WO2017182416A1

WO2017182416A1 - Ultrasound transducer positioning

Info

Publication number: WO2017182416A1
Application number: PCT/EP2017/059085
Authority: WO
Inventors: David Andrew Fish; Mark Thomas Johnson
Original assignee: Koninklijke Philips N.V.
Priority date: 2016-04-19
Filing date: 2017-04-18
Publication date: 2017-10-26

Abstract

Disclosed is an ultrasound system (1) comprising an ultrasound transducer array (110). The array comprises a carrier (160) carrying an actuator arrangement comprising a plurality of actuators, each actuator comprising a material (54) having an adjustable shape in response to an electromagnetic stimulus; a plurality of ultrasound transducer element tiles (100) on the actuator arrangement such that each actuator is arranged to adjust the orientation an ultrasound transducer element tile in response to said electromagnetic stimulus, each ultrasound transducer element tile comprising at least one ultrasound transducer element; and a plurality of capacitive sensors (70), each capacitive sensor comprising a first sensing electrode (141) on a surface (103) of one of the ultrasound transducer element tiles facing a surface portion (162) of the carrier and a second sensing electrode (161, 16Γ) οη said surface portion. The actuator arrangement further comprises a controller arrangement for each actuator, the controller arrangement adapted to generate the electromagnetic stimulus for said actuator in response to capacitive sensor data provided by a capacitive sensor having a first sensing electrode on the surface of the ultrasound transducer element tile mounted on said actuator. A method of controlling such a system is also disclosed.

Description

Ultrasound transducer positioning

FIELD OF THE INVENTION

The present invention relates to an ultrasound system including an ultrasound transducer array comprising a plurality of transducer elements mounted on a carrier.

The present invention further relates to a method of controlling such an ultrasound system.

BACKGROUND OF THE INVENTION

Ultrasound waves find several applications in medicine. One such application is ultrasound imaging, wherein ultrasound waves are emitted by an array of ultrasound transducers into the body of a patient and echoes of the ultrasound waves are collected by the ultrasound transducers or by dedicated ultrasound receivers and processed to generate an ultrasound image, e.g. a ID, 2D or 3D ultrasound image. Another application is ultrasound therapy such as high intensity focused ultrasound (HIFU) therapy in which ultrasound beams are generated by ultrasound transducer elements and are focused on diseased tissue. The significant energy deposition at the focus creates local temperatures in the range of about 65°C to 85°C, which destroys the deceased tissue by coagulative necrosis.

Such applications face several challenges. For instance, in imaging applications it is far from trivial to achieve a good contact between the ultrasound transducer array and the part of the body to be imaged. This is typically achieved by using special gels that improve the contact between the ultrasound transducer array and the body part.

However, a drawback of this approach is that usually large amounts of gel have to be used, which may contain air bubbles that interfere with the transmission or reception of the ultrasound signals. Moreover, the ultrasound transducer array, e.g. in the form of the probe, is typically hand-held during an imaging procedure, which makes the procedure prone to errors.

Similar challenges exist in therapeutic applications, where the focused beam requires periodic readjustment to treat multiple regions of the diseased tissue. This may be done manually by adjusting a focusing element or by beam steering by adjustment of the relative phases of the signals generated by the respective ultrasound transducer elements. The manual adjustment is prone to inaccuracies and the range of phase controlled beam steering may not be sufficient to reach all diseased tissue without array displacement. The use of such contact gels is furthermore becoming increasingly

cumbersome with increasing size of the ultrasound transducer element tiles onto which individual ultrasound transducer elements are formed, as air bubble removal becomes practically impossible. Such large size ultrasound systems are particularly attractive because they are capable of reproducing fast, high-quality the imagery (in case of an ultrasound imaging system) and ease-of-use by the reduced need for specialist sonographers. It is desirable for any ultrasound system, and for such large area ultrasound systems in particular, that a good conformal contact between the transducer array and the body to be imaged can be achieved in order to facilitate high-quality coverage of (large) areas of the body to be imaged or treated.

SUMMARY OF THE INVENTION

The present invention seeks to provide an ultrasound system that can establish high-quality adjustable conformal contact between the ultrasound transducer array and a body to be imaged or treated.

The present invention further seeks to provide a method of controlling such an ultrasound system.

According to an aspect, there is provided an ultrasound system comprising an ultrasound transducer array comprising a carrier carrying an actuator arrangement comprising a plurality of actuators, each actuator comprising a material having an adjustable shape in response to an electromagnetic stimulus; a plurality of ultrasound transducer element tiles on the actuator arrangement such that each actuator is arranged to adjust the orientation of an individual ultrasound transducer element tile relative to the carrier in response to said electromagnetic stimulus, each ultrasound transducer element tile comprising at least one ultrasound transducer element; and a plurality of capacitive sensors, each capacitive sensor comprising a first sensing electrode on a surface of one of the ultrasound transducer element tiles facing a surface portion of the carrier and a second sensing electrode on said surface portion; the actuator arrangement further comprising a controller arrangement for each actuator, the controller arrangement adapted to generate the electromagnetic stimulus for said actuator in response to capacitive sensor data provided by a capacitive sensor having a first sensing electrode on the surface of the ultrasound transducer element tile mounted on said actuator. The provision of an ultrasound system comprising an ultrasound transducer array in which the orientation of the individual ultrasound transducer element tiles can be adjusted relative to the carrier by the actuator arrangement under control of a controller that is responsive to one or more capacitive sensors that can accurately determine the actual orientation of the ultrasound transducer element tiles facilitates accurate control over the respective orientations of the ultrasound transducer element tiles in the ultrasound transducer array, such that the ultrasound system can be accurately configured for large area imaging or treatment applications.

The controller arrangement may comprise a plurality of controllers, wherein each controller is dedicated to a particular actuator. For example, such controllers may be located in the respective ultrasound transducer element tiles. Alternatively, the control arrangement may comprise a central controller, which for example may be housed in a control unit connected to an ultrasound probe containing the ultrasound transducer array.

In an embodiment, the surface of each ultrasound transducer element tile carries the respective first sensing electrodes of a further plurality of capacitive sensors distributed across said surface, the further plurality forming a further subset of the plurality of capacitive sensors. By providing each ultrasound transducer element tile with multiple capacitive sensors across the surface of the tile facing the carrier, the orientation of each ultrasound transducer element tile relative to the carrier may be more accurately determined. For example, the respective first sensing electrodes of the capacitive sensors of said further plurality may be located along respective edges or in respective corners of said surface.

In an embodiment, the controller arrangement is adapted to derive an actual orientation of a particular ultrasound transducer element tile from the capacitive sensor data provided by a capacitive sensor having a first sensing electrode on the surface of said particular ultrasound transducer element tile; and generate the electromagnetic stimulus based on a difference between said actual orientation and an intended orientation of the particular ultrasound transducer element tile. For example, the controller arrangement may receive orientation instructions for the respective ultrasound transducer element tiles from beam forming circuitry of the ultrasound system, in which case the orientation feedback

information for the respective ultrasound transducer element tiles is provided by the one or more capacitive sensors may be used by the controller arrangement to accurately position the respective ultrasound transducer element tiles in accordance with the provided orientation instructions. Alternatively, the controller arrangement may be adapted to provide the actuator of a particular ultrasound transducer element tile with an initial electromagnetic stimulus; derive a change in actual orientation of the particular ultrasound transducer element tile from the capacitive sensor data provided by a capacitive sensor having a first sensing electrode on the surface of the particular ultrasound transducer element tile in response to the controller arrangement providing said initial electromagnetic stimulus; and provide the actuator of the particular ultrasound transducer element tile with an adjusted electromagnetic stimulus based on the derived change in actual orientation of the particular ultrasound transducer element tile. In this embodiment, the control arrangement may systematically vary, e.g. increase, the strength of the electromagnetic stimulus applied to a particular actuator until the corresponding ultrasound transducer element tile no longer (significantly) changes its orientation, which may be an indication that the acoustic coupling between the tile and the body to be imaged or treated has been optimized.

According to yet another embodiment, the ultrasound system may further comprise beam shaping circuitry for shaping an ultrasound beam produced with at least a selection of the plurality of ultrasound transducer elements, wherein the controller arrangement is adapted to derive an actual orientation of a particular ultrasound transducer element tile from the capacitive sensor data provided by a capacitive sensor having a first sensing electrode on the surface of said particular ultrasound transducer element tile and communicate the derived actual orientation of said ultrasound transducer element tile to the beam shaping circuitry; and the beam shaping circuitry is adapted to shape said ultrasound beam in response to the communicated derived actual orientation. In this manner, highly accurate beam shaping can be achieved due to the fact that the actual orientation of the respective ultrasound transducer element tiles as determined by the one or more capacitive sensors associated with the styles is utilized by the beam shaping circuitry.

Each actuator of a particular ultrasound transducer element tile may comprise at least one elongate portion of the actuator material, the actuator further comprising an electrode assembly conductively coupled to the controller arrangement, the electrode assembly including a first electrode arrangement on the surface of one of the ultrasound transducer element tiles and a second electrode arrangement on the carrier, wherein the first electrode arrangement and the second electrode arrangement are arranged such that the provision of the electromagnetic stimulus to the electrode assembly causes the at least one elongate portion of the actuator material to exhibit at least one of a lateral deformation and an out-of-plane deformation in order to control the orientation of the associated ultrasound transducer element tile.

To this end, opposing terminal portions of the at least one elongate portion of the actuator material may be anchored to the carrier; and the first electrode arrangement may comprise a first electrode conductively coupled to a central region of the at least one elongate portion of the actuator material; and the second electrode arrangement may comprise a second electrode and a third electrode anchoring the respective opposing terminal portions of the at least one elongate portion, and optionally further comprises at least one intermediate electrode opposing the first electrode in order to invoke the desired out-of-p laying information.

To invoke the lateral deformation, the first electrode arrangement may comprise a first further electrode conductively coupled to a first region of the elongate material portion and the second electrode arrangement may comprise a second further electrode coupled to a second region of the elongate material portion, wherein the first region is laterally displaced relative to the second region.

To increase control over the orientation of the ultrasound transducer element tiles, each ultrasound transducer element tile may be mounted on a plurality of actuators arranged along respective edges or in respective corners of the ultrasound transducer element tile.

In an embodiment, the ultrasound system further comprises a plurality of storage capacitors, each storage capacitor being conductively coupled one of the actuators, wherein the controller is further adapted to provide an electromagnetic stimulus to a particular actuator by storing a charge on the storage capacitor conductively coupled to the particular actuator. The provision of such storage capacitors has the advantage that the required refresh rate of the actuators, i.e. the rate at which the electromagnetic stimulus needs to be provided to the actuator in order for it to retain its desired shape, can be reduced.

In a preferred embodiment, the material comprises an electroactive polymer (EAP) optionally coated with an electrically conductive flexible material. The material may be coated or otherwise supplied with separate portions of the electrically conductive flexible material, with the separate portions being electrically insulating from each other such that these are separate portions can access further electrodes for applying the electromagnetic stimulus to the EAP.

According to another aspect, there is provided a method of controlling the ultrasound system of any of the above embodiments, the method comprising obtaining a capacitive sensor reading from each of the capacitive sensors; determining the respective orientations of the ultrasound transducer element tiles from the obtained capacitive sensor readings; and generating respective control signals for the actuators of the ultrasound transducer element tiles in response to their determined respective orientations. With this method, the respective ultrasound transducer element tiles of the transducer array of the ultrasound system may be accurately positioned, thereby facilitating high-quality imaging or treatment through accurate control over the ultrasound beam to be formed or shaped with the ultrasound system.

In an embodiment, generating respective control signals for the ultrasound transducer element tiles in response to the determined respective orientations of the ultrasound transducer element tiles comprises configuring an ultrasound beam having a predetermined form in response to the determined respective orientations of the ultrasound transducer element tiles. In this embodiment, the orientation information of the tiles as provided by the respective capacitive sensors can be utilized by for example beamforming circuitry of the ultrasound system to accurately shape or otherwise form the ultrasound beam to be produced with the ultrasound system.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are described in more detail and by way of non- limiting examples with reference to the accompanying drawings, wherein:

FIG. 1 is a schematic block diagram of an ultrasound system according to an embodiment;

FIG. 2 schematically depicts a cross-section of an aspect of an example ultrasound transducer element tile in such an ultrasound system;

FIG. 3 schematically depicts the operating principle of a known electroactive polymer device that is not clamped;

FIG. 4 schematically depicts the operating principle of a known electroactive polymer device constrained by a backing layer;

FIG. 5 schematically depicts a part of an ultrasound transducer array according to an embodiment;

FIG. 6 schematically depicts an example embodiment of an ultrasound transducer element tile of such an ultrasound transducer array;

FIG. 7 schematically depicts another example embodiment of an ultrasound transducer element tile of such an ultrasound transducer array; FIG. 8 schematically depicts yet another example embodiment of an ultrasound transducer element tile of such an ultrasound transducer array;

FIG. 9 schematically depicts a detail of a part of an ultrasound transducer array according to an embodiment;

FIG. 10 schematically depicts an aspect of an operating principle of an ultrasound transducer element tile according to an embodiment;

FIG. 11 schematically depicts a detail of an ultrasound transducer array according to an embodiment;

FIG. 12 schematically depicts a detail of an ultrasound transducer array according to another embodiment;

FIG. 13 schematically depicts an example circuit diagram of an aspect of the ultrasound system according to an embodiment;

FIG. 14 schematically depicts an example circuit diagram of another aspect of the ultrasound system according to an embodiment; and

FIG. 15 is a flowchart of a method of controlling an ultrasound system according to an embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

It should be understood that the Figures are merely schematic and are not drawn to scale. It should also be understood that the same reference numerals are used throughout the Figures to indicate the same or similar parts.

In the context of the present application, an ultrasound transducer element tile is a discrete element, which may comprise any suitable type and number of ultrasound transducer elements; for example, the ultrasound transducer elements may be capacitive micromachined ultrasound transducer elements (CMUTs). The ultrasound transducer element tile for example may be a chip or the like of a semiconductor substrate such as a silicon substrate carrying circuitry including one or more ultrasound transducer elements. Each tile may comprise a plurality of CMUTs, e.g. organized as sub-arrays. Such tiles may have any suitable dimensions, e.g. the tiles may be square tiles having an area of several cm squared, e.g. may have dimensions of 2x2 cm, by way of non-limiting example. Such sizes allow for the simplification of beamforming processing because a regular active aperture of the ultrasound beam fits onto one tile and only one orientation position (of said tile) needs to be taking into account during the image reconstruction. Further, the aperture can either change its active size or "slide" to another tile during an anatomy scan. In the context of the present application, where reference is made to a material having an adjustable shape in response to an electromagnetic stimulus, this may be any material that has a shape that can be controlled by providing the material with an

electromagnetic stimulus such as a voltage, current or light. Preferably, the adjustment of the shape of the material is at least approximately proportional to the strength of the applied electromagnetic stimulus. In this context, 'at least approximately proportional' is intended to cover materials that have a proportional response to the strength of such an electromagnetic stimulus (up to a maximum shape adjustment) as well as materials that respond

proportionally to a change in strength of such an electromagnetic stimulus but may exhibit hysteresis effects for some changes in shape. For the avoidance of doubt, shape change materials that can be (reversibly) changed between a first shape and a second shape only are not intended to be covered by the term 'material having an adjustable shape in response to an electromagnetic stimulus'.

FIG. 1 shows an example embodiment of an ultrasound system 1 including an ultrasound probe 10 having a transducer array 110 comprising ultrasound transducer element tiles 100 comprising one or more ultrasound transducer elements (not shown). The tile 100 for example may be a diced chip or the like onto which the one or more ultrasound transducer elements have been formed or mounted. In the present invention, the ultrasound transducer elements may be implemented in any suitable manner. For example, the ultrasound transducer elements may be implemented by a piezoelectric ceramic material such as a lead zirconate titanate (PZT)-based material, a piezoelectric single crystal or composite material, a capacitive micromachined ultrasound transducer (CMUT) and so on. The ultrasound transducer element tiles 100 may have any suitable shape, e.g. a circular shape or polygonal shape. A polygonal shape such as a rectangular, e.g. square, shape is particularly mentioned as such a shape facilitates a close packing of the ultrasound transducer element tiles 100 within the transducer array 110, wherein the gap between adjacent ultrasound transducer element tiles 100 is minimized. The avoidance of relatively large gaps between adjacent ultrasound transducer element tiles 100 ensures that a substantially continuous image may be generated with the ultrasound probe 10 and may at least reduce the formation of ultrasound artifacts such as grating lobes. The transducer array 110 may have any suitable shape, e.g. may be a 1 -dimensional or 2-dimensional transducer array. The ultrasound probe 10 may be for transmitting ultrasonic waves and receiving echo information.

The transducer array 110 may be coupled to a microbeam former 12 in the probe 10 which controls transmission and reception of signals by the ultrasound transducer cells 100. Microbeam formers are capable of at least partial beam forming of the signals received by groups or "patches" of transducer element tiles for instance as described in US patents US 5,997,479 (Savord et al), US 6,013,032 (Savord), and US 6,623,432 (Powers et al.)

The microbeam former 12 may be coupled by a probe cable, e.g. coaxial wire, to a terminal, e.g. a user console device or the like, comprising a transmit/receive (T/R) switch 16 which switches between transmission and reception modes and protects the main beam former 20 from high energy transmit signals when a microbeam former is not present or used and the transducer array 110 is operated directly by the main system beam former 20. The transmission of ultrasonic beams from the transducer array 110 under control of the microbeam former 12 may be directed by a transducer controller 18 coupled to the microbeam former by the T/R switch 16 and the main system beam former 20, which receives input from the user's operation of the user interface or control panel 38. One of the functions controlled by the transducer controller 18 is the direction in which beams are steered and focused. Beams may be steered straight ahead from (orthogonal to) the transducer array 110, or at different angles for a wider field of view. The transducer controller 18 may be coupled to control the aforementioned voltage source 45 for the ultrasound transducer array 110. For instance, the voltage source 45 sets the DC and AC bias voltage(s) that are applied to CMUT elements of a CMUT array 110, e.g. to operate the CMUT elements in collapse mode, as is well-known per se.

The partially beam- formed signals produced by the microbeam former 12 may be forwarded to the main beam former 20 where partially beam- formed signals from individual patches of transducer elements are combined into a fully beam- formed signal. For example, the main beam former 20 may have 128 channels, each of which receives a partially beam- formed signal from a patch of dozens or hundreds of ultrasound transducer cells 100. In this way the signals received by thousands of transducer elements of a transducer array 110 can contribute efficiently to a single beam- formed signal.

The beam-formed signals are coupled to a signal processor 22. The signal processor 22 can process the received echo signals in various ways, such as bandpass filtering, decimation, I and Q component separation, and harmonic signal separation which acts to separate linear and nonlinear signals so as to enable the identification of nonlinear (higher harmonics of the fundamental frequency) echo signals returned from tissue and microbubbles. The signal processor 22 optionally may perform additional signal

enhancement such as speckle reduction, signal compounding, and noise elimination. The bandpass filter in the signal processor 22 may be a tracking filter, with its passband sliding from a higher frequency band to a lower frequency band as echo signals are received from increasing depths, thereby rejecting the noise at higher frequencies from greater depths where these frequencies are devoid of anatomical information.

The processed signals may be forwarded to a B-mode processor 26 and optionally to a Doppler processor 28. The B-mode processor 26 employs detection of an amplitude of the received ultrasound signal for the imaging of structures in the body such as the tissue of organs and vessels in the body. B-mode images of structure of the body may be formed in either the harmonic image mode or the fundamental image mode or a combination of both for instance as described in US Patents US 6,283,919 (Roundhill et al.) and US 6,458,083 (Jago et al.)

The Doppler processor 28, if present, processes temporally distinct signals from tissue movement and blood flow for the detection of the motion of substances, such as the flow of blood cells in the image field. The Doppler processor typically includes a wall filter with parameters which may be set to pass and/or reject echoes returned from selected types of materials in the body. For instance, the wall filter can be set to have a passband characteristic which passes signal of relatively low amplitude from higher velocity materials while rejecting relatively strong signals from lower or zero velocity material.

This passband characteristic will pass signals from flowing blood while rejecting signals from nearby stationary or slowing moving objects such as the wall of the heart. An inverse characteristic would pass signals from moving tissue of the heart while rejecting blood flow signals for what is referred to as tissue Doppler imaging, detecting and depicting the motion of tissue. The Doppler processor may receive and process a sequence of temporally discrete echo signals from different points in an image field, the sequence of echoes from a particular point referred to as an ensemble. An ensemble of echoes received in rapid succession over a relatively short interval can be used to estimate the Doppler shift frequency of flowing blood, with the correspondence of the Doppler frequency to velocity indicating the blood flow velocity. An ensemble of echoes received over a longer period of time is used to estimate the velocity of slower flowing blood or slowly moving tissue.

The structural and motion signals produced by the B-mode (and Doppler) processor(s) are coupled to a scan converter 32 and a multiplanar reformatter 44. The scan converter 32 arranges the echo signals in the spatial relationship from which they were received in a desired image format. For instance, the scan converter may arrange the echo signal into a two dimensional (2D) sector-shaped format, or a pyramidal three dimensional (3D) image.

The scan converter can overlay a B-mode structural image with colors corresponding to motion at points in the image field with their Doppler-estimated velocities to produce a color Doppler image which depicts the motion of tissue and blood flow in the image field. The multiplanar reformatter 44 will convert echoes which are received from points in a common plane in a volumetric region of the body into an ultrasonic image of that plane, for instance as described in US Patent US 6,443,896 (Detmer). A volume renderer 42 converts the echo signals of a 3D data set into a projected 3D image as viewed from a given reference point as described in US Pat. 6,530,885 (Entrekin et al.)

The 2D or 3D images are coupled from the scan converter 32, multiplanar reformatter 44, and volume renderer 42 to an image processor 30 for further enhancement, buffering and temporary storage for display on an image display 40. In addition to being used for imaging, the blood flow values produced by the Doppler processor 28 and tissue structure information produced by the B-mode processor 26 are coupled to a quantification processor 34. The quantification processor produces measures of different flow conditions such as the volume rate of blood flow as well as structural measurements such as the sizes of organs and gestational age. The quantification processor may receive input from the user control panel 38, such as the point in the anatomy of an image where a measurement is to be made.

Output data from the quantification processor is coupled to a graphics processor 36 for the reproduction of measurement graphics and values with the image on the display 40. The graphics processor 36 can also generate graphic overlays for display with the ultrasound images. These graphic overlays can contain standard identifying information such as patient name, date and time of the image, imaging parameters, and the like. For these purposes the graphics processor receives input from the user interface 38, such as patient name.

The user interface is also coupled to the transmit controller 18 to control the generation of ultrasound signals from the transducer array 110 and hence the images produced by the transducer array and the ultrasound system. The user interface is also coupled to the multiplanar reformatter 44 for selection and control of the planes of multiple multiplanar reformatted (MPR) images which may be used to perform quantified measures in the image field of the MPR images. As will be understood by the skilled person, the above embodiment of an ultrasonic diagnostic imaging system 1 is intended to give a non-limiting example of such an ultrasonic diagnostic imaging system. The skilled person will immediately realize that several variations in the architecture of the ultrasonic diagnostic imaging system are feasible without departing from the teachings of the present invention. For instance, as also indicated in the above embodiment, the microbeam former 12 and/or the Doppler processor 28 may be omitted, the ultrasound probe 10 may not have 3D imaging capabilities and so on. Other variations will be apparent to the skilled person.

Moreover, it will be understood that the present invention is not limited to an ultrasonic diagnostic imaging system 1. The teachings of the present invention are equally applicable to ultrasonic therapeutic systems in which the ultrasound transducer elements of the probe 10 may be operable in transmission mode only as there is no need to receive pulse echoes. As will be immediately apparent to the skilled person, in such therapeutic systems the system components described with the aid of FIG. 1 and required to receive, process and display pulse echoes may be omitted without departing from the teachings of the present application.

An example embodiment of a CMUT cell of an ultrasound transducer element tile 100 is schematically depicted in FIG. 2. It is reiterated for the avoidance of doubt that the tile 100 may comprise a plurality of such CMUT cells. The CMUT cell typically comprises a flexible membrane or diaphragm 114 suspended above a silicon substrate 112 with a gap or cavity 118 there between. A top electrode 120 is located on the diaphragm 114 and moves with the diaphragm. A bottom electrode is located on the floor of the cell on the upper surface of the substrate 112 in this example. Other realizations of the electrode 120 design can be considered, such as electrode 120 may be embedded in the membrane 114 or it may be deposited on the membrane 114 as an additional layer. In this example, the bottom electrode 122 is circularly configured and embedded in the substrate layer 112 by way of non- limiting example. Other suitable arrangements, e.g. other electrode shapes and other locations of the bottom electrode 122, e.g. on the substrate layer 112 such that the bottom electrode 112 is directly exposed to the gap 118 or separated from the gap 118 by an electrically insulating layer or film to prevent a short-circuit between the top electrode 120 and the bottom electrode 122. In addition, the membrane layer 114 is fixed relative to the top face of the substrate layer 112 and configured and dimensioned so as to define a spherical or cylindrical cavity 118 between the membrane layer 114 and the substrate layer 112. It is noted for the avoidance of doubt that in FIG. 2 the bottom electrode 122 is grounded by way of non- limiting example. Other arrangements, e.g. a grounded top electrode 120 or both top electrode 120 and bottom electrode 122 floating are of course equally feasible.

The cell and its cavity 118 may exhibit alternative geometries. For example, cavity 118 could exhibit a rectangular or square cross-section, a hexagonal cross-section, an elliptical cross-section, or an irregular cross-section. Herein, reference to the diameter of the CMUT cell shall be understood as the biggest lateral dimension of the cell.

The bottom electrode 122 may be insulated on its cavity- facing surface with an additional layer (not pictured). A preferred electrically insulating layer is an oxide-nitride- oxide (ONO) dielectric layer formed above the substrate electrode 122 and below the membrane electrode 120 although it should be understood any electrically insulating material may be contemplated for this layer. The ONO-dielectric layer advantageously reduces charge accumulation on the electrodes which leads to device instability and drift and reduction in acoustic output pressure.

An example fabrication of ONO-dielectric layers on a CMUT is discussed in detail in European patent application EP 2,326,432 A2 by Klootwijk et al., filed September 16, 2008 and entitled "Capacitive micromachined ultrasound transducer." Use of the ONO- dielectric layer is desirable with pre-collapsed CMUTs, which are more susceptible to charge retention than CMUTs operated with suspended membranes. The disclosed components may be fabricated from CMOS compatible materials, e.g., Al, Ti, nitrides (e.g., silicon nitride), oxides (various grades), tetra ethyl oxysilane (TEOS), poly-silicon and the like. In a CMOS fabrication, for example, the oxide and nitride layers may be formed by chemical vapor deposition and the metallization (electrode) layer put down by a sputtering process.

Suitable CMOS processes are LPCVD and PECVD, the latter having a relatively low operating temperature of less than 400°C. Exemplary techniques for producing the disclosed cavity 118 involve defining the cavity in an initial portion of the membrane layer 114 before adding a top face of the membrane layer 114. Other fabrication details may be found in US Pat. 6,328,697 (Fraser).

In FIG. 2, the diameter of the cylindrical cavity 118 is larger than the diameter of the circularly configured electrode plate 122. Electrode 120 may have the same outer diameter as the circularly configured electrode plate 122, although such conformance is not required. Thus, the membrane electrode 120 may be fixed relative to the top face of the membrane layer 114 so as to align with the electrode plate 122 below. The electrodes of the CMUT cell provide the capacitive plates of the device and the gap 118 is the dielectric between the plates of the capacitor. When the diaphragm vibrates, the changing dimension of the dielectric gap between the plates provides a changing capacitance which is sensed as the response of the CMUT cell to a received acoustic echo.

The spacing between the electrodes is controlled by applying a static voltage, e.g. a DC bias voltage, to the electrodes with a voltage supply 45. The voltage supply 45 may optionally comprise separate stages 102, 104 for providing the DC and AC or stimulus components respectively of the drive voltage of the CMUT cells 100, e.g. in transmission mode. The first stage 102 may be adapted to generate the static (DC) voltage component and the second stage 104 may be adapted to generate an alternating variable voltage component or stimulus having a set alternating frequency, which signal typically is the difference between the overall drive voltage and the aforementioned static component thereof. The static or bias component of the applied drive voltage preferably meets or exceeds the threshold voltage when forcing the CMUT cells 100 into their collapsed states, i.e. when operating the CMUT cells in collapsed mode. This has the advantage that the first stage 102 may include relatively large capacitors, e.g. smoothing capacitors, in order to generate a particularly low-noise static component of the overall voltage, which static component typically dominates the overall voltage such that the noise characteristics of the overall voltage signal will be dominated by the noise characteristics of this static component.

Other suitable embodiments of the voltage source supply 45 should be apparent, such as for instance an embodiment in which the voltage source supply 45 contains three discrete stages including a first stage for generating the static DC component of the CMUT drive voltage, a second stage for generating the variable DC component of the drive voltage and a third stage for generating the frequency modulation or stimulus component of the signal, e.g. a pulse circuit or the like. It is summarized that the voltage source supply 45 may be implemented in any suitable manner.

In embodiments of the present invention, the ultrasound probe 10 comprises a carrier onto which the ultrasound transducer element tiles 100 are mounted. This may be a rigid carrier made of any suitable rigid material, e.g. a metal or metal alloy, a composite material, a polymer material, combinations thereof and so on. As will be explained in further detail below, the ultrasound transducer element tiles 100 are mounted on the carrier such that the orientation of individual ultrasound transducer element tiles 100 can be adjusted. To this end, a carrier carries an actuator arrangement comprising a plurality of actuators, each actuator comprising a material having an adjustable shape in response to an electromagnetic stimulus. The ultrasound transducer element tiles are mounted on the actuator arrangement such that each actuator is arranged to adjust the orientation an ultrasound transducer element tile in response to an electromagnetic stimulus applied to the actuator. The ultrasound transducer element tiles 100 may be bonded to the actuators in any suitable manner, e.g. using (conductive) glue or ultrasonic bonding.

In at least some embodiments of the present invention, the material having material having an adjustable shape in response to an electromagnetic stimulus is a piezoelectric material or an electroactive material such as an electroactive polymer (EAP).

The use of such materials, for example EAPs, enables functions which were not possible before, or offers a big advantage over common actuator solutions, due to the combination of a relatively large deformation and force in a small volume or thin form factor, compared to common actuators. EAPs also give noiseless operation, accurate electronic control, fast response, and a large range of possible actuation frequencies, such as 0 - 20 kHz.

Electroactive polymers can be subdivided into field-driven and ionic-driven materials. Field-driven EAP's are actuated by an electric field through direct

electromechanical coupling, while the actuation mechanism for ionic EAP's involves the diffusion of ions. Both classes have multiple family members, each having their own advantages and disadvantages. Examples of field-driven EAPs are dielectric elastomers, electrostrictive polymers (such as PVDF based relaxor polymers or polyurethanes) and liquid crystal elastomers (LCE). Examples of ionic-driven EAPs are conjugated polymers, carbon nanotube (CNT) polymer composites and Ionic Polymer Metal Composites (IPMC).

FIG. 3 and 4 schematically depict two possible operating modes for an EAP- based actuator. The actuator comprises an electroactive polymer layer 54 sandwiched between electrodes 50, 52 on opposite sides of the electroactive polymer layer 54.

FIG. 3 schematically depict an actuator that is not clamped. A voltage is used to cause the electroactive polymer layer to expand in all directions as shown.

FIG. 4 schematically depict an actuator designed so that the expansion arises only in one direction. The device is supported by a carrier layer 56. A voltage is used to cause the electroactive polymer layer 52 to curve or bow. The nature of this movement for example arises from the interaction between the active layer which expands when actuated, and the passive carrier layer. To obtain the asymmetric curving around an axis as shown, molecular orientation (film stretching) may for example be applied, forcing the movement in one direction. The expansion in one direction may result from the asymmetry in the electroactive polymer, or it may result from asymmetry in the properties of the carrier layer, or a combination of both. Materials suitable for the EAP layer 54 are known. Suitable electro-active polymers include, but are not limited to, the sub-classes: piezoelectric polymers,

electromechanical polymers, relaxor ferroelectric polymers, electrostrictive polymers, dielectric elastomers, liquid crystal elastomers, conjugated polymers, Ionic Polymer Metal Composites, ionic gels and polymer gels.

The sub-class electrostrictive polymers includes, but is not limited to:

Polyvinylidene fluoride (PVDF), Polyvinylidene fluoride - trifluoroethylene (PVDF-TrFE), Polyvinylidene fluoride - trifluoroethylene - chlorofluoroethylene (PVDF-TrFE-CFE), Polyvinylidene fluoride - trifluoroethylene - chlorotrifluoroethylene) (PVDF-TrFE-CTFE), Polyvinylidene fluoride- hexafluoropropylene (PVDF - HFP) , polyurethanes or blends thereof.

The sub-class dielectric elastomers includes, but is not limited to: acrylates, polyurethanes, silicones.

The sub-class conjugated polymers includes, but is not limited to: polypyrrole, poly-3,4-ethylenedioxythiophene, poly(p-phenylene sulfide), polyanilines.

Additional passive layers may be provided for influencing the behavior of the EAP layer in response to an applied electric field.

The EAP layer 54 may be sandwiched between electrodes 50, 52. The electrodes 50, 52 may be stretchable so that they follow the deformation of the EAP material layer 54. Materials suitable for the electrodes are also known, and may for example be selected from the group consisting of thin metal films, such as gold, copper, or aluminum or organic conductors such as carbon black, carbon nanotubes, graphene, poly-aniline (PANI), poly(3,4-ethylenedioxythiophene) (PEDOT), e.g. poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS). Metalized polyester films may also be used, such as metalized polyethylene terephthalate (PET), for example using an aluminum coating.

The materials for the different layers will be selected for example taking account of the elastic moduli (Young's moduli) of the different layers.

Additional layers to those discussed above may be used to adapt the electrical or mechanical behavior of the device, such as additional polymer layers.

The EAP actuators may be electric field driven actuators or ionic actuators.

Ionic actuators may be based on ionic polymer - metal composites (IPMCs) or conjugated polymers. An ionic polymer - metal composite (IPMC) is a synthetic composite nanomaterial that displays artificial muscle behavior under an applied voltage or electric field. IPMCs are composed of an ionic polymer like Nafion or Flemion whose surfaces are chemically plated or physically coated with conductors such as platinum or gold, or carbon-based electrodes. Under an applied voltage, ion migration and redistribution due to the imposed voltage across a strip of IPMCs result in a bending deformation. The polymer is a solvent swollen ion-exchange polymer membrane. The field causes cations travel to cathode side together with water. This leads to reorganization of hydrophilic clusters and to polymer expansion. Strain in the cathode area leads to stress in rest of the polymer matrix resulting in bending towards the anode. Reversing the applied voltage inverts the bending. If the plated electrodes are arranged in a non- symmetrical configuration, the imposed voltage can induce several kinds of deformations such as twisting, rolling, torsioning, turning, and non-symmetric bending deformation for example.

In embodiments of the present invention, the orientation of the individual ultrasound transducer element tiles 100 may be controlled using the respective actuators on which the ultrasound transducer element tiles 100 are mounted. This is schematically depicted in FIG. 5, in which a 2-D transducer array 110 is shown. The side view 101 along the two dimensions of the transducer array 110 shows the different relative orientations adopted by the respective ultrasound transducer element tiles 100 is invoked by the actuators underneath these tiles. In this manner, the ultrasound transducer array 110 may be controlled (by individually controlling the respective actuators) to produce an ultrasound beam that is focused in a region 99 by focusing the respective beam portions (indicated by the dashed lines) produced with the respective ultrasound transducer element tiles 100 onto the region 99. This for example facilitates imaging or treatment of the region 99 using the focused ultrasound beam.

FIG. 6 schematically depicts an example embodiment of an ultrasound transducer element tile 100 according to an aspect of the present invention. In this embodiment, the ultrasound transducer element tile 100 is arranged on an elongate portion of the actuator material 54 to facilitate an out-of-plane displacement of the ultrasound transducer element tile 100 relative to the carrier 160. To this end, the surface 103 of the ultrasound transducer element tile 100 facing the surface 162 of the carrier 160 carries an electrode arrangement 143 that is conductively coupled to the upper electrode 52 of the actuator material 54. The electrode arrangement 143 may be made of any suitable material, e.g. a metal or metal alloy that is applied to the surface 103 and subsequently patterned to form the electrode arrangement 143. The electrode arrangement 143 is conductively coupled to a controller 200 of the actuator. In an embodiment, each ultrasound transducer element tile 100 may comprise its own controller 200, although in alternative embodiments a central controller 200 adapted to generate a plurality of control signals to the respective actuators of the transducer array 110 may be provided. The controller 200 is typically adapted to provide the electrodes 50, 52 with an electromagnetic stimulus to actuate the actuator material 54 accordingly, as will be explained in further detail below. Although not specifically shown, each actuator may be conductively coupled to its controller 200 via a storage capacitor onto which the

electromagnetic stimulus is stored, e.g. by storing a voltage across the storage capacitor, which has the advantage that the controller 200 does not need to continuously provide the electromagnetic stimulus in order to retain the actuator in its intended shape.

The ultrasound transducer element tile 100 may comprise a substrate 140 such as a silicon substrate on which an integrated circuit (IC) arrangement such as an application- specific integrated circuit (ASIC) is formed, which may further comprise components such as the micro-beam former 12 for example.

The IC arrangement may comprise the controller 200 as previously explained, in which case the electrode arrangement 143 for example may be conductively coupled to the controller 200 using through- silicon vias 145 (or any other type of suitable via).

The end portions of the elongate portion of the actuator material 54 are anchored onto grounding electrodes 161 on the surface 162 of the carrier 160 through connection points 163. As will be explained in further detail below, at least some of the grounding electrodes 161 may further form part of a capacitive sensor 70 further comprising an opposing sensing electrode 141 on the surface 103 of the tile 100. The connection points 163 for example may be drops of (conductive) glue or ultrasonic bonding points. As such bonding techniques are well-known per se, this will not be explained in further detail for the sake of brevity only.

The grounding electrodes 161 may be made of any suitable material, e.g. a metal or metal alloy that is applied to the surface 162 and subsequently patterned to form the grounding electrodes 161. By anchoring the end portions of the elongate portion of the actuator material 54 to the carrier 160 through grounding electrodes 161 that are conductively coupled to the lower electrode 50 of the actuator material 54 and providing an electrode arrangement 143 that is conductively coupled to the upper electrode 52 in an intermediate region of the elongate portion of the actuator material 54, a vertical displacement of the actuator material 54 may be invoked by applying an appropriate electromagnetic stimulus across the electrodes 50, 52 of the actuator material 54.

Conductive tracks, e.g. conductive copper tracks embedded in an electrically insulating flexible foil such as a polyimide foil may be used to connect the ultrasound transducer element tile 100 to further circuitry of the ultrasound system 1, e.g. to a coaxial cable attached to the ultrasound probe 10 via a printed circuit board (PCB) or the like. The carrier 160 may include a printed circuit board comprising the conductive tracks, with the printed circuit board being connected to the further contacts in any suitable manner, e.g. through a ball grid array.

In FIG. 7, an embodiment of the ultrasound transducer element tile 100 is shown in which lateral (horizontal) displacement of the tile may be invoked with the actuator material 54. In this embodiment, the electrode arrangement 143 is conductively coupled to the upper electrode 52 in a terminal region of the actuator material 54 whilst a grounding electrode 161 is conductively coupled to the lower electrode 50 in an opposing terminal region of the actuator material 54. The lateral displacement of the electrode arrangement 143 to the grounding electrode 161 facilitates the horizontal displacement of the ultrasound transducer element tile 100 relative to the carrier 160. Such horizontal displacement for instance may be deployed to control the gap size G between the ultrasound transducer element tile 100 and a neighboring tile, for example if both tiles are to be used to form an ultrasound beam with the ultrasound system 1. In such beamforming, the gap size G preferably is less than half the ultrasound wavelength to avoid the generation of grating effects, which are well-known per se and are therefore not explained in further detail for the sake of brevity.

In order to invoke out-of-plane bending (angular displacement) of an ultrasound transducer element tile 100, the tile 100 may be mounted on a plurality of actuators that are each individually addressable by respective electrode arrangements 143 on the surface 103 of the tile. FIG. 8 schematically depicts a cross-section of such an arrangement in which such angular displacement is facilitated by respective actuator materials 54 in the corners of the ultrasound transducer element tile 100. FIG. 9

schematically depicts an example embodiment in which the actuator materials 54 are striped across the respective corners of the ultrasound transducer element tiles 100 of a transducer array 110. However, it will be immediately understood by the skilled person that other arrangements, e.g. arrangement in which the actuator materials 54 are positioned in a different manner in the corners of the ultrasound transducer element tiles 100 or alternatively are positioned along the edges of the ultrasound transducer element tiles 100 are equally feasible.

In a preferred embodiment, each of the actuator materials 54 is individually addressable by an electrode arrangement 143 comprising a plurality of individually addressable electrodes. Such an electrode arrangement 143 is preferably arranged such that the individually addressable electrodes may invoke a horizontal displacement, a vertical displacement or a combination of both a horizontal displacement and a vertical displacement by the application of an appropriate electromagnetic stimulus to a selection of the

individually addressable electrodes, for example by including electrodes in the locations shown in FIG. 6 and FIG.7. Each ultrasound transducer element tile 100 may comprise a controller 200 arranged to individually control the respective electrode arrangements 143 of the actuator materials 54 associated with that tile or alternatively a central controller 200 may be provided that provides these respective control signals.

In this manner, the orientation of each ultrasound transducer element tile 100 may be accurately controlled with its controller 200 by providing the appropriate electrodes of the electrode arrangements 143 with the appropriate control signal, i.e. appropriate electromagnetic stimuli. Such tile reorientation may be used to assist ultrasound

beamforming across tile boundaries, ultrasound beam steering, e.g. to complement phased array steering, as well as to apply pressure for acoustic coupling of the transducer array 110 to a surface to be subjected to the ultrasound beam, e.g. for imaging or treatment purposes. In an embodiment, the controller 200 may control the respective actuator materials 54 sequentially to modulate the pressure applied to the body of a subject to be imaged or treated. This for example is particularly advantageous if the transducer array 110 is acoustically coupled to the body via a gel, in which case the pressure modulation may be used to force air bubbles from the gel, thereby improving the quality of the acoustic coupling. This for example is desirable in imaging applications where such air bubbles can degrade the quality of the images captured with the ultrasound system 1.

In a particular advantageous embodiment, the one or more controllers 200 are integral to control circuit for controlling the ultrasound transducers of the tiles 100, e.g. into voltage source 45. Because both the ultrasound transducers and the actuators are typically controlled by a high voltage in some embodiments, integration of the one or more controllers 200 in the control circuitry of the ultrasound transducers therefore obviates the need for a separate controller arrangement for the actuators, thereby reducing the overall cost of the ultrasound system. In order to determine the actual displacement of the ultrasound transducer element tile 100, each tile may further comprise one or more capacitive sensors 70 as shown in FIG. 6 and FIG. 7 that include a first sensing electrode 141 on the surface 103 of the ultrasound transducer element tile 100 and an opposing grounding electrode 161 acting as a second sensing electrode 161 or a dedicated sensing electrode 161 '.

The first sensing electrode 141 and the second sensing electrode 161 (or 161 ') preferably perfectly oppose each other when the first sensing electrode 141 is oriented parallel to the second sensing electrode 161 although other configurations, e.g. in which the first sensing electrode 141 is laterally displaced to the second sensing electrode 161 when the first sensing electrode 141 is oriented parallel to the second sensing electrode 161 may also be contemplated. The first sensing electrode 141 and the second sensing electrode 161 may have any suitable shape, e.g. may be plate electrodes, patterned electrodes, and so on.

The capacitance C of a capacitive sensor 70 having a plate-shaped first sensing electrode 141 parallel to a plate-shaped second sensing electrode 161 may be expressed by equation (1):

In equation (1), A is the area of overlap of the first sensing electrode 141 and the second sensing electrode 161 (in m²); ε_Γ is the relative static permittivity (sometimes called the dielectric constant) of the medium in between the first sensing electrode 141 and the second sensing electrode 161; εο is the electric constant (εθ ~ 8.854x 10-12 F-m ¹); and d is the separation between the first sensing electrode 141 and the second sensing electrode 161 (in m). From equation (1), it can be seen that the capacitance C is a function of the distance d between the first sensing electrode 141 and the second sensing electrode 161. In some embodiments, the respective second sensing electrodes 161 may be implemented as a common electrode, e.g. a ground plate or the like.

Therefore, by storing a unit charge q on the first sensing electrode 141 and the second sensing electrode 161, the distance d may be determined by measuring the capacitance of the capacitive sensor 70 by determining the voltage across the capacitive sensor 70, as expressed in equation (2): C

V

A time- varying voltage V(t) may be measured across the capacitive sensor 70 using a time- varying (e.g. alternating) current I(t), from which its capacitance may be derived using equation (3):

/«) = ^

dt

Equations (l)-(3) are applicable for a capacitive sensor 70 having parallel plates. It will be immediately understood that for a capacitive sensor 70 in which the first sensing electrode 141 and the second sensing electrode 161 are not embodied by parallel plates, other equations may be applicable. As such equations are well-known per se, this is not explained in further detail for the sake of brevity only.

The capacitive sensors 70 are conductively coupled to the control circuit 200 of the actuator material 54. The control circuit 200 may be adapted to store the defined amount of charge on the respective capacitive sensors 70 and to measure the respective voltages across the capacitive sensors 70 as explained above in order to derive the respective distances between the first sensing electrode 141 and the second sensing electrode 161 of the capacitive sensors 70. To this end, the control circuit 200 may include a processor for processing the sensor signals from the respective capacitive sensors 70 and to derive the distance d between the respective first sensing electrodes 141 and the second sensing electrodes 161 from these processed sensor signals.

The determined distance may be indicative of the amount of shape change in the actuator material 54 and thus may provide an indication of the relative orientation of the ultrasound transducer element tile 100 associated with the capacitive sensor 70 for which this distance is determined. This is particularly the case if the first sensing electrode 141 is positioned off-center on the surface 103, e.g. along an edge of the surface 103 or in a corner of the surface 101, such that a tilt of the ultrasound transducer element tile 100 can be determined as a function of the determined distance d between the first sensing electrode 141 and the second sensing electrode 161 of the capacitive sensor 70 associated with the ultrasound transducer element tile 100. In order to further refine the accuracy of the determination of the relative orientation of a particular ultrasound transducer element tile 100, the surface 103 of the ultrasound transducer element tile 100 facing the carrier 160 may comprise a plurality of first sensing electrodes 141 that are spatially distributed across the surface 103 to define a further plurality of capacitive sensors 70 on the surface 103 that form part of the overall plurality of capacitive sensors 70 across the ultrasound probe 10. As schematically depicted in FIG. 10, by locating the respective first sensing electrodes 141a, 141b of such capacitive sensors 70a, 70b in different locations on the surface 103 of the ultrasound transducer element tile 100, a change in orientation (bottom pane) of the ultrasound transducer element tile 100 relative to the carrier 160 results in a different change in capacitance for the capacitive sensors 70a, 70b due to a different change in the distance between the respective first sensing electrodes 141a, 141b and their counter sensing electrodes 161a, 161b on the carrier 160.

As will be readily understood, the controller 200 may determine the relative orientation of the respective first sensing electrodes 141a, 141b from the respective capacitances of the capacitive sensors 70a, 70b by deriving the distance between the first and second sensing electrodes for each capacitive sensor from its determined capacitance. In this manner, by quantifying the change in capacitance for each of the capacitive sensors 70 on the ultrasound transducer element tile 100, the orientation of the ultrasound transducer element tile 100 relative to the carrier 160 may be accurately determined by the controller 200.

FIG. 11 schematically depicts an example embodiment in which the surface

101 of each ultrasound transducer element tile 100 comprises first sensing electrodes 141a-d along the respective edges of the surface 103 and FIG. 12 schematically depicts an example embodiment in which the surface 103 of each ultrasound transducer element tile 100 comprises first sensing electrodes 141a-d in the respective corners of the surface 103.

Although not explicitly shown, the carrier 160 may comprise a separate counter electrode 161 (i.e. second sensing electrode) for each of the first sensing electrodes 141a-d or may comprise a common counter electrode for at least some of the first sensing electrodes 141a-d, e.g. a common counter electrode for each of the ultrasound transducer elements 100 or a single common counter electrode for the respective first sensing electrodes 141a-d of the ultrasound transducer element tile 100.

The controller 200 may utilise the orientation information provided by the one or more capacitive sensors 70 of a particular ultrasound transducer element tile 100 in a number of different ways. In a first embodiment, the controller 200 utilises the orientation information as feedback information to determine if the ultrasound transducer element tile 100 under control of the controller 200 has reached a desirable orientation. Such a desirable orientation for example may be an orientation instruction provided to the controller 200 by the beam former 20 in order to bring the ultrasound transducer element tile 100 in a particular orientation as selected by the beam former 20 in order for the ultrasound transducer element tile 100 to produce a part of the ultrasound beam to be formed in a desired direction. The controller 200 may be adapted to compare the actual orientation of the ultrasound transducer element tile 100 against this desired orientation and adjust the strength of the electromagnetic stimuli provided to the respective actuator materials 54 on which the ultrasound transducer element tile 100 is mounted in case of a difference between this actual orientation and the desired orientation in order to reduce this difference. This process may be repeated until the actual orientation of the ultrasound transducer element tile 100 matches the desired orientation of this tile.

In a second embodiment, the controller 200 may be adapted to systematically vary the electromagnetic stimuli applied to the respective actuator materials 54 on which the ultrasound transducer element tile 100 is mounted in order to evacuate air bubbles from a gel between the ultrasound probe 10 and a body onto which the probe is placed, as previously explained.

In a third embodiment, the controller 200 may be adapted to the respective actuator materials 54 on which the ultrasound transducer element tile 100 is mounted in order to maximize the acoustic contact between the ultrasound transducer element tile 100 and the body on which the ultrasound probe 10 is placed. For example, the controller 200 may be adapted to systematically increase the strength of an electric stimulus to a particular actuator electrode (or selection of actuator electrodes) and monitor if this increase causes a change in the orientation of the ultrasound transducer element tile 100. If such a change is detected, this may be interpreted as an indication that acoustic contact between the tile 100 and the body of a patient to be monitored or treated is not yet optimal and the strength of the electromagnetic stimulus may be increased accordingly until the orientation of the ultrasound transducer element tile 100 no longer changes (or changes by less than a predetermined amount) in response to such an increased strength of the electromagnetic stimulus.

The controller 200 may be further adapted to forward the determined relative orientation of the ultrasound transducer element tile 100 to the beamforming circuitry of the ultrasound system 1, e.g. to the main beam former 20 and/or micro-beam former 12. The beam forming circuitry may use the determined relative orientations of the respective ultrasound transducer element tiles 100 to determine which ultrasound transducer element tiles 100 are to be selected for forming the desired ultrasound beam and to determine the timing sequence of the electrical pulses for controlling the selected ultrasound transducer element tiles 100 in order to cause the selected ultrasound transducer cells to remit corresponding pressure waves that are phased to form a transmit beam that propagates in a predetermined direction from the ultrasound probe 10 when these electrical pulses are applied to the selected ultrasound transducer element tiles 100 in accordance with the determined timing sequence.

For example, in a transmit or receive beamforming event, beam forming is performed across tiles 100 for which the relative displacement and orientations of each tile is known from the capacitive sensor measurements. Such beam forming may comprise choosing a focus point in the body of a subject to be images or treated. For each tile 100, the time delays to and from the tile to the selected focus point can be calculated. As is well- known per se, in beamforming the delays relative a central reference element within the tile are subtracted and then summed the result to give the reflection from the focus point upon which the ultrasound beam was focused. When beam forming across tiles 100, it may be assumed that a particular tile 100 is the reference such that from the displacement and orientation of the second tile with respect to the reference tile the delays or advances that the elements in the displaced second tile may be calculated. The calculated delays (or advances) may then be applied to the signals from the second tile before summation of signals across both tiles to give the ultrasound beam reflection from the focus point.

FIG. 13 schematically depicts a simplified example circuit diagram of the controller 200 and a plurality of actuators 54 under control of the controller 200. The controller 200 may individually address each actuator material 54, for example by enabling a switch 203, e.g. a transistor or the like, connecting a voltage or current supply 201 to the actuator such that the actuator capacitance provided by the electrodes 50, 52 and the actuator material 54 in between these electrodes and symbolized by capacitor 205 can be charged with a predetermined charge to provide an electromagnetic stimulus of predetermined strength. As previously explained, a storage capacitor (not shown) may be provided in parallel with the EAP capacitance 205 to reduce the required refresh rate of this electromagnetic stimulus.

FIG. 14 schematically depicts a simplified example circuit diagram of the responsiveness of the controller 200 of the actuator arrangement of a particular ultrasound transducer element tile 100 to the one or more capacitive sensors 70 associated with that tile in order to provide the controller 200 with the aforementioned feedback information based on which the controller 200 may generate the electromagnetic stimuli for the respective actuators on which the tile 100 is mounted. In order to increase the signal strength sensitivity of each capacitive sensor 70, the capacitive sensor may be coupled to the controller 200 through an amplification circuit 303 that provides an amplified capacitive sensor reading of the capacitive sensor 70 to a terminal 301 of the controller 200.

FIG. 15 is a flowchart of a method 400 for controlling the ultrasound system 1 according to embodiments of the present invention, i.e. to control the respective orientations of the ultrasound transducer element tiles 100 of the ultrasound transducer probe 10. The method 400 starts in 401 in which the ultrasound transducer probe 10 is positioned on a body to be imaged or treated with ultrasound beams. This step may further involve the provision of orientation instructions for at least a selection of the ultrasound transducer element tiles 100 to the one or more controllers 200 associated with those tiles and the generation of corresponding electromagnetic stimuli by the one or more controllers 200 to adjust the orientations of their corresponding ultrasound transducer element tiles 100 accordingly. Alternatively, 401 may comprise bringing the ultrasound transducer element tiles 100 in a first orientation with the one or more controllers 200 in an attempt to optimize the acoustic coupling between the ultrasound transducer probe 10 and the patient's body.

In 403, the capacitive sensors 70 associated with the respective ultrasound transducer element tiles 100 are interrogated in order to determine the actual capacitance C of these capacitive sensors as explained above. This for instance may include storing a charge on each capacitive sensor and determining the voltage across the first sensing electrode 141 and the second sensing electrode 161 to determine the actual capacitance C in 405. Other suitable ways of determining the actual capacitance C may be contemplated and will be immediately apparent to the skilled person.

Upon determination of actual capacitance of the respective capacitive sensors 70, the method 400 may proceed to 407 in which the relative orientation of the respective ultrasound transducer element tiles 100 is determined based on the distance(s) between the first sensing electrode 141 and the second sensing electrode 143 as derived from the actual capacitance of the respective capacitive sensors 70. The thus obtained relative orientations of the respective ultrasound transducer elements 100 may be used to generate control signals, i.e. adjusted electromagnetic stimuli, for the respective ultrasound transducer element tiles 100 based on their relative orientations, e.g. to reduce a difference between the actual orientation and the desired orientation of the respective tiles 100 or to further improve the acoustic coupling between the respective tiles 100 and the patient's body.

In an embodiment in which the respective controllers 200 have not been provided with orientation instructions by the beamforming circuitry of the ultrasound system 1 , it may be checked in 409 if the actual orientations of the respective ultrasound transducer element tiles 100 as determined in 407 should be forwarded to the beamforming circuitry for beamforming purposes. If this is the case, the method may proceed to 411 in which the beamforming circuitry, e.g. main beam former 20 or micro-beam former 12, may utilize the determined actual relative orientations of the respective tiles 100 to select ultrasound transducer element tiles 100 and generate timing sequences for the control signals to be applied to the ultrasound transducer elements 100 of the selected tiles 100 in order to produce an ultrasound beam having a predetermined form or shape. Such an ultrasound beam for example may be used to generate an ultrasound image of a particular area within the body being imaged with an ultrasound imaging system 1 or alternatively may be used to target a tissue anomaly in a particular location within a body being treated with ultrasound therapy system 1.

It is subsequently checked in 413 if the method 400 may be terminated. If this is not the case, the method 400 may revert back to previously described operation 403;

otherwise, the method 400 may terminate in 413.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word "comprising" does not exclude the presence of elements or steps other than those listed in a claim. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The invention can be implemented by means of hardware comprising several distinct elements. In the device claim enumerating several means, several of these means can be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

CLAIMS:

1. An ultrasound system ( 1 ) comprising an ultrasound transducer array (110) comprising:

a carrier (160) carrying an actuator arrangement comprising a plurality of actuators, each actuator comprising a material (54) having an adjustable shape in response to an electromagnetic stimulus;

a plurality of ultrasound transducer element tiles (100) coupled to the actuator arrangement such that each actuator is arranged to adjust the orientation of an individual ultrasound transducer element tile relative to the carrier in response to said electromagnetic stimulus, each ultrasound transducer element tile comprising at least one ultrasound transducer element; and

a plurality of capacitive sensors (70), each capacitive sensor comprising a first sensing electrode (141) on a surface (103) of one of the ultrasound transducer element tiles facing a surface portion (162) of the carrier and a second sensing electrode (161, 161 ') on said surface portion;

the actuator arrangement further comprising a controller arrangement for each actuator, the controller arrangement adapted to generate the electromagnetic stimulus for said actuator in response to capacitive sensor data provided by a capacitive sensor having a first sensing electrode on the surface of the ultrasound transducer element tile mounted on said actuator.

2. The ultrasound system (1) of claim 1, wherein the controller arrangement comprises a plurality of controllers (200), wherein each controller is dedicated to a particular actuator.

3. The ultrasound system (1) of claim 2, wherein the surface (103) of each ultrasound transducer element tile (100) carries the respective first sensing electrodes (141a- d) of a further plurality of capacitive sensors (70a, 70b) distributed across said surface (103), the further plurality forming a further subset of the plurality of capacitive sensors.

4. The ultrasound system (1) of claim 3, wherein the respective first sensing electrodes (141a-d) of the capacitive sensors (70a, 70b) of said further plurality are located along respective edges or in respective corners of said surface (103).

5. The ultrasound system (1) of any of claims 1-4, wherein the controller arrangement is adapted to:

derive an actual orientation of a particular ultrasound transducer element tile (100) from the capacitive sensor data provided by a capacitive sensor (70) having a first sensing electrode (141) on the surface (103) of said particular ultrasound transducer element tile; and

generate the electromagnetic stimulus based on a difference between said actual orientation and an intended orientation of the particular ultrasound transducer element tile.

6. The ultrasound system (1) of any of claims 1-4, wherein the controller arrangement is adapted to:

provide the actuator of a particular ultrasound transducer element tile (100) with an initial electromagnetic stimulus;

derive a change in actual orientation of the particular ultrasound transducer element tile from the capacitive sensor data provided by a capacitive sensor (70) having a first sensing electrode (141) on the surface (103) of the particular ultrasound transducer element tile in response to the controller arrangement providing said initial electromagnetic stimulus; and provide the actuator of the particular ultrasound transducer element tile with an adjusted electromagnetic stimulus based on the derived change in actual orientation of the particular ultrasound transducer element tile.

7. The ultrasound system (1) of any of claims 1-4, further comprising beam shaping circuitry (12, 20) for shaping an ultrasound beam produced with at least a selection of the plurality of ultrasound transducer element tiles (100), wherein:

the controller arrangement is adapted to derive an actual orientation of a particular ultrasound transducer element tile (100) from the capacitive sensor data provided by a capacitive sensor (70) having a first sensing electrode (141) on the surface (103) of said particular ultrasound transducer element tile and communicate the derived actual orientation of said ultrasound transducer element tile to the beam shaping circuitry; and the beam shaping circuitry is adapted to shape said ultrasound beam in response to the communicated derived actual orientation.

8. The ultrasound system (1) of any of claims 1-7, wherein each actuator of a particular ultrasound transducer element tile comprises at least one elongate portion of the material (54), the actuator further comprising an electrode assembly conductively coupled to the controller arrangement, the electrode assembly including a first electrode arrangement (143) on the surface (103) of one of the ultrasound transducer element tiles (100) and a second electrode arrangement (161) on the carrier (160), wherein the first electrode arrangement and the second electrode arrangement are arranged such that the provision of the electromagnetic stimulus to the electrode assembly causes the at least one elongate portion to exhibit at least one of a lateral deformation and an out-of-plane deformation.

9. The ultrasound system (1) of claim 8, wherein:

opposing terminal portions of the at least one elongate portion of the actuator material (54) are anchored to the carrier (160);

the first electrode arrangement (143) comprises a first electrode conductively coupled to a central region of the at least one elongate portion; and

the second electrode arrangement (161) further comprises a second electrode and a third electrode anchoring the respective opposing terminal portions of the at least one elongate portion, optionally wherein the second electrode arrangement comprises at least one intermediate electrode opposing the first electrode.

10. The ultrasound system (1) of claim 8 or 9, wherein the first electrode arrangement (143) comprises a first further electrode conductively coupled to a first region of the elongate portion of the actuator material (54) and the second electrode arrangement (161) comprises a second further electrode coupled to a second region of the elongate portion of the actuator material, wherein the first region is laterally displaced relative to the second region.

11. The ultrasound system (1) of any of claims 8-10, wherein each ultrasound transducer element tile (100) is mounted on a plurality of actuators arranged along respective edges or in respective corners of the ultrasound transducer element tile.

12. The ultrasound system (1) of any of claims 1-11, further comprising a plurality of storage capacitors, each storage capacitor being conductively coupled one of the actuators, wherein the controller is further adapted to provide an electromagnetic stimulus to a particular actuator by storing a charge on the storage capacitor conductively coupled to the particular actuator.

13. The ultrasound system (1) of any of claims 1-12, wherein the material (54) comprises an electroactive polymer optionally coated with an electrically conductive flexible material (50, 52).

14. A method (400) of controlling the ultrasound system (1) of any of claims 1-13, comprising:

obtaining (403) a capacitive sensor reading from each of the capacitive sensors

(70);

determining (405) the respective orientations of the ultrasound transducer element tiles (100) from the obtained capacitive sensor readings; and

generating (407) respective control signals for the actuators of the ultrasound transducer element tiles in response to their determined respective orientations.

15. The method (400) of claim 14, wherein generating respective control signals for the actuators of the ultrasound transducer element tiles (100) in response to the determined respective orientations of the ultrasound transducer element tiles comprises configuring an ultrasound beam having a predetermined form in response to the determined respective orientations of the ultrasound transducer element tiles.