Asymmetrical ultrasound transducer array

An array of micromachined ultrasonic transducers (MUTs). The array has first and second rows, the MUTs in the first row being equally spaced by a horizontal pitch in a horizontal direction, the MUTs in the second row being equally spaced by the horizontal pitch in the horizontal direction. The MUTs in the second row are shifted along the horizontal direction by a first horizontal distance relative to the MUTs in the first row and shifted along a vertical direction by a first vertical distance relative to the MUTs in the first row. The first horizontal distance is greater than zero and less than the horizontal pitch. The first vertical distance ranges from one tenth of a horizontal width of a MUT to a half of a vertical height of a MUT.

BACKGROUND

A. Technical Field

The present invention relates to imaging devices, and more particularly, to imaging devices having micromachined ultrasound transducers (MUTs).

B. Background of the Invention

A non-intrusive imaging system for imaging internal organs of a human body and displaying images of the internal organs transmits signals into the human body and receives signals reflected from the organ. Typically, transducers that are used in an imaging system are referred to as transceivers and some of the transceivers are based on photo-acoustic or ultrasonic effects. In general, transceivers are used for imaging as well as other applications, such as medical imaging, flow measurements in pipes, speaker, microphone, lithotripsy, heating tissue for therapeutics, and highly intensive focused ultrasound (HIFU) for surgery.

Advances in micro-machining technologies allow sensors and actuators to be efficiently incorporated on a substrate. In particular, micromachined ultrasound transducers (MUTs), using capacitive transducers (cMUTs) or piezoelectric transducers (pMUTs), are particularly advantageous compared to the conventional MUTs having a large form factor.FIG. 1shows a two dimensional rectilinear transceiver array50in a conventional system. As depicted, the transceiver array50may include: a set of MUTs52that generates and transmit pressure waves in a transmit mode/process and that receive pressure waves and develop electrical charge in response to the received pressure waves in a receive mode/process. As depicted, the MUTs52are uniformly spaced in the x- and y-directions, i.e., the distance from one MUT to a neighboring MUT along the x-direction (or the y-direction) is the same throughout the array. The MUTs52tend to have a limited number of vibrational resonances, i.e., the MUTs array52may have a limited bandwidth in the frequency domain. In general, the wider bandwidth the MUTs52have, the more sophisticated operational modes the MUTs52may be operated in and the better images the transceiver array50may be able to generate. As such, there is a strong need to design MUTs that have increased bandwidth for enhanced acoustic performances.

SUMMARY OF THE DISCLOSURE

In embodiments, a transducer array including a plurality of micromachined ultrasonic transducers (MUTs) arranged in an asymmetric arrangement.

In embodiments, an array of micromachined ultrasonic transducers (MUTs) includes MUTs arranged in a two dimensional array that has first and second rows, the MUTs in the first row being equally spaced by a horizontal pitch in a horizontal direction, the MUTs in the second row being equally spaced by the horizontal pitch in the horizontal direction. The MUTs in the second row are shifted along the horizontal direction by a first horizontal distance relative to the MUTs in the first row and shifted along a vertical direction by a first vertical distance relative to the MUTs in the first row. The first horizontal distance is greater than zero and less than the horizontal pitch. The first vertical distance ranges from one tenth of a horizontal width of a MUT of the plurality of MUTs to a half of a vertical height of the MUT.

In embodiments, an imaging system includes a transceiver tile for generating a pressure wave and converting an external pressure wave into an electrical signal, and a control unit for controlling the transceiver tile. The transceiver tile includes an array of micromachined ultrasonic transducers (MUTs), where the array includes MUTs arranged in a two dimensional array that has first and second rows, the MUTs in the first row being equally spaced by a horizontal pitch in a horizontal direction, the MUTs in the second row being equally spaced by the horizontal pitch in the horizontal direction. The MUTs in the second row are shifted along the horizontal direction by a first horizontal distance relative to the MUTs in the first row and shifted along a vertical direction by a first vertical distance relative to the MUTs in the first row. The first horizontal distance is greater than zero and less than the horizontal pitch. The first vertical distance ranges from one tenth of a horizontal width of a MUT of the plurality of MUTs to a half of a vertical height of the MUT.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Elements/components shown in diagrams are illustrative of exemplary embodiments of the disclosure and are meant to avoid obscuring the disclosure. Reference in the specification to “one embodiment,” “preferred embodiment,” “an embodiment,” or “embodiments” means that a particular feature, structure, characteristic, or function described in connection with the embodiment is included in at least one embodiment of the disclosure and may be in more than one embodiment. The appearances of the phrases “in one embodiment,” “in an embodiment,” or “in embodiments” in various places in the specification are not necessarily all referring to the same embodiment or embodiments. The terms “include,” “including,” “comprise,” and “comprising” shall be understood to be open terms and any lists that follow are examples and not meant to be limited to the listed items. Any headings used herein are for organizational purposes only and shall not be used to limit the scope of the description or the claims. Furthermore, the use of certain terms in various places in the specification is for illustration and should not be construed as limiting.

FIG. 2shows an imaging system100according to embodiments of the present disclosure. As depicted, the system100may include: an imager120that generates and transmit pressure waves122toward an internal organ112, such as heart, in a transmit mode/process; and a device102that communicates signals to the imager through a communication channel130. In embodiments, the internal organ112may reflect a portion of the pressure waves122toward the imager120, and the imager120may capture the reflected pressure waves and generate electrical signals in a receive mode/process. The imager120may communicate the electrical signals to the device102and the device102may display images of the human organ on a display/screen104using the electrical signals.

It is noted that the imager120may be used to get an image of internal organs of an animal, too. It is also noted that the pressure wave122may be acoustic, ultrasonic, or photo-acoustic waves that can travel through the human/animal body and be reflected by the internal organs.

In embodiments, the imager120may be a portable device and communicate signals through the communication channel130, either wirelessly or via a cable, with the device102. In embodiments, the device102may be a mobile device, such as cell phone or iPad, or a stationary computing device that can display images to a user.

FIG. 3shows a schematic diagram of the imager120according to embodiments of the present disclosure. In embodiments, the imager120may be an ultrasonic imager. As depicted inFIG. 2, the imager120may include: a transceiver tile(s)210for transmitting and receiving pressure waves; a coating layer212that operates as a lens for focusing the pressure waves and also functions as an impedance interface between the transceiver tile and the human body110; a control unit202, such as ASIC chip, for controlling the transceiver tile(s)210; a microprocessor214for controlling the components of the imager120; a communication unit208for communicating data with an external device, such as the device102, through one or more ports230; a memory218for storing data; a battery206for providing electrical power to the components of the imager; and optionally a display216for displaying images of the target organs.

In embodiments, the device102may have a display/screen. In such a case, the display may not be included in the imager120. In embodiments, the imager120may receive electrical power from the device102through one of the ports230. In such a case, the imager120may not include the battery206. It is noted that one or more of the components of the imager120may be combined into one integral electrical element. Likewise, each component of the imager120may be implemented in one or more electrical elements.

In embodiments, the user may apply gel on the coating layer212so that the impedance matching between the coating layer212and the human body110may be improved, i.e., the power loss at the interface is reduced.

FIG. 4shows an enlarged view of an asymmetric (or staggered) rectilinear transceiver array400including MUTs402according to embodiments of the present disclosure. In embodiments, the array400may be included in the transceiver tile210. The MUTs402may be arranged in a staggered configuration to bring a benefit of the array acoustic performance. Hereinafter, the term staggered (or asymmetric) array refers to an array of MUTs, where the MUTs in a first row are shifted along the x-direction403relative to the MUTs in a second row. In embodiments, the MUTs in a row may be equally spaced by a horizontal distance (pitch) P1430and the MUTs in a column may be equally spaced by a vertical distance (pitch) P2432.

In embodiments, each MUT402may by a pMUT and include a piezoelectric layer formed of at least one of PZT, KNN, PZT-N, PMN-Pt, AlN, Sc—AlN, ZnO, PVDF, and LiNiO3. In alternative embodiments, each MUT402may be a cMUT. InFIG. 4, each MUT402is shown to have a rectangular shape. More specifically, each MUT may include a top electrode that has a rectangular projection area. It should be apparent to those of ordinary skill in the art that the top electrode may have other suitable geometrical shape, such as, square, circle, ellipse, oval, so on. For the purpose of illustration, in the drawings of the present application, each MUT is symbolically represented by the geometrical shape of the top electrode.

FIG. 5shows an enlarged view of a MUT array500according to embodiments of the present disclosure. In embodiments, the array500may correspond to the portion of array404inFIG. 4. As depicted, the array500may include MUTs502and electrical pads504. In embodiments, the MUTs502and pads504are arranged in a staggered configuration. In embodiments, each electrical pad504may electrically couple one or more of the MUTs502to a substrate, such as an ASIC or an electrical board (not shown inFIG. 5), where the substrate may contain electronics to send/receive electrical signals to/from the MUTs502. In embodiments, the substrate may be disposed under the MUT array and each pad504may extend in a vertical direction (i.e., in a direction normal to the paper). It is noted that other electrical connections between the MUTs502and pads504are not shown inFIG. 5, but it should be apparent to those of ordinary skill in the art that suitable electrical connections, such as traces and wires, may be used to electrically connect the MUTs502to the pads504.

FIG. 6shows an enlarged view of a MUT array600according to embodiments of the present disclosure. In embodiments, the array600may correspond to the portion of array404inFIG. 4. In embodiments, the MUTs600may be arranged in a staggered or asymmetric configuration and also certain amount of randomness may be introduced to the orientation of each MUT. In embodiments, the randomness may bring acoustic signal enhancement to an imager by reducing the crosstalk among MUTs602. In embodiments, the randomly rotated MUT602may remain on the x-y plane, while each electrical pad604may be disposed in a comparable way to a pad location in the MUT array500.

FIG. 7shows two pairs of MUTs702and pads704that are arranged in a staggered configuration according to embodiments of the present disclosure. For the purpose of illustration, each MUT is represented by a rectangle that is a projection area of the top electrode of the MUT. In embodiments, the two MUTs702aand702binFIG. 7may be two neighboring MUTs in the MUT array400. As depicted, the MUTs702aand702bmay be separated by a horizontal distance, HD,706in the x-direction and by a vertical distance, VD,708in the y-direction. Each MUT702may have a rectangular shape with the width, W,712and height, H,714. In embodiments, the horizontal distance HD706may be greater than zero and less than four times the horizontal width712of the MUT and less than the pitch in the x-direction.

Unlike the conventional MUT array50, in embodiments, the MUTs702aand702bmay be arranged in a staggered configuration, i.e., the pair of MUT702aand pad704ain the first row may be shifted along the x-direction relative to the pair of MUT702aand pad704bin the second row. As a result of the staggered configuration, the MUT array400may have one or more asymmetric vibrational modes (or, shortly, asymmetric modes), resulting in a wider bandwidth than the conventional MUT array50. As the MUT array400may have wider bandwidth, the MUT array may be operated in more sophisticated operational modes.

In general, the number density of the MUTs in a MUT array may affect the resolution of the images generated by the MUT array. In the conventional MUT array50, the number density of the MUTs may be increased by decreasing the horizontal distance (or equivalently horizontal pitch) between the MUTs. However, in the conventional MUT array, the mutual impedance between two neighboring MUTs may also increase as the horizontal pitch decreases, which may negate the advantage obtained by the increase of number density. Hereinafter, the mutual impedance refers to the acoustic coupling between two MUTs. In contrast, in embodiments, the diagonal distance, P,730may be the effective separation between the MUTs702aand702b. As such, in embodiments, the mutual impedance may be less than the conventional symmetric MUT array that has the same horizontal separation HD706. Stated differently, the staggering configuration may allow the number density to be increased without out increasing mutual impedance significantly.

In embodiments, the vertical distance708may affect the characteristics of the asymmetric modes of vibration, such as the frequencies of the asymmetric modes and acoustic pressures at vibrational modes, as explained in conjunction withFIGS. 8A-9. Hereinafter, the term acoustic pressure refers to the level of acoustic power generated by each MUT. In embodiments, the vertical distance708may be preferably greater than one tenth of the width712and less than the half of the height714. In embodiments, as the VD708increases up to less than one half of the height714, an acoustic pressure amplitude at the asymmetrical modes may increase.

FIGS. 8A-8Dshow a set of vibrational mode shapes of the MUT702b, taken along the direction7-7inFIG. 7, according to embodiments of the present disclosure. For the purpose of illustration, the MUT702bis represented by a single line inFIGS. 8A-8D. However, it should be apparent to those of ordinary skill in the art that the MUT may include a stack of layers. As depicted,FIG. 8AandFIG. 8Cpresent a first vibrational mode801and a third vibrational mode807of the MUT702bat the first and third resonance frequencies, respectively, where an arrow804indicates the direction of motion of the MUT702b. In embodiments, the first and third vibrational modes may be symmetric, i.e., each mode shape is symmetrical with respect to the centerline820of the MUT720b. In embodiments, the symmetric modes may be generated even when the MUTs are not staggered, i.e., the symmetric MUT array50may have the symmetric vibrational modes inFIGS. 8A and 8C.

In embodiments,FIGS. 8B and 8Dshow the second vibrational mode805and fourth vibrational mode809at the second and fourth resonance frequencies of the MUT702b, respectively. As depicted, the second and fourth vibrational modes may be asymmetric, i.e., the MUT is not symmetric with respect to the centerline820. In embodiments, the asymmetry of the vibrational mode may be obtained by arranging the MUTs in the staggered (asymmetric) configuration, as shown inFIG. 4.

In general, the acoustic pressure performance, which refers to the energy of an acoustic pressure wave generated by each MUT at a frequency, may increase as the peak amplitude of the MUT increases at the frequency. In embodiments, an asymmetric mode may enable wider bandwidth than a symmetric mode when they are vibrating in the same order. For instance, the third mode807and fourth mode809may have the same order, i.e., the same number of nodal points, and the peak amplitude840of the third mode807is smaller than the peak amplitude842of the fourth mode809.

FIG. 9shows a frequency response plot900of the asymmetrical MUT array400according to embodiments of the present disclosure. InFIG. 9, the curve912shows the response (y-axis) of the array400as a function of frequency, where the response refers to the peak amplitude of the pressure waves generated by the array during the transmit mode or the electrical charge developed during the receive mode. InFIG. 9, the curve910shows the response of a symmetric array50as a function of frequency.

As depicted, the staggered MUT array400may have a resonance vibrational mode near the frequency914, where the frequency914may be also the resonance vibrational mode of the symmetric MUT array50. In embodiments, the staggered MUT array400inFIG. 7may have additional resonance frequency at the frequency916, which is referred to as asymmetric resonance frequency. In embodiments, with both symmetrical and asymmetrical modes of vibration, as depicted inFIG. 9, the gain of acoustic response may increase, and the bandwidth may improve since the MUT array400may be operated at both the center symmetric frequency914and a high asymmetric frequency916.

It is noted that the frequency response curve912may include the contribution from all of the MUTs in the array400. Since each MUT in the staggered MUT array400may have the same frequency response characteristics, each MUT has the similar frequency response curve to the curve912, i.e., the each MUT in the asymmetric array400may have resonance frequencies at both the center symmetric frequency914and an asymmetric frequency916.

In embodiments, a beamforming technique may be used to direct the pressure waves transmitted by the imager120to a particular angle, i.e., the pressure waves from the MUT array400may be combined in such a way that pressure waves at a particular angle (i.e., beamforming direction) experience constructive interference while others experience destructive interference. In embodiments, the control unit202may control the phase and/or amplitude of the pressure waves generated by the MUT array400to steer the beamforming direction.FIG. 10shows a plot of acoustic beam pattern responses of MUT arrays as functions of elevation angle according to embodiments of the present disclosure. InFIG. 10, each curve shows the acoustic response (y-axis) of a MUT array as a function of elevation angle, where the acoustic response refers to the peak amplitude of the pressure waves generated by the MUT array during the transmit mode (or the electrical charge developed during the receive mode), and the elevation angle refers to the angular distance relative to the beamforming direction.

In general, the directivity, which refers to blocking of noise outside the direction of interest1020, affects the signal-to-noise ratio in the beamforming. (Hereinafter, the term direction of interest refers to a preset angular range around the beamforming direction.) InFIG. 10, a curve1002may indicate a normalized power directivity for both an symmetric (staggered) MUT array (such as400) and asymmetric (non-staggered) array (such as50) at the frequency of 1.5 MHz. Curves1006aand1006bshow the directivity of symmetric and asymmetric arrays, respectively, at the frequency of 3.0 MHz. As depicted, the symmetric MUT array may have similar beam patterns as the asymmetric MUT array at the frequencies of 1.5 MHz and 3.0 MHz.

Curves1004aand1004bshow beam patterns of symmetric and asymmetric arrays, respectively, at the frequency of 5.7 MHz. As depicted, the asymmetric array has higher (improved) directivity than the symmetric array, resulting in improved signal-to-noise ratio and image quality. For instance, the curves1004aand1004bhave regions1010aand1010bthat are outside the direction of interest1020. As the power level at the region1010bis lower than the power level at the region1010a, the asymmetric array may have improved signal-to-noise ratio, which in turn improves the image quality.

In embodiments, the top electrodes of the MUTs in the array400may have different geometrical shapes, such as circle, ellipse, oval, so on.FIG. 11shows two pairs of elliptical MUTs and circular pads that are arranged in a staggered configuration according to embodiments of the present disclosure. As depicted, the MUTs1102may be separated by a horizontal distance, HD,1106in the x-direction and by a vertical distance, VD,1108in the y-direction. Each MUT1102may have an elliptical shape with the width, W,1112and height, H,1114.

Unlike the conventional MUT array50, in embodiments, the MUTs1102aand1102bmay be arranged in a staggered configuration, i.e., the pair of MUT1102aand pad1104ain the first row may be shifted along the x-direction relative to the pair of MUT1104band pad1104bin the second row. In embodiments, the vertical distance1108may be preferably greater than one tenth of the horizontal width1112and less than one half of the vertical height1114. In embodiments, as the VD1108increases up to one half of the vertical height1114, an acoustic pressure amplitude at the asymmetrical modes may increase.

As a result of the staggered configuration, the MUT array having the staggered configuration inFIG. 11may have the similar advantages as the MUT array having the staggered configuration inFIG. 7, i.e., the staggered MUT array inFIG. 11may have improved bandwidth, image resolution, field of view, acoustic pressure, and mutual impedance between MUTs, compared to non-staggered MUT array. In embodiments, the MUTs may be separated by a horizontal distance1106, where the horizontal distance1106may be greater than zero and less than four times the horizontal width1112of the MUT and less than the pitch in the x-direction.

FIG. 12shows an enlarged view of an asymmetric (or staggered) rectilinear transceiver array1200including MUTs1202according to embodiments of the present disclosure. The MUTs1202may be arranged in a staggered configuration to bring a benefit of the array acoustic performance. As depicted, the MUTs in each row may be equally spaced by a horizontal distance (pitch) and MUTs in each column may be equally spaced by a vertical distance (pitch). In embodiments, the MUTs in the second row may be shifted along the x-direction1203relative to the MUTs in the first row by a first horizontal distance, and the MUTs in the third row may be shifted along the x-direction relative to the MUTs in the first row by a second horizontal distance, where the first and second horizontal distances may be greater than zero and less than the horizontal pitch, P1.

FIG. 13Ashows a top view of an exemplary MUT1300according to embodiments of the present disclosure.FIG. 13Bshows a cross-sectional view of the MUT1300inFIG. 13A, taken along the line13-13, according to embodiments of the present disclosure. As depicted, the MUT may include: a membrane layer1306, suspended from a substrate1302; a bottom electrode (O)1308disposed on the membrane layer (or, shortly membrane)1306; a piezoelectric layer1310disposed on the bottom electrode (O)1308; and a top electrode (X)1312disposed on the piezoelectric layer1310. In embodiments, an electrical pad1314, which may be a via filled with electrically conducting material, may be formed so that the bottom electrode (O)1308may be electrically connected to an electrical conductor1320. In embodiments, an electrical conductor1322may be electrically connected to the top electrode1312. In embodiments, the electrical conductors1320and1322may be electrical wires or traces formed by patterning a metal layer. In embodiments, the pad1314and top electrode1312may correspond to the pad704(or1104) and MUT1102(or1102), respectively.

In embodiments, the substrate1302and the membrane1306may be one monolithic body and the cavity1304may be formed to define the membrane1306. In embodiments, the cavity1304may be filled with a gas at a predetermined pressure or an acoustic damping material to control the vibration of the membrane1306.

It is noted that the MUTs in the transceiver arrays400and1200may have other configuration than the MUT1300inFIG. 13A. For instance, each MUT may have more than one top electrode. It should be apparent to those of ordinary skill in the art that each rectangle (or ellipse) inFIGS. 4-7(orFIGS. 11-12) symbolically represents a MUT, where the MUT may have one or more top electrodes and the top electrodes may have suitable geometrical shapes, such as circle, rectangle, ellipse, so on.

While the invention is susceptible to various modifications and alternative forms, specific examples thereof have been shown in the drawings and are herein described in detail. It should be understood, however, that the invention is not to be limited to the particular forms disclosed, but to the contrary, the invention is to cover all modifications, equivalents, and alternatives falling within the scope of the appended claims.