Method for operating an ultrasonic sensor

Abstract

Signal shaping of chirp signals of an automotive ultrasonic measuring system. The invention relates to a method for operating an ultrasonic sensor, comprising emitting an ultrasonic pulse train as a series of ultrasonic pulses having a pulse length T1 and a pulse interval T2. The sum of the pulse length T1 and the pulse interval T2 represents a pulse period length T = T1 + T2. The ultrasonic pulse train starts at a first time t1 and ends at a second time t2. A momentary pulse frequency f m,NL = 1 / T corresponds to the inverse of the momentary pulse length T. The momentary pulse frequency f m,NL passes through a first frequency range Af u during a first time period At u , passes through an intermediate frequency range Af c during a subsequent intermediate time period At c , and passes through a second frequency range Af l during a subsequent second time period At2. The time length of the intermediate time period At c is equal to or greater than the sum of the first time period At u and the second time period At l .

Description

TECHNICAL FIELD

[0001] The present invention relates to a method for operating an ultrasonic sensor with a chirp signal. BACKGROUND

[0002] DE 10 2017 104 145 A1 discloses a known method for operating an ultrasonic sensor arrangement of a motor vehicle by a changed excitation of a membrane and a related ultrasonic sensor arrangement, a driver assistance system and a motor vehicle. The technical teaching of DE 10 2017 104 145 A1 relates to a method for operating an ultrasonic sensor arrangement of a motor vehicle, wherein a membrane in a first ultrasonic sensor is excited to emit a first ultrasonic signal and a membrane in a second ultrasonic sensor is excited to emit a second ultrasonic signal, wherein the membrane in the first ultrasonic sensor and the membrane in the second ultrasonic sensor have the same resonance frequency f and wherein the membrane in the first ultrasonic sensor is excited with a first frequency f1 which is lower than the resonance frequency f by a predetermined frequency difference Af and the membrane in the second ultrasonic sensor is excited with a second frequency f2 which is higher than the resonance frequency f by the predetermined frequency difference Af. Furthermore, DE 10 2017 104 145 A1 discloses the idea that the frequency difference Af is changed depending on a control signal which is transmitted to the first ultrasonic sensor and the second ultrasonic sensor. DE 10 2017 104 145 A1 likewise discloses the idea that a first coding of the first ultrasonic signal from the first ultrasonic sensor and / or a second coding of the second ultrasonic signal from the second ultrasonic sensor is provided by frequency shift keying, by phase shift keying as a chirp and / or by a digital modulation method.

[0003] DE 10 2017 123 049 B3, DE 10 2017 123 050 B3, DE 10 2017 123 052 B3 and DE 10 2017 123 051 B3 also disclose the use of chirp signals. In these documents, the term “chirp-up” is explained as a strictly monotonic frequency change of the ultrasonic transmission signal from a lower ultrasonic transmission frequency to a higher ultrasonic transmission frequency and “chirp-down” is understood as a strictly monotonic frequency change of the ultrasonic transmission signal from a higher ultrasonic transmission frequency to a lower ultrasonic transmission frequency.

[0004] All these documents have in common that they do not examine or disclose an optimal coding of the chirp signal.

[0005] As explained in documents DE 10 2017 123 049 B3, DE 10 2017 123 050 B3, DE 10 2017 123 052 B3 and DE 10 2017 123 051 B3, positive chirp and negative chirp, while exhibiting an orthogonal signal shape, are only applicable for very large bandwidth-time products. In order to improve the orthogonality, the chirp signals can also be operated at different center frequencies, however, this significantly increases the bandwidth requirement.

[0006] According to the technical teaching of DE 10 2017 104 145 A1, positive chirp and negative chirp, while exhibiting an orthogonal signal shape, are only applicable for very large bandwidth-time products. In particular, due to the narrow bandwidth of the ultrasound transducers, the bandwidth can only be chosen to be very small (typically 7 KHz, e.g. 58 Hz + / - 3.5 kHz). Therefore, the inventors of DE 10 2017 104 145 A1 propose in their patent application to pull apart the center frequencies of the chirp signals of two ultrasound emitters and thereby reduce the spectral overlap.

[0007] It is the object of the disclosure of the technical teaching described herein to minimize the spectral overlap of the prior art ultrasound technology without pulling apart the center frequencies too far apart in order to minimize the necessary bandwidth.

[0008] Practical tests have shown that the method of DE 10 2017 104 145 A1 is ineffective. Therefore, in order to work, the spectra of the two ultrasound signals (i.e. the two chirp signals) of the two ultrasound emitters must in fact not overlap, which leads to signal distortion and amplitude reduction, because the necessary separation of the center frequencies requires the two ultrasound transducers to operate at a frequency that is much lower than the resonance frequency of the ultrasound transducers, thereby resulting in a large damping. This is shown in Figure 5 .

[0009] JP 2011-038 948 A discloses the use of a non-linear chirp. According to the technical teaching of JP 2011-038 948 A, a method for generating an ultrasound pulse train comprises transmitting the ultrasound pulse train as a series of ultrasound pulses, wherein the instantaneous pulse frequency of the ultrasound pulse train is different at the beginning and at the end of the pulse train, and wherein the temporal change of the instantaneous pulse frequency is different at two different times of the ultrasound pulse train.

[0010] DE 2017 122 477 A1 discloses a continuous linear change of the instantaneous pulse frequency of an ultrasound pulse train during transmission. In the technical teaching of DE 2017 122 477 A1, this change is used to be able to infer from the reception frequency of the echoes whether at least one of a plurality of echoes has been reflected during the transmission phase or whether this is an overtake

[0011] With regard to the term "Ultraschall-Burst", reference is made here by way of example to the explanation in paragraph

[0013] of DE 102018 106251 A1.

[0012] Here, an Ultraschall-Burst is understood to be a continuous fluctuation of the air pressure caused by a sound wave. Here, the Ultraschall-Burst comprises a plurality of ultrasound pulses. An ultrasound pulse is characterized by an air pressure rise caused by a sound wave and a subsequent air pressure drop caused by a sound wave.

[0013] A series of such ultrasound pulses with an ultrasound pulse sequence frequency is referred to hereinafter as an Ultraschall-Burst. Here, the time interval between the air pressure rise caused by a sound wave and the air pressure drop caused by a sound wave is understood to be the pulse length T1. Here, the time interval between the air pressure drop caused by a sound wave and the air pressure rise caused by a sound wave is understood to be the pulse interval T2. The temporal pulse period length T = T1 + T2 is then the temporal sum of the pulse length T1 and the pulse interval T2. Here, the instantaneous pulse frequency f m,NL = 1 / T corresponds to the inverse of the pulse period length T. SUMMARY

[0014] It is therefore an object of the present application to provide a solution which does not have the above-mentioned disadvantages of the prior art and which has further advantages. The advantages, however, are not restricted to these.

[0015] This object is achieved by the subject matter of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 A schematic simplified frequency spectrum of an ultrasound transmission signal (i.e. a linear chirp signal) of an ultrasound transmitter with a constant rate of change of frequency and a frequency spectrum of an ultrasound transmission signal (i.e. a non-linear chirp signal) of an ultrasound transmitter with a non-constant rate of change of frequency .

[0017] Figure 2 A frequency spectrum of a linear positive chirp pulse (rising non-linear chirp) and a frequency spectrum of a linear negative chirp pulse (falling non-linear chirp) are shown.

[0018] Figure 3 A frequency spectrum of a non-linear positive chirp pulse (rising non-linear chirp) and a frequency spectrum of a non-linear negative chirp pulse (falling non-linear chirp) are shown.

[0019] Figure 4 Exemplary frequency curves over time of a linear chirp signal and a non-linear chirp signal are shown.

[0020] Figure 5 The spectrum of two ultrasonic signals (i.e., two chirped signals) from two ultrasonic transmitters that must actually not overlap is shown.

[0021] Figure 6 The curves showing the frequency-time correspondence of nonlinear positive chirp signals and nonlinear negative chirp signals are presented.

[0022] exist Figure 7 It shows the corresponding Figure 6 The instantaneous pulse frequency f of an exemplary nonlinear negatively chirped ultrasonic pulse train m,NL The time curve. Detailed Implementation

[0023] First, as disclosed in DE 10 2017 123 049 B3, DE 10 2017 123 050 B3, DE 10 2017123052 B3 and DE 10 2017 123 051 B3, the simplest and most obvious chirp shape is linear chirp, in which, per unit time frequency change (i.e., the rate of frequency change) () is constant.

[0024] Now, during the establishment of this invention, it has been recognized that the rate of change is at a non-constant frequency. t replaces the constant frequency change rate It is beneficial to carry out the work.

[0025] The basic idea is to shape the spectra of two ultrasound signals to make them narrower. Therefore, the center frequency interval can be chosen to be smaller. In the technical inspiration of DE 10 2017 104 145 A1, amplitude weighting is proposed for spectral shaping and sidelobe reduction. This will be achieved through... Figures 1 to 7 Please provide an explanation.

[0026] Figure 1 It shows a constant frequency change rate A schematic simplified spectrum of the ultrasonic transmission signal (i.e., the linear chirped signal) from an ultrasonic transmitter, and a frequency variation rate with non-constant characteristics. The spectrum of the ultrasonic transmission signal (i.e., the nonlinear chirped signal) from the ultrasonic transmitter is shown. It is easy to see that the spectrum of the nonlinear chirped signal is narrower than that of the linear chirped signal. The preferred nonlinear chirped signal will be further explained below.

[0027] Now, let's assume the use of a first ultrasonic sensor emitting a linear chirp signal with a first center frequency f1 and a second ultrasonic sensor emitting a linear chirp signal with a second center frequency f2. The first center frequency f1 and the second center frequency f2 shall have a center frequency separation Df 12 = f1 - f2.

[0028] If this center frequency separation Df 12 is numerically smaller than the bandwidth of the linear chirp signal, they will overlap.

[0029] This case is illustrated in Figure 2 .

[0030] If non-linear chirp signals are used at different starting frequencies, the narrower spectrum of the two non-linear chirp signals makes the overlap of the two chirp signals smaller.

[0031] This case is illustrated in Figure 3 . Figure 6 The respective curves of the frequency of a non-linear positive chirp signal and a non-linear negative chirp signal over time are shown.

[0032] Figure 4 Exemplary frequency curves of a linear chirp signal and a non-linear chirp signal over time are shown. They correspond to Figure 2 the signal curves shown.

[0033] This approach can be summarized as follows: By using a non-linear chirp, it is possible to shape the spectrum of the chirp signal to have a narrower frequency band, thereby significantly reducing the bandwidth requirement without reducing the signal-to-noise ratio.

[0034] Thus, the approach describes a method for operating an ultrasonic sensor, the method comprising the step of emitting an ultrasonic pulse train as a series of ultrasonic pulses. The ultrasonic pulses have a pulse length T1 and a pulse interval T2. Here, the sum of the pulse length T1 and the pulse interval T2 is the pulse period length T = T1 + T2. Here, the ultrasonic pulse train starts at a first time t1 and ends at a second time t2. Here, the instantaneous pulse frequency f m,NL = 1 / T corresponds to the inverse of the pulse period length T. Here, the pulse period length T at the first time t1 and thus the instantaneous pulse frequency f m = 1 / T is different from the pulse period length T at the second time t2 and thus the instantaneous pulse frequency f m = 1 / T.

[0035] The instantaneous pulse frequency f m,NL (t) of a non-linear chirp pulse over time (t) can here be expressed by the following equation:

[0036]

[0037] The above equation only refers to the time t at which the ultrasound pulse starts between the first time t1 and the second time t2, or only to the time t at which the ultrasound pulse ends between the first time t1 and the second time t2. In this respect, the above equation does not describe a continuous curve, but rather discrete values of the time t between the first time t1 and the second time t2. In fact, the instantaneous pulse frequency f m,NL (t) deviates from this curve by less than 10% in value, preferably less than 5%, preferably less than 2%, preferably less than 1%, preferably less than 0.5%. Thus, the instantaneous pulse frequency f m,NL (t) only substantially follows the above equation. Thus, the instantaneous pulse frequency of the non-linear chirped pulse varies not constantly. Here, B L is the bandwidth factor of the linear part, B C is the bandwidth factor of the non-linear part.

[0038] Here, the instantaneous pulse frequency at a third time t3 between the first time t1 and the second time t2 varies differently than the instantaneous pulse frequency at a fourth time t4 between the first time t1 and the second time t2.

[0039] In contrast, the instantaneous pulse frequency f m,L (t) of the linear chirped pulse is represented by the following equation:

[0040]

[0041] Thus, the instantaneous pulse frequency of the linear chirped pulse varies constantly.

[0042] Figure 1 The spectrum of a linear chirp (linear chirp) and the spectrum of a non-linear chirp (non-linear chirp) are shown.

[0043] Alternatively, the approach can also have the following features: the spectral bandwidth of the non-linear chirped ultrasound pulse train with respect to the -3 dB level compared to the amplitude maximum of its spectrum is reduced by more than 25% and / or preferably by more than 30% and / or preferably by more than 35% compared to the spectral bandwidth of the linear chirped ultrasound pulse train with respect to the -3 dB level compared to the amplitude maximum of its spectrum.

[0044] Figure 3 The spectrum of a non-linear positive chirp pulse (rising non-linear chirp) and the spectrum of a non-linear negative chirp pulse (falling non-linear chirp) are shown.

[0045] As an alternative to the two features mentioned, the solution can also be characterized in that the spectrum of the nonlinearly positively chirped pulse at the intersection with the spectrum of the nonlinearly negatively chirped pulse decreases by at least -12 dB compared to the maximum. At the same time, the spectrum of the nonlinearly negatively chirped pulse at the intersection with the spectrum of the nonlinearly positively chirped pulse decreases by at least -12 dB compared to the maximum.

[0046] In a variant of the three basic methods, the temporal pulse frequency variation of the nonlinearly chirped pulse decreases monotonically or increases monotonically between a first time tl and a second time t2. Particularly preferably, the temporal pulse frequency variation of the nonlinearly chirped pulse decreases strictly monotonically or increases strictly monotonically between a first time tl and a second time t2.

[0047] In a second variant of the three basic methods, the temporal variation of the temporal pulse frequency variation of the nonlinearly chirped pulse (i.e. the rate of temporal variation of the temporal pulse frequency variation of the nonlinearly chirped pulse) decreases monotonically or increases monotonically between a first time tl and a second time t2. Particularly preferably, the temporal variation of the temporal pulse frequency variation of the nonlinearly chirped pulse (i.e. the rate of temporal variation of the temporal pulse frequency variation of the nonlinearly chirped pulse) decreases strictly monotonically or increases strictly monotonically between a first time tl and a second time t2.

[0048] Particularly preferably, the temporal curve of the value of the temporal pulse frequency variation of the nonlinearly chirped pulse between a first time tl and a second time t2 has a minimum.

[0049] In a third, broad variant of the three basic methods, the temporal variation of the temporal pulse frequency variation of the nonlinearly chirped pulse between a first time tl and a second time t2 is constant at least at a third time t3 (with tl < t3 < t2), thus applying at this time t3

[0050] Figure 7 The frequency curve is better illustrated. In Figure 7 , only the temporal curve of the instantaneous pulse frequency f m,NL of the exemplary nonlinearly negatively chirped ultrasound pulse train is shown. It corresponds to the negatively chirped ultrasound pulse train of Figure 6 The following explanations certainly also apply in an analogous manner to the exemplary nonlinearly positively chirped ultrasound pulse train, which is not described here again. It corresponds to the positively chirped ultrasound pulse train of Figure 6 ​​of the positive chirp ultrasound pulse train. The invention claimed solution also comprises a time sequence of a plurality of sub-ultrasound pulse trains in the form of an overall ultrasound pulse train, in which at least one sub-ultrasound pulse train is in accordance with the ultrasound pulse train described herein.

[0051] The above described method for operating an ultrasound sensor can also be characterized differently. Another feature emphasizes that the instantaneous pulse frequency f m,NL deviates from the intermediate instantaneous pulse frequency f c slightly. The frequency deviation is only larger for a short time at the beginning and at the end of the ultrasound pulse train.

[0052] Particularly preferably, the intermediate instantaneous pulse frequency f c of the ultrasound pulse train deviates from the frequency of the ultrasound transmitter and / or the ultrasound transducer used. If the instantaneous pulse frequency f c deviates from the resonance frequency only for a relatively short time, the ultrasound transmitter or the ultrasound transducer can emit with almost maximum transmission power for a relatively long period of time within the transmission period of the ultrasound pulse train. Thus, when used in an ultrasonic parking aid system of a motor vehicle, the range of the system is maximized and significantly exceeds the range of a system with a linear chirp. This correspondence between the resonance frequency of the ultrasound transducer or the ultrasound transmitter and the intermediate instantaneous pulse frequency f c can be expressed quantitatively. In the sense of the invention, this frequency can be assumed to be the resonance frequency of the ultrasound transducer or the ultrasound transmitter, at which the acoustic power of the acoustic radiation from the associated ultrasound transducer or the associated ultrasound transmitter is greatest. Thus, particularly preferably, in the emission method of the ultrasound pulse train presented here, the intermediate instantaneous pulse frequency f c deviates from the resonance frequency or the nominal frequency of the ultrasound transmitter by no more than 10% and / or preferably by no more than 5% and / or preferably by no more than 2% and / or preferably by no more than 1% and / or preferably by no more than 0.5% and / or preferably by no more than 0.2% and / or preferably by no more than 0.1% and / or preferably by no more than 0.05% and / or preferably by no more than 0.02% and / or preferably by no more than 0.01%, and / or from the resonance frequency or the nominal frequency of the ultrasound transducer by no more than 10% and / or preferably by no more than 5% and / or preferably by no more than 2% and / or preferably by no more than 1% and / or preferably by no more than 0.5% and / or preferably by no more than 0.2% and / or preferably by no more than 0.1% and / or preferably by no more than 0.05% and / or preferably by no more than 0.02% and / or preferably by no more than 0.01%.

[0053] As mentioned before, the transmission of the ultrasound burst takes place as a transmission of a series of ultrasound pulses with a pulse length T1 and a pulse interval T2. The pulse length T1 and the pulse interval T2 represent the pulse period length T = T1 + T2 as the sum of the time from the beginning of one pulse to the beginning of the next pulse. The ultrasound burst starts at a first time t1 and ends at a second time t2. The start of the ultrasound burst is at the beginning of the first pulse in the ultrasound burst. In the sense of this text, the end of the ultrasound burst is at a time after the elapse of a time corresponding to the pulse interval T2 between the last pulse of the ultrasound burst and the second last pulse of the ultrasound burst, wherein the elapse of this time is from the end of the last pulse of the ultrasound burst. In the sense of this text, the time at which this time elapses is the second time t2.

[0054] Thus, the ultrasound burst has an ultrasound burst length At s = t2 - t1 in time. Here, at a time t during the ultrasound burst (t1 < t < t2), the instantaneous pulse frequency f m,NL = |1 / T| numerically corresponds to the inverse of the instantaneous pulse period length T. In the following, the pulse period length T at the first time t1 and thus the instantaneous pulse frequency f m,NL = |1 / T| is called the first instantaneous pulse frequency f u , and the pulse period length T at the second time t2 and thus the instantaneous pulse frequency f m,NL = |1 / T| is called the second instantaneous pulse frequency f l . Preferably, the first instantaneous pulse frequency f u is different from the second instantaneous pulse frequency f l . As mentioned above, the ultrasound burst has an intermediate instantaneous pulse frequency f c = |f u - f l | / 2. In the following, the total change of the instantaneous pulse frequency f m,NL = |1 / T| between the first time t1 and the second time t2 is called the total frequency change Af s . Here, the first boundary frequency f cu is a frequency which is spaced by half the frequency value of the first instantaneous pulse frequency f u from the frequency value of the second instantaneous pulse frequency f l . Here, the second boundary frequency f cl is a frequency which is spaced by half the frequency value of the second instantaneous pulse frequency f u from the frequency value of the first instantaneous pulse frequency f m,NL . Here, preferably, the instantaneous pulse frequency f cu at the first boundary time t cuPreferably, the instantaneous pulse frequency f m,NL Second boundary time t cl Equal to the second boundary frequency f cl First boundary time t cu Preferably, in time, it occurs after the first time t1 and at the second boundary time t. cl Preferably, in time, at the first boundary time t cu Subsequently, and preferably at the second boundary time t2, the second time t2 is in time at the second boundary time t cl Subsequently, preferably, starting from the first time t1 and ending at the first boundary time t... cu The first time period Δt ends u During this period, the instantaneous pulse frequency f m,NL The pulse frequency f at the first instant u and the first boundary frequency f cu The first frequency range Δf u The pulse frequency f is at the first instant. u and the first boundary frequency f cu Between. Preferably, from the first boundary time t cu Start at the second boundary time t cl The middle period Δt at the end c During this period, the instantaneous pulse frequency f m,NL First boundary frequency f cu Second boundary frequency f cl The intermediate frequency range Δf c The inner frequency is at the first boundary frequency f cu Second boundary frequency f cl Between. Preferably, from the second boundary time t cl The second time interval Δt begins and ends at the second time t2. l During this period, the instantaneous pulse frequency f m,NL Second boundary frequency f cl The second frequency range Δf between the second instantaneous pulse frequency f1 and the second instantaneous pulse frequency f1 l The inner frequency is at the second boundary frequency f cl Between the second instantaneous pulse frequency f1. The decisive factor here is the intermediate time interval Δt. c The duration is greater than the first period Δt u The duration of the second period Δt l The sum of durations, or the intermediate time interval Δt c The duration is equal to the first time interval Δt u The duration of the second period Δt l The sum of the durations. Therefore, the focus of sound transmission can be initially placed on the resonant frequency of the ultrasonic transducer or ultrasonic transmitter, thereby maximizing the range of the ultrasonic parking assist system.

[0055] Thus, preferably, the instantaneous pulse frequency variation is different from the instantaneous pulse frequency variation

[0056] Preferably, the instantaneous pulse frequency variation m,NL (t) is expressed by the equation:

[0057]

[0058] where B L is the bandwidth coefficient of the linear part, B C is the bandwidth coefficient of the non-linear part.

[0059] Preferably, the instantaneous pulse frequency variation monotonically decreases or monotonically increases again between the first time tl and the second time t2.

[0060] Preferably, the temporal variation of the instantaneous pulse frequency variation monotonically decreases or monotonically increases between the first time tl and the second time t2.

[0061] However, the temporal variation of the instantaneous pulse frequency variation may also be constant.

[0062] The temporal variation of the temporal variation of the instantaneous pulse frequency variation may also be constant

[0063] Preferably, the ultrasound pulse train spectrum has a spectral width about the -3 dB level compared to the amplitude maximum which is reduced by more than 25 % and / or preferably by more than 30 % and / or preferably by more than 35 % relative to the ultrasound pulse train spectrum with a constant instantaneous pulse frequency variation

[0064] As mentioned above, the transmission of the entire ultrasound pulse train can also be carried out as a direct sequence in time of the transmission of partial ultrasound pulse trains, wherein at least the partial ultrasound pulse trains (preferably all partial ultrasound pulse trains) of these partial ultrasound pulse trains transmit correspond to one of the above-mentioned methods.

[0065] Advantages

[0066] ​Instead of amplitude weighting, which also reduces the signal-to-noise ratio, the dwell time of the ultrasound emitter system can also be adapted to the individual instantaneous pulse frequencies f m Optimizations are made so that the spectrum is optimally shaped. This leads to the use of a nonlinear chirp. Practical tests have shown that the spacing between the center frequencies of the spectra of two different ultrasound pulse trains of two different ultrasound emitters can thereby be reduced, for example, from 7 kHz to 4 kHz. The nonlinear chirp signals can even slightly overlap here. The signal amplitude and the signal waveform, including the sidelobe reduction, and the signal-to-noise ratio become better.

[0067] Since the instantaneous pulse frequencies f c Preferably, this does not deviate from the frequency of the ultrasound emitters and / or ultrasound transducers used, and since the instantaneous pulse frequencies f c Since the resonance frequency is only deviated from for a relatively short period of time during the transmission of the ultrasound pulse train and only slightly, the ultrasound emitters or ultrasound transducers can emit with almost maximum emission power in a relatively long period of time within the transmission period of the ultrasound pulse train. When applied in an ultrasonic parking aid system in a car, the range of the system is thereby maximized and significantly exceeds the range of a system with a linear chirp.

[0068] List of cited documents

[0069] DE 10 2017 104 145 A1; DE 10 2017 123 049 B3; DE 10 2017 123 050 B3; DE 10 2017 123 052 B3; DE 10 2017 123 051 B3; JP 2011-038 948 A; DE 2017 122 477; DE 10 2018 106 251 A1

Claims

1. A method for operating an ultrasonic sensor, comprising: performing transmission of a total ultrasonic pulse train by directly sequencing in time transmission of partial ultrasonic pulse trains, wherein transmission of at least one of the partial ultrasonic pulse trains comprises transmitting the partial ultrasonic pulse train as a series of ultrasonic pulses having a pulse length T1 and a pulse interval T2, wherein the sum of the pulse length T1 and the pulse interval T2 equals a pulse period length T = T1 + T2, and wherein the partial ultrasonic pulse trains start at a first time t1 and end at a second time t2, and wherein the partial ultrasound pulse train has an ultrasound pulse train length Δ ts = t2 - t1, and wherein a time t during said partial ultrasound burst, a pulse frequency f of said partial ultrasound pulse at said time t m,NL = |1 / T t corresponds to the inverse of said pulse period length T t , wherein T t denotes a pulse period length at said time t, and t1 < t < t2, and wherein the pulse frequency f of the part of the ultrasound pulses at the first time t1 m,NL = |1 / T t1 is called first pulse frequency f u and wherein the pulse frequency f of the part of the ultrasound pulse at the second time t2 m,NL = |1 / T t2 is called second pulse frequency f l and wherein the first pulse frequency f u different from the second pulse frequency f2, and wherein the partial ultrasound pulse train has an intermediate pulse frequency f c = |f u -f l | / 2, and wherein the pulse frequency f m,NL = |1 / T t | the total change between the first time tl and the second time t2 is called the total frequency change Af s , and Wherein, the first boundary frequency f cu It is related to the first pulse frequency f u The frequency interval is the same as the second pulse frequency f l The frequency interval is half the frequency, and Wherein, the second boundary frequency f cl It is the frequency f of the second pulse. l The frequency interval is the same as the first pulse frequency f. u The frequency interval is half the frequency, and wherein, at a first boundary time t cu the pulse frequency f m,NL equals the first boundary frequency f cu , and wherein, at a second boundary time t cl the pulse frequency f m,NL equals the second boundary frequency f cl , and wherein the first boundary time t cu after the first time t1, and wherein the second boundary time t cl at the first boundary time t cu and thereafter, and wherein the second time t2 is after the second boundary time t cl and thereafter, and wherein, during a first period Δt cu ending at the first boundary time t u after the first time t m,NL the pulse frequency f u lies within a first frequency range Δf cu between the first pulse frequency f u and the first boundary frequency f u and the first boundary frequency f cu , and wherein, during an intermediate period Δt cu starting from the first boundary time t cl ending at the second boundary time t c the pulse frequency f m,NL is within an intermediate frequency range Δf cu between the first boundary frequency f cl and the second boundary frequency f c and the first boundary frequency f cu and the second boundary frequency f cl , and Wherein, from the second boundary time t cl The second time interval Δt begins and ends at the second time t2. l During this period, the pulse frequency f m,NL At the second boundary frequency f cl The second frequency range Δf between the second pulse frequency f1 and the second pulse frequency f1 l The inner frequency is at the second boundary frequency f cl Between and the second pulse frequency f1, and wherein the intermediate period Δ t c has a length greater than the first period Δ t u has a length greater than the second period Δ t l. Alternatively, the intermediate period Δ t c has a length equal to the sum of the first period Δ t u and the second period Δ t l.

2. A method for operating an ultrasonic sensor, comprising the steps of: transmitting an ultrasonic pulse train as a series of ultrasonic pulses having a pulse length T1 and a pulse interval T2, wherein the sum of the pulse length T1 and the pulse interval T2 represents a pulse period length T = T1 + T2, and wherein the ultrasonic pulse train starts at a first time t1 and ends at a second time t2, and where the time-varying instantaneous pulse frequency f at time t is described by the equation m,NL (t), where T t denotes the pulse period length at said time t, and t1≤t≤t2: where B L is a coefficient of the bandwidth of the linear part, and B C is a coefficient of the bandwidth of the nonlinear part.

3. The method according to claim 2, wherein a change in the time-varying instantaneous pulse frequency monotonically decreases or increases between the first time t1 and the second time t2.

4. The method according to claim 2 or 3, wherein a temporal variation of the time-varying instantaneous pulse frequency monotonically decreases or increases between the first time t1 and the second time t2.

5. The method according to claim 2 or 3, wherein a temporal change of the change of the time-varying instantaneous pulse frequency between the first time t1 and the second time t2 is constant at least at time t3, such that is applicable at the time t3, with t1 < t3 < t2.

6. A method for operating an ultrasonic sensor, comprising the steps of: performing transmission of an ultrasonic pulse train by directly sequencing in time transmission of partial ultrasonic pulse trains, wherein transmission of at least one of the partial ultrasonic pulse trains corresponds to the method according to any one of claims 2 to 5.

7. A method for operating an ultrasonic sensor, comprising the steps of: transmitting an ultrasonic pulse train as a series of ultrasonic pulses having a pulse length T1 and a pulse interval T2, wherein the sum of the pulse length T1 and the pulse interval T2 represents a pulse period length T = T1 + T2, and wherein the ultrasonic pulse train starts at a first time t1 and ends at a second time t2, and wherein the ultrasound pulse train has an ultrasound pulse train length Δt in time s = t2 - t1, and wherein a time t during the ultrasound pulse train, a pulse frequency f of the ultrasound pulse at the time t m,NL = |1 / T t corresponds to the inverse of the pulse period length T t , wherein T t denotes the pulse period length at the time t, and t1 t2 wherein the following will be referred to as the pulse frequency f of the ultrasound pulse at the first time t1 m,NL = |1 / T t1 | referred to as the first pulse frequency f u , and wherein the following will be referred to as the pulse frequency f of the ultrasound pulse at the second time t2 m,NL = | 1 / T t2 | referred to as the second pulse frequency f l and wherein the first pulse frequency f u different from the second pulse frequency f l and wherein the ultrasound pulse train has an intermediate pulse frequency f c = |f u -f l | / 2, and wherein the pulse frequency f m,NL = |1 / T t | the total change between the first time tl and the second time t2 is called the total frequency change Af s , and Wherein, the first boundary frequency f cu It is related to the first pulse frequency f u The frequency interval is the same as the second pulse frequency f l The frequency interval is half the frequency, and Wherein, the second boundary frequency f cl It is the frequency f of the second pulse. l The frequency interval is the same as the first pulse frequency f. u The frequency interval is half the frequency, and wherein, at a first boundary time t cu the pulse frequency f m,NL equals the first boundary frequency f cu , and wherein, at a second boundary time t cl the pulse frequency f m,NL equals the second boundary frequency f cl , and wherein the first boundary time t cu after the first time t1, and wherein the second boundary time t cl at the first boundary time t cu and thereafter, and wherein the second time t2 is after the second boundary time t cl and thereafter, and wherein, during a first period Δt cu ending at the first boundary time t u after the first time t m,NL the pulse frequency f u is within a first frequency range Δf cu between the first pulse frequency f u and the first boundary frequency f u and the first boundary frequency f cu , and Wherein, from the first boundary time t cu Start at the second boundary time t cl The middle period Δt at the end c During this period, the pulse frequency f m,NL At the first boundary frequency f cu and the second boundary frequency f cl The intermediate frequency range Δf c The inner frequency is at the first boundary frequency f cu and the second boundary frequency f cl Between, and Wherein, from the second boundary time t cl The second time interval Δt begins and ends at the second time t2. l During this period, the pulse frequency f m,NL At the second boundary frequency f cl The second pulse frequency f1 is located at the second boundary frequency f. cl The second frequency range Δf between the second pulse frequency f1 and the second pulse frequency f1 l Inside, and Wherein, the intermediate time period Δt c The length is greater than the first time period Δt u The length of the second time period Δt l The sum of the lengths, or where the intermediate time period Δt is... c The length is equal to the first time period Δt u The length of the second time period Δt l The sum of the lengths, and where the time-varying instantaneous pulse frequency f at the time t is described by the following equation m,NL (t): where B L is a coefficient of the bandwidth of the linear part, and B C is a coefficient of the bandwidth of the nonlinear part.

8. A method for operating an ultrasonic sensor, comprising the steps of performing transmission of a total ultrasonic pulse train by directly sequencing in time transmission of partial ultrasonic pulse trains, wherein wherein transmission of at least one of the partial ultrasonic pulse trains corresponds to the method according to claim 7.

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