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JP2016539666

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DESCRIPTION JP2016539666
Abstract An ultrasonic transducer assembly 10 is disclosed having a plurality of transducer
elements 32 for transmitting and receiving ultrasonic waves 24, each having a flexible membrane
46 and a substrate 40 located at a distance from the substrate. An AC voltage control unit 56 is
provided to control the AC voltage supplied to each of the transducer elements and controls the
DC bias voltage supplied to the transducer elements in order to bring the flexible membrane in
collapse mode into contact with the substrate. DC voltage control unit 60 is provided. The DC
voltage control unit is configured to temporarily disconnect the DC bias voltage from the
transducer element during operation of the ultrasound transducer assembly to limit the collapse
mode.
Ultrasonic transducer assembly and method for transmitting and receiving ultrasonic waves
[0001]
The present invention relates to an ultrasound transducer assembly and a method for
transmitting and receiving ultrasound waves by an ultrasound transducer assembly. In particular,
the present invention relates to an ultrasound imaging unit with capacitive micromachined
ultrasound transducer elements for emitting and receiving ultrasound and for providing an
ultrasound image.
[0002]
Capacitive micromachined ultrasound transducers (CMUTs) are a well-known technology for use
in ultrasound imaging applications, and offer the possibility for low-cost replacement of
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ultrasound transducers based on piezoelectric technology.
[0003]
The CMUT cell has a cavity under the flexible membrane.
In order to detect ultrasound, the vibration of the flexible membrane, which is moved or vibrated
by the receiving ultrasound, is detected by measuring the change in capacitance between the
electrodes of the flexible membrane and the substrate of the CMUT cell Can. Conversely, an
electrical signal applied to the electrodes of the CMUT causes the membrane cell to vibrate and
thereby emit ultrasound.
[0004]
In order to increase the sensitivity of the CMUT cell, a "collapse mode" has been developed, and a
DC bias voltage is used to bring the membrane into contact with the CMUT substrate, whereby
the sensitivity of the cell can be doubled. A collapsed mode operable CMUT comprising a
contoured substrate is known, for example, from US 2011/040189 A1.
[0005]
However, CMUT cells operated in the collapse mode are subject to electrical charging and
breakdown, which significantly reduces the lifetime of the CMUT cells. Improved CMUT
structures have been developed that can be operated in the high sensitivity, collapsing mode,
with longer insulation life. However, the insulating components of the CMUT cell must be
ensured that they do not charge or break up during the lifetime of the ultrasound transducer.
[0006]
From US 2007/0140515 A1 a transducer static discharge device is known in which light is
exposed to the capacitive membrane transducer element of an ultrasound transducer assembly in
order to reduce the static charge inside the transducer element.
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[0007]
From US 2005/0119575 A1 a capacitive microfabricated transducer array is known for 3D
imaging with bias control of the elevation aperture in space and time and a relatively large
elevation dimension.
[0008]
From US2012 / 0194107 A1 a control device for a capacitive electromechanical transducer is
known which comprises cells each comprising first and second electrodes facing each other via a
gap, a drive / detection unit and an external stressing unit. And the drive / detection unit causes
the second electrode to vibrate to transmit an elastic wave by generating an AC electrostatic
attraction between the electrodes or to detect a charge on the capacitance between the
electrodes. The charge is provided by the second electrode vibrating upon receipt of the elastic
wave.
[0009]
Accordingly, it is an object of the present invention to provide an ultrasound transducer assembly
having high sensitivity and improved lifetime.
A further object of the present invention is to provide an ultrasound imaging unit having high
sensitivity and improved lifetime.
Finally, it is an object of the present invention to provide a method for transmitting and receiving
ultrasound with an ultrasound transducer assembly having high sensitivity and improved
lifetime.
[0010]
According to one aspect of the invention, a plurality of transducer elements for transmitting and
receiving ultrasound, each having a flexible membrane and a substrate located at a distance from
the substrate, supplied to each of the transducer elements An AC voltage control unit for
controlling the AC voltage, and a DC voltage control unit for controlling the DC bias voltage
supplied to the transducer element in order to bring the flexible membrane in collapse mode into
contact with the substrate; An ultrasound transducer assembly, wherein the DC voltage control
unit is configured to temporarily disconnect the DC bias voltage from the transducer element
during operation of the ultrasound transducer assembly to limit the collapse mode. A transducer
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assembly is provided.
[0011]
According to another aspect of the present invention, there is provided an ultrasound imaging
unit having an ultrasound transducer assembly for emitting and receiving ultrasound according
to the present invention.
[0012]
According to yet another aspect of the present invention, a method for transmitting and receiving
ultrasound waves by an ultrasound transducer assembly, the method comprising: a plurality of
flexible membranes and a substrate each disposed at a distance from the substrate. Applying an
AC voltage to the transducer elements of the second module, -providing a DC bias voltage to the
plurality of transducer elements to bring the flexible membrane in contact with the substrate in
the collapse mode, ultrasonic to limit the collapse mode. Temporarily disconnecting the DC bias
voltage during operation of the transducer assembly.
[0013]
Preferred embodiments of the invention are defined in the dependent claims.
It will be appreciated that the method according to the claims has similar and / or identical
preferred embodiments as those defined in the dependent claims and the device according to the
claims.
[0014]
The invention is based on the idea of reducing the time that the transducer cell is in the collapsed
mode and the time for the flexible membrane to contact the substrate.
When the flexible membrane contacts the substrate, the dielectric breakdown of the transducer
cell occurs when the conductive path is formed through the insulating layer, so the time when
the flexible membrane contacts the substrate is reduced or limited, the lifetime Can be increased.
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In accordance with the present invention, a DC bias voltage that initiates the collapse mode and
brings the flexible membrane into contact with the substrate is disconnected from the transducer
cell to reduce the collapse mode time during operation of the ultrasound transducer assembly.
Therefore, the ultrasound transducer element can be operated with high sensitivity in the
collapse mode, and the time that the transducer element is operated in the collapse mode is
reduced, so the lifetime of the transducer element is increased.
[0015]
In a preferred embodiment, the DC voltage control unit is configured to limit the collapse mode
to a predetermined time period. In particular, the DC voltage control unit is configured to
disconnect the DC bias voltage from the transducer element after a predetermined time period
has been reached, and reconnects the DC bias voltage to the transducer element when desired.
The limit time of the collapsing mode can limit the duration of continuous contact of the flexible
membrane with the substrate so that the lifetime of the transducer element can be improved.
[0016]
In a preferred embodiment, the DC voltage control unit is configured to limit the collapse mode
based on the temperature of the transducer element. In particular, the DC voltage control unit is
configured to disconnect the DC bias voltage from the transducer element when the
predetermined temperature of the transducer element is reached. It can be taken into account
that the temperature of the transducer element, which is a parameter affecting the further
lifetime, can be limited.
[0017]
In a preferred embodiment, the DC voltage control unit is configured to disconnect the DC bias
voltage from the transducer element during transmission and reception of ultrasound by the
transducer element. This becomes a simple possibility of interrupting the collapse mode at the
non-conduction time of the transducer element between the transmit mode and the receive
mode.
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[0018]
In a preferred embodiment, the ultrasound transducer assembly further includes a transducer
including a transducer element and a mainframe including a DC voltage source. This can lead to
flexible use of the ultrasound transducer assembly.
[0019]
It is further preferred if the DC voltage control unit is integrated at the connector connecting the
mainframe and the transducer. This has the potential to reduce technical effort, as the DC bias
voltage can be easily switched off by disconnecting the transducer from the DC voltage source in
the mainframe.
[0020]
In a further preferred embodiment, the DC voltage control unit is integrated in the mainframe.
This becomes a simple possibility of integrating a DC voltage control unit and a DC bias voltage
source, which can be easily controlled by a central processing unit in the mainframe.
[0021]
According to a preferred embodiment, the mainframe and the transducer are separated and
electrically connected to one another via connection wires. This is a simple possibility to provide
an electrical connection between the mainframe and the transducer for driving the transducer
element.
[0022]
In a preferred embodiment, the transducer elements are configured in an array of transducer
elements, the array being controlled by the control unit for ultrasound imaging. This is a
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favorable possibility to provide ultrasound imaging with low technical effort.
[0023]
In a preferred embodiment, the DC voltage control unit is configured to disconnect the DC bias
voltage from the transducer element in an imaging mode during transmission and reception of
ultrasound. This becomes a simple possibility to interrupt the decay mode in the non-conduction
time during the imaging scan in order to increase the lifetime of the transducer element.
[0024]
It is further preferred if the DC voltage control unit is configured to disconnect the transducer
element in the imaging mode after receiving the ultrasound and before transmitting the
ultrasound. This is an effective possibility to increase the lifetime as the non-conduction time
between transmission and reception may be a relatively long non-conduction time of the
transducer element during an imaging scan.
[0025]
In a preferred embodiment, the DC voltage control unit is configured to disconnect the DC
voltage from the transducer element while the control unit stores image data received from the
transducer array. Since the non-conduction time of the transducer element can be effectively
used while storing the image data, this has the further possibility of reducing the time of the
collapse mode and increasing the lifetime of the transducer element.
[0026]
In a preferred embodiment, the DC voltage control unit is configured to disconnect the
transducer elements while the control unit receives data for controlling the transducer array. In
particular, the control unit receives or downloads control data, such as setup data, steering data
or digital beamforming data, for the ultrasound transducer element, while the DC voltage control
unit converts the transducer element from the DC bias voltage Cut. This is a further possibility of
effectively limiting the collapse mode with low technical effort, as a non-conduction time can be
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used to upload control data.
[0027]
In a preferred embodiment, the DC voltage control unit is configured to disconnect the
transducer element after a period without a predetermined control signal. This makes it possible
to switch off the collapse mode when the transducer is not used. Hence, the transducer element
can be switched to standby mode when control signals are not received from the input device
after a predetermined period of time.
[0028]
In a preferred embodiment, the ultrasound transducer assembly comprises a contact
measurement unit for detecting contact of the transducer with the object, and a DC voltage
control unit disconnects the transducer element while the transducer is disconnected from the
object Configured to This makes it possible to limit the collapse mode to the time at which the
transducer is used to transmit ultrasound to the object and / or receive ultrasound from the
object to be measured.
[0029]
As mentioned above, the present invention can effectively increase the life of the transducer
element since the time of decay mode can be effectively reduced by disconnecting the DC bias
voltage from the transducer element The sensitivity of the assembly is increased due to the use
of the decay mode. The lifetime can be increased without reducing the function of the transducer
assembly, since the non-conduction time of the transducer assembly is used to switch off the
collapse mode, especially during an imaging scan. In addition, the life can be improved, as the
most significant and wasting impact values, such as the duration of the collapse mode, are taken
into account.
[0030]
These and other aspects of the invention are apparent from and will be elucidated with reference
to the embodiments described hereinafter.
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[0031]
FIG. 1 shows a schematic view of an embodiment of an ultrasound assembly.
FIG. 7 shows a block diagram illustrating the processing of signals and data in an ultrasound
transducer assembly. Fig. 3 shows an example of a schematic detail view of a transducer array
and a beamformer. FIG. 1 shows a schematic cross-sectional view of a capacitive micromachined
transducer cell in non-collapse mode. FIG. 1 shows a schematic cross-sectional view of a
capacitive micromachined transducer cell in a collapsed mode. Fig. 2 shows a schematic view of a
transducer assembly. 2 illustrates an embodiment of an ultrasound transducer assembly.
[0032]
FIG. 1 illustrates the design principle of an ultrasound transducer assembly, in particular an
ultrasound imaging system. This figure is used to explain the background and principle of
operation of the ultrasound system. It will be appreciated that the ultrasound transducer
assembly and the ultrasound imaging unit as claimed in the claims are not limited to such type of
system.
[0033]
The ultrasound transducer assembly in FIG. 1 is generally referred to by the reference numeral
10. The ultrasound transducer assembly 10 is used to scan an area or volume of a patient's body
12. It should be understood that the ultrasound transducer assembly 10 may be used to scan
other areas or volumes, for example sites of animals or other organisms.
[0034]
An ultrasound transducer 14 may be provided to scan the patient's body 12. In the embodiment
shown in FIG. 1, the ultrasound transducer 14 is connected to the ultrasound mainframe 16 as a
console device. Mainframe 16 is shown in FIG. 1 as a mobile console. However, the mainframe 16
may be formed as a stationary device. The mainframe 16 is connected to the ultrasound
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transducer 14 via an interface 18 formed in a wired manner. Furthermore, it is contemplated that
the mainframe 16 may be connected to the ultrasound transducer in a wireless manner, for
example using UWB transmission techniques. The mainframe may further include an input
device 20. Input device 20 may include buttons, a keypad, and / or a touch screen to provide an
input mechanism to a user of ultrasound transducer assembly 10. Additionally or alternatively,
other mechanisms may be provided at the input device 20 to allow the user to control the
ultrasound imaging system 10.
[0035]
In addition, the mainframe 16 has a display 22 for displaying data generated by the ultrasound
transducer assembly 10 to the user. This allows the volume within the patient's body 12 to be
scanned through the ultrasound transducer 14 to be displayed on the display 22 of the
mainframe 16 by the user of the ultrasound transducer assembly 10.
[0036]
FIG. 2a shows a block diagram illustrating the normal operation of a two-dimensional or threedimensional ultrasound imaging unit. The ultrasound transducer 14 emits ultrasound 24 that
produces a response 25 that is returned to the transducer 14 from the volume 26 of the patient's
body 12. The received signal from volume 26 is converted by transducer 14 to an electrical
signal. These electrical signals are provided to the image processor 28. An image processor 28
generates image data from detected acoustic data received from the ultrasound transducer 14.
The image processor 28 converts the image data into display data to be displayed on the display
22. Image processor 28 may prepare a two-dimensional topographic slice of volume 26 to be
displayed, or may convert or render the image data into a three-dimensional image to be
displayed on display 22.
[0037]
FIG. 2 b is a schematic detail view of the ultrasound transducer 14. The ultrasound transducer 14
has an ultrasound transducer array 30 formed of a plurality of acoustic elements, shown here as
transducer elements 32. According to the invention, these transducer elements 32 are formed as
capacitive micromachined ultrasound transducer (CMUT) cells, which are arranged in a matrix to
form a transducer array 30. The transducer array 30 is connected to a microbeamformer 34 for
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beamforming, and the microbeamformer 34 is connected to a main beamformer 36, which drives
the microbeamformer 34. Transducer element 32 transmits ultrasound signal 24 and receives
generated response 25. Transducer array 30 may have thousands of transducer elements 32
forming a number of sub-arrays.
[0038]
3a and 3b show cross-sectional views of the capacitive micromachined transducer element 32.
FIG. The transducer element 32 comprises a substrate 40 having a first (bottom) electrode 42
covered by an insulating layer 44. The transducer element 32 further comprises a flexible
membrane 46 having an insulating layer 49 for insulating the electrode 48 and a second (top)
electrode 48. The flexible membrane 46 is disposed at a distance relative to the insulating layer
44 such that the cavity 50 is formed between the substrate 40 and the membrane 46. The
insulating layer is preferably an oxide layer, most preferably a silicon oxide layer formed on a
silicon substrate 40.
[0039]
To transmit ultrasound 24, an electrical signal is provided to electrodes 42 and 48 to allow
membrane 46 to move or vibrate. In order to receive ultrasound, the membrane 46 is moved by
the ultrasound 25 so that a change in capacitance between the electrodes 42 and 48 can be
detected and a corresponding electrical signal can be formed, or It is made to vibrate.
[0040]
In FIG. 3b, a cross-sectional view of the transducer element 32 is illustrated in the collapsed
mode. A DC bias voltage is applied to the electrodes 42 and 48 so that the membrane 46 is in
contact with the surface of the insulating layer 44 of the substrate 40 in the collapse mode. In
this collapse mode, the sensitivity of the transducer element 32 is substantially increased.
Because the electrode 48 contacts the insulating layer 44, leakage current through the insulating
layer 44 can result in the breakdown of the insulating layer 44 if a conductive path is formed
through the insulating layer 44. The cause of such breakdown is intrinsic breakdown during
device operation due to high electric field resulting in injection of electrons, or extrinsic
breakdown due to defects in the insulating layer 44 brought about during processing .
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[0041]
The time to failure of insulating layer 44 and insulating layer 49 can be used to estimate the
overall lifetime of transducer array 30 under a DC bias voltage. The insulation lifetime is
inversely proportional to the total duration under bias and the DC bias voltage.
[0042]
Therefore, the lifetime of the transducer array 30 is biased by actively disconnecting the DC bias
voltage from the transducer elements 32 during their non-conduction time of the transducer
array 30, as described below. It can be increased by reducing the time under.
[0043]
FIG. 4 shows a schematic block diagram of the transducer assembly 10.
The same elements are indicated by the same reference numbers, and here only the differences
are described in detail.
[0044]
The mainframe 16 has a driver device 52 for driving the transducer elements 32 of the
transducer array 30 in the ultrasound transducer 14. The driver device comprises an AC voltage
control unit and an AC voltage source 54 for controlling the AC voltage supplied to the
transducer element 32 to emit ultrasound waves 24. The driver device 52 has a DC voltage
control unit 60 and a DC voltage source 58 for providing a DC voltage V DC to the transducer
element 32 in order to bring the membrane 46 into contact with the substrate 40 to operate the
transducer element 32 in the collapse mode. Furthermore, it has.
[0045]
Main frame 16 also includes an image processor 28 connected to transducer array 30 to form
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image data from the detected acoustic signal and provide the image data to display 22. The
mainframe 16 further comprises a central processing unit 62 connected to the driver device 52,
the image processor 28, the input device 20 and the display device 22. A central processing unit
is provided to control the driver device 52 and the image processor 28.
[0046]
The DC voltage control unit 60 switches off the DC voltage provided by the DC voltage source 58
or disconnects the DC voltage source 58 from the transducer element 32 to limit or interrupt the
collapse mode of the transducer element 32. The DC voltage control unit 60 disconnects the DC
voltage source 58 from the transducer element 32 during non-conducting periods of the
transducer element 32, for example during transmission of the ultrasound wave 24 and
reception of the ultrasound wave 25. Control data, such as setup data, steering data, or digital
beamforming data used by driver device 52, for central processing unit 62 to store image data in
memory 64 or to drive transducer array 30. The DC voltage may be disconnected while being
downloaded, for example from the input device 20.
[0047]
In a further embodiment, the duration of the collapse mode is measured and limited to a
predetermined period such that the period of contact of the flexible membrane 46 with the
substrate is limited. In a further embodiment, the temperature of the transducer element 32 is
measured or estimated, and the collapse mode is switched off or interrupted when the
temperature of the transducer element 32 is allowed to reach a predetermined temperature. In a
further embodiment, the temperature of the volume 26 of the patient's body 12 is calculated or
estimated, and the collapse mode is switched off or interrupted when the predetermined
temperature of the volume 26 is reached. .
[0048]
In a further embodiment, a contact sensor (not shown) detects whether the transducer 14 is in
contact with the volume 26 to be measured or the patient's body 12 and the transducer 14 is to
be measured in the volume 26 or patient The DC voltage control unit 60 disconnects the DC
voltage from the transducer element 32 when not in contact with the body 12 of the The contact
sensor may be a pressure sensor and may measure ultrasound imaging.
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[0049]
In a further embodiment, DC voltage control unit 60 disconnects DC voltage from transducer
element 32 when input device 20 does not receive an input signal for a predetermined period of
time. In other words, the ultrasound transducer 10 switches in the standby mode or the freeze
mode, and the collapse mode is switched off after a predetermined period without a control
signal.
[0050]
In a further embodiment, the transducer 14 comprises a plurality of transducer units or
transducer arrays 30. In this case, the DC voltage control unit 60 disconnects the DC voltage
from the transducer element 32 when the respective transducer unit or transducer array 30 is
not used or deselected to limit the collapse mode.
[0051]
FIG. 5 shows a schematic view of an embodiment of the transducer assembly 10. The same
elements are indicated by the same reference numerals, where only the differences are described
in detail. The DC voltage control unit 60 in this embodiment is a connector between the
mainframe 16 and the interface 18 so as to form a connector between the DC voltage source 58
and the connecting wire 18 connecting the ultrasound transducer 14 to the mainframe 16.
Alternatively, they are arranged as connection wires 18. Therefore, the DC voltage control unit
60 can easily disconnect the DC voltage V DC to interrupt the decay mode. In this embodiment,
the DC voltage control unit 60 can simply be provided as a retrofit device or add-on kit
connected, for example, between the wire connection 18 and the mainframe 16 by means of
corresponding plug connections.
[0052]
While the present invention is illustrated and described in detail in the drawings and the
foregoing description, it should be considered that such drawings and descriptions are
illustrative and not limiting. Is not limited to the disclosed embodiments.
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[0053]
Other variations to the disclosed embodiments can be understood and effected by those skilled in
the art in practicing the claimed invention, from a study of the drawings, the disclosure and the
dependent claims.
[0054]
In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite
article "a" or "an" does not exclude a plurality.
A single element or other unit may fulfill the function of several items recited in the claims.
The mere fact that certain measures are recited in mutually different dependent claims does not
indicate that a combination of these measures can not be used to advantage.
[0055]
Reference numerals in the claims do not limit the protective scope of the claims.
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