METHOD AND DEVICE FOR DETECTING THE PRESENCE OF ICING ON A COMPONENT OF AN AIRCRAFT STRUCTURE

Abstract

The present invention relates to a method and device for detecting the presence of frost on an aircraft structural element in which at least one piezoelectric transducer is disposed on the surface of the aircraft structural element. According to the invention: - a first and a second electrical signal received from at least one piezoelectric transducer are measured (E42), - the measurement of the first and second signals is transposed (E42) into the frequency domain, - a spectral density of each transposed measurement is calculated (E43), - an indicator is calculated (E43) from the spectral densities of the transposed measurements of the first and second signals, - the value of the indicator is compared (E44) to a predetermined threshold, and the presence or absence of frost on the aircraft structural element is detected (E44) based on the comparison. Figure to be published with the abstract: Fig. 4

Description

Title of the invention: METHOD AND DEVICE FOR DETECTION OF THE PRESENCE OF FROST ON AN ELEMENT OF AN AIRCRAFT STRUCTURE Technical field

[0001] The present invention relates to a method and a device for detecting the presence of frost on an element of an aircraft structure. STATE OF PRIOR ART

[0002] In the field of aeronautics, in-flight icing destroys normal air circulation, increasing drag while reducing the structure's ability to create lift.

[0003] Frost accumulates on all exposed surfaces of the aircraft.

[0004] In order to overcome this phenomenon in flight, certain aircraft are equipped with anti-icing or de-icing systems such as, for example, electrical heating systems, air heating systems, mechanical systems based on tubes which inflate on the leading edges of the lifting surfaces to break the ice, etc.

[0005] Today, the trend is towards a sharp increase in the diameter of blowers, which will proportionally increase the power demand for thermal defrosting. All high-pressure and high-temperature pipes will become increasingly difficult to route through these new types of engines.

[0006] Furthermore, the evolution of engines, in particular the hot zone, will make them less and less capable of providing large quantities of hot air for defrosting. Consequently, a thermal system will be difficult to transpose to defrost an aeronautical part such as an engine inlet.

[0007] In order to achieve an efficient defrosting function, it is important to be able to trigger the defrosting system and then stop it at the appropriate times.

[0008] It is particularly desirable to provide a solution which makes it possible to quickly detect the appearance of frost as well as the absence of frost after defrosting so as to minimize the energy consumption linked to this functionality. Presentation of the invention

[0009] A method is proposed for detecting the presence of frost on an element of a structure of an aircraft, characterized in that at least one piezoelectric transducer is arranged on the surface of the element of the structure of the aircraft, and in that the method comprises the steps of:

[0010] - measurement of a first electrical signal received from the at least one piezo-transducer electric,

[0011] - transposition of the measurement of the first signal into the frequency domain,

[0012] - calculation of a spectral density of the measurement of the first signal transposed into the frequency domain,

[0013] - measurement of a second electrical signal received from at least one piezo transducer electrical in a frequency band,

[0014] - transposition of the measurement of the second signal into the frequency domain,

[0015] - calculation of a spectral density of the measurement of the second signal transposed into the frequency domain,

[0016] - calculation of an indicator from the spectral density of the measurement of the first signal transposed into the frequency domain and the measurement of the second signal transposed into the frequency domain,

[0017] - comparison of the indicator value with a predetermined threshold,

[0018] - detection of the presence or absence of frost on the element of the aircraft structure depending on the comparison.

[0019] The invention also relates to a device for detecting the presence of frost on an element of a structure of an aircraft, characterized in that at least one piezoelectric transducer is arranged on the surface of the element of the structure of the aircraft, and in that the device comprises:

[0020] - means for measuring a first electrical signal received from the at least one piezoelectric transducer,

[0021] - means for transposing the measurement of the first signal into the frequency domain quantitative,

[0022] - calculation of a spectral density of the measurement of the first signal transposed into the frequency domain,

[0023] - means for measuring a second electrical signal received from the at least one piezoelectric transducer in a frequency band,

[0024] - means for transposing the measurement of the second signal into the frequency domain quantitative,

[0025] - means for calculating a spectral density of the measurement of the second signal transposed into the frequency domain,

[0026] - means for calculating an indicator from the spectral density of the measurement of the first signal transposed into the frequency domain and the measurement of the second signal transposed into the frequency domain,

[0027] - means for comparing the value of the indicator with a predetermined threshold,

[0028] - means for detecting the presence or absence of frost on the element of the structure of the aircraft based on the comparison.

[0029] Thus the present invention makes it possible to quickly detect the appearance of frost as well that the absence of frost after defrosting so as to minimize the energy consumption linked to this functionality. In addition, by using at least one piezoelectric transducer, the size of the detection device is reduced and allows the device to be placed on elements of the aircraft structure for which the solutions of the state of the art are not suitable.

[0030] According to a particular embodiment, a plurality of piezoelectric transducers are arranged on the surface of the element of the structure of the aircraft, at least one piezoelectric transducer is excited by an electrical signal in a frequency band and the steps of measurement, transposition, calculation, comparison and detection are carried out for the signals received from each piezoelectric transducer which is not excited by the electrical signal in the frequency band.

[0031] Thus the detection is precise and is adapted to large elements of the aircraft structure.

[0032] According to a particular embodiment, the indicator is calculated according to the following formula: m — 1 V 7 1 TA-] - ' • TA1 Ï-AM 1=2 -'-^J 7 TA-]

[0033] where Sy k ( f ) j and Sv y, are respectively the spectral densities calculated for the measurement of the first signal transposed into the frequency domain and for the measurement of the second signal transposed into the frequency domain, fstart is the low frequency of the frequency band, fstop is the high frequency of the frequency band and N is the number of piezoelectric transducers.

[0034] Thus the detection is simple and precise.

[0035] According to a particular embodiment, the indicator is calculated according to the following formula: 1 Ni^i=2 y- ( . f' ' TA-]

[0036] where with 5uv ( f ) is the spectral density of the first electrical signal received from a piezoelectric transducer not excited by the electrical signal and Suu(f ) is the spectral density of the first electrical signal exciting the piezoelectric transducer, „ i _Suy^f) with Sur ( / ) is the density spectral of the second electrical signal received from an unexcited piezoelectric transducer by the electrical signal and Sltu ( f ) is the spectral density of the second electrical signal exciting the piezoelectric transducer, / ,„,., is the low frequency of the frequency band, / „op is the high frequency of the frequency band and N is the number of piezoelectric transducers.

[0037] According to a particular embodiment, a plurality of piezoelectric transducers are arranged on the surface of the element of the aircraft structure and the steps of measurement, transposition, calculation, comparison and detection are carried out for the signals received from each piezoelectric transducer.

[0038] Thus the accuracy of detection is increased.

[0039] According to a particular embodiment, the indicator is calculated according to the following formula: iD - j_rv

[0040] where Sy y; ( f ) 1 and Sv y; ( / )( / ) are respectively the spectral densities calculated for the measurement of the first signal transposed into the frequency domain and for the measurement of the second signal transposed into the frequency domain, / ,„,., is the low frequency of the frequency band, / „op is the high frequency of the frequency band and N is the number of piezoelectric transducers.

[0041] According to a particular embodiment, the steps of measurement, transposition, calculation, comparison and detection are carried out with a periodicity of between 1 and 10 minutes.

[0042] Thus the accuracy of detection is increased.

[0043] According to a particular embodiment, the steps of measurement, transposition, calculation, comparison and detection are carried out only if the temperature measured by a temperature sensor is negative.

[0044] Thus the present invention is energy efficient.

[0045] There is also provided a computer program which can be stored on a medium and / or downloaded from a communication network, in order to be read by a processor. This computer program comprises instructions for implementing the method performed by an internet gateway, as mentioned above, when said program is executed by the processor. The invention also relates to an information storage medium storing such a computer program. Brief description of the drawings

[0046] The above-mentioned and other features of the invention will become more clearly apparent from the following description of at least one example of embodiment, said description being made in relation to the attached drawings, among which:

[0047] [Fig.l] illustrates an example of an element of an aircraft structure on which piezoelectric transducers are arranged according to the present invention;

[0048] [Fig.2a] illustrates a first embodiment of a system for detecting the presence or absence of frost according to the present invention;

[0049] [Fig.2b] illustrates a first embodiment of a system for detecting the presence or absence of frost according to the present invention;

[0050] [Fig.3] schematically illustrates an example of a hardware arrangement of a processing device according to the present invention;

[0051] [Fig.4] schematically illustrates an example of an algorithm executed by a processing device according to the present invention;

[0052] [Fig.5] illustrates an example of signal measurements obtained from a piezoelectric transducer in the case where frost is present or not on an element El of the structure of the aircraft.

[0053] DETAILED DESCRIPTION OF EMBODIMENTS

[0054] [Fig.l] illustrates an example of an element of an aircraft structure on which piezoelectric transducers are arranged according to the present invention.

[0055] The element El of the structure of the aircraft is for example an air intake lip of an engine.

[0056] On the element El of the structure of the aircraft are arranged N piezoelectric transducers Pzl, Pz2 to PzN, where N is an integer.

[0057] Piezoelectricity is a property based on the ability of certain crystals to generate electrical charges when they are subjected to mechanical deformation; this is the direct piezoelectric effect (sensor mode). On the other hand, these same crystals generate a deformation under the action of an electric field; this is the inverse piezoelectric effect (actuator mode). The operation by which the ceramic is made piezoelectric is called polarization. It consists of heating the material to the lower vicinity of the Curie temperature (for lead zirconate titanoates (PZT), this temperature is of the order of 200°C). The ceramic is then cooled under a high electric field. This has the effect of aligning the dipoles in the direction of the electric field. Finally, when the electric field is brought back to zero, the dipoles retain their position in each crystal domain.

[0058] The most widely used piezoelectric materials in industry are PZT synthetic ceramics due to their strong electromechanical couplings, their low costs and the diversity of their shapes and volumes. Thus, they are easily integrated into aeronautical parts without risk of disturbing the air flow in the engine.

[0059] According to the first embodiment, at least one of the piezoelectric transducers is in a so-called active mode, that is to say that it is excited by an electrical signal which generates deformations under the action of an electric field. The other piezoelectric transducers are in a so-called passive mode, that is to say that they generate electrical charges when they are subjected to a mechanical deformation generated by the active piezoelectric transducer.

[0060] According to the second embodiment, all the piezoelectric transducers are in a so-called passive mode, that is to say that they generate electrical charges when they are subjected to a mechanical deformation generated by the moving mechanical elements close to the aircraft structure on which the piezoelectric transducers are arranged.

[0061] [Fig.2a] illustrates a first embodiment of a system for detecting the presence or absence of frost according to the present invention.

[0062] According to the first embodiment, one of the piezoelectric transducers, for example the piezoelectric transducer Pzl is in the so-called active mode.

[0063] The other piezoelectric transducers Pz2 to PzN are in a so-called passive mode.

[0064] The piezoelectric transducer Pzl is excited by an electrical signal generated by a generator Gen which causes deformations of the piezoelectric transducer Pzl under the action of an electric field.

[0065] The generator Gen generates an electrical signal in a given frequency band. The electrical signal is a frequency sweep signal, for example in a frequency band between 100 Hz and 5 kHz. It should be noted that the choice of this frequency band is linked to the type of the element of the aircraft structure, its vibration dynamics and the sampling frequency to comply with Shannon's theorem.

[0066] The piezoelectric transducers Pz2 to PzN are in passive mode, that is to say that they generate electrical charges when they are subjected to mechanical deformation generated by the active piezoelectric transducer.

[0067] The electrical charges generated by each transducer Pz2 to PzN are processed by a processing unit Trai.

[0068] The piezoelectric transducer Pzl is in active mode and is excited with an electrical signal denoted (w) in a determined frequency band and the piezoelectric transducers Pz2 to PzN capture the vibrations generated by the piezoelectric transducer Pzl and transform them into electrical signals denoted (y? with i = 2... N). The processing device Trai receives the electrical signals, measures them and stores the measurements for processing. These measurements are denoted (y? i — 2... N). The signals are measured with a sampling frequency f and with a measurement duration defined as follows: t = ~-M

[0069] where M is the number of samples; defined with a power of 2. This choice is linked to the optimization of the Fourier transform algorithm; necessary to extract operating characteristics.

[0070] The processing device Trai comprises a module for calculating a Fourier transform Trans, for example a module for calculating a fast Fourier transform noted FFT which transposes into the frequency domain the measurements which in a particular mode have been filtered to include only the signals included in the frequency band of the signal generated by the generator Gen.

[0071] The Trai processing module includes a temperature sensor Temp which makes it possible to determine whether the temperature of the element of the aircraft structure is close to 0°C.

[0072] The Trai processing module includes a Cal calculation unit.

[0073] The calculation unit Cal determines a spectral density for each transformed signal noted Syy (f).

[0074] The processing module Trai includes a decision unit Dec which calculates, for each calculated spectral density: ID, - 1 M 1=2

[0075] where Sy.y. (f)TA ] ct Sy^y. ( f ) ( f ) are respectively the spectral densities calculated at the time intervals (TA - 1) and TA,fstart is the low frequency of the frequency band eifstop is the high frequency of the frequency band.

[0076] The decision unit Dec determines whether ice is present and whether the indicator IDi is greater than a first predetermined threshold. The predetermined threshold is for example equal to 0.95. If at the previous iteration, no ice had been detected as present, the decision module Dec commands, if the indicator IDi is greater than the first predetermined threshold, a procedure for deicing the element of the aircraft structure.

[0077] If, at the previous iteration, no ice had been detected as present, the decision module Dec commands, if the indicator ID} is lower than the first predetermined threshold, the stopping of the deicing procedure of the element El of the structure of the aircraft.

[0078] An example of a defrosting technique is disclosed in patent EP2209715.

[0079] It should be noted here that the acquisition of measurements and their processing is carried out with a periodicity of 1 min to 10 min.

[0080] In a particular mode of the first embodiment, the calculation unit Cal determines an inter-spectral density for each transformed signal noted Su,y (f ).

[0081] The calculation unit Cal contains in memory a spectral density SI(U(f) of the signal generated by the generator Gen.

[0082] The calculation unit Cal determines the ratio 1 ■' 1

[0083] Where Suy, (f) is the inter-spectral density between the piezoelectric transducer Pzl and the Pzi piezoelectric transducer.

[0084] The decision unit Dec calculates for each calculated spectral density: H 1“ AM ^=2 Lf ^nact ' TA-]

[0085] The decision unit Dec determines whether ice is present and whether the indicator ID\ is greater than a second predetermined threshold. The predetermined threshold is for example equal to 0.95. If at the previous iteration, no ice had been detected as present, the decision module Dec commands, if the indicator is greater than the second predetermined threshold, a procedure for deicing the element El of the structure of the aircraft.

[0086] If, at the previous iteration, no ice had been detected as present, the decision module Dec commands, if the indicator ID\ is lower than the second predetermined threshold, the stopping of the deicing procedure of the element El of the structure of the aircraft.

[0087] [Fig.2b] illustrates a second embodiment of a system for detecting the presence or absence of frost according to the present invention.

[0088] The piezoelectric transducers Pzl to PzN are in the passive mode, that is to say that they generate electrical charges when they are subjected to a mechanical deformation generated by the moving mechanical elements close to the aircraft structure on which piezoelectric transducers are arranged.

[0089] The electrical charges generated by each transducer Pzl to PzN are processed by a processing unit Trai.

[0090] The piezoelectric transducers Pzl to PzN capture the vibrations related to the structural element El of the aircraft and transform them into electrical signals noted ( y., with i = 1... / V). The processing device Trai receives the electrical signals, measures them and stores the measurements for processing. These measurements are noted ( y, i = 1... N). The signals are measured with a sampling frequency fe and with a measurement duration defined as follows: t = ~M

[0091] where M is the number of samples; defined with a power of 2. This choice is linked to the optimization of the Fourier transform algorithm; necessary to extract operating characteristics.

[0092] The processing device Trai comprises a module Trans for calculating a Fourier transform, for example a module for calculating a fast Fourier transform noted FFT which transposes into the frequency domain the measurements which in a particular mode have been filtered to include only the signals included for example in the frequency band between 100 Hz and 5 kHz.

[0093] The Trai processing module includes a temperature sensor Temp which makes it possible to determine whether the temperature of the element of the aircraft structure is close to 0°C.

[0094] The Trai processing module includes a Cal calculation unit.

[0095] The calculation unit Cal determines a spectral density for each transformed signal noted Svv(f).

[0096] The processing module Trai includes a decision unit Dec which calculates, for each calculated spectral density: , -^(f) 1 jyy _ ly" -'w1 'ta-] j ta'

[0097] where Sy.y. ( f ) j and Sy.y. ( f ) ( f ) are respectively the spectral densities calculated at time intervals (TA -1) and TA,fstart is the low frequency of the frequency band and / stop is the high frequency of the frequency band.

[0098] The decision unit Dec determines whether ice is present and whether the indicator ID2 is greater than a third predetermined threshold. The predetermined threshold is for example equal to 0.95. If at the previous iteration, no ice had been detected as present, the decision module Dec commands, if the indicator ID2 is greater than the third predetermined threshold, a procedure for deicing the element of the aircraft structure.

[0099] If, at the previous iteration, no ice had been detected as present, the decision module Dec commands, if the indicator ID2 is lower than the second predetermined threshold, the stopping of the deicing procedure of the element of the aircraft structure.

[0100] An example of a defrosting technique is disclosed in patent EP2209715.

[0101] It should be noted here that the acquisition of measurements and their processing are carried out with a periodicity of 1 min to 10 min.

[0102] [Fig.3] schematically illustrates an example of a hardware arrangement of a processing device according to the present invention.

[0103] The example of hardware arrangement presented comprises, connected by a communication bus 201: a processor Proc 300; a RAM (Random Access Memory” in English) 303; a ROM (“Read Only Memory” in English) 302 or a Flash memory and an input / output interface 306.

[0104] The input / output interface 306 makes it possible to obtain the signals from the piezoelectric transducers PZ2 to PZN according to the first embodiment or from the piezoelectric transducers PZ1 to PZN according to the second embodiment.

[0105] The CPU processor 301 is capable of executing instructions loaded into the RAM memory 303 from the ROM memory 302, an external memory (such as an SD card), a storage medium (such as the HDD hard disk), or a communication network. When the processing module Trai is powered up, the processor Proc 300 is capable of reading instructions from the RAM memory 303 and executing them. These instructions form a computer program causing the processor Proc 300 to implement all or part of the behaviors, algorithms and steps described herein.

[0106] Thus, all or part of the algorithms and steps described herein may be implemented in software form by executing a set of instructions by a programmable machine, such as a DSP (Digital Signal Processor) or a microcontroller or a processor. All or part of the algorithms and steps described herein may also be implemented in hardware form by a machine or a component (chip), such as an FPGA (Field-Programmable Gate Array) or an ASIC (Application-Specified Integrated Circuit). Thus, the Proc 300 controller comprises electronic circuitry adapted and configured to implement the behaviors, algorithms and steps described herein.

[0107] [Fig.4] schematically illustrates an example of an algorithm executed by a processing device according to the present invention.

[0108] The present algorithm is executed with a periodicity of between 1 and 10 minutes.

[0109] In step E40, the processing device Trai checks whether the temperature measured by the temperature sensor Temp is negative.

[0110] If so, the processing device Trai proceeds to step E41 according to the first embodiment or to step E42 according to the second embodiment. If not, the processing device Trai interrupts the present algorithm.

[0111] In step E41, the processing device Trai controls the generator Gen so that it generates a scanning signal in a given frequency band and goes to step E42.

[0112] In step E42, the processing device Trai receives the electrical signals from the piezoelectric transducers PZ2 to PZN according to the first embodiment or from the piezoelectric transducers PZ1 to PZN according to the second embodiment. The signals are measured with a sampling frequency f and with a duration of measure defined as follows: t = ~-M

[0113] The processing device Trai performs at this same stage a calculation of a Fourier transform which transposes into the frequency domain the measurements which in a particular mode have been filtered to include only the signals included in the given frequency band.

[0114] In step E43, the processing module Trai determines a spectral density or an inter-spectral density for each transformed signal as described with reference to [Fig.2a] or 2b. and an indicator 1D] or 1D' 2 or 1D2 as described with reference to [Fig.2a] or 2b.

[0115] In step E44, the processing module Trai determines whether or not frost is present by comparing the indicator 1D] to the first predetermined threshold or by comparing the indicator 1D' 2 to the second predetermined threshold or by comparing the indicator 1D2 to the third predetermined threshold.

[0116] [Fig.5] illustrates an example of signal measurements obtained from a piezoelectric transducer in the case where frost is present or not on an element El of the structure of the aircraft.

[0117] The measurements are carried out in a frequency band between 0Hz and 20KHz.

[0118] The ordinate axes show the amplitudes of the measured signals expressed in dB.

[0119] The dotted line curve represents the signals measured when no frost is present on the element of the aircraft structure and the solid line curve represents the signals measured when a thickness of 2 mm of frost is present on the element of the aircraft structure.

[0120] As these curves show, the spectral or inter-spectral densities s are different in the frequency band and it is thus possible to determine whether frost is present or not by comparing the indicator 1D] to the first predetermined threshold or by comparing the indicator 1D'2 to the second predetermined threshold or by comparing the indicator 1D2 to the third predetermined threshold.

Claims

1.

2.

3. Claims Method for detecting the presence of frost on an element of an aircraft structure, characterized in that at least one piezoelectric transducer is arranged on the surface of the element of the aircraft structure, and in that the method comprises the steps of: - measurement (E42) of a first electrical signal received from at least one piezoelectric transducer, - transposition (E42) of the measurement of the first signal in the frequency domain, - calculation (E43) of a spectral density of the measurement of the first signal transposed into the frequency domain, - measurement (E42) of a second electrical signal received from at least one piezoelectric transducer in a frequency band, - transposition (E42) of the measurement of the second signal in the frequency domain, - calculation (E43) of a spectral density of the measurement of the second signal transposed into the frequency domain, - calculation (E43) of an indicator from the spectral density of the measurement of the first signal transposed into the frequency domain and of the measurement of the second signal transposed into the frequency domain, - comparison (E44) of the indicator value with a predetermined threshold, - detection (E44) of the presence or absence of frost on the element of the aircraft structure based on the comparison. Method according to claim 1, characterized in that a plurality of piezoelectric transducers are arranged on the surface of the element of the aircraft structure, at least one piezoelectric transducer is excited by an electrical signal in a frequency band and in that the steps of measurement, transposition, calculation, comparison and detection are carried out for the signals received from each piezoelectric transducer which is not excited by the electrical signal in the frequency band. Method according to claim 2, characterized in that the indicator is calculated according to the following formula: ID, = ■'7 744

4.

5.

6. where 5y.y. ( f ) i and Sy.yt ( / )( / ) ta are the densities respectively spectral values ​​calculated for the measurement of the first signal transposed into the frequency domain and for the measurement of the second signal transposed into the frequency domain, fstart is the low frequency of the frequency band, fstop is the high frequency of the frequency band and N is the number of piezoelectric transducers. Method according to claim 2, characterized in that the indicator is calculated according to the following formula: TTV - । where r, / f) with Su? ( f) is the spectral density of the first electrical signal received from a piezoelectric transducer not excited by the electrical signal and Suu( f) is the spectral density of the first electrical signal exciting the piezoelectric transducer, „ / with Suv ( f) is the spectral density of the second electrical signal received from a piezoelectric transducer not excited by the electrical signal and Suu ( f ) is the spectral density of the second electrical signal exciting the piezoelectric transducer, / „„,., is the low frequency of the frequency band, / „op is the high frequency of the frequency band and N is the number of piezoelectric transducers. Method according to claim 1, characterized in that a plurality of piezoelectric transducers are arranged on the surface of the element of the aircraft structure and in that the steps of measurement, transposition, calculation, comparison and detection are carried out for the signals received from each piezoelectric transducer. Method according to claim 5, characterized in that the indicator is calculated according to the following formula: ID2=^^ts^ where Sy.y. ( f ) and Sy.y. ( / )( / ) TA are respectively the spectral densities calculated for the measurement of the first signal transposed in the frequency domain and for the measurement of the second signal transposed into the frequency domain, fstart is the low frequency of the frequency band, fstop is the high frequency of the frequency band and N is the number of piezoelectric transducers.

7. Method according to any one of the preceding claims, characterized in that the steps of measurement, transposition, calculation, comparison and detection are carried out with a periodicity of between 1 and 10 minutes.

8. Method according to any one of the preceding claims, characterized in that the steps of measuring, transposing, calculating, comparing and detecting are carried out only if the temperature measured by a temperature sensor is negative.

9. Device for detecting the presence of frost on an element of a structure of an aircraft, characterized in that at least one piezoelectric transducer is arranged on the surface of the element of the structure of the aircraft, and in that the device comprises: - means for measuring a first electrical signal received from the at least one piezoelectric transducer, - means for transposing the measurement of the first signal into the frequency domain, - calculating a spectral density of the measurement of the first signal transposed into the frequency domain, - means for measuring a second electrical signal received from the at least one piezoelectric transducer in a frequency band, - means for transposing the measurement of the second signal into the frequency domain, - means for calculating a spectral density of the measurement of the second signal transposed into the frequency domain,- means for calculating an indicator from the spectral density of the measurement of the first signal transposed into the frequency domain and the measurement of the second signal transposed into the frequency domain, - means for comparing the value of the indicator with a predetermined threshold, - means for detecting the presence or absence of frost on the element of the aircraft structure as a function of the comparison.,

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