Ultrasonic transducer, method for operating an ultrasonic transducer, and method for measuring a distance

Abstract

The ultrasonic transducer (1) comprises a diaphragm (4) in a housing (11), an excitation means (21), and a damping means (22). The excitation means (21) is designed to excite the diaphragm (4) so as to vibrate in a transmission mode (12) in order to transmit an ultrasonic wave (7). The damping means (22) is designed to dampen a reverberation of the diaphragm (4) occurring after the excitation. The damping means (22) is additionally designed to excite at least one damping mode (55) which differs from the transmission mode (12). At least one lateral wall (14) of the housing (11) has at least one thickness (15) such that the transmission mode (12) and the damping mode (55) can be excited in a stable manner.

Description

[0001] Description

[0002] Ultrasonic transducer, method for operating an ultrasonic transducer and method for distance measurement

[0003] The invention relates to an ultrasonic transducer and a method for operating an ultrasonic transducer and a method for distance measurement.

[0004] Piezoelectric ultrasonic transducers are used for both transmitting and receiving ultrasonic signals and are used, for example, as distance sensors in motor vehicles. However, such ultrasonic transducers typically continue to emit ultrasound even after all excitation of the ultrasonic signal has ceased. The reason for this is primarily the post-oscillation of a membrane of the ultrasonic transducer, which generates the ultrasonic signals. This post-oscillation is also referred to as "ringing" and makes it difficult to detect an ultrasonic signal using the same membrane.

[0005] Ultrasonic transducers and methods for operating ultrasonic transducers are known from the publications US 4,580,251, US 6,731,596 B2, GB 2593477 A, as well as Lio et al. "Reducing ring-down time of pMUTs with phase shift of driving waveform". Sensors and Actuators A 281 (2018) 100 - 107, and Wu et al. "A Novel Transfer Function Based Ring-Down Suppression System for PMUTs". Sensors 2021, 21, 6414.

[0006] One problem to be solved is to provide an improved ultrasonic transducer and an improved method for operating an ultrasonic transducer. These problems are solved by an object with the

[0007] Features of independent patent claim 1 and by a method having the features of patent claim 19.

[0008] An ultrasonic transducer is proposed which comprises a membrane in a housing, an excitation means and a damping means. The excitation means is designed to excite the membrane to oscillate in a transmission mode for emitting an ultrasonic wave. The damping means is designed to dampen any post-oscillation of the membrane which occurs after excitation. The damping means is further designed to excite at least one damping mode which is different from the transmission mode. At least one side wall of the housing has at least a thickness such that the transmission mode and the damping mode can be stably excited.

[0009] For example, the transmission mode has a transmission frequency. The damping mode, for example, has a damping frequency. The transmission frequency and the damping frequency preferably differ. The damping mode and the transmission mode can be eigenmodes of the membrane or the ultrasonic transducer, respectively. The membrane comprises, for example, aluminum or is formed from it.

[0010] The transmission mode and the attenuation mode can differ in the transmission frequency and the attenuation frequency. In particular, the attenuation frequency is higher than the transmission frequency. Furthermore, the transmission mode and the attenuation mode can differ, for example, in the arrangement of extreme points and vibration nodes. The excitation means is in particular designed to excite the membrane to emit an ultrasonic wave that can be used to measure distances. The excitation means excites the transmission mode. This causes the membrane to vibrate and the ultrasonic wave is generated. The membrane preferably vibrates in resonance, which allows the ultrasonic wave to be generated particularly efficiently. Furthermore, the transmission mode preferably has a relatively low dissipation or as low a dissipation as possible in order to achieve effective transmission of the ultrasonic wave.

[0011] During operation of the ultrasonic transducer, the emitted ultrasonic wave is reflected by an object to which a distance is to be determined. The reflected ultrasonic wave is then preferably registered by causing the membrane to vibrate. This means that the reflected wave excites the membrane to vibrate. Since the reflected wave results from the ultrasonic wave generated and emitted by means of the transmission mode, the reflected wave excites in particular the transmission mode or a mode similar to the transmission mode. Since the intensity of the excitation by the reflected wave is lower than the excitation by the excitation medium, the transmission mode preferably has comparatively low dissipation or attenuation so that it can be stably excited by the reflected wave.Furthermore, the post-oscillation of the membrane after the transmission of the ultrasonic wave has preferably decayed or substantially decayed so that a change in the membrane vibration due to the reflected wave is detectable. In other words, the membrane or the ultrasonic transducer is sensitive to the reflected wave after damping. The damping means is in particular designed to dampen the post-oscillation of the membrane by exciting the damping mode or damping modes. The post-oscillation occurs in particular because, during operation, the membrane was excited by the excitation means to a resonant vibration which has comparatively low dissipation. The membrane vibration therefore decays only relatively slowly and improved damping, for example active damping, is required.

[0012] The damping mode or modes excited for damping is / are, in particular, a stable mode exhibiting a relatively high dissipation. This means that if the membrane oscillates with the damping mode or modes, energy is dissipated and the oscillation decays. In particular, the damping mode or modes exhibit a higher damping or dissipation than the transmission mode. Thus, by specifically exciting at least one damping mode, active and effective damping of the post-oscillation can be achieved.

[0013] If a feature is disclosed in connection with the damping mode hereinafter , this is also disclosed accordingly for several damping modes , unless otherwise stated .

[0014] The housing is preferably designed such that the transmission mode and the attenuation mode can be excited in a stable manner. In particular, a side wall of the housing has at least one thickness such that the transmission mode and the attenuation mode can be excited in a stable manner. The housing can, for example, have a plurality of thicknesses, for example in a plurality of regions. It is also possible for the side wall to have only one thickness. By “has at least one thickness” is meant in particular that one of these thicknesses or all of these thicknesses are adapted or selected such that the transmission mode and the attenuation mode can be excited in a stable manner. This means that the housing has, for example, in certain regions or at certain locations a wall thickness which enables the stable excitation of the transmission mode and attenuation mode.

[0015] A "stable mode" is understood here and in the following to mean a mode that is stable over a certain period of time. For example, the damping mode is stable in order to achieve continuous damping and thus effective decay of the post-oscillation. The transmission mode is preferably stable in order to achieve effective transmission of the ultrasonic wave.

[0016] The housing has in particular one or more side walls which extend transversely or perpendicularly to a main extension plane of the membrane.

[0017] The housing is preferably rotationally symmetrical. For example, the housing has a central axis of symmetry. The axis of symmetry can be a center axis of the housing. The housing is preferably a pot housing.

[0018] The membrane is arranged, for example, in a base region of the housing. This means, in particular, that the side wall extends from the membrane in a direction transverse or perpendicular to the membrane.

[0019] The housing comprises, for example, a metal and is formed in one piece. The membrane preferably also comprises a metal. The housing and / or the membrane comprise, for example, aluminum.

[0020] The sidewall preferably has at least a first region and at least a second region. In the first region, the sidewall has, for example, a thickness that is greater than a thickness of the sidewall in the second region. The first region of the sidewall preferably borders directly on the membrane.

[0021] It is also possible for the side wall to have more than two regions. Preferably, the side wall has a different thickness in each of the regions.

[0022] Alternatively or additionally, it is possible for the sidewall to have a thickness gradient in one region or across its entire extent. This means, in particular, that the thickness of the sidewall changes continuously in a direction away from the membrane, which may in particular be perpendicular to the main direction of extension of the membrane. For example, the thickness of the sidewall decreases continuously in this direction.

[0023] The membrane together with the housing in particular form an oscillation system. The oscillation system is preferably designed in such a way that the damping mode and the transmission mode can be excited in a stable manner and are preferably eigenmodes of the oscillation system. This means that the membrane and the housing are preferably matched to one another in such a way that the transmission mode and damping mode can be excited in a stable manner. In particular, at least one thickness of the side wall of the housing is adapted in such a way that the transmission mode and the damping mode can be excited in a stable manner. When the damping mode and / or transmission mode is excited, the oscillation system can be set into motion or oscillation at least in part. In particular, when the damping mode and / or transmission mode is excited, the housing can be set into motion or oscillation at least in part.

[0024] The housing design is preferably selected such that, in addition to the transmission mode, the damping mode is also stable. This can be achieved, for example, by having the housing, as part of the oscillation system, a side wall with several regions of different thicknesses. In other words, by forming the first region and the second region of the side wall of the housing, it can be achieved that the transmission mode and the damping mode can be stably excited.

[0025] The thicknesses of the side wall in the first and second regions are selected, for example, such that it is possible both to stably excite the transmission mode without radiating an ultrasonic wave via an edge region of the membrane or side walls of the housing, and to excite a stable damping mode. In the case of the damping mode, preferably both an edge region of the membrane and / or the second region of the side wall are excited. This means that the second region of the side wall, in which the side wall has a smaller thickness, can be set in motion or oscillated when the damping mode is excited.

[0026] The peripheral area of ​​the membrane surrounds a central area of ​​the

[0027] Membrane preferably completely. In a top view of the membrane, the edge region forms, for example, a ring-shaped or frame-shaped area surrounding the central region. In the edge region, the membrane can be in direct or indirect contact with the housing or the side wall of the housing.

[0028] The ultrasonic transducer can further comprise at least one piezoelectric element. For example, the excitation means and the damping means comprise the piezoelectric element for exciting the transmission mode and the damping mode, respectively. The piezoelectric element converts, in particular, an electrical signal into mechanical movement, by means of which the transmission mode and the damping mode can be excited. The piezoelectric element can be a piezoelectric disk. The piezoelectric element can, in particular, be part of the oscillation system. In this case, the piezoelectric element can be coordinated with the other components of the oscillation system such that the damping mode and the transmission mode can be stably excited.

[0029] To excite the transmission mode, the membrane is excited, for example, at the transmission frequency during operation of the ultrasonic transducer, in particular by the piezoelectric element. The transmission frequency is, for example, between 50 kHz and 100 kHz, for example, approximately 75 kHz. For this purpose, the piezoelectric element can receive an excitation signal. In other words, the excitation means is particularly designed to excite the membrane at the transmission frequency.

[0030] To excite the damping mode, the membrane is excited, for example, at the damping frequency during operation of the ultrasonic transducer, particularly by the piezoelectric element. The damping frequency is, for example, between 200 kHz and 400 kHz, for example, approximately 300 kHz. For this purpose, the piezoelectric element can receive a damping signal. In other words, the excitation means is particularly designed to excite the membrane at the damping frequency.

[0031] It is possible for the ultrasonic transducer and preferably at least one of the excitation means and damping means to comprise control electronics. The control electronics, for example, provide a signal for the piezoelectric element.

[0032] It is possible for the piezoelectric element to be connected to the control electronics of the ultrasonic transducer. For example, the control electronics comprise at least one of the following electronic components: a microcontroller, an application-specific integrated circuit (ASIC), and a field-programmable gate array (FPGA).

[0033] The electronic component of the control electronics can be arranged on a carrier such as a printed circuit board. The carrier or the printed circuit board can also be part of the oscillation system. In this case, the control electronics can be coordinated with the other components of the oscillation system such that the damping mode and the transmission mode can be excited in a stable manner. The control electronics can thus contribute to damping the after-oscillation of the membrane. The transmission mode preferably has a maximum in the central region of the membrane. In particular, the transmission mode has an oscillation node in the edge region of the membrane and / or preferably in defined regions of the side walls of the housing. This means in particular that maxima and minima can alternate in the central region during the membrane oscillation, so that the membrane is in motion in the central region during excitation by the excitation means.In the edge region, the membrane and / or preferably at the defined areas of the side walls of the housing, the oscillation system is preferably at rest during excitation of the transmission mode. This allows attenuation of the transmission mode, which can occur, for example, in the edge region and / or on the side wall of the housing due to edge effects or friction or movement of the housing, to be reduced. This allows the transmission mode to be excited with comparatively low attenuation.

[0034] More preferably, the damping mode has a maximum in an edge region of the membrane. Thus, the membrane is in motion in the edge region, i.e., at the edge, during damping of the post-oscillation. This allows a comparatively high dissipation or damping for the damping mode or post-oscillation to be achieved.

[0035] Alternatively or additionally, it is possible for the damping mode to have a maximum in a region of the side walls of the housing. The region of the side walls in which the damping mode has a maximum is, for example, the second region or borders the second region. Thus, the side walls of the housing are in motion in certain regions during damping of the post-oscillation. This allows a comparatively high dissipation or damping for the damping mode or post-oscillation to be achieved.

[0036] Preferably, a ratio of a thickness of the side wall in a region bordering the membrane to a membrane thickness is between 2 and 4, or preferably between 2.5 and 3.5, or more preferably 3 or approximately 3. The region of the side wall bordering the membrane is, for example, the first region. By means of this ratio of the thickness of the side wall to the membrane thickness, undesired lateral radiation of an ultrasonic wave due to oscillation of an edge region of the membrane in the region of the side wall can be suppressed or avoided.

[0037] The membrane of the ultrasonic transducer can have a freely vibrating surface of at least one square millimeter. This makes the membrane more robust and allows the ultrasonic transducer to be used under less favorable external conditions than, for example, a piezoelectric micromechanical ultrasonic transducer, which has a membrane with a surface area of ​​less than one square millimeter.

[0038] The housing can comprise at least one damping element, which is preferably arranged in at least one region in which the damping mode has a maximum. In particular, the at least one damping element is arranged in a region in which a movement of the oscillation system has a maximum, for example during excitation of the damping mode. The damping element can, for example, be a mechanical damper such as a foam, for example a polymer foam or a silicone foam or the like. Alternatively or additionally, the damping element can comprise a silicone or a polymer as a solid material.

[0039] In particular, the damping element is designed to absorb and dissipate energy from the diaphragm vibration. The damping element is therefore a dissipative element. The damping element can be arranged, for example, on a suspension of the diaphragm in the housing. Furthermore, the damping element can be arranged in a region which the diaphragm touches during vibration in the damping mode, but not during vibration in the transmission mode. Alternatively or additionally, an interior space of the housing can be filled with the damping element.

[0040] The damping element can, in particular, be part of the oscillation system. Thus, a material, arrangement, or geometric shape of the damping element is preferably selected such that the transmission mode and the damping mode can be stably excited and are preferably eigenmodes of the oscillation system.

[0041] The housing can in particular have at least two damping elements. A first of the damping elements can border on the first region of the side wall and a second damping element can border on the second region of the side wall. The first damping element and the second damping element preferably have different damping coefficients. For example, the first damping element has a lower damping coefficient than the second damping element. The first damping element can fill a first part of the interior of the housing. The first part of the interior can be delimited in one direction, for example a lateral direction, by the first region of the side wall. The lateral direction is in particular a direction parallel to the main extension plane of the diaphragm. In a direction perpendicular to the lateral direction, the first damping element can be delimited by the diaphragm and the second damping element.In this case, the first damping element is adjacent to the membrane, for example. The first damping element comprises, for example, a foamed polymer or a silicone foam.

[0042] The second damping element can fill a second part of the interior of the housing. The second part of the interior can be delimited in the lateral direction by the second region of the side wall. In the direction perpendicular to the lateral direction, the second damping element can be delimited by the first damping element and a space outside the housing. The second damping element comprises, for example, a polymer or a highly cross-linked polymer or silicone as a solid material.

[0043] In particular, the first and second damping elements can comprise the same base material. The base material is, for example, silicone. For example, in the case of the first damping element, the base material is foamed, while in the case of the second damping element, the base material is solid.

[0044] Preferably, the second damping element is arranged in a region of the housing or the side wall or the oscillation system that is in motion upon excitation of the damping mode. This allows the energy of this motion to be effectively dissipated, and the post-oscillation of the membrane can be effectively damped.

[0045] In a preferred embodiment of the ultrasonic transducer, the damping means is configured to excite the membrane with a damping signal. The damping signal preferably has a fixed component and a variable component. The damping means is further configured to excite the fixed component after the membrane has been excited with the excitation means and to excite the variable component after the fixed component. For example, the fixed component follows directly after the excitation signal, and the variable component follows directly after the fixed component.

[0046] For example, the damping signal is provided to the damping element via the control electronics. The damping element is electrically connected to the control electronics.

[0047] In particular, the excitation means is configured to excite the membrane using an excitation signal. The excitation signal is provided, for example, by the control electronics. The excitation signal preferably essentially determines the ultrasonic wave emitted by the membrane and thus by the ultrasonic transducer. By specifying the excitation signal, the shape, length, frequencies, etc., of the ultrasonic wave can be determined.

[0048] The damping signal, in particular the fixed part of the

[0049] damping signal can be 180 ° phase shifted to the excitation signal. By the phase shift of the

[0050] Efficient damping is possible by using the damping signal.

[0051] The excitation signal and the damping signal, especially the fixed component of the damping signal, can have the same amplitude. This allows for particularly simple operation of the ultrasonic transducer, since the excitation signal and the damping signal can be generated in essentially the same way.

[0052] The damping means is preferably configured to excite the damping mode using the variable component of the damping signal. For example, during operation of the ultrasonic transducer, the amplitude of the post-oscillation is damped by the fixed component of the damping signal to such an extent that the damping mode can be excited using the variable component. This means, in particular, that the membrane is excited at the damping frequency using the variable component. This allows effective damping of the post-oscillations of the membrane by dividing the damping signal into a fixed component and a variable component.

[0053] In a further preferred embodiment or according to one of the other embodiments described above, the ultrasonic transducer comprises a detection means and an adaptation means. The detection means is particularly designed to detect at least one oscillation parameter of the post-oscillation during the excitation of the fixed component of the damping signal. The adaptation means is then particularly designed to determine the variable component of the damping signal during the excitation of the fixed component based on the detected oscillation parameter. The oscillation parameter can be an amplitude of the post-oscillation of the membrane or an amplitude of a specific frequency component of the post-oscillation.

[0054] In particular, the variable component is determined or adjusted during operation of the ultrasonic transducer. For example, the variable component is optimized with regard to the recorded vibration parameter. For example, the optimization is carried out using an optimization algorithm such as a population algorithm or the least squares method. It is also possible for the variable component to be optimized using a Kl method. The optimization is preferably carried out on the control electronics. This means that the control electronics are set up to carry out the optimization.

[0055] The adaptation means and the detection means can be part of the control electronics and integrated therein.

[0056] The adaptation means can further be configured to determine the fixed component of the damping signal before the membrane is excited by the excitation means. For example, the fixed component is determined before a distance measurement is carried out using the ultrasonic transducer. It is also possible for the fixed component to be determined once for several distance measurements. This saves computing time during operation of the ultrasonic transducer and enables effective optimization of the damping signal with regard to post-oscillation. The fixed component can be stored in a memory unit of the control electronics and retrieved by the adaptation means during operation of the ultrasonic transducer. The excitation means is particularly configured to determine the fixed component of the damping signal using a population algorithm. Alternatively, the fixed component can also be determined using a KL method.For the population algorithm, for example, an amplitude of the post-oscillation, particularly at a fixed point in time during the post-oscillation, is used as a fitness parameter. Alternatively, the amplitude of a specific frequency component of the post-oscillation can be selected as the fitness parameter. The population algorithm is particularly executed on the control electronics. This means that the control electronics are configured to execute the population algorithm.

[0057] In particular, in a population algorithm such as in the present embodiment, a population with a large number of individuals is generated randomly or pseudorandomly, with each individual corresponding to a damping signal or a fixed proportion of the damping signal. A degree of adaptation or fitness of the individual individuals is then determined by damping a post-oscillation with each damping signal and comparing the amplitude of this post-oscillation with the fitness parameter. Preferably, all individuals whose fitness does not reach a predefined value are subsequently deleted. For example, all individuals which achieve a deviation from the fitness parameter of more than 10% are deleted.

[0058] In a further random step, a new generation of individuals is created from the remaining individuals. These individuals are allowed to differ from the previous generation in some parameters by a fixed interval of, for example, 10%. This generation of individuals is then tested for fitness as described above. By repeating the steps of creating a new generation, determining the fitness of the new generation, and subsequent selection, an optimized attenuation signal or an optimized fixed or variable component can be obtained.

[0059] It is possible for the damping signal to comprise at least one damping pulse. The adaptation means is particularly configured to define a plurality of the following parameters for the fixed portion of the damping signal and precisely one of the following parameters for the variable portion of the damping signal: number of damping pulses, width of the at least one damping pulse, sequence of the at least one damping pulse, amplitude of the damping pulse.

[0060] For example, the adaptation means is configured to determine the number of damping pulses, the sequence of the damping pulses, and the width of the damping pulses, particularly for the fixed component. Furthermore, in this example, the adaptation means is configured to determine and optimize the sequence or temporal position of the damping pulses for the variable component of the damping signal. In this case, the parameters specified for the fixed component are preferably adopted for the variable component.

[0061] If all of the above-mentioned parameters for the attenuation signal are to be optimized, a relatively large parameter space results in which the optimal parameters must be found. Depending on the parameter and the optimization method used, this can be computationally intensive and take up to minutes. By dividing the attenuation signal into a fixed and a variable component, the fixed component in the relatively large parameter space can be optimized before the ultrasonic transducer is used for measurement.

[0062] The variable component can then be dynamically optimized using a single parameter during the measurement operation of the ultrasonic transducer. This optimization advantageously has a much smaller parameter space and can therefore be performed much more quickly. In particular, it is possible for the variable component to be determined and optimized while the fixed component of the damping signal is being provided. Therefore, the damping of the post-oscillation can be carried out effectively and optimized during the operation of the ultrasonic transducer.

[0063] A width of the at least one damping pulse is determined in particular based on the time during which the damping signal exhibits the damping pulse. For example, the damping pulses are rectangular pulses. This means that during the time during which the damping signal exhibits the damping pulse, the damping signal exhibits a predetermined voltage that is not equal to zero. The time period during which the damping signal exhibits this voltage determines in particular the width of the damping pulse.

[0064] If, for example, the damping signal has only one damping pulse, the sequence of the one damping pulse can indicate the time period after termination of the excitation of the membrane with the excitation means that the damping pulse occurs. In the case that the damping signal comprises several damping pulses, the sequence indicates, for example, alternatively or additionally, the temporal sequence in which the damping pulses in the

[0065] Damping signals follow one another.

[0066] A width of the at least one damping pulse can be, for example, between 0.002 milliseconds and 0.1 milliseconds inclusive.

[0067] The damping signal comprises, for example, between two and 20 damping pulses inclusive.

[0068] For example, the time interval between two damping pulses is between 0.002 milliseconds and 0.1 milliseconds. In this case, the damping signal comprises, in particular, at least two damping pulses.

[0069] The waiting time between the end of the excitation of the membrane with the excitation agent and the first damping pulse of the damping signal can be between 0.002 milliseconds and 0.1 milliseconds inclusive. The waiting time is thus measured, for example, from the time between the end of the excitation signal and the first occurrence of a damping pulse of the damping signal. The sequence of the damping pulses is determined, in particular, by the waiting time and the time interval between the damping pulses.

[0070] If the damping signal comprises at least two damping pulses, the damping pulses of the damping signal preferably have the same amplitude. For example, the damping pulses are generated by switching a damping voltage on and off. The damping voltage is constant and varies, for example, only in sign. This makes the damping signal particularly simple and therefore cost-effective to generate, since no amplitude adjustment is necessary.

[0071] Alternatively or additionally, the damping pulses have the same pulse shape. For example, the damping pulses are rectangular pulses. The damping pulses preferably differ from one another only in their width and sign.

[0072] In a further embodiment or according to one of the embodiments described above, the ultrasonic transducer has at least one environmental sensor. The environmental sensor is configured to detect at least one environmental parameter. The environmental parameter can be an ambient temperature of the environment of the ultrasonic transducer or a relative humidity or the like. Of particular interest are those environmental parameters that can influence the functionality or functioning of the ultrasonic transducer. The environmental sensor can be, for example, a temperature sensor and / or a humidity sensor.

[0073] The environmental sensor is preferably connected to the control electronics or can be integrated into the control electronics. For example, the environmental parameter(s) can be stored in a memory unit of the control electronics.

[0074] The adjustment means can further be configured to determine the fixed component of the attenuation signal taking the environmental parameter into account. For example, the fixed component can be redefined if the temperature and / or humidity of the environment surrounding the ultrasonic transducer changes.

[0075] It is also possible for the fixed component to be determined for a plurality of environmental parameters prior to the measurement operation of the ultrasonic transducer and to be stored in the memory unit of the control electronics as a function of the environmental parameter. This advantageously allows the fixed component to be quickly adjusted when the environmental parameter changes. In this case, the ultrasonic transducer preferably comprises control electronics with a memory unit.

[0076] In this and all other embodiments, the memory unit can have multiple registers. For example, the memory unit is configured to store an environmental parameter in one register and the fixed portion of the damping signal in another register. The variable portion of the damping signal can also be stored in another register.

[0077] According to at least one embodiment or one of the embodiments described above, the adaptation means is configured to store the flexible portion of a first damping signal in a second register of the memory unit. The detection means is preferably configured to detect a second oscillation parameter of the post-oscillation during the application of a fixed portion of a second damping signal. The adaptation means is further configured in particular to determine a variable portion of the second damping signal, which follows the first damping signal, on the basis of the stored variable portion of the first damping signal and the detected second oscillation parameter. The damping means is preferably further configured to apply the second damping signal to the membrane.In this case, a post-oscillation of the membrane which is damped with the first damping signal has a phase shift of, for example, 180° compared to a post-oscillation of the membrane which is damped with the second damping signal.

[0078] The first damping signal preferably follows the second damping signal directly. For example, the membrane is excited to emit a first ultrasonic wave. The post-oscillation of this excitation is dampened by the first damping signal. A first reflected wave is then detected for distance measurement. The membrane is then excited to emit a second ultrasonic wave, and the post-oscillation of this excitation is dampened by the second damping signal. A second reflected wave is then detected for distance measurement. Here and in the following, “first” and “second” do not refer to the absolute first excitation or damping in the overall operation of the ultrasonic transducer, but are intended merely to relate two excitation and damping processes to one another.

[0079] Despite the damping of the membrane's post-oscillation, when the ultrasonic transducer is operating, the membrane may exhibit a slight vibration upon detection of a reflected wave, which overlaps with the reflected wave. Depending on the phase relationship between the post-oscillation and the reflected wave, the post-oscillation and the reflected wave can overlap constructively or negatively. In the first case, the membrane's vibration amplitude increases, and in the second case, the membrane's vibration amplitude decreases, for example, to zero. In both cases, the arrival of the reflected wave can be detected by a change in amplitude.

[0080] However, it is also possible that the phase relationship between the post-oscillation and the reflected wave is such that the amplitude of the membrane does not change. For example, the post-oscillation and the amplitude exhibit a phase shift of 2 / 3 n, or 120°. In this case, the arrival of the reflected wave cannot be determined because no change in amplitude is detectable.

[0081] To exclude this case, the second damping signal can be adjusted so that the post-oscillation after the first excitation and the post-oscillation after the second excitation are phase-shifted by n or 180 °.

[0082] In many applications of ultrasonic transducers, for example in the automotive sector, the intervals between two measuring cycles consisting of emitting an ultrasonic wave and detecting the reflected wave are so small that it can be assumed to be a good approximation that the first reflected wave and the second reflected wave have identical phases. This means that if the first or second post-oscillation overlaps with the reflected waves in such a way that no change in amplitude can be detected, the change in amplitude can be determined from the superposition with the other reflected wave. If measurement results can be determined from both measuring cycles, these can be averaged in order to increase the accuracy of the measurement results.A phase shift of 180° between the first post-oscillation and the second post-oscillation is achieved in particular by storing the flexible portion of the first damping signal in the memory unit. The flexible portion of the first damping signal is determined, for example, based on an amplitude of the damping mode as the first oscillation parameter.

[0083] Subsequently, a second vibration parameter, for example an amplitude, is recorded during the fixed portion of the second damping signal. The first and second vibration parameters can be different from one another. The first and second vibration parameters can, for example, be an amplitude of the membrane vibration at a fixed time or an amplitude of a specific frequency component of the membrane vibration.

[0084] The variable component of the second damping signal is determined based on the stored variable component of the first damping signal and the detected second vibration parameter. For example, to determine the variable component of the second damping signal, the amplitude of the diaphragm is superimposed on the variable component of the first damping signal. This method can achieve a phase shift of 180° between the first post-oscillation and the second post-oscillation.

[0085] Preferably, the first attenuation signal and the second attenuation signal have a common fixed component. The fixed component is stored, for example, in a first register of the memory unit. Furthermore, a method for operating an ultrasonic transducer is specified. The ultrasonic transducer described here can be operated, in particular, using the method for operating an ultrasonic transducer. This means that all features disclosed for the ultrasonic transducer are also disclosed for the method, and vice versa.

[0086] The method for operating an ultrasonic transducer comprising a membrane in a housing comprises the following steps:

[0087] - Excitation of the membrane to emit an ultrasonic wave, wherein a membrane oscillation comprising a stable transmission mode is excited with a transmission frequency,

[0088] - Damping a post-oscillation occurring after excitation, wherein a membrane oscillation comprising a stable damping mode is excited with a damping frequency, wherein the damping frequency and the transmission frequency are different.

[0089] These steps are performed in the order specified. Preferably, these steps are performed multiple times in succession.

[0090] In particular, the method achieves the advantages and effects explained above in connection with the embodiments of the ultrasonic transducer.

[0091] In one embodiment of the method, the post-oscillation is damped by applying a damping signal, the damping signal comprising a fixed component and a variable component. The variable component follows the fixed component in time. The fixed component is determined in particular before the excitation of the transmission mode. The variable component is preferably determined dynamically using at least one parameter of the post-oscillation, which is determined while the fixed component is being applied. As described above, by dividing the damping signal into a fixed component and a variable component, the computing time for optimizing the damping signal can be reduced and effective damping is enabled.

[0092] In a further embodiment of the method or one of the embodiments described above, the membrane is repeatedly excited to emit an ultrasonic wave, with damping occurring between two excitations by means of the damping signal. The fixed component of the damping signal is determined before the membrane is repeatedly excited. The variable component of the damping signal is determined during the damping of the post-oscillations based on at least one oscillation parameter of the post-oscillation.

[0093] This means that the variable component is continuously optimized and adjusted during operation of the ultrasonic transducer. To adapt the variable component, for example, fewer parameters, in particular just one parameter, of the damping signal are optimized. This reduces the parameter space that has to be optimized during operation of the ultrasonic transducer compared to optimizing the entire damping signal. This enables optimization of the damping signal during operation of the ultrasonic transducer. In a further embodiment of the method or one of the embodiments described above, the variable component of the first damping signal is stored in a second register of a memory unit during damping of a first post-oscillation with a first damping signal.During a subsequent damping of a second post-oscillation with a second damping signal, a second oscillation parameter of a second post-oscillation is detected and the variable component of the second damping signal is determined based on the detected second oscillation parameter and the stored variable component of the first damping signal, so that the first post-oscillation is 180° out of phase with the second post-oscillation.

[0094] With this method it is possible, as described above, to obtain a measurement signal regardless of the phase relationship between the first post-oscillation of the membrane and the reflected wave, in the event that the post-oscillation has not completely decayed after damping. The reason for this is that even if no changes in the amplitude of the membrane vibration can be detected due to the phase relationship between the first post-oscillation and the reflected wave, the reflected wave with the second post-oscillation leads to a change in amplitude because the first and second post-oscillations have a fixed phase relationship to one another. The phase relationship between the first and second post-oscillation is preferably achieved as described above.

[0095] Furthermore, a method for distance measurement is specified. The method for distance measurement uses an ultrasonic transducer described here, which is operated in particular with a method for operating an ultrasonic transducer described here. This means that all features disclosed for the method for operating the ultrasonic transducer and for the ultrasonic transducer are also disclosed for the method for distance measurement, and vice versa.

[0096] Preferably, the distance measurement method uses exactly one ultrasonic transducer. This means that the ultrasonic transducer serves both as a transmitter element for an ultrasonic wave and as a detector element for an ultrasonic signal reflected by the object to be measured.

[0097] In a transmitting mode, an ultrasonic signal, for example in the form of an ultrasonic wave, is emitted as a pulse from the ultrasonic transducer in the distance measurement process. After the pulse hits an object, it is at least partially reflected back. In a receiving mode, this reflected pulse is detected, allowing a propagation time to be determined. Since ultrasonic signals propagate in air and water at known sound speeds, the distance to the target to be measured can be calculated using the propagation time.

[0098] If the distance to the object is short, for example, less than 10 cm, the membrane's post-oscillation typically has not yet decayed after the pulse has been emitted in conventional ultrasonic transducers, which is why such ultrasonic transducers often cannot be used simultaneously as a transmitting and receiving element. With the ultrasonic transducer described here, it is possible to measure even particularly short pulse propagation times, i.e., particularly short distances, with just a single ultrasonic transducer, since effective damping of the membrane's post-oscillation is achieved.

[0099] In particular, the distance measurement method can be used to measure objects at a distance of between 4 cm and 2 m. In particular, distances of less than 10 cm can be measured.

[0100] Further advantages and advantageous embodiments and further developments of the method for operating an ultrasonic transducer and of the ultrasonic transducer emerge from the exemplary embodiments presented below in conjunction with schematic drawings. Identical, similar and similarly acting elements are provided with the same reference symbols in the figures. The figures and the relative sizes of the elements shown in the figures are not generally to scale. Rather, individual elements may be shown exaggeratedly large for clarity and / or clarity of understanding.

[0101] It shows :

[0102] Figures 1 to 3 show an ultrasonic transducer described here according to an embodiment,

[0103] Figure 4 is an illustration of a transmission mode,

[0104] Figure 5 is an illustration of an attenuation mode, Figure 6 is a graphical representation of an impedance of an ultrasonic transducer described here according to the embodiment,

[0105] Figures 7 to 11 show sectional views of an ultrasonic transducer described here according to several embodiments,

[0106] Figure 12 shows an example of an excitation signal and a damping signal as used in the method described here,

[0107] Figure 13 Possibilities for adapting a damping signal as used in the method described here,

[0108] Figure 14 is a schematic representation of a method described here for operating an ultrasonic transducer according to a first embodiment,

[0109] Figure 15 is a graphical representation of a post-oscillation of a membrane damped with a damping signal described here, compared to a membrane without a damping signal,

[0110] Figure 16 is a graphical representation of a frequency analysis of a post-oscillation of a membrane damped with a damping signal described here, compared to a membrane without a damping signal,

[0111] Figure 17 is a graphical representation of a signal of a damped membrane movement,

[0112] Figures 18 and 19 are graphic representations of signals of a reflected wave reflected from an object to be measured and received by the ultrasonic transducer,

[0113] Figure 20 is a schematic representation of a method described here for operating an ultrasonic transducer according to a second embodiment,

[0114] Figures 21 to 25 Illustrations of a superposition of reflected waves and a post-oscillation.

[0115] The ultrasonic transducer 1 according to Figures 1 to 3 has an excitation means 21, a damping means 22, a detection means 23 and an adaptation means 24. The excitation means 21, the damping means 22 and the detection means 23 comprise a piezoelectric element 2. The adaptation means 24 comprises control electronics 3. The control electronics 3 are designed to excite a membrane 4 coupled to the piezoelectric element 2. Due to an excitation, the membrane 4 can perform a movement 60. The piezoelectric element 2 and the membrane 4 are arranged in a housing 11. It is possible that the control electronics 3 is also arranged in the housing 11. The control electronics 3 comprise, for example, an application-specific integrated circuit (AS IC) or is integrated in an application-specific integrated circuit.

[0116] The excitation means 21 can excite the membrane 4 with an excitation signal 6 so that an ultrasonic wave 7 is emitted. After the ultrasonic wave 7 has been emitted, the membrane 4 typically continues to oscillate, i.e. it continues to perform an after-oscillation 40. When excited to emit the ultrasonic wave 7, the membrane 4 is excited to oscillate with a transmission mode 12. The transmission mode 12 is an eigenmode of the ultrasonic transducer 1 and has a maximum in a central region of the membrane 4 (see Figures 2 and 4). Oscillation nodes of the transmission mode 12 are preferably arranged in an edge region or at the edge of the membrane. As a result, the transmission mode 12 preferably has low attenuation.

[0117] To dampen the post-oscillation 40, the damping means 22 excites the membrane 4 to oscillate with a damping mode 55. The damping mode 55 has a significantly higher damping than the vibration mode 12. In particular, the damping mode 55 has a maximum in an edge region or at the edge of the membrane 4 (see Figures 3 and 5), whereby the damping mode 55 has a high dissipation or damping.

[0118] The housing 11 of the ultrasonic transducer 1 is a rotationally symmetrical pot housing and forms, for example, together with the membrane 4, the piezoelectric element 2, and the damping element 10, an oscillation system. The housing 11 and / or other elements of the oscillation system are adapted such that the transmission mode 12 and the damping mode 55 can be stably excited and are preferably eigenmodes of the ultrasonic transducer 1. For this purpose, the housing 11 has, for example, a side wall 14 with a thickness 15.

[0119] A stable damping mode 55 allows energy from the post-oscillation 40 to be effectively dissipated, and the post-oscillation 40 can be effectively damped. In particular, when the damping mode 55 is excited, part of the housing 11 oscillates. This means that the oscillation system is partially in motion. The oscillation system exhibits a housing movement 58, particularly at the side wall 14. The housing movement 58 allows the post-oscillation 40 to be further damped.

[0120] Figure 6 illustrates an impedance of the ultrasonic transducer 1 according to the present embodiment. In Figure 6, both the real part of the impedance 106 and the imaginary part of the impedance 107 are plotted as a function of a frequency 104 in kHz. The frequency 104 is an oscillation frequency of the membrane 4. In both the real part 106 and the imaginary part 107, the transmission mode 12 and the damping mode 55 can be seen as resonance modes or eigenmodes of the membrane 4. The transmission mode 12 has a transmission frequency 13 of approximately 75 kHz. The damping mode 55 has a damping frequency 56 of approximately 300 kHz.

[0121] Figures 7 to 11 show sectional views of an ultrasonic transducer 1 described here according to several exemplary embodiments. In each case, a sectional plane runs perpendicular to a main extension plane of a membrane 4 of the respective ultrasonic transducer 1. The ultrasonic transducers 1 according to Figures 7 to 11 are based in particular on the same functional principles and effects as the ultrasonic transducer 1 according to Figure 1. Therefore, the ultrasonic transducers 1, in particular according to Figures 7 to 11, also comprise excitation means 21, damping means 22, detection means 23 and adaptation means 24 as well as control electronics 3 and a piezoelectric element 2. In order to simplify the description, only the differences and special features of the ultrasonic transducers of Figures 7 to 11 compared to the ultrasonic transducer of Figure 1 are explained below.

[0122] The ultrasonic transducer 1 according to Figure 7 comprises a membrane 4 and a housing 11. The housing 11 has a side wall 14 that extends perpendicular to the main extension plane of the membrane 4. The housing is rotationally symmetrical.

[0123] The side wall 14 has a first region 14a with a thickness 15a. Furthermore, the side wall 14 has a second region 14b with a thickness 15b. The thickness 15a of the side wall 14 in the first region 14a is greater than the thickness 15b of the side wall 14 in the second region 14b.

[0124] The thicknesses 15a, 15b of the side wall 14 are in particular selected such that the transmission mode 12 and the damping mode 55 can be stably excited.

[0125] The housing 11 with the side wall 14 is, in particular, part of an oscillation system, to which the diaphragm 4 also belongs. Upon excitation of the damping mode 55, part of the oscillation system can be set in motion or oscillated. In particular, the second region 14b of the side wall 14 can perform a housing movement 58.

[0126] An interior of the housing 11 is filled with a first damping element 10a and a second damping element 10b. The first damping element 10a borders the membrane 4 and the first region 14a of the side wall 14. The second damping element 10b borders the first damping element 10a and the second region 14a of the side wall 14. The first damping element 10a is a silicone foam, for example, a foamed silicone. The second damping element 10b is a solid silicone. Thus, the second damping element 10b has a higher damping coefficient than the first damping element 10a.

[0127] The second damping element 10b is advantageously arranged adjacent to the second region 14b. In this region 14b, the housing movement 58 is excited upon excitation of the damping mode 55. Thus, the energy of the damping mode 55 can be effectively dissipated.

[0128] Figure 7 further illustrates that the membrane 4 has a membrane thickness 41. A ratio of the thickness 15a of the side wall 14 in the first region 14a to the membrane thickness 41 is preferably 3. This ratio of the thickness 15a of the side wall 14 to the membrane thickness 41 can suppress unwanted lateral radiation of an ultrasonic wave caused by vibration of an edge region of the membrane 4 in the region of the side wall 14.

[0129] In contrast to Figure 7, the control electronics 3 of the ultrasonic transducer 1 according to Figure 8 comprises a printed circuit board 34 on which an integrated circuit 33 is arranged. The integrated circuit 33 is, in particular, an AS IC. The control electronics 3 can be electrically contacted and controlled during operation via a line 35.

[0130] The printed circuit board 34 and the integrated circuit 33 are arranged at least partially in the interior of the housing 11. For example, the printed circuit board 34 is suspended in the second region 14b of the side wall 14. The printed circuit board 34 and the integrated circuit 33 are thus part of the oscillation system. The printed circuit board 34 and the integrated circuit 33 can thus be set in motion upon excitation of the damping mode 55 and contribute to damping the post-oscillation 40 of the membrane 4. Furthermore, the printed circuit board 34 and the integrated circuit 33 are preferably adapted such that the damping mode 55 and the transmission mode 12 can be excited in a stable manner.

[0131] Compared to Figure 7, the first region 14a of the side wall 14 of the housing 11 of the ultrasonic transducer 1 of Figure 9 has a greater thickness 15a. The thickness 15a is, in particular, such that the side wall 14 has a straight outer side. The outer side of the side wall 14 is a side of the side wall 14 that faces away from the interior of the housing 11 and is accessible from the outside. This means that the outer side does not have a step.

[0132] In contrast to Figure 8, the ultrasonic transducer 1 of Figure 10 has only one damping element 10. The damping element 10 is a silicone foam.

[0133] Furthermore, the side wall 14 has a thickness gradient. This means, in particular, that the thickness 15 of the side wall 14 decreases continuously in a direction away from the membrane 4. The thickness gradient is selected, in particular, such that the damping mode 55 and the transmission mode 12 can be stably excited.

[0134] In contrast to Figure 10, the ultrasonic transducer 1 in Figure 11 does not have a thickness gradient. The side wall 14 has a uniform thickness 14. The thickness 14 is adapted in particular such that the damping mode 55 and the transmission mode 12 can be excited in a stable manner. In the ultrasonic transducers 1 in Figures 10 and 11, the damping mode 55 preferably excites no or only an insignificant housing movement. The damping of the post-oscillation 40 takes place in particular by a movement of the membrane 4 in the edge region of the membrane 4. The damping thus takes place in particular by friction at the edge of the membrane 4.

[0135] To dampen the post-oscillation 40 of the membrane 4, a damping signal 5 can be applied to the ultrasonic transducer 1 according to one of the above embodiments, which follows the excitation signal 6 for exciting the transmission mode 12, as illustrated in Figure 12. The excitation signal 6 comprises rectangular pulses that are applied in a temporal sequence 102 with a voltage 101. The voltage 101 has a fixed amplitude, with a sign changing after each rectangular pulse.

[0136] In order to dampen the post-oscillation 40 of the membrane 4, the damping signal 5 for the damping means 22 is provided by means of the control electronics 3. The damping signal 5 comprises at least one damping pulse 50. The control electronics 3 is designed to define at least one parameter of the damping signal from the following parameters: number 51 of the damping pulses, width 52 of the damping pulses 50 and sequence 53 of the damping pulses 50. The damping signal 5 follows in particular immediately after the excitation signal 6. This means that there is no waiting time between the excitation signal 6 and the damping signal 5.

[0137] The damping signal 5 has a fixed component 5a and a variable component 5b which follows the fixed component 5a. To determine the fixed component 5a, for example, several of the above-mentioned parameters of the damping signal 5 are determined. The determination of the fixed component 5a preferably takes place before the excitation signal 6 is provided, using an oscillation parameter 8 of the post-oscillation 40. The oscillation parameter 8 is, for example, an amplitude of the post-oscillation 40 at a fixed point in time. By determining a plurality of parameters, the parameter space which must be optimized is relatively large and determining the fixed component 5a is time-consuming. By determining the fixed component 5a before the excitation signal 6 is provided, time-consuming optimization after the excitation of the membrane can be dispensed with.

[0138] The fixed component 5a of the damping signal 5 is configured, in particular, to reduce the amplitude of the post-oscillation 40. The variable component 5b is provided, in particular, to excite the damping mode 55.

[0139] For the variable component 5b, only one of the above-mentioned parameters is specified and optimized, while the other parameters are taken from the fixed component 5a. Thus, the parameter space to be optimized is much smaller, and optimization of the variable component 5b can occur while the fixed component 5b is being prepared.

[0140] Figure 13 illustrates options for adapting the damping signal 5, as used in the method described here for operating an ultrasonic transducer 1. Both the fixed component 5a and the variable component 5b of the damping signal 5 can be adapted according to the options shown in Figure 13, wherein preferably only one adaptation option is selected for the variable component 5b. The damping signal 5 comprises a plurality of damping pulses 50, all of which have the same amplitude. The signs of the damping pulses 50 can vary and are determined, for example, by the control electronics 3.

[0141] For example, the control electronics 3 determines the width 52 of the damping pulses 50. The width 52 results from the time 102 during which the voltage 101 is applied.

[0142] Furthermore, for example, the number 51 of damping pulses 50 is determined by the control electronics, as is a sequence 53 of the damping pulses 50. The sequence 53 of the damping pulses 50 indicates the temporal sequence in which the damping points 50 occur in the damping signal 5. Furthermore, the sequence 53 indicates the waiting time 54 after which a first damping pulse 50 occurs in the damping signal 5.

[0143] For the variable part 5b, for example, the sequence 53 is optimized.

[0144] Figure 14 illustrates a method described here for operating an ultrasonic transducer according to a first exemplary embodiment. The method can be carried out on the control electronics 3. The method comprises determining the fixed component 5a of the attenuation signal 5 by means of the adaptation means 24. The fixed component 5a is defined, for example, by means of an optimization algorithm such as a population algorithm. The fixed component 5a is stored in a memory unit 30 of the control electronics 3. For example, the fixed component 5a is stored in a first register 30a of the memory unit 30.

[0145] Optionally, the fixed component 5a is additionally determined based on an environmental parameter 32. The environmental parameter 32 is, for example, an ambient temperature and is determined using an environmental sensor 31, for example, a temperature sensor. The environmental parameter 32 can be stored in the memory unit 30.

[0146] During operation of the ultrasonic transducer, the membrane 4 is excited by means of the excitation means 21 and the excitation signal 6. After the ultrasonic wave 7 has been emitted, the post-oscillation 40 is damped by means of the damping means 22 and the fixed portion 5a of the damping signal 5 in order to reduce an amplitude of the post-oscillation 40. In this case, an oscillation parameter 8, for example an amplitude of the post-oscillation 40, is detected by the detection means 23 and the variable portion 5b of the damping signal 5 is determined by means of the adaptation means 24. For this purpose, a parameter of the damping signal 5 can be optimized while the fixed portion 5a is being provided.

[0147] Subsequently, the variable component 5b is provided, and the post-oscillation 40 is further damped by the damping means 22. In particular, the damping mode 55 is excited, and the post-oscillation 40 is effectively damped.

[0148] Subsequently, a reflected wave is detected by the detection means 23. From the time interval between the emission of the ultrasonic wave 7 and the detection of the reflected wave, a distance 105 to an object can be calculated and output as the result of a distance measurement.

[0149] Subsequently, the transmission of an ultrasonic wave 7 can be stimulated again, and a new distance 105 can be determined. The method just described is repeated, whereby the fixed component 5a of the attenuation signal 5 is not calculated at each repetition, but is retrieved by the attenuation means 22 from the first register 30a.

[0150] Figure 15 shows the signal of a membrane movement 62 of a membrane 4 that is damped using a method described here, in comparison to a comparative example of a membrane movement signal 63 that is not damped. The membrane movements can be converted into a voltage 101 (specified in V) via the piezoelectric effect, which voltage is plotted in Figure 4 as a function of time 102 (specified in ms). During excitation with the excitation means 21, a voltage 101 associated with both membrane movements 60, 61 is over 10 V. The excitation signal 6 is present for approximately 0.1 ms.

[0151] In the case of the membrane movement 60, the damping signal 5 immediately follows the excitation signal 6. The damping signal 5 is present for approximately 0.1 ms. A comparison of the curves of the voltages 101 of the damped membrane movement 60 and the undamped membrane movement of the comparison example shows that the voltage 101 of the damped membrane movement 60 is approximately two orders of magnitude lower than the voltage 101 of the comparison example from approximately 0.4 ms. The membrane movement 60 is therefore effectively damped by the damping signal 5. Dashed vertical lines in Figure 10 illustrate times at which, after an ultrasonic wave 7 has been emitted by the ultrasonic transducer 1 to an object 5 cm or 10 cm away, a wave reflected by the object reaches the ultrasonic transducer 1 again. A relationship between distance 105 and time results from the speed of sound of the ultrasonic wave 7 .For both an object at a distance of 5 cm and an object at a distance of 10 cm, the voltage 101 associated with the damped membrane movement 60 is approximately two orders of magnitude smaller than the voltage 101 associated with the undamped membrane movement 61. Thus, the distance to these objects with a damped membrane movement 60 can be effectively determined using the ultrasonic transducer.

[0152] Figure 16 illustrates which frequency components are present in the post-oscillation 40 of the membrane 4 when the damping signal 5 is applied and in a comparison example in which no damping signal 5 is applied. In this case, an amplitude 103 of an oscillation signal, which is obtained in particular from the membrane movements 60, 61, is shown as a function of the frequency 104 (specified in kHz). When the post-oscillation 40 is damped (compare curve 70), a damping mode 55 is excited. The damping mode 55 is not present in the comparison example. The damped membrane movement 60 is effectively damped by the damping mode 55.

[0153] Figure 17 shows a signal 80 of a damped membrane movement 60 as a voltage 101 specified in mV as a function of time 102 specified in ms. The signal 80 is detected, for example, after damping with the damping means 22 by the detection means 23. Figure 17 further illustrates that the signal 80 contains a frequency 81 of the excitation signal 6 and the damping mode 55. For this purpose, the signal 80 was filtered with a narrowband bandpass filter around the frequency 81 of the excitation signal 6 and the damping mode 55.

[0154] As can be seen in Figure 17, the signal 80 contains both the excitation signal 6 and the damping mode 55.

[0155] Figure 18 shows a signal 90 of an ultrasonic signal that was reflected by an object to be measured and is received by the ultrasonic transducer 1. The reflected ultrasonic signal generates a membrane movement 60, which can be represented as a voltage 101 in mV via the piezoelectric effect. The signal 90 contains a signal each with the frequency 91 of the excitation signal 6 and the damping mode 55, which can be represented from the signal 90 in a similar way to Figure 17.

[0156] As can be seen in Figure 18, the attenuation mode 55 accounts for only a small portion of the signal 90. Thus, the attenuation mode 55 only insignificantly influences the result of a distance measurement. Furthermore, a maximum of an envelope of the signal 90 is visible, which can be used to determine the distance of the object. In the present example, the distance of the object from the ultrasonic transducer is 15 cm.

[0157] In contrast to Figure 18, Figure 19 shows a comparison signal 95 of an ultrasonic signal reflected by the object to be measured, without damping the post-oscillation 40 of the membrane 4. As can be seen in Figure 19, the comparison signal 95 is essentially determined by a frequency 96 of the excitation signal 6, and an envelope of the comparison signal 95 decreases continuously. Therefore, the distance of the object from the ultrasonic transducer cannot be determined.

[0158] Furthermore, a comparison with Figure 18 shows that the comparison signal 95 has an amplitude one order of magnitude higher than the signal 90. This means that all information in the comparison signal 95, from which the distance of the object could be determined, is masked by the post-oscillation 40 of the membrane 4, so that the distance of the object cannot be determined.

[0159] Figure 20 illustrates a method described here for operating an ultrasonic transducer according to a second exemplary embodiment. As in the first exemplary embodiment of Figure 9, the fixed component 5a of the damping signal 5 is determined before the excitation of the membrane 4 with the excitation means 21 and stored in the first register 30a of the memory unit 30. In this case, the environmental parameter 32 can be taken into account.

[0160] As in the embodiment of Figure 9, the distance 105 is determined in a first measuring cycle 200, wherein the first variable component 5b of the first attenuation signal 5 of the first measuring cycle 200 is additionally stored in a second register 30b of the memory unit.

[0161] The first measurement cycle 200 is followed by a second measurement cycle 201, during which the membrane 4 is excited by the excitation signal 6 to emit a second ultrasonic wave 7. Subsequently, the second post-oscillation 40 of the membrane 4 is damped by means of the damping means 22 by providing the second fixed component 5aa of the second damping signal 57. The second fixed component 5aa is, in particular, identical to the first fixed component 5a and is retrieved from the first register 30a.

[0162] While the fixed component 5aa is provided, the detection means detects a second vibration parameter 9. The adaptation means 24 determines a second variable component 5bb of the second damping signal 57 from the second vibration parameter 9 and the first variable component 5b of the first damping signal 5.

[0163] Subsequently, the second variable portion 5bb is provided to the damping means 22 in order to further damp the second post-oscillation.

[0164] Subsequently, the detection means 23 detects a second reflected wave, from which a distance can be determined. The distance 105 is finally obtained as a result from the distance of the first measuring cycle 200 and the distance of the second measuring cycle 201. Subsequently, the measuring cycles 200, 201 can be repeated.

[0165] The method according to the second embodiment can be carried out in particular when, despite the effective damping with the damping means 22, the post-oscillation is not completely suppressed.

[0166] In this case, it is possible for a reflected ultrasonic wave to interfere with the post-oscillation. The result of the interference depends on the phase relationship between the reflected wave and the not fully decayed post-oscillation. As illustrated in Figures 21A to 21BC, interference between the reflected wave (illustrated by signal 90) and the not fully decayed post-oscillation (illustrated by signal 92) results in an amplitude of the membrane vibration of essentially zero (illustrated by signal 94). The phase shift between the reflected wave and the post-oscillation in this example is n or 180°.

[0167] As illustrated in Figures 22A to 22C, in another example, a superposition of the reflected wave (illustrated by signal 90) and the not fully decayed post-oscillation (illustrated by signal 92) results in an increased amplitude of the membrane vibration (illustrated by signal 94). The phase shift between the reflected wave and the post-oscillation is n / 2 or 90° in this example.

[0168] In another example, superposition of the reflected wave (illustrated by signal 90) and the not fully decayed post-oscillation (illustrated by signal 92) results in a substantially unchanged amplitude of the membrane vibration (illustrated by signal 94), as illustrated in Figures 23A to 23C. The phase shift between the reflected wave and the post-oscillation is 2 / 3 n or 120° in this example.

[0169] In the example of Figures 23A to 23C, no measurement of the distance is possible because the reflected wave does not lead to any change in the amplitude of the membrane vibration and thus the time of arrival of the reflected wave cannot be determined. In this case, a second ultrasonic wave 7 can be emitted in the second measuring cycle 201 using the method of Figure 20. Since the measuring cycles 200, 201 follow one another directly and the duration of a measuring cycle 200, 201 is relatively short, it can be assumed in many applications that the distance 105 and thus the reflected wave do not change or change only insignificantly between the measuring cycles 200, 201.

[0170] By the method of Figure 20, the second post-oscillation is damped in such a way that a second post-oscillation which has not completely decayed (illustrated by signal 93 in Figure 24) is phase-shifted by n or 180° relative to the first post-oscillation (illustrated by signal 92 in Figure 24). As a result, the second post-oscillation and the reflected wave have a phase relationship to one another such that, upon superposition, an amplitude of the membrane oscillation changes (illustrated by signal 94 in Figure 25). Thus, upon superposition of the second post-oscillation and the reflected wave, a change in the amplitude can be determined and the distance 105 can be determined.

[0171] The invention is not limited to the embodiments by the description thereof. Rather, the invention encompasses each new feature and each combination of features, which in particular includes each combination of features in the patent claims, even if this feature or combination itself is not explicitly stated in the patent claims or embodiments. This patent application claims the priority of the German

[0172] Patent application 102023111922.2, the disclosure of which is hereby incorporated by reference.

[0173] Reference sign

[0174] 1 ultrasonic transducer piezoelectric element

[0175] Control electronics

[0176] membrane

[0177] 5 Damping signal

[0178] 5a, 5aa fixed part of the damping signal

[0179] 5b, 5bb variable part of the damping signal

[0180] 6 Excitation signal

[0181] 7 Ultrasonic wave

[0182] 8 , 9 first, second vibration parameter

[0183] 10 Damping element

[0184] 10a, 10b first, second damping element

[0185] 11 housings

[0186] 12 Transmission mode

[0187] 13 Transmission frequency

[0188] 14 Side panel of the housing

[0189] 14a, 14b first, second area of ​​the side wall

[0190] 15 , 15a, 15b Thickness of the side wall

[0191] 21 stimulants

[0192] 22 Damping agents

[0193] 23 means of recording

[0194] 24 adjustment means

[0195] 30 storage units

[0196] 30a, 30b first, second register of the memory unit

[0197] 31 Environmental sensor

[0198] 32 environmental parameters

[0199] 33 integrated circuits

[0200] 34 circuit board

[0201] 35 Line

[0202] 40 Membrane reverberation

[0203] 41 Membrane thickness damping pulse

[0204] Number of damping pulses

[0205] Width of the damping pulse

[0206] Sequence of damping pulses

[0207] Waiting time

[0208] Damping mode

[0209] Damping frequency second damping signal

[0210] Case movement

[0211] Membrane movement

[0212] Signal of membrane movement

[0213] Frequency of membrane movement

[0214] Frequency of the comparison example

[0215] Signal of damped membrane movement, 91 , 96 Frequency of the excitation signal

[0216] Signal of the ultrasonic wave reflected from an object to be measured

[0217] Signal of the after-oscillation

[0218] Signal of the second post-oscillation

[0219] Superimposed signal

[0220] Comparison signal 1 Voltage 2 Time 3 Amplitude 4 Frequency 5 Distance 6 Real part of the impedance 7 Imaginary part of the impedance 0 , 201 first, second measurement cycle

Claims

Patent claims 1. Ultrasonic transducer (1) comprising a membrane (4) in a housing (11), an excitation means (21) and a damping means (22), wherein - the excitation means (21) is designed to excite the membrane (4) to excite an oscillation with a transmission mode (12) for emitting an ultrasonic wave (7), - the damping means (22) is designed to dampen any post-oscillation of the membrane (4) occurring after excitation, - the damping means (22) is further configured to excite at least one damping mode (55) which is different from the transmission mode (12), and - at least one side wall (14) of the housing (11) has at least one thickness (15) so that the transmission mode (12) and the damping mode (55) can be stably excited.

2. Ultrasonic transducer (1) according to claim 1, wherein a side wall (14) of the housing (11) has at least a first region (14a) and a second region (14b), and in the first region (14a) the side wall (14) has a thickness (15a) which is greater than a thickness (15b) of the side wall (14) in the second region (14b).

3. Ultrasonic transducer (1) according to claim 1 or 2, wherein the transmission mode (12) has a maximum in a central region of the membrane (4).

4. Ultrasonic transducer (1) according to one of the preceding claims, wherein the damping mode (55) has a maximum in an edge region of the membrane (4).

5. Ultrasonic transducer (1) according to one of the preceding claims, wherein the attenuation mode has a maximum in a region of the side walls of the housing.

6. Ultrasonic transducer (1) according to one of the preceding claims, wherein a ratio of a thickness (15) of the side wall (14) in a region bordering the membrane (4) to a membrane thickness (41) is 3.

7. Ultrasonic transducer (1) according to one of the preceding claims, wherein the housing (11) comprises at least one damping element (10) arranged in at least one region in which the damping mode (55) has a maximum.

8. Ultrasonic transducer (1) according to claim 7 with reference to at least claim 2, wherein a first damping element (10a) borders the first region (14a) of the side wall (14) and a second damping element (10b) borders the second region (14b) of the side wall (14), and the first damping element (10a) and the second damping element (14b) have different damping coefficients.

9. Ultrasonic transducer (1) according to one of the preceding claims, wherein the damping means (22) is arranged to: - to excite the membrane with a damping signal (5), wherein the damping signal (5) has a fixed component (5a) and a variable component (5b), - to excite the fixed part (5a) after exciting the membrane (4) with the excitation agent (21) and - to stimulate the variable part (5b) after the fixed part (5a).

10. Ultrasonic transducer (1) according to claim 9, wherein the damping means (22) is configured to excite the damping mode (55) by means of the variable portion (5b) of the damping signal (5).

11. Ultrasonic transducer (1) according to claim 9 or 10, further comprising a detection means (23) and an adaptation means (24), wherein - the detection means (23) is designed to detect at least one vibration parameter (8) of the post-oscillation during the excitation of the fixed component (5a) of the damping signal (5), and - the adaptation means (24) is designed to determine the variable component (5b) of the damping signal (5) during the excitation of the fixed component (5a) of the damping signal (5) on the basis of the detected vibration parameter (8).

12. Ultrasonic transducer (1) according to claim 11, wherein the adaptation means (24) is arranged to determine the fixed portion (5a) of the damping signal (5) before the excitation of the membrane (4) by the excitation means (21).

13. Ultrasonic transducer (1) according to claim 12, wherein the adaptation means (24) is arranged to determine the fixed component (5a) by means of a population algorithm, wherein an amplitude of the post-oscillation is used as a fitness parameter.

14. Ultrasonic transducer (1) according to one of claims 11 to 13, wherein the damping signal (5) comprises at least one damping pulse (50) and the adaptation means (24) is configured to define a plurality of the following parameters for the fixed portion (5a) of the damping signal (5) and precisely one of the following parameters for the variable portion (5b) of the damping signal (5): number (51) of the damping pulses (50), width (52) of the at least one damping pulse (50), sequence (53) of the at least one damping pulse (50).

15. Ultrasonic transducer (1) according to one of claims 11 to 14, further comprising at least one environmental sensor (31) for detecting at least one environmental parameter (32), wherein the adaptation means (24) is configured to determine the fixed component (5a) of the damping signal (5) taking into account the environmental parameter (32).

16. Ultrasonic transducer (1) according to claim 15, further comprising control electronics (3) with a memory unit (30), wherein the adaptation means (24) is configured to store the fixed portion (5a) in the memory unit (30) as a function of the environmental parameter (32).

17. Ultrasonic transducer (1) according to one of claims 11 to 16, where - the adaptation means (24) is designed to store the flexible portion (5b) of a first attenuation signal (5) in a second register (30b) of a memory unit (30), - the detection means (23) is designed to detect a second oscillation parameter (9) of the post-oscillation during the application of a fixed portion (5aa) of a second damping signal (57), - the adaptation means (24) is designed to determine a variable component (5bb) of a second damping signal (57) following the first damping signal (5) on the basis of the stored variable component (5b) of the first damping signal (5) and the detected second vibration parameter (9), - the damping means (22) is further configured to apply the second damping signal (57) to the membrane (4), and wherein - a post-oscillation of the membrane (4) which is damped with the first damping signal (5) has a phase shift of 180° compared to a post-oscillation of the membrane (4) which is damped with the second damping signal (57).

18. Ultrasonic transducer (1) according to claim 17, wherein the first attenuation signal (5) and the second attenuation signal (57) have a common fixed component (5a).

19. Method for operating an ultrasonic transducer (1) comprising a membrane (4) in a housing (11) with the following steps: - Excitation of the membrane (4) to emit an ultrasonic wave (7), wherein a membrane oscillation comprising a stable transmission mode (12) is excited with a transmission frequency (13), - Damping a post-oscillation occurring after excitation, wherein a membrane oscillation comprising a stable damping mode (55) is excited with a damping frequency (56), wherein the damping frequency (56) and the transmission frequency (13) are different.

20. The method according to claim 19, wherein - the damping of the post-oscillation is carried out by applying a damping signal (5), wherein the damping signal comprises a fixed component (5a) and a variable component (5b), - the variable portion (5b) follows the fixed portion (5a) in time, - the fixed component (5a) of the damping signal (5) is determined before the excitation of the transmission mode (12) and - the variable component (5b) is determined on the basis of at least one oscillation parameter of the post-oscillation, which is determined during application of the fixed component (5a).

21. The method according to claim 19, wherein - the membrane (4) is repeatedly excited to emit an ultrasonic wave (7) and between two excitations an attenuation takes place by means of the attenuation signal (5), - the fixed component (5a) of the damping signal (5) is determined before the membrane (4) is excited several times and - the variable component (5b) of the damping signal (5) is determined during each damping of the post-oscillation based on at least one oscillation parameter of the post-oscillation.

22. The method according to claim 21, wherein - during damping of a first post-oscillation with a first damping signal (5), the variable component (5b) of the first damping signal (5) is stored in a second register (30b) of a memory unit (30), - during a subsequent damping of a second post-oscillation with a second damping signal (57), a second oscillation parameter (9) of a second post-oscillation is detected and - the variable component (5bb) of the second damping signal (57) is determined on the basis of the detected second vibration parameter (9) and the stored variable component (5b) of the first damping signal (5), so that the first post-oscillation is phase-shifted by 180° with respect to the second post-oscillation.

23. Method for distance measurement, in which exactly one ultrasonic transducer (1) according to one of claims 1 to 18 is used and an object to be measured is measured at a distance of between 4 cm and 2 m inclusive.

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