Ultrasound imaging device

Abstract

Ultrasonic Imaging Device This description relates to an ultrasonic imaging device (100), comprising: - a first array (102) of micro-machined capacitive ultrasonic transducers, CMUTs; - a transmit and receive circuit (106) electrically coupled to the first CMUT array, and configured to send electrical signals to the first CMUT array for emission 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) through which the transmit and receive circuit is electrically coupled to the first CMUT array, configured to select and operate in transmit and / or receive mode only a portion of the CMUTs by applying at least a first biasing voltage to them, causing them to operate in retracted mode. Figure for the abbreviation: Fig. 1

Description

Title of the invention: Ultrasonic imaging device technical field

[0001] The present 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 ultrasonic imaging device, or ultrasonic capture device, may include different types of ultrasonic transducers.

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

[0004] One possible operating mode of a CMUT, called "collapse mode," consists of 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. Ultrasonic transduction, both in transmission and reception, is then achieved through the electrical capacitance formed by the peripheral portions of the membrane surrounding this central portion, which are not in contact with the bottom of the cavity. This collapsed operating mode has the advantage, compared to the conventional operating mode of a CMUT in which the membrane is not in contact with the bottom of the cavity during ultrasonic transduction, of obtaining a higher acoustic pressure from the CMUT during ultrasound emission as well as improved detection sensitivity during ultrasound reception.

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

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

[0007] Several transmitting and receiving circuits can also be used in an ultrasonic imaging device comprising a single array of ultrasonic transducers and in which groups of transducers are selected and driven independently of each other and / or alternately, for example by row or by column. Summary of the invention

[0008] There is a need to propose an ultrasonic imaging device allowing selection and control of only part of its transducers while having reduced control electronics in transmission and / or reception compared to existing devices.

[0009] To this end, one embodiment proposes an ultrasonic imaging device, comprising at least: - a first array of micro-machined capacitive ultrasonic transducers, CMUT; - a transmitting and receiving circuit electrically coupled to the first CMUT array, and configured to send electrical signals to the first CMUT array 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 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 ultrasonic imaging device comprises at least one second CMUT matrix to which the transmitting and receiving circuit is electrically coupled via the biasing circuit 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 by applying at least one second biasing voltage to them, causing them to operate in retracted mode.

[0011] 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.

[0012] According to a particular embodiment, the biasing 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 biasing circuit includes at least one second capacitive decoupling element through which the transmitting and receiving circuit is electrically coupled to the second CMUT matrix.

[0013] 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.

[0014] According to a particular embodiment, the biasing circuit includes at least one first resistive element through which the first biasing voltage is intended to be applied to at least a part of the CMUTs of the first CMUT matrix and / or, when the ultrasound imaging device includes said at least one second CMUT matrix, the biasing circuit includes at least one second resistive element through which the second biasing voltage is intended to be applied to at least a part of the CMUTs of the second CMUT matrix.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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 together, and / or - when the ultrasound imaging device includes said at least one second CMUT matrix, the second electrodes of the CMUTs in the same column of the second CMUT matrix are electrically coupled together.

[0019] According to a particular embodiment, the transmission and reception circuit is configured to implement at least: - amplification and analog-to-digital conversion of the electrical signals transmitted by the first CMUT matrix, and / or, where the ultrasound imaging device includes said at least one second CMUT matrix, transmitted by said at least one 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, where the ultrasound imaging device includes said at least one second CMUT matrix, by said at least one second CMUT matrix.

[0020] According to a particular embodiment, the biasing circuit is configured to select and operate a number M of rows of the first CMUT matrix less than the total number of rows of the first CMUT matrix, and / or a number N2 of columns of the first CMUT matrix less than the total number of columns of the first CMUT matrix, with Mj and N2 corresponding to integers each greater than or equal to 1.

[0021] According to a particular embodiment, when the ultrasonic imaging device includes said at least one second CMUT matrix, the biasing circuit is configured to select and operate a number M 2 of rows of the second CMUT matrix less than the total number of rows of the second CMUT matrix, and / or a number N 2 of columns of the second CMUT matrix less than the total number of columns of the second CMUT matrix, with M 2 and N 2 corresponding to integers each greater than or equal to 1.

[0022] 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.

[0023] An ultrasonic imaging method implemented with an ultrasonic imaging device comprising at least: is also proposed - a first array of micro-machined capacitive ultrasonic transducers (CMUTs); - a transmitting and receiving circuit electrically coupled to the first CMUT array, and configured to send signals to the first CMUT array 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 bias voltage causing them to operate in retracted mode. Brief description of the drawings

[0024] These features and advantages, as well as others, will be described in detail in the following description of particular embodiments, given by way of non-limiting example, in relation to the accompanying figures, among which:

[0025] - Figure 1 schematically represents part of an imaging device ultrasonic according to a particular embodiment;

[0026] - [Fig.2] schematically represents an electrical model of a part of an ultrasound imaging device according to a particular embodiment;

[0027] - Figure 3 represents a diagram of the acoustic pressure obtained during a emission of ultrasound by an ultrasound imaging device according to a particular embodiment;

[0028] - [Fig. 4] represents a diagram of the voltage delivered by a CMUT during of ultrasound reception by an ultrasound imaging device according to a particular embodiment. Description of the implementation methods

[0029] 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 have identical structural, dimensional, and material properties. In the figures, to facilitate their reading, the different elements are not represented at the same scale relative to each other.

[0030] For the sake of clarity, only the steps and elements useful for understanding the described embodiments 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, transmitting and receiving circuit, control circuit, etc.) of the ultrasound imaging device and various steps implemented (processing of acquired images, details of calculations performed, etc.) are not are not detailed. A person skilled in the art will be able to create a detailed description of these elements based on the functional description provided here.

[0031] Unless otherwise specified, when referring to two interconnected elements, this means directly connected without any intervening elements other than conductors, and when referring to two elements linked or coupled, 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 denote electrical couplings, links, or connections.

[0032] Unless otherwise specified, the expressions "approximately", "roughly", and "in the order of" mean within 10%, preferably within 5%.

[0033] 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 according to its orientation.

[0034] Unless otherwise indicated, the ranges of values ​​shown include the limits of these ranges.

[0035] An example of the embodiment of an ultrasonic imaging device 100 is described below in relation to [Fig.1].

[0036] The device 100 includes a first matrix 102 of CMUTs. The first matrix 102 is for example of type RCA (“Row-Column Array”, or “Row-Column Addressed” in English, i.e. with a network of rows and columns, or with row-column addressing 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.

[0037] Alternatively, the first matrix 102 may comprise 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.

[0038] 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 the 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.

[0039] In the described embodiment, each of the CMUTs of the first matrix 102 comprises 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.

[0040] 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 of the first matrix 102 is equal to the number of portions of material that each form the first electrodes of the CMUTs arranged on the same row of the first matrix 102, and the number of columns of pixels of the first matrix 102 is equal to the number of portions of material forming the second electrodes of the CMUTs arranged on the same column of the first matrix 102. More generally, the electrodes of the CMUTs of the matrices 102, 104 can be such that the first electrodes of the CMUTs of the same row of the first matrix 102 are coupled to each other, and / or the second electrodes of the CMUTs of the same column of the first matrix 102 are coupled to each other.

[0041] Other configurations of the CMUT electrodes of the first matrix 102 are possible. For example, the electrodes of each CMUT can be independent of the electrodes of the other CMUTs.

[0042] The first matrix 102 is configured to ensure the transduction of analog electrical input signals, or electrical excitation signals, into ultrasound, as well as the transduction of received ultrasound into analog electrical output signals, or electrical response signals.

[0043] 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 may 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.

[0044] The device 100 further comprises 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, i.e., to send excitation electrical signals causing the emission of ultrasonic waves by the CMUTs of the first matrix 102. The transmitting and receiving circuit 106 is also configured to receive and amplify analog electrical signals transmitted by the first matrix 102 upon receiving ultrasound by the first matrix 102, i.e., to receive response electrical signals generated by the CMUTs of the first matrix 102 under the effect of receiving ultrasonic waves. thoughtful.The transmitting and receiving circuit 106 can correspond to an analog electronic circuit.

[0045] In the described embodiment, the transmitting and receiving circuit 106 is also coupled to the second matrix 104. As with the first matrix 102, the transmitting and receiving 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 an ultrasonic reception by the second matrix 104.

[0046] The receiving section of the circuit 106 may include at least one analog front-end circuit, or AFE, for receiving 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 102, 104. The transmitting and receiving circuit 106 may 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, 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 the matrices 102, 104.

[0047] In the described embodiment, the transmission part of the circuit 106 can be configured in particular 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.

[0048] 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, for example, comprise 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.

[0049] The device 100 further includes a biasing circuit 108 for the CMUTs through which the transmitting and receiving circuit 106 is coupled to the first matrix 102. In the example described, the transmitting and receiving circuit 106 is also coupled to the second matrix 104 via the biasing circuit 108.

[0050] The biasing circuit 108 is configured to select and operate in transmit and / or receive mode only a portion of the CMUTs of the device 100 by applying at least one biasing voltage to them, causing them to operate in retracted mode. Thus, in the 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.

[0051] In the described embodiment, 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.

[0052] 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, in a retracted operating mode, biases only the CMUTs of one of the matrices 102, 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 include a single receiving section coupled to the matrices 102, 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.

[0053] The selection of one or the other of the matrices 102, 104 by the biasing circuit 108 can be carried out for the emission and / or reception of ultrasound by these matrices 102, 104. For example, the emission and reception circuit 106 may include common elements for the emission of signals by the matrices 102, 104 when the biasing of the CMUTs of the matrices 102, 104 is carried out for the emission of ultrasound by the matrices 102, 104, and / or the emission and reception 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.

[0054] In the example of [Fig. 1], the biasing circuit 108 comprises 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, the device 100 also comprises 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 and receive circuit 106 to the CMUTs of the matrices 102, 104..

[0055] In the described embodiment, the biasing circuit 108 also includes at least one first resistive element 114 through which the biasing voltage is intended to be applied to at least some of the CMUTs of the first matrix 102 when said at least some of the CMUTs of the first matrix 102 are intended to implement the transmission and / or reception of ultrasonic signals. More particularly, in the described example, the biasing voltage is intended to be 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.

[0056] Furthermore, in this embodiment in which the 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 intended to be applied to at least some of the CMUTs of the second matrix 104 when said at least some of the CMUTs of the second matrix 104 are intended to implement the transmission and / or reception of ultrasonic signals. More particularly, in the example described, the biasing voltage is intended to be 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.

[0057] The bias voltage applied to the CMUTs of the first matrix 102, called Vbias1 on the [Fig.1], can be equal to or different from the bias voltage applied to the CMUTs of the second matrix 104, called Vbias2 on the [Fig.1].

[0058] In the described embodiment, the biasing circuit 108 further comprises at least one control circuit, not visible in [Fig. 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 put into works an emission and / or reception of ultrasonic signals. The values ​​of the bias voltages Vbias 1 and Vbias2 are chosen in particular according to the characteristics of the CMUT of matrices 102, 104.

[0059] The transmitting and receiving circuit 106 is coupled to at least one digital control and processing circuit 118 generating the control signals sent to the transmitting and receiving circuit 106 and implementing 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.

[0060] In the described embodiment, the biasing circuit 108 is configured to apply the bias voltage Vbias 1 or Vbias 2 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 of the matrices 102 and 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 resistive element 116 is coupled to one of the first and second electrodes of each of the CMUTs of the second matrix 104.

[0061] The bias voltage values ​​Vbias 1 and Vbias 2 are such that the central portion 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.

[0062] Figure 2 schematically represents an electrical model of a part of the device 100 previously described in connection with [Fig.l].

[0063] In [Fig. 2], each of the matrices 102, 104 forms an electrical capacitance whose value is, for example, 70 pF when the CMUTs of the matrix are biased by one of the bias voltages Vbias 1 and Vbias 2, and 40 pF when the CMUTs of the matrix are not biased with one 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, whose value is, for example, 10 pF, is present between the bias circuit 108 and each of the matrices 102, 104, and a second parasitic capacitance 122, whose value is, for example, 20 pF. is present between the biasing circuit 108 and the transmitting and receiving 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 reception of the device 100 as little as possible.

[0064] The values ​​of the different capacities present in the device 100 are examples and may vary according to the characteristics of the different elements of the device 100.

[0065] Figure 3 shows a sound pressure level diagram obtained during ultrasound emission by one of the matrices 102, 104 of the 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.

[0066] Figure 4 shows a diagram of the voltage delivered by 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 biasing or with low biasing voltages, the voltages delivered in reception by the CMUTs are zero or very low, at any frequency.

[0067] 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.

[0068] The impedance of the CMUTs, and therefore the value of the peak of their resonant frequency, changes according to the value of the applied bias voltage, which allows for attenuation strongly attenuates echoes located outside the expected reception frequency band and avoids generating spurious signals in the 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 value of the CMUT's response can be obtained for 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 for a frequency of around 2 MHz.

[0069] Furthermore, in the device 100, the same transmit and receive circuit 106 is used for sending and receiving signals to the matrices of the 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.

[0070] In the particular embodiment described, the device 100 corresponds to a biometric identification device. Furthermore, in this example, this device 100 is configured to perform fingerprint capture. More specifically, when the device 100 comprises several CMUT matrices, as is the case in the example described above, each of the CMUT matrices can be used to capture a fingerprint of one of the fingers of the user of the device 100.

[0071] In such an application, the device 100 is intended to implement an acquisition of at least one fingerprint image formed of ridges and valleys present on the surface of the skin of the finger(s) located on the CMUT matrix(ies) 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.

[0072] For example, the device 100 acquires at least one surface image of the finger present on a CMUT matrix of the 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 the device 100 or in an external memory of the device 100, for example, connected to the device 100 by a communication link.

[0073] From the previously acquired surface image, the device 100 can determine or extract minutiae of the fingerprint obtained on 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 (minutiae type, position in the surface image plane, minutiae orientation, orientation relative to other minutiae, etc.).

[0074] The characteristics of the minutiae can then be compared with expected minutiae characteristics, for example, previously determined during a preliminary user enrollment step, 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.

[0075] These steps related to biometric identification are known to a person skilled in the art and are not described in detail in this description.

[0076] The device 100 can be configured to implement other functions, such as volume image capture to determine a finger microvasculature and implement liveness detection (via blood circulation detection in the finger microvasculature) and / or complementary biometric identification from the characteristics of the determined microvasculature.

[0077] 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 M; 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 M; rows and not those of the other rows of the first matrix 102, and / or to select and operate a number N; 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 N; columns and not those of the other columns of the first matrix 102, with M; and N; corresponding to integers each greater than or equal to 1.

[0078] Such operation of the device 100 can also be applied when the 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 TV2 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.

[0079] According to another embodiment, the device 100 may comprise more than two CMUT matrices coupled to the biasing circuit 108. In this case, the biasing circuit 108 may 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.

[0080] The device 100 is compatible with operating modes other than the contracted mode, such as the mode called "collapse-snapback".

[0081] Various embodiments and variations have been described. A person skilled in the art will understand that certain features of these various embodiments and variations could be combined, and other variations will become apparent to a person skilled in the art.

[0082] Finally, the practical implementation of the embodiments and variants described is within the reach of a person skilled in the art, based on the functional indications given above.

Claims

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 CMUT biasing circuit (108) 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 mode only a portion of the CMUT by applying to them at least a first biasing voltage causing them to operate in retracted mode.

2. Ultrasonic imaging device (100) according to claim 1, comprising at least a second CMUT matrix (104) to which the transmit and receive circuit (106) is electrically coupled via the biasing circuit (108) which is configured to select and operate in transmit and / or receive at least a portion of the CMUTs of the second CMUT matrix (104) by applying at least a second biasing voltage to them 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. An 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 circuit polarization (108) includes at least one second capacitive decoupling element (112) through which the transmit and receive circuit (106) is electrically coupled to the second matrix (104) of CMUT.

5. 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 biasing circuit (108) comprises at least one first resistive element (114) through which the first biasing voltage is intended to be applied to at least a portion of the CMUTs of 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 resistive element (116) through which a second biasing 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 - wherein the ultrasonic imaging device (100) comprises at least one second CMUT array (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 at least a second bias voltage to them 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 CMUT matrix (104).

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. An ultrasound 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 ultrasound imaging device (100) comprises said at least one second CMUT matrix (104), the first electrodes of the CMUTs in the same row of the second CMUT matrix (104) are electrically coupled to each other, and / or - when the ultrasound imaging device (100) comprises said at least one second CMUT matrix (104), the second electrodes of the CMUTs in the same column of the second CMUT matrix (104) are electrically coupled to each other.

11. An ultrasound 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, when the ultrasound imaging device (100) includes at least one second CMUT matrix (104), transmitted by said at least one second CMUT matrix (104), and / or - a digital-to-analog conversion of the electrical signals intended to be emitted by the first CMUT matrix (102) and / or, when the ultrasound imaging device (100) includes at least one second CMUT matrix (104), by said at least one second CMUT matrix (104).

12. 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 M of rows of the first CMUT matrix (102) less than the total number of rows of the first CMUT matrix (102), and / or a number N of columns of the first CMUT matrix (102) less than the total number of columns of the first CMUT matrix (102), with Mj&iNt 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 capture of at least one fingerprint.

15. Ultrasonic imaging method implemented with an ultrasonic imaging device (100) comprising at least: - a first array (102) of micro-machined capacitive ultrasonic transducers, CMUT; - a transmitting and receiving 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 transmitting and receiving circuit (106) is electrically coupled to the first CMUT matrix (102); including a selection and operation in transmit and / or receive of only a part of the CMUTs by applying on them at least a first bias voltage causing them to operate in retracted mode.

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