Process and system for acoustic jamming

Abstract

The invention relates to an acoustic jamming method for jamming an acoustic signal of interest (Sv) with a frequency between 20 Hz and 20 kHz, comprising the generation and transmission of at least one electrical control signal (Sxe) having at least a first component with a frequency f1 equal to or greater than 20 kHz, and a second component with a frequency f2 equal to or greater than 20 kHz, the conversion of the electrical control signal (Sxe) into a chaotic ultrasonic acoustic signal (Sac), the transmission of the chaotic ultrasonic acoustic signal (Sac), the capture of the chaotic ultrasonic acoustic signal (Sac) together with the acoustic signal of interest (Sv), the conversion of the signals (Sac) and (Sv) into a wide, low-frequency jammed signal (Se), and the transmission of the wide, low-frequency jammed signal (Se). It also relates to a jamming system.

Description

Domaine technique de l'invention

[0001] The present invention relates to a method and system for acoustic jamming. This invention falls within the field of hardware-based cybersecurity.

[0002] Due to the increasing number of technologies surrounding us, it is becoming more and more difficult to secure face-to-face conversations.

[0003] Whether in a professional setting during a confidential meeting, or even in a private setting, where one believes oneself to be safe from any malicious ear, everyday electronic devices, such as a smartphone equipped with a voice assistant, have already been accused of listening to surrounding conversations, for example for the purposes of solicitation, generating statistics, or industrial espionage.

[0004] An "environmental conversation" here refers to a conversation held in the presence of the electronic device, but not necessarily by means of the electronic device; that is, for example, when the electronic device is placed, for example, on a table or in an individual's pocket, but not directly used in a telephone conversation.

[0005] The electronic device would therefore then have an activity, without the knowledge of people in the vicinity of the electronic device. State of the art

[0006] To address this problem, some "physical" solutions (as opposed to "software" solutions) have been developed.

[0007] One of the most conventional, but less comfortable, solutions involves a mini-speaker that generates white noise within the audible spectrum. The idea is to directly drown out the surrounding conversation with white noise. However, this has the drawback of allowing the other participants to hear the white noise as well. Such a device is relatively expensive and bulky (about the size of a smartphone). Furthermore, generating white noise can quickly become energy-intensive and predictable.

[0008] Predictable here means that it is possible to identify a pattern corresponding to the generation of said white noise.

[0009] Avoiding predictability then becomes all the more energy-intensive, because the generator becomes more complex, and therefore generally more expensive, to produce. Exposé de l'invention

[0010] The present invention aims to overcome at least partially the aforementioned disadvantages, and may also lead to other advantages.

[0011] To this end, according to a first aspect of the invention, an acoustic jamming system is proposed, configured to jam an acoustic signal of interest with a frequency between 20 Hz and 20 kHz, the system comprising at least: an electrical excitation device, configured to generate at least one electrical control signal, the electrical control signal comprising at least a first component having a frequency f 1 equal to or greater than 20 kHz, and a second component having a frequency f2. equal to or greater than 20 kHz, a nonlinear ultrasonic component configured to capture the electrical control signal generated by the electrical excitation device, and to emit a wide chaotic ultrasonic acoustic signal that is a function of the electrical control signal, and a microphone configured to capture the acoustic signal of interest and the wide chaotic ultrasonic acoustic signal emitted by the nonlinear ultrasonic component, and to emit a scrambled signal S and low frequency and wide.

[0012] A microphone typically contains a mechanical diaphragm that captures any acoustic wave within an audible frequency range, that is, between approximately 20 Hz and 20 kHz. However, in practice, a microphone can also capture much higher frequencies, for example, up to at least 400 kHz.

[0013] A microphone here generally refers to any acoustic sensor / receiver or any voice recorder.

[0014] Such a microphone is generally designed to have a linear response up to a certain threshold; beyond this threshold, the response is non-linear.

[0015] Because of this non-linearity, the microphone, when exposed to an ultrasonic signal (also referred to more directly as "ultrasound"), in particular a multi-frequency ultrasonic signal, actually generates a signal in the audible part, following well-known principles which are explained below, at least in part.

[0016] The acoustic jamming system according to the invention is based in particular on ultrasound and the inherent non-linearity of a microphone.

[0017] An ultrasound here refers to a sound signal with a frequency equal to or greater than 20 kHz, for example between 20 kHz and 10 MHz.

[0018] Traditionally, a microphone translates an acoustic signal Sa into an electrical signal Se in a linear fashion: S e = αS a , Or α is a microphone sensitivity coefficient.

[0019] However, when the measured sound pressure is too high, i.e., exceeds a threshold specific to the microphone, the microphone no longer reacts linearly and additional harmonics appear: S e , n = α 1 S a + α 2 S a 2 + ⋯ + α n S a n

[0020] Where n (a positive integer) is the rank of the harmonic.

[0021] The higher the sound pressure, the more it will be preferable to take into account higher order terms (i.e., large n) to correctly describe the microphone response, that is to say, to model it more faithfully.

[0022] Commonly, the state of the art is limited to the second order: S e , 2 = α 1 S a + α 2 S a 2

[0023] It should be noted, however, that the present invention can also function in a general context: Yes, and no (n>1, or even n>2).

[0024] In the remainder of this description, for the sake of simplicity and readability: S e =S e,n ., for all n ≥ 1.

[0025] The quadratic term in equation (2) is a key element for ultrasound-based acoustic jamming.

[0026] By simultaneously generating two acoustic waves S a,1 = A 1 cos ω 1 t And S a,2 =

[0027] A 2 cos ω 2 t, with t time, To the the signal amplitude S a,i And ω i the pulse of the signal S a,i , Or ω i = 2 πf i , we obtain: S e = α 1 A 1 cos ω 1 t + A 2 cos ω 2 t + α 2 A 1 cos ω 1 t + A 2 cos ω 2 t 2

[0028] Either: S e = α 1 A 1 cos ω 1 t + A 2 cos ω 2 t + α 2 1 2 A 1 2 1 + cos 2 ω 1 t + 1 2 A 2 2 1 + cos 2 ω 2 t + A 1 A 2 cos ω 1 + ω 2 t + cos ω 1 − ω 2 t

[0029] The last term of equation (3.b), namely (cos( ω 1 - ω 2) t ) , transcribes the interest of using ultrasound, i.e. high frequencies: by using two ultrasonic acoustic waves (for example 50 kHz and 45 kHz), the quadratic term of equation (2) creates additional terms, including a low frequency term (for example: 50-45 = 5 kHz).

[0030] More generally, a broad, high-frequency signal, between the two pulses f 1 and f 2, will result in a broad, low-frequency signal, between 0 and ( f 2 - f 1) .

[0031] In an interesting implementation example, a difference, in absolute value, between the frequency f 1 of the first component and the frequency fThe second component of the electrical control signal is equal to or less than 20 kHz, so as to generate a broad, low-frequency signal over the audible range (0–20 kHz). According to another implementation example, and more generally, the electrical control signal can be described by a set of n frequencies f 1 , f 2 , ...,fn , the whole being noted E .

[0032] We define the set of combinations C associated with E as the set of 2" frequencies obtained by the formula ∑ 1 n ± f i .

[0033] For example, for a set E comprising three frequencies f 1 , f 2 , f 3 , the associated set C is { f 1 + f 2 + f 3 , f 1 + f 2 - f 3 , f 1 - f 2 + f 3 , f 1 - f 2 - f 3, - f 1 + f 2 +f 3, - f 1 + f 2 - f 3 ,- f 1 - f 2 + f 3 ,- f 1 - f 2 - f 3 } .

[0034] According to one embodiment of the invention, the electrical control signal then comprises at least one pair of frequencies in the associated set C having a difference of less than 20 kHz.

[0035] Thus, the non-linear ultrasonic component that captures the electrical control signal generated by the electrical excitation device emits a wide chaotic ultrasonic acoustic signal, typically over a range of about 20 kHz.

[0036] Thanks to the non-linearity of the microphone, ultrasound at different frequencies can therefore have an effect in the audible range.

[0037] Within the framework of the present invention, the system is then configured so that, when the microphone picks up an acoustic signal of interest, for example a conversation, the microphone also picks up a chaotic ultrasonic acoustic signal emitted by the non-linear ultrasonic component.

[0038] As a result, the microphone then emits a scrambled signal. S and low frequency and wide, in which a signal corresponding to the acoustic signal of interest is unidentifiable.

[0039] In one example implementation, the signal is scrambled S and Low frequency and broad is an electrical signal.

[0040] The microphone is thus configured to generate, at output, a low frequency noise, that is to say a low frequency electrical signal (in the above example, of at most about 5 kHz, but this depends on the acoustic signals sent to the microphone, which can be chosen via the electrical excitation signal, i.e. the electrical control signal generated by the electrical excitation device), which limits, or even prevents, the identification of a discussion, or any information shared acoustically, in the vicinity of the microphone.

[0041] Here, a low frequency electrical signal refers to a signal with frequencies lower than those of the ultrasonic signal, particularly in the audible range (i.e. about 20Hz - 20kHz), for example in the range traditionally associated with speech, i.e. having a frequency below 5 kHz, or even for example below 3 kHz, or even 1 kHz, for example about 440 Hz (e.g. + / - 50 Hz).

[0042] In other words, a low-frequency electrical signal here refers to an electrical signal centered on a frequency between approximately 200 Hz and 5 kHz, or even between approximately 200 Hz and 3 kHz.

[0043] Furthermore, within the framework of the present invention, the system is then configured so that, at the output of the microphone, the signal is a wide signal.

[0044] Here, a "wide" signal refers to a signal with a bandwidth sufficient to cover at least a portion of the voice spectrum, for example, a bandwidth of at least 1 kHz. The wider the signal, the better the jamming effect.

[0045] Such a signal is sufficient to scramble information in a human acoustic signal (conversation).

[0046] According to an interesting option, the system is configured so that the low-frequency, wide-area scrambled signal is centered on a frequency between approximately 200 Hz and 5 kHz, or even between approximately 200 Hz and 3 kHz.

[0047] The invention, according to one embodiment, relies on at least one component of the type "MEMS" (for "micro-electro-mechanical system"), in particular on at least one "MUT" (for "Micromachined Ultrasonic Transducer") or, for example, a ceramic acoustic component (PZT).

[0048] A MUT here refers for example to a PMUT (“Piezoelectric Micromachined Ultrasonic Transducer”: a piezoelectric MUT), or a CMUT (“Capacitive Micromachined Ultrasonic Transducer”: a capacitive MUT).

[0049] A non-linear ultrasonic component makes it possible to generate, therefore emit, and / or capture, or even measure, ultrasonic waves.

[0050] In a particular usage mode, the non-linear ultrasonic component can therefore be used as a microphone; in other words, the non-linear ultrasonic component can form a microphone, and thus have a behavior analogous to that described above.

[0051] Within the framework of the present invention, the non-linear ultrasonic component is used as an acoustic ultrasonic wave emitter.

[0052] In one embodiment, the nonlinear ultrasonic component is configured to emit the chaotic ultrasonic acoustic signal having at least a frequency spectrum between approximately 20 kHz and 400 kHz.

[0053] Indeed, a non-linear ultrasonic component can behave chaotically on demand, allowing for a rich, noise-like spectral response at high frequencies (ultrasound).

[0054] Chaos is a physical phenomenon found everywhere in nature, in the movement of planets in the solar system, the evolution of weather patterns, and even the behavior of the human brain under certain constraints. This phenomenon can be summarized as the "butterfly effect": infinitesimal variations generate drastic changes in the dynamics of the system.

[0055] Therefore, the intrinsic noise of a component placed in chaotic mode is amplified, making the component's dynamics unpredictable.

[0056] In the use of a non-linear ultrasonic component, there is often talk of resonance, that is to say that the mechanical structure of the non-linear ultrasonic component will vibrate with a relatively exacerbated amplitude, close to a characteristic frequency: the resonance frequency.

[0057] For example, the non-linear ultrasonic component has a resonance frequency between 20 kHz and 400 kHz.

[0058] Just like a microphone as described above, a nonlinear ultrasonic component has nonlinear behavior when excited with a high voltage.

[0059] The dynamic behavior of a non-linear ultrasonic component is described, for example, by the following equation, called the Duffing equation: x ¨ + Δ ω x ˙ + ω 0 2 x + γ x 3 = F 0 cos ω t

[0060] With x the movement of the mobile structure, ẋ its first time derivative (velocity), and ẍ its second time derivative (acceleration), Δ ω the dissipation of the system, ω 0 the resonance frequency such that f 0 = ω 0 2 π the resonant frequency, γ the non-linearity coefficient, F 0 the excitation force normalized by the mass of the resonator, and ω the pulse such as f = ω 2 π the excitation frequency.

[0061] The introduction of non-linearity causes a curvature of the resonance, leading to hysteresis. Within this hysteresis, at a fixed excitation frequency, the resonator can vibrate at either a high amplitude (upper branch of the curve) or a low amplitude (lower branch of the curve). This choice is determined by the system's history.

[0062] Depending on the operating point chosen in this hysteresis and by applying a predetermined modulation in amplitude and / or frequency, it is possible to branch from one branch of the hysteresis to the other.

[0063] This configuration can also be found when considering two components at two distinct excitation frequencies, instead of performing signal modulation. This configuration is a more general case than modulation and is particularly relevant to this invention.

[0064] Depending on the characteristics of this modulation, for example the frequency, or of the two components, the resonator may then be out of equilibrium: rather than periodically switching from one branch to the other of the hysteresis, the resonator will have chaotic behavior, spending time on one branch and then the other for longer or shorter periods, never repeating the same path.

[0065] In one example implementation, the system may include a modulated voltage source.

[0066] For example, the modulated voltage source is coupled to the non-linear ultrasonic component.

[0067] This helps to generate ultrasound with a chaotic envelope, the signal then being very close to that of noise, using at least one non-linear ultrasonic component, and a modulated voltage source.

[0068] In a frequency domain, the (frequency) spectrum of the chaotic signal emitted by the non-linear ultrasonic component is then wide.

[0069] Similarly, here, a "wide" signal refers to a signal with a bandwidth of at least 1 kHz.

[0070] One advantage, for example, is that this configuration is adaptable without prerequisites on the design, manufacturing, implementation or packaging of the system.

[0071] In one embodiment, the non-linear ultrasonic component can further be configured to generate a signal having a high sound level, i.e. having a sound level, in decibels, of at least 60 dB SPL (Sound Pressure Level), for example between 60 dB SPL and 100 dB SPL.

[0072] The measurements here are taken under normal conditions, including temperature and pressure, i.e. at ambient pressure, ambient temperature, and standard humidity, i.e. of about 40%.

[0073] Thus, the chaotic ultrasonic acoustic signal can have a very high sound volume, but a human ear generally does not perceive it.

[0074] For example, the nonlinear ultrasonic component is configured to generate the chaotic ultrasonic acoustic signal with a sound level of at least 60 dB SPL, for example between 60 dB SPL and 100 dB SPL, for example approximately 80 dB SPL. In one embodiment, the nonlinear ultrasonic component can be placed strategically in an area to be restricted, for example near the microphone, for example within 5 m (meters) of the microphone, or even within 1 m, or even within 50 cm, or even within 10 cm.

[0075] According to the invention, as mentioned previously, the electrical excitation device is configured to generate at least one electrical control signal to excite the nonlinear ultrasonic component, which can consequently emit the chaotic wide ultrasonic acoustic signal.

[0076] In one interesting embodiment, the electrical excitation device can be positioned strategically relative to the nonlinear ultrasonic component, for example, close to the nonlinear ultrasonic component, less than 5 m (meters) from the nonlinear ultrasonic component, or even less than 1 m, 50 cm, or 10 cm. In an embodiment within an integrated system, the electrical excitation device and the nonlinear ultrasonic component can be adjacent.

[0077] The electrical excitation device is configured here to generate at least one electrical control signal, the electrical control signal having at least a first component having a frequency f 1 equal to or greater than 20 kHz, and a second component having a frequency f 2 equal to or greater than 20 kHz.

[0078] In practice, the operation involves, for example, two frequency bands, for example at least 10 Hz wide, centered on the frequency fi .

[0079] In one example of implementation, the frequency fi at least one of the two components of the electrical control signal is between 40 kHz and 80 kHz. In one example implementation, the frequency f 1 and the frequency f 2 of each of the two components of the electrical control signal is between 40 kHz and 80 kHz.

[0080] In one example embodiment, the electrical control signal generated by the electrical excitation device is configured to generate the chaotic ultrasonic acoustic signal generated by the nonlinear ultrasonic component with a high sound level, i.e. having a sound level of at least 60 dB SPL, for example between 60 dB SPL and 100 dB SPL.

[0081] In one embodiment, the system includes an acoustic emitter, which comprises the electrical excitation device and the nonlinear ultrasonic component. The acoustic emitter is thus configured to emit the chaotic ultrasonic acoustic signal.

[0082] Depending on one option, the system may include a jamming detector that is configured to indicate if jamming is active.

[0083] Such a jamming detector makes it possible to validate whether jamming is active or not.

[0084] For example, it includes a high-performance microphone or set of microphones that are weakly nonlinear, i.e., for example, whose nonlinearity coefficient γ (as mentioned in Eq. 4 below) is at least one order of magnitude lower than that of the scrambled microphone.

[0085] For example, the jamming detector is more linear than the microphone of the acoustic jamming system.

[0086] According to another option, the system can also include a received signal monitoring device that is configured to listen to and / or view a received signal, highlighting, for example, the jamming being implemented.

[0087] In one embodiment, the acoustic jamming system may include an electronic device, for example a smartphone, the electronic device having a microphone.

[0088] In a preferred embodiment example, the microphone of the electronic device includes the microphone of the jamming system.

[0089] In one embodiment, the electronic device may further include the non-linear ultrasonic component.

[0090] In one embodiment, the electronic device may further include the electrical excitation device.

[0091] In other words, at least some of the components of the acoustic jamming system can be included in the electronic device.

[0092] Another approach also proposes a method for acoustically jamming an acoustic signal of interest. S v to scramble the acoustic signal of interest S v the acoustic signal of interest S v having a frequency between 20 Hz and 20 kHz, the process comprising at least: A step of generating and transmitting at least one electrical control signal S xe , for example by an electrical excitation device, the electrical control signal comprising at least a first component having a frequency f 1 equal to or greater than 20 kHz, and a second component having a frequency f 2 equal to or greater than 20 kHz; A step of electrical control signal conversion S xe , for example by a non-linear ultrasonic component, in a chaotic ultrasonic acoustic signal S ac ; A chaotic ultrasonic acoustic signal emission stage S ac , for example by the non-linear ultrasonic component; A capture step, for example by a microphone, in particular by a non-linear microphone over at least a frequency range equal to or greater than 20 kHz, for example between 20 kHz and 10 MHz, of the chaotic ultrasonic acoustic signal S actogether with the acoustic signal of interest S v ; A conversion step, for example by the microphone, of the chaotic ultrasonic acoustic signal S ac and the acoustic signal of interest S v into a scrambled signal S and Low frequency and broad; A transmission stage, for example via the microphone, of the scrambled signal S and low frequency and wide.

[0093] Such a process presents characteristics and advantages similar to those of the system for corresponding characteristics.

[0094] Such a process is implemented, for example, by a device as described above.

[0095] As described previously, a low frequency signal refers to a signal with a frequency between 0 Hz and 20 kHz, or even between 20 Hz and 20 kHz.

[0096] Similarly, a wide signal refers to a signal with a bandwidth of at least 1 kHz.

[0097] For example, the step of emitting the scrambled signal S and is configured to emit the scrambled signal S and centered on a frequency between approximately 200 Hz and 5 kHz, for example between approximately 200 Hz and 3 kHz.

[0098] For example, the chaotic ultrasonic acoustic signal emission stage is configured to generate the chaotic ultrasonic acoustic signal with a frequency spectrum of at least 20 kHz, for example between 20 kHz and 400 kHz.

[0099] For example, the chaotic ultrasonic acoustic signal is broadband.

[0100] For example, the chaotic ultrasonic acoustic signal exhibits a frequency continuum across its spectrum.

[0101] For example, the chaotic ultrasonic acoustic signal emission stage is configured to generate the chaotic ultrasonic acoustic signal with a sound level of at least 60 dB SPL, for example between 60 dB SPL and 100 dB SPL.

[0102] For example, the electrical control signal generation and transmission stage is configured to generate at least one of the two components with a frequency fi between 40 kHz and 80 kHz.

[0103] For example, the stage of generating and transmitting the electrical control signal S xe is configured to generate both components with a frequency fi between 40 kHz and 80 kHz.

[0104] For example, the two components have a frequency fi which is predetermined, i.e. fixed.

[0105] For example, at least one of the two components of the electrical control signal S xe is periodic, or even the two components of the electrical control signal S xe are periodic.

[0106] For example, the acoustic signal of interest S v and the non-linear conversion of the chaotic acoustic signal S acare then superimposed, making the acoustic signal of interest S v indistinguishable. Brief description of the figures

[0107] The invention, according to an exemplary embodiment, will be better understood and its advantages will become clearer upon reading the following detailed description, given by way of example and in no way limiting, with reference to the attached drawings in which: there figure 1 schematically represents a jamming system according to an embodiment of the present invention; the figure 2 represents a micrograph of a structure, a MUT, according to an exemplary embodiment of the invention; the figure 3illustrates the chaotic behavior of a MUT by representing, by amplitude (in millivolts) on the ordinate as a function of frequency (in kilohertz) on the abscissa, a frequency response of a MUT in the linear regime (solid curve) and non-linear regime (dashed curve) with high and low amplitudes coexisting for the same excitation frequency (hysteresis); the figure 4 illustrates the chaotic behavior of the MUT according to the figure 3 by representing, by amplitude (in millivolts) on the ordinate as a function of time (in seconds) on the abscissa, three successive temporal measurements of the structure in the chaotic regime with similar initial conditions; the figure 5 represents the Fourier transform of the MUT response of the figure 4 In the chaotic regime, the system emits not only at its excitation frequency, but over a "wide" range around it; and the figure 6illustrates a jamming method according to an example of implementation of the present invention. Detailed description

[0108] The present invention is based on a MEMS component and a way of electrically controlling it, to "interfere" with a microphone, i.e. any acoustic receiver, in order to limit the risk, or even prevent, the recording of a signal of interest, for example a private or even confidential conversation.

[0109] To this end, the invention makes it possible to temporarily render a microphone unusable, or inoperable, to prevent any recording and thwart any software hacking of an electronic device (i.e., phone, computer) containing the microphone. As illustrated by the figure 1 An acoustic jamming system 1, according to an embodiment of the invention, is configured to jam an acoustic signal of interest. S v .

[0110] The acoustic signal of interest S v is typically a private, even confidential, conversation.

[0111] The acoustic signal of interest S v has, for example, a frequency in the range of human hearing, for example between 20 Hz and 20 kHz.

[0112] On the figure 1 The acoustic jamming system 1 comprises: an electrical excitation device 11, configured to generate at least one electrical control signal S xe , the electrical control signal S xe comprising at least a first component having a frequency f 1 equal to or greater than 20 kHz, and a second component having a frequency f 2 equal to or greater than 20 kHz, a non-linear ultrasonic component 12 configured to capture the electrical control signal S xe generated by the electrical excitation device 11, and emit a chaotic ultrasonic acoustic signal S acwhich is a function of the electrical control signal S xe , and a microphone 13 configured to capture the acoustic signal of interest S v and the chaotic ultrasonic acoustic signal S ac emitted by the non-linear ultrasonic component 12, and emit a scrambled signal S and low frequency and wide.

[0113] The electrical excitation device 11 is configured to generate at least one electrical control signal to excite the nonlinear ultrasonic component, which can consequently emit the chaotic ultrasonic acoustic signal.

[0114] In particular, the electrical excitation device 11 is configured here to generate an electrical control signal S xe comprising at least a first component having a frequency f 1 equal to or greater than 20 kHz, and a second component having a frequency f 2 equal to or greater than 20 kHz.

[0115] The electrical excitation device 11 generates a signal, at a frequency close to the resonance frequency of the non-linear ultrasonic component (typically between 20 and 400 kHz), modulated in amplitude or frequency.

[0116] More specifically, it can generate, for example, a high-amplitude signal, typically with a peak-to-peak voltage between 1 V and 10 V, at a frequency close to the resonance frequency of the non-linear ultrasonic component 12, typically between 20 kHz and 400 kHz, modulated either in amplitude, with a modulation percentage between 50% and 100%, or in frequency, with a modulation frequency typically between 1 kHz and 20 kHz.

[0117] The electrical excitation device 11 is presented, for example, in the form of discrete electronics or an integrated circuit.

[0118] In relative terms, tension allows for the appearance of hysteresis (illustrated figure 3, described below) equivalent to at least three bandwidths of the nonlinear ultrasonic component 12 (in linear regime), with an excitation frequency in the vicinity of this hysteresis, and with a modulation allowing entry / exit from this hysteresis.

[0119] The non-linear ultrasonic component 12 may, for example, include a micro-machined ultrasonic transducer (MUT), for example a piezoelectric MUT (PMUT), or a capacitive MUT (CMUT), or even a ceramic acoustic component (PZT).

[0120] There figure 2 represents, for example, a micrograph of a structure, a PMUT, according to an example of an embodiment of the invention.

[0121] The non-linear ultrasonic component is driven by the control signal from the electrical excitation device 11 and generates a chaotic ultrasonic acoustic signal S ac .

[0122] Indeed, a non-linear ultrasonic component can behave chaotically on demand, allowing for a rich, noise-like spectral response at high frequencies (ultrasound).

[0123] A chaotic signal here refers to a non-periodic signal, exponentially sensitive to variations, making it practically unpredictable.

[0124] This chaotic ultrasonic acoustic signal is highly dependent on initial conditions and cannot be corrected by a reference measurement, or filtered.

[0125] The non-linear ultrasonic component, for example, has a resonance frequency between 20 kHz and 400 kHz.

[0126] Here, the non-linear ultrasonic component is configured to emit the chaotic ultrasonic acoustic signal with a frequency between approximately 20 kHz and 400 kHz, for example between approximately 40 kHz and 80 kHz.

[0127] The nonlinear ultrasonic component 12 exhibits nonlinear behavior when excited with a high voltage.

[0128] The dynamic behavior of a non-linear ultrasonic component is described, for example, by the following equation, called the Duffing equation: x ¨ + Δ ω x ˙ + ω 0 2 x + γ x 3 = F 0 cos ω t

[0129] With x being the displacement of the moving structure, ẋ its first time derivative (velocity), and ẍ its second time derivative (acceleration), Δ ω the dissipation of the system, ω 0 the resonance frequency such that f 0 = ω 0 2 π the resonance frequency, y the non-linearity coefficient, F 0 the excitation force normalized by the mass of the resonator, and ω the pulse such as f = ω 2 π the excitation frequency.

[0130] The appearance of non-linearity introduces a curvature of the resonance leading to the appearance of hysteresis, illustrated for example on the figure 3 .

[0131] There figure 3 illustrates the chaotic behavior of a MUT by representing, by amplitude (in millivolts) on the ordinate as a function of frequency (in kilohertz) on the abscissa, a frequency response of a MUT in the linear regime (solid curve) and non-linear regime (dotted curve) with high and low amplitudes coexisting for the same excitation frequency (hysteresis).

[0132] Considering, for example, the curve representing the non-linear behavior, shown in dotted lines, this curve exhibits hysteresis.

[0133] In this hysteresis, at a given excitation frequency, for example 74 kHz, the resonator can either vibrate at high amplitude (upper branch of the curve: point AH) or at low amplitude (lower branch of the curve: point AB).

[0134] The choice is determined by the system's history.

[0135] Depending on the operating point chosen in this hysteresis and by applying a predetermined modulation in amplitude and / or frequency, it is possible to branch from one branch of the hysteresis to the other.

[0136] This configuration can also be found when considering two components at two distinct excitation frequencies, instead of performing signal modulation. This configuration is a more general case than modulation and is particularly relevant to this invention.

[0137] Depending on the characteristics of this modulation, for example the frequency, or of the two components of the signal, the resonator may then be out of equilibrium: rather than periodically switching from one branch to the other of the hysteresis, the resonator will have chaotic behavior by spending time on one branch and then the other for longer or shorter periods, never repeating the same path.

[0138] In a frequency domain, the (frequency) spectrum of the chaotic signal S ac emitted by the non-linear ultrasonic component 12 is then wide (as illustrated by the figure 5 ). Similarly, here, a "wide" signal refers to a signal with a bandwidth of at least 1 kHz.

[0139] Here, the chaotic ultrasonic acoustic signal S ac emits, for example, on a frequency band between 71 kHz and 77 kHz.

[0140] In addition, the non-linear ultrasonic component can also be configured to generate a signal with a high sound level, i.e. with a sound level of at least 60 dB SPL (Sound Pressure Level), for example between 60 dB SPL and 100 dB SPL.

[0141] Thus, the chaotic ultrasonic acoustic signal can have a very high sound volume, which a human ear generally does not perceive.

[0142] THE figures 4 and 5illustrate, in the time domain and the frequency domain, the chaotic ultrasonic acoustic signal S ac .

[0143] There figure 4 illustrates, for example, the chaotic behavior of a MUT according to the figure 3 by representing, by amplitude (in millivolts) on the ordinate as a function of time (in seconds) on the abscissa, three successive temporal measurements of the structure in the chaotic regime with similar initial conditions; and the figure 5 represents the Fourier transform of the MUT response of the figure 4 : in the chaotic regime, the system does not emit only at its excitation frequency, but over a "wide" range around it.

[0144] The chaotic ultrasonic acoustic signal S ac is then perceived by microphone 13. Microphone 13 here refers to any acoustic sensor that can be jammed by the non-linear ultrasonic component 12.

[0145] System 1 is then configured so that, when microphone 13 picks up an acoustic signal of interest, for example a conversation, the microphone also picks up the chaotic ultrasonic acoustic signal emitted by the non-linear ultrasonic component 12.

[0146] As a result, the microphone then emits a scrambled signal. S and low frequency, i.e. around 5 kHz maximum, and wide, in which a signal corresponding to the acoustic signal of interest is hidden, or even unidentifiable.

[0147] The non-linear microphone and the chaotic ultrasonic acoustic signal thus make it possible to generate the scrambled signal S and which is low frequency and wide.

[0148] This operating principle does not require high sensitivity to high frequencies: low sensitivity, outside the microphone's bandwidth, combined with an acoustic signal S vof sufficiently large amplitude is enough to ensure the generation of a signal in the useful (audible) part of the microphone.

[0149] Thus, the signal was scrambled S and Low frequency is a broad signal, covering a significant portion of the audible spectrum, for example between 500 Hz and 5 kHz.

[0150] The signal was scrambled S and The output of microphone 13 then contains the signal of interest S v and this chaotic signal S ac , which is very difficult or even impossible to filter or predict, so the signal of interest S v is not accessible, or is too difficult to access, regardless of the means used to intercept the signal S and .

[0151] Since the human ear is considered more linear than a microphone, the high-frequency acoustic signals generated by the non-linear ultrasonic component 12 do not induce signals audible to humans.

[0152] Here, the signal is scrambled. S and low frequency and wide is centered on a frequency of at most about 5 kHz, for example about 2.5 kHz.

[0153] The non-linear ultrasonic component 12 is preferably placed in a strategic location in an area to be privatized, for example near the microphone, for example less than 5 m (meters) from the microphone, or even less than 1 m, or even less than 50 cm, or even less than 10 cm.

[0154] Likewise, the electrical excitation device 11 is preferably located in a strategic position relative to the nonlinear ultrasonic component 12, for example close to the nonlinear ultrasonic component, for example less than 5 m (meters) from the nonlinear ultrasonic component, or even less than 1 m, or even less than 50 cm, or even less than 10 cm.

[0155] For example, the system includes an acoustic emitter 10, which comprises the electrical excitation device 11 and the nonlinear ultrasonic component 12. The acoustic emitter 10 is thus configured to emit the chaotic ultrasonic acoustic signal S ac .

[0156] System 1 may, for example, include an electronic device, such as a smartphone, which traditionally includes at least one built-in microphone.

[0157] Where applicable, the microphone of the electronic device includes, or even constitutes, the microphone of system 1.

[0158] In one interesting embodiment, the electronic device includes the nonlinear ultrasonic component 12, and possibly also the electrical excitation device 11. According to an option not shown, the system 1 may further include a jamming detector configured to indicate whether jamming is active. For example, the jamming detector may include at least one weakly nonlinear microphone. For example, the jamming detector may further include a received signal monitoring device configured to listen to and / or visualize a received signal, highlighting, for example, the jamming being implemented.

[0159] Using a device such as the one described above, it is possible to implement a method of acoustic jamming of an acoustic signal of interest. S v , in particular with a frequency between 20 Hz and 20 kHz.

[0160] For example, the process involves steps such as the following: A step S1 of generating and transmitting at least one electrical control signal S xe by an electrical excitation device 11, the electrical control signal S xe comprising at least a first component having a frequency f 1 equal to or greater than 20 kHz, and a second component having a frequency f 2 equal to or greater than 20 kHz; An S2 stage of electrical control signal conversion S xe by a non-linear ultrasonic component 12, into a chaotic ultrasonic acoustic signal S ac ; A chaotic ultrasonic acoustic signal emission stage S3 S ac by the non-linear ultrasonic component 12; A stage S4 of capturing, by a microphone 13, the chaotic ultrasonic acoustic signal S ac together with the acoustic signal of interest S v ; A step S5 of conversion, by the microphone, of the chaotic ultrasonic acoustic signal S acand the acoustic signal of interest S v into a scrambled signal S and low frequency and wide; A step S6 of transmission, by the microphone, of the scrambled signal S and .

[0161] Such a process presents characteristics and advantages similar to those of the system for corresponding characteristics.

[0162] For example, step S6 of scrambled signal transmission S and is configured to emit the scrambled signal S and centered on a frequency between approximately 200 Hz and 5 kHz.

[0163] For example, the S3 stage of chaotic ultrasonic acoustic signal emission S ac is configured to generate chaotic ultrasonic acoustic signals with a frequency spectrum between 20 kHz and 400 kHz.

[0164] For example, the S3 stage of chaotic ultrasonic acoustic signal emission S acis configured to generate the chaotic ultrasonic acoustic signal with a sound level of at least 60 dB SPL, for example between 60 dB SPL and 100 dB SPL.

[0165] For example, the S1 stage of generating and transmitting the electrical control signal is configured to generate at least one or both of the two components with the frequency fi between 40 kHz and 80 kHz.

[0166] Within the scope of the present invention, a jamming system and method are proposed, utilizing non-linear ultrasonic components already integrated into most electronic devices (smartphones, voice assistants, etc.) to generate a chaotic ultrasonic signal, ideally positioned close to microphones that could record a conversation, thereby rendering them unusable. The acoustic jammer thus utilizes existing resources, with moderate power, positioned as close as possible to potentially malicious devices.

Claims

1. Acoustic jamming method for jamming an acoustic signal of interest ( S v ) with a frequency between 20 Hz and 20 kHz, the process comprising at least: • A generation and transmission step of at least one electrical control signal ( S xe ), the electrical control signal comprising at least a first component having a frequency f 1 equal to or greater than 20 kHz, and a second component having a frequency f 2 equal to or greater than 20 kHz; • An electrical control signal conversion step ( S xe ) into a chaotic ultrasonic acoustic signal ( S ac ) ; • A chaotic ultrasonic acoustic signal emission stage ( S ac ) ; • A chaotic ultrasonic acoustic signal capture stage ( S ac ) jointly with the acoustic signal of interest ( S v ) ; • A chaotic ultrasonic acoustic signal conversion step ( S ac ) and the acoustic signal of interest ( S v ) into a scrambled signal ( S e ) low frequency and wide; • A stage of scrambled signal emission ( S e ) low frequency and wide.

2. A method according to claim 1, wherein the step of emitting the scrambled signal ( S e ) is configured to emit the scrambled signal ( S e ) centered on a frequency between approximately 200 Hz and 5 kHz.

3. A method according to any one of claims 1 or 2, wherein the step of emitting the chaotic ultrasonic acoustic signal ( S ac ) is configured to generate the chaotic ultrasonic acoustic signal ( S ac ) with a frequency spectrum between 20 kHz and 400 kHz.

4. A method according to any one of claims 1 to 3, wherein the chaotic ultrasonic acoustic signal emission step ( S ac ) is configured to generate the chaotic ultrasonic acoustic signal (S ac ) with a sound level of at least 60 dB SPL.

5. A method according to any one of claims 1 to 4, wherein the generation and transmission step of the electrical control signal is configured to generate at least one of the two components with a frequency f i between 40 kHz and 80 kHz.

6. A method according to any one of claims 1 to 5, wherein the chaotic ultrasonic acoustic signal is broadband.

7. A method according to any one of claims 1 to 6, wherein the two components have a frequency ( f 1, f 2) which is predetermined, i.e. fixed.

8. A method according to any one of claims 1 to 7, wherein at least one of the two components of the electrical control signal S xe is periodic.

9. Acoustic jamming system configured to jam an acoustic signal of interest ( S v ) with a frequency between 20 Hz and 20 kHz, the system comprising at least: • an electrical excitation device (11), configured to generate at least one electrical control signal ( S xe ), the electrical control signal comprising at least a first component having a frequency f 1 equal to or greater than 20 kHz, and a second component having a frequency f 2 equal to or greater than 20 kHz, • a non-linear ultrasonic component configured to capture the electrical control signal ( S xe ) generated by the electrical excitation device, and emit a chaotic ultrasonic acoustic signal ( S ac ) large which is a function of the electrical control signal ( S xe ), and • a microphone configured to capture the acoustic signal of interest ( S v ) and the chaotic ultrasonic acoustic signal ( S ac ) large emitted by the non-linear ultrasonic component, and emit a scrambled signal ( S e ) low frequency and wide.

10. System according to claim 9, characterized in that the non-linear ultrasonic component includes a ceramic acoustic component (PZT), or a micro-machined ultrasonic transducer (MUT), for example a piezoelectric MUT (PMUT), or a capacitive MUT (CMUT).

11. System according to any one of claims 9 or 10, characterized in that the non-linear ultrasonic component is configured to emit the chaotic ultrasonic acoustic signal ( S ac ) having at least a frequency spectrum between 20 kHz and 400 kHz.

12. System according to any one of claims 9 to 11, characterized in that It also includes a jamming detector which is configured to indicate if jamming is active.

13. System according to any one of claims 9 to 12, characterized in that It includes an electronic device, for example a smartphone, the electronic device having a microphone, and in thatThe microphone of the electronic device includes the system microphone.

14. System according to claim 13, characterized in that The electronic device includes the non-linear ultrasonic component.

15. System according to any one of claims 13 or 14, characterized in that The electronic device includes the electrical excitation device.

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