acoustic energy being reflected back to the piezoelectric <NUM> from the imaging volume <NUM>, which may result in image degradation.

In the illustrated embodiment, the backing <NUM> includes multiple layers (e.g., first layer <NUM> and second layer <NUM>). Of course, it should be understood that the backing <NUM> may also be formed of a single layer. Regardless, at least a portion of the backing <NUM> may contain the polymer composition of the present invention to serve as an acoustic attenuation material. In one embodiment, for instance, the second layer <NUM> and/or first layer <NUM> may be formed from the polymer composition. Of course, such layers may also contain other materials known to those skilled in the art of ultrasonic transducer design, such as, for example epoxy resins, silicone rubber, tungsten, aluminum oxide, mica, microspheres, or a combination thereof.

The components of the ultrasonic probe that are formed from the polymer composition (e.g., backing, housing, etc.) may be formed using a variety of different techniques. Suitable techniques may include, for instance, injection molding, low-pressure injection molding, extrusion compression molding, gas injection molding, foam injection molding, low-pressure gas injection molding, low-pressure foam injection molding, gas extrusion compression molding, foam extrusion compression molding, extrusion molding, foam extrusion molding, compression molding, foam compression molding, gas compression molding, etc. For example, an injection molding system may be employed that includes a mold within which the polymer composition may be injected. The time inside the injector may be controlled and optimized so that polymer matrix is not pre-solidified. When the cycle time is reached and the barrel is full for discharge, a piston may be used to inject the composition to the mold cavity. Compression molding systems may also be employed. As with injection molding, the shaping of the polymer composition into the desired article also occurs within a mold. The composition may be placed into the compression mold using any known technique, such as by being picked up by an automated robot arm. The temperature of the mold may be maintained at or above the solidification temperature of the polymer matrix for a desired time period to allow for solidification. The molded product may then be solidified by bringing it to a temperature below that of the melting temperature. The resulting product may be de-molded. The cycle time for each molding process may be adjusted to suit the polymer matrix, to achieve sufficient bonding, and to enhance overall process productivity.

The present invention may be better understood with reference to the following example.

Thermal Conductivity: In-plane and through-plane thermal conductivity values are determined in accordance with ASTM E1461-<NUM>.

Melt Viscosity: The melt viscosity (Pa-s) may be determined in accordance with ISO Test No. <NUM>:<NUM> at a shear rate of <NUM>-<NUM> and temperature <NUM> above the melting temperature (e.g., about <NUM>) using a Dynisco LCR7001 capillary rheometer. The rheometer orifice (die) had a diameter of <NUM>, length of <NUM>, LID ratio of <NUM>, and an entrance angle of <NUM>°. The diameter of the barrel was <NUM> + <NUM> and the length of the rod was <NUM>.

Melting Temperature: The melting temperature ("Tm") may be determined by differential scanning calorimetry ("DSC") as is known in the art. The melting temperature is the differential scanning calorimetry (DSC) peak melt temperature as determined by ISO Test No. <NUM>-<NUM>:<NUM>. Under the DSC procedure, samples were heated and cooled at <NUM> per minute as stated in ISO Standard <NUM> using DSC measurements conducted on a TA Q2000 Instrument.

Deflection Temperature Under Load ("DTUL"): The deflection under load temperature may be determined in accordance with ISO Test No. <NUM>-<NUM>:<NUM> (technically equivalent to ASTM D648-<NUM>). More particularly, a test strip sample having a length of <NUM>, thickness of <NUM>, and width of <NUM> may be subjected to an edgewise three-point bending test in which the specified load (maximum outer fibers stress) was <NUM> Megapascals. The specimen may be lowered into a silicone oil bath where the temperature is raised at <NUM> per minute until it deflects <NUM> (<NUM> for ISO Test No. <NUM>-<NUM>:<NUM>).

Tensile Modulus, Tensile Stress, and Tensile Elongation: Tensile properties may be tested according to ISO Test No. <NUM>:<NUM> (technically equivalent to ASTM D638-<NUM>). Modulus and strength measurements may be made on the same test strip sample having a length of <NUM>, thickness of <NUM>, and width of <NUM>. The testing temperature may be <NUM>, and the testing speeds may be <NUM> or <NUM>/min.

Flexural Modulus, Flexural Stress, and Flexural Elongation: Flexural properties may be tested according to ISO Test No. <NUM>:<NUM> (technically equivalent to ASTM D790-<NUM>). This test may be performed on a <NUM> support span. Tests may be run on the center portions of uncut ISO <NUM> multi-purpose bars. The testing temperature may be <NUM> and the testing speed may be <NUM>/min.

Unnotched Charpy Impact Strength: Charpy properties may be tested according to ISO Test No. ISO <NUM>-<NUM>:<NUM>) (technically equivalent to ASTM D256-<NUM>, Method B). This test may be run using a Type <NUM> specimen size (length of <NUM>, width of <NUM>, and thickness of <NUM>). The testing temperature may be <NUM>.

A polymer composition for use in an ultrasonic probe may be formed from <NUM> wt. % graphite flakes and <NUM> wt. % of a liquid crystalline polymer as described herein. The composition may exhibit the thermal and mechanical properties set forth in the table below.

Claim 1:
An ultrasonic probe (<NUM>, <NUM>) comprising:
an ultrasonic transducer (<NUM>, <NUM>) that includes an array of transducer elements capable of converting electrical energy to ultrasonic acoustic energy for emission towards a region of interest; and
an attenuation material (<NUM>, <NUM>) that is capable of inhibiting the return of the ultrasonic acoustic energy back towards the ultrasonic transducer (<NUM>, <NUM>) after emission towards the region of interest, wherein the attenuation material (<NUM>, <NUM>) comprises a polymer composition that includes a liquid crystalline polymer and a thermally conductive particulate material,
characterized in that the thermally conductive particulate material is present in the polymer composition in an amount of from about <NUM> to about <NUM> parts per <NUM> parts of the liquid crystalline polymer, the liquid crystalline polymer has a melting temperature of about <NUM> or more and a melt viscosity of about <NUM> Pa-s or less as determined at a temperature of <NUM> above the melting temperature and shear rate of <NUM>-<NUM> in accordance with ISO Test No. <NUM>:<NUM>, and the polymer composition has a through-plane conductivity of about <NUM> W/m-K or more.