Ultrasonic imaging device

Abstract

The present invention relates to an ultrasonic imaging device (100) comprising: - a first array (102) of capacitive micromachined ultrasonic transducers, CMUTs; - a transmitting and receiving circuit (106) electrically coupled to the first CMUT array, and configured to send, to the first CMUT array, electrical signals intended to be emitted by the first CMUT array in the form of ultrasonic signals and to receive and amplify electrical signals transmitted by the first CMUT array; - a CMUT biasing circuit (108) via which the transmitting and receiving circuit is electrically coupled to the first CMUT array, the CMUT biasing circuit being configured to select only some of the CMUTs and have these operate in transmitting and / or receiving mode by applying at least a first bias voltage to them, causing them to operate in collapsed mode.

Description

B24050PCT - Dual Sensors 1 DESCRIPTION Ultrasound imaging device The present application claims priority from French patent application number 24 / 13896, filed on December 11, 2024, entitled "Ultrasonic Imaging Device", which is incorporated by reference to the fullest extent permitted by law. technical field

[0001] This description relates generally to the field of ultrasound imaging, or ultrasound imaging, and more particularly to that of image capture by ultrasound transduction. Previous technique

[0002] An ultrasound imaging device, or ultrasound capture device, may include different types of ultrasound transducers.

[0003] A CMUT (Capacitive Micromachined Ultrasonic Transducer) ultrasonic transducer consists of a membrane of material positioned above a cavity. An upper electrode is placed on the membrane, and a lower electrode is positioned at the bottom of the cavity or behind it.

[0004] One possible operating mode of a CMUT, called "collapse mode," involves applying a sufficiently high bias voltage to the CMUT electrodes so that a central portion of the CMUT membrane is in contact with the bottom of the cavity during operation. Transduction B24050PCT - Dual Sensors Ultrasound transmission, both in emission and reception, is achieved through the electrical capacitance formed by the peripheral parts of the membrane surrounding the central portion, which are not in contact with the cavity floor. This retracted operating mode has the advantage, compared to the conventional operating mode of a CMUT (Computerized Microwave Occlusion Device) in which the membrane is not in contact with the cavity floor during ultrasonic transduction, of achieving a higher acoustic pressure of the CMUT during ultrasound emission as well as improved detection sensitivity during ultrasound reception.

[0005] Some ultrasonic imaging devices include multiple arrays of ultrasonic transducers designed to operate independently and / or alternately. These ultrasonic transducer arrays are, for example, intended to perform different functions and / or capture different images, as is the case in a biometric fingerprint identification device equipped with multiple ultrasonic transducer arrays designed to capture the fingerprints of different fingers of a user's hand.

[0006] In such a multi-array ultrasonic transducer device, several transmit and receive circuits are used. The different transmit circuits are used to select and drive the ultrasonic transducer arrays. The device also includes one or more bias circuits that continuously apply the required bias voltages to the transducers in the different arrays.

[0007] Multiple transmitting and receiving circuits can also be used in an ultrasound imaging device comprising a single array of transducers. B24050PCT - Dual Sensors 3 ultrasound and in which groups of transducers are selected and driven independently of each other and / or alternately, for example by line or by column. Summary of the invention

[0008] There is a need to offer an ultrasonic imaging device that allows selection and control of only a portion of its transducers while having reduced transmission and / or reception control electronics compared to existing devices.

[0009] To this end, one embodiment proposes an ultrasonic imaging device, comprising at least: - a first matrix of micro-machined capacitive ultrasonic transducers, CMUT; - a transmitting and receiving circuit electrically coupled to the first CMUT matrix, and configured to send to the first CMUT matrix electrical signals intended to be emitted by the first CMUT matrix in the form of ultrasonic signals and to receive and amplify electrical signals transmitted by the first CMUT matrix; - a CMUT biasing circuit through which the transmit and receive circuit is electrically coupled to the first CMUT matrix, configured to select and operate in transmit and / or receive only a portion of the CMUTs by applying at least a first biasing voltage to them, causing them to operate in retracted mode.

[0010] According to a particular embodiment, the biasing circuit is configured so as not to bias the unselected CMUTs.

[0011] According to a particular embodiment, the ultrasound imaging device comprises at least one B24050PCT - Dual Sensors 4 second CMUT matrix to which the transmit and receive circuit is electrically coupled via the biasing circuit which is configured to select and operate in transmit and / or receive at least some of the CMUTs of the second CMUT matrix by applying at least a second biasing voltage to them causing them to operate in retracted mode.

[0012] According to a particular embodiment, the CMUT biasing circuit is configured to select and operate in transmit and / or receive all the CMUTs of only one of the first and second CMUT matrices.

[0013] According to a particular embodiment, the polarization circuit includes at least one first capacitive decoupling element through which the transmitting and receiving circuit is electrically coupled to the first CMUT matrix, and / or, when the ultrasound imaging device includes said at least one second CMUT matrix, the polarization circuit includes at least one second capacitive decoupling element through which the transmitting and receiving circuit is electrically coupled to the second CMUT matrix.

[0014] According to a particular embodiment, the first capacitive decoupling element comprises at least one first capacitor and / or the second capacitive decoupling element comprises at least one second capacitor.

[0015] According to a particular embodiment, the biasing circuit comprises at least one first resistive element through which the first biasing voltage is intended to be applied to at least a portion of the CMUTs of the first CMUT matrix and / or, when the ultrasound imaging device comprises said at least one second CMUT matrix, the biasing circuit B24050PCT - Dual Sensors 5 comprises at least one second resistive element through which the second bias voltage is intended to be applied to at least a portion of the CMUTs of the second CMUT matrix.

[0016] According to a particular embodiment, the biasing circuit includes at least one control circuit configured to deliver the first bias voltage to the first resistive element and / or to deliver the second bias voltage to the second resistive element.

[0017] According to a particular embodiment, each of the CMUTs comprises at least one membrane disposed between first and second electrodes, and the biasing circuit is configured to apply the first bias voltage and / or the second bias voltage across the terminals of the first and second electrodes of each of the CMUTs of said part only of the CMUTs.

[0018] According to a particular embodiment, the first resistive element is coupled to one of the first and second electrodes of each of the CMUTs of the first CMUT matrix and / or the second resistive element is coupled to one of the first and second electrodes of each of the CMUTs of the second CMUT matrix.

[0019] According to a particular embodiment: - the first electrodes of the CMUTs in the same row of the first CMUT matrix are electrically coupled to each other, and / or - the second electrodes of the CMUTs in the same column of the first CMUT matrix are electrically coupled to each other, and / or when the ultrasound imaging device includes said at least one second CMUT matrix, the first electrodes of the CMUTs in the same row of the second CMUT matrix are electrically coupled to each other, and / or B24050PCT - Dual Sensors 6 when the ultrasonic imaging device includes said at least one second CMUT matrix, the second electrodes of the CMUTs of the same column of the second CMUT matrix are electrically coupled to each other.

[0020] According to a particular embodiment, the transmission and reception circuit is configured to implement at least: - an amplification and an analog-to-digital conversion of the electrical signals transmitted by the first CMUT matrix, and / or, when the ultrasound imaging device includes said at least a second CMUT matrix, transmitted by said at least a second CMUT matrix, and / or a digital-to-analog conversion of the electrical signals intended to be emitted by the first CMUT matrix and / or, when the ultrasound imaging device includes said at least a second CMUT matrix, by said at least a second CMUT matrix.

[0021] According to a particular embodiment, the biasing circuit is configured to select and operate a number Mi of rows of the first CMUT matrix less than the total number of rows of the first CMUT matrix, and / or a number Ni of columns of the first CMUT matrix less than the total number of columns of the first CMUT matrix, with Mi and Ni corresponding to integers each greater than or equal to 1.

[0022] According to a particular embodiment, when the ultrasound imaging device includes at least one second CMUT matrix, the polarization circuit is configured to select and operate a number M2 of rows from the second CMUT matrix less than the total number of rows in the second CMUT matrix, and / or a number N2 of columns from the second CMUT matrix less than B24050PCT - Dual Sensors 7 to the total number of columns of the second CMUT matrix, with M2 and N2 corresponding to integers each greater than or equal to 1.

[0023] According to a particular embodiment, the ultrasonic imaging device corresponds to a biometric identification device configured to implement the capture of at least one fingerprint.

[0024] An ultrasound imaging method is also proposed, implemented with an ultrasound imaging device comprising at least: - a first matrix of micro-machined capacitive ultrasonic transducers, CMUT; - a transmitting and receiving circuit electrically coupled to the first CMUT matrix, and configured to send to the first CMUT matrix electrical signals intended to be emitted by the first CMUT matrix in the form of ultrasonic signals and to receive and amplify electrical signals transmitted by the first CMUT matrix; - a CMUT biasing circuit through which the transmit and receive circuit is electrically coupled to the first CMUT matrix; and comprising a selection and operation in transmit and / or receive of only a part of the CMUTs by applying on them at least a first biasing voltage causing them to operate in retracted mode. Brief description of the drawings

[0025] These features and advantages, as well as others, will be described in detail in the following non-limiting description of particular embodiments in relation to the accompanying figures, among which: B24050PCT - Dual Sensors 8

[0026] - Figure 1 schematically represents part of an ultrasound imaging device according to a particular embodiment;

[0027] - Figure 2 schematically represents an electrical model of part of an ultrasound imaging device according to a particular embodiment;

[0028] - Figure 3 represents a diagram of the acoustic pressure obtained during an emission of ultrasound by an ultrasound imaging device according to a particular embodiment;

[0029] - Figure 4 represents a diagram of the voltage delivered by a CMUT during the reception of ultrasound by an ultrasound imaging device according to a particular embodiment. Description of the implementation methods

[0030] The same elements have been designated by the same reference numerals in the different figures. In particular, structural and / or functional elements common to the different embodiments may have the same reference numerals and may possess identical structural, dimensional, and material properties. In the figures, to facilitate their interpretation, the different elements are not shown at the same scale relative to one another.

[0031] For the sake of clarity, only the steps and elements necessary for understanding the described implementation examples have been shown and are detailed. In particular, only a portion of the electrical and electronic circuits and components of an ultrasound imaging device are described and shown in the figures. Furthermore, various elements (ultrasonic transducer arrays, circuit B24050PCT - Dual Sensors The transmission and reception components, control circuit, etc.) of the ultrasound imaging device and the various steps involved (processing of acquired images, details of calculations performed, etc.) are not detailed. A person skilled in the art will be able to perform these elements in detail based on the functional description provided here.

[0032] Unless otherwise specified, when referring to two connected elements, this means directly connected without any intervening elements other than conductors, and when referring to two connected or coupled elements, this means that these two elements can be connected or linked via one or more other elements. Furthermore, the terms "coupled," "linked," and "connected" are used here to refer to electrical couplings, links, or connections.

[0033] Unless otherwise specified, the expressions "approximately", "roughly", "about", and "on the order of" mean within 10%, preferably within 5%.

[0034] Throughout the description, the terms "row" and "column" are used considering an arbitrary orientation given to the described device, these terms being able to be interchanged depending on its orientation.

[0035] Unless otherwise stated, the ranges of values ​​indicated include the limits of those ranges.

[0036] An example of the realization of an ultrasonic imaging device 100 is described below in relation to figure 1.

[0037] Device 100 includes a first CMUT matrix 102. The first matrix 102 is, for example, of type RCA ("Row-Column Array", or "Row-Column Addressed" in English, i.e., a network of rows and columns, or with addressing). B24050PCT - Dual Sensors 10 rows-columns in French), in which the CMUTs of the same row of the matrix have a common electrode and the CMUTs of the same column of the matrix have a common electrode.

[0038] Alternatively, the first 102 matrix may contain several groups of CMUTs linked together, for example of bar type and each forming one or more rows or one or more columns of CMUTs.

[0039] The number of CMUTs in the first matrix 102 can depend on various desired characteristics and constraints, such as the dimensions of the capture surface of device 100, the dimensions of the CMUTs, the desired resolution for the first matrix 102, etc. According to one embodiment, the first matrix 102 can have 128 rows and 128 columns of CMUTs.

[0040] In the example embodiment described, each of the CMUTs of the first matrix 102 includes at least one membrane disposed above a cavity and between first and second electrodes, one being disposed on the membrane and the other being disposed at the bottom of the cavity and behind it.

[0041] Each CMUT of the first matrix 102 can form a pixel of the first matrix 102. In the described embodiment, the number of rows of pixels in the first matrix 102 is equal to the number of material portions that each form the first electrodes of the CMUTs arranged in the same row of the first matrix 102, and the number of columns of pixels in the first matrix 102 is equal to the number of material portions forming the second electrodes of the CMUTs arranged in the same column of the first matrix 102. More generally, the electrodes of the CMUTs of matrices 102, 104 can be such that the first electrodes of the CMUTs in the same row of the first B24050PCT - Dual Sensors 11 matrix 102 are coupled together, and / or the second electrodes of the CMUTs of the same column of the first matrix 102 are coupled together.

[0042] Other configurations of the CMUT electrodes in the first matrix 102 are possible. For example, the electrodes of each CMUT can be independent of the electrodes of the other CMUTs.

[0043] The first matrix 102 is configured to provide transduction of analog electrical input signals, or electrical excitation signals, into ultrasound, as well as transduction of received ultrasound into analog electrical output signals, or electrical response signals.

[0044] In the described embodiment, the device 100 also includes a second CMUT matrix 104, for example similar to the first matrix 102. The various characteristics and variants previously described for the first matrix 102 can be applied to the second matrix 104. Alternatively, the second matrix 104 can have different characteristics from those of the first matrix 102: number of rows, number of columns, number of pixels, connection of the CMUT electrodes, etc.

[0045] The device 100 further includes at least one transmitting and receiving circuit 106 coupled to the first matrix 102, and more particularly to the first and second electrodes of the CMUTs of the first matrix 102. The transmitting and receiving circuit 106 is configured to send analog electrical signals to the first matrix 102, intended to be emitted by the first matrix 102 in the form of ultrasonic signals; that is, to send electrical excitation signals causing the CMUTs of the first matrix 102 to emit ultrasonic waves. The transmitting and receiving circuit 106 is also configured to receive and amplify electrical signals B24050PCT - Dual Sensors 12 analog signals are transmitted by the first matrix 102 during the reception of ultrasound by the first matrix 102; that is, receiving electrical response signals generated by the CMUTs of the first matrix 102 under the effect of receiving reflected ultrasonic waves. The transmitting and receiving circuit 106 can correspond to an analog electronic circuit.

[0046] In the described embodiment, the transmit and receive circuit 106 is also coupled to the second matrix 104. As with the first matrix 102, the transmit and receive circuit 106 is configured to send analog electrical signals to the second matrix 104, intended to be emitted by the CMUTs of the second matrix 104 in the form of ultrasonic signals, and is also configured to receive and amplify analog electrical signals generated by the CMUTs of the second matrix 104 during ultrasonic reception by the second matrix 104.

[0047] The receiving section of circuit 106 may include at least one analog front-end (AFE) circuit designed to receive the output electrical signals transmitted by the first and second matrices 102, 104. The transmitting and receiving circuit 106 is specifically configured to perform an analog-to-digital conversion of the electrical signals transmitted by the first and second matrices 102, 104 following the reception of ultrasonic echoes previously emitted by these matrices. The transmitting and receiving circuit 106 can implement various functions based on the received signals: amplification, filtering, analog-to-digital conversion, demodulation, etc. Alternatively, the transmitting and receiving circuit 106 may include several AFEs, each coupled to at least a portion of the CMUTs of one of the first and second matrices 102 and 104. B24050PCT - Dual Sensors 13 matrices 102, 104. The transmitting and receiving circuit 106 may include at least one multiplexer allowing it to be coupled to different electrodes of the CMUTs of matrices 102, 104.

[0048] In the example embodiment described, the emission part of the circuit 106 can in particular be configured to perform a digital-to-analog conversion of the electrical signals intended to be transmitted to the first and second matrices 102, 104 for an ultrasound emission.

[0049] In the described embodiment, the transmitting and receiving circuit 106 is composed of several sets of components, some for implementing functions dedicated to signal transmission and others for implementing functions dedicated to signal reception. In this example, the transmitting and receiving circuit 106 is implemented as a single integrated circuit. Alternatively, the device 100 could include, for example, at least one signal transmission circuit separate from at least one signal reception circuit. In this case, the transmitting and receiving circuit 106 could be implemented as several separate integrated circuits.

[0050] The device 100 further includes a CMUT biasing circuit 108 through which the transmit and receive circuit 106 is coupled to the first matrix 102. In the example described, the transmit and receive circuit 106 is also coupled to the second matrix 104 through the biasing circuit 108.

[0051] The biasing circuit 108 is configured to select and operate in transmit and / or receive only a portion of the CMUTs of device 100 by applying at least one biasing voltage to them. B24050PCT - Dual Sensors 14 operating in retracted mode. Thus, in device 100, the function of selecting, or activating, the CMUTs intended to implement a transmit and / or receive function at a given time is performed by the biasing circuit 108 and not by the transmit and receive circuit 106. Furthermore, the unselected CMUTs of device 100 are not biased by the biasing circuit 108.

[0052] In the described embodiment example, the biasing circuit 108 is configured to select and operate in transmit and / or receive mode the CMUTs of only one of the first and second matrices 102, 104.

[0053] The transmitting and receiving circuit 106 may include a single transmitting section configured to send transmitting signals to all the CMUTs of the device 100. The selection of the ultrasound emission by the first matrix 102 or by the second matrix 104 is then performed by the biasing circuit 108, which biases, in a retracted operating mode, only the CMUTs of one of the matrices 102 or 104. The CMUTs of the other matrix, which are not biased, also receive the signals sent by the transmitting and receiving circuit 106 but do not emit ultrasound with significant acoustic pressure. The transmitting and receiving circuit 106 may also include a single receiving section coupled to matrices 102 and 104, and subsequently receiving the signals from the matrix whose CMUTs are biased by the biasing circuit 108.The unpolarized CMUTs of the other matrix do not deliver signals with sufficient power to be confused with those sent by the polarized CMUTs.

[0054] The selection of either matrix 102 or 104 by the biasing circuit 108 can be performed for the emission and / or reception of ultrasound by these matrices. B24050PCT - Dual Sensors 15 102, 104. For example, the transmitting and receiving circuit 106 may include common elements for the transmission of signals by the matrices 102, 104 when the biasing of the CMUTs of the matrices 102, 104 is carried out for the transmission of ultrasound by the matrices 102, 104, and / or the transmitting and receiving circuit 106 may include common elements for the reception of signals by the matrices 102, 104 when the biasing of the CMUTs of the matrices 102, 104 is carried out for the reception of ultrasound by the matrices 102, 104.

[0055] In the example of Figure 1, the biasing circuit 108 includes at least one first capacitive decoupling element 110 through which the transmitting and receiving circuit 106 is coupled to the first matrix 102. Furthermore, in this embodiment where the device 100 also includes the second matrix 104, the biasing circuit 108 includes at least one second capacitive decoupling element 112 through which the transmitting and receiving circuit 106 is coupled to the second matrix 104. For example, the first capacitive element 110 includes at least one first capacitor, and / or the second capacitive element 112 includes at least one second capacitor.The capacitive elements 110, 112 serve in particular to ensure that the DC bias voltages intended to be applied to the CMUTs of the matrices 102, 104 are not applied to the transmit and receive circuit 106 or to the matrix for which each of these bias voltages is not intended, while allowing the voltages measured by the CMUTs of the matrices 102, 104 to pass to the transmit and receive circuit 106 as well as the AC control voltages sent by the transmit circuit. B24050PCT - Dual Sensors 16 and reception 106 destined for the CMUT of matrices 102, 104.

[0056] In the described embodiment, the biasing circuit 108 also includes at least one first resistive element 114 through which the biasing voltage is applied to at least some of the CMUTs of the first matrix 102 when said CMUTs of the first matrix 102 are intended to implement the transmission and / or reception of ultrasonic signals. More specifically, in the described example, the biasing voltage is applied to all of the CMUTs of the first matrix 102 when the first matrix 102 is intended to implement the transmission and / or reception of ultrasonic signals.

[0057] Furthermore, in this embodiment, where device 100 also includes the second matrix 104, the biasing circuit 108 includes at least one second resistive element 116 through which the biasing voltage is applied to at least some of the CMUTs of the second matrix 104 when said CMUTs of the second matrix 104 are intended to implement the transmission and / or reception of ultrasonic signals. More specifically, in the example described, the biasing voltage is applied to all of the CMUTs of the second matrix 104 when the second matrix 104 is intended to implement the transmission and / or reception of ultrasonic signals.

[0058] The bias voltage applied to the CMUTs of the first matrix 102, called Vbias1 in Figure 1, can be equal to or different from the bias voltage applied to the CMUTs of the second matrix 104, called Vbias2 in Figure 1. B24050PCT - Dual Sensors 17

[0059] In the described embodiment, the biasing circuit 108 further includes at least one control circuit, not visible in Figure 1, configured to deliver one of the bias voltages Vbias1 and Vbias2 to the first or second resistive elements 114, 116, depending on the CMUT matrix selected, to implement the transmission and / or reception of ultrasonic signals. The values ​​of the bias voltages Vbias1 and Vbias2 are chosen, in particular, according to the characteristics of the CMUT matrices 102, 104.

[0060] The transmitting and receiving circuit 106 is coupled to at least one digital control and processing circuit 118, which generates the control signals sent to the transmitting and receiving circuit 106 and implements the processing and algorithms applied to the resulting response signals. The digital control and processing circuit 118 includes, for example, at least one FPGA (Field Programmable Gate Array), or at least one ASIC (Application-Specific Integrated Circuit), or at least one microcontroller, or at least one microprocessor configured to perform digital processing of the data intended to be transmitted and received by the matrices 102, 104.

[0061] In the described embodiment, the biasing circuit 108 is configured to apply the bias voltage Vbias1 or Vbias2 across the terminals of the first and second electrodes of each of the CMUTs of the first matrix 102 or the second matrix 104, depending on whether one or the other matrix 102 or 104 is selected to implement the transmission and / or reception of ultrasonic signals. In the described embodiment, the first resistive element 114 is coupled to one of the first and second electrodes of each of the CMUTs of the first matrix 102, and the second B24050PCT - Dual Sensors 18 resistive element 116 is coupled to one of the first and second electrodes of each of the CMUTs of the second matrix 104.

[0062] The bias voltage values ​​Vbias1 and Vbias2 are such that the central portion of the diaphragm of the CMUTs to which these bias voltages are applied comes into contact with the bottom of their cavity, thus causing them to operate in a retracted mode. These values ​​depend in particular on the characteristics of the CMUTs and can, for example, range from 15 V to 30 V. These values ​​are adjusted according to the values ​​of the alternating control signals sent by circuit 106.

[0063] Figure 2 schematically represents an electrical model of part of device 100 previously described in relation to figure 1.

[0064] In Figure 2, each of the matrices 102, 104 forms an electrical capacitance whose value is, for example, 70 pF when the matrix's CMUTs are biased by one of the bias voltages Vbias1 and Vbias2, and 40 pF when the matrix's CMUTs are not biased with either of these bias voltages. The value of each of the capacitive elements 110, 112 is, for example, 10 nF. In addition, a first parasitic capacitance 120, with a value for example of 10 pF, is present between the biasing circuit 108 and each of the matrices 102, 104, and a second parasitic capacitance 122, with a value for example of 20 pF, is present between the biasing circuit 108 and the transmit and receive circuit 106. The matrices 102, 104 can be designed such that the values ​​of the parasitic capacitances obtained are as low as possible in order to degrade the signal-to-noise ratio in the receive of the device 100 as little as possible. B24050PCT - Dual Sensors 19

[0065] The values ​​of the different capacities present in device 100 are examples and may vary according to the characteristics of the different elements of device 100.

[0066] Figure 3 shows a sound pressure level diagram obtained during ultrasound emission from one of the matrices 102, 104 of device 100 previously described in connection with Figure 1. This figure illustrates that a first maximum sound pressure level of 222.8 kPa is obtained when the CMUTs of this matrix receive a bias voltage Vbias of 40 V and an alternating control signal with a frequency of 13.33 MHz, and that a second maximum sound pressure level of 224.56 kPa is obtained when the CMUTs of this matrix receive a bias voltage of -40 V and an alternating control signal with a frequency of 9.23 MHz. Conversely, in the absence of bias or with low bias voltages, the sound pressure level emitted by the CMUTs receiving an alternating control signal, regardless of its frequency, is zero or very low.

[0067] Figure 4 shows a voltage diagram of the output of the CMUTs of device 100 during ultrasound reception by one of the matrices 102, 104 of device 100 previously described in connection with Figure 1. This figure illustrates that a first maximum received voltage value of 296.14 mVpp (millivolt peak-to-peak) is obtained when the CMUTs of this matrix receive a bias voltage of 30 V and an alternating control signal with a frequency of 9.23 MHz, and that a second maximum received voltage value of 291.99 mVpp is obtained when the CMUTs receive a bias voltage of -32 V and an alternating control signal with a frequency of 9.23 MHz. However, in the absence of B24050PCT - Dual Sensors 20 polarization or with low polarization voltages, the voltages delivered in reception by the CMUTs are zero or very low, at any frequency.

[0068] The diagrams in Figures 3 and 4 clearly show that for CMUTs operating in retracted mode, the bias applied to the CMUTs is well suited to also serve as a selection signal for CMUTs intended to perform an emission and / or reception of ultrasound, given the strong dependence of the sensitivity of the CMUTs on the bias voltage applied to them.

[0069] The impedance of CMUTs, and therefore the peak value of their resonant frequency, changes according to the applied bias voltage. This allows for significant attenuation of echoes outside the expected reception frequency band and prevents the generation of spurious signals in captured images. For example, in the case of a CMUT whose diaphragm is subjected to a bias voltage causing it to operate in retracted mode, the maximum CMUT response can be obtained at a frequency between approximately 10 MHz and 20 MHz, whereas when the diaphragm is not in contact with the bottom of the cavity, the response can be maximum at a frequency of around 2 MHz.

[0070] Furthermore, in device 100, the same transmit and receive circuit 106 is used for sending and receiving signals to the matrices of device 100 because the transmit and receive circuit 106 does not perform the function of selecting the CMUTs intended to implement an emission and / or reception of ultrasound.

[0071] In the specific embodiment described, device 100 corresponds to a biometric identification device. Furthermore, in this example, this device 100 is configured to perform fingerprint capture. B24050PCT - Dual Sensors 21 digital. More specifically, when the device 100 has several CMUT matrices, as is the case in the example described above, each of the CMUT matrices can be intended to capture a fingerprint of one of the fingers of the user of the device 100.

[0072] In such an application, the device 100 is intended to implement an acquisition of at least one image of a fingerprint formed of ridges and valleys present on the surface of the skin of the finger(s) located on the CMUT matrix(s) of the device 100. Such an acquisition is based on the fact that the ultrasound emitted by a CMUT matrix is ​​reflected more significantly against the air present in the valleys of the fingerprint than against the ridges of the fingerprint, thus allowing their distinction in the images obtained.

[0073] For example, device 100 acquires at least one surface image of the finger present on a CMUT matrix of device 100. This acquisition includes, for example, the emission of a series of ultrasound pulses by the CMUT matrix, followed by the reception of the echoes by this CMUT matrix and the processing of the responses obtained to obtain the surface image of the finger, i.e., the image of the fingerprint. The acquisition of the surface image of the finger may also include the implementation of other steps not detailed here: filtering of the response signal obtained, envelope detection, logarithmic compression, etc. The data relating to the acquired image is, for example, stored in a memory of device 100 or in an external memory of device 100, for example, connected to device 100 by a communication link.

[0074] From the previously acquired surface image, device 100 can determine or extract minutiae of B24050PCT - Dual Sensors 22. The fingerprint obtained from this image. This determination of minutiae can be performed by one or more image processing algorithms not described in detail here but known to those skilled in the art. Each of the minutiae extracted from the surface image can be characterized (type of minutiae, position in the plane of the surface image, orientation of the minutiae, orientation relative to other minutiae, etc.).

[0075] The characteristics of the minutiae can then be compared with expected minutiae characteristics, for example, previously determined during a preliminary user enrollment stage, to confirm or refute the user's identity. This comparison may involve calculating a score whose value depends on the correlations between, on the one hand, the previously determined minutiae characteristics and, on the other hand, the expected minutiae characteristics for confirming or refuting the user's identity. The resulting score can then be compared with a threshold value to assess the correspondence between the biometric measurement performed and the expected biometric data, and thus confirm or refute the user's identity.

[0076] These steps related to biometric identification are known to those skilled in the art and are not described in detail in this description.

[0077] The 100 device can be configured to implement other functions, such as volumetric image capture to determine the finger microvasculature and implement liveness detection (via blood flow detection in the finger microvasculature) and / or complementary biometric identification based on the characteristics of the determined microvasculature. B24050PCT - Dual Sensors 23

[0078] As an alternative to the embodiment described above, the device 100 could include only the first matrix 102 and not the second matrix 104. In this case, the biasing circuit 108 can be used to select a portion of the CMUTs of the first matrix 102 to implement the transmission and / or reception of ultrasonic signals.For example, the biasing circuit 108 can be configured to select and operate a number Mi of rows of the first matrix 102 less than the total number of rows of the first matrix 102 by biasing only the CMUTs of these Mi rows and not those of the other rows of the first matrix 102, and / or to select and operate a number Ni of columns of the first matrix 102 less than the total number of columns of the first matrix 102 by biasing only the CMUTs of these Ni columns and not those of the other columns of the first matrix 102, with Mi and Ni corresponding to integers each greater than or equal to 1.

[0079] Such operation of device 100 can also be applied when device 100 comprises the first and second matrices 102, 104. In this case, in addition to the operation indicated above for the first matrix 102, the biasing circuit 108 can be configured to select and operate a number M2 of rows of the second matrix 104 less than the total number of rows of the second matrix 104 by biasing only the CMUTs of these M2 rows and not those of the other rows of the second matrix 104, and / or to select a number N2 of columns of the second matrix 104 less than the total number of columns of the second matrix 104 by biasing only the CMUTs of these N2 columns and not those of the other columns of the second matrix 104, with M2 and N2 corresponding to integers each greater than or equal to 1. B24050PCT - Dual Sensors 24

[0080] According to another variant, the device 100 can include more than two CMUT matrices coupled to the biasing circuit 108. In this case, the biasing circuit 108 can be configured to select and operate only a part of the CMUTs of these matrices, for example at least a part of the CMUTs of one or more matrices while leaving the CMUTs of one or more other matrices unbiased, or by selecting only a part of the CMUTs of all the matrices of the device 100 while leaving the other CMUTs of these matrices unbiased.

[0081] Device 100 is compatible with operating modes other than the contracted mode, such as the mode called "collapse-snapback".

[0082] Various embodiments and variations have been described. A person skilled in the art will understand that some features of these various embodiments and variations could be combined, and other variations will become apparent to a person skilled in the art.

[0083] Finally, the practical implementation of the described methods and variants is within the reach of the person in the trade, based on the functional indications given above.

Claims

B24050PCT - Dual Sensors 25 DEMANDS 1. Ultrasonic imaging device (100), comprising at least: - a first array (102) of micro-machined capacitive ultrasonic transducers, CMUT; a transmit and receive circuit (106) electrically coupled to the first array (102) of CMUT, and configured to send to the first array (102) of CMUT electrical signals intended to be emitted by the first array (102) of CMUT in the form of ultrasonic signals and to receive and amplify electrical signals transmitted by the first array (102) of CMUT; a biasing circuit (108) of the CMUT through which the transmit and receive circuit (106) is electrically coupled to the first array (102) of CMUT, configured to select and operate in transmit and / or receive only a part of the CMUT by applying on them at least a first biasing voltage causing them to operate in retracted mode, and not to bias the unselected CMUT.

2. An ultrasonic imaging device (100) according to claim 1, comprising at least a second CMUT matrix (104) to which the transmitting and receiving circuit (106) is electrically coupled via the biasing circuit (108) which is configured to select and operate in transmitting and / or receiving mode at least a portion of the CMUTs of the second CMUT matrix (104) by applying to them B24050PCT - Dual Sensors 26 at least a second bias voltage causing them to operate in retracted mode.

3. Ultrasonic imaging device (100) according to claim 2, wherein the CMUT polarization circuit (108) is configured to select and operate in transmit and / or receive all the CMUTs of only one of the first and second matrices (102, 104) of CMUTs.

4. Ultrasonic imaging device (100) according to any one of the preceding claims, wherein the biasing circuit (108) comprises at least one first capacitive decoupling element (110) through which the transmitting and receiving circuit (106) is electrically coupled to the first CMUT matrix (102), and / or, where the ultrasonic imaging device (100) comprises at least one second CMUT matrix (104), the biasing circuit (108) comprises at least one second capacitive decoupling element (112) through which the transmitting and receiving circuit (106) is electrically coupled to the second CMUT matrix (104).

5. An ultrasonic imaging device (100) according to claim 4, wherein the first capacitive decoupling element (110) comprises at least one first capacitor and / or the second capacitive decoupling element (112) comprises at least one second capacitor 6. Ultrasonic imaging device (100) according to any one of the preceding claims, wherein the B24050PCT - Dual Sensors The biasing circuit (108) includes at least one first resistive element (114) through which the first bias voltage is intended to be applied to at least a portion of the CMUTs of the first CMUT matrix (102) and / or, when the ultrasound imaging device (100) includes at least one second CMUT matrix (104), the biasing circuit (108) includes at least one second resistive element (116) through which a second bias voltage is intended to be applied to at least a portion of the CMUTs of the second CMUT matrix (104).

7. Ultrasonic imaging device (100) according to claim 6, wherein the biasing circuit (108) comprises at least one control circuit configured to deliver the first bias voltage to the first resistive element (114) and / or to deliver the second bias voltage to the second resistive element (116).

8. An ultrasonic imaging device (100) according to any one of the preceding claims, wherein each CMUT comprises at least one membrane disposed between first and second electrodes, and wherein: the biasing circuit (108) is configured to apply the first biasing voltage across the terminals of the first and second electrodes of each of the CMUTs of said portion only of the CMUTs of the first CMUT array (102), and / or where the ultrasonic imaging device (100) comprises at least a second CMUT array (104) B24050PCT - Dual Sensors 28 wherein the transmit and receive circuit (106) is electrically coupled via the bias circuit (108) which is configured to select and operate in transmit and / or receive at least a portion of the CMUTs of the second matrix (104) of CMUTs by applying to them at least a second bias voltage causing them to operate in retracted mode, the bias circuit (108) is configured to apply the second bias voltage across the terminals of the first and second electrodes of each of the CMUTs of said portion only of the CMUTs of the second matrix (104) of CMUTs.

9. Ultrasonic imaging device (100) according to claim 8 and according to any one of claims 6 or 7, wherein the first resistive element (114) is coupled to one of the first and second electrodes of each of the CMUTs of the first CMUT matrix (102) and / or wherein the second resistive element (116) is coupled to one of the first and second electrodes of each of the CMUTs of the second CMUT matrix (104).

10. Ultrasonic imaging device (100) according to any one of claims 8 or 9, wherein: the first electrodes of the CMUTs in the same row of the first CMUT matrix (102) are electrically coupled to each other, and / or the second electrodes of the CMUTs in the same column of the first CMUT matrix (102) are electrically coupled to each other, and / or when the ultrasonic imaging device (100) comprises said at least one second CMUT matrix (104), B24050PCT - Dual Sensors 29 the first electrodes of the CMUTs of the same row of the second matrix (104) of CMUTs are electrically coupled to each other, and / or when the ultrasound imaging device (100) includes said at least one second matrix (104) of CMUTs, the second electrodes of the CMUTs of the same column of the second matrix (104) of CMUTs are electrically coupled to each other.

11. Ultrasonic imaging device (100) according to any one of the preceding claims, wherein the transmitting and receiving circuit (106) is configured to implement at least: amplification and analog-to-digital conversion of the electrical signals transmitted by the first CMUT matrix (102), and / or, where the ultrasonic imaging device (100) comprises at least one second CMUT matrix (104), transmitted by said at least one second CMUT matrix (104), and / or digital-to-analog conversion of the electrical signals intended to be emitted by the first CMUT matrix (102), and / or, where the ultrasonic imaging device (100) comprises at least one second CMUT matrix (104), by said at least one second CMUT matrix (104).

12. An ultrasonic imaging device (100) according to any one of the preceding claims, wherein the biasing circuit (108) is configured to select and operate a number Mi of lines from the first CMUT matrix (102) less than the total number B24050PCT - Dual Sensors 30 rows of the first (102) CMUT matrix, and / or a number Ni of columns of the first (102) CMUT matrix less than the total number of columns of the first (102) CMUT matrix, with Mi and Ni corresponding to integers each greater than or equal to 1.

13. Ultrasonic imaging device (100) according to any one of claims 2 to 12, wherein, when the ultrasonic imaging device (100) comprises at least one second CMUT matrix (104), the biasing circuit (108) is configured to select and operate a number M2 of rows of the second CMUT matrix (104) less than the total number of rows of the second CMUT matrix (104), and / or a number N2 of columns of the second CMUT matrix (104) less than the total number of columns of the second CMUT matrix (104), with M2 and N2 corresponding to integers each greater than or equal to 1.

14. Ultrasonic imaging device (100) according to any one of the preceding claims and corresponding to a biometric identification device configured to implement the capture of at least one fingerprint.

15. Ultrasonic imaging method implemented with an ultrasonic imaging device (100) comprising at least: - a first matrix (102) of micro-machined capacitive ultrasonic transducers, CMUT; B24050PCT - Dual Sensors 31 a transmit and receive circuit (106) electrically coupled to the first CMUT matrix (102), and configured to send to the first CMUT matrix (102) electrical signals intended to be emitted by the first CMUT matrix (102) in the form of ultrasonic signals and to receive and amplify electrical signals transmitted by the first CMUT matrix (102); a CMUT biasing circuit (108) through which the transmit and receive circuit (106) is electrically coupled to the first CMUT matrix (102); comprising a selection and operation in transmit and / or receive of only a part of the CMUTs by applying on them at least a first biasing voltage causing them to operate in retracted mode, the unselected CMUTs not being biased.

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