Ultrasonic transducer, backing structure and related methods

Abstract

An ultrasonic transducer is provided having a sample contacting portion and a rear portion opposite the sample contacting portion. The transducer includes a piezoelectric material configured to be in acoustic communication with the sample and a backing structure in acoustic communication with the piezoelectric material. The backing structure is configured to reflect acoustic energy toward the sample contacting portion and away from the rear portion of the ultrasonic transducer. The backing structure includes a low acoustic impedance layer and a high acoustic impedance layer. The transducer may also include a second double-layer mismatched backing. The second double-layer mismatched backing includes a second low acoustic impedance layer and a second high acoustic impedance layer. Also provided is an ultrasonic transducer including a one-dimensional piezoelectric array or a two-dimensional piezoelectric matrix and a backing structure configured to reflect acoustic energy.

Description

[Technical Field]

[0001] The technical field relates generally to the field of acoustic energy, and more particularly to ultrasound transducers, related devices, apparatus, methods and techniques. [Background technology]

[0002] Piezoelectric acoustic transducers are widely used in many industries and for a wide variety of applications. For example, piezoelectric ultrasonic transducers can be used in medical applications, such as diagnostic imaging and / or therapeutic applications. Other applications include, but are not limited to, ultrasonic non-destructive testing, ultrasonic machining, and ultrasonic welding. Piezoelectric ultrasonic transducers convert electrical energy into mechanical energy and convert sound waves into electrical signals and vice versa. Summary of the Invention [Problem to be solved by the invention]

[0003] There remains a need for techniques, apparatus, devices and methods that alleviate or mitigate the problems of the prior art. [Means for solving the problem]

[0004] According to one aspect, there is provided an ultrasonic transducer, the ultrasonic transducer comprising: a piezoelectric material having a front surface and a back surface, the piezoelectric material configured to be in acoustic communication with the sample; a thermally and electrically conductive backing structure disposed on the back surface of the piezoelectric material and configured to reflect acoustic energy toward the front surface of the piezoelectric material; The first two-layer mismatched backing material is a first graphite layer; and a layer of tungsten in contact with the first graphite layer; the first two-layered mismatched backing material having a second dual-layer mismatched backing material in contact with the first dual-layer mismatched backing material; a second graphite layer; and a copper layer in contact with the second graphite layer; the second two-layered mismatched backing material having the backing structure comprising: a heat sink in thermal contact with the backing structure; and one or more electrodes in electrical communication with the piezoelectric material; Equipped with.

[0005] In some embodiments, the heat sink comprises at least one channel configured to receive and circulate a heat transfer fluid therein.

[0006] In some embodiments, the heat transfer fluid is a liquid.

[0007] In some embodiments, the heat sink is electrically isolated from the backing structure.

[0008] In some embodiments, the ultrasonic transducer is operable at an operating frequency related to an operating wavelength (λ), and the first graphite layer, the layer of tungsten in contact with the first graphite layer, the second graphite layer, and the copper layer each have a thickness corresponding to approximately λ / 4 or an odd integer multiple of λ / 4.

[0009] In some embodiments, the piezoelectric material is configured to resonate at a half-wavelength at the operating frequency.

[0010] In some embodiments, the ultrasonic transducer comprises a single mismatching layer disposed between the piezoelectric material and the backing structure, the single mismatching layer being in acoustic communication with the piezoelectric material and the backing structure, the single mismatching layer having a corresponding acoustic impedance relatively higher than the acoustic impedance of the piezoelectric material, and the piezoelectric material being configured to resonate at a quarter wavelength at an operating frequency.

[0011] In some embodiments, the piezoelectric material has a resonant frequency, the resonant frequency is related to a resonant wavelength λr, and the single mismatch layer has a thickness less than 2λr / 5 relative to the resonant frequency of the piezoelectric material.

[0012] In some embodiments, the single mismatched layer has a thickness of about λr / 10 to about λr / 20.

[0013] In some embodiments, the single mismatch layer is made of tungsten.

[0014] In some embodiments, the piezoelectric material has acoustic properties with an acoustic impedance of about 27.5 Megarayleigh.

[0015] In some embodiments, the first graphite layer has an acoustic impedance of about 5.1 Megarayleigh.

[0016] In some embodiments, the first graphite layer has a thickness of about 1.5 mm to about 1.6 mm.

[0017] In some embodiments, the tungsten layer has an acoustic impedance of about 100 Megarayleigh.

[0018] In some embodiments, the tungsten layer has a thickness of about 2.6 mm to about 2.7 mm.

[0019] In some embodiments, the second graphite layer has an acoustic impedance of about 5.1 Megarayleigh.

[0020] In some embodiments, the second graphite layer has a thickness of about 1.5 mm to about 1.6 mm.

[0021] In some embodiments, the copper layer has an acoustic impedance of about 41.5 Megarayleigh.

[0022] In some embodiments, the copper layer has a thickness of about 2.5 mm to about 2.6 mm.

[0023] In some embodiments, the piezoelectric material is a polarized composite piezoelectric disk.

[0024] In some embodiments, the polarized composite piezoelectric disc is in a 1_3 configuration.

[0025] In some embodiments, the piezoelectric material is a composite of PZT4, with 1000 μm×1000 μm posts separated by 200 μm kerfs, the kerfs cut at a pitch of approximately 1200 μm.

[0026] In some embodiments, the piezoelectric material has a thickness of about 2.35 mm to about 2.45 mm.

[0027] In some embodiments, the kerfs are filled with a composite filler, the composite filler including particles of hafnium dioxide doped in an epoxy.

[0028] In some embodiments, the composite filler is in the 0_3 configuration.

[0029] In some embodiments, the epoxy is Epo-Tek® 301.

[0030] In some embodiments, the piezoelectric material comprises a piezoelectric layer.

[0031] In some embodiments, the ultrasonic transducer comprises a thermally conductive structure in contact with the backing structure.

[0032] In some embodiments, the thermally conductive structure is electrically insulated from the backing structure.

[0033] In some embodiments, the thermally conductive structure is a layer made of AlN or a layer made of beryllium oxide.

[0034] In some embodiments, the thermally conductive structure extends over a lateral portion of the backing structure.

[0035] In some embodiments, the thermally conductive structure has at least one electrically conductive via extending therethrough.

[0036] In some embodiments, the ultrasound transducer comprises a control unit electrically connected to at least one of the piezoelectric material, the backing structure, and the one or more electrodes.

[0037] In some embodiments, one or more electrodes are electrically connected to the piezoelectric material through a backing structure.

[0038] In some embodiments, the ultrasonic transducer includes a wear layer that is wear resistant.

[0039] In some embodiments, the wear layer is made of titanium.

[0040] In some embodiments, the ultrasound transducer has a diameter of about 50 mm.

[0041] In some embodiments, the backing structure is further configured to reflect acoustic energy in phase.

[0042] In some embodiments, the backing structure is further configured to spatially and temporally disperse undesirable acoustic reflections within the backing structure.

[0043] According to one aspect, there is provided an ultrasonic transducer, the ultrasonic transducer comprising: a piezoelectric material having a front surface and a back surface, the piezoelectric material being configured to be in acoustic communication with the sample; and a backing structure disposed on the back surface of the piezoelectric material and configured to reflect acoustic energy toward the front surface of the piezoelectric material, a first two-layer mismatched backing material including a first low acoustic impedance layer and a first high acoustic impedance layer; and a second two-layer mismatched backing material connected to the first two-layer matching backing material, the second two-layer mismatched backing material including a second low acoustic impedance layer and a second high acoustic impedance layer; the backing structure having Prepare.

[0044] In some embodiments, the ultrasonic transducer comprises at least one of a heat sink in thermal contact with the backing structure or a thermally conductive layer acoustically matched to the piezoelectric material.

[0045] In some embodiments, the ultrasound transducer comprises one or more electrodes in electrical communication with the piezoelectric material.

[0046] In some embodiments, the backing structure is both thermally and electrically conductive.

[0047] In some embodiments, the ultrasonic transducer includes a pre-assembled electrical circuit that is in electrical communication with the top of the backing structure and, therefore, with the piezoelectric material.

[0048] In some embodiments, the pre-assembled electrical circuit comprises at least one of a printed circuit board, an interposer, an integrated circuit, and an application specific integrated circuit.

[0049] In some embodiments, the heat sink has at least one channel configured to receive and circulate a heat transfer fluid therein.

[0050] In some embodiments, the heat transfer fluid is a liquid.

[0051] In some embodiments, the heat sink is electrically isolated from the backing structure.

[0052] In some embodiments, the ultrasonic transducer is operable at an operating frequency related to an operating wavelength (λo); and The first low acoustic impedance layer, the first high acoustic impedance layer, the second low acoustic impedance layer, and the second high acoustic impedance layer each have a thickness that corresponds to approximately λo / 4 or an odd multiple of λo / 4.

[0053] In some embodiments, the piezoelectric material is configured to resonate at a half-wavelength at the operating frequency.

[0054] In some embodiments, the ultrasonic transducer comprises a single mismatching layer disposed between the piezoelectric material and the backing structure, the single mismatching layer being in acoustic communication with the piezoelectric material and the backing structure, the single mismatching layer having a corresponding acoustic impedance relatively higher than the acoustic impedance of the piezoelectric material, and the piezoelectric material being configured to resonate at a quarter wavelength at the operating frequency.

[0055] In some embodiments, the piezoelectric material has a resonant frequency, the resonant frequency is related to a resonant wavelength λr, and the single mismatch layer has a thickness less than 2λr / 5 relative to the resonant frequency of the piezoelectric material.

[0056] In some embodiments, the single mismatched layer has a thickness of about λr / 10 to about λr / 20.

[0057] In some embodiments, the single mismatch layer is made of tungsten.

[0058] In some embodiments, the piezoelectric material has acoustic properties with an acoustic impedance of about 27.5 Megarayleigh.

[0059] In some embodiments, the piezoelectric material is a polarized composite piezoelectric disk.

[0060] In some embodiments, the polarized composite piezoelectric disc has a thickness of about 2.4 mm.

[0061] In some embodiments, the polarized composite piezoelectric disc is in a 1_3 configuration.

[0062] In some embodiments, the piezoelectric material is a composite of PZT4, with 1000 μm×1000 μm posts separated by 200 μm kerfs, the kerfs cut at a pitch of approximately 1200 μm.

[0063] In some embodiments, the kerfs are filled with a composite filler, the composite filler including particles of hafnium dioxide doped in an epoxy.

[0064] In some embodiments, the composite filler is in the 0_3 configuration.

[0065] In some embodiments, the epoxy is Epo-Tek® 301.

[0066] In some embodiments, the piezoelectric material comprises a piezoelectric layer.

[0067] In some embodiments, the ultrasonic transducer comprises a thermally conductive structure in contact with the backing structure.

[0068] In some embodiments, the thermally conductive structure is electrically insulated from the backing structure.

[0069] In some embodiments, the thermally conductive structure is a layer made of AlN or a layer made of beryllium oxide.

[0070] In some embodiments, the thermally conductive structure extends over a lateral portion of the backing structure.

[0071] In some embodiments, the thermally conductive structure has at least one electrically conductive via extending therethrough.

[0072] In some embodiments, the ultrasonic transducer comprises a control unit electrically connected to at least one of the piezoelectric material and the backing structure.

[0073] In some embodiments, one or more electrodes are electrically connected to the piezoelectric material through a backing structure.

[0074] In some embodiments, the ultrasonic transducer comprises a wear layer that is wear resistant.

[0075] In some embodiments, the wear layer is made of titanium.

[0076] In some embodiments, the ultrasound transducer has a diameter of about 50 mm.

[0077] In some embodiments, the backing structure is further configured to reflect acoustic energy in phase.

[0078] In some embodiments, the backing structure is further configured to spatially and temporally disperse undesirable acoustic reflections within the backing structure.

[0079] According to one aspect, there is provided an ultrasonic transducer having a sample contacting portion and a back portion opposite the sample contacting portion, the ultrasonic transducer comprising: a piezoelectric material configured to be in acoustic communication with the sample; and a backing structure in acoustic communication with the piezoelectric material and configured to reflect acoustic energy toward the sample contact and away from the back of the ultrasonic transducer; a low acoustic impedance layer, and High acoustic impedance layer, the backing structure having Equipped with.

[0080] In some embodiments, the low acoustic impedance layer and the high acoustic impedance layer form a first dual-layer mismatched backing material, and the ultrasonic transducer comprises a second dual-layer mismatched backing material, the second dual-layer mismatched backing material having a second low acoustic impedance layer and a second high acoustic impedance layer.

[0081] In some embodiments, the ultrasonic transducer comprises a heat sink in thermal contact with the backing structure.

[0082] In some embodiments, the ultrasound transducer comprises one or more electrodes in electrical communication with the piezoelectric material.

[0083] In some embodiments, the backing structure is both thermally and electrically conductive.

[0084] In some embodiments, the ultrasonic transducer includes a pre-assembled electrical circuit that is in electrical communication with the top of the backing structure and, therefore, with the piezoelectric material.

[0085] In some embodiments, the pre-assembled electrical circuit comprises at least one of a printed circuit board, an interposer, an integrated circuit, and an application specific integrated circuit.

[0086] In some embodiments, the heat sink has at least one channel configured to receive and circulate a heat transfer fluid therein.

[0087] In some embodiments, the heat transfer fluid is a liquid.

[0088] In some embodiments, the heat sink is electrically isolated from the backing structure.

[0089] In some embodiments, the ultrasonic transducer is operable at an operating frequency related to an operating wavelength (λ), and the low acoustic impedance layer, the high acoustic impedance layer, the second low acoustic impedance layer, and the second high acoustic impedance layer each have a thickness corresponding to approximately λ / 4 or an odd integer multiple of λ / 4.

[0090] In some embodiments, the piezoelectric material is configured to resonate at a half-wavelength at the operating frequency.

[0091] In some embodiments, the ultrasonic transducer comprises a single mismatching layer disposed between the piezoelectric material and the backing structure, the single mismatching layer being in acoustic communication with the piezoelectric material and the backing structure, the single mismatching layer having a corresponding acoustic impedance relatively higher than the acoustic impedance of the piezoelectric material, and the piezoelectric material being configured to resonate at a quarter wavelength at the operating frequency.

[0092] In some embodiments, the piezoelectric material has a resonant frequency, the resonant frequency is related to a resonant wavelength λr, and the single mismatch layer has a thickness less than 2λr / 5 relative to the resonant frequency of the piezoelectric material.

[0093] In some embodiments, the single mismatched layer has a thickness of about λr / 10 to about λr / 20.

[0094] In some embodiments, the single mismatch layer is made of tungsten.

[0095] In some embodiments, the piezoelectric material has acoustic properties with an acoustic impedance of about 27.5 Megarayleigh.

[0096] In some embodiments, the piezoelectric material is a polarized composite piezoelectric disk.

[0097] In some embodiments, the polarized composite piezoelectric disc has a thickness of about 2.4 mm.

[0098] In some embodiments, the polarized composite piezoelectric disc is in a 1_3 configuration.

[0099] In some embodiments, the piezoelectric material is a composite of PZT4, with 1000 μm×1000 μm posts separated by 200 μm kerfs, the kerfs being cut at a pitch of approximately 1200 μm.

[0100] In some embodiments, the kerfs are filled with a composite filler, the composite filler including particles of hafnium dioxide doped in an epoxy.

[0101] In some embodiments, the composite filler is in the 0_3 configuration.

[0102] In some embodiments, the epoxy is Epo-Tek® 301.

[0103] In some embodiments, the piezoelectric material comprises a piezoelectric layer.

[0104] In some embodiments, the ultrasonic transducer comprises a thermally conductive structure in contact with the backing structure.

[0105] In some embodiments, the thermally conductive structure is electrically insulated from the backing structure.

[0106] In some embodiments, the thermally conductive structure is a layer made of AlN or a layer made of beryllium oxide.

[0107] In some embodiments, the thermally conductive structure extends over a lateral portion of the backing structure.

[0108] In some embodiments, the thermally conductive structure has at least one electrically conductive via extending therethrough.

[0109] In some embodiments, the ultrasonic transducer comprises a control unit electrically connected to at least one of the piezoelectric material and the backing structure.

[0110] In some embodiments, one or more electrodes are electrically connected to the piezoelectric material through a backing structure.

[0111] In some embodiments, the ultrasonic transducer comprises a wear layer that is wear resistant.

[0112] In some embodiments, the wear layer is made of titanium.

[0113] In some embodiments, the ultrasound transducer has a diameter of about 50 mm.

[0114] In some embodiments, the backing structure is further configured to reflect acoustic energy in phase.

[0115] In some embodiments, the backing structure is further configured to spatially and temporally disperse undesirable acoustic reflections within the backing structure.

[0116] In some embodiments, the piezoelectric material is diced into a plurality of piezoelectric regions separated by gaps, the gaps being electrically and acoustically insulating; at least one of the low acoustic impedance layer and the high acoustic impedance layer is diced into a plurality of first elements separated by a first set of gaps, each gap in the first set aligned with a corresponding gap separating the piezoelectric regions, the gaps being electrically and acoustically insulating; and at least one of the second low acoustic impedance layer and the second high acoustic impedance layer is diced into a plurality of second elements separated by a second set of gaps, each gap in the second set aligned with a corresponding gap separating the piezoelectric regions, the gaps being electrically and acoustically insulating.

[0117] In some embodiments, the gaps, the gaps in the first set, and the gaps in the second set are thermally conductive.

[0118] According to one aspect, there is provided an ultrasonic transducer, the ultrasonic transducer comprising: a one-dimensional piezoelectric array having a front surface and a back surface, the one-dimensional piezoelectric array being configured to be in acoustic communication with the sample and having a plurality of piezoelectric regions arranged in a one-dimensional array; a backing structure disposed on a back surface of the one-dimensional piezoelectric array and configured to reflect acoustic energy toward a front surface of the one-dimensional piezoelectric array, the backing structure having a two-layer mismatched backing material comprised of a low acoustic impedance layer and a high acoustic impedance layer; a pre-assembled electrical circuit in electrical communication with the top of the backing structure and, therefore, in electrical communication with the one-dimensional piezoelectric array; Equipped with.

[0119] In some embodiments, the ultrasound transducer comprises a second dual-layer mismatched backing material, the second dual-layer mismatched backing material having a second low acoustic impedance layer and a second high acoustic impedance layer.

[0120] In some embodiments, the ultrasonic transducer comprises a heat sink in thermal contact with the backing structure.

[0121] In some embodiments, the ultrasound transducer comprises one or more electrodes in electrical communication with the one-dimensional piezoelectric array.

[0122] In some embodiments, the backing structure is both thermally and electrically conductive.

[0123] In some embodiments, the pre-assembled electrical circuit comprises at least one of a printed circuit board, an interposer, an integrated circuit, and an application specific integrated circuit.

[0124] In some embodiments, the piezoelectric regions are separated from one another by a gap, which is both electrically insulating and acoustically insulating.

[0125] In some embodiments, at least one of the low acoustic impedance layer and the high acoustic impedance layer is diced into a plurality of first elements separated from one another by a first set of gaps, each gap in the first set aligned with a corresponding one of the gaps separating the piezoelectric regions, and the gaps in the first set are electrically insulating and acoustically insulating.

[0126] At least one of the second low acoustic impedance layer and the second high acoustic impedance layer is diced into a plurality of second elements separated from one another by a second set of gaps, each gap in the second set aligned with a corresponding one of the gaps separating the piezoelectric regions, and the gaps in the second set are electrically insulating and acoustically insulating.

[0127] In some embodiments, the gaps, the gaps in the first set, and the gaps in the second set are thermally conductive.

[0128] In some embodiments, the top of the backing structure is made from an electrically insulating material.

[0129] In some embodiments, the electrically insulating material is thermally conductive.

[0130] In some embodiments, the top portion comprises a layer of AlN traversed by conductive vias, each conductive via aligned with a corresponding piezoelectric region in a one-dimensional array of piezoelectric regions.

[0131] In some embodiments, the layer of AIN has a front surface, and the layer of AIN is partially diced from the front surface side to enhance acoustic isolation between adjacent piezoelectric regions in a one-dimensional array of piezoelectric regions.

[0132] In some embodiments, the heat sink has at least one channel configured to receive and circulate a heat transfer fluid therein.

[0133] In some embodiments, the heat transfer fluid is a liquid.

[0134] In some embodiments, the heat sink is electrically isolated from the backing structure.

[0135] In some embodiments, the ultrasonic transducer is operable at an operating frequency related to an operating wavelength (λo); The low acoustic impedance layer, the high acoustic impedance layer, the second low acoustic impedance layer, and the second high acoustic impedance layer each have a thickness corresponding to approximately λo / 4 or an odd multiple of λo / 4.

[0136] In some embodiments, the one-dimensional piezoelectric array is configured to resonate half a wavelength at the operating frequency.

[0137] In some embodiments, the ultrasonic transducer comprises a single mismatching layer disposed between the one-dimensional piezoelectric array and a backing structure, the single mismatching layer being in acoustic communication with the one-dimensional piezoelectric array and the backing structure, the single mismatching layer having a corresponding acoustic impedance that is relatively higher than the acoustic impedance of the one-dimensional piezoelectric array, and the one-dimensional piezoelectric array being configured to resonate at a quarter wavelength at an operating frequency.

[0138] In some embodiments, the one-dimensional piezoelectric array has a resonant frequency, the resonant frequency is related to a resonant wavelength λr, and the single mismatch layer has a thickness less than 2λr / 5 relative to the resonant frequency of the one-dimensional piezoelectric array.

[0139] In some embodiments, the single mismatched layer has a thickness of about λr / 10 to about λr / 20.

[0140] In some embodiments, the single mismatch layer is made of tungsten.

[0141] In some embodiments, the piezoelectric regions have posts separated by kerfs.

[0142] In some embodiments, the kerfs are filled with a composite filler, the composite filler including particles of hafnium dioxide doped in an epoxy.

[0143] In some embodiments, the composite filler is in the 0_3 configuration.

[0144] In some embodiments, the epoxy is Epo-Tek® 301.

[0145] In some embodiments, the piezoelectric region is comprised of a piezoelectric layer.

[0146] In some embodiments, the ultrasonic transducer comprises a thermally conductive structure in contact with the backing structure.

[0147] In some embodiments, the thermally conductive structure is electrically insulated from the backing structure.

[0148] In some embodiments, the thermally conductive structure is a layer made of AlN or a layer made of beryllium oxide.

[0149] In some embodiments, the thermally conductive structure extends over a lateral portion of the backing structure.

[0150] In some embodiments, the ultrasound transducer comprises a control unit electrically connected to at least one of the one-dimensional piezoelectric array and the backing structure.

[0151] In some embodiments, one or more electrodes are electrically connected to the one-dimensional piezoelectric array through a backing structure.

[0152] In some embodiments, the ultrasonic transducer comprises a wear layer that is wear resistant.

[0153] In some embodiments, the wear layer is made of titanium.

[0154] In some embodiments, the ultrasound transducer has a diameter of about 50 mm.

[0155] In some embodiments, the backing structure is further configured to reflect acoustic energy in phase.

[0156] In some embodiments, the backing structure is further configured to spatially and temporally disperse undesirable acoustic reflections within the backing structure.

[0157] According to one aspect, there is provided an ultrasonic transducer, the ultrasonic transducer comprising: a two-dimensional piezoelectric matrix having a front surface and a back surface, the two-dimensional piezoelectric matrix being configured to be in acoustic communication with the sample; a backing structure disposed on a back surface of the one-dimensional piezoelectric matrix and configured to reflect acoustic energy toward a front surface of the two-dimensional piezoelectric matrix, the backing structure comprising a two-layer mismatched backing material comprising a low acoustic impedance layer and a high acoustic impedance layer; a pre-assembled electrical circuit in electrical communication with the top of the backing structure and, therefore, in electrical communication with the two-dimensional piezoelectric matrix; Equipped with.

[0158] In some embodiments, the ultrasound transducer comprises a second dual-layer mismatched backing material, the second dual-layer mismatched backing material having a second low acoustic impedance layer and a second high acoustic impedance layer.

[0159] In some embodiments, the ultrasonic transducer comprises a heat sink in thermal contact with the backing structure.

[0160] In some embodiments, the ultrasound transducer comprises one or more electrodes in electrical communication with the two-dimensional piezoelectric matrix.

[0161] In some embodiments, the backing structure is both thermally and electrically conductive.

[0162] In some embodiments, the pre-assembled electrical circuit comprises at least one of a printed circuit board, an interposer, an integrated circuit, and an application specific integrated circuit.

[0163] In some embodiments, the two-dimensional piezoelectric matrix has a plurality of piezoelectric regions, each piezoelectric region separated from the others by a gap, which is electrically and acoustically insulating.

[0164] In some embodiments, at least one of the low acoustic impedance layer and the high acoustic impedance layer is diced into a plurality of first elements separated from one another by a first set of gaps, each gap in the first set aligned with a corresponding one of the gaps separating the piezoelectric regions, and the gaps in the first set are electrically and acoustically insulating.

[0165] In some embodiments, at least one of the second low acoustic impedance layer and the second high acoustic impedance layer is diced into a plurality of second elements separated from one another by a second set of gaps, each of the gaps in the second set aligned with a corresponding one of the gaps separating the piezoelectric regions, and the gaps in the second set are electrically and acoustically insulating.

[0166] In some embodiments, the gaps, the gaps in the first set, and the gaps in the second set are thermally conductive.

[0167] In some embodiments, the top of the backing structure is made from an electrically insulating material.

[0168] In some embodiments, the electrically insulating material is thermally conductive.

[0169] In some embodiments, the top portion has a layer of AlN traversed by conductive vias, each conductive via aligned with a corresponding one of the plurality of piezoelectric regions.

[0170] In some embodiments, the layer of AIN has a front surface, and the layer of AIN is partially diced from the front surface side to enhance acoustic isolation between adjacent piezoelectric regions in a one-dimensional array of piezoelectric regions.

[0171] In some embodiments, the heat sink has at least one channel configured to receive and circulate a heat transfer fluid therein.

[0172] In some embodiments, the heat transfer fluid is a liquid.

[0173] In some embodiments, the heat sink is electrically isolated from the backing structure.

[0174] In some embodiments, the ultrasonic transducer is operable at an operating frequency related to an operating wavelength (λo); and The low acoustic impedance layer, the high acoustic impedance layer, the second low acoustic impedance layer, and the second high acoustic impedance layer each have a thickness corresponding to approximately λo / 4 or an odd multiple of λo / 4.

[0175] In some embodiments, the two-dimensional piezoelectric matrix is ​​configured to resonate at a half-wavelength at the operating frequency.

[0176] In some embodiments, the ultrasonic transducer comprises a single mismatching layer disposed between a two-dimensional piezoelectric matrix and a backing structure, the single mismatching layer being in acoustic communication with the two-dimensional piezoelectric matrix and the backing structure, the single mismatching layer having a corresponding acoustic impedance relatively higher than the acoustic impedance of the two-dimensional piezoelectric matrix, and the two-dimensional piezoelectric matrix being configured to resonate at a quarter-wavelength at an operating frequency.

[0177] In some embodiments, the two-dimensional piezoelectric matrix has a resonant frequency, the resonant frequency is related to a resonant wavelength λr, and the single mismatch layer has a thickness less than 2λr / 5 relative to the resonant frequency of the two-dimensional piezoelectric matrix.

[0178] In some embodiments, the single mismatched layer has a thickness of about λr / 10 to about λr / 20.

[0179] In some embodiments, the single mismatch layer is made of tungsten.

[0180] In some embodiments, the two-dimensional piezoelectric matrix has posts separated by kerfs.

[0181] In some embodiments, the kerfs are filled with a composite filler, the composite filler including particles of hafnium dioxide doped in an epoxy.

[0182] In some embodiments, the composite filler is in the 0_3 configuration.

[0183] In some embodiments, the epoxy is Epo-Tek® 301.

[0184] In some embodiments, the two-dimensional piezoelectric matrix is ​​composed of piezoelectric layers.

[0185] In some embodiments, the ultrasonic transducer comprises a thermally conductive structure in contact with the backing structure.

[0186] In some embodiments, the thermally conductive structure is electrically insulated from the backing structure.

[0187] In some embodiments, the thermally conductive structure is a layer made of AlN or a layer made of beryllium oxide.

[0188] In some embodiments, the thermally conductive structure extends over a lateral portion of the backing structure.

[0189] In some embodiments, the ultrasonic transducer comprises a control unit electrically connected to at least one of the two-dimensional piezoelectric matrix and the backing structure.

[0190] In some embodiments, one or more electrodes are electrically connected to the two-dimensional piezoelectric matrix via a backing structure.

[0191] In some embodiments, the ultrasonic transducer comprises a wear layer that is wear resistant.

[0192] In some embodiments, the wear layer is made of titanium.

[0193] In some embodiments, the ultrasound transducer has a diameter of about 50 mm.

[0194] In some embodiments, the backing structure is further configured to reflect acoustic energy in phase.

[0195] In some embodiments, the backing structure is further configured to spatially and temporally disperse undesirable acoustic reflections within the backing structure.

[0196] According to another aspect, a multi-layer ultrasound transducer backing structure is provided. In some embodiments, the backing structure reflects most, and in some cases virtually all, of the acoustic energy out the front face of the transducer, and such transducers are generally unaffected by physical contact at the back face of the backing stack.

[0197] According to another aspect, a single-element liquid-cooled specific-material transducer designed to match titanium is provided. The transducer includes a mismatched structure, such as a dual-layer mismatched backing (DLDB). The DLDB can be designed to operate at 680 kHz. The transducer includes a first DLDB pair having a piezoelectric composite element with an acoustic impedance of 27.5 Megarayleigh (MR) and bonded to a second DLDB pair. The first DLDB pair includes a first graphite layer having an acoustic impedance of approximately 5.1 MR and a thickness of 1.03 mm, and a second tungsten metal layer having an acoustic impedance of approximately 100 MR and a thickness of 1.53 mm. The second DLDB pair includes a first graphite layer having an acoustic impedance of approximately 5.1 MR and a thickness of approximately 0.905 mm, and a second copper metal layer having an acoustic impedance of approximately 41.5 MR and a thickness of 1.71 mm.

[0198] In some embodiments, the DLDB includes a first backing layer and a second backing layer, each having a distal surface and a proximal surface. The proximal surface can be in acoustic contact with the distal surface of the second backing layer. The DLDB can be placed in acoustic contact with a piezoelectric element having a distal surface and a proximal surface, with the distal surface of the first backing layer contacting the proximal surface of the piezoelectric element. The first and second backing layers of the DLDB can be designed to be approximately ¼λ thick relative to the design resonant frequency of the piezoelectric element. The first backing layer can be made of a material having a relatively low acoustic impedance compared to the piezoelectric element. The second backing layer can be made of a material having a relatively high acoustic impedance compared to the first backing layer.

[0199] In some embodiments, the transducer includes a 2.4 mm thick, polarized composite piezoelectric disc in a 1-3 configuration. The thickness corresponds to approximately 0.35-0.4λ, but the polarized composite piezoelectric disc operates in 1 / 2λ mode, with the positive pole on the proximal surface and the negative pole on the distal surface. To compensate for the mass loading effect of the DLDB backing, the thickness of the piezoelectric disc can be selected to be thinner than 1 / 2λ. The piezoelectric composite can be fabricated by dicing and filling polarized PZT4 material with 200 μm kerfs cut at a 1200 μm pitch, leaving 1000 μm x 1000 μm posts separated by 200 μm kerfs. For example, but not by way of limitation, the kerfs can be filled with a composite filler of approximately 5 μm hafnium dioxide particles doped in Epotek 301 epoxy, such that the acoustic impedance of the composite filler filling the kerfs is approximately 7-8 Megarayleigh (MR), closely matching the acoustic impedance of the entire piezoelectric composite layer to that of titanium (approximately 27.5 MR). The negative surface of the piezoelectric composite layer can be bonded to the proximal surface of a 6 mm thick ZA-8 zinc-aluminum alloy disk using, for example, tungsten powder-filled epoxy. The distal surface of the ZA-8 disk can then be bonded to the proximal surface of an alumina composite disk using Epotek 301 epoxy filled with submicron hafnium oxide particles. The alumina composite disk can include 750 μm x 750 μm x 1400 μm (high) pillars separated by 200 μm kerfs, which are filled with the same hafnium particle-filled epoxy used to fabricate the piezoelectric composite disk. The distal face of the alumina composite can then be bonded to the proximal face of a 3 mm thick titanium disk using a layer of submicron hafnium oxide filled Epotek 301 epoxy. Two sets of dual layer mismatched backing materials (DLDBs) can then be bonded to the proximal face of the piezoelectric disk using submicron tungsten powder filled Epotek 301 epoxy as follows:The proximal surface of the piezoelectric composite disk was bonded to the distal surface of a 1030 μm thick Poco DFP-1 graphite disk, which had an acoustic impedance of 5.1 MR and a thickness of 905 μm. This thickness corresponded to 1 / 4 λ at the transducer's center frequency of 680 kHz. The proximal surface of the graphite disk was then bonded to the distal surface of a 1530 μm thick tungsten disk, which had an acoustic impedance of 100 MR and a thickness of 1 / 4 λ at approximately 850 kHz, slightly above the transducer's center frequency. The proximal surface of the tungsten disk was then bonded to the proximal surface of a 905 μm thick Poco DFP-1 graphite disk, which had an acoustic impedance of 5.1 MR and a thickness of 1 / 4 λ at approximately 800 kHz, slightly above the transducer's center frequency. The proximal surface of the graphite disk is bonded to the distal surface of a 1710 μm thick copper disk with an acoustic impedance of 41.5 MR. The thickness corresponds to ¼λ at 680 kHz. The graphite disk and tungsten disk constitute a first dual-layer mismatched backing stack, and the graphite disk and copper disk constitute a second DLDB stack. These two stacks work together to acoustically isolate the piezoelectric composite disk from the thermal cooling element of the transducer, allowing a thermal cooling solution to be directly bonded to the proximal surface of the copper disk without substantially impairing the acoustic performance of the transducer. In these embodiments, the distal surface of a 1 mm thick, highly thermally conductive AIN disk is bonded to the proximal surface of the copper disk using thermally conductive epoxy. The AIN disk is notched to accommodate space for electrical connection to the copper disk using soldered wire or conductive epoxy bonded wire. Note that the entire DLDB stack in this embodiment is electrically and thermally conductive, allowing electrical connections to be made directly through the DLDB stack to the signal electrodes of the piezoelectric composite disk.Furthermore, beyond the materials explicitly listed in this exemplary embodiment, it should be noted that there are many materials that can actually be used in applications of the disclosed technology, some of which are electrically conductive, thermally conductive, both, or neither. In this exemplary embodiment, all of the DLDB layers are electrically and thermally conductive. The proximal surface of the copper heat sink base is brazed or soldered to the distal end of the heat sink top to form a hollow copper heat sink assembly, and the distal surface of the heat sink assembly is bonded directly to the proximal surface of the AIN disk using a thermally conductive but electrically insulating epoxy. In the illustrated embodiment, the proximal surface of the hollow heat sink top is bonded to the distal surface of the AIN disk using the same thermally conductive epoxy. The AIN disk has two clearance holes and one notch in the AIN disk to receive cooling tubes that are secured to integral barbed tubes in the heat sink top, and the notch allows a clearance path for signal wires attached to the copper DLDB layer. The proximal surface of the AIN disk can be bonded to the distal surface of the copper heat spreader using thermally conductive epoxy. A copper housing shell can be fitted around the ZA-8 disk and bonded to the completed acoustic and thermal stack using electrically and thermally conductive epoxy. In some embodiments, all voids are filled with thermally and electrically conductive epoxy. Thus, the entire assembly is solid except for the hollow interior of the heat sink assembly (i.e., the top and bottom of the heat sink). A rubber hose is fitted over the barbed hose prongs on top of the copper heat sink and secured in place with a hose clamp. The rubber hose may have, for example, but not by way of limitation, a 3 / 8-inch inner diameter. The transducer includes electrical contacts, which can be embodied by a BNC RF electrical connector soldered to the copper lid. Furthermore, the center conductor of the BNC connector can be soldered to a signal wire. Thus, the BNC signal conductor can be electrically connected to the positive signal electrode of the piezoelectric composite disk.In some embodiments, a copper lid can be soldered or bonded to the proximal lip of the copper shell using conductive epoxy to complete the electrical connection from the ground terminal of the BNC connector and the negative pole of the piezoelectric composite disk through the copper shell and the ZA-8 disk. The transducer also includes an electrically insulating plastic housing that is bonded to the copper lid and copper shell, at least partially covers the edge of the alumina composite disk, and rests on the front surface of the titanium disk. The completed transducer (i.e., the assembly of the aforementioned components) is then connected to a liquid-circulating air-to-liquid heat exchanger and filled with a suitable coolant. A non-limiting example of the coolant is a 50% propylene glycol / water mixture.

[0200] According to another aspect, a 1-D linear array is provided that has a single DLDB backing layer that is fully diced and electrically attached directly to a PCB, as described herein. This configuration allows for relatively easy electrical interconnection of the array and even allows for relatively direct application of ASICs or high-density connectors to the stack. The array includes a protective wear layer, which may alternatively be a lens or matching layer depending on the application. The piezoelectric elements form a 1-D linear array, with each piezoelectric element separated from the others by gaps (or kerfs). The array also includes a DLDB structure with a first low acoustic impedance 1 / 4λ layer, which is separated into elements with gaps between them and aligned with the arrayed piezoelectric elements. A second high acoustic impedance 1 / 4λ layer, which may be made of tungsten, is disposed on the low acoustic impedance layer. The high acoustic impedance layer is separated into elements with gaps between them and aligned with the arrayed piezoelectric elements. The array also includes electrodes on the surface of the PCB, the PCB, and vias in the printed circuit board, which connect the electrodes from one side to the other.

[0201] According to yet another aspect of the present invention, a 1-D linear array with dual DLDBs is provided, having a second pair of DLDBs overlying a first pair of DLDBs, the second pair of DLDBs including a low acoustic impedance 1 / 4λ layer overlaid by a laterally thermally continuous high acoustic impedance 1 / 4λ layer. The thermally conductive layer is AlN, but may also be beryllium oxide or another suitable thermally conductive and electrically insulating material, and includes conductive vias for connection to the transducer elements. This allows the array to be cooled from the edges and allows for direct electrical connection, for example, using a PCB.

[0202] According to another aspect, a 2-D matrix transducer is provided. In some embodiments, the 2-D matrix is ​​a dual DLDB 16x16 element matrix array with laterally thermally continuous layers. The matrix transducer includes a protective wear layer, which can alternatively be replaced by a lens or matching layer depending on the overall application of the 2D transducer array. The matrix transducer includes piezoelectric elements separated from each other by gaps (or kerfs) in two axial directions to form a 2-D linear or matrix array. The matrix transducer includes a first DLDB stack having a low acoustic impedance 1 / 4λ layer and a high acoustic impedance 1 / 4λ layer, where the low acoustic impedance 1 / 4λ layer is separated into elements with gaps between elements in the two axial directions and aligned with the arrayed piezoelectric elements, and the high acoustic impedance 1 / 4λ layer can be made of tungsten. The high acoustic impedance 1 / 4λ layer can be aligned with the arrayed piezoelectric elements and separated into elements with gaps between elements in the two axial directions. These layers define a first stack. The matrix transducer also includes a second stack. The second DLDB stack has a low acoustic impedance 1 / 4λ layer and a high acoustic impedance 1 / 4λ layer, with the low acoustic impedance 1 / 4λ layer separated into elements with gaps between them in two axial directions and aligned with the arrayed piezoelectric elements. The high acoustic impedance 1 / 4λ layer is generally continuous and made of AlN. In this context, "continuous" means that the stack has no gaps and provides lateral thermal conductivity along both axes of the array. Vertical conductivity is provided by vias in the AlN layer. This layer is particularly useful for maintaining isothermal conditions within the 2-D array relative to the edge elements.

[0203] Other features and advantages of the present specification will become more apparent on reading the following non-limiting description of particular embodiments thereof, given by way of example only and with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0204] [Figure 1a] 1 illustrates a liquid-cooled ultrasonic transducer according to one embodiment. [Figure 1b] 1b shows a backing structure in contact with the piezoelectric material of the ultrasound transducer of FIG. 1a. [Figure 1c] FIG. 1b is a cross-sectional view of FIG. [Figure 1d] FIG. 1b is a cross-sectional view of FIG. [Figure 2] FIG. 1 is an exploded view of a liquid-cooled ultrasonic transducer according to another embodiment. [Figure 3] 3 is another exploded view of the liquid-cooled ultrasonic transducer shown in FIG. 2. [Figure 4] 1 illustrates a backing structure in contact with the piezoelectric material of an ultrasonic transducer and a heat sink in thermal contact with the backing structure, according to one embodiment. [Figure 5] 1 illustrates a single mismatched layer sandwiched between a piezoelectric material and a two-layer mismatched backing material, according to one embodiment. [Figure 6] FIG. 6 is a cross-sectional view of FIG. 5. [Figure 7] 1 illustrates a 16-element one-dimensional linear array according to one embodiment. [Figure 8] FIG. 8 is a cross-sectional view of FIG. 7 illustrating the layers forming the 16-element one-dimensional linear array. [Figure 9] FIG. 8 is another cross-sectional view of FIG. 7 illustrating the layers forming the 16-element one-dimensional linear array. [Figure 10] 1 illustrates a 16-element one-dimensional linear array according to another embodiment. [Figure 11] FIG. 11 is a cross-sectional view of FIG. 10 illustrating the layers forming the 16-element one-dimensional linear array. [Figure 12] FIG. 11 is another cross-sectional view of FIG. 10 illustrating the layers forming the 16-element one-dimensional linear array. [Figure 13]This is a simplified diagram of the operating principle of an ultrasonic transducer. More specifically, considering a relatively narrowband case, the reflection coefficient and the specific arrangement of low and high acoustic impedance layers within the DLDB interact to ensure that only in-phase reflections reach the output (front) face of the transducer. Due to the resonance of each DLDB layer and the resulting alternating pair phasing, the energy interferes to remain in phase after every four reflections through the layers and to cause partial breakdown after every two reflections. As a result, once trapped in the DLDB layer, the energy rings down at a very low amplitude over a relatively long period of time. [Figure 14] 1 illustrates a two-dimensional piezoelectric matrix according to one embodiment. [Figure 15] FIG. 15 is an exploded view of FIG. [Figure 16] FIG. 15 is a cross-sectional view of FIG. [Figure 17] 1 illustrates an ultrasound transducer according to another embodiment. [Figure 18] 1 illustrates an ultrasound transducer according to another embodiment. [Figure 19a] A comparison of a state-of-the-art air-backed specific material transducer (top) without a heat sink transmitting in titanium at 680 kHz with the ultrasonic transducer of Figure 1a (bottom) under identical conditions. [Figure 19b] A logarithmic comparison of the envelope between a state-of-the-art air-backed specific material transducer transmitting in titanium (top) and the ultrasonic transducer of Figure 1a transmitting in titanium (bottom). [Figure 20]Three 680 kHz specific material transducers with copper heat sinks attached to the backside of the piezoelectric stack are compared: an air-backed specific material transducer with a heat sink bonded directly to the backside of the transducer's piezoelectric element (top); a state-of-the-art approach in which the heat sink is bonded to the transducer's piezoelectric element with an acoustically lossy, thermally conductive material such as alumina-filled silicone foam (center); and the ultrasonic transducer of Figure 1a with the heat sink bonded directly to the backing structure (bottom). [Figure 21] 21 shows a logarithmic graph of the envelope of the waveform shown in FIG. 20. [Figure 22a] A comparison is made for a 10 MHz single element transducer, comparing the pulse-echo pulse response of a 1 / 4λ resonant piezoelectric element with an approximately 1 / 10λ thick tungsten mismatch layer, and showing the effect of adding a single DLDB to the backside of the mismatch layer. [Figure 22b] The logarithmic envelope of the waveform of a 10 MHz single-element transducer is compared in Figure 22a. [Figure 23a] Comparison of the effect of adding a 3mm thick copper heat sink directly to the backside of the 10MHz acoustic stack in Figure 22a. The DML backing bonded directly to the 3mm copper heat sink develops multiple internal reflections that result in undesirable artifacts in imaging or inspection applications (top). When the heat sink is bonded directly to the front side of the acoustic stack, the stack with DLDB experiences no measurable change (bottom). [Figure 23b] A comparison of the logarithmic envelope of the pulse-echo waveform of a 10 MHz transducer is shown in Figure 23a. [Figure 24]Pulse-echo response from a 550 μm x 5 mm material-specific 5 MHz 1D array element with PZT composite piezoelectric elements matched for transmission in titanium, with a dual DLDB backing, compared to an air backing. Minimal differences are observed between the air-backed transducer (top) and the transducer with DLDBs (bottom), except for a slight increase in pulse length seen in the stack with DLDBs. [Figure 25] The pulse-echo response of the transducer element described in Figure 24 is compared with that of the element described in Figure 24, with the addition of a 6 mm copper heat sink bonded directly to the backside of the acoustic stack (top). Significant internal reverberation artifacts are observed when the heat sink is bonded to the back of the air-backed transducer (bottom). DETAILED DESCRIPTION OF THE INVENTION

[0205] In the following description, like features within the figures will be given like reference numerals, and to avoid unduly cluttering the figures, some elements may not be shown in some figures if they have already been identified in one or more previous figures. Furthermore, it should be understood herein that elements in the figures are not necessarily drawn to scale, with emphasis placed on clearly illustrating the elements and structure of the present embodiments. The prefixes "a," "an," and "one" are defined herein to mean "at least one," i.e., unless expressly stated otherwise, these prefixes do not exclude a plurality of elements. Furthermore, it should be understood that terms such as "substantially," "generally," and "about," which modify a value, condition, or characteristic of an exemplary embodiment, should be understood to mean that the value, condition, or characteristic is defined within an acceptable range for proper operation of the exemplary embodiment for its intended use.

[0206] As used herein, "connected," "coupled," and variations and derivations thereof, mean any direct or indirect connection or coupling between two or more elements. The connection or coupling between the elements may be acoustic, mechanical, physical, optical, operational, electrical, wireless, or any combination thereof.

[0207] It will be understood that position descriptors indicating the location or orientation of one element relative to another are used herein for ease and clarity of description and, unless otherwise specified, should be interpreted in the context of the drawings and should not be considered limiting. Spatially relative terms (e.g., "outer" and "inner," "outside" and "inside," "periphery" and "central," "over" and "under," and "top" and "bottom") will be understood to encompass different positions and orientations in use or operation of the present embodiments in addition to the positions and orientations illustrated in the drawings.

[0208] <General theoretical context> Generally, a piezoelectric ultrasonic transducer consists of a piezoelectric element having two opposing surfaces. The piezoelectric element can be selected to operate at a desired frequency. Examples of such operation include acoustic resonance of the piezoelectric element. A piezoelectric acoustic transducer can include multiple layers, for example, but not limited to, these layers can be stacked or overlaid. In addition to the piezoelectric element, piezoelectric acoustic transducers can include at least one of signal and ground electrodes, matching layers, acoustic backing materials, lenses, and many other layers or structures to improve performance in their intended applications. Some transducers can be designed to output acoustic energy (i.e., transmitters), while other transducers can detect impinging acoustic energy (i.e., receivers). Note that some transducers can be optimized to perform both functions (i.e., transceivers). Different technologies in the field of ultrasound transducers can be implemented to vary the type of piezoelectric ultrasonic transducer produced.

[0209] In most cases, designing a piezoelectric transducer involves many challenges, such as optimizing and / or directing acoustic energy to an intended target, and minimizing acoustic energy away from the intended target. For example, one can consider the relatively simple case of a thin, disk-shaped piezoelectric element, which tends to generate equal acoustic waves from both the front and back sides of the disk when an appropriate frequency voltage is applied across the piezoelectric disk.

[0210] A variety of techniques exist for modifying the properties of such piezoelectric disks to increase the output of acoustic energy from one side (e.g., the front or distal side) and decrease the output of acoustic energy from the other side (the back or proximal side). Those skilled in the art will recognize that such piezoelectric elements are typically positioned such that each side is in contact with a conductive electrode. An example of a conductive electrode is a sputtered metal, which allows the piezoelectric element to be connected to an electronic system and / or other appropriate circuitry. In embodiments where an RF voltage signal is applied to the electrodes, the piezoelectric element is subjected to a mechanical perturbation. If the frequency of the electrical RF signal and the thickness of the one-dimensional piezoelectric array match the correct operating conditions, the piezoelectric element may mechanically resonate at ultrasonic frequencies. Note that this possibility depends on the properties of the piezoelectric material.

[0211] It is generally known in the art that backing materials can be used in piezoelectric ultrasonic transducers. Examples of backing materials include, but are not limited to, absorptive backing materials that have a much lower acoustic impedance than the piezoelectric layer, backing materials with composite morphologies for dissipating and absorbing acoustic energy, mismatched layers that have a much higher acoustic impedance than the piezoelectric layer and a thickness typically less than 1 / 4λ, designed to efficiently reflect all energy to the transducer output while allowing for tunable mass loading effects, and other technologies such as air backings and many other variations including delay line backings.

[0212] Many transducer backing materials are low acoustic impedance absorptive backing materials designed to reflect most, or at least most, of the energy toward the front (or "working face") of the transducer and absorb and disperse the unreflected energy within the backing. Typically, such absorptive backing materials have a predetermined geometry. For example, the backing may be large enough to absorb sufficient acoustic energy and have a specific configuration that prevents unwanted internal reflections from returning to the piezoelectric crystal. Typically, these low acoustic impedance backing materials require the piezoelectric layer to operate in a 1 / 2λ resonant mode.

[0213] Another common backing technique is a de-matching layer, which is designed to reflect energy back to the front face of the transducer while providing some tunable mass loading to adjust the attenuation. Generally, the effect of adding a mismatching layer requires the design of a quarter-wave resonant transducer. In some embodiments, the mismatching layer can be operated to reflect close to 100 percent of the energy, or at least a majority of the energy.

[0214] Another example includes air-backed transducers, which are also capable of reflecting close to 100 percent, or at least a majority, of the energy from the front. However, while such transducers cannot be mass loaded or damped, they operate in the same mode as light-absorbing backings, in that the piezoelectric element resonates at 1 / 2λ.

[0215] One limitation of most backing technologies is, among other things, that the back of the transducer is inaccessible for electrical connections without compromising the acoustic signal, and the sides, which generally have the smallest footprint, should be avoided to minimize acoustic artifacts and losses. A further limitation of existing technologies is the difficulty of providing an efficient thermal cooling solution in direct contact with the transducer's piezoelectric element. This challenge becomes increasingly important as modern relaxor-based polycrystalline and single-crystal ferroelectrics become increasingly efficient at the expense of thermal robustness.

[0216] It should be noted that for 2-D array transducers, due to limited access to the internal elements of the matrix transducer, it may be more difficult to consider both cooling and electrical interconnections and acoustic backing. Therefore, there is a need to develop acoustically efficient, electrically conductive backings, as described herein. There is also a need to develop acoustically efficient, thermally conductive backing technologies, as described herein. There is also a need to develop acoustically and spatially efficient backings, as described herein, that can reflect substantially all of the acoustic energy of a piezoelectric transducer while leaving the proximal surface of the backing relatively free of acoustic energy and allowing for the connection of electrical and / or thermal devices without compromising the performance of the transducer. There is also a need to develop thermally and electrically conductive, acoustically efficient backings that can be connected to 1-D or 2-D array transducers that electrically connect to and cool each element, as described herein.

[0217] <Backing structure for ultrasonic transducer> Broadly described, this specification relates to multilayer ultrasound transducer backing structures or similar technology. In some embodiments, this technology can reflect most, and in some cases, virtually all, acoustic energy away from the front surface of the transducer. Furthermore, systems or devices fabricated according to this technology are generally immune to physical contact at the backside of the backing stack. The transducers presented herein are relatively efficient thermally, electrically, and acoustically, since very little energy is absorbed by the backing layer.

[0218] In the context of this disclosure, as described in more detail below, the backing structure includes one or more mismatched backing materials, each of which includes two layers. In this regard, each mismatched backing is referred to as a "dual layer de-matching backing," or simply a "DLDB." In some embodiments, a DLDB pair can be used as the backing structure. That is, the ultrasound transducer includes a first DLDB and a second DLDB, each of which includes two layers. In other embodiments, two or more DLDB pairs can be used as the backing structure, for example, but not limited to, to further acoustically isolate the backside.

[0219] Notably, the layers forming the DLDB have electrical, acoustic, thermal, and mechanical properties that may vary depending on the intended application. For example, without limitation, the DLDB may include layers that are both electrically and thermally conductive, layers that are neither electrically nor thermally conductive, or any combination thereof.

[0220] An embodiment of an ultrasonic transducer 100 will be described with reference to FIGS.

[0221] Generally, the ultrasonic transducer 100 includes a piezoelectric material 102, a backing structure 108, a heat sink 122, and one or more electrodes 126 (referred to as electrodes 126). Although the ultrasonic transducer embodiments described throughout this specification are described as including a piezoelectric material, those skilled in the art will recognize that the ultrasonic transducers of the present disclosure can include, instead of a piezoelectric material, any ferroelectric material, any single-crystal or polycrystalline material, or any electromechanical transduction material, where such materials have one or more of ferroelectric, pyroelectric, piezoelectric, electrostrictive, and / or other related properties. It should be noted that, as will be readily understood by those skilled in the art, in the context of this specification, the expression "piezoelectric material" can also refer to ferroelectric materials, pyroelectric materials, relaxor materials, and electrostrictive materials.

[0222] The piezoelectric material 102 has a front surface 104 and a back surface 106. The piezoelectric material 102 is configured to be in acoustic communication with a sample (not shown). The piezoelectric material 102 has acoustic properties. For example, but not limited to, the acoustic properties may include an acoustic impedance of about 27.5 Mrayleigh.

[0223] In some embodiments, the piezoelectric material 102 may be a polarized composite piezoelectric disc. The polarized composite piezoelectric disc may be in a 1_3 configuration.

[0224] In some embodiments, the piezoelectric material 102 may be a PZT4 composite and may include struts. For example, without limitation, the struts may be 1000 μm x 1000 μm struts separated by 200 μm kerfs. The kerfs may be cut at a pitch of approximately 1200 μm. The kerfs may be filled with a composite filler. In some embodiments, the composite filler may have an O_3 composition. The composite filler may include hafnium dioxide particles doped in an epoxy. A non-limiting example of an epoxy is Epo-Tek® 301. In some embodiments, the piezoelectric material 102 may have a thickness within a range of approximately 2.35 mm to approximately 2.45 mm.

[0225] In some embodiments, the piezoelectric material 102 is comprised of a piezoelectric layer.

[0226] The backing structure 108 is disposed on the back surface 106 of the piezoelectric material 102. The backing structure 108 is configured to reflect acoustic energy toward the front surface 104 of the piezoelectric material 102. In some embodiments, the backing structure 108 is further configured to reflect acoustic energy in phase. In some embodiments, the backing structure 108 is further configured to spatially and temporally distribute undesired acoustic reverberations within the backing structure 108. The backing structure 108 is thermally and electrically conductive. The backing structure 108 shown in FIGS. 1-6 includes a first dual-layer mismatched backing material 110 and a second dual-layer mismatched backing material 116.

[0227] The first two-layer mismatched backing material 110 includes a first graphite layer 112 and a tungsten layer 114 in contact with the first graphite layer 112. In some embodiments, the first graphite layer 112 has an acoustic impedance of about 5.1 Mrayl and a thickness in the range of about 1.5 mm to about 1.6 mm. In some embodiments, the tungsten layer 114 has an acoustic impedance of about 100 Mrayl and a thickness in the range of about 2.6 mm to about 2.7 mm. Those skilled in the art will readily appreciate that the acoustic impedance and thickness of the first graphite layer 112 and the tungsten layer 114 will depend on the intended application and, therefore, may differ from the examples recited above.

[0228] A second bi-layer mismatched backing material 116 contacts the first bi-layer mismatched backing material 110. The second bi-layer mismatched backing material 116 includes a second graphite layer 118 and a copper layer 120 in contact with the second graphite layer 118. In some embodiments, the second graphite layer 118 has an acoustic impedance of about 5.1 Mrayl and a thickness in the range of about 1.5 mm to about 1.6 mm. In some embodiments, the copper layer 120 has an acoustic impedance of about 41.5 Mrayl and a thickness in the range of about 2.5 mm to about 2.6 mm. Those skilled in the art will readily appreciate that the acoustic impedance and thickness of the second graphite layer 118 and the copper layer 120 depend on the intended application and may therefore differ from the examples recited above.

[0229] The heat sink 122 is in thermal contact with the backing structure 108. In some embodiments, the heat sink 122 includes at least one channel 124. Such channel 124 is configured to receive and circulate a heat transfer fluid therein. The heat transfer fluid may be a liquid, a gas, or any mixture thereof. In some embodiments, the heat sink 122 is electrically insulated from the backing structure 108.

[0230] The electrodes 126 are in electrical communication with the piezoelectric material 102. In some embodiments, the ultrasonic transducer 100 includes a control unit (not shown) electrically connected to at least one of the piezoelectric material 102, the backing structure 108, and the electrodes 126. Such a control unit may be useful for controlling the ultrasonic transducer 100. In some embodiments, the electrodes 126 are electrically connected to the piezoelectric material 102 through the backing structure 108.

[0231] Ultrasonic transducer 100 can operate at an operating frequency, which is related to an operating wavelength, λo. In some embodiments, first graphite layer 112, tungsten layer 114 in contact with first graphite layer 112, second graphite layer 118, and copper layer 120 each have a thickness corresponding to approximately λo / 4 or an odd multiple of λo / 4. In some embodiments, the operating wavelength, λo, may be approximately 530 kHz.

[0232] In one embodiment, the piezoelectric material 102 is configured to resonate at a half-wavelength at the operating frequency.

[0233] In another embodiment, the ultrasonic transducer 100 includes a single mismatching layer 128 disposed between the piezoelectric material 102 and the backing structure 108. The single mismatching layer 128 is in acoustic communication with the piezoelectric material 102 and the backing structure 108. The single mismatching layer 128 has a corresponding acoustic impedance that is relatively higher than the acoustic impedance of the piezoelectric material 102. In this embodiment, the piezoelectric material 102 is configured to resonate at a quarter wavelength at the operating frequency. The piezoelectric material 102 has a resonant frequency, which is related to a resonant wavelength λr. The single mismatching layer 128 has a thickness less than 2λr / 5 relative to the resonant frequency of the piezoelectric material 102. The single mismatching layer 128 may have a thickness of about λr / 10 to about λr / 20. The single mismatching layer 128 may be made of, for example, but not limited to, tungsten. Other materials may also be used for the single mismatching layer 128. In some embodiments, the resonant wavelength λr may be about 530 kHz.

[0234] In some embodiments, the ultrasonic transducer includes a thermally conductive structure 130 in contact with the backing structure 108. In some embodiments, the thermally conductive structure 130 is electrically insulated from the backing structure 108. In some embodiments, the thermally conductive structure 130 may be a layer made of AIN or a layer made of beryllium oxide. In some embodiments, the thermally conductive structure 130 may extend over a lateral portion of the backing structure 108. In some embodiments, the thermally conductive structure 130 includes at least one electrically conductive via extending therethrough.

[0235] In some embodiments, the ultrasonic transducer 100 includes a wear-resistant wear layer 132. The wear layer 132 may be made of, for example, but not limited to, titanium.

[0236] In some embodiments, the ultrasonic transducer 100 includes a thermally conductive layer 133 that acoustically matches the piezoelectric material 102. As shown in FIG. 1d, the thermally conductive layer 133 may be disposed between the piezoelectric material 102 and the wear layer 132. Such a thermally conductive layer may be in thermal contact with the heat sink 122 via a copper lid 135. Of note, the lid 135 may be made of any other thermally conductive material.

[0237] In some embodiments, the ultrasonic transducer 100 has a diameter of about 50 mm.

[0238] <Example> Next, other embodiments of the ultrasonic transducers described above will be presented.

[0239] In some embodiments, an ultrasound transducer includes two stacked DLDBs (dual DLDB stacks) stacked into a single-element liquid-cooled material-specific transducer, which is designed to be titanium-compatible. One exemplary embodiment of a DLDB designed to operate a 680 kHz piezoelectric transducer with a piezoelectric composite element having an acoustic impedance of 27.5 Megarayleigh (MR) includes a first DLDB pair coupled to a second DLDB pair. The first DLDB pair includes a first graphite layer having an acoustic impedance of approximately 5.1 MR and a thickness of 1.03 mm, and a second tungsten metal layer having an acoustic impedance of approximately 100 MR and a thickness of 1.53 mm. The second DLDB pair includes a first graphite layer having an acoustic impedance of approximately 5.1 MR and a thickness of 0.905 mm, and a second copper metal layer having an acoustic impedance of approximately 41.5 MR and a thickness of 1.71 mm.

[0240] In some embodiments, one or two DLDBs of a single-element transducer have a high acoustic impedance mismatch layer (DML) of less than 2 / 5λ, typically less than 1 / 4λ, interposed between the DLDB stack and the piezoelectric element.

[0241] In some embodiments, the DLDB includes a first backing layer and a second backing layer, each backing layer having a distal surface and a proximal surface. The proximal surface of the first backing layer can be in acoustic contact with the distal surface of the second backing layer, and these two layers together comprise a DLDB structure. The DLDB can be positioned in acoustic contact with a piezoelectric element having a distal surface and a proximal surface, and the distal surface of the first backing layer can be in contact with the proximal surface of the piezoelectric element. The first and second backing layers of the DLDB can be designed to be approximately ¼λ thick relative to the design resonant frequency of the piezoelectric element. The first backing layer can be made of a material having a relatively low acoustic impedance compared to the piezoelectric element. The second backing layer can be made of a material having a relatively high acoustic impedance compared to the first backing layer.

[0242] In embodiments where two or more DLDBs are stacked, improved or increased acoustic isolation from the electrical and thermal structures connected to the transducer through the DLDBs can be achieved.

[0243] In some embodiments, during operation, the first surface of the first layer of the first DLDB reflects most of the acoustic energy directed toward the back surface of the transducer from the active surface of the transducer toward the transducer backing, while the back surface of the first layer also reflects, and in doing so, aligns, most of the energy reaching the back surface. Then, due to the alternating sign of the reflection coefficients caused by the quarter-wave layer and the transition from low to high acoustic impedance within the layers included in the DLDB, the layers of the DLDB begin to resonate with the remaining energy within the backing material across the bandwidth of the transducer. The resonant layer then radiates energy in phase both forward and backward through the backing stack over a relatively long period of time and at very low amplitude, effectively diffusing undesired reflections outward at acceptably low amplitudes over time.

[0244] The DLDB embodiments described thus far may be useful for acoustic stacks designed for ½λ resonant piezoelectric transducers and for intended loads that are greater than the acoustic impedance of the optical layer of the DLDB and sufficiently match the acoustic impedance of the piezoelectric layer. Examples of such structures can be found in PCT patent application PCT / CA2019 / 051046, the contents of which are incorporated herein by reference.

[0245] The DLDB embodiments described herein may also be effective for acoustic stacks designed for ½λ resonant piezoelectric transducers and intended loads greater than the acoustic impedance of the optical layers of the DLDB. If the load is comparable to or lower than the low acoustic impedance layer of the first DLDB layer, the transducer can include a piezoelectric layer with an acoustic impedance higher than the load and one or more matching layers.

[0246] In some embodiments, the DLDDB can be used with a 1 / 4λ stack in conjunction with a mismatched layer. In another example, the DLDDB can be included in the design of a 1 / 4λ resonant piezoelectric transducer along with a high acoustic impedance mismatched layer. The high acoustic impedance mismatched layer is inserted between the DLDDB and the piezoelectric material, placing little or no restriction on the acoustic impedance of the load material. This technique can be applied to specific material transducers, transducers with matching layers, or any other practical load matching method.

[0247] Varying the thickness of the DLDB layer can increase the bandwidth of the transducer and improve the reflectivity of the backing material over a wider frequency spectrum, depending on the intended application.

[0248] Due to the relatively high acoustic insulation achieved by the DLDB and the ability to make the layer thermally conductive, it is possible to provide a heat sink directly on the proximal surface of the DLDB, thereby allowing heat to be removed directly and efficiently from the back surface of the piezoelectric element without compromising the acoustic properties of the transducer.

[0249] Because the DLDB provides relatively high acoustic insulation and the layer can be made conductive, it is possible to make a direct electrical connection to the proximal surface of the DLDB by using, for example, soldering, wire bonding, or conductive epoxy to attach wires or other electrical circuits to the top layer of the DLDB.

[0250] In some embodiments, the DLDB can also be diced into elements that align with the piezoelectric elements of a transducer array, such as a 1-D linear array, a 2-D matrix array, or other multi-element transducer array, allowing a printed circuit board, ASIC interposer, electrical connector, or other electrical circuitry to be mounted directly on the proximal surface of the DLDB, enabling efficient electrical connection to the transducer. This can be useful when the ultrasound probe is a 2D multi-element array, allowing a relatively large number of elements to be directly connected to the DLDB, each corresponding to a respective element of the array, without compromising the acoustic properties of the transducer. These embodiments are described in other sections of this specification.

[0251] Due to the relatively low profile of the backing material and the ability to make direct electrical connections to the low profile DLDB through the backing material, this technology can provide design advantages when making low profile ultrasound probes, including but not limited to those used in intracavity medical probes, endoscopes, and NDT tubular transducers and arrays.

[0252] In some embodiments, the DLDB has one or more layers, each made of a thermally conductive material that is laterally electrically insulating and axially conductive, resulting in isotropic thermal conductivity and anisotropic thermal conductivity for the electrically conductive layer. In one embodiment, the high acoustic impedance layer is made of, for example, aluminum nitride (AIN) ceramic. The high acoustic impedance layer has a plurality of conductive vias arranged to align with the multi-element array elements. Other layers of the DLDB can be separated, for example, by dicing, etching, machining, or other methods, into laterally electrically isolated and acoustically separated elements aligned with the elements of the piezoelectric array. The combination of these two layers results in a backing material that provides electrical connection from each transducer element to the proximal surface of the DLDB, lateral electrical isolation from one element to another throughout the DLDB and piezoelectric stack, and unbroken and / or continuous lateral thermal conductivity throughout the array of elements. Those skilled in the art will appreciate that transducer heat dissipation can then be achieved by removing heat from the surrounding AIN layer using some cooling technology, such as an air-to-air heat exchanger or a liquid-cooled heat sink, while still allowing direct electrical connection of the array to a PCB or interposer. Those skilled in the art will readily appreciate that this approach can be applied to stacking multiple DLDBs to enhance acoustic isolation and / or thermal conductivity. The use of this electrically isolated, thermally unbroken and / or continuous DLDB for 1-D, and especially 2-D, transducer arrays provides a relatively simple and cost-effective means of direct cooling of large arrays without compromising acoustic performance and for electrical interconnection.

[0253] In some embodiments, the DLDB may be liquid cooled.

[0254] In some embodiments, a specific transducer of 680 kHz material with a liquid-cooled DLDB is provided for use with titanium and other similar acoustic impedance materials (such as zirconium). The transducer can have a 50 mm diameter and a stack with dual DLDBs.

[0255] It should be noted that the transducer is an exemplary embodiment of the present technology and serves for illustrative purposes only. Apart from those disclosed herein, the transducer may include several other elements known to those skilled in the art.

[0256] In some embodiments, the transducer includes a 2.4 mm thick, polarized composite piezoelectric disc in a 1-3 configuration. This thickness corresponds to approximately 0.35-0.4 λ at unloaded free resonance, but the polarized composite piezoelectric disc operates in 1 / 2 λ mode, with the positive pole on the proximal surface and the negative pole on the distal surface. As will be appreciated by those skilled in the art, the thickness of the piezoelectric disc is selected to be less than 1 / 2 λ to compensate for the mass loading effect and acoustic loading of the DLDB backing material. The piezoelectric composite can be fabricated by dicing and filling polarized PZT4 material with 200 μm kerfs cut at a 1200 μm pitch, leaving 1000 μm x 1000 μm struts separated by 200 μm kerfs. For example, but not by way of limitation, the kerfs can be filled with a composite filler of approximately 5 μm hafnium dioxide particles doped in Epotek® 301 epoxy, such that the acoustic impedance of the composite filler filling the kerfs is approximately 7-8 Megarayleigh (MR), closely matching the acoustic impedance of the entire piezoelectric composite layer to that of titanium (approximately 27.5 MR). The negative face of the piezoelectric composite layer can be bonded to the proximal face of a 6 mm thick ZA-8 zinc-aluminum alloy disk using, for example, tungsten powder-filled epoxy. The distal face of the ZA-8 disk can then be bonded to the proximal face of an alumina composite disk using Epotek 301 epoxy filled with submicron hafnium oxide particles. The alumina composite disk can include 750 μm x 750 μm x 1400 μm (high) struts separated by 200 μm kerfs, which are filled with the same hafnium particle-filled epoxy used to fabricate the piezoelectric composite disk. The distal surface of the alumina composite can be bonded to the proximal surface of a 3 mm thick titanium disk using a layer of submicron hafnium oxide filled Epotek 301 epoxy. Two sets of dual layered mismatched backing materials (DLDBs) are then bonded to the proximal surface of the piezoelectric disk using submicron tungsten powder filled Epotek 301 epoxy as follows:The proximal surface of the piezoelectric composite disk was bonded to the distal surface of a 1030 μm thick Poco DFP-1 graphite disk, which had an acoustic impedance of 5.1 MR and a thickness of 905 μm, corresponding to ¼λ at the transducer's center frequency of 680 kHz. The proximal surface of the graphite disk was then bonded to the distal surface of a 1530 μm thick tungsten disk, which had an acoustic impedance of 100 MR and a thickness corresponding to ¼λ at approximately 850 kHz, slightly above the transducer's center frequency. The proximal surface of the tungsten disk was then bonded to the proximal surface of a 905 μm thick Poco DFP-1 graphite disk, which had an acoustic impedance of 5.1 MR and a thickness corresponding to ¼λ at approximately 800 kHz, slightly above the transducer's center frequency. The proximal surface of the graphite disk is bonded to the distal surface of a 1710 μm thick copper disk with an acoustic impedance of 41.5 MR. The thickness corresponds to ¼λ at 680 kHz. The graphite disk and tungsten disk constitute a first dual-layer mismatched backing stack, and the graphite disk and copper disk constitute a second DLDB stack. These two stacks work together to acoustically isolate the piezoelectric composite disk from the transducer's thermal cooling solution, allowing a thermal cooling element to be directly bonded to the proximal surface of the copper disk without substantially compromising the transducer's acoustic performance. In these embodiments, the distal surface of a 1 mm thick, highly thermally conductive AIN disk is bonded to the proximal surface of the copper disk using thermally conductive epoxy. The AIN disk is notched to accommodate a space for electrical connection to the copper disk using soldered wire or conductive epoxy bonded wire. Note that the entire DLDB stack in this embodiment is electrically and thermally conductive, allowing electrical connections to be made directly through the DLDB stack to the signal electrodes of the piezoelectric composite disk.Furthermore, beyond the materials explicitly listed in this exemplary embodiment, it should be noted that there are many materials that can actually be used in applications of the disclosed technology, some of which are electrically conductive, thermally conductive, both, or neither. In this exemplary embodiment, all of the DLDB layers are electrically and thermally conductive. The proximal surface of the copper heat sink base is brazed or soldered to the distal end of the heat sink top to form a hollow copper heat sink assembly. The distal surface of the heat sink assembly is bonded directly to the proximal surface of the AIN disk using a thermally conductive but electrically insulating epoxy. In the illustrated embodiment, the proximal surface of the hollow heat sink top is bonded to the distal surface of the AIN disk using the same thermally conductive epoxy. The AIN disk has two clearance holes and one notch in the AIN disk to accommodate cooling tubes that are secured to integral barbed tubes in the heat sink top, and the notch allows for clearance passages for signal wires attached to the copper DLDB layer. The proximal surface of the AIN disk can be bonded to the distal surface of the copper heat spreader using thermally conductive epoxy. A copper housing shell can be fitted around the ZA-8 disk and bonded to the completed acoustic and thermal stack using electrically insulating and thermally conductive epoxy. In some embodiments, all voids are filled with thermally conductive and electrically insulating epoxy. Thus, the entire assembly is solid except for the hollow interior of the heat sink assembly (i.e., the top and bottom of the heat sink). A rubber hose is fitted onto the barbed hose boss on top of the copper heat sink and secured in place with a hose clamp. The rubber hose may have an inner diameter of, for example, but not limited to, 9.525 mm (3 / 8 inch). The transducer includes electrical contacts, which can be embodied by a BNC RF electrical connector soldered to the copper lid. Furthermore, the center conductor of the BNC connector can be soldered to a signal wire. Thus, the BNC signal conductor can be electrically connected to the positive signal electrode of the piezoelectric composite disc.In some embodiments, a copper lid can be soldered or bonded to the proximal lip of the copper shell using conductive epoxy to complete the electrical connection from the ground terminal of the BNC connector and the negative terminal of the piezoelectric composite disk through the copper shell and ZA-8 disk. The transducer also includes an electrically insulating plastic housing that is bonded to the copper lid and copper shell, at least partially covers the edge of the alumina composite disk, and rests on the front surface of the titanium disk. The completed transducer (i.e., the assembly of the aforementioned components) is then connected to a liquid-circulating air-to-liquid heat exchanger and filled with a suitable coolant. A non-limiting example of the coolant is a 50% propylene glycol / water mixture.

[0257] These embodiments can be used to directly cool the signal electrode of the piezoelectric composite disk via the dual DLDB stack and indirectly cool the ground electrode of the piezoelectric composite disk via the copper shell and ZA-8 disk. This allows for the removal of hundreds of watts of heat and the heat exchanger to do so at coolant flow rates of approximately a few liters per minute. More specifically, in some embodiments, the ultrasonic transducer may include a thermally conductive layer that acoustically matches the piezoelectric material to enable such indirect cooling. Additionally, the designs described herein can achieve high unidirectional bandwidths of over 90% (e.g., 6 dB bandwidth for the exemplary transducer) and negligible reverberation artifacts while directly cooling the piezoelectric element with an efficient liquid-filled metal heat sink.

[0258] In some embodiments, a stack of piezoelectric layers and DLDBs for a liquid-cooled transducer is provided. While five layers may be stacked, it will be readily understood that these layers may extend equally along all or only a portion of their surface. A layer is a single-element 1 / 2λ piezoelectric composite layer matched to titanium. A layer is a low acoustic impedance 1 / 4λ graphite layer of a first DLDB stack. A layer is a high acoustic impedance 1 / 4λ tungsten layer of a first DLDB stack. A layer is a low acoustic impedance 1 / 4λ graphite layer of a second DLDB stack. A layer is a high acoustic impedance 1 / 4λ copper layer of a first DLDB stack.

[0259] In some embodiments, an ultrasound transducer includes a titanium wear layer, an aluminum oxide (AIN) composite electrically insulating layer, a thermally conductive layer, an electrically conductive layer, and an acoustically conductive layer. These layers may be made of, for example, but not limited to, zinc or a zinc alloy, which is a good thermal conductor and can be acoustically matched to titanium. The transducer further includes a single-element approximately ½λ piezoelectric composite layer. This layer can be matched to titanium. The transducer includes first and second DLDB stacks, each including a low acoustic impedance layer and a high acoustic impedance layer. More specifically, the first DLDB stack includes a low acoustic impedance ¼λ graphite layer and a high acoustic impedance ¼λ tungsten layer, and the second DLDB stack includes a low acoustic impedance ¼λ graphite layer and a high acoustic impedance ¼λ copper layer. The transducer according to this embodiment further includes a thermally conductive and electrically insulating layer. This layer may be made of, for example, but not limited to, aluminum nitride. The transducer also includes an electrically and thermally conductive housing and an electrically insulating plastic outer housing. Other components of the transducer include, but are not limited to, an electrically insulating disk that may be made of AlN with a hose cutout, a water block heat exchanger base, a water block heat exchanger top, a copper heat transfer layer with a hose cutout, a copper housing lid, a BNC RF electrical connector, and a liquid cooling hose.

[0260] In some embodiments, an acoustic stack is provided with two DLDB stacks in place with a fully electrically isolated liquid-cooled heat exchanger in direct thermal contact with the copper layers of the DLDBs through an electrically insulating layer made of AlN.

[0261] In some embodiments, a 10 MHz piezoelectric single-element transducer stack is provided in which a 0.12λ (62.5 μm) thick tungsten mismatch layer is inserted between a bilayer mismatched backing stack including a ¼λ (70 μm) thick low-impedance graphite layer and a ¼λ (130 μm) thick high-impedance tungsten layer. The transducer stack includes a 10 MHz piezoelectric stack with a 115 μm thick 1_3 configuration PZT composite stack, a 62.5 μm thick tungsten mismatch layer, and a bilayer mismatched backing stack. The transducer according to this embodiment includes a single-element ¼λ piezoelectric composite layer that can be matched to titanium. The transducer also includes a 0.12λ mismatch layer, which can be made of tungsten. The transducer also includes a DLDB stack, which includes a low acoustic impedance 1 / 4λ layer, which can be made of graphite, and a high acoustic impedance 1 / 4λ layer, which can be made of tungsten.

[0262] In some embodiments, a 10 MHz piezoelectric composite transducer design is provided. The acoustic stack may include a piezoelectric composite disk and a tungsten mismatch layer, and the dual mismatched backing stack includes a graphite layer and a tungsten layer. The piezoelectric composite disk has an acoustic impedance of approximately 25 MR and a thickness of 115 μm, which corresponds to approximately 1 / 4λ. The piezoelectric composite disk has a positive pole and an electrode on the proximal surface of the disk and a negative pole and an electrode on the distal surface. The tungsten mismatch layer is 62.5 μm thick, which corresponds to approximately 0.12λ. The graphite layer of the DLDB is 70 μm thick, which corresponds to 1 / 4λ at 10 MHz. The tungsten layer is 130 μm thick, which corresponds to 1 / 4λ at 10 MHz. The acoustic stack is bonded to each other using a low-viscosity epoxy, such as Cotronics 4461. Electrical connections are made, if necessary, by filling the epoxy with a small amount of submicron tungsten powder. Those skilled in the art will appreciate that quarter-wave matching layers may be used to match the piezoelectric composite element to water. For purposes of this exemplary embodiment, two quarter-wave matching layers are used, with the first matching layer bonded to the distal surface of the piezoelectric composite layer. The acoustic impedance of the first matching layer is approximately 10 MR, and the acoustic impedance of the second matching layer is approximately 3 MR. Results of simulated testing of this stack with and without a copper heat sink bonded to the proximal surface of the DLDB's high acoustic impedance layer are shown in Figures 22a, 22b, 23a, and 23b.

[0263] Next, different embodiments of ultrasound transducers including one-dimensional piezoelectric arrays will be described.

[0264] <Ultrasonic transducer including one-dimensional piezoelectric array> 7-12, an ultrasonic transducer array 200 is shown.

[0265] The ultrasound transducer array 200 includes a one-dimensional piezoelectric array 202 having a front surface 204 and a back surface 206. The one-dimensional piezoelectric array 202 is configured to be in acoustic communication with a sample (not shown). As shown, the array 202 includes a plurality of piezoelectric regions 203 aligned in one dimension.

[0266] The ultrasound transducer array 200 also includes a backing structure 208 disposed on the back surface 206 of the one-dimensional piezoelectric array 202. The backing structure 208 is configured to reflect acoustic energy toward the front surface 204 of the one-dimensional piezoelectric array 202. In some embodiments, the backing structure 208 is further configured to reflect acoustic energy in phase. In some embodiments, the backing structure 208 is further configured to spatially and temporally distribute undesired acoustic reverberations within the backing structure 208. The backing structure 208 includes a dual-layer mismatched backing material 210. In some embodiments, the backing structure 208 is thermally and electrically conductive. In some embodiments, a top portion 209 of the backing structure 208 is composed of an electrically insulating material. In some embodiments, the top 209 of the backing structure 208 includes a layer of AIN traversed by conductive vias 236, each aligned with a corresponding one of the plurality of linearly arranged piezoelectric regions 203. In some embodiments, the layer of AIN has a front surface, and the layer of AIN is partially diced from the front surface to enhance acoustic isolation between adjacent ones of the plurality of linearly arranged piezoelectric regions 203.

[0267] The dual-layer mismatched backing material 210 includes a low acoustic impedance layer 212 and a high acoustic impedance layer 214. In some embodiments, the low impedance layer 212 and the high acoustic impedance layer 214 form a first dual-layer mismatched backing material 210, and the ultrasonic transducer includes a second dual-layer mismatched backing material 216. The second dual-layer mismatched backing material 216 includes a second low acoustic impedance layer 218 and a second high acoustic impedance layer 220.

[0268] The ultrasonic transducer 200 also includes a pre-assembled electrical circuit 234. The pre-assembled electrical circuit 234 is in electrical communication with the top 209 of the backing structure 208, which in turn is in electrical communication with the piezoelectric material 202. In some embodiments, the pre-assembled electrical circuit 234 includes at least one of a printed circuit board, an interposer, an integrated circuit, and an application specific integrated circuit.

[0269] In some embodiments, the ultrasonic transducer 200 includes a heat sink similar to those described above. The heat sink is in thermal contact with the backing structure 208. In some embodiments, the heat sink includes at least one channel. Such a channel is configured to receive and circulate a heat transfer fluid therein. The heat transfer fluid may be a liquid, a gas, or any mixture thereof.

[0270] In some embodiments, the heat sink is electrically isolated from the backing structure 208. In some embodiments, the ultrasonic transducer 200 includes one or more electrodes electrically connected to the one-dimensional piezoelectric array 202 through the backing structure 208. The ultrasonic transducer 200 may include a control unit electrically connected to at least one of the one-dimensional piezoelectric array 202 and the backing structure 208.

[0271] As shown, the piezoelectric regions 203 are separated from one another by gaps 238. The gaps 238 are electrically insulating and preferably acoustically insulating. Similarly, in some embodiments, at least one of the low acoustic impedance layer 210 and the high acoustic impedance layer 212 may be diced into a plurality of first elements 240 and separated from one another by a first set of gaps 242. Each gap 242 in the first set is aligned with a corresponding gap 238 in the gaps 238 separating the piezoelectric regions 203. The gaps 242 in the first set are electrically insulating and preferably acoustically insulating. In some embodiments, at least one of the second low acoustic impedance layer 218 and the second high acoustic impedance layer 220 may be diced into a plurality of second elements 244 and separated from one another by a second set of gaps 246. Each gap 246 in the second set is aligned with a corresponding gap 238 in the gaps 238 separating the piezoelectric regions 203. The gaps 246 in the second set are electrically insulating and preferably also acoustically insulating. In some embodiments, the gaps 238, the gaps 242 in the first set, and the gaps 246 in the second set are thermally conductive.

[0272] In some embodiments, the ultrasonic transducer 200 is operable at an operating frequency, which is related to an operating wavelength λo. The low acoustic impedance layer 212, the high acoustic impedance layer 214, the second low acoustic impedance layer 218, and the second high acoustic impedance layer 220 each have a thickness corresponding to approximately λo / 4 or an odd integer multiple of λo / 4.

[0273] In one embodiment, the one-dimensional piezoelectric array 202 is configured to resonate at a half-wavelength at the operating frequency.

[0274] In another embodiment, the ultrasonic transducer 202 includes a single mismatching layer 228 disposed between the one-dimensional piezoelectric array 202 and the backing structure 208. The single mismatching layer 228 is in acoustic communication with the one-dimensional piezoelectric array and the matching backing structure 208. The single mismatching layer 228 has a corresponding acoustic impedance that is relatively higher than the acoustic impedance of the one-dimensional piezoelectric array 202. The one-dimensional piezoelectric array 202 is configured for quarter-wave resonance at the operating frequency. In some embodiments, the one-dimensional piezoelectric array 202 has a resonant frequency related to a resonant wavelength λr, and the single mismatching layer 228 has a thickness less than 2λr / 5 relative to the resonant frequency of the one-dimensional piezoelectric array 202. In some embodiments, the single mismatching layer 228 has a thickness of about λr / 10 to about λr / 20. In some embodiments, the single mismatching layer 228 is made of tungsten.

[0275] In some embodiments, the one-dimensional piezoelectric array 202 includes posts separated by kerfs. In some embodiments, the kerfs are filled with a composite filler. The composite filler may include hafnium dioxide particles doped in epoxy. In some embodiments, the composite filler may be in the 0_3 configuration. In some embodiments, the epoxy may be Epo-Tek® 301.

[0276] In some embodiments, the piezoelectric region 203 is comprised of a piezoelectric layer.

[0277] In some embodiments, the ultrasonic transducer 200 includes a thermally conductive structure 230 in contact with the backing structure 208. In some embodiments, the thermally conductive structure 230 is electrically insulated from the backing structure 208. In some embodiments, the thermally conductive structure 230 is a layer of AIN or a layer of beryllium oxide. In some embodiments, the thermally conductive structure 230 extends over a lateral portion of the backing structure 208.

[0278] In some embodiments, the ultrasonic transducer 200 includes a wear-resistant wear layer 232. In some embodiments, the wear layer 232 is made of titanium.

[0279] In some embodiments, the ultrasonic transducer 200 has a diameter of about 50 mm.

[0280] <Example> Below, other embodiments of ultrasound transducers are presented that include one-dimensional piezoelectric arrays.

[0281] In some embodiments, a 1-D linear array is provided with a single DLDB backing layer that is fully diced and electrically attached directly to the PCB, allowing for relatively easy electrical interconnection of the array and even allowing for relatively direct application of ASICs or high-density connectors to the stack.

[0282] In some embodiments, a 16-element 1-D linear array is provided that has a single DLDB backing layer that is fully diced and electrically attached directly to the PCB. As previously mentioned, this configuration allows for relatively easy electrical interconnection of the array, even allowing for relatively direct application of ASICs or high-density connectors to the stack. The array may include a protective wear layer, which may alternatively be a lens or matching layer, depending on the application. The piezoelectric elements form a 1-D linear array, with each piezoelectric element separated from the others by gaps (or kerfs). The array also includes a low acoustic impedance 1 / 4λ layer, which is separated into elements with gaps between them and aligned with the arrayed piezoelectric elements. A high acoustic impedance 1 / 4λ layer, which may be made of tungsten, is disposed on the low acoustic impedance layer. The high acoustic impedance layer is separated into elements with gaps between them and aligned with the arrayed piezoelectric elements. The array is also provided with electrodes on the PCB side, and vias in the PCB and printed circuit board connect the electrodes from one side to the opposite side.

[0283] In some embodiments, elements and layers forming a one-dimensional array or two-dimensional matrix may be further separated into sub-elements to optimize acoustic properties, as will be understood by those skilled in the art. In some embodiments, piezoelectric layers may be sub-diced. In still other embodiments, DLDB backing structures may be sub-diced, and in still other embodiments, some layers of some DLDBs may be sub-diced. Note that these examples of arrayed transducers serve for illustrative purposes only and should not be considered limiting. More specifically, ultrasound transducers (or components thereof) of the present disclosure may implement any method of improving acoustic properties through sub-dicing and aspect ratio manipulation (e.g., by forming additional gaps). Furthermore, DLDB backing configurations may be adapted to these methods and techniques.

[0284] In some embodiments, a dual DLDB 16-element linear array is provided with a laterally thermally continuous layer in the second (top) DLDB stack. The thermally conductive layer is AlN, but may also be beryllium oxide or another suitable thermally conductive and electrically insulating material, and includes conductive vias for connection to the transducer elements. This allows the array to be cooled from the edge and allows for direct electrical connection, for example, using a PCB. As one skilled in the art will appreciate, this trade-off between cooling area and PCB coverage may be a trade-off depending on space and design needs.

[0285] In some embodiments, a dual DLDB 16-element linear array is provided, with a laterally thermally continuous layer in the second (top) DLDB stack. The array includes a protective wear layer. Alternatively, the protective wear layer may be a lens or matching layer(s), depending on the application. The array also includes piezoelectric elements, each separated from the other by a gap (or kerf), forming a 1-D linear array. The array includes a low acoustic impedance 1 / 4λ layer, which is aligned with the arrayed piezoelectric elements, separated into elements with gaps between elements, and a high acoustic impedance 1 / 4λ layer, which may be made of tungsten. The high acoustic impedance 1 / 4λ layer, which is aligned with the arrayed piezoelectric elements, separated into elements with gaps between elements, and another low acoustic impedance 1 / 4λ layer, which is aligned with the arrayed piezoelectric elements, separated into elements with gaps between elements, and another high acoustic impedance 1 / 4λ layer. The high acoustic impedance 1 / 4λ layer, which may be made of AlN, does not have a gap. By gap-free, we mean that the layers are continuous. The layers transfer heat laterally along the array. Vertical conductivity is provided by vias in the AIN layers. The vias in the AIN layers provide electrical continuity between vertically adjacent layers. The array also includes electrodes on the PCB surface, the printed circuit board, and vias in the circuit board that connect the electrodes from one surface to the other.

[0286] Next, an embodiment of an ultrasound transducer including a two-dimensional piezoelectric matrix is ​​presented.

[0287] <Ultrasonic transducer containing a two-dimensional piezoelectric matrix> 14 to 16, an ultrasonic transducer 300 is shown.

[0288] The ultrasonic transducer 300 includes a two-dimensional piezoelectric matrix 302 having a front surface 304 and a back surface 306. The two-dimensional piezoelectric matrix 302 is configured to be in acoustic communication with a sample (not shown). While the following paragraphs explicitly refer to a 2D matrix, those skilled in the art will readily appreciate that such a 2D structure may also be implemented by an annular array with circular gaps symmetrically positioned about the center of the ultrasonic transducer. In fact, the 2D matrix may be implemented by any array shape.

[0289] The ultrasonic transducer 300 also includes a backing structure 308 disposed on the back surface 306 of the two-dimensional piezoelectric matrix 302. The backing structure 308 is configured to reflect acoustic energy toward the front surface 304 of the two-dimensional piezoelectric matrix 302. In some embodiments, the backing structure 308 is further configured to reflect acoustic energy in phase. In some embodiments, the backing structure 308 is further configured to spatially and temporally distribute undesired acoustic reverberations within the backing structure 308. The backing structure 308 includes a dual-layer mismatched backing 310. In some embodiments, the backing structure 308 is thermally and electrically conductive. In some embodiments, the top portion 309 of the backing structure 308 is made of an electrically insulating material. In some embodiments, the top portion 309 of the backing structure 308 includes a layer of AlN traversed by conductive vias 336, each of which is aligned with a corresponding one of the plurality of piezoelectric regions 303. In some embodiments, the layer of AIN has a front surface, and the layer of AIN is partially diced from the front side to enhance acoustic isolation between adjacent piezoelectric regions 303 of the plurality of piezoelectric regions 303.

[0290] The dual-layer mismatched backing 310 includes a low acoustic impedance layer 312 and a high acoustic impedance layer 314. In some embodiments, the low acoustic impedance layer 312 and the high acoustic impedance layer 314 form a first dual-layer mismatched backing material 310, and the ultrasonic transducer includes a second dual-layer mismatched backing material 316. The second dual-layer mismatched backing material 316 includes a second low acoustic impedance layer 318 and a second high acoustic impedance layer 320.

[0291] The ultrasonic transducer 300 also includes a pre-assembled electrical circuit 334. The pre-assembled electrical circuit 334 is in electrical communication with the top 309 of the backing structure 308, which in turn is in electrical communication with the piezoelectric material 302. In some embodiments, the pre-assembled electrical circuit 334 includes at least one of a printed circuit board, an interposer, an integrated circuit, and an application specific integrated circuit.

[0292] In some embodiments, the ultrasonic transducer 300 includes a heat sink similar to those described above. The heat sink should be in thermal contact with the backing structure 308. In some embodiments, the heat sink includes at least one channel. Such a channel is configured to receive and circulate a heat transfer fluid therethrough. The heat transfer fluid may be a liquid, a gas, or any mixture thereof. In some embodiments, the heat sink is electrically insulated from the backing structure 308.

[0293] In some embodiments, the ultrasonic transducer 300 includes one or more electrodes electrically connected to the two-dimensional piezoelectric matrix 302 through a backing structure 308. The ultrasonic transducer 300 may include a control unit electrically connected to at least one of the two-dimensional piezoelectric matrix 302 and the backing structure 308.

[0294] As shown, the piezoelectric regions 303 are separated from one another by gaps 338. The gaps 338 are electrically and acoustically insulating. Similarly, in some embodiments, at least one of the low acoustic impedance layer 310 and the high acoustic impedance layer 312 may be diced into a plurality of first elements 340 and separated from one another by a first set of gaps 342. Each gap 342 in the first set is aligned with a corresponding gap 338 in the gaps 338 separating the piezoelectric regions 303. The gaps 342 in the set are electrically and acoustically insulating. In some embodiments, at least one of the second low acoustic impedance layer 318 and the second high acoustic impedance layer 320 may be diced into a plurality of second elements 344 and separated from one another by a second set of gaps 346. Each gap 346 in the second set is aligned with a corresponding gap 338 in the gaps 338 separating the piezoelectric regions 303. The gaps 346 in the second set are electrically and acoustically insulating. In some embodiments, gaps 338, gaps in the first set 342, and gaps in the second set 346 are thermally conductive.

[0295] In some embodiments, the ultrasonic transducer 300 is operable at an operating frequency, which is related to an operating wavelength λo, and the low acoustic impedance layer 312, the high acoustic impedance layer 314, the second low acoustic impedance layer 318, and the second high acoustic impedance layer 320 each have a thickness corresponding to approximately λo / 4 or an odd integer multiple of λo / 4.

[0296] In one embodiment, the two-dimensional piezoelectric matrix 302 is configured to resonate at a half-wavelength at the operating frequency.

[0297] In another embodiment, the ultrasonic transducer 300 includes a single mismatching layer 328 disposed between the two-dimensional piezoelectric matrix 302 and the backing structure 308. The single mismatching layer 328 is in acoustic communication with the two-dimensional piezoelectric matrix and the matching backing structure 308. The single mismatching layer 328 may have gaps that align with gaps formed in the piezoelectric matrix 302. The single mismatching layer 328 may be conductive. The single mismatching layer 328 has a corresponding acoustic impedance that is relatively higher than the acoustic impedance of the two-dimensional piezoelectric matrix 302. The two-dimensional piezoelectric matrix 302 is configured to resonate at a quarter wavelength at the operating frequency. In some embodiments, the two-dimensional piezoelectric matrix 302 has a resonant frequency related to a resonant wavelength λr, and the single mismatching layer 328 has a thickness less than 2λr / 5 relative to the resonant frequency of the two-dimensional piezoelectric matrix 302. In some embodiments, the single mismatching layer 328 has a thickness of about λr / 10 to about λr / 20. In some embodiments, the single mismatch layer 328 is made of tungsten.

[0298] In some embodiments, the two-dimensional piezoelectric matrix 302 includes posts separated by kerfs. In some embodiments, the kerfs are filled with a composite filler. The composite filler may include hafnium dioxide particles doped in epoxy. In some embodiments, the composite filler may be of the 0_3 configuration. In some embodiments, the epoxy may be Epo-Tek® 301.

[0299] In some embodiments, the piezoelectric region 303 is comprised of a piezoelectric layer.

[0300] In some embodiments, the ultrasonic transducer 300 includes a thermally conductive structure 330 in contact with the backing structure 308. In some embodiments, the thermally conductive structure 330 is electrically insulated from the backing structure 308. In some embodiments, the thermally conductive structure 330 is a layer of AIN or a layer of beryllium oxide. In some embodiments, the thermally conductive structure 330 extends over a lateral portion of the backing structure 308.

[0301] In some embodiments, the ultrasonic transducer 300 includes a wear-resistant wear layer 332. In some embodiments, the wear layer 332 is made of titanium.

[0302] In some embodiments, the ultrasonic transducer 300 has a diameter of about 50 mm.

[0303] <Example> Next, another embodiment of an ultrasound transducer including a two-dimensional piezoelectric matrix is ​​presented.

[0304] In some embodiments, a 2-D matrix transducer is provided having two DLDB stacks, where the top layer of the second stack comprises a continuous thermally conductive layer made of AIN with conductive vias, which corresponds to a 2D version of the 1D transducer described above.

[0305] In some embodiments, a dual DLDB 16x16 element matrix array is provided, with a laterally thermally continuous layer in a second (top) DLDB stack. The matrix transducer includes a protective wear layer. The protective wear layer can alternatively be replaced by a lens, matching layer, or other acoustic structure depending on the overall application of the 2D transducer array. The matrix transducer includes piezoelectric elements separated from each other by gaps (or kerfs) in two axial directions to form a 2-D linear or matrix array. The matrix transducer includes a low acoustic impedance 1 / 4λ layer aligned with the arrayed piezoelectric elements, separated into elements with gaps between elements in two axial directions, and a high acoustic impedance 1 / 4λ layer, which can be made of tungsten. The high acoustic impedance 1 / 4λ layer can be aligned with the arrayed piezoelectric elements, separated into elements with gaps between elements in two axial directions. These layers define a first DLDB stack. The matrix transducer also includes a second DLDB stack. The second DLDB stack is separated into elements with gaps between them in both axial directions and includes a low acoustic impedance 1 / 4λ layer aligned with the arrayed piezoelectric elements, and a high acoustic impedance 1 / 4λ layer. This layer is entirely continuous and made of AlN. In this context, "continuous" means that the stack has no gaps and conducts heat laterally along both axes of the array. Vertical conductivity is provided by conductive vias in the AlN layer. This layer is particularly useful for maintaining isothermal conditions within the 2D array relative to the edge elements.

[0306] <Low acoustic impedance layer and high acoustic impedance layer for ultrasonic transducer> 17, an ultrasonic transducer 400 is shown. The ultrasonic transducer 400 includes a piezoelectric material 402 having a front surface 404 and a back surface 406. The piezoelectric material 402 is configured to be in acoustic communication with a sample (not shown in FIG. 17). The ultrasonic transducer includes a backing structure 408 disposed on the back surface 406 of the piezoelectric material 402 and configured to reflect acoustic energy toward the front surface 404 of the piezoelectric material 402. The backing structure 408 includes a first dual-layer mismatched backing material 410 and a second dual-layer mismatched backing material 416.

[0307] The first dual-layer mismatched backing material 410 includes a first low acoustic impedance layer 412 and a first high acoustic impedance layer 414. The second dual-layer mismatched backing material 416 is connected to the first dual-layer mismatched backing material 410. The second dual-layer mismatched backing material 416 includes a second low acoustic impedance layer 418 and a second high acoustic impedance layer 420.

[0308] It should be noted that ultrasonic transducer 400 may include one or more of any of the features described with respect to ultrasonic transducer 100, ultrasonic transducer 200, and ultrasonic transducer 300.

[0309] 18 , an ultrasonic transducer 500 is shown having a sample contacting portion 504 and a back portion 506. The back portion 506 is opposite the sample contacting portion 504. The ultrasonic transducer 500 includes a piezoelectric material 502 configured to be in acoustic communication with a sample (not shown in FIG. 18 ). The ultrasonic transducer 500 includes a backing structure 508 in acoustic communication with the piezoelectric material 502. The backing structure 508 is configured to reflect acoustic energy toward the sample contacting portion 504 and away from the back portion 506 of the ultrasonic transducer 500. The backing structure 508 includes a low acoustic impedance layer 512 and a high acoustic impedance layer 514. In some embodiments, the low acoustic impedance layer 512 and the high acoustic impedance layer 514 form a first dual-layer mismatched backing material 510, and the ultrasonic transducer includes a second dual-layer mismatched backing material 516. The second dual-layer mismatched backing material 516 includes a second low acoustic impedance layer 518 and a second high acoustic impedance layer 520 .

[0310] In some embodiments, the piezoelectric material 502 is diced into a plurality of piezoelectric regions separated by gaps. The gaps are electrically and acoustically insulating. At least one of the low acoustic impedance layer 510 and the high acoustic impedance layer 512 may be diced into a plurality of first elements separated by a first set of gaps. Each gap in the first set may be aligned with a corresponding gap separating the piezoelectric regions. The gaps in the first set are electrically and acoustically insulating. Similarly, at least one of the second low acoustic impedance layer 518 and the second high acoustic impedance layer 520 is diced into a plurality of second elements separated by a second set of gaps. Each gap in the second set is aligned with a corresponding gap separating the piezoelectric regions. The gaps in the second set are electrically insulating and acoustically insulating.

[0311] It should be noted that ultrasonic transducer 500 may include one or more of any of the features described with respect to ultrasonic transducer 100, ultrasonic transducer 200, ultrasonic transducer 300, and ultrasonic transducer 400.

[0312] Having now described various embodiments of ultrasound transducers, the performance of some of these embodiments will now be described, and more particularly, the results that can be obtained using the ultrasound transducers described herein.

[0313] <Example of results> Figure 19a compares an existing air-backed specific material transducer (top) transmitting in titanium at 680 kHz without a heat sink (see PCT / CA2019 / 051046, the contents of which are incorporated herein by reference) with the dual DLDB specific material transducer disclosed herein operating under the same conditions. Due to the additional in-phase reflections created by the DLDB, there is a typical slight reduction in bandwidth, from 105%, or -6 dB, for the air-backed transducer to 91% for the DLDB version, a slight efficiency loss of approximately 1 dB compared to state-of-the-art air-backed designs.

[0314] Figure 19b compares the logarithmic envelope of an existing air-backed material-specific transducer transmitting through titanium (top) with the logarithmic envelope of the present technology exemplified in the dual DLDB described herein (bottom). Those skilled in the art will note the exponential decay of the reflected energy from the backing material as it propagates through the DLDB over time. The energy in the tail of the transmitted wave is approximately 40 dB higher than in the air-backed case. While this is undesirable in itself, it is desirable when considering the application of a heat sink to the backside of the stack, as discussed above.

[0315] Figure 20 compares three 680 kHz specific-material transducers with copper heat sinks attached to the backside of the piezoelectric stack: an air-backed specific-material transducer (top), in which the heat sink is directly bonded to the backside of the transducer's piezoelectric element; a conventional method of bonding the heat sink to the transducer's piezoelectric element using an acoustically lossy, thermally conductive material such as alumina-filled silicone foam (middle); and a specific-material transducer with a dual DLDB stack and a heat sink directly bonded to the top layer of the DLDB stack (bottom). As can be seen, the design with dual DLDBs does not suffer from the internal reflections seen in typical current-state-of-the-art transducers when a heat sink is attached to the stack. Furthermore, in the first two graphs, the transducer output is reduced by 4 dB in the top graph and by approximately 3 dB in the middle design due to acoustic energy lost to the heat sink. However, the transducer with dual DLDBs did not suffer from any loss in sensitivity or bandwidth. Note that while existing approaches that use thermally conductive but acoustically lossy layers to bond or couple a heat sink to a piezoelectric stack typically require relatively significant compromises in both acoustic performance and thermal conductivity to obtain a useful device, the thermal conductivity of the DLDB design is more than an order of magnitude higher than that of the transducer design in the center figure, while at the same time exhibiting no reverberation artifacts.

[0316] Figure 21 is a logarithmic scale plot of the envelope of the waveform shown in Figure 20. Note that when a heat sink is attached to the backside of the stack, the unwanted reverberations in the transducer with DLDB (bottom) are significantly reduced. Also note that the SNR in the stack with DLDB (bottom) is still over 35 dB, while the SNR in the existing stack (top and center) is less than 3 dB and is essentially unusable.

[0317] Figure 22a compares the pulse-echo (bidirectional) pulse response of a 10 MHz single-element transducer with a 1 / 4λ resonant piezoelectric element and an approximately 1 / 10λ thick tungsten mismatched layer backing (DML) to demonstrate the effect of adding a single DLDB backing behind the mismatched layer backing. Note that there is little change in the performance of the transducers. More specifically, the insertion loss is less than 0.5 dB, and the bandwidth is similar.

[0318] Figure 22b shows a logarithmic graph of the envelope comparison of the waveforms from the 10 MHz single-element transducer shown in Figure 22a. Note that the effect of the DLDB is to redistribute the reflected energy from the backing at a low level and spread it out over time. This effect is flat when viewed in the pulse-echo (two-way) signal. The SNR of the DLDB stack (bottom) is limited to approximately 47 dB compared to the SNR of over 70 dB for the existing DML stack (top), while medical imaging applications often require an SNR of at least 60 dB. Therefore, this SNR is acceptable for even demanding medical imaging applications. For therapeutic medical applications, as well as NDT and other industrial applications, the stack with DLDB is generally acceptable. Note that the length of the ringing tail is improved with the stack with DLDB.

[0319] Figure 23a compares the effect of adding a 3mm thick copper heat sink directly to the backside of the 10MHz acoustic stack in Figure 22a. The DML backing material bonded directly to the 3mm copper heat sink creates multiple internal reflections that result in artifacts that are undesirable for imaging or inspection applications (top), while the stack with DLDB undergoes no measurable change when the heat sink is bonded directly to the front side of the acoustic stack (bottom).

[0320] Figure 23b compares the logarithmic envelope of the pulse-echo waveform for the 10 MHz transducer shown in Figure 23a. Adding a copper heat sink to the backside of an existing transducer with DML (top) results in an SNR of less than 3 dB, making it virtually unusable for most applications. Note, however, that transducers with this technology exhibit an SNR of over 50 dB when a copper heat sink or similar device, such as a PCB, is directly bonded to the proximal layer of the DLDB stack.

[0321] Figure 24 compares the pulse-echo response from a 550 μm × 5 mm material-specific 5 MHz 1D array element with PZT composite piezoelectric elements matched for transmission in titanium with a dual DLDB backing and an air backing. Minimal differences are observed between the air-backed transducer (top) and the transducer with DLDBs (bottom), except for a slight increase in pulse length seen in the stack with DLDBs.

[0322] Figure 25 compares the pulse-echo response of the transducer element described in Figure 24 with that of an acoustic stack with the addition of a 6 mm copper heat sink bonded directly to the backside of the element. Note that the air-backed transducer with the heat sink bonded to the backside exhibits significant inter-reverberation artifacts (top panel), while the acoustic stack with DLDB is unaffected by the addition of the heat sink (bottom panel). More specifically, the bottom panel corresponds to the one-dimensional piezoelectric array described above. Note also that soldering wires or bonding or soldering PCB or ceramic holes to the backside of the DLDB element does not degrade the acoustic performance of the transducer element, opening the door to relatively simplified array transducer designs.

[0323] <Further theoretical considerations> Having described different embodiments of the technology and performance, further theoretical details will now be presented. As previously mentioned, the backing structure can include one or more double-layered mismatched backing material (DLDB) stacks, each including two layers, which may be in direct acoustic communication, for example, but not limited to, the layers. In some embodiments, the layers can be adhesively bonded to one another. The thickness of each layer in the DLDB stack can be approximately 1 / 10λ to 1 / 2λ, and in some embodiments, approximately 1 / 4λ. In some embodiments, the ultrasound transducer includes two DLDB stacks, i.e., four layers including a graphite disk, a tungsten disk, a graphite disk, and a copper disk. These four layers define two sets of double-layered mismatched backing materials (DLDBs) that act in conjunction to reflect most or virtually all of the acoustic energy emitted proximally from the piezoelectric composite disk, thereby transmitting nearly all of the acoustic energy emitted from the piezoelectric composite disk out the distal surface of the titanium disk. In these embodiments, the titanium disk serves as the outer wear layer and serves as the primary point of ultrasonic coupling into the intended titanium load into which the transducer transmits. However, it should be noted that a transducer comprising a DLDB stack can also function with any number of output configurations known or yet to be known in the art, such as lenses, matching layers, and delay lines. Sound pressure reflections occurring at the interface of materials with different acoustic impedances are calculated according to the reflection coefficient R given by the following equation:

[0324] R = (Z2 - Z1) / (Z2 + Z1) (1)

[0325] At the same time, the pressure transmitted from one material to the other is calculated from the transmission coefficient T according to the following formula:

[0326] T=2Z2 / (Z2+Z1) (2)

[0327] where Z1 is the acoustic impedance of the medium from which the sound wave is traveling, and Z2 is the acoustic impedance of the medium through which the sound wave is traveling. Based on these equations, one skilled in the art will understand that the reflection coefficient will be positive if the sound wave is traveling from a low acoustic impedance to a high acoustic impedance medium, and negative if the sound wave is traveling from a high acoustic impedance medium to a low acoustic impedance medium. The transmission coefficient is always positive. The arrangement of layers within the DLDB effectively ensures that nearly all acoustic energy is reflected in phase toward the distal surface of the titanium wear layer within the first layer of the DLDB. Furthermore, the presence of alternating, highly acoustically mismatched quarter-wave layers in the DLDB causes each layer to resonate and redistribute the acoustic energy entering that layer at very low amplitudes over a very long time frame. This results in undesired backing reflections being diffused at low amplitudes over time. Early reflections occurring between the piezoelectric element and the first low acoustic impedance layer of the DLDB, or between the back surface of the DML and the first low acoustic impedance layer of the DLDB, have a significant effect on the overall efficiency of the transducer. For half-wave resonant transducers, care is typically taken to maximize the acoustic impedance mismatch between the piezoelectric element and the first low acoustic impedance layer of the DLDB. This effect is less significant when using a quarter-lambda transducer design with a DML, but still affects the overall performance of the DLDB.

[0328] By using materials such as graphite, silver-plated hollow glass spheres, low-density conductive epoxy, or composites of low acoustic impedance metals such as magnesium and epoxy as the first layer of the DLDB, it is possible to maintain both thermal and electrical conductivity throughout the DLDB stack while maintaining a high initial reflection coefficient between the piezoelectric element and the first layer of the DLDB. Using the exemplary materials listed above, acoustic impedances of 1.5 to 6 MR can be easily achieved, with electrical and thermal conductivities varied as needed. However, it is not necessary for the layers of the DLDB to be made from electrically or thermally conductive materials, and this should not be construed as limiting the scope of this specification. There may be applications where it is desirable for some or all layers of one or more DLDB stacks to be made from thermally or electrically insulating materials. One example of a non-conductive DLDB stack is an approximately quarter-wave thick layer of Rexolite (cross-linked polystyrene) bonded to an approximately quarter-wave thick layer of alumina. Furthermore, the layers of the DLDB stack can be made from hybrid materials such as AlN with conductive vias. The second layer, next to the DLDB, should be selected to maximize the acoustic impedance mismatch between itself and the low acoustic impedance layer. Materials such as tungsten metal, molybdenum metal, tungsten carbide, and other high acoustic impedance materials offer a good combination of high acoustic impedance, good thermal conductivity, and good electrical conductivity. It should be noted that there are many other materials that can be tailored to specific applications and still fall within the scope of this technology.

[0329] The effect of a DLDB stack can be explained by the following simplified theory. The first step is to consider operation over an infinitely narrow bandwidth at the center frequency of the transducer. The second step is to consider each layer to be exactly 1 / 4λ at the center frequency. Those skilled in the art will readily appreciate that these assumptions are not the case for actual devices, where each DLDB layer is relatively wideband, optimized to extend the device's effective bandwidth. However, to clarify the overall function of the DLDB stack, we will consider the narrowband case in detail, treating all DLDB layers as being 1 / 4 times the wavelength of the center frequency. Stacking 1 / 4 wavelength layers of highly contrasting acoustic impedances adjacent to a piezoelectric composite layer in the case of a 1 / 2λ resonant piezoelectric design, or adjacent to a mismatched layer in the case of a 1 / 4λ resonant piezoelectric design, creates a series of strongly resonant layers that are highly acoustically isolated from each other due to the high reflection coefficient at each interface (e.g., preferably greater than 80%). The explanation of the effect of the backing is more easily followed by an example and with reference to Figure 13. Using the acoustic stack embodiments disclosed herein, it can be seen that sound waves traveling from the piezoelectric layer to the first graphite layer first undergo a 180° phase change (negative reflection coefficient), with 69% of the sound wave reflected back into the piezoelectric layer and the remaining 31% of the sound wave transmitted to the graphite layer. Upon entering the graphite layer, the sound waves reverberate within the graphite layer, resulting in all trips across the layer being in phase, causing the layer to resonate at a quarter wavelength. The waves experience a 90% reflection at the boundary with the tungsten layer and a 69% reflection at the boundary with the piezoelectric layer. Those skilled in the art will appreciate that the reverberating sound waves within the graphite layer are in phase when reflected back into the piezoelectric layer only after an odd number of reflections from the proximal wall of the graphite layer, i.e., after the first, third, fifth, etc. reflections. It will also be noticed that the sound waves within the graphite layer are out of phase after an even number of reflections from the near wall of the graphite layer, i.e., after the second, fourth, sixth, etc. reflections.Note also that acoustic pressure waves transmitted from a graphite layer to an adjacent tungsten layer are in phase after an even number of reflections from the graphite layer's distal wall, resulting in the zeroth, second, fourth, etc. reflections traveling to the tungsten layer and experiencing constructive interference within the tungsten layer, while the first, third, fifth, etc. reflections experience destructive interference within the tungsten layer. A first-order approximation of the combined effect of each DLDB is to spread the energy of each acoustic pulse over time, causing the amplitude of each echo to decay exponentially. This results in a very low-level, exponentially decaying acoustic "tail" being added to the transducer's impulse response, as clearly shown in Figures 19a and 19b. While adding a decaying ringdown to an ultrasonic transducer's impulse response is generally undesirable, DLDBs compensate for this negative effect in two ways. First, the ringdown is very low, typically -35 dB for unidirectional applications and -50 dB for bidirectional applications. Second, the impulse response of a transducer with DLDBs is generally unaffected by the addition of optional devices such as heat sinks and electrical connections to the transducer stack. Those skilled in the art will note that if a heat sink, PCB, or other similar structure, in substantial acoustic communication with the backing, the proximal surface of the piezoelectric material, or the proximal surface of the transducer's mismatched layer, is bonded directly to the transducer, the impulse response of the transducer is typically improved by approximately -20 dB to -30 dB by interposing a DLDB stack between them, due to the superior phase reflectivity of the first layer of the DLDBs. Similarly, because energy transmitted to the backside of the DLDB stack is transmitted through the resonant layer and also spreads and decreases in amplitude over time, the amplitude of the wave arriving at the proximal surface of the DLDB pair is very small and spreads over time. Therefore, a heat sink, PCB, and / or the like can be bonded to or otherwise adjacently contacted with the proximal surface of the last DLDB stack with little or no effect on the stack's acoustic performance.If Figure 13 is adapted to present the broadband case, in-phase reflections toward the front face of the ultrasonic transducer may be observed, as out-of-phase reflections occur at other frequencies. Note that the out-of-phase reflections interfere with each other randomly and often destructively. Therefore, the out-of-phase reflections will be less significant than the in-phase reflections occurring at the designed operating frequency.

[0330] The effect of the temporal diffusion of acoustic energy within the DLDB layer can be clearly seen by observing the logarithmic envelope plots of the 680 kHz liquid-cooled transducer shown in Figures 19b and 21.

[0331] The effect of this highly effective isolation within a relatively small space is to allow direct connection of heat sinks, PCBs, soldered wires, ASICs, and other desired structures to the transducer's acoustic stack. Those skilled in the art will appreciate the benefits of being able to electrically connect, for example, by soldering, the PCB to the array's acoustic stack, and the imaging array with electrical interconnect wiring pre-soldered to the PCB, for example, via off-the-shelf high-density electrical connectors. Furthermore, those skilled in the art will appreciate that ASICs can be relatively easily affixed directly to 1D or 2D arrays without compromising acoustic performance, for example, by using anisotropic conductive tape.

[0332] Embodiments of the technology described herein are associated with several advantages presented herein. Overall, the use of DLDBs rather than existing low acoustic impedance absorbent backings or simple DML layers allows electrical components, heat sinks, or other desired structures to be directly connected to the acoustic stack in minimal (and / or limited) space. Furthermore, DLDBs can enable the assembly of transducers in more space-constrained applications, such as, for example, but not limited to, catheter-based transducers, due to the small space required by DLDBs.

[0333] In embodiments where the pair of DLDBs includes graphite and tungsten, up to 97% of the acoustic energy can be reflected in phase from the front of the transducer before reaching the back wall of the tungsten layer. If the transducer includes a second pair of DLDB layers, the second pair of DLDB layers can reduce the sound pressure reaching the back surface of the second tungsten layer by more than 70 dB, and any reflections or reverberations generated at that surface by the PCB or heat sink are further reduced as they return through the dB stack. Even if the second DLDB utilizes a second layer with low acoustic impedance, such as copper or aluminum nitride, for electrical or thermal properties, practical results are good, and in some cases, it can provide nearly complete acoustic isolation of the electrical interconnect wiring and / or heat sink from the acoustic stack.

[0334] It should be noted that the high and low acoustic impedance layers of the DLDB can be made from solid materials, such as, but not limited to, conductive acoustic composites such as diced graphite that are then sputtered after dicing and filled with epoxy to form layers with high electrical and thermal conductivity with acoustic impedances of about 2.5 MR to about 4 MR, or from silver plated microballoons that are mixed into epoxy, for example.

[0335] The electrical properties of the backing can be useful in that a conductive backing allows for direct attachment of PCBs, ASICs, or soldered or wired joints that currently adversely affect the acoustic performance of the device.

[0336] The thermal properties of the backing can also be useful in that the use of thermally conductive backing materials in DLDBs allows for efficient heat dissipation from the piezoelectric elements, which are becoming increasingly critical with the development of high performance relaxor materials such as PMN-PT and related materials.

[0337] It should be noted that from a theoretical standpoint, there is generally no limit to the range of frequencies that DLDB backing will work in. From a practical standpoint, frequencies can be used from at least 10 MHz or in some circumstances 100 kHz, and possibly up to 50 MHz or 100 MHz with sufficient process control.

[0338] Several alternative embodiments and examples are described and illustrated herein. The above-described embodiments have been described for illustrative purposes only. Those skilled in the art will recognize the features of each embodiment and the possible combinations and variations of the components. Moreover, those skilled in the art will recognize that any embodiment may be provided in any combination with the other embodiments disclosed herein. The present examples and embodiments are therefore to be considered in all respects as illustrative and not restrictive. Thus, while particular embodiments have been illustrated and described above, numerous modifications will occur to those skilled in the art without significantly departing from the scope defined herein.

Claims

1. In an ultrasonic transducer, a piezoelectric material having a front surface and a back surface, the piezoelectric material configured to be in acoustic communication with the sample; a thermally and electrically conductive backing structure disposed on the back surface of the piezoelectric material and configured to reflect acoustic energy toward the front surface of the piezoelectric material; a first two-layer mismatched backing material; a first graphite layer; and a layer of tungsten in contact with the first graphite layer; the first two-layered mismatched backing material having a second two-layer mismatched backing material in contact with the first two-layer mismatched backing material; a second graphite layer; and a copper layer in contact with the second graphite layer; the second two-layered mismatched backing material having the backing structure comprising: a heat sink in thermal contact with the backing structure; and one or more electrodes in electrical communication with the piezoelectric material; An ultrasonic transducer comprising:

2. 10. The ultrasonic transducer of claim 1, wherein the heat sink has at least one channel configured to receive and circulate a heat transfer fluid therein.

3. 3. The ultrasonic transducer according to claim 1 or 2, wherein the ultrasonic transducer is operable at an operating frequency related to an operating wavelength (λo); and an ultrasonic transducer, wherein the first graphite layer, the tungsten layer in contact with the first graphite layer, the second graphite layer, and the copper layer each have a thickness corresponding to approximately λo / 4 or an odd multiple of λo / 4;

4. 4. The ultrasonic transducer of claim 3, wherein the piezoelectric material is configured to resonate at a half-wavelength at the operating frequency.

5. 5. The ultrasonic transducer of claim 4, further comprising a single mismatching layer disposed between the piezoelectric material and the backing structure, the single mismatching layer being in acoustic communication with the piezoelectric material and the backing structure, the single mismatching layer having a corresponding acoustic impedance relatively higher than an acoustic impedance of the piezoelectric material, and the piezoelectric material being configured to resonate at a quarter wavelength at the operating frequency.

6. 6. The ultrasonic transducer of claim 5, wherein the piezoelectric material has a resonant frequency, the resonant frequency is related to a resonant wavelength λr, and the single mismatching layer has a thickness that is less than 2λr / 5 relative to the resonant frequency of the piezoelectric material.

7. 7. The ultrasonic transducer of claim 6, wherein the single mismatching layer has a thickness of about λr / 10 to about λr / 20.

8. 8. An ultrasonic transducer according to any one of claims 1 to 7, wherein the piezoelectric material is a polarized composite piezoelectric disc.

9. 9. The ultrasonic transducer of claim 1, further comprising a thermally conductive structure in contact with the backing structure.

10. 10. The ultrasonic transducer of claim 9, wherein the thermally conductive structure includes at least one electrically conductive via extending therethrough.

11. 11. An ultrasonic transducer according to any one of claims 1 to 10, wherein the backing structure is further configured to reflect the acoustic energy in phase and / or to spatially and temporally distribute undesired acoustic reverberations within the backing structure.

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