Method for detecting a blocked state of a membrane of an ultrasonic sensor of a vehicle by evaluating statistical moments of an amplitude distribution, computing device and ultrasonic sensor device

Abstract

Method for detecting a blocked state of a membrane of an ultrasonic sensor (4) of a vehicle (1), in which the membrane of the ultrasonic sensor (4) is excited to vibrate during an excitation phase (11), during a subsequent decay phase (12) a decay signal (13) is determined which describes a vibration of the membrane, and the blocked state of the membrane is detected on the basis of the decay signal (13), characterized in that an amplitude distribution of the decay signal (13) is determined, at least two statistical moments (S1, S2) of the amplitude distribution are determined and the blocked state is detected on the basis of the at least two statistical moments (S1, S2).

Description

[0001] The present invention relates to a method for detecting a blocked state of a membrane in a vehicle's ultrasonic sensor. In this method, the membrane of the ultrasonic sensor is excited to vibrate during an excitation phase. During a subsequent decay phase, a decay signal is determined, which describes the vibration of the membrane. Furthermore, the blocked state of the membrane is detected based on this decay signal. The present invention further relates to a computing device and an ultrasonic sensor device. It also relates to a computer program and a computer-readable (storage) medium.

[0002] The focus here is on ultrasonic sensors for vehicles. Such ultrasonic sensors can, for example, be components of a vehicle's driver assistance system. These sensors can detect objects in the vehicle's vicinity and, in particular, determine their distance. For this purpose, an ultrasonic signal is emitted to the respective sensor, and the reflected signal is then received. Based on the travel time between the emission of the ultrasonic signal and the reception of the reflected signal, and taking into account the propagation speed of the ultrasonic signal, the distance can then be determined. The ultrasonic sensors typically contain a diaphragm that is vibrated to emit the ultrasonic signal.During reception, the membrane is excited to vibrate by the reflected ultrasound signal. This vibration can then be detected using a transducer element.

[0003] Contamination of the ultrasonic sensor can significantly impair its functionality. Such contamination occurs, for example, when ice, snow, or slush is present on or in front of the ultrasonic sensor's diaphragm. When contamination is present on or in front of the diaphragm, this can also be described as a blocked condition. Detecting this blocked condition is possible in modern systems using special measurement methods. Known methods, for example, evaluate the impedance behavior of the diaphragm across different frequencies. This is disclosed, for instance, in DE 10 2014 201 482 A1. While this approach can determine whether contamination is present, it requires a specific measurement cycle. During this measurement cycle, however, no distance measurement can be performed and evaluated with the ultrasonic sensor.This results in a certain period of time during which the ultrasonic sensor no longer performs its actual function and the sensor system or ultrasonic sensor device is blind or cannot detect objects.

[0004] Another way to detect contamination or a blocked condition is to analyze the diaphragm's resonant frequency. The buildup of contamination on the diaphragm changes its resonant frequency. Therefore, the contamination can be determined by analyzing the resonant frequency during a resonant phase. However, the resonant frequency also changes with varying ambient temperatures. While this approach can detect contamination directly on the diaphragm, in many cases, for example, a layer of ice is present on the bumper and not directly on the ultrasonic sensor's diaphragm. In such cases, there is usually a small gap between the diaphragm and the ice, filled with air, so the resonant behavior is similar to that of a free or uncontaminated diaphragm.

[0005] Furthermore, DE 10 2010 021 960 A1 describes a method for detecting a blocked state of a motor vehicle's ultrasonic sensor. In this method, during a measurement cycle of the ultrasonic sensor, the sensor's diaphragm is excited for a predetermined excitation duration, generating a received signal that characterizes the diaphragm's vibration. The received signal, generated in at least two separate measurement cycles, is evaluated by a control unit, which then determines whether the ultrasonic sensor is blocked or not. The evaluation can also include the length of the decay time, the change in the decay time, the change in the number of incident echoes, and / or the change in the echo transit times. The absence of any changes indicates a blocked sensor.

[0006] The object of the present invention is to provide a solution for more reliably detecting a blocked state of an ultrasonic sensor. Furthermore, a corresponding ultrasonic sensor device is to be provided.

[0007] This problem is solved according to the invention by a method, a computing device, an ultrasonic sensor device, a computer program product, and a computer-readable (storage) medium with the features of the independent claims. Advantageous embodiments of the present invention are specified in the dependent claims.

[0008] A method according to the invention serves to detect a blocked state of a membrane in a vehicle's ultrasonic sensor. Here, the membrane of the ultrasonic sensor is excited to vibrate during an excitation phase. During a subsequent decay phase, a decay signal is determined, which describes the vibration of the membrane. Furthermore, the blocked state of the membrane is detected based on this decay signal. It is provided that an amplitude distribution of the decay signal is determined, at least two statistical moments of the amplitude distribution are determined, and the blocked state is detected based on these at least two statistical moments.

[0009] The method is designed to detect a blocked membrane in the ultrasonic sensor. A "blocked state" refers specifically to a contamination of the membrane. This means that a deposit, layer, or contaminant may be present on the membrane or a portion thereof. For example, ice, snow, slush, or similar substances may be present. The deposit or contaminant may also be located at a certain distance from the membrane, in which case an air gap may exist between the membrane and the contaminant. The ultrasonic sensor membrane may, for example, be cup-shaped and made of metal. The membrane, or a membrane base, can be excited to mechanical vibrations by a transducer, such as a piezoelectric element, in order to emit an ultrasonic signal.Furthermore, the ultrasonic sensor can receive the ultrasonic signal reflected in the vehicle's surroundings or from an object. The reflected ultrasonic signal, or its echo, strikes the diaphragm, causing it to vibrate mechanically. These vibrations can then be detected by the transducer element and output as a time-varying electrical voltage or as a sensor signal.

[0010] As previously explained, the membrane is excited to emit the ultrasonic signal. This excitation occurs during the excitation phase. During this phase, the transducer element can be stimulated to vibrate by a predetermined excitation signal, such as a time-varying electrical voltage. This vibration of the transducer element is then transmitted to the membrane. During the decay phase, which follows the excitation phase, the transducer element, and therefore the membrane, is no longer excited. The membrane then vibrates at the decay frequency. During this decay phase, the transducer element determines the decay signal, which describes the mechanical vibration of the membrane during this period. Overall, the ultrasonic sensor can output a sensor signal or a so-called raw signal. This sensor signal describes the vibration of the membrane.The decay signal can be a sub-area or section of the sensor signal that describes the decay of the membrane.

[0011] According to a key aspect of the present invention, the amplitude distribution of the decay signal is determined. The amplitude distribution describes, in particular, the distribution of the amplitudes, or rather the maxima and / or minima, of the decay signal. Based on the amplitude distribution, at least two statistical moments are determined, and the blocked state of the membrane is detected using these at least two statistical moments. It is specifically intended that the amplitude distribution of the decay signal be assumed to be Gaussian. Such a Gaussian function, or normal distribution, can be described by the statistical moments. The amplitude distribution can be assumed to be a random variable. The statistical moment can, for example, be the expected value or the variance.In addition, further statistical moments can be used to describe the amplitude distribution or the Gaussian function more precisely. For example, skewness, kurtosis, hyperskewness, or hypercurvature can be used. All these parameters can be referred to as statistical moments or central moments. Based on the statistical moments, the Gaussian-shaped amplitude distribution can be characterized. Using the at least two statistical moments determined by the amplitude distribution, the shape of the amplitude distribution can be determined, and from this, an influence on the diaphragm's decay behavior can be derived. This makes it possible to detect the blocked state of the membrane more reliably.Furthermore, the advantage is that no dedicated measurement mode is necessary for the procedure or the detection of the blocked state, since the evaluation of the decay time can be carried out in the usual measurement operation or during normal distance measurement with the ultrasonic sensor.

[0012] Preferably, to detect the blocked state, at least two statistical moments are compared with statistical reference moments, whereby the reference moments are determined in reference measurements for predetermined types of contamination on the membrane. Corresponding reference measurements can be performed before commissioning the ultrasonic sensor. During the reference measurements, the predetermined types of contamination can be applied to the membrane, and the resulting decay signal is then determined and used to calculate the statistical reference moments. Different types of contamination can be applied to the membrane during the reference measurements. In particular, it is intended that the predetermined types of contamination describe ice, snow, and / or mud, which are present at least partially on the membrane.To simulate the different types of contamination that the ultrasonic sensor is intended to detect during real-world operation, various contaminants can be applied to the membrane during reference measurements. For example, snow or, in particular, a layer of ice can be applied to the membrane or parts thereof. Furthermore, damp or dry mud can be applied to the membrane. The contaminants examined during the reference measurements can have varying layer thicknesses and / or positions. The reference measurements can also be performed without any contamination of the membrane. Depending on the type of contamination, the statistical moments exhibit different values.If, during operation of the ultrasonic sensor, at least two statistical moments are compared with the statistical reference moments, it is possible not only to detect the blocked state or the contamination, but also to determine the type of contamination.

[0013] In another embodiment, one of the predetermined types of contamination describes a contaminant that is at least partially separated from the membrane by an air gap. The ultrasonic sensors are typically installed on the vehicle's bumpers. Particularly in winter, it can happen that a layer of ice is present on the bumper and not directly on the membrane of the ultrasonic sensor. In this case, there is an air gap between the membrane of the ultrasonic sensor and the ice layer. The ultrasonic signal emitted by the ultrasonic sensor as a result of excitation may then be reflected by the spaced-off ice layer and return to the ultrasonic sensor. The oscillation of the membrane is then superimposed on the excitation of the membrane caused by the reflected ultrasonic signal.One of the predefined contamination types examined during the reference measurements can describe the case where the contamination is spaced away from the membrane. This allows for the evaluation of scenarios where an air gap exists between the contamination and the membrane. Thus, the proposed approach can detect not only direct contamination of the membrane but also cases where the contamination is located close to the sensor. Furthermore, the method can also be used to detect objects in the sensor's immediate vicinity, for example, at a distance of less than 20 cm from the ultrasonic sensor or the vehicle.

[0014] According to a further embodiment, a plurality of reference measurements are performed for respective types of contamination, and the statistical reference moments determined in these measurements are grouped. Investigations and tests have shown that multiple measurements for different types of contamination result in a grouping of the measurements. It has been demonstrated that different types of contamination, for example, measurements with wet mud, differ significantly from measurements with a layer of ice. The plurality of reference measurements improves the detection and classification of the contamination. For grouping, the at least two statistical moments can be plotted against each other. It is also possible to determine a plurality of statistical moments, for example, eight statistical moments.Dimension reduction can be performed for evaluation.

[0015] In a further embodiment, membrane fouling is classified by comparing at least two statistical moments with statistical reference moments. As already explained, the type of fouling can also be identified by comparing these at least two statistical moments with statistical reference moments. The proposed method for evaluating the statistical moments of the decay time thus provides not only a detailed fouling classification but also enables the coverage of specific fouling cases. In particular, it is intended that the fouling classification be performed using a support vector machine. The support vector machine, which can also be referred to as a support vector machine, can be used to classify the respective statistical moments.Reference measurements or statistical reference moments can be used as the basis for creating the Support Vector Machine. This allows for a simple and reliable classification of the contamination. For a more detailed classification of different types of contamination, other classifiers, such as ensemble classifiers, can also be used.

[0016] In another embodiment, the amplitude distribution is assumed to be Gaussian. As already explained, the diaphragm's decay signal is a sinusoidal oscillation. Due to this sinusoidal oscillation, the assumption that the amplitude distribution is Gaussian is only correct within a specific amplitude range. Applying the Gaussian distribution to the entire amplitude range, or the amplitude distribution in general, would theoretically introduce an error, but this is not relevant for the application. Based on the statistical moments, the change in the Gaussian distribution caused by contamination can be detected with minimal computational effort and within a short timeframe.

[0017] Furthermore, it is advantageous to determine at least eight statistical moments of the amplitude distribution and to detect the blocked state of the membrane based on these eight statistical moments. Evaluating at least eight statistical moments has proven particularly beneficial for detecting dirt and ice. These eight statistical moments can be the central moments of the first to eighth order. In addition to the typical parameters of the Gaussian function, which are described by the first two statistical moments, any number of further moments can be included for a more precise description of the Gaussian function. It is also possible to determine more than eight statistical moments and use them to detect the blocked state.

[0018] In a further embodiment, the decay phase is assigned a time range between 2.5 ms and 5 ms after excitation of the membrane. This time range depends on the duration of the excitation phase. As already explained, the sensor signal can be output via the transducer element. The so-called raw signal is used as the sensor signal. This raw signal can correspond to the electrical voltage output by the transducer element. This electrical voltage can also be amplified. In particular, it is intended that the electrical voltage is not filtered. The decay signal can be a sub-range or segment of the raw signal or sensor signal. This decay signal can be sampled accordingly to determine the amplitude distribution. For this purpose, it is specifically intended that the membrane vibration in this time range is sampled and digitized at a sufficiently high sampling frequency.The sampling frequency can be chosen such that it corresponds to at least twice, and in particular at least four times, the resonant frequency of the diaphragm. The resonant frequency of the diaphragm can be in the range of 50 kHz. This allows for a reliable determination of the amplitude distribution and thus the statistical moments.

[0019] Furthermore, a message can be issued to the driver or vehicle user if the ultrasonic sensor's diaphragm is detected as blocked. This message can be visual or audible. If the vehicle has multiple ultrasonic sensors, the message can indicate which sensor(s) are blocked. The message can also state that the ultrasonic sensor is currently unavailable. Additionally, the message can indicate that the ultrasonic sensor should be cleaned or that the dirt should be removed.

[0020] A computing device according to the invention for an ultrasonic sensor device is configured to carry out a method according to the invention and its advantageous embodiments. The computing device can, for example, be provided by an electronic control unit. The computing device can output an excitation signal, which excites the transducer element of the ultrasonic sensor to vibrate during the excitation phase. Furthermore, the computing device can receive the decay signal generated by the transducer element during the decay phase. The computing device can also be configured to sample or digitize the decay signal at a predetermined sampling frequency. In addition, the computing device can determine or calculate the statistical moments.Furthermore, the computer can use statistical moments to detect the blocked state of the membrane of the ultrasonic sensor and to classify the contamination.

[0021] An ultrasonic sensor device according to the invention for a vehicle detects a computing device according to the invention and at least one ultrasonic sensor. In particular, it is provided that the ultrasonic sensor device comprises a plurality of ultrasonic sensors. These ultrasonic sensors can then be arranged distributed throughout the vehicle. The ultrasonic sensor device can also have an output device by means of which an output can be provided if the blocked state of the ultrasonic sensor has been detected.

[0022] A driver assistance system according to the invention comprises an ultrasonic sensor device according to the invention. The driver assistance system, which can also be referred to as a driver assistance system, can, for example, be designed as a parking aid system.

[0023] A vehicle according to the invention comprises a driver assistance system or an ultrasonic sensor device according to the invention. The vehicle can, in particular, be a passenger car. The vehicle can also be a rental vehicle.

[0024] Another aspect of the invention relates to a computer program comprising instructions which, when executed by a computing device, cause the device to execute a method according to the invention and its advantageous embodiments. Another aspect of the invention relates to a computer-readable (storage) medium comprising instructions which, when executed by a computing device, cause the device to execute a method according to the invention and its advantageous embodiments.

[0025] With reference to the preferred embodiments and their advantages presented in the method according to the invention, the following apply accordingly to the computing device according to the invention, to the ultrasonic sensor device according to the invention, to the driver assistance system according to the invention, to the vehicle according to the invention, to the computer program product according to the invention, and to the computer-readable (storage) medium according to the invention.

[0026] Further features of the invention are evident from the claims, the figures, and the description of the figures. The features and combinations of features mentioned above in the description, as well as those subsequently mentioned in the description of the figures and / or shown in the figures alone, are not only usable in the combinations specified but also in other combinations without departing from the scope of the invention. Thus, embodiments that are not explicitly shown and explained in the figures but can be derived and generated from the explained embodiments by separate combinations of features are also to be considered as encompassed and disclosed by the invention. Embodiments and combinations of features that do not exhibit all the features of an originally formulated independent claim are also to be considered disclosed.Furthermore, embodiments and combinations of features, in particular those set out above, are to be considered disclosed which go beyond or deviate from the combinations of features set out in the cross-references of the claims.

[0027] The invention will now be explained in more detail with reference to preferred embodiments and the accompanying drawings. These show: Fig. 1 a schematic representation of a vehicle which has a plurality of ultrasonic sensors; Fig. 2. a time course of a vibration of a membrane of an ultrasonic sensor; Fig. 3 an enlarged representation of the time course according to Fig. 2, where a decay signal describes a decay phase of the membrane; Fig. 4 a plurality of measurement results of statistical moments, which were determined for different types of contamination on the membrane based on an amplitude distribution of the decay signal; Fig. 5. Another presentation of different measurement results for different types of contamination.

[0028] In the figures, identical or functionally equivalent elements are given the same reference symbols.

[0029] Fig. Figure 1 shows a vehicle 1, designed as a passenger car, in a top view. The vehicle 1 includes a driver assistance system 2, which serves to support a driver or user of the vehicle 1 in operating the vehicle 1. For example, the driver assistance system 2 can be designed as a parking aid system, by means of which the driver can be supported when parking the vehicle 1 in a parking space and / or when exiting the parking space.

[0030] The driver assistance system 2 comprises an ultrasonic sensor device 3, which includes at least one ultrasonic sensor. In the present embodiment, the ultrasonic sensor device 3 comprises twelve ultrasonic sensors 4. Six ultrasonic sensors 4 are arranged in a front area 6 of the vehicle 1 and six ultrasonic sensors 4 are arranged in a rear area 7 of the vehicle 1. The ultrasonic sensors 4 can, in particular, be mounted on a bumper of the vehicle 1. The ultrasonic sensors 4 can be arranged, at least partially, in corresponding recesses or through-openings of the bumper. It can also be provided that the ultrasonic sensors 4 are arranged concealed behind the bumper.

[0031] Using the respective ultrasonic sensors, sensor signals can be provided that describe at least one object 8 in an area 9 surrounding the vehicle 1. An object 8 in the area 9 is shown schematically below. To detect the object 8, an ultrasonic signal can be emitted from each of the ultrasonic sensors 4. Subsequently, the ultrasonic signal reflected by the object 8 can be received. Based on the time of flight between the emission of the ultrasonic signal and the reception of the ultrasonic signal reflected by the object 8, a distance between the ultrasonic sensor 4 and the object can then be determined.

[0032] Furthermore, the ultrasonic sensor device includes a computing unit 5, which is connected to the ultrasonic sensors 4 for data transmission. For the sake of clarity, the corresponding data line is not shown here. Based on the signals transmitted from the respective ultrasonic sensors 4 to the computing unit 5, the computing unit 5 can check whether the object 8 is located in the surrounding area 9 and at what position the object 8 is located. This information can then be used by the driver assistance system 2 to output a corresponding message to the driver of the vehicle 1. In addition, it can be provided that the driver assistance system maneuvers the vehicle 1 at least semi-autonomously, depending on the at least one detected object 8.

[0033] Fig. Figure 2 shows a lateral waveform of a sensor signal 10, which can be provided by one of the ultrasonic sensors 4. The abscissa represents time t and the ordinate A represents the amplitude of the sensor signal 10. Each ultrasonic sensor 4 comprises a diaphragm coupled to a transducer element for vibration transmission. During an excitation phase 11, the diaphragm or the transducer element can be excited to vibrate. A corresponding excitation signal can be output by the computer 5 for this purpose. In a decay phase 12 following the excitation phase, the diaphragm of the ultrasonic sensor 4 vibrates. This vibration of the diaphragm can be detected by the transducer element and output as an electrical voltage.The sensor signal 10 is in particular the electrical voltage or the so-called raw signal, which is output by the converter element and may be amplified.

[0034] The aim here is to determine whether the membrane of the ultrasonic sensor 4 is blocked. This means checking whether the membrane of the ultrasonic sensor 4 is contaminated, for example, by ice or mud. For this purpose, the sensor signal 10 is examined more closely during the decay phase 12. This decay phase can be assigned a time range between 2.5 ms and 5 ms after the membrane is excited.

[0035] Fig. Figure 3 shows an enlarged representation of the sensor signal 10 during the decay phase 12. The portion of the sensor signal 10 during the decay phase is referred to here as the decay signal 13. This decay signal 13 is examined in more detail to detect the blocked state of the ultrasonic sensor 4. Limiting the analysis to the decay signal 13, or rather its decay time, is advantageous for reducing computational effort. Furthermore, objects 8 or reflections are usually absent in this area, allowing the evaluation to be performed independently of other detections or the floor surface. This decay signal 13 can now be sampled or digitized accordingly using the computing unit 5. Subsequently, an amplitude distribution of the decay signal 13 can be determined. The amplitude distribution describes, in particular, the distribution of the amplitudes A of the decay signal 13.Based on the amplitude distribution, at least two statistical moments S1 and S2 are determined. Specifically, at least eight statistical moments S1 and S2 are intended to be determined. These statistical moments S1 and S2 are then used to detect the blocked state of the ultrasonic sensor 4. Furthermore, the statistical moments S1 and S2 are used to classify the contamination.

[0036] Before commissioning the ultrasonic sensor device 3, corresponding reference measurements are performed. These reference measurements are carried out for different types of contamination. In particular, multiple measurements are preferably performed for each of these different types of contamination. The different types of contamination can be, for example, wet mud, dry mud, and a layer of ice. Reference measurements can also be performed without any contamination on the membrane. During each reference measurement, the decay signal 13 can be determined, and the at least two statistical moments S1 and S2 can be ascertained. [The following appears to be a separate, unrelated section:] For this purpose, [the following appears to be a separate, unrelated section:] Fig. Four exemplary results of the reference measurements for different types of contamination. The first statistical moment S1 is plotted on the abscissa and the second statistical moment S2 on the ordinate. The representation of Fig. Figure 4 is to be understood as an example. The respective reference measurements and evaluations can be carried out for the eight statistical moments described above. Results 14 describe wet mud, results 15 describe dry mud, results 16 describe ice, and results 17 describe no contamination. It is already apparent that results 14 to 17 group together according to the different types of contamination.

[0037] The grouping of these pollutants is made clear in Fig. 5. Here, the respective results 14 to 17 are assigned to the respective characteristics F1, F2, and F3. Through dimensional reduction, the information with the eight statistical moments was transformed into a three-dimensional representation. It is clearly evident that results 14, which describe wet mud, differ significantly from results 16, which describe ice. Furthermore, results 14 and 16 differ significantly from the normal operation of the ultrasonic sensor 4 and from results 17, which describe no contamination, respectively. Although dried mud was tested as contamination, it hardly impairs the functionality of the ultrasonic sensor 4, thus explaining the overlap between measurement results 15, which describe dry mud, and results 17, which describe no contamination.This overlap of results 15 and 17 does not pose a problem, however, since the primary aim is to detect contaminants that impair the functionality of the ultrasonic sensors 4. Based on . Fig. As can be seen in section 5, reliable detection of contamination is possible using linear classification methods, such as a support vector machine. For a more detailed classification of different types and intensities of contamination, other classifiers, such as ensemble classifiers, can be used.

Claims

[1] Method for detecting a blocked state of a membrane of an ultrasonic sensor (4) of a vehicle (1), in which the membrane of the ultrasonic sensor (4) is excited to vibrate during an excitation phase (11), during a subsequent decay phase (12) a decay signal (13) is determined which describes a vibration of the membrane, and the blocked state of the membrane is detected on the basis of the decay signal (13), characterized by , that an amplitude distribution of the decay signal (13) is determined, at least two statistical moments (S1, S2) of the amplitude distribution are determined and the blocked state is recognized based on the at least two statistical moments (S1, S2). [2] Method according to claim 1 characterized by, that to detect the blocked state, at least two statistical moments (S1, S2) are compared with statistical reference moments, the reference moments being determined in reference measurements with predetermined types of membrane contamination. [3] Method according to claim 2, characterized by , that the predetermined types of contaminants describe ice, snow and / or slush, which are at least partially present on the membrane. [4] Method according to claim 2 or 3, characterized by , that one of the predetermined types of contamination describes a contamination which is at least partially separated from the membrane by an air gap. [5] Method according to any one of claims 2 to 4, characterized by , that a plurality of reference measurements are carried out for each type of pollution and the statistical reference moments determined in this process are grouped. [6] Method according to any one of claims 2 to 5, characterized by , that the contamination of the membrane is classified by comparing at least two statistical moments (S1, S2) with the statistical reference moments. [7] Method according to claim 6, characterized by that the classification of the contamination is carried out using a Support Vector Machine. [8] Method according to any one of the preceding claims, characterized by that the amplitude distribution is assumed to be Gaussian. [9] Method according to any one of the preceding claims, characterized by , that at least eight statistical moments (S1, S2) of the amplitude distribution are determined and the blocked state of the membrane is recognized based on the eight statistical moments (S1, S2). [10] Method according to any one of the preceding claims, characterized by, that the decay phase (12) is assigned to a time range between 2.5 ms and 5 ms after excitation of the membrane. [11] Computing device (5) for an ultrasonic sensor device (3), wherein the computing device (5) is configured to carry out a method according to one of the preceding claims. [12] Ultrasonic sensor device (3) for a vehicle (1) with a computing device (5) according to claim 11 and with at least one ultrasonic sensor (4). [13] Computer program comprising instructions which, when the program is executed by a computing device (5), cause it to execute a method according to any one of claims 1 to 10. [14] Computer-readable (storage) medium comprising instructions which, when executed by a computing device (5), cause it to execute a method according to any one of claims 1 to 10.

Images