Acoustic jamming system

Abstract

The invention relates to an acoustic jamming system configured to jam an acoustic signal of interest ( ) with a frequency between 20 Hz and 20 kHz, comprising an electrical excitation device (11) configured to generate at least one electrical control signal ( ) comprising at least a first component having a frequency equal to or greater than 20 kHz, and a second component having a frequency 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 wide, low-frequency jammed signal ( ). It also relates to a jamming method.Figure for the abridged version: Fig. 1.

Description

Title of the invention: Acoustic jamming system Technical field of the invention

[0001] The present invention relates to an acoustic jamming system.

[0002] This invention falls within the field of "hardware" cybersecurity.

[0003] Due to the increase in technologies surrounding us, it is becoming more and more difficult to secure face-to-face conversations.

[0004] 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 canvassing, generating statistics, or industrial espionage.

[0005] A “surrounding conversation” here means a conversation held in the presence of the electronic device, but not necessarily by means of the electronic device; that is to say, for example, when the electronic device is placed, for example, on a table or in an individual’s pocket, but not directly used in telephone conversation.

[0006] 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

[0007] In order to overcome this problem, some "physical" solutions (as opposed to "software" solutions) have been developed.

[0008] One of the most conventional, but less comfortable, methods involves a small speaker that generates white noise in the audible spectrum. The idea is to directly cover the surrounding conversation with white noise. However, this has the drawback that the participants in the conversation also hear this white noise. 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.

[0009] Predictable here means that it is possible to identify a pattern corresponding to the generation of said white noise.

[0010] Avoiding predictability then becomes all the more energy-intensive, because the generator becomes more complex, and therefore generally more expensive, to produce. Description of the invention

[0011] The present invention aims to overcome, at least in part, the aforementioned drawbacks, which could also lead to other advantages.

[0012] 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 f2 equal to or greater than 20 kHz, and a second component having a frequency f2 equal to or greater than 20 kHz, • a non-linear ultrasonic component configured to capture the electrical control signal generated by the electrical excitation device, and 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 chaotic wide ultrasonic acoustic signal emitted by the non-linear ultrasonic component, and emit a scrambled low-frequency, wide-ranging Se signal.

[0013] A microphone generally comprises a mechanical diaphragm capable of capturing any acoustic wave within an audible frequency range, i.e., 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.

[0014] A microphone here generally refers to any acoustic sensor / receiver or any voice recorder.

[0015] Such a microphone is generally designed to have a linear response up to a certain threshold; beyond this threshold, the response is non-linear.

[0016] Due to this non-linearity, the microphone, exposed to an ultrasonic signal (also referred to more directly as "ultrasound"), in particular a multi-frequency ultrasonic signal, in fact generates a signal in the audible part, following well-known principles which are explained below, at least in part.

[0017] The acoustic jamming system according to the invention is notably based on ultrasound and the inherent non-linearity of a microphone.

[0018] 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.

[0019] Traditionally, a microphone translates an acoustic signal Sa into an electrical signal Se in a linear manner: Se = aSa, where a is a sensitivity coefficient of the microphone.

[0020] 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:

[0021] S^a^ + a^ ... + anSa”^

[0022] Where n (a positive integer) is the rank of the harmonic.

[0023] The higher the acoustic pressure, the more it will be preferable to take into account higher order terms (i.e., large n) to correctly describe the microphone response, i.e., to model it more faithfully.

[0024] Commonly, the state of the art is limited to the second order:

[0025] Se2=O|S„ + a,S?(2)

[0026] It should be noted, however, that the present invention can also operate in the general context: Sen (n>l, or even n>2).

[0027] In the remainder of this description, for the sake of simplicity of writing and ease of reading: Se=Se^., for all n > 1.

[0028] The quadratic term of equation (2) is a key element for ultrasound-based acoustic jamming.

[0029] By simultaneously generating two acoustic waves Sa । = AjCOSû)^ and “ ^COStt^Z, with 1 being time, A the amplitude of the signal Sai and °-î the angular frequency of the signal Sai, where = 2^ / ., we obtain:

[0030] Se = (AjCGSm / T A2coSM2t)+a2 (A^osm / T A2coso;2 / )~

[0031] That is:

[0032] Se = a, (4)008+.- / + 42cosw,t) + a2 [^4,^1+0082 + + + ] (3-b)

[0033] The last term of equation (3.b), namely transcribes the interest to use 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).

[0034] More generally, a broad, high-frequency signal, between the two pulsations f and , will result in a broad, low-frequency signal, between 0 and (AA)-

[0035] In an interesting implementation example, the absolute value difference between the frequency of the first component and the frequency / 2 of the 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).

[0036] According to another example of implementation, and more generally, the electrical control signal can be described by a set of n frequency f, fn, the whole being denoted E.

[0037] The set of combinations C associated with E is defined as the set of 2n frequencies obtained by the formula + y.

[0038] For example, for a set E comprising three frequencies The associated set C is {f} + f2 + fy f} + f2~ f3, f}-.f2 + fy - f^fy -a- / 2-4

[0039] 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.

[0040] Thus, the non-linear ultrasonic component which 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.

[0041] Thanks to the non-linearity of the microphone, ultrasound at different frequencies can therefore have an effect in the audible range.

[0042] 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.

[0043] As a result, the microphone then emits a scrambled low-frequency and wide Se signal, in which a signal corresponding to the acoustic signal of interest is unidentifiable.

[0044] In one embodiment, the scrambled low-frequency, wide-band signal Se is an electrical signal.

[0045] The microphone is thus configured to generate, at its output, low-frequency noise, i.e., a low-frequency electrical signal (in the aforementioned example, of at most approximately 5 kHz, but this depends on the acoustic signals sent to the microphone, which can be selected via the electrical excitation signal, i.e., the electrical control signal generated by the electrical excitation device), which limits, or even prevents, to identify a discussion, or any information shared acoustically, in the vicinity of the microphone.

[0046] Here, a low frequency electrical signal means a signal with frequencies lower than those of the ultrasonic signal, in particular 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 for example below 3 kHz, or even 1 kHz, for example about 440 Hz (for example + / - 50 Hz).

[0047] 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.

[0048] 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.

[0049] Here, a “wide” signal means a signal with a bandwidth that allows at least a voice spectrum to be covered, for example with a width of at least 1 kHz.

[0050] The wider the signal, the better the jamming.

[0051] Such a signal is sufficient to scramble information in a human acoustic signal (conversation).

[0052] 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.

[0053] 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).

[0054] A MUT here designates for example a PMUT (“Piezoelectric Micromachined Ultrasonic Transducer”: a piezoelectric MUT), or a CMUT (“Capacitive Micromachined Ultrasonic Transducer”: a capacitive MUT).

[0055] A non-linear ultrasonic component makes it possible to generate, therefore emit, and / or capture, or even measure, ultrasonic waves.

[0056] In a particular mode of use, 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.

[0057] In the context of the present invention, the non-linear ultrasonic component is used as an acoustic ultrasonic wave emitter.

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[0069] 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. Indeed, a non-linear ultrasonic component can behave chaotically on demand, allowing for a rich, noise-like spectral response at high frequencies (ultrasound). 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. Therefore, the intrinsic noise of a component placed in chaotic mode is amplified, making the component's dynamics unpredictable. 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. For example, the non-linear ultrasonic component has a resonance frequency between 20 kHz and 400 kHz. Just like a microphone as described above, a nonlinear ultrasonic component has nonlinear behavior when excited with a high voltage. The dynamic behavior of a non-linear ultrasonic component is described, for example, by the following equation, called the Duffing equation: x + Aw x + x + yx 3 - F q cos(vt (4) With x the displacement of the moving structure, * its first time derivative (velocity), and * its second time derivative (acceleration), Au; the dissipation of the system, the resonant angular frequency such that f — the resonant frequency, J q 2rr Y is the non-linearity coefficient, Fo is the excitation force normalized by the mass of the resonator, and the angular frequency such that f = -^ is the excitation frequency. 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. 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.

[0070] This configuration is also 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.

[0071] Depending on the characteristics of this modulation, for example the frequency, or of the two components, the resonator can 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.

[0072] In one embodiment, the system may include a modulated voltage source.

[0073] For example, the modulated voltage source is coupled to the non-linear ultrasonic component.

[0074] This contributes to generating ultrasound with a chaotic envelope, the signal then being however very close to that of noise, using at least one non-linear ultrasonic component, and a modulated voltage source.

[0075] In a frequency domain, the (frequency) spectrum of the chaotic signal emitted by the non-linear ultrasonic component is then wide.

[0076] Similarly, here, a “wide” signal means a signal with a bandwidth of at least 1 kHz.

[0077] One advantage, for example, is that this configuration is adaptable without prerequisites on the design, manufacture, implementation or packaging of the system.

[0078] 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.

[0079] The measurements here are taken under normal conditions, in particular of temperature and pressure, i.e. at ambient pressure, ambient temperature, and standard humidity, i.e. of about 40%.

[0080] Thus, the chaotic ultrasonic acoustic signal can have a very high sound volume, but a human ear does not generally perceive it.

[0081] For example, the non-linear 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 about 80 dB SPL.

[0082] In one embodiment, the non-linear ultrasonic component can be 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.

[0083] 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.

[0084] In an interesting embodiment, the electrical excitation device can be positioned strategically relative to the nonlinear ultrasonic component, 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 less than 50 cm, or even less than 10 cm. In an embodiment within an integrated system, the electrical excitation device and the nonlinear ultrasonic component can be adjacent.

[0085] The electrical excitation device is configured here to generate at least one electrical control signal, the electrical control signal comprising at least a first component having a frequency ff equal to or greater than 20 kHz, and a second component having a frequency f-, equal to or greater than 20 kHz.

[0086] In practice, the operation involves, for example, two frequency bands, for example at least 10 Hz wide, centered on the frequency f.

[0087] In one example of implementation, the frequency f of at least one of the two components of the electrical control signal is between 40 kHz and 80 kHz.

[0088] In one example of implementation, the frequency ff and the frequency f2 of each of the two components of the electrical control signal is between 40 kHz and 80 kHz.

[0089] In one 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.

[0090] In one embodiment, the system includes an acoustic emitter, which includes the electrical excitation device and the non-linear ultrasonic component.

[0091] The acoustic emitter is thus configured to emit the chaotic ultrasonic acoustic signal.

[0092] According to one option, the system may include a jamming detector which is configured to indicate if jamming is active.

[0093] Such a jamming detector makes it possible to validate whether jamming is active or not.

[0094] For example, it comprises a high-performance microphone or set of microphones, which is weakly nonlinear, i.e., for example, whose nonlinear coefficient linearity y (as mentioned in Eq. 4 below) is at least an order of magnitude lower than that of the scrambled microphone.

[0095] For example, the jamming detector is more linear than the microphone of the acoustic jamming system.

[0096] According to another option, the system may also include a received signal monitoring device which is configured to listen to and / or view a received signal, highlighting for example the jamming implemented.

[0097] In one embodiment, the acoustic jamming system may include an electronic device, for example a smartphone, the electronic device having a microphone.

[0098] In a preferred embodiment, the microphone of the electronic device includes the microphone of the jamming system.

[0099] In one embodiment, the electronic device may further include the non-linear ultrasonic component.

[0100] In one embodiment, the electronic device may further include the electrical excitation device.

[0101] In other words, at least part of the components of the acoustic jamming system can be included in the electronic device.

[0102] Also proposed, according to another aspect, is a method for acoustically jamming an acoustic signal of interest with a frequency between 20 Hz and 20 kHz, the method comprising at least: • A generation and emission step of at least one electrical control signal, for example by an electrical excitation device, the electrical control signal comprising at least a first component having a frequency f} equal to or greater than 20 kHz, and a second component having a frequency / 2 equal to or greater than 20 kHz; • A step of converting the electrical control signal, for example by a non-linear ultrasonic component, into a chaotic ultrasonic acoustic signal; • A chaotic ultrasonic acoustic signal emission step, for example by the non-linear ultrasonic component; • A capture step, for example by a microphone, of the chaotic ultrasonic acoustic signal together with the acoustic signal of interest; • A conversion step, for example by the microphone, of the chaotic ultrasonic acoustic signal and the acoustic signal of interest into a scrambled low frequency and wide Se signal; • A transmission stage, for example via the microphone, of the scrambled low-frequency and wide-ranging signal Se.

[0103] Such a method has characteristics and advantages similar to those of the system for corresponding characteristics.

[0104] Such a process is implemented for example by a device as described above.

[0105] For example, the scrambled signal emission step Se is configured to emit the scrambled signal Se centered on a frequency between about 200 Hz and 5 kHz, for example between about 200 Hz and 3 kHz.

[0106] For example, the chaotic ultrasonic acoustic signal emission stage is configured to generate the chaotic ultrasonic acoustic signal with a frequency spectrum between 20 kHz and 400 kHz.

[0107] 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.

[0108] For example, the electrical control signal generation and transmission stage is configured to generate at least one of the two components with a frequency f between 40 kHz and 80 kHz.

[0109] For example, the electrical control signal generation and transmission stage is configured to generate the two components with a frequency fi between 40 kHz and 80 kHz. Brief description of the figures

[0110] The invention, according to an exemplary embodiment, will be better understood and its advantages will become more apparent upon reading the following detailed description, given by way of example and not limitation, with reference to the accompanying drawings in which:

[0111] [Fig.1] schematically represents a jamming system according to an example of an embodiment of the present invention;

[0112] [Fig.2] represents a micrograph of a MUT structure according to an example of an embodiment of the invention;

[0113] [Fig.3] illustrates the chaotic behavior of a MUT by representing, by the amplitude (in millivolts) on the ordinates as a function of the frequency (in kilohertz) on the abscissas, a frequency response of a MUT in the linear regime (continuous curve) and non-linear regime (dotted curve) with the high and low amplitudes coexisting for the same excitation frequency (hysteresis);

[0114] Figure 4 illustrates the chaotic behavior of the MUT according to Figure 3 by representing, by the amplitude (in millivolts) on the ordinates as a function of time (in seconds) on the x-axis, three successive time measurements of the structure in the chaotic regime with similar initial conditions;

[0115] [Fig. 5] represents the Fourier transform of the response of the MUT of [Fig. 4]: in the chaotic regime, the system emits not only at its excitation frequency, but over a "wide" range around it; and

[0116] [Fig.6] illustrates a jamming method according to an example of implementation of the present invention. Detailed description

[0117] The present invention is based on a MEMS component and a way of electrically driving it, to "interfere" with a microphone, i.e. any acoustic receiver, in order to limit a risk, or even prevent, the recording of a signal of interest, for example a private or even confidential conversation.

[0118] For this purpose, the invention makes it possible to temporarily render a microphone unusable, or inoperable, to prevent any recording and to render ineffective any software hacking of an electronic device (i.e. telephone, computer) containing the microphone.

[0119] As illustrated in Figure 1, an acoustic jamming system 1 according to one embodiment of the invention is configured to jam an acoustic signal of interest Sv.

[0120] The acoustic signal of interest Sr is typically a private, or even confidential, conversation.

[0121] The acoustic signal of interest Sv therefore has, for example, a frequency in the range of human hearing, for example between 20 Hz and 20 kHz.

[0122] In [Fig. 1], the acoustic jamming system 1 comprises: • an electrical excitation device 11, configured to generate at least one electrical control signal Sxe, the electrical control signal Sxe comprising at least a first component having a frequency f { equal to or greater than 20 kHz, and a second component having a frequency equal to or greater than 20 kHz, • a non-linear ultrasonic component 12 configured to capture the electrical control signal Sxe generated by the electrical excitation device 11, and emit a chaotic ultrasonic acoustic signal that is a function of the electrical control signal Sxe, and • a microphone 13 configured to capture the acoustic signal of interest Sv and the chaotic ultrasonic acoustic signal Sac emitted by the non-linear ultrasonic component 12, and emit a scrambled low-frequency, wide-ranging signal Se.

[0123] 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.

[0124] In particular, the electrical excitation device 11 is configured here to generate an electrical control signal Sxe comprising at least a first component having a frequency f} equal to or greater than 20 kHz, and a second component having a frequency equal to or greater than 20 kHz.

[0125] 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 in frequency.

[0126] 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 percentage of modulation between 50% and 100%, or in frequency, with a modulation frequency typically between 1 kHz and 20 kHz.

[0127] The electrical excitation device 11 is, for example, in the form of discrete electronics or an integrated circuit.

[0128] In relative terms, the voltage allows the appearance of a hysteresis (illustrated [Fig.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.

[0129] 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).

[0130] Figure [Fig.2] represents, for example, a micrograph of a PMUT structure according to an example of an embodiment of the invention.

[0131] The non-linear ultrasonic component is actuated by the control signal of the electrical excitation device 11 and generates a chaotic ultrasonic acoustic signal S(K.

[0132] Indeed, a non-linear ultrasonic component can behave chaotically on demand, making it possible to obtain a rich spectral response, similar to noise, at high frequency (ultrasound).

[0133] A chaotic signal here refers to a non-periodic signal, exponentially sensitive to variations, making it practically unpredictable.

[0134] This chaotic ultrasonic acoustic signal is highly dependent on initial conditions and cannot be corrected by a reference measurement, or filtered.

[0135] The non-linear ultrasonic component has, for example, a resonance frequency between 20 kHz and 400 kHz.

[0136] Here, the non-linear ultrasonic component is configured to emit the chaotic ultrasonic acoustic signal with a frequency between about 20 kHz and 400 kHz, for example between about 40 kHz and 80 kHz.

[0137] The non-linear ultrasonic component 12 has non-linear behavior when excited with a high voltage.

[0138] The dynamic behavior of a non-linear ultrasonic component is described, for example, by the following equation, called the Duffing equation:

[0139] x + Aw x + x + yx 3 = F0COSw t (4)

[0140] With x the displacement of the moving structure, * its first time derivative (velocity), and * its second time derivative (acceleration), a₀ the dissipation of the system, the resonance frequency such that f = 24 the resonance frequency, J₀² Ÿ the non-linearity coefficient, Fo the excitation force normalized by the mass of the resonator, and w the angular frequency such that f = the excitation frequency.

[0141] The appearance of non-linearity introduces a curvature of the resonance leading to the appearance of hysteresis, illustrated for example in [Fig.3].

[0142] Fig. 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).

[0143] Considering for example the curve representing the non-linear behavior, in dotted lines, this includes a hysteresis.

[0144] In this hysteresis, at a determined 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).

[0145] The choice is determined by the system history.

[0146] 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 to the other of the hysteresis.

[0147] This configuration is also 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.

[0148] Depending on the characteristics of this modulation, for example the frequency, or of the two components of the signal, the resonator can 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.

[0149] In a frequency domain, the (frequency) spectrum of the chaotic Sac signal emitted by the non-linear ultrasonic component 12 is then broad (as illustrated in [Fig.5]).

[0150] Similarly, here, a “wide” signal means a signal with a bandwidth of at least 1 kHz.

[0151] Here, the chaotic ultrasonic acoustic signal Sac emits for example on a frequency band between 71 kHz and 77 kHz.

[0152] In addition, the non-linear ultrasonic component can further be configured to generate a signal having a high sound level, i.e. having a sound level of at least 60 dB SPL (Sound Pressure Level), for example between 60 dB SPL and 100 dB SPL.

[0153] Thus, the chaotic ultrasonic acoustic signal can have a very high sound volume, which a human ear generally does not perceive.

[0154] Figures 4 and 5 illustrate, in the time domain and the frequency domain, the chaotic ultrasonic acoustic signal S^.

[0155] Fig. 4 illustrates, for example, the chaotic behavior of a MUT according to Fig. 3 by representing, by amplitude (in millivolts) on the ordinate as a function of time (in seconds) on the abscissa, three successive time measurements of the structure in the chaotic regime with similar initial conditions; and Fig. 5 represents the Fourier transform of the response of the MUT of Fig. 4: in the chaotic regime, the system does not emit only at its excitation frequency, but over a "wide" range around it.

[0156] The chaotic ultrasonic acoustic signal Sac is then perceived by the microphone 13.

[0157] The microphone 13 here refers to any acoustic sensor that can be jammed by the non-linear ultrasonic component 12.

[0158] The system 1 is then configured so that, when the 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.

[0159] As a result, the microphone then emits a scrambled low-frequency Se signal, here around 5 kHz maximum, and wide, in which a signal corresponding to the acoustic signal of interest is hidden, or even unidentifiable.

[0160] The non-linear microphone and the chaotic ultrasonic acoustic signal thus make it possible to generate the scrambled signal Se which is low frequency and wide.

[0161] This operating principle does not require high sensitivity to high frequencies: low sensitivity, outside the bandwidth of the microphone, combined with an acoustic signal Sv of sufficiently large amplitude, is sufficient to ensure the generation of a signal in the useful (audible) part of the microphone.

[0162] Thus, the scrambled low-frequency Se signal is a broad signal, covering a significant part of the audible spectrum, for example between 500 Hz and 5 kHz.

[0163] The scrambled signal Se output from microphone 13 then contains the signal of interest Sv and this chaotic signal Sac, which is very difficult or even impossible to filter or predict, so that the signal of interest Sv is not accessible, or is too difficult to access, regardless of the means used to intercept the signal Se.

[0164] Since the human ear is considered to be 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.

[0165] Here, the scrambled low-frequency, wide-band signal Se is centered on a frequency of at most about 5 kHz, for example about 2.5 kHz.

[0166] The non-linear ultrasonic component 12 is preferably located in a strategic position 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.

[0167] Likewise, the electrical excitation device 11 is preferably located in a strategic position relative to the nonlinear ultrasonic component 12, for example in the vicinity of 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.

[0168] For example, the system includes an acoustic emitter 10, which includes the electrical excitation device 11 and the non-linear ultrasonic component 12.

[0169] The acoustic emitter 10 is thus configured to emit the chaotic ultrasonic acoustic signal S^..

[0170] System 1 may for example include an electronic device, for example a smartphone, which traditionally includes at least one integrated microphone.

[0171] Where appropriate, the microphone of the electronic device includes, or even constitutes, the microphone of system 1.

[0172] In an interesting embodiment example, the electronic device includes the non-linear ultrasonic component 12, or even also the electrical excitation device 11.

[0173] According to an option not shown, 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 view a received signal, highlighting, for example, the jamming being implemented.

[0174] Thanks to a device such as described above, it is possible to implement a method of acoustic jamming of an acoustic signal of interest Sv, in particular of frequency between 20 Hz and 20 kHz.

[0175] For example, the process includes steps such as the following: • A step SI of generation and emission of at least one electrical control signal Sxe by an electrical excitation device 11, the electrical control signal Sxe comprising at least a first component having a frequency ff equal to or greater than 20 kHz, and a second component having a frequency / 2 equal to or greater than 20 kHz; • A step S2 of conversion of the electrical control signal Sxe by a non-linear ultrasonic component 12, into a chaotic ultrasonic acoustic signal Sac; • A step S3 of emission of the chaotic ultrasonic acoustic signal SM. by the non-linear ultrasonic component 12; • A step S4 of capturing, by a microphone 13, the chaotic ultrasonic acoustic signal Sac together with the acoustic signal of interest Sv • A step S5 of conversion, by the microphone, of the chaotic ultrasonic acoustic signal Sac and the acoustic signal of interest Sv into a scrambled low frequency and wide signal Se; • A step S6 of emission, by the microphone, of the scrambled signal Se.

[0176] Such a method has characteristics and advantages similar to those of the system for corresponding characteristics.

[0177] For example, the S6 scrambled signal emission step Se is configured to emit the scrambled signal Se centered on a frequency between approximately 200 Hz and 5 kHz.

[0178] For example, the S3 chaotic ultrasonic acoustic signal emission step Sac is configured to generate the chaotic ultrasonic acoustic signal with a frequency spectrum between 20 kHz and 400 kHz.

[0179] For example, the chaotic ultrasonic acoustic signal emission stage S3 Sac 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.

[0180] For example, the SI stage of generating and transmitting the electrical control signal is configured to generate at least one of the two components, or both, with the frequency f between 40 kHz and 80 kHz.

[0181] Within the scope of the present invention, a jamming system and a jamming method are therefore proposed, using non-linear ultrasonic components already integrated into most electronic devices (smartphones, voice assistants, etc.) to generate a chaotic ultrasonic signal, ideally close to microphones that could record a conversation, in order to render them unusable. The acoustic jammer thus utilizes existing resources, with moderate power, as close as possible to potentially malicious devices.

Claims

Demands

1. An acoustic jamming system configured to jam an acoustic signal of interest (Sv) 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), the electrical control signal comprising at least a first component having a frequency f(e) equal to or greater than 20 kHz, and a second component having a frequency equal to or greater than 20 kHz, • a nonlinear ultrasonic component configured to capture the electrical control signal (Sxe) generated by the electrical excitation device, and to emit a broad chaotic ultrasonic acoustic signal (Sae) that is a function of the electrical control signal (Sxe), and • a microphone configured to capture the acoustic signal of interest (Sv) and the broad chaotic ultrasonic acoustic signal (Saf) emitted by the nonlinear ultrasonic component,and emit a low-frequency, broad-band, garbled signal (Se).

2. System according to claim 1, characterized in that it is configured so that the low frequency and wide scrambled signal (Se) is centered on a frequency between about 200 Hz and 5 kHz.

3. System according to any one of claims 1 or 2, characterized in that the nonlinear ultrasonic component comprises a ceramic acoustic component (PZT), or a micro-machined ultrasonic transducer (MUT), for example a piezoelectric MUT (PMUT), or a capacitive MUT (CMUT).

4. System according to any one of claims 1 to 3, characterized in that the nonlinear ultrasonic component is configured to emit the chaotic ultrasonic acoustic signal (S^) having at least a frequency spectrum between 20 kHz and 400 kHz.

5. System according to any one of claims 1 to 4, characterized in that the nonlinear ultrasonic component is configured to generate the chaotic ultrasonic acoustic signal (Sac) with a sound level of at least 60 dB SPL.

6. System according to any one of claims 1 to 5, characterized in that the frequency f of at least one of the two components of the electrical control signal is between 40 kHz and 80 kHz.

7. System according to any one of claims 1 to 6, characterized in that it further comprises a jamming detector which is configured to indicate whether jamming is active.

8. System according to any one of claims 1 to 7, characterized in that it comprises an electronic device, for example a smartphone, the electronic device comprising a microphone, and in that the microphone of the electronic device comprises the microphone of the system.

9. System according to claim 8, characterized in that the electronic device comprises the non-linear ultrasonic component.

10. System according to any one of claims 8 or 9, characterized in that the electronic apparatus comprises the electrical excitation device.

11. A method for acoustically jamming an acoustic signal of interest (Sv) with a frequency between 20 Hz and 20 kHz, the method comprising at least: • A step of generating and emitting at least one electrical control signal (Sxe), the electrical control signal comprising at least a first component having a frequency equal to or greater than 20 kHz, and a second component having a frequency equal to or greater than 20 kHz; • A step of converting the electrical control signal (Sxe) into a chaotic ultrasonic acoustic signal (Sac); • A step of emitting the chaotic ultrasonic acoustic signal (Sv).); • A stage of capturing the chaotic ultrasonic acoustic signal together with the acoustic signal of interest (Sv); • A stage of converting the chaotic ultrasonic acoustic signal and the acoustic signal of interest (Sr) into a scrambled signal (¾ low frequency and wide); • A stage of emitting the scrambled signal (Se) low frequency and wide.

12. A method according to claim 11, wherein the scrambled signal (Se) emission step is configured to emit the scrambled signal (Se) centered on a frequency between approximately 200 Hz and 5 kHz.

13. A method according to any one of claims 11 or 12, wherein the chaotic ultrasonic acoustic signal (Sac) emission step is configured to generate the chaotic ultrasonic acoustic signal (Sac) with a frequency spectrum between 20 kHz and 400 kHz.

14. A method according to any one of claims 11 to 13, wherein the chaotic ultrasonic acoustic signal (Sac) emission step is configured to generate the chaotic ultrasonic acoustic signal (Sac) with a sound level of at least 60 dB SPL.

15. A method according to any one of claims 11 to 14, 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 between 40 kHz and 80 kHz.

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