Apodizing backing structure for ultrasonic transducers and related methods - Patents.com

Abstract

An apodizing wedge structure for a LIPUS treatment head is provided. The LIPUS treatment head includes a low volume fraction piezoelectric composite disk. The apodizing wedge structure includes an annular body for contacting a surface of the piezoelectric disk, the annular body including an inner circumference having an inner thickness and an outer circumference having an outer thickness. The annular body includes a sloping surface that forms a continuous slope extending from the inner circumference to the outer circumference, the inner thickness being less than the outer thickness. The apodizing wedge is configured to change the apparent thickness of the piezoelectric disk relative to the resonant characteristics of the piezoelectric disk when the apodizing wedge structure is in acoustic communication with the piezoelectric disk, thereby enabling the LIPUS treatment head to generate a uniform near-field. A LIPUS treatment head and an ultrasound transducer including such an apodizing wedge structure are also provided.

Description

[Technical field]

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

[0002] Ultrasonic transducers are widely used in many industries and are used in a variety of applications. For example, ultrasonic transducers can be used in medical applications, including diagnostic imaging or therapeutic applications. Other applications include, but are not limited to, ultrasonic non-destructive testing and ultrasonic machining and welding. Ultrasonic transducers can be configured to convert electrical energy into mechanical energy, acoustic energy into electrical energy, or both, interchangeably.

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

[0004] The present technique relates generally to low-intensity pulsed ultrasound (LIPUS) treatment heads, and more particularly to an apodizing backing structure for a LIPUS treatment head configured to generate a substantially uniform near-field or to generate an acoustic field including at least one substantially uniform near-field component or portion.

[0005] According to one aspect, an ultrasonic transducer is provided, comprising: a low volume fraction piezoelectric composite disk having resonant properties; at least one electrode in electrical contact with the low volume fraction piezoelectric composite disc; and an annular apodizing backing structure in acoustic contact with the low volume fraction piezoelectric composite disk, the annular apodizing backing structure comprising: an inner circumference and corresponding inner thickness; a circumference and corresponding outer thickness; a sloped surface forming a substantially continuous slope extending from the inner periphery to the outer periphery, the inner thickness being less than the outer thickness; The annular apodizing backing structure is configured to vary the apparent thickness of the low volume fraction piezoelectric composite disk relative to a resonant characteristic of the low volume fraction piezoelectric composite disk, thereby enabling the ultrasonic transducer to generate an acoustic field that includes at least one substantially uniform near-field portion.

[0006] In some embodiments, the ultrasound transducer further comprises a circuit board. In some embodiments, the circuit board is a printed circuit board. In some embodiments, the printed circuit board is a ring-shaped printed circuit board.

[0007] In some embodiments, the low volume fraction piezoelectric composite disk is in a 1 / 3 configuration.

[0008] In some embodiments, the low volume fraction piezoelectric composite disk comprises 280 μm×280 μm pillars distributed in a 2D matrix pattern with a pitch of about 480 μm in both transverse axes.

[0009] In some embodiments, the low volume fraction piezoelectric composite disk is configured to operate in a half-wave resonant mode at 1.5 MHz.

[0010] In some embodiments, the low volume fraction piezoelectric composite disk has an acoustic impedance that falls within the range extending from about 9 MR to about 13 MR.

[0011] In some embodiments, the acoustic impedance is about 11 MR.

[0012] In some embodiments, the low volume fraction piezoelectric composite disk has a thickness of about λ / 2 at 1.5 MHz.

[0013] In some embodiments, the low volume fraction piezoelectric composite disk comprises a Lead Zirconate Titanate (PZT) based material.

[0014] In some embodiments, the PZT based material is PZT5H.

[0015] In some embodiments, the low volume fraction piezoelectric composite disk comprises about 35% PZT5H and about 65% polymer matrix.

[0016] In some embodiments, the polymer matrix comprises an epoxy filled with microglass balloons and silicone particles.

[0017] In some embodiments, the PZT5H pillars have a first bar mode longitudinal acoustic velocity and the polymer matrix has a second longitudinal acoustic velocity, the second longitudinal velocity being approximately 60%-70% of the first longitudinal velocity.

[0018] In some embodiments, the first longitudinal bar mode acoustic velocity is about 3850 m / s and the second longitudinal acoustic velocity is about 251 m / s.

[0019] In some embodiments, the ultrasonic transducer further comprises a ring-shaped printed circuit board having an inner diameter, and the low volume fraction piezoelectric composite disc has an outer diameter, the inner diameter of the ring-shaped printed circuit board being greater than the outer diameter of the low volume fraction piezoelectric composite disc.

[0020] In some embodiments, the ultrasound transducer further includes a housing, the housing being made from plastic.

[0021] In some embodiments, the housing includes a matching layer in acoustic communication with the low volume fraction piezoelectric composite disk.

[0022] In some embodiments, the matching layer has a thickness of about λ / 4.

[0023] In some embodiments, the matching layer is integrally formed with the housing.

[0024] In some embodiments, the matching layer has an acoustic impedance that falls within the range extending from about 2.1 MR to about 2.5 MR.

[0025] In some embodiments, the acoustic impedance is about 2.3 MR.

[0026] In some embodiments, the ultrasonic transducer further comprises a 2λ / 3 acoustic layer in acoustic communication with the low volume fraction piezoelectric composite disk.

[0027] In some embodiments, the 2λ / 3 acoustic layer is made from nonyl plastic and has a thickness of about 953 μm.

[0028] In some embodiments, the ultrasonic transducer further comprises a 0.9λ acoustic layer in acoustic communication with the low volume fraction piezoelectric composite disk.

[0029] In some embodiments, the 0.9λ acoustic layer is made from nonyl plastic and has a thickness of about 1.28 mm.

[0030] In some embodiments, the ring-shaped printed circuit board includes two opposing planar surfaces, each planar surface being made from copper.

[0031] In some embodiments, a ring-shaped printed circuit board is bonded to the periphery of the low volume fraction piezoelectric composite disk.

[0032] In some embodiments, the ultrasonic transducer further includes an inductor connected in parallel with the piezoelectric composite of the low volume fraction piezoelectric composite disk, the inductor configured to resonate with the low volume fraction piezoelectric composite disk, the annular apodizing backing structure, and the ¼ lambda acoustic matching layer such that an impedance maximum is generated at approximately 1.5 MHz when the distal face of the transducer is air-loaded.

[0033] In some embodiments, the ultrasonic transducer further includes an inductor connected in series with the low volume fraction piezoelectric composite disk, the inductor configured to resonate with the low volume fraction piezoelectric composite disk, the annular apodizing backing structure, and the ¼ lambda matching layer such that an impedance minimum is generated at approximately 1.5 MHz when the distal face of the transducer is air-loaded.

[0034] In some embodiments, the annular apodizing backing structure comprises Epotek 301 epoxy.

[0035] In some embodiments, the annular apodizing backing structure has an acoustic impedance of about 2.8 MR.

[0036] In some embodiments, the tilt is comprised between 0 degrees and 30 degrees.

[0037] In some embodiments, the slope is about 14 degrees relative to the top surface of the low volume fraction piezoelectric composite disk.

[0038] In some embodiments, the ultrasonic transducer is operable at a frequency of about 1.5 MHz.

[0039] In some embodiments, the ultrasonic transducer is operable in a narrow bandwidth tone burst mode.

[0040] In some embodiments, the narrow bandwidth tone burst mode is a 20% duty cycle sinusoidal pulse mode, preferably at a pulse repetition frequency of about 1 kHz.

[0041] In some embodiments, the ultrasound transducer has a beam nonuniformity ratio of less than 3.5.

[0042] In some embodiments, when the ultrasonic transducer is operated at 1.5 MHz using a 20% pulsed transmit waveform, at least one substantially uniform near-field component or portion exhibits less than 2 dB ripple at a plane located approximately 3 mm from the outer surface of the ultrasonic transducer.

[0043] According to another aspect, a low power pulsed wave ultrasound (LIPUS) treatment head having an operating frequency, the LIPUS treatment head comprising: 1. An acoustic stack comprising: a piezoelectric disc, the piezoelectric disc comprising a low volume fraction piezoelectric composite disc, the low volume fraction piezoelectric composite disc configured to operate in a half wave resonant mode at an operating frequency of the LIPUS treatment head; an annular apodizing backing structure in acoustic communication with the low volume fraction piezoelectric composite disc, the annular apodizing backing structure having an inner periphery and an outer periphery, each having an inner thickness and an outer thickness, the inner thickness being less than the outer thickness, the annular apodizing backing structure being configured to vary an apparent thickness of the low volume fraction piezoelectric composite disc relative to a resonant characteristic of the low volume fraction piezoelectric composite disc, thereby enabling the LIPUS treatment head to generate an acoustic field including at least one substantially uniform near-field portion; at least one electrode in electrical communication with the low volume fraction piezoelectric composite disc; A LIPUS treatment head is provided that includes an acoustic stack and a housing for supporting at least one electrode.

[0044] In some embodiments, the LIPUS treatment head further comprises a circuit board. In some embodiments, the circuit board is a printed circuit board. In some embodiments, the printed circuit board is a ring-shaped printed circuit board.

[0045] In some embodiments, the low volume fraction piezoelectric composite disk is in a 1 / 3 configuration.

[0046] In some embodiments, the low volume fraction piezoelectric composite disk comprises 280 μm×280 μm pillars distributed in a 2D matrix pattern with a pitch of about 480 μm in both transverse axes.

[0047] In some embodiments, the operating frequency of the LIPUS treatment head is about 1.5 MHz.

[0048] In some embodiments, the low volume fraction piezoelectric composite disk has an acoustic impedance that falls within the range extending from about 9 MR to about 13 MR.

[0049] In some embodiments, the acoustic impedance is about 11 MR.

[0050] In some embodiments, the low volume fraction piezoelectric composite disk has a thickness of about λ / 2 at 1.5 MHz.

[0051] In some embodiments, the low volume fraction piezoelectric composite disk comprises a Lead Zirconate Titanate (PZT) based material.

[0052] In some embodiments, the PZT based material is PZT5H.

[0053] In some embodiments, the low volume fraction piezoelectric composite disk comprises about 35% PZT5H and about 65% polymer matrix.

[0054] In some embodiments, the polymer matrix comprises an epoxy filled with microglass balloons and silicone particles.

[0055] In some embodiments, the PZT5H pillars have a first bar mode longitudinal acoustic velocity and the polymer matrix has a second longitudinal acoustic velocity, the second longitudinal velocity being approximately 60-70% of the first longitudinal velocity.

[0056] In some embodiments, the first longitudinal acoustic velocity is about 3850 m / s and the second longitudinal acoustic velocity is about 2515 m / s.

[0057] In some embodiments, the ring-shaped printed circuit board has an inner diameter and the low volume fraction piezoelectric composite disc has an outer diameter, the inner diameter of the ring-shaped printed circuit board being greater than the outer diameter of the low volume fraction piezoelectric composite disc.

[0058] In some embodiments, the housing is made from plastic.

[0059] In some embodiments, the housing includes a matching layer in acoustic communication with the low volume fraction piezoelectric composite disk.

[0060] In some embodiments, the matching layer has a thickness of about λ / 4.

[0061] In some embodiments, the matching layer is integrally formed with the housing.

[0062] In some embodiments, the matching layer has an acoustic impedance that falls within the range extending from about 2.1 MR to about 2.5 MR.

[0063] In some embodiments, the acoustic impedance is about 2.3 MR.

[0064] In some embodiments, the LIPUS treatment head further comprises a 2λ / 3 acoustic layer in acoustic communication with the low volume fraction piezoelectric composite disc.

[0065] In some embodiments, the 2λ / 3 acoustic layer is made from nonyl plastic and has a thickness of about 953 μm.

[0066] In some embodiments, the LIPUS treatment head further comprises a 0.9λ acoustic layer in acoustic communication with the low volume fraction piezoelectric composite disc.

[0067] In some embodiments, the 0.9λ acoustic layer is made from nonyl plastic and has a thickness of about 1.28 mm.

[0068] In some embodiments, the ring-shaped printed circuit board includes two opposing planar surfaces, each planar surface being made from copper.

[0069] In some embodiments, a ring-shaped printed circuit board is bonded to the outer periphery of the low volume fraction piezoelectric composite disk.

[0070] In some embodiments, the LIPUS treatment head further includes an inductor connected in parallel with the piezoelectric composite of the low volume fraction piezoelectric composite disk, the inductor configured to resonate with the low volume fraction piezoelectric composite disk, the annular apodizing backing structure, and the ¼ lambda acoustic matching layer such that an impedance maximum is generated at approximately 1.5 MHz when the distal face of the transducer is air loaded.

[0071] In some embodiments, the LIPUS treatment head further includes an inductor connected in series with the piezoelectric composite of the low volume fraction piezoelectric composite disk, the inductor configured to resonate with the low volume fraction piezoelectric composite disk, the annular apodizing backing structure, and the ¼ lambda matching layer such that an impedance minimum is generated at approximately 1.5 MHz when the distal face of the transducer is air loaded.

[0072] In some embodiments, the annular apodizing backing structure comprises Epotek 301 epoxy.

[0073] In some embodiments, the annular apodizing backing structure has an acoustic impedance of about 2.8 MR.

[0074] In some embodiments, the tilt is comprised between 0 degrees and 30 degrees.

[0075] In some embodiments, the slope is about 14 degrees relative to the top surface of the low volume fraction piezoelectric composite disk.

[0076] In some embodiments, the operating frequency of the LIPUS treatment head is about 1.5 MHz.

[0077] In some embodiments, the LIPUS treatment head is operable in a narrow bandwidth tone burst mode.

[0078] In some embodiments, the narrow bandwidth tone burst mode is a 20% duty cycle sine wave pulse mode.

[0079] In some embodiments, the LIPUS treatment head has a beam nonuniformity ratio of less than 3.5.

[0080] In some embodiments, when the LIPUS treatment head is operated at 1.5 MHz using a 20% pulsed transmit waveform, at least one substantially uniform near-field component or portion exhibits less than 2 dB ripple at a plane located approximately 3 mm from the outer surface of the LIPUS treatment head.

[0081] According to another aspect, an apodizing wedge structure for a low power pulsed wave ultrasound (LIPUS) treatment head is provided, the LIPUS treatment head including a low volume fraction piezoelectric composite disk, the apodizing wedge structure comprising: an annular body for contacting a surface of the low volume fraction piezoelectric composite disk, the annular body including an inner periphery having a corresponding inner thickness and an outer periphery having a corresponding outer thickness; The annular body includes an inclined surface that forms a substantially continuous slope extending from the inner circumference to the outer circumference, the inner thickness being less than the outer thickness, and when the apodizing wedge structure is in acoustic communication with the low volume fraction piezoelectric composite disk, the apodizing wedge is configured to vary the apparent thickness of the low volume fraction piezoelectric composite disk in response to the resonant characteristics of the low volume fraction piezoelectric composite disk, thereby enabling the LIPUS treatment head to generate an acoustic field that includes at least one substantially uniform near-field component or portion.

[0082] In some embodiments, the toroid is made from Epotek 301 epoxy.

[0083] In some embodiments, the toroid has an acoustic impedance of about 2.8 MR.

[0084] In some embodiments, the tilt is comprised between 0 degrees and 30 degrees.

[0085] In some embodiments, the slope is about 14 degrees relative to the top surface of the low volume fraction piezoelectric composite disk.

[0086] In some embodiments, the LIPUS treatment head is capable of operating at a frequency of about 1.5 MHz.

[0087] In some embodiments, the LIPUS treatment head is operable in a narrow bandwidth tone burst mode.

[0088] In some embodiments, the narrow bandwidth tone burst mode is a 20% duty cycle sine wave pulse mode.

[0089] In some embodiments, the LIPUS treatment head has a beam nonuniformity ratio of less than 3.5.

[0090] In some embodiments, when the LIPUS treatment head is operated at 1.5 MHz using a 20% pulsed transmit waveform, at least one substantially uniform near-field component or portion exhibits less than 2 dB ripple at a plane located approximately 3 mm from the outer surface of the LIPUS treatment head.

[0091] According to another aspect, a backing structure for a low power pulsed wave ultrasound (LIPUS) treatment head, the LIPUS treatment head including a low volume fraction piezoelectric composite element, the backing structure comprising: A backing structure is provided that includes a body for contacting a surface of the low volume fraction piezoelectric composite element, where when the body contacts the low volume fraction piezoelectric composite element, destructive interference is generated within the backing structure and the low volume fraction piezoelectric component, thereby shaping the acoustic field generated by the LIPUS treatment head, the destructive interference being dependent on a thickness of the backing structure.

[0092] In some embodiments, destructive interference results in maximum attenuation at approximately λ / 4 or an odd multiple thereof.

[0093] In some embodiments, the body is made from Epotek 301 epoxy.

[0094] In some embodiments, the LIPUS treatment head is capable of operating at a frequency of about 1.5 MHz.

[0095] In some embodiments, the LIPUS treatment head is operable in a narrow bandwidth tone burst mode.

[0096] In some embodiments, the narrow bandwidth tone burst mode is a 20% duty cycle sine wave pulse mode.

[0097] In some embodiments, the LIPUS treatment head has a beam nonuniformity ratio of less than 3.5.

[0098] In some embodiments, the acoustic field includes at least one substantially uniform near-field component or portion, and when the LIPUS treatment head is operated at 1.5 MHz using a 20% pulsed transmit waveform, the at least one substantially uniform near-field portion exhibits less than 2 dB ripple at a plane located approximately 3 mm from the outer surface of the LIPUS treatment head.

[0099] According to another aspect, a method of apodizing an acoustic field is provided, the method comprising: operating an ultrasonic transducer to generate an acoustic field, the ultrasonic transducer including a low volume fraction piezoelectric composite disk, the low volume fraction piezoelectric composite having resonant properties; and conditioning the acoustic field with an annular apodizing backing structure to generate an apodized acoustic field, the apodized acoustic field including at least one substantially uniform near-field component or portion, the annular apodizing backing structure being in acoustic contact with the low volume fraction piezoelectric composite disk, the annular apodizing backing structure comprising: an inner circumference and corresponding inner thickness; a circumference and corresponding outer thickness; a ramp surface forming a substantially continuous slope extending from the inner periphery to the outer periphery, the inner thickness being less than the outer thickness; The annular apodizing backing structure is configured to change the apparent thickness of the low volume fraction piezoelectric composite disk relative to the resonant characteristics of the low volume fraction piezoelectric composite disk.

[0100] In some embodiments The ultrasonic transducer was operated at 1.5 MHz using a 20% pulsed transmit waveform. At least one substantially uniform near-field component or portion exhibits less than 2 dB ripple at a plane located approximately 3 mm from the outer surface of the ultrasonic transducer.

[0101] In some embodiments, the low volume fraction piezoelectric composite disk is in a 1 / 3 configuration.

[0102] In some embodiments, the low volume fraction piezoelectric composite disk comprises 280 μm×280 μm pillars distributed in a 2D matrix pattern with a pitch of about 480 μm in both transverse axes.

[0103] According to another aspect, a method is provided for generating an acoustic field using a Low Power Pulsed Wave Ultrasound (LIPUS) treatment head having an operating frequency, the method comprising: Operate LIPUS treatment to generate an acoustic field, the LIPUS treatment head comprising: 1. An acoustic stack comprising: a piezoelectric disc, the piezoelectric disc comprising a low volume fraction piezoelectric composite disc, the low volume fraction piezoelectric composite disc configured to operate in a half wave resonant mode at an operating frequency of the LIPUS treatment head; an acoustic stack comprising: an annular apodizing backing structure in acoustic communication with the low volume fraction piezoelectric composite disk, the annular apodizing backing structure having an inner periphery and an outer periphery, each having an inner thickness and an outer thickness, the inner thickness being less than the outer thickness; at least one electrode in electrical communication with the low volume fraction piezoelectric composite disc; a housing for supporting the acoustic stack and the at least one electrode; A method is provided that includes adjusting an acoustic field with an annular apodizing backing structure to generate an apodized acoustic field, the apodized acoustic field including at least one substantially uniform near-field component or portion.

[0104] In some embodiments, the LIPUS treatment head further comprises a circuit board. In some embodiments, the circuit board is a printed circuit board. In some embodiments, the printed circuit board is a ring-shaped printed circuit board.

[0105] In some embodiments The ultrasonic transducer was operated at 1.5 MHz using a 20% pulsed transmit waveform. At least one substantially uniform near-field component or portion exhibits less than 2 dB ripple at a plane located approximately 3 mm from the outer surface of the ultrasonic transducer.

[0106] In some embodiments, the low volume fraction piezoelectric composite disk is in a 1 / 3 configuration.

[0107] In some embodiments, the low volume fraction piezoelectric composite disk comprises 280 μm×280 μm pillars distributed in a 2D matrix pattern with a pitch of about 480 μm in both transverse axes.

[0108] Other features and advantages of the present description will appear more clearly on reading the following non-limiting description of particular embodiments thereof, given by way of example only with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0109] [Figure 1] 1 illustrates an ultrasound transducer according to one embodiment. [Diagram 2] 2 illustrates an exploded view of the ultrasonic transducer shown in FIG. 1. [Diagram 3] 2 illustrates an exploded view of the ultrasonic transducer shown in FIG. 1. [Figure 4] FIG. 2 is a cross-sectional perspective view of a low volume fraction piezoelectric composite disk in acoustic communication with an annular backing structure according to one embodiment. [Diagram 5] FIG. 5 is another cross-sectional perspective view of the low volume fraction piezoelectric composite disk in acoustic communication with the annular backing structure shown in FIG. [Figure 6] FIG. 2 is an exploded view of a low volume fraction piezoelectric composite disk and annular backing structure according to one embodiment. [Figure 7] FIG. 7 is another view of the low volume fraction piezoelectric composite disk and PSPCB structure shown in FIG. [Figure 8] FIG. 7 is another view of the low volume fraction piezoelectric composite disk and annular backing structure shown in FIG. [Figure 9] 1 shows a linear graph of the pressure intensity response of a conventional ultrasound transducer (left part) and of an ultrasound transducer designed according to the present technique (right part). [Figure 10] 1 shows a simulated field (top left portion) showing the outer maximum ring present within the 3 mm field of a 1 / 3 composite system LIPUS treatment head without an apodization ring or structure, a measured acoustic field (top right portion) showing the outer maximum ring present within the 3 mm field of a 1 / 3 composite system LIPUS treatment head, a simulated field (bottom left portion) showing the suppressed outer maximum ring resulting from including an apodizing wedge (or "annular apodizing backing structure") on the rear peripheral portion of the 1 / 3 composite system disc, and a measured acoustic field (bottom right portion) from a prototype LIPUS treatment head showing the suppressed outer maximum ring achieved by an apodizing ring (or annular apodizing backing structure) on the 1 / 3 composite system disc. [Figure 11] Shown is the intensity measured at a 3 mm plane and at the plane containing the final axial maximum for a LIPUS treatment head incorporating the present technique. [Figure 12A] FIG. 12A shows the effect of air loading without an inductor (FIG. 12B) compared to air loading with a parallel inductor configured to resonate at 1.5 MHz of the present technology, where the parallel inductor resonance is tuned to match the operating frequency when the ultrasonic transducer is air loaded. [Figure 12B] FIG. 12A shows the effect of air loading without an inductor (FIG. 12B) compared to air loading with a parallel inductor configured to resonate at 1.5 MHz of the present technology, where the parallel inductor resonance is tuned to match the operating frequency when the ultrasonic transducer is air loaded. [Figure 13A] 1 shows the impedance of a non-limiting embodiment of a LIPUS treatment head having a λ / 4 matching layer and a resonant parallel inductor with air and water loading. [Figure 13B]1 shows the impedance of an exemplary transducer of a non-limiting embodiment of a LIPUS treatment head with a λ / 4 matching layer but without a resonant inductor, along with air and water load cases. [Figure 14] 13 is a 3D plot of the apodized acoustic field produced using the present technique, measured in a water tank with a hydrophone, at a plane located 3 mm from the distal surface of the treatment head. [Figure 15] A 2λ / 3 front layer is shown tuned to provide an impedance maximum (shown in the bottom half of the figure) at the operating frequency in air without the use of an in-circuit resonant inductor, compared to the response in water (shown in the top half of the figure), with the air-coupled maximum being approximately 5 times higher than the water-coupled minimum. [Figure 16] It shows a 0.9λ front layer tuned to provide an impedance minimum in air (shown in the bottom half of the figure) and a higher impedance when water-coupled (shown in the top portion of the figure), with the air-coupled impedance minimum being approximately 3 times lower than when water-coupled (bottom portion). [Figure 17A] The axial pressure response of an ultrasonic transducer according to the present technique is shown in Fig. 17A, which shows a highly uniform on-axis pressure field in the first 10 cm of the near-field and the absence of high amplitude peaks throughout the near-field. Fig. 17B shows the lack of near-field axial uniformity seen in the absence of an apodized backing structure and corresponding acoustic field. [Figure 17B] The axial pressure response of an ultrasonic transducer according to the present technique is shown in Fig. 17A, which shows a highly uniform on-axis pressure field in the first 10 cm of the near-field and the absence of high amplitude peaks throughout the near-field. Fig. 17B shows the lack of near-field axial uniformity seen in the absence of an apodized backing structure and corresponding acoustic field. [Figure 18] 1 shows the local attenuation of a transmitted acoustic field due to destructive interference produced by the presence of a backing structure versus the thickness of the backing structure as a fraction of a wavelength. [Figure 19]1 illustrates a method of achieving an impedance difference at the operating frequency of the device, where the magnitude of the air impedance is several times lower than the water impedance, achieved using a series resonant inductor; this configuration produces similar results to those seen with a 0.9λ matching layer, but uses a series resonant inductor and a λ / 4 matching layer. [Figure 20A] 1 shows a cross-sectional perspective view of an ultrasonic transducer according to another embodiment. [Figure 20B] 1 shows a cross-sectional perspective view of an ultrasonic transducer according to another embodiment. [Figure 20C] 1 shows a cross-sectional perspective view of an ultrasonic transducer according to another embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0110] In the following description, like features in the figures are given like reference numbers, and some elements may not be shown in some figures if they have already been identified in one or more previous figures, so as not to unduly distract from the figures. It should also be understood that the elements in the figures are not necessarily drawn to scale, with emphasis being placed on clearly illustrating the elements and structures of the present embodiment. The terms "a", "an" and "one" are defined herein to mean "at least one", i.e., these terms do not exclude a plurality of elements, unless otherwise stated. It should be noted that terms such as "substantially", "generally, generally", and "about" that 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 tolerance for the proper operation of this exemplary embodiment for its intended use.

[0111] In this description, the terms "connected" and "coupled," along with their derivatives and variations, refer to any connection or coupling, either direct or indirect, between two or more elements. The connection or coupling between the elements may be acoustic, mechanical, physical, optical, operational, electrical, wireless, or a combination thereof.

[0112] The terms "to," "matching," and "matched," as used herein, are intended to refer to a state in which two elements are the same or within some predetermined tolerance of one another. That is, these terms are meant to encompass not only "exactly" or "identically" matching two elements, but also "substantially," "approximately," or "subjectively" matching two elements, as well as providing a higher or best match among multiple possible matches.

[0113] In this description, the phrase "based on" is intended to mean "based at least in part on," i.e., it can mean "based only on" or "based in part on," and therefore should not be interpreted as limiting. More specifically, the phrase "based on" can be understood to mean "depends on," "represents," "indicates," "associated with," or similar phrases.

[0114] It will be understood that positional descriptors indicating the location or orientation of one element relative to another are used herein for ease and clarity of description and, unless otherwise indicated, should be interpreted in the context of the drawings and should not be considered limiting. It will be understood that spatially relative terms (e.g., "external" and "internal", "outer" and "inner", "periphery" and "center", "upper" and "lower", and "top" and "bottom") are intended 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.

[0115] The present description generally relates to an ultrasonic transducer assembly, and more specifically to a LIPUS treatment head configured to generate a substantially uniform near-field (or an acoustic field including at least one substantially uniform near-field component or portion), and related methods. The present technology and its advantages will become more apparent from the following detailed description and examples that describe various embodiments of the technology. More specifically, the following description presents a LIPUS treatment head that can be used for therapeutic applications. Therapeutic applications include, but are not limited to, the treatment of living tissue, bone, cartilage, tendons, and the like. For example, the present technique can be used to treat tissue damage or to assist bone healing.

[0116] In the context of the present disclosure, the terms "apodizing", "apodization", "apodized", their synonyms and derivatives refer to techniques that can be used to change, modify or shape a field intensity profile, such as, but not limited to, the spatial profile of an acoustic field. In some embodiments, the apodization technique can be used to spatially attenuate the acoustic field at its edges, or along its "periphery", or at least in a portion thereof. Notably, the present technology allows for the acquisition or generation of an apodized acoustic field using an apodizing or backing structure that is provided at the rear of an ultrasonic transducer and allows for the acquisition or generation of an apodized acoustic field by taking advantage of the destructive interference generated therein, without relying on techniques for absorbing energy.

[0117] Although the ultrasound transducer embodiments described throughout the description are described as including a piezoelectric material, those skilled in the art will note that the ultrasound transducers of the present disclosure may instead include any ferroelectric material, any single crystal or polycrystalline material, any electromechanical transducer material, such materials having one or more of the following properties: ferroelectric, pyroelectric, piezoelectric, electrostrictive, and / or other related properties. It should be noted that in the context of this specification, the expression "piezoelectric material" may also refer to ferroelectric, pyroelectric, relaxor, and electrostrictive materials, as will be readily understood by those skilled in the art.

[0118] According to one aspect, referring to Figs. 1-19A, 19B, an ultrasonic transducer 20 is provided. Broadly described, the ultrasonic transducer 20 includes a low volume fraction piezoelectric composite disk 22 having a resonant characteristic, at least one electrode (which may be embodied or replaced by a ring-shaped printed circuit board 24), and an annular backing structure 26 configured to provide attenuation of the acoustic field generated by the low volume fraction piezoelectric transducer disk 22 based on local destructive interference. In some embodiments, the ultrasonic transducer 20 may include a low volume fraction piezoelectric composite element instead of a disk. In these embodiments, the low volume fraction piezoelectric composite element may be embodied by various plate structures and shapes, such as, but not limited to, rectangular, annular, or curved piezoelectric structures, e.g., curved focusing composite plates. The annular apodizing backing structure 26 is configured to vary the apparent thickness of the low volume fraction piezoelectric composite disk 22 relative to the resonant characteristics of the low volume fraction piezoelectric composite disk 22, thereby enabling the ultrasonic transducer 20 to generate a substantially uniform near-field or an acoustic field including at least one substantially uniform near-field component or portion. Interactions between the low volume fraction piezoelectric composite disk 22, the annular apodizing backing structure 26, and other components of the ultrasonic transducer 20, such as electrodes, allow the acoustic or "apparent" thickness of the low volume fraction piezoelectric composite disk 22 to be effectively varied without changing the actual or "real" or "physical" thickness of the low volume fraction piezoelectric composite disk 22. Also, the acoustic or "apparent" thickness of the low volume fraction piezoelectric composite disk 22 can be effectively varied without substantially changing the electrical impedance of the low volume fraction piezoelectric composite disk 22. Thus, it is possible to change the resonant frequency of the low volume fraction piezoelectric composite disk 22 without changing the wavelength or electroacoustic frequency of the waves generated by the piezoelectric material forming the low volume fraction piezoelectric disk 22, shifting the resonant characteristics of the low volume fraction piezoelectric composite disk 22 rather than the electroacoustic frequency response of the low volume fraction piezoelectric composite disk 22 itself.As the thickness of the apodizing backing structure 26 approaches ¼ lambda or an odd multiple of ¼ lambda, for example ¾ lambda or 5 / 4 lambda, strong destructive interference is generated within the low volume fraction piezoelectric composite disk 22 and the backing structure 26, resulting in attenuation of the acoustic field in the region of the backing structure 26. In some embodiments, the backing structure 26 can be a wedge located around the periphery of the low volume fraction piezoelectric composite disk 22 and can function as an apodizing backing structure. In some embodiments, the ultrasonic transducer 20 is configured to operate in a relatively narrowband mode, since the effect of the annular apodizing backing structure 26 has a relatively strong effect in narrowband operating modes, including, for example, but not limited to, toneburst or CW. In some embodiments, the annular apodizing backing structure 26 allows the transmitted acoustic power of the low volume fraction piezoelectric composite disk 22 in the region of the annular apodizing structure 26 to be reduced by more than 25 dB. The ultrasonic transducer 20 operates in a similar manner in a receive mode. The effect of the annular apodizing backing structure 26 can have a limited damping effect on broadband modes of operation, since the phase changes produced by the apodizing backing structure 26 can result in destructive interference within the low volume fraction piezoelectric composite disk 22 only if there are a sufficient number of cycles within the pulse to interfere within the disk. This technique can be relatively effective for more than about 5 cycles, but even very short single cycle or impulse type waveforms can be beneficial in some applications. The annular apodizing backing structure 26 allows for damping and shaping of the edges of the acoustic field, generally producing a smooth transition from the peak value of the acoustic field and the edges of the acoustic field. This modification of the field edges reduces side lobes, reduces transverse modes within the piezo elements, and improves the uniformity of the edges of the beam. This technique for modifying the edges and characteristics of the acoustic field, thus smoothing and potentially shaping the perimeter of the acoustic field, is referred to herein as apodization of acoustic fields typically produced using only the low volume fraction piezoelectric composite disk 22, i.e., producing an apodized acoustic field.It should be noted that this destructive interference based backing structure 26 can be used not only for apodizing the field perimeter, but also for general beam shaping.

[0119] Having generally described the ultrasonic transducer 20, different embodiments of the low volume fraction piezoelectric composite disk 22, the ring-shaped printed circuit 24, and the annular apodizing backing structure 26 are presented.

[0120] In some embodiments, the low volume fraction piezoelectric composite disk 22 may include square pillars 28. For example, and without limitation, the dimensions of the square pillars 28 may be about 280 μm by about 280 μm per pillar 28. The square pillars 28 may be distributed in a 2D matrix pattern with a pitch of about 480 μm in both transverse axes. Notably, the transverse axes extend in a plane parallel to one surface of the low volume fraction piezoelectric composite disk 22, i.e., each transverse axis is parallel to a corresponding one of the radii or diameters of the low volume fraction piezoelectric composite disk 22.

[0121] The ultrasonic transducer 20 is generally configured to operate at an operating frequency, and the low volume fraction piezoelectric composite disk 22 is configured to operate in a mode that substantially matches the operating frequency of the ultrasonic transducer 20. In some embodiments, the operating frequency of the ultrasonic transducer 20 is 1.5 MHz, and the low volume fraction piezoelectric composite disk 22 is configured to operate in a half-wave resonant mode at 1.5 MHz.

[0122] In some embodiments, the low volume fraction piezoelectric composite disk 22 has an acoustic impedance included in a range extending from about 9 MR to about 13 MR. In some embodiments, the acoustic impedance is about 11 MR. It is noted that the low volume fraction piezoelectric composite disk 22 can include any material or combination of materials that allows the recited acoustic impedance to be reached. For example, without limitation, in some embodiments, the low volume fraction piezoelectric composite disk 22 can include about 35% PZT5H and about 65% polymer matrix. The polymer matrix can include epoxy filled with microglass balloons and silicone particles. In some embodiments, the PZT5H has a first longitudinal acoustic velocity and the polymer matrix has a second longitudinal acoustic velocity, the second longitudinal acoustic velocity being equal to approximately 60% to 70% of the first longitudinal acoustic velocity. For example, without limitation, the first longitudinal acoustic velocity can be about 3850 m / s and the second longitudinal acoustic velocity can be about 2515 m / s.

[0123] In some embodiments, the low volume fraction piezoelectric composite disk 22 has a thickness of about λ / 2 at the operating frequency of the ultrasonic transducer. For example, and without limitation, the thickness of the low volume fraction piezoelectric composite disk 22 can be about λ / 2 at about 1.5 MHz.

[0124] As shown, a ring-shaped printed circuit board 24 is in electrical contact with the low volume fraction piezoelectric composite disk 22 .

[0125] In some embodiments, the ring-shaped printed circuit board 24 has an inner diameter and the low volume fraction piezoelectric composite disc 22 has an outer diameter. As shown, the inner diameter of the ring-shaped printed circuit board 24 can be greater than the outer diameter of the low volume fraction piezoelectric composite disc 22. In some embodiments, the ultrasonic transducer 20 further includes a housing 30. The housing 30 can be made of plastic. In some embodiments, the housing 30 can include a matching layer in acoustic communication with the low volume fraction piezoelectric composite disc 22. The matching layer can be integrally formed with the housing or alternatively provided as a separate component. In some embodiments, the matching layer can have a thickness of about λ / 4. In some embodiments, the matching layer can have an acoustic impedance included in a range extending from about 2.1 MR to about 2.5 MR. In some embodiments, the acoustic impedance can be about 2.3 MR.

[0126] In some embodiments, the ultrasonic transducer 20 further includes a 2λ / 3 acoustic layer in acoustic communication with the low volume fraction piezoelectric composite disk 22. In some embodiments, the 2λ / 3 acoustic layer may be made from nonyl plastic. Of note, other materials may be used. In some embodiments, the 2λ / 3 acoustic layer may have a thickness of about 953 μm.

[0127] In some embodiments, the ultrasonic transducer 20 further includes a 0.9λ acoustic layer in acoustic communication with the low volume fraction piezoelectric composite disc 22. In some embodiments, the 0.9λ acoustic layer may be made from nonyl plastic. Of note, other materials may be used. In some embodiments, the 0.9λ acoustic layer may have a thickness of about 1.28 mm.

[0128] In some embodiments, the ring-shaped printed circuit board 24 includes two opposing planar surfaces, with each planar surface being made from copper.

[0129] In some embodiments, a ring-shaped printed circuit board 24 is bonded to the periphery of the low volume fraction piezoelectric composite disc 22 .

[0130] In some embodiments, an inductor is provided connected in parallel with the piezoelectric composite of the low volume fraction piezoelectric composite disk 22, and the inductor is configured to electrically resonate with the acoustic stack, including the low volume fraction piezoelectric composite disk 22, the annular apodizing backing structure 26, and the ¼ lambda matching layer, such that an electrical impedance maximum is generated at approximately 1.5 MHz when the distal face of the ultrasonic transducer 20 is air loaded.

[0131] In some other embodiments, an inductor may be configured in series with the low volume fraction piezoelectric composite to provide an impedance minimum rather than an impedance maximum, as shown in Figures 19A, 19B, which are presented in more detail below.

[0132] The annular apodizing backing structure 26 is in acoustic contact with the low volume fraction piezoelectric composite disk 22. The annular apodizing backing structure 26 includes an inner periphery 32 having a corresponding inner thickness 34 and an outer periphery 36 having a corresponding outer thickness 38. The annular apodizing backing structure 26 includes a sloped surface 40 that forms a substantially continuous slope extending from the inner periphery 32 to the outer periphery 36. The inner thickness 34 is less than the outer thickness 28.

[0133] It should be noted that the apodizing backing structure 26 may have any shape or configuration that allows for shaping the acoustic field to reach a predetermined target, which may be determined by the intended application. For example, but not by way of limitation, the apodizing backing structure 26 may have a surface profile that includes a non-monotonic curve, a non-continuous curve, or even a non-continuous step. The geometry of the backing structure 26 depends on the need for apodizing, i.e., the optimal shape or profile of the acoustic field, or the optimal transition in the profile of the acoustic field. It should be noted that the present technique, which relies on attenuating an acoustic field or a portion thereof using destructive interference, is generally flexible and can be used to improve the acoustic properties of a wide variety of ultrasound transducers. For example, but not by way of limitation, the techniques described herein may be used with kerfless arrays or to shape the directivity of an acoustic field generated by annular array elements.

[0134] In some embodiments, the annular apodizing backing structure 26 may include Epotek 301 epoxy.

[0135] In some embodiments, the annular apodizing backing structure 26 may have an acoustic impedance of about 2.8 MR. The annular apodizing backing structure 26 may include any material or combination of materials that allows it to reach this acoustic impedance.

[0136] In some embodiments, the slope extending from the inner periphery 32 to the outer periphery 36 may be in a range extending from about 0 degrees to about 30 degrees. In some embodiments, the slope may be about 14 degrees relative to the top surface of the low volume fraction piezoelectric composite disc 22.

[0137] In some embodiments, the ultrasonic transducer 20 can operate at a frequency of about 1.5 MHz. In some embodiments, the ultrasonic transducer 20 can operate in a narrow bandwidth tone burst mode, such as, for example and without limitation, a 20% duty cycle sinusoidal pulse mode with a pulse repetition frequency of 1 kHz PRF.

[0138] Now, referring to some figures of merit of the ultrasound transducer, the present technique provides an ultrasound transducer 20 having a beam nonuniformity ratio of less than 3.5, which is less than 8, i.e., this level is defined as the minimum safe level for physical therapy and other medical applications. In some embodiments, the substantially uniform near-field (or at least one substantially uniform near-field component or portion) exhibits less than 2 dB ripple at a plane located about 3 mm from the outer surface of the ultrasound transducer 20 when the ultrasound transducer 20 is operated at 1.5 MHz with a 20% pulsed transmit waveform.

[0139] According to another broad aspect, a LIPUS treatment head having an operating frequency is provided. The LIPUS treatment head includes an acoustic stack and at least one electrode (which may be replaced or embodied by a printed circuit board and a housing). These components may be similar to one or more embodiments described herein. The acoustic stack includes a piezoelectric disk including a low volume fraction piezoelectric composite disk. The low volume fraction piezoelectric composite disk is configured to operate in a half-wave resonant mode at the operating frequency of the LIPUS treatment head. The acoustic stack also includes an annular apodizing backing structure in acoustic communication with the low volume fraction piezoelectric composite disk. The annular apodizing backing structure has an inner periphery and an outer periphery, each having an inner thickness and an outer thickness. The inner thickness is less than the outer thickness. The annular apodizing backing structure is configured to vary the apparent thickness of the low volume fraction piezoelectric composite disk relative to the resonant characteristics of the low volume fraction piezoelectric composite disk, thereby enabling the LIPUS treatment head to generate an acoustic field including a substantially uniform near-field or at least one substantially uniform near-field component or portion. The printed circuit board is in electrical communication with the low volume fraction piezoelectric composite disc, and the housing is shaped and sized to support the acoustic stack and the printed circuit board.

[0140] Notably, the LIPUS treatment head and each of its components are compatible with the embodiments previously described with respect to the ultrasound transducer.

[0141] According to another broad aspect, an apodizing wedge structure for a LIPUS treatment head is provided, the LIPUS treatment head including a low volume fraction piezoelectric composite disk. The apodizing wedge structure includes an annular body for contacting a surface of the low volume fraction piezoelectric composite disk. The annular body includes an inner circumference having a corresponding inner thickness and an outer circumference having a corresponding outer thickness. The annular body includes a sloped surface forming a substantially continuous slope extending from the inner circumference to the outer circumference, the inner thickness being less than the outer thickness. The apodizing wedge is configured such that when the apodizing wedge structure is in acoustic communication with the low volume fraction piezoelectric composite disk, it changes the apparent thickness of the low volume fraction piezoelectric composite disk relative to a resonant characteristic of the low volume fraction piezoelectric composite disk, thereby enabling the LIPUS treatment head to generate a substantially uniform near field or an acoustic field including at least one substantially uniform near field component or portion.

[0142] In some embodiments, the toroid is made from Epotek 301 epoxy.

[0143] In some embodiments, the toroid has an acoustic impedance of about 2.8 MR.

[0144] In some embodiments, the tilt is comprised between 0 degrees and 30 degrees, In some embodiments, the tilt is about 14 degrees relative to the top surface of the low volume fraction piezoelectric composite disk.

[0145] In some embodiments, the LIPUS treatment head is capable of operating at a frequency of about 1.5 MHz.

[0146] In some embodiments, the LIPUS treatment head is operable in a narrow bandwidth tone burst mode. In some embodiments, the narrow bandwidth tone burst mode is a 20% duty cycle sine wave pulse mode.

[0147] In some embodiments, the LIPUS treatment head has a beam nonuniformity ratio of less than 3.5.

[0148] In some embodiments, the substantially uniform near-field (or at least one substantially near-field component or portion) exhibits less than 2 dB of ripple at a plane located approximately 3 mm from the outer surface of the LIPUS treatment head when the LIPUS treatment head is operated at 1.5 MHz using a 20% pulsed transmit waveform.

[0149] 20A-20C show an ultrasonic transducer according to another embodiment. Notably, the ultrasonic transducer of FIG. 20A-20C does not include a ring-shaped printed circuit, as described elsewhere. However, the ultrasonic transducer according to this embodiment may include a low volume fraction piezoelectric composite, at least one electrode, and an annular apodizing backing structure, as presented herein. In the embodiment shown in FIG. 20A-20C, the at least one electrode is represented as a ring that at least partially surrounds the low volume fraction piezoelectric composite. The electrode may be made of a metallic material, such as gold.

[0150] The techniques described so far may be described with respect to the following non-limiting embodiment of a LIPUS treatment head. In this non-limiting embodiment, the LIPUS treatment head is configured to operate at a frequency of approximately 1.5 MHz. Such a LIPUS treatment head may be used in a fracture healing treatment system or similar system. The LIPUS treatment head according to this embodiment may be used to assist or promote the healing of relatively complex or difficult open fractures, and in physical therapy diathermy systems, to reduce or optimize the time required to heal a fracture.

[0151] Broadly described, the LIPUS treatment head according to this embodiment includes an ultrasound transducer and an integrated gel that senses electrical impedance function. More specifically, the LIPUS treatment head may include a low volume fraction 1 / 3 piezoelectric composite disk, a ring-shaped printed circuit board, a ground electrode, a signal electrode, a twisted pair of wires, a plastic housing, an apodizing wedge, and a printed circuit board.

[0152] The low volume fraction 1 3 piezoelectric composite disk may have a diameter in the range of 23 mm to 24 mm, preferably about 23.6 mm. The low volume fraction 1 3 piezoelectric composite disk may have a thickness in the longitudinal axis of about 1 / 2 lambda, or about 960 μm, at 1.5 MHz. The low volume fraction 1 3 piezoelectric composite disk may include 280 μm square pillars forming a 2D matrix pattern. The 2D matrix may have a pitch of about 480 μm in both transverse axes. The low volume fraction 1 3 piezoelectric / piezoelectric composite disk may be configured to operate in a half-wave resonant mode at about 1.5 MHz. The piezoelectric composite disk may exhibit an acoustic impedance in the range of, for example, but not limited to, about 9 MR to about 13 MR, preferably about 11 MR. The piezoelectric composite disk may include, by volume, about 35% PZT5H pillars and about 65% or the remainder polymer matrix. The piezoelectric composite disk can be manufactured according to a die and fill method. The polymer matrix can include, for example, but not limited to, approximately 2.2 MR powder-filled Epotek 301 epoxy filled with microglass balloons and silicone particles. The polymer matrix can have a longitudinal acoustic velocity equal to approximately 2515 m / s, or approximately 60%-70% of the longitudinal bar mode velocity of the PZT pillar. In some embodiments, the longitudinal bar mode velocity of the PZT pillar can be about 3850 m / s.

[0153] The ring-shaped printed circuit may act as a perimeter support for the piezoelectric composite disc and may be referred to as a perimeter support PCB (PSPCB). The PSPCB generally has an inner diameter slightly larger than the outer diameter of the piezoelectric composite disc and an outer diameter designed to accommodate the inner diameter of the LIPUS treatment housing. The PCB may have copper conductive planes on the distal and proximal faces covering most of the respective faces, and the proximal electrode may be separated into two regions, each electrically insulated from the other. One of the two regions may include a via that creates electrical communication between the distal copper plane and the portion of the proximal plane that includes the via. It will be appreciated that the PSPCB generally includes multiple different layers and thus may be provided in many different configurations. The PSPCB may be bonded to the perimeter of the piezoelectric composite disc using, for example, but not limited to, epoxy such that the distal face of the piezoelectric composite disc extends slightly beyond the distal face of the PSPCB, for example, but not limited to, by approximately 50 μm to approximately 100 μm.

[0154] The conductive electrodes may be provided according to methods and techniques known in the art. A non-limiting example of the conductive electrodes are chromium-gold electrodes, which may be provided on the proximal and distal surfaces of the piezoelectric composite disc. In some embodiments, the conductive electrodes may be formed using deposition techniques, such as, but not limited to, sputtering. Of note, the conductive electrode provided on the distal surface of the piezoelectric composite disc (sometimes referred to as the "distal electrode") may function as a ground electrode for the LIPUS treatment head. The distal electrode may establish electrical communication between the distal surface of the piezoelectric composite disc and the distal copper plane of the PSPCB. The conductive electrode provided on the proximal surface (sometimes referred to as the "proximal electrode") may function as a signal electrode for the LIPUS treatment head. The proximal electrode may establish electrical communication between the proximal surface of the piezoelectric composite disc and the insulated proximal copper plane of the PSPCB.

[0155] The twisted wire pair may be electrically connected to a proximal surface of the PSPCB, for example, but not limited to, soldered to the proximal surface of the PSPCB. A first twisted wire of the twisted wire pair may be a ground wire and may be configured to make electrical contact with a distal or ground electrode by a portion of the proximal copper plane that includes a via in the PSPCB. A second twisted wire of the twisted wire pair may be a wire and may be configured to make contact with a proximal piezoelectric composite electrode by an insulated proximal copper plane of the PSPCB.

[0156] The plastic housing may include an integral single quarter-wave thick matching layer. The matching layer has an acoustic impedance in the range of about 2.1 MR to about 2.5 MR, preferably about 2.3 MR. The matching layer may be made from, for example, but not limited to, HNA055 Noryl PPO plastic. The matching layer may have a thickness of about 360 μm. The matching layer is in acoustic communication with the front or distal surface of the piezoelectric composite disc and may be configured to function optimally in continuous wave or narrowband tone burst modes. The acoustic impedance of the material may be significantly lower at continuous wave resonant conditions, and the quarter-wave matching layer may be optimized for a variety of acoustic applications.

[0157] The apodizing wedge is in acoustic communication with a portion of the back or proximal surface of the piezoelectric composite disk, with the proximal electrode interposed therebetween. The apodizing wedge has an acoustic impedance that is comparable to or somewhat higher than the acoustic impedance of the matrix material of the piezoelectric composite. The apodizing wedge may include, for example, but is not limited to, Epotek 301 epoxy. The apodizing wedge may have an acoustic impedance of approximately 2.8 MR. The apodizing wedge functions to change the apparent thickness of the piezoelectric composite disk relative to the resonant properties of the piezoelectric composite disk at the location of communication between the piezoelectric composite disk and the apodizing wedge. More specifically, the apodizing wedge increases the acoustic path length of the piezoelectric composite disk, producing a strong destructive 180 out-of-phase reflection from the proximal surface of the apodizing wedge when the apodizing wedge is λ / 4 thick. In some embodiments, the λ / 4 thickness may be about 440 μm. The apodizing wedge radially tapers in thickness relative to the radial dimension of the piezoelectric composite disk, such that the wedge is λ / 4 thick around the periphery of the piezoelectric composite disk and tapers to a thickness of zero near the inner diameter, for example. The apodizing wedge may be radially taped at an angle of about 14 degrees to the proximal surface of the piezoelectric composite disk. The apodizing wedge and the piezoelectric composite work together to effectively create a monotonically decreasing level of destructive interference as the thickness decreases monotonically to zero, at which point the piezoelectric composite disk experiences the usual λ / 2 perfect constructive interference between the front and back wall reflections of the low volume fraction piezoelectric composite disk and the apodizing backing structure.

[0158] Notably, a volume of air is in contact with the proximal surface of the apodizing wedge and the exposed portions of the proximal surface of the piezoelectric composite disc, and thus the proximal surface of the transducer in the LIPUS treatment head according to this non-limiting embodiment is acoustically loaded with air.

[0159] The LIPUS treatment head may include a series or parallel connected inductor, e.g., a 2 μH inductor, connected in parallel with the piezoelectric composite disk of the LIPUS treatment head. This inductor may be configured to electrically resonate with the acoustic stack when air loaded to produce an impedance maximum at the operating frequency of the LIPUS treatment head for a parallel inductor, or an impedance minimum for a series resonant inductor. The operating frequency of the LIPUS treatment head may be 1.5 MHz, and the distal surface (or at least a portion of the distal surface) of the LIPUS treatment head is acoustically loaded with air.

[0160] The ultrasound transducer according to this non-limiting embodiment is configured to generate a very uniform acoustic field, which one skilled in the art will appreciate may be beneficial in many applications, particularly in medical LIPUS applications such as physical therapy transducers and fracture healing applications where low energy is applied to the patient without image guidance. One example of a fracture healing system may be configured to operate in a narrow bandwidth tone burst mode at a center frequency of about 1.5 MHz. A non-limiting example of a narrow bandwidth tone burst mode is a 20% duty cycle sinusoidal pulse mode with a PRF of about 1 kHz.

[0161] Those skilled in the art will recognize that the beam nonuniformity ratio BN This is for example, but not limited to, in IEC 61689:2013, where the spatial-averaged temporal average (I SATA ) spatial-peak time-averaged intensity of the acoustic field of the transducer divided by the I SPTA ) is explained as the ratio of R BN is a figure of merit for the safety and effectiveness of physical therapy and medical LIPUS transducers in many applications, with an R of less than 8 BNis defined as the minimum safe level for physical therapy and other medical applications. Of note, the actual industry average is typically below 6, with the median typically being around 3.7. The present technology achieves an R of less than 3.5. BN It is possible to generate a highly uniform near-field that exhibits less than 2 dB ripple in a 3 mm plane of the near-field when operated at 1.5 MHz with a 20% pulsed transmit waveform. BN In addition, the non-limiting embodiments of the LIPUS treatment head described exhibit a very uniform axial response in the near field, which can be a desirable quality for patient comfort and uniform treatment of the patient.

[0162] In addition, the LIPUS treatment head according to this non-limiting embodiment is highly efficient and has no absorbing structures in the acoustic stack due to the combination of an air-bag low volume fraction piezoelectric composite disk and a destructive interference based apodization wedge. eff For example, the k value for normal PZT5H is eff The lack of loss absorbing structures combined with efficient low volume fraction piezoelectric composite disks exhibiting a low R BN This allows for an efficiency advantage over existing solutions that generally rely on absorbing backing structures and attenuating filters on the front face of an ultrasound transducer to generate an acoustic field. Thus, the technology could potentially enable extended battery life and allow cost-effective electronics to be used to power it in many typical physical therapy and other medical applications.

[0163] In addition to efficient operation, a key advantage of the present technology is the realization of an efficient acoustic design that generates a uniform apodized acoustic field and does so using air backing. The use of a non-damped air backing design allows for very efficient impedance sensing of the acoustic load on the front surface of the LIPUS treatment head. Those skilled in the art will appreciate that state-of-the-art LIPUS treatment heads (and their inherent transducers) typically exhibit impedance changes due to the distal surface of the treatment head being either air or gel / water coupled, and these impedance changes are generally observed to be higher impedance in the water coupled state compared to the air coupled state, and in many cases more than two times higher. Due to this impedance change, the transducer typically exhibits higher current flow when air coupled or imperfectly water coupled compared to water or tissue coupled.

[0164] The intrinsic impedance change exhibited by this technique can be used to enable gel sensing functionality, for example, by measuring the average current flowing through a transmission circuit connected to a LIPUS treatment head. The difference in impedance when water is coupled compared to when air is coupled simplifies gel sensing for system designers and allows potentially greater discrimination between ideal coupling, partial acoustic coupling with patient tissue, or no acoustic coupling, such as when a patient may have forgotten to use a typical acoustic couplant gel, thus allowing the system to signal an error condition with potentially large feedback to the patient or physician. Notably, some characteristics or figures of merit, such as high Q, high impedance resonance maximum, cannot be achieved in this manner on conventional ultrasound transducers that include acoustically attenuated backing structures or otherwise highly attenuated acoustic structures.

[0165] The magnitude of the impedance when air or water is coupled changes by less than 10% when an optimal acoustic matching layer is used on the distal surface of the piezoelectric composite disk when a resonant inductor is not included in the LIPUS treatment head. This is generally considered to be too small an impedance difference to be used for medical or physical therapy gel sensing functions. However, in the case of the present technology, due to the largely undamped and therefore largely resonant condition of the airbag piezoelectric composite disk, and in conjunction with the use of an efficient λ / 4 matching layer in acoustic communication with the distal surface of the piezoelectric composite disk, one preferred embodiment of the present technology incorporates the use of a parallel inductor, e.g., 2 μH, selected to resonate with the capacitive reactance of the piezoelectric composite disk when air is loaded on the distal surface, in conjunction with the use of the λ / 4 matching layer. The resulting LC resonance produces a high Q impedance maximum at the desired operating frequency when the distal surface of the λ / 4 matching layer is air loaded. When the transducer is placed in contact with gel or tissue, or another similar acoustically conductive medium, the resonant maximum decreases as the transducer becomes increasingly coupled to the gel or tissue, resulting in a lower impedance at the operating frequency until it no longer electrically resonates with the water or gel loaded impedance of the piezoelectric composite. This approach can result in a maximum impedance magnitude between 80-100 ohms and approximately +40 degrees phase at 1.5 MHz when air loaded, compared to 18-24 ohms at approximately +36 degrees phase when coupled to water, or a 3-5 times difference in impedance magnitude exhibited when the distal surface of the LIPUS treatment head is in contact with water, gel, or tissue (i.e., when the LIPUS treatment head is coupled to the patient). Furthermore, the effect of the parallel inductor is harmless to the function of the transducer when coupled to a patient, results in less than 1 dB output drop when driven by a suitable low output impedance transmit circuit, such as, but not limited to, a transmit circuit having an output impedance of less than 10 ohms, and enables built-in impedance-based gel sensing within the transducer that is several times more sensitive than relying on the inherent impedance changes of the acoustic structure of the transducer alone.In addition, this method decouples the thickness and other acoustic properties of the layers on the front or distal surface of the LTH from their function of generating a gel-sensing impedance change, allowing the designer to optimize both the gel-sensing impedance sensitivity and the layers on the front surface of the transducer for maximum acoustic efficiency, improved bandwidth or impulse response, or other desired acoustic properties.

[0166] Those skilled in the art will readily appreciate that the present technology can be combined with many different configurations of acoustic and protective front layers in acoustic communication with the distal surface of the piezoelectric composite disk, thereby enabling a variety of impedance changes without limiting or compromising the acoustic uniformity provided by the disclosed combination of low volume fraction piezoelectric composite disk and apodizing wedge.

[0167] In one variation of this non-limiting embodiment of the LIPUS treatment head, the LIPUS treatment head includes a 0.66λ acoustic layer. The 0.66λ can be a 953 μm thick nonyl plastic layer. The 0.66λ is in acoustic communication with the distal surface of the piezoelectric composite disc (instead of the λ / 4 layer), resulting in an impedance maximum occurring at an operating frequency of 1.5 MHz when air is loaded onto the distal surface, with a magnitude 3-5 times greater than the water-bound condition. Notably, the thickness tolerance of the 0.66λ can be controlled, for example, during the manufacturing process, to maintain the impedance change required to sense the presence of an appropriate gel or tissue binding to the patient. Additionally, the present technology in this configuration provides an R of less than 3.5. BN Note that this results in a very uniform beam with

[0168] In another variation of this non-limiting embodiment of the LIPUS treatment head, the LIPUS treatment head may include a 0.9λ acoustic layer. The 0.9λ acoustic layer may be 1.28 mm thick Noryl to achieve an impedance minimum at an operating frequency of 1.5 MHz when air is loaded onto the distal surface of the layer, achieving approximately a three-fold difference from that of the water-bound state. This embodiment also provides an R of less than 3.5. BNThis can also be configured in conjunction with the present technology to generate an acoustic field having

[0169] However, it should be noted that any acoustic matching layer other than, for example, 1 / 4 lambda or an odd multiple of 1 / 4 lambda (e.g., 3 / 4 lambda or 5 / 4 lambda) limits the bandwidth and potentially the efficiency of the ultrasonic transducer. In light of this consideration, it may sometimes be advantageous to utilize one aspect of the present technology, the inclusion of a resonant inductor, to enable large impedance changes that are sensitive to the acoustic load present at the distal surface of the LIPUS treatment head, for example, in a manner that does not limit the use of 1 / 4 wavelength matching layers. In general, low bandwidth applications, such as LIPUS applications, do not strictly require a transducer with a short, wideband impulse response, but there remain aspects of ultrasonic transducer performance that benefit from a wider bandwidth, such as the ability to quickly achieve steady-state pulse strength and limit ring-down after the transmit pulse is terminated.

[0170] Of note, numerous methods are known in the art for preparing low volume fraction piezoelectric composite disks (or similar structures). Non-limiting examples of such methods include die and fill methods, which are equally applicable to the present technology. In some embodiments, the apodization techniques described herein can be applied to many different geometries to achieve apodization or beam shaping of the output of a transducer with a wide array of possible beam shapes. The apodization techniques can be applied to 1D arrays, 2D matrix arrays, annular arrays, single element broadband transducers, and material specific carbon fiber transducers for NDT and many other applications.

[0171] According to another aspect, a method of apodizing an acoustic field is provided. The method includes operating an ultrasonic transducer to generate an acoustic field, the ultrasonic transducer being similar to one or more of the embodiments described herein. The method also includes conditioning the acoustic field with an annular apodized backing structure to generate an apodized acoustic field, the apodized acoustic field being within at least one substantially uniform near-field component or portion, the annular apodized backing structure being in acoustic contact with a low volume fraction piezoelectric composite disk. The annular apodizing backing structure is similar to one or more of the embodiments described herein.

[0172] In some embodiments, the ultrasonic transducer is operated at 1.5 MHz using a 20% pulsed transmit waveform and the substantially uniform near field exhibits less than 2 dB ripple at a plane located approximately 3 mm from the outer surface of the ultrasonic transducer.

[0173] In some embodiments, the low volume fraction piezoelectric composite disk is in a 1 / 3 configuration.

[0174] In some embodiments, the low volume fraction piezoelectric composite disk comprises 280 μm×280 μm pillars distributed in a 2D matrix pattern with a pitch of about 480 μm in both transverse axes.

[0175] According to another aspect, a method is provided for generating an acoustic field using a low-power pulsed wave ultrasound (LIPUS) treatment head having an operating frequency. The method includes operating a LIPUS treatment to generate an acoustic field, the LIPUS treatment head being similar to one or more of the embodiments described herein. The method also includes conditioning the acoustic field with an annular apodized backing structure to generate an apodized acoustic field, the apodized acoustic field having a substantially uniform near-field region.

[0176] In some embodiments, the ultrasonic transducer is operated at 1.5 MHz using a 20% pulsed transmit waveform and the substantially uniform near field exhibits less than 2 dB ripple at a plane located approximately 3 mm from the outer surface of the ultrasonic transducer.

[0177] In some embodiments, the low volume fraction piezoelectric composite disk is in a 1 / 3 configuration.

[0178] In some embodiments, the low volume fraction piezoelectric composite disk comprises 280 μm×280 μm pillars distributed in a 2D matrix pattern with a pitch of about 480 μm in both transverse axes.

[0179] result Now that different embodiments of the present technology have been described, the performance of some of these embodiments will be discussed, more specifically with respect to the results that can be obtained using the present technique, non-limiting examples of which are shown in Figures 9A, 9B to 19A, 19B.

[0180] Figure 9A, Figure 9B show the linear pressure intensity response of a conventional ultrasonic transducer (left part) and the linear pressure intensity response of an ultrasonic transducer designed according to the present technique (right part). These results show the 2D lateral acoustic pressure in a plane 3 mm from the face of the ultrasonic transducer. The effect of the apodization wedge, i.e., the annular apodizing backing structure, on the uniformity of the acoustic field is clearly shown.

[0181] 10A-10D show a simulated field showing the outer maximum ring present within the 3 mm field of a 1 / 3 composite system LIPUS treatment head without an apodization ring or structure (top left portion), a measured acoustic field showing the outer maximum ring present within the 3 mm field of a 1 / 3 composite system LIPUS treatment head (top right portion), a simulated field showing the suppressed outer maximum ring resulting from including an apodizing wedge (or "annular apodizing backing structure") on the rear peripheral edge of the 1 / 3 composite system disc (bottom left portion), and a measured acoustic field from a prototype LIPUS treatment head showing the suppressed outer maximum ring achieved by an apodizing ring (or annular apodizing backing structure) on the 1 / 3 composite system disc (bottom right portion).

[0182] 11A and 11B show the 3 mm intensity and final axial maximum intensity of the technique. These results show that the beams produced using the technique have desirable properties for medical and physical therapy applications. The figure of merit is AER=3.9 cm. 2 , RBN=3.25, output power of 117 mW and 30 mW / cm measured at a plane located 3 mm away from the distal surface of the LIPUS treatment head. 2 Includes collimated beam type with intensity of

[0183] 12A and 12B show the effect of air loading without an inductor (FIG. 12A) compared to air loading with a parallel inductor configured to resonate at 1.5 MHz of the present technology (FIG. 12B), where the parallel inductor resonance is tuned to match the operating frequency when the ultrasonic transducer is air loaded.

[0184] Figure 13A shows the impedance of a non-limiting embodiment of a LIPUS treatment head having a λ / 4 matching layer and a resonant parallel inductor with air and water loading, and Figure 13B shows the impedance of an exemplary transducer of a non-limiting embodiment of a LIPUS treatment head having a λ / 4 matching layer but no resonant inductor with air and water loading cases.

[0185] FIG. 14 is a 3D plot of the apodized acoustic field produced using the present technique, measured in a water tank with a hydrophone.

[0186] 15A and 15B show a thicker 2λ / 3 front layer tuned to provide an impedance maximum at the operating frequency in air without the use of an in-circuit resonant inductor (shown in the bottom half of the figure) compared to the response in water (shown in the top half of the figure), with the air-coupled maximum being approximately 5 times higher than the water-coupled minimum.

[0187] 16A and 16B show an even thicker 0.9λ front layer tuned to provide an impedance minimum in air (shown in the bottom half of the figure) and a higher impedance when water-coupled (shown in the top portion of the figure), with the air-coupled impedance minimum being approximately three times lower than when water-coupled (bottom portion).

[0188] Figures 17A and 17B show the axial pressure response of an ultrasonic transducer according to the present technique. Figure 17A shows a highly uniform on-axis pressure field in the first 10 cm of the near-field and the absence of high amplitude peaks throughout the near-field. Figure 17B shows the lack of near-field axial uniformity seen in the absence of an apodized backing structure and corresponding acoustic field.

[0189] Figure 18 shows the local attenuation of the transmitted acoustic field due to destructive interference created by the presence of the backing structure versus the thickness of the backing structure as a fraction of a wavelength. Notably, the combined thickness of the backing structure and the composite kerf-filled matrix should be approximately equal to 3 / 4 lambda for maximum attenuation, and thus, if the speed of sound in the composite matrix is ​​slower than the speed of sound in the backing structure, a minimum will be observed at a thickness of approximately 1 / 4 lambda of the backing structure.

[0190] 19A-B show a method of achieving the results seen for 0.9λ but using a series resonant inductor and a λ / 4 matching layer. More specifically, FIG. 19A-B show an impedance comparison of a variation of an exemplary embodiment LIPUS treatment head including a series resonant inductor and a λ / 4 matching layer design configured to create an impedance minimum when air-coupled, which is less than the impedance when water-loaded, allowing the gel-sensing circuit to detect proper coupling when the current through the gel-sensing circuit is at a lower level than when the transducer is air-coupled. In this example, the air minimum is about 4 ohms, and the magnitude of the water-coupled impedance at the operating frequency is about 24 ohms (a 6-fold increment), which may be useful in gel-sensing applications.

[0191] It should be noted that the results described serve for illustrative purposes only and therefore should not be considered limiting. EXAMPLES

[0192] Now that different embodiments of an apodizing backing structure and its integration in an ultrasonic transducer have been described along with results that can be obtained using the present technique, non-limiting examples of the present technique are described below.

[0193] In a first embodiment, an ultrasound transducer or LIPUS treatment head includes a 1 / 3 piezoelectric composite disk containing a low volume fraction of piezoelectric material (35% PZT5H). The remainder of the piezoelectric composite disk includes a filled epoxy matrix (65% filled epoxy matrix). The filled epoxy matrix has an acoustic impedance of approximately 2 MR, effectively isolating the lateral vibration of each pillar from adjacent pillars and reducing the k-axis vibration from the PZT pillars. 33The piezoelectric composite disk has a low lateral coupling efficiency between the PZT pillars, resulting in a majority of the acoustic energy being generated axially of the disk. The ultrasound transducer or LIPUS treatment head also includes an apodizing ring with a wedge-shaped cross section located on a portion of the back surface of the piezoelectric composite located near the periphery of the disk, the apodizing wedge containing an epoxy with an acoustic impedance that closely matches the acoustic impedance of the matrix portion of the piezoelectric composite. The wedge may contain Epotek 301 epoxy with an acoustic impedance of approximately 2.8 MR. The apodizing wedge effectively changes the acoustic resonance frequency of the low volume fraction 1 3 composite disk, shifting the disk's resonance frequency lower as the wedge thickens. The wedge ultimately approaches a thickness equal to λ / 4 at the transducer's driving frequency, thus promoting destructive interference within the piezoelectric composite disk, and the wedge structure creates a strong damping effect that varies with the thickness of the wedge. The apodizing structure on the back surface of the piezoelectric composite achieves localized damping of the resonant behavior of the piezoelectric composite disk without absorbing significant acoustic energy that would cause it to behave as a piezoelectric disk of different thickness. The apodizing wedge provides strong destructive interference for narrowband acoustic signals, such as tone bursts, and thus can dampen the acoustic output of the transducer by approximately 25 dB for a 50 cycle tone burst, for example. The shape of the apodizing structure, such as the wedge, can shape the spatial apodization, resulting in a gradual increase in amplitude with radial distance from the center of the disk as the phase of the interference within the apodizing wedge and the thickness of the disk increase from fully constructive λ / 2 to fully destructive 3λ / 4 lambda. A parallel tuned inductor circuit can be provided, which is designed to resonate with the air-loaded impedance of the ultrasound transducer or LIPUS treatment head at the operating frequency of the LIPUS transducer, such that an impedance maximum is generated at the operating frequency of the transducer.The matching layers of the transducer work in conjunction with the stack and parallel inductors such that the inductors do not induce substantial resonance at the operating frequency of the LIPUS transducer when the LIPUS transducer is water-loaded, gel-loaded, or tissue-loaded.

[0194] The second example concerns the acoustic field and lateral reverberation in a 1 3 piezoelectric composite with an apodizing wedge in a narrow bandwidth mode of operation. In this second example, an ultrasound transducer or LIPUS treatment head includes a 1 3 piezoelectric composite with an apodizing wedge to reduce side lobe amplitudes by applying apodization around the periphery of the composite piezoelectric element. The use of a low volume fraction 1 3 piezoelectric composite helps to reduce lateral resonances in the circular disk, which reduces the complexity of the near-field interference pattern produced by the disk and homogenizes the near field laterally to less than about 2 dB. This idealized near field results in very low ripples in the 3 mm plane used to characterize medical physiotherapy, diathermy, and fracture healing LIPUS transducers. The low lateral resonances in the disk also reduce on-axis non-idealities that can result from constructive and destructive interferences between the principal axial modes of the piezoelectric composite disk and the axial components produced by the lateral resonances in the disk. Axial uniformity is an important consideration in the efficacy and patient comfort of LIPUS-based medical devices. The ability to shape the edges of the acoustic field through the apodizing backing structure disclosed herein is important in that it goes beyond simply reducing side lobes and allows the acoustic field to be shaped so that the main lobe is of an ideal shape. The apodizing backing structure can be optimized to reduce the transducer output by more than -25 dB for narrowband operation while using only a λ / 4 thick backing structure. In addition, it can be shaped to produce graduated apodization filter shapes that allow complex beam shaping. A uniform acoustic field is important to ensure that uniform treatment is obtained without the need for image-based guidance.

[0195] Gel sensing applications The ability to sense the effective acoustic coupling of an ultrasound transducer to a patient is beneficial. The technology can incorporate an inductively tuned design element that allows for a high impedance resonance when the transducer is in air (air coupled) and a low electrical impedance when the transducer is in contact with water, gel, or tissue, e.g., coupled to the patient's skin via gel. Using an inductor or other electrical element or circuit to resonate with an ideal λ / 4 matching structure further benefits the designer by isolating the gel-sensing impedance characteristics of the transducer from the actual acoustic layers, so that the impedance maximum value for a given acoustic stack can be maximized, for example, by simply selecting a slightly different value inductor to compensate for manufacturing tolerances. By incorporating this impedance response directly into the transducer, any LIPUS system can simply measure the average current flowing through the transducer to determine if effective coupling has been achieved. The technology can also accurately recognize a partially coupled state, as more than five times the magnitude of impedance can be achieved while air coupled compared to when effectively coupled to the patient.

[0196] Several alternative embodiments and examples are described and illustrated herein. The above-described embodiments are intended to be illustrative only. Those skilled in the art will appreciate the features of the individual embodiments and the possible combinations and variations of the components. Those skilled in the art will further appreciate that any of the embodiments may be provided in any combination with the other embodiments disclosed herein. The present examples and embodiments should therefore be considered in all respects as illustrative and not restrictive. Thus, while specific embodiments have been illustrated and described, numerous modifications are envisioned without significantly departing from the scope defined herein.

Claims

1. 1. An ultrasonic transducer comprising: a low volume fraction piezoelectric composite disk having resonant properties; at least one electrode in electrical contact with the low volume fraction piezoelectric composite disc; and an annular apodizing backing structure in acoustic contact with the low volume fraction piezoelectric composite disk, the annular apodizing backing structure comprising: an inner circumference and corresponding inner thickness; a circumference and corresponding outer thickness; a ramp surface forming a substantially continuous slope extending from the inner periphery to the outer periphery, the inner thickness being less than the outer thickness; An ultrasonic transducer, wherein the annular apodizing backing structure is configured to vary the apparent thickness of the low volume fraction piezoelectric composite disk relative to the resonant characteristics of the low volume fraction piezoelectric composite disk, thereby enabling the ultrasonic transducer to generate an acoustic field that includes at least one substantially uniform near-field portion.

2. The ultrasonic transducer of claim 1 , wherein the low volume fraction piezoelectric composite disk is in a 1:3 configuration.

3. 3. The ultrasonic transducer of claim 2, wherein the low volume fraction piezoelectric composite disk comprises 280 μm×280 μm pillars distributed in a 2D matrix pattern with a pitch of about 480 μm in both transverse axes.

4. The ultrasonic transducer of any one of claims 1 to 3, wherein the low volume fraction piezoelectric composite disc is configured to operate in a half-wave resonant mode at 1.5 MHz.

5. The ultrasonic transducer of any one of claims 1 to 4, wherein the low volume fraction piezoelectric composite disc has an acoustic impedance comprised in a range extending from about 9 MR to about 13 MR.

6. 6. The ultrasonic transducer of claim 5, wherein the acoustic impedance is about 11 MR.

7. The ultrasonic transducer of any one of claims 1 to 6, wherein the low volume fraction piezoelectric composite disc has a thickness of about λ / 2 at 1.5 MHz.

8. The ultrasonic transducer of any one of claims 1 to 7, wherein the low volume fraction piezoelectric composite disc comprises a lead zirconate titanate (PZT) based material.

9. The ultrasonic transducer of claim 8 , wherein the PZT-based material is PZT5H.

10. 10. The ultrasonic transducer of claim 8 or 9, wherein the low volume fraction piezoelectric composite disk comprises about 35% PZT5H and about 65% polymer matrix.

11. The ultrasonic transducer of claim 10 , wherein the polymer matrix comprises an epoxy filled with microglass balloons and silicone particles.

12. 12. The ultrasonic transducer of claim 9, wherein the PZT5H pillars have a first bar mode longitudinal acoustic velocity and the polymer matrix has a second longitudinal acoustic velocity, the second longitudinal velocity being approximately 60% to 70% of the first longitudinal velocity.

13. 13. The ultrasonic transducer of claim 12, wherein the first longitudinal bar mode acoustic velocity is about 3850 m / s and the second longitudinal acoustic velocity is about 2515 m / s.

14. a ring-shaped printed circuit board having an inner diameter; An ultrasonic transducer as described in any one of claims 1 to 13, wherein the low volume fraction piezoelectric composite disk has an outer diameter, and the inner diameter of the ring-shaped printed circuit board is larger than the outer diameter of the low volume fraction piezoelectric composite disk.

15. 15. The ultrasonic transducer of claim 14, further comprising a housing, the housing being made from plastic.

16. The ultrasonic transducer of claim 15 , wherein the housing comprises a matching layer in acoustic communication with the low volume fraction piezoelectric composite disc.

17. 17. The ultrasonic transducer of claim 16, wherein the matching layer has a thickness of about λ / 4.

18. 18. The ultrasonic transducer of claim 16 or 17, wherein the matching layer is integrally formed with the housing.

19. The ultrasonic transducer of any one of claims 16 to 18, wherein the matching layer has an acoustic impedance comprised in a range extending from about 2.1 MR to about 2.5 MR.

20. 20. The ultrasonic transducer of claim 19, wherein the acoustic impedance is about 2.3 MR.

21. 16. The ultrasonic transducer of claim 1, further comprising a 2λ / 3 acoustic layer in acoustic communication with the low volume fraction piezoelectric composite disc.

22. 22. The ultrasonic transducer of claim 21, wherein the 2λ / 3 acoustic layer is made from nonyl plastic and has a thickness of about 953 μm.

23. 16. The ultrasonic transducer of claim 1, further comprising a 0.9λ acoustic layer in acoustic communication with the low volume fraction piezoelectric composite disc.

24. 24. The ultrasonic transducer of claim 23, wherein the 0.9λ acoustic layer is made from nonyl plastic and has a thickness of about 1.28 mm.

25. 15. The ultrasonic transducer of claim 14, wherein the ring-shaped printed circuit board comprises two opposing planar surfaces, each planar surface being made from copper.

26. 26. The ultrasonic transducer of claim 25, wherein the ring-shaped printed circuit board is bonded to a periphery of the low volume fraction piezoelectric composite disc.

27. An ultrasonic transducer as described in any one of claims 1 to 20, further comprising an inductor connected in parallel with the piezoelectric composite of the low volume fraction piezoelectric composite disk, the inductor configured to resonate with the low volume fraction piezoelectric composite disk, the annular apodizing backing structure, and the 1 / 4 lambda acoustic matching layer such that an impedance maximum is generated at approximately 1.5 MHz when the distal face of the transducer is air loaded.

28. 21. The ultrasonic transducer of claim 1, further comprising an inductor connected in series with the low volume fraction piezoelectric composite disk, the inductor configured to resonate with the low volume fraction piezoelectric composite disk, the annular apodizing backing structure, and the ¼ lambda matching layer such that an impedance minimum is produced at approximately 1.5 MHz when the distal face of the transducer is air loaded.

29. The ultrasonic transducer of any one of claims 1 to 28, wherein the annular apodizing backing structure comprises Epotek 301 epoxy.

30. 30. The ultrasonic transducer of claim 1, wherein the annular apodizing backing structure has an acoustic impedance of about 2.8 MR.

31. 31. The ultrasonic transducer of claim 1, wherein the tilt is comprised between 0 degrees and 30 degrees.

32. 32. The ultrasonic transducer of claim 31, wherein the inclination is about 14 degrees relative to a top surface of the low volume fraction piezoelectric composite disk.

33. An ultrasonic transducer according to any one of claims 1 to 32, wherein the ultrasonic transducer is operable at a frequency of about 1.5 MHz.

34. An ultrasonic transducer according to any one of claims 1 to 33, wherein the ultrasonic transducer is operable in a narrow bandwidth tone burst mode.

35. 35. The ultrasonic transducer of claim 34, wherein the narrow bandwidth tone burst mode is a 20% duty cycle sinusoidal pulse mode, preferably at a pulse repetition frequency of about 1 kHz.

36. 36. The ultrasonic transducer of claim 1, wherein the ultrasonic transducer has a beam nonuniformity ratio of less than 3.

5.

37. An ultrasonic transducer as described in any one of claims 1 to 36, wherein the at least one substantially uniform near-field portion exhibits less than 2 dB ripple at a plane located approximately 3 mm from an outer surface of the ultrasonic transducer when the ultrasonic transducer is operated at 1.5 MHz using a 20% pulsed transmit waveform.

38. 1. An apodizing wedge structure for a low power pulsed wave ultrasound (LIPUS) treatment head, the LIPUS treatment head comprising a low volume fraction piezoelectric composite disk, the apodizing wedge structure comprising: an annular body for contacting a surface of the low volume fraction piezoelectric composite disk, the annular body having an inner periphery with a corresponding inner thickness and an outer periphery with a corresponding outer thickness; An apodizing wedge structure, wherein the annular body includes an inclined surface forming a substantially continuous slope extending from the inner circumference to the outer circumference, the inner thickness being less than the outer thickness, and wherein when the apodizing wedge structure is in acoustic communication with the low volume fraction piezoelectric composite disk, the apodizing wedge is configured to vary the apparent thickness of the low volume fraction piezoelectric composite disk in response to a resonant characteristic of the low volume fraction piezoelectric composite disk, thereby enabling the LIPUS treatment head to generate an acoustic field including at least one substantially uniform near-field portion.

39. 1. A method of apodizing an acoustic field, comprising the steps of: operating an ultrasonic transducer to generate the acoustic field, the ultrasonic transducer comprising a low volume fraction piezoelectric composite disk, the low volume fraction piezoelectric composite having resonant properties; conditioning the acoustic field with an annular apodizing backing structure to generate an apodized acoustic field, the apodized acoustic field including at least one substantially uniform near-field portion, the annular apodizing backing structure being in acoustic contact with the low volume fraction piezoelectric composite disk, the annular apodizing backing structure comprising: an inner circumference and corresponding inner thickness; a circumference and corresponding outer thickness; and generating an inclined surface forming a substantially continuous slope extending from the inner periphery to the outer periphery, the inner thickness being less than the outer thickness; The method, wherein the annular apodizing backing structure is configured to change an apparent thickness of the low volume fraction piezoelectric composite disk relative to the resonant characteristics of the low volume fraction piezoelectric composite disk.

40. the ultrasonic transducer is operated at 1.5 MHz using a 20% pulsed transmit waveform; 40. The method of claim 39, wherein the at least one substantially uniform near-field portion exhibits less than 2 dB ripple at a plane located about 3 mm from an outer surface of the ultrasonic transducer.

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