WO2009001157A1 - Transducteur ultrasonore micro-usiné capacitif destiné à des ouvertures de transducteur à éléments - Google Patents

Transducteur ultrasonore micro-usiné capacitif destiné à des ouvertures de transducteur à éléments Download PDF

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Publication number
WO2009001157A1
WO2009001157A1 PCT/IB2007/002658 IB2007002658W WO2009001157A1 WO 2009001157 A1 WO2009001157 A1 WO 2009001157A1 IB 2007002658 W IB2007002658 W IB 2007002658W WO 2009001157 A1 WO2009001157 A1 WO 2009001157A1
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Prior art keywords
transducer
array
cells
capacitive micromachined
cmms
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PCT/IB2007/002658
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English (en)
Inventor
Nicolas Felix
Aime Flesch
Remi Dufait
An Nguyen-Dinh
Ross F. Hunt
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Vermon
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Priority to PCT/IB2007/002658 priority Critical patent/WO2009001157A1/fr
Publication of WO2009001157A1 publication Critical patent/WO2009001157A1/fr

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B06—GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS IN GENERAL
    • B06B—METHODS OR APPARATUS FOR GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS OF INFRASONIC, SONIC, OR ULTRASONIC FREQUENCY, e.g. FOR PERFORMING MECHANICAL WORK IN GENERAL
    • B06B1/00—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency
    • B06B1/02—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy
    • B06B1/0292—Electrostatic transducers, e.g. electret-type

Definitions

  • the present invention relates to ultrasonic transducers and, more particularly, to capacitive micro-machined ultrasonic transducers.
  • Ultrasonic transducers are typically formed with one vibrating surface or a plurality of vibrating surfaces capable of converting electrical energy into mechanical displacements and vice-versa. Because the acoustic pressure produced by such devices obeys diffracting laws, physical parameters such as area, frequency, bandwidth, geometry and surface apodization (weighting) are key factors in transducer design and actually govern the radiating acoustic beam pattern produced by the transducer. The operation of single area transducers is often characterized by spurious boundary effects, which are manifested by secondary lobes occurring laterally of the main lobe. These effects generally occur when the ratio factor between the Z and the X-Y dimensions does not satisfy a certain value.
  • array transducers require substantially perfect and well controlled angular directivities of the corresponding transducer element apertures in order to produce smooth radiating acoustic beam patterns compatible with the formation of a high quality image. Based on the above considerations, designers of ultrasonic transducers often seek to balance performance with the geometry of the transducer.
  • piezoelectric array transducers are principally of a bulky design wherein a portion of the piezoelectric material is slotted into narrow independent blocks which are isolated from each other and arranged in side by side relation in the azimuth direction.
  • the piezoelectric material is uniformly poled and is of a thickness that is predetermined to provide the desired resonant frequency.
  • the geometry of elemental transducers is, therefore, essentially determined or set at this initial design stage. Further modification of the geometric parameters set at this initial stage is difficult to effect, and, further, will strongly affect the intrinsic acoustic behavior of the transducer device.
  • taking advantage of any trade-offs with respect to the geometrical specifications of a transducer involves compromise regarding performance and/or cost.
  • CMUTs Capacitive Micromachined LJItrasonic Transducers
  • semiconductor capacitive micromachined cavities for producing ultrasound
  • CMUT devices generally have the advantage that, on one hand, collective manufacturing processes (mass production) can be used in making the devices, and, on the other hand, the devices exhibit a broader bandwidth as compared to piezoelectric assemblies.
  • the basic principles of such a device are quite simple and these principles have been successfully implemented for years in the manufacturing of condenser microphones.
  • capacitive transducers the transducer is governed by a voltage oscillation over an electrostatic field (bias voltage).
  • CMUT devices exhibit certain unique advantages such as the ability of these devices to be integrated readily with microelectronics for immediate signal processing so as to improve the quality of the received information, and the higher degree of miniaturization that can be achieved using these devices. Thus, it can be predicted that in the near future CMUT devices will outperform conventional transducer technologies. A number of manufacturing methods for CMUT devices have been developed and are currently well known in the art.
  • a common basic method for manufacturing CMUTs comprises at least the following steps: a silicon substrate is provided with an oxide layer deposited on the surface of the substrate; electrodes are patterned over the oxide layer; a sacrificial layer is then deposited thereon and then photolithographically patterned to define cavities to be created in further steps; a silicon nitride layer is deposited over the substrate; vias are dry-etched, and the membrane is released using wet etching techniques on sacrificial layer; the vias so obtained are then sealed; and finally, an outer electrode is sputtered on the top of the membranes.
  • U.S. Patent Nos. 5,894,452 and 5,870,351 to Ladabaum et al and U.S. Patent No. 5,870,351 to Haller.
  • CMUT devices Methods for integrating electronics on the substrates of CMUT devices have been developed which use a BiCMOS process or low temperature process. This has made the capacitive transducing devices very attractive for the future development of highly integrated ultrasonic imaging systems. Since the devices are manufactured as silicon components or ICs, the packaging and interconnect aspects of manufacture will advantageously benefit from the most recent developments in these fields so as to keep manufacturing of CMUT devices at the leading edge of the relevant technology.
  • a method for reducing undesirable interaction between elemental transducers (transducer elements) of an array is disclosed in U.S. Patent No. 6,918,877 to Hossack et al.
  • the cross talk between the adjacent transducer elements of an array is measured or calculated, and modified excitation signals, derived from signals relating to the selected element, are then applied to the neighboring elements to interfere with any cross talk and thus reduce the effect of the cross talk.
  • the method can be implemented in most array designs and is especially well adapted to silicon substrate-based MEMS (Micromachined Electro Mechanical Systems) transducers.
  • MEMS Micromachined Electro Mechanical Systems
  • This patent discloses a CMUT device that includes a variable gain control for MUT cells which are integrated into the substrate of the device.
  • the patent is principally concerned with the use of integrated electronic control circuitry implemented on a common substrate rather than the CMUT devices, switches or microrelays which are provided as well as the passive components such as resistors or capacitors used to control the bias voltage source for the MUT cells.
  • CMUT cells there is provided another method of gain control for CMUT cells wherein the diameter of CMUT cells can be changed or the distance between the CMUT cells can be varied or a combination of the two approaches can be used.
  • the patent discloses that with respect to a change in cell diameter, the larger the CMUT cells, the higher the acoustic energy provided.
  • This approach is applied to circular shaped CMUT cells as disclosed by Savord et al.
  • the approach suffers several shortcomings For example, the variation in the diameter of the cells will inherently result in more wasted or void area between the cells, and, therefore, the density of cells on the transducer or the effective vibrating surface of the transducer will not change.
  • this approach as applied to circular shaped CMUT cells has no significant impact on the acoustic output of the device and will, at best, only affect the resonant frequency of the transducer.
  • the silicon substrate is generally populated with thousands of CMMs (Capacitive Micromachined Membrane) which are organized in small groups which are connected together. Thus, each group of CMMs forms an elemental transducer (transducer element).
  • a suitable interconnection means is then optionally provided at the sides of the transducer to facilitate further assembly operations.
  • the elemental transducers are formed as a combination of a plurality of shunted CMMs. These transducer elements are separated from each other by a kerf or small space that physically isolates the adjacent elements. The kerfs are made as narrow as possible to prevent the loss of sensitivity but should be of such a width as to provide an adequate acoustic barrier against acoustic cross talk between adjacent transducer elements.
  • CMUT construction includes improvements in the transducer characteristics provided by implementing dicing, and using polymer filled kerfs in combination with high loss backing members to better meet the requirements of high quality beamformers. Dicing of the CMUT device will further provide the device with the ability to bend longitudinally. This enables the formation of curved arrays of the type that are in widespread use in medical applications.
  • ultrasonic devices whether single elements or arrays
  • that are used for imaging and that employ capacitive micromachined membranes are greatly improved through the implementation of novel methods of mapping transducer surfaces so as to customize the acoustic radiation of the transducer apertures according to the requirements of high quality or harmonic imaging systems and so as to enhance the electrical impedance characteristics of the transducer devices with respect to the associated electronics.
  • Another aspect of the present invention concerns the provision of a method of shaping a CMUT device which includes customized optimization or apodization (weighting) of the CMMs forming the transducer surface.
  • the apodization of the CMMs is performed in amplitude and/or in frequency to enhance the quality of the acoustic beam pattern and, in particular, so as to decrease the side lobes (for arrays) or the lateral lobes (for single surfaces) of the devices.
  • Another aspect of the invention concerns a method of frequency apodization applied to the surface of a transducer which involves providing a specific geometry of
  • CMMs in a manner so that the CMMs operate with a graded frequency distribution from the center of the transducer surface to the edges thereof.
  • Yet another aspect of the invention concerns the implementation of a frequency apodization function with respect to elemental apertures of an array transducer (whether 1 D, 1 .5D or 2D) so as to improve the lateral radiating pattern.
  • the apodization function used is preferably determined according to gaussian or hamming distribution laws or the like.
  • Yet another aspect of the invention relates to optimization of the dimensions and geometry of CMMs in such a manner as to improve the behavior of a transducer element of a corresponding array.
  • This behavior can be electrical and acoustical.
  • each element has a specific CMM design and distribution.
  • the present invention relates to particular surface mapping configurations of a Capacitive Micromachined Ultrasonic
  • CMUT Capacitive Micromachined Membranes
  • the method is also applicable to single surface (area) transducing devices, and when so implemented, this method prevents edge effects and significantly improves the acoustical beam pattern and/or frequency response, thereby enabling a designer to custom shape of the acoustical output of the transducer device whatever the footprint of device.
  • the arrangement of the CMMs over the surface CMUT provides the surface with an optimized apodization function, thus improving the output acoustical beam pattern.
  • the apodization functions that can be employed include those based on well known gaussian or hamming distribution functions commonly used in advanced imaging.
  • the apodization obtained with specific sampling of the CMMs can be used to simultaneously control both the amplitude and resonant frequency of the transducer device without any compromising of the intrinsic performance of the device.
  • an array transducer designed for use in imaging applications is comprised of a plurality of independently individually addressable elements or element apertures.
  • the addressable elements are individually formed by a plurality of CMMs having a shape and an area which are optimized to provide an amplitude and frequency apodization function in both the azimuth and elevation directions.
  • Application of this method to transducer array devices provides a customized smoothing of the physical boundaries of the transducer elements, thereby preventing the occurrence of side lobes.
  • a further aspect of the invention is concerned with an improvement of the electrical behavior of the CMUT devices, particularly in arrayed transducer constructions wherein the transducer elements are of very narrow dimensions and the electrical impedance thereof is inherently highly mismatched to that of the transmission line, thereby creating spurious reflections and signal disturbances that affect the pulse shape and frequency response accordingly.
  • the physical characteristics of the CMMs are tailored so as to maximize the capacitance of the membranes, thereby enhancing the efficiency of the elements of the transducer array.
  • the value of the electrical impedance (specifically, the imaginary part) of the array elements is, therefore, reduced, and thus the elements are seen as more resistive than in conventional CMUT designs.
  • Figure 1 is a schematic perspective view of an ultrasonic transducer assembly
  • Figure 2 is a schematic side elevational view of a piezoelectric plate member demonstrating the principle of a piezoelectric plate member vibrating in a thickness mode to provide propagation of ultrasonic waves;
  • FIG. 3 is a cross sectional view of a CMM (capacitive micromachined membrane);
  • Figure 4 is a cross sectional view of a CMUT (capacitive micromachined ultrasonic transducer) device including a plurality of CMMs arranged on a major surface thereof;
  • Figure 5a is a plan view of a CMM while Figure 5b shows a frequency curve versus membrane size of the CMM;
  • Figures 6a and 6b show the influence of the electrode coverage on he surface of a CMM, with Figure 6a showing a collapse voltage curve plotted as a function of the percentage of metallization percentage for the CMM and Figure 6a showing frequency plotted as a function of the percentage of this metallization;
  • Figures 7a to 7e are curves showing he impact of membrane optimization on different characteristics of the CMM
  • Figure 7f is a plan view of an exemplary cell used in explaining Figures 7a and 7b;
  • Figure 8a depicts modeling of an acoustic beam pattern for a non-apodized element of a CMUT
  • Figure 8b depicts modeling of an acoustic beam pattern for an apodized element of a CMUT
  • Figure 9 is a schematic perspective view of a CMUT array device used for imaging
  • Figure 10 is a plan view showing conventional mapping of an element transducer of a CMUT array having capacitive membranes of an identical shape
  • Figure 1 1 is a plan view illustrating a method of apodization of an element transducer in accordance with one embodiment of the invention
  • Figure 12 is a plan view illustrating another method of apodization of an element transducer in accordance with another embodiment of the invention
  • Figure 13 is a plan view illustrating yet another method of apodizing a transducer element of CMUT matrice array in accordance with a further embodiment of the invention
  • Figure 14 is a plan view showing the front surface of a CMUT matrix array in accordance with yet another embodiment of the invention.
  • Figure 15 is a plan view of an arrangement of CMMs for a CMUT annular array in accordance with a further embodiment of the invention.
  • Figure 16 is a plan view illustrating an electrode mapping method for CMMs in accordance with another embodiment of the invention.
  • the term “element transducer” refers to a sub-element aperture of an array transducer and usually comprises a plurality of transducer elements arranged on the full aperture. The term is only applicable to array type transducer apparatus and is not used in connection with single surface transducers.
  • the term “CMM” (or “CMMs”) designates capacitive cells that are machined on or etched into the surface of a silicon substrate in such a manner as to form a transducer surface when a sufficient number of cells are provided.
  • CMUT (or “CMUTs”) designates an ultrasonic transducer comprising a plurality of CMMs or a plurality of CMM groups.
  • CMUT devices can be shaped in various ultrasonic transducer configurations whatever the application or modality.
  • Figures 1 and 2 depict, respectively, a conventional ultrasonic piezoelectric transducer ( Figure 1 ) and the mechanism involved in the emission and reception of ultrasonic waves through pulse excitation of a piezoelectric element or plate ( Figure 2).
  • a typical transducer 1 comprises a piezoelectric member 2 having electrodes 5a and 5b plated or otherwise provided on the major faces thereof in a manner so as to preferably excite the thickness mode of the transducer along with the Z axis, perpendicular to the major surfaces of the transducer.
  • the front face of the piezoelectric member 2 is attached to a set of matching layers adapted to provide smooth transmission and reception of acoustic energy.
  • a backing block 3 is provided which is adapted to cancel reverberations or reflections that are undesirable in the production of acceptable images.
  • the piezoelectric member 2 is manufactured using a high pressure and temperature process, surface displacements are quite uniform over the area of the member, so that control of the acoustic beam produced by the transducer can be carried out by shaping the dimensions of the piezoelectric member 2 using well known principles relating to radiating effects through a finite aperture.
  • CMUT devices In a capacitive apparatus such as a CMUT device, the operating principles are quite different than those associated with conventional transducers.
  • the transducer of such CMUT devices is of a planar type which means that the thickness of the transducer substrate has no impact on the frequency and amplitude of the output acoustic beam.
  • a typical ultrasonic capacitive device that can be used to build CMMs is shown in Figure 3 wherein a cell 6 is formed by depositing a membrane 8 of non-conductive material onto a substrate 7. Substrate 7 includes a thin gap or shallow recess thereon which results in the formation of a cavity 9. Electrodes of the capacitive cell 6 are provided by conductive layers 10a and 10b respectively deposited on the front and back surfaces of the cell 6.
  • CMOS processing technology is used to produce silicon-based capacitive cells of the type shown in Figure 3.
  • substrate 7 which is referred to as the carrier for the electrostatic cells, is made up of a silicon.
  • An intrinsic silicon substrate can also be used with the addition of metal electrodes deposited in the cavity of the cells on the surface of the substrate.
  • an oxide layer e.g., a silicon dioxide (SiO 2 ) layer
  • an oxide layer e.g., a silicon dioxide (SiO 2 ) layer
  • Doped polysilicon is deposited by LPCVD to create the bottom electrode, and the deposit can be patterned so as to reduce parasitic capacitance.
  • a sacrificial layer process is preferably used to create cavities above the membranes. The sacrificial layer can beneficially be an oxide which exhibits a higher etch rate as compared to a nitride.
  • a layer of silicon nitride is then deposited on the oxide layer to form the membrane 8.
  • the silicon nitride layer may, for instance, be produced using a LPCVD (Low Pressure Chemical Vapor Deposition) process or PECVD (Plasma Enhanced Chemical Vapor Deposition) process in order to obtain a low stressed layer on the front face of device.
  • LPCVD Low Pressure Chemical Vapor Deposition
  • PECVD Pasma Enhanced Chemical Vapor Deposition
  • a residual stress of less than 250 MPs for the silicon nitride layer is desired.
  • this stress can vary according to the particular specifications of the transducer.
  • the front electrode 10a is provided at this stage of the manufacturing process. Electrode 10a is advantageously produced by a sputtering process and can be sputtered to a thickness of within 250nm. Because the dimensions of capacitive cells are very small (in the micron range), a combination of a plurality of CMMs electrically connected together is used to form a transducer area for emitting and receiving ultrasonic waves. Referring to Figure 4, a schematic representation of an ultrasonic transducer 1 1 is shown wherein a plurality of CMMs, denoted 6, and corresponding to CMMs 6 1 ... 6 n , are connected to a common ground electrode at the bottom side of the transducer. The front electrodes of the CMMs 6 can be also connected together but this is not required because a plurality of pulsers can be used to drive the front electrodes individually.
  • transducer 1 1 is shown as being formed by a group of similar CMMs uniformly disposed on the upper surface of transducer 1 1 . It is to be understood that this representation is provided for the sake of simplicity, i.e., to simplify the description of the applicable principles here. However, it will be appreciated that CMMs can be designed so as to have many different kinds of shapes and dimensions in order to optimize use of the available transducer surface and thus to maximize the sensitivity of the device. For example, CMMS shapes such as polygons or rectangles have been used. Further, it will be understood that the CMMs are also mapped out over the transducer surface in two directions as well.
  • FIGs 5a and 5b and 6a and 6b illustrate the impact of CMM membrane size and electrode surface ratio on the frequency and the collapse voltage of the corresponding transducer device. It is of particular interest to observe in Figure 5b how the membrane size or membrane shape ratio affects and controls the variation in resonant frequency of the transducer device.
  • the frequency f in Figure 5b is plotted as a function of the quantity 1/p 2 +1/w 2 .
  • the plot shown in Figure 5b demonstrates that control of the membrane shape ratio is a powerful tool for adjusting the frequency distribution over the surface of the transducer, as is further described below in the description of specific preferred embodiments.
  • Figure 6a shows how the percentage of the electrode area, i.e., percentage of the metallization of the cell surface (a partially metallized surface being shown in Figure 5a) can impact on the "collapse voltage" phenomenon which is commonly observed in CMUT devices.
  • the maximum acceptable voltage before the membrane comes into contact with the bottom surface of the cavity is commonly referred to as the "collapse voltage” and can be approximated by
  • V coll ⁇ with k being the rigidity constant of membrane / electrode sandwich, ⁇ 0 being the permittivity of free space, S being the membrane surface, and d 0 being the gap thickness
  • k being the rigidity constant of membrane / electrode sandwich
  • ⁇ 0 being the permittivity of free space
  • S being the membrane surface
  • d 0 being the gap thickness
  • Figures 7a to 7e summarize the expected effects of these variations on different parameters of the device.
  • Figures 7a to 7e respectively show the effect of variations in cell length (p CMUT cell), % of electrode coverage or metallization (%M), voltage (voltage collapse), frequency f and output pressure Pr.
  • Figure 7f is a plan view of capacitive membrane provided to better show how the cell surface can be shaped with respect to the footprint thereof (p CMUT cell) and the percentage of the electrode coverage, i.e., metallization (%M).
  • FIGs 8a and 8b modeling of the acoustic beam patterns from the transducer aperture without apodization is shown in Figure 8a and with apodization in Figure 8b. These figures clearly show the benefit that can be obtained when apodization is adequately applied. In particular, the effect of the apodization function on the shape of the beam patterns is illustrated, and, as shown, a significant improvement in the beam shape is obtained. Of course, further enhancement of the beam pattern can be achieved by providing other apodization functions with respect to the corresponding transducer aperture.
  • apodization functions have much greater impact when applied to array designs wherein the sizing of different components of the array strongly affects the final performance by the array in terms of the size of the side lobes, the shape of the beam pattern and the pulse shape of the transducer.
  • Conventional piezoelectric array imaging systems often provide electronic apodization functions to synthetic acoustic apertures (electronic linear array systems) in order to improve the quality of the images obtained.
  • the output level of the excitation provided for every transducer element is individually controlled by the system so as to produce a smooth gaussian shape over the width of the aperture.
  • CMUT 12 comprises a silicon substrate 16 serving as carrier for a plurality of CMMs 13 carried thereby.
  • the arrayed CMUT device 12 includes a plurality of element transducer surfaces 15 which are formed by a plurality of CMMs 13 separated by associated passive kerfs 14 which preferably comprise bulk silicon.
  • the arrayed CMUT device 12 has two major axes, viz., an azimuth axis where the element transducers are arranged with apertures (a) and an elevation axis wherein the geometrical focus is defined by curving the array or by adding a (e.g., silicon rubber) lens or lens assembly.
  • a e.g., silicon rubber
  • the transducer elements extending in the azimuth direction are controlled by the system, while in the elevation direction, a hard focus must be employed in order to perform a focal adjustment.
  • the arrayed transducer 12 has a much larger azimuth dimension than elevation dimension, but in phased array devices there can be only a small difference between the two dimensions since the phase shift of the transducer excitations is applied to steer the acoustic beam and, as a result, the synthetic aperture does not physically move (slide).
  • FIG. 10 perhaps better illustrates the details of a single element transducer 15 formed by arrangement of CMMs 13 as described above in connection with Figure 9.
  • the shape of the CMMs 13 in Figure 10 is an example of one of many possible shapes, i.e., the
  • CMMs can be designed in many different ways so long as the designs are technologically feasible based on the technologies that are available at the time or that become available.
  • the footprint of the element transducer 15 is obtained by mapping the surface thereof with single CMMs 13.
  • the rectangular footprint shown is only shown for purposes of clarity of the illustration, and essentially any other shape can be obtained without difficulty. This is in contrast to conventional array transducers where dicing is required to physically separate two adjacent elements, thus making it difficult to produce any element shapes other than rectangular.
  • an arrayed CMUT device is provided with an element transducer similar to that shown in Figure 9 wherein a plurality of the elements of the CMMs are regularly disposed along the azimuth axis and each elemental transducer is composed of, and its surface defined by, an arrangement of CMMs which exhibit a first, smaller dimension "a" in the azimuth direction and a second larger dimension "L” in the elevation direction as shown in Figure 9.
  • all element transducers are assumed to be identical in size and frequency in the preferred embodiment, so that this approach is compatible with linear array construction and operations (wherein the synthetic acoustic aperture shifts back and forth along the azimuth axis).
  • the element aperture size is defined according to the requirements of synthetic electronic array systems wherein the pitch is usually of a value ranging from one- half to two wavelengths of the transducer. Every element is independently driven by excitation circuitry so that electronic apodization functions can still be applied, as is the case in existing transducer devices.
  • One feature of the method and apparatus disclosed herein concerns the apodization of the element transducer itself by implementing shifting functions with respect to the sizes of the single CMMs that cover the surface of the element transducer.
  • This is illustrated in Figure 1 1 , wherein CMMs 17 are arranged in two orthogonal directions (the t direction in Figure 1 1 ) to form the active surface of the element transducer 15, i.e., in the width direction as viewed in Figure 1 1 .
  • the pitch of CMMs 17 is uniform so that each vertical line of CMMs 17 is identical to the others.
  • all CMMs 17 located on the same horizontal line are identical in construction and will operate the same way.
  • a plurality of horizontal lines of CMMs 17 are formed wherein the heights of the individual CMMs 17 vary progressively from the center of the element transducer to both outermost edges, so that the height of the CMMs 17 is relatively small in the middle and relatively large at the two ends.
  • the height variation function i.e., the manner in which the heights of the CMMs 17 vary, can be determined based on linear or gaussian or any other mathematical shifting functions. The choice of shifting function is determined by the final acoustical beam shape that is desired. As previously discussed in connection with Figures 5 and 7, the membrane dimensions of a CMM strongly impact on such intrinsic parameters of the transducer as output sensitivity and frequency.
  • the resultant element transducer 15 will have the amplitude and frequency thereof shifted from the center to the outermost edges. This will result in a vibration function that is implemented with a customized apodization, in this case, in the w direction, as illustrated.
  • the configuration of the element transducer shown in Figure 1 1 would then correspond to an elevational apodization that would be beneficial to a transverse transducer focus.
  • the w dimension is made much smaller than the t dimension then apodization effect will be applied to the azimuth direction of the transducer, as shown in Figure 9, so the angular directivity of the element transducer is affected.
  • apodization of the CMMs is provided in either the azimuth direction or the elevation direction on a single element transducer surface in such a manner as to improve the acoustical and electrical behavior of the transducer.
  • improvements can be afforded by providing amplitude and/or frequency apodization in both major directions of the transducer simultaneously as shown in Figure 12.
  • the embodiment of Figure 12 is distinguished from that of Figure 1 1 by the fact that CMMs 17 of the two dimensions t and w are apodized independently so as to provide the desired acoustical radiating effects required by high performance array transducers wherein a large element transducer width is desirable (i.e., a width greater than 2 wavelengths) wherein a smooth acoustical radiation pattern in elevation is required (it being noted that most NDT or high intensity ultrasound devices are designed to meet these requirements).
  • the CMMs 17 are arranged in a pattern wherein the width dimensions thereof increase progressively from the center to the outermost edges of the element transducer 15 to create a weighting effect along the t dimension.
  • This arrangement is provided to emphasize the "pre-accentuation" function of sensitivity and/or frequency distribution so that the acoustic response in this embodiment is improved.
  • the pre-accentuation function can also be reversed, i.e., the arrangement can be such that the CMMs 17 decrease in size from the center to the edges, without departing from the basic principle here.
  • the arrangement and dimensional shift of the CMMs 17 can be similarly implemented. The fact is that the w dimension for a conventional array CMUT is normally much larger than the t dimension so that the apodization function applied here can be advantageously customized to obtain the results desired.
  • FIG. 13 One example of a customized CMM combination for a square shaped element transducer surface 15 is illustrated in Figure 13 wherein the dimension of the CMMs 17 is progressively changed from the center of the surface to the edges or external boundaries thereof, and with symmetry being maintained in both perpendicular directions.
  • the embodiment of Figure 13 actually provides an apodization wherein the CMMs 17 increase in size from the center area to the edges, but it will be understood that the inverse apodization can, of course, be used, and will be used as desired by the designer or required by the particular application.
  • square and rectangular shapes for element transducer surface 15 are not the only shapes to which the method of the invention is applicable. For example, other shapes such as ovoid, circular, or polygonal can also be used.
  • a 2D combination of CMMs 17 arranged as shown in Figure 13 form a matrix (2D) array CMUT wherein each element transducer 15 thereof can be implemented as previously described.
  • the matrix CMUT so obtained exhibits a unique opportunity in providing customization of the elements thereof in order to minimize inter-element cross-coupling and to reduce the side lobes when operated in strong steering positions.
  • apodization of the CMMs 17 can be done differently in one area of the array than another so that predetermined apodization can be implemented on the array itself, if desired. Since each CMM 17 can be defined or implemented individually, any 2D array configuration is, therefore, possible
  • FIG. 15 Yet another example of a combination of CMMs or groups of CMMs is disclosed in Figure 15 for an annular array CMUT device.
  • Annular array devices are commonly used for high performance imaging applications including continuous focusing for better lateral resolution.
  • the transducer has concentric active areas that are electrically isolated from each other.
  • annular arrays produced by this approach includes rings of unequal area and because of this, major difficulties are encountered in perfectly matching the rings to the pulser/receiver.
  • an annular array 18 has three concentric rings 19, 20, 21 . It will be appreciated that the number of rings employed is obviously not limited to three but the number is preferably between 2 and 20 for most applications. However, higher numbers of rings can, of course, be used. As is evident from Figure 15, the "ring" located at the center position (ring 21 ) is actually a disc or circular member having only an external diameter while the other rings 19 and 20 have both internal and external dimensions that cannot overlap, according to Fresnel principles.
  • disc 21 is located at the center of the device and comprises CMMs 21 a that map the surface of the disc. It is important to note that CMMs of the same ring or element transducer of the annular array CMUT can be identically shaped or can have different shapes and dimensions so as to exhibit the desired effects. In the preferred embodiment shown in Figure 15, element transducers having the same types of CMMs are illustrated for ease of representation and purposes of clarity.
  • Ring 20 is disposed adjacent to central disc 21 and comprises a plurality of CMMS 20a that can be the same as, or different from, those of the immediate neighboring ring.
  • outer ring 19 is disposed outwardly of ring 20 and comprises CMMS 19a.
  • additional rings can be employed if desired.
  • Figure 15 illustrates am embodiment comprising rings with CMMs having dimensions which increase progressively from the center outwardly, but it will be understood that this is only one example of the many possibilities available in mapping out the annular array.
  • the difference between the internal and external diameters of a ring can decrease or diminish outwardly toward the edge of the array, and the CMMs can be shaped individually for each ring. Further, the sizes of CMMs can decrease and can be smallest at the edge of the array.
  • element transducer 22 is a rectangular aperture having t and w dimensions (only the t dimension is labeled) which can be much different from each other.
  • CMMs are arranged along these two perpendicular axes and are of the same shape and size.
  • CMMs 23, 24 and 25 have respective electrodes 23a, 24a, 25a which partially or totally cover the surface of the vibrating membrane of the CMMs.
  • the covering percentage of the electrodes increases from the center to the outside but this percentage can be the opposite of this without departing from the basic principle here.
  • the variation in the electrode covering percentage can be also applied to the w dimension, with the same principle of identical or different distribution, to obtain the desired effect in this direction.

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  • Transducers For Ultrasonic Waves (AREA)

Abstract

L'invention concerne un réseau de transducteurs ultrasonores micro-usinés capacitifs (CMUT), qui inclut une ouverture élémentaire améliorée pour des opérations d'imagerie. Le transducteur peut présenter une configuration à surface linéaire, linéaire incurvée, annulaire, matricielle ou même à surface unique. Les ouvertures élémentaires sont formées par un ensemble spécifique de membranes micro-usinées capacitives (CMM) de manière à avoir un comportement électrique et acoustique idéal en fonctionnement avec des systèmes d'imagerie. Les ensembles de CMM peuvent être soit classiques lorsque les transducteurs à éléments du réseau sont uniformément formés par des CMMs prédéfinies de manière à avoir un comportement acoustique similaire à un transducteur piézoélectrique, soit plus sophistiqués, chaque transducteur à éléments étant alors formé par une combinaison spécifique de différentes CMMs (c'est-à-dire, d'une forme et/ou dimension différente) de sorte à conférer au transducteur une apodisation acoustique intégrée qui peut être implémentée dans l'azimut et/ou la verticale du dispositif.
PCT/IB2007/002658 2007-06-26 2007-06-26 Transducteur ultrasonore micro-usiné capacitif destiné à des ouvertures de transducteur à éléments WO2009001157A1 (fr)

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PCT/IB2007/002658 WO2009001157A1 (fr) 2007-06-26 2007-06-26 Transducteur ultrasonore micro-usiné capacitif destiné à des ouvertures de transducteur à éléments

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PCT/IB2007/002658 WO2009001157A1 (fr) 2007-06-26 2007-06-26 Transducteur ultrasonore micro-usiné capacitif destiné à des ouvertures de transducteur à éléments

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WO2009001157A1 true WO2009001157A1 (fr) 2008-12-31

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20070193354A1 (en) * 2006-02-21 2007-08-23 Nicolas Felix Capacitive micro-machined ultrasonic transducer for element transducer apertures
WO2014066991A1 (fr) * 2012-11-02 2014-05-08 University Of Windsor Microréseau de capteur ultrasonique et son procédé de fabrication
US9187316B2 (en) 2013-07-19 2015-11-17 University Of Windsor Ultrasonic sensor microarray and method of manufacturing same
US9364862B2 (en) 2012-11-02 2016-06-14 University Of Windsor Ultrasonic sensor microarray and method of manufacturing same
US9997425B2 (en) 2015-07-14 2018-06-12 University Of Windsor Layered benzocyclobutene interconnected circuit and method of manufacturing same

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Publication number Priority date Publication date Assignee Title
US6262946B1 (en) * 1999-09-29 2001-07-17 The Board Of Trustees Of The Leland Stanford Junior University Capacitive micromachined ultrasonic transducer arrays with reduced cross-coupling
US6381197B1 (en) * 1999-05-11 2002-04-30 Bernard J Savord Aperture control and apodization in a micro-machined ultrasonic transducer
WO2007013814A2 (fr) * 2005-07-26 2007-02-01 Angelsen Bjoern A J Reseaux de transducteur ultrasonore a bande de frequence double
EP1764162A1 (fr) * 2005-09-14 2007-03-21 Esaote S.p.A. Transducteur capacitif ultrasonique microfabriqué pour applications haute fréquence
EP1779784A1 (fr) * 2004-06-07 2007-05-02 Olympus Corporation Transducteur ultrasonique à capacité électrostatique

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6381197B1 (en) * 1999-05-11 2002-04-30 Bernard J Savord Aperture control and apodization in a micro-machined ultrasonic transducer
US6262946B1 (en) * 1999-09-29 2001-07-17 The Board Of Trustees Of The Leland Stanford Junior University Capacitive micromachined ultrasonic transducer arrays with reduced cross-coupling
EP1779784A1 (fr) * 2004-06-07 2007-05-02 Olympus Corporation Transducteur ultrasonique à capacité électrostatique
WO2007013814A2 (fr) * 2005-07-26 2007-02-01 Angelsen Bjoern A J Reseaux de transducteur ultrasonore a bande de frequence double
EP1764162A1 (fr) * 2005-09-14 2007-03-21 Esaote S.p.A. Transducteur capacitif ultrasonique microfabriqué pour applications haute fréquence

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20070193354A1 (en) * 2006-02-21 2007-08-23 Nicolas Felix Capacitive micro-machined ultrasonic transducer for element transducer apertures
US8456958B2 (en) * 2006-02-21 2013-06-04 Vermon S.A. Capacitive micro-machined ultrasonic transducer for element transducer apertures
WO2014066991A1 (fr) * 2012-11-02 2014-05-08 University Of Windsor Microréseau de capteur ultrasonique et son procédé de fabrication
US9364862B2 (en) 2012-11-02 2016-06-14 University Of Windsor Ultrasonic sensor microarray and method of manufacturing same
US9187316B2 (en) 2013-07-19 2015-11-17 University Of Windsor Ultrasonic sensor microarray and method of manufacturing same
US9997425B2 (en) 2015-07-14 2018-06-12 University Of Windsor Layered benzocyclobutene interconnected circuit and method of manufacturing same

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