DE102022128997A1 - Adapted control for ultrasonic transducers - Google Patents

Abstract

The invention relates to a use of non-linear frequency-modulated excitation signals (I) for an ultrasonic transducer (100), wherein air serves as a transmission medium for the operation of the ultrasonic transducer (100). The ultrasonic transducer (100) comprises a transmitter (101) and a receiver (102). The transmitter (101) is designed to receive the non-linear frequency-modulated excitation signal (I) and to transmit a transmission signal (II) in accordance with the excitation signal (I), wherein the transmission signal (II) is a burst signal with a specific temporal burst length, and wherein the transmission signal (II) has a mean frequency, which mean frequency lies in a frequency range between 20 kHz and 200 kHz, in particular in a frequency range between 30 kHz and 60 kHz. A frequency response of the transmission signal (II) sent by the transmitter (101) corresponds to a frequency response of the ultrasonic transducer (100). The invention further relates to methods for adapting a non-linear frequency-modulated excitation signal (I) for use in operating the ultrasonic transducer (100) as a function of a temperature of a transmission medium of the ultrasonic transducer, wherein the excitation signal (I) is generated in accordance with a temperature-dependent transfer function H(f,T) of the ultrasonic transducer (100).

Description

The invention relates to a use of non-linear frequency-modulated excitation signals (I) for an ultrasonic transducer.

The invention further relates to a method for adapting a non-linear frequency-modulated excitation signal for use in operating an ultrasonic transducer as a function of a temperature of a transmission medium of the ultrasonic transducer.

Chirp signals are used as transmission signals in ultrasonic systems for location methods, especially for distance measurement in the automotive sector, where air serves as the transmission medium.

A chirp signal is a signal whose frequency changes over time.

In order to filter out echo signals from distant reflecting objects from the noise of the received signal, a certain minimum energy must be received. However, for precise distance measurements, the shortest possible transmission pulses are required, since with a 1 ms transmission pulse a corresponding wave packet is already about 30 cm long. Increasing the transmission amplitude is hardly possible with conventional ultrasonic transducers.

A solution to this problem is the pulse compression method. In this method, a linear frequency modulated chirp pulse with a longer total duration is sent.

A linear chirp signal has a constant amplitude. The frequency of the linear chirp signal, on the other hand, increases or decreases linearly with time at a constant.

When the reflected signal (echo signal) is received, it is compressed into a considerably shorter pulse using special filters (matched filters) or mathematical methods. Due to the longer temporal excitation of the transmitted signal, the amplitude of the echo signal can be increased after processing by a matched filter. The received signal can therefore be easily detected.

This also increases the maximum achievable range.

In ultrasonic systems for locating objects where air serves as the transmission medium, linear chirp signals in a frequency range of approximately 30 kHz to 60 kHz are used.

Ultrasonic transducers have a bandpass behavior. If an ultrasonic transducer is excited by a broadband signal (short pulse, chirp signal), the efficiency is reduced due to the spectrum of the signal not matching the transfer function of the ultrasonic transducer.

However, especially in road traffic, a high efficiency of ultrasonic transducers that determine the distance of an object from a moving vehicle is relevant for safety reasons.

The task is therefore to achieve an improved signal-to-noise ratio for a location method using an ultrasonic transducer using air as a transmission medium.

In the field of non-destructive testing methods for the purpose of material testing, Pollakovsky et al. al (IEEE Transactions on ultrasonics, ferroelectrics, and frequency control, Vol.41, No.5, Sep. 1994 ) already showed that by taking into account the bandpass-like transfer function of an ultrasonic transducer and by using matched nonlinear chirp signals instead of linear chirp signals, the amplitude of echo signals of a chirp pulse compression system can be increased without changing the amplitude or duration of the transmission signal.

In material testing, ultrasound systems are used, among other things, to determine material properties without damaging the material being tested.
The non-destructive testing method using ultrasound control is carried out in accordance with standardized guidelines. A coupling agent (e.g. paste, gel, water or oil) is applied to the surface of the material to be tested. The surface to be tested is scanned using a test head that emits and receives ultrasound at a frequency of 0.02 MHz to 50 MHz.

Nonlinear frequency modulated chirp signals are sensitive to frequency shift.
As disclosed in Pollakowski et al., it is advantageous in the ultrasonic method for non-destructive material testing that the material to be tested does not move relative to the ultrasonic transducer, so that when using nonlinear frequency-modulated chirp signals, no Doppler effect occurs, which leads to a frequency shift.

Surprisingly, it was found that the use of nonlinear frequency modulated chirp signals disclosed by Pollakowski et al. nals in material testing using ultrasound of material surfaces that are not moving relative to the ultrasound system at ultrasound frequencies in the MHz range using coupling agents commonly used in material testing (e.g. gel, water or oil) to an ultrasound system, with air serving as the transmission medium and frequencies in the kHz range being used. In particular, it was found that the use of non-linear frequency-modulated chirp signals in such ultrasound systems leads to increased efficiency even when there is a relative movement of the object to be detected with respect to the ultrasound transducer.

für das Filter-Ausgangssignal z(t)=f_m(t)*(y(t)+n(t)), mit f_m(t) als Impulsantwort des matched Filters, maximiert, wobei, z²(t₀) die Signalstärke des Filter-Ausgangssignals z(t) am Zeitpunkt t₀ ist, an dem z(t) sein Maximum hat, und wobei E(N²(t)) die mittlere Stärke des Rauschprozesses ist.
Die Filterfunktion des matched Filters F_m(f) ist durch die Konjugation des komplexen Signalspektrums (X(f)H(f)) gegeben, wobei H(f) die Sende-Empfangs-Übertragungsfunktion des Ultraschallwandlers ist.The echo signals y(t) of a transmission system can be filtered with respect to a specific criterion (e.g. signal-to-noise ratio (SNR) or bandwidth).
Matched filtering is a method for detecting a known signal that is disturbed by noise. If a received signal y(t)+n(t), which consists of an echo signal y(t) and an additional noise signal n(t), is filtered using a matched filter F _m (f), the signal-to-noise ratio SNR is $$\text{SNR}=\frac{{\text{z}}^2\left({\text{t}}_0\right)}{\text{E}\left({\text{N}}^2\left(\text{t}\right)\right)}$$

for the filter output signal z(t)=f _m (t)*(y(t)+n(t)), with f _m (t) as the impulse response of the matched filter, where z ² (t ₀ ) is the signal strength of the filter output signal z(t) at time t ₀ at which z(t) has its maximum, and where E(N ² (t)) is the average strength of the noise process.
The filter function of the matched filter F _m (f) is given by the conjugation of the complex signal spectrum (X(f)H(f)), where H(f) is the transmit-receive transfer function of the ultrasonic transducer.

Such matching of the transmission signal to the transfer function can be achieved by means of nonlinear frequency modulation of chirp signals.
Nonlinear frequency modulation offers the advantage that a spectrum of a transmission signal can be shaped in a predetermined manner by means of a suitable modulation. In this way, chirp signals suitable for an ultrasonic transducer, so-called matched nonlinear modulation technique signals (MNLFM signals), can be generated.

berechnen für 0≤t≤T_Chirp, und wobei C₁ und C₂ Konstanten sind.Due to the fact that the pulse compression filter is an all-pass filter, i.e. |F(f)|=1, the necessary form of the transmission signal spectrum X(f) is given by |X(f) | = | H(f) |, where H(f) corresponds to the frequency-dependent transmit-receive transfer function of the ultrasonic transducer. A nonlinear frequency-modulated chirp signal x(t) which approximates this spectrum can be correspondingly given by $$\text{x}\left(\text{t}\right)=\text{sin}\left(2\mathrm{\pi }{\displaystyle {\int }_0^{\text{t}}\frac{1}{2\mathrm{\pi }}}{\left[{\displaystyle {\int }_0^{\text{e}}{\text{C}}_1}{|\text{H}\left(\text{v}\right)|}^2\text{dv}+{\text{C}}_2\right]}^{-1}\text{d}\mathrm{\tau }\right)$$

calculate for 0≤t≤T _Chirp , and where C ₁ and C ₂ are constants.

Since the amplitude of chirp signals is constant, such an excitation signal can be realized with a simple driver circuit. This switches back and forth between a positive and negative voltage.

In the present invention, a nonlinear frequency-modulated excitation signal generated in this way is used for an ultrasonic transducer, with air serving as a transmission medium for the operation of the ultrasonic transducer.

In particular, the ultrasonic transducer comprises a transmitter and a receiver.

In particular, the transmitter is configured to receive the non-linear frequency-modulated excitation signal and to transmit a transmission signal corresponding to the excitation signal.

In particular, the excitation signal specifies a voltage with which the transmitter generates the transmission signal.

In particular, the transmission signal is a burst signal with a specific temporal burst length. In particular, the transmission signal has a mean frequency. In particular, the mean frequency of the transmission signal is in a frequency range between 20 kHz and 200 kHz. In particular, the mean frequency of the transmission signal is in a frequency range between 30 kHz and 60 kHz. In particular, a frequency response of the transmission signal sent by the transmitter corresponds to a frequency response of the ultrasonic transducer.

In particular, the transmission signal sent as a burst signal has the form of a chirp signal.

In one use, the receiver of the ultrasonic transducer is configured to receive an echo signal. In particular, the echo signal is a transmission signal reflected from an object. In particular, the receiver is configured to amplify the received echo signal, in particular to amplify it in analog form.
In particular, the receiver is configured to sample the received echo signal. In particular, the receiver is configured to demodulate the received echo signal.

In one use, the receiver is configured to send a received signal to a filter. In particular, the received signal comprises the echo signal amplified by the receiver. In particular, the received signal corresponds to the echo signal amplified by the receiver. In particular, the received signal sent by the receiver to the filter comprises noise n(t) caused by the electronics of the receiver.
In particular, the filter is integrated into the ultrasonic transducer.

In particular, the filter is located outside the ultrasonic transducer.

In one use, the filter is designed to receive and filter the received signal. In particular, the filter is designed to take into account a phase response of the ultrasonic transducer.
In particular, the filter is designed to filter out the noise n(t) from the received signal.

In one use, the filter is configured to send a filter output signal. In particular, the filter output signal comprises the filtered received signal. In particular, the filter output signal corresponds to the filtered received signal.

In one use, the ultrasonic transducer is excited with an impulse response of the ultrasonic transducer.

In one use, the excitation signal has arbitrary voltage values. In particular, the excitation signal has only two voltage levels. In particular, the excitation signal is a square wave signal.

In one use, a transfer function H(f) of the ultrasonic transducer is measured. In particular, the excitation signal is non-linearly frequency modulated in correlation with the transfer function of the ultrasonic transducer.

berechnen, wobei 0≤t≤T_Chirp, und wobei T_Chirp einer zeitlichen Dauer des Anregungssignals entspricht.In one application, the excitation signal can be converted to the transfer function H(f) of the ultrasonic transducer $${\text{x}}_{\text{r}}\left(\text{t}\right)=\text{sign}\left(\text{sin}\left(2\mathrm{\pi }{\displaystyle {\int }_0^{\text{t}}\frac{1}{2\mathrm{\pi }}}{\left[{\displaystyle {\int }_0^{\text{e}}{\text{C}}_1}{|\text{H}\left(\text{v}\right)|}^2\text{dv}+{\text{C}}_2\right]}^{-1}\text{d}\mathrm{\tau }\right)\right)$$

where 0≤t≤T _Chirp , and where T _Chirp corresponds to a temporal duration of the excitation signal.

bestimmen, wobei X(f) der Fouriertransformierten des Anregungssignals x_r(t) entspricht, und wobei H(f) der Übertragungsfunktion des Ultraschallwandlers entspricht. In one use, a filter function F(f) of the filter can be expressed by the complex conjugation $$\text{F}\left(\text{e}\right)=\left(\text{X}\left(\text{e}\right)\text{H}\left(\text{e}\right)\right)*$$

where X(f) corresponds to the Fourier transform of the excitation signal x _r (t), and where H(f) corresponds to the transfer function of the ultrasonic transducer.

Measurements using ultrasound systems in material testing sometimes take place during the manufacturing process of the material to be tested in a factory hall at almost constant temperatures.
For ultrasonic systems that are not operated at constant temperatures, especially in ultrasonic systems where air is used as the transmission medium, the transmit-receive transfer function H(f) may vary depending on the temperature, so it should be corrected according to the ambient temperature, especially the temperature of the transmission medium, in order to achieve high efficiency.

This raises the further task of temperature-dependent adaptation of the transfer function of an ultrasonic transducer.

The object is achieved by a method for adapting a non-linear frequency-modulated excitation signal for use in an ultrasonic transducer as a function of a temperature of a transmission medium of the ultrasonic transducer.

In particular, the excitation signal is generated according to a temperature-dependent transfer function H(f, T) of the ultrasonic transducer.

In particular, the transmission medium is air.

In particular, the temperature-dependent transfer function H(f,T) is determined empirically by a calibration measurement.

In particular, during operation, an excitation signal adapted to the temperature-dependent transfer function H(f,T) is selected using a known temperature value. In particular, the known temperature value is a measured temperature value.

In particular, the known temperature value is determined by the ultrasonic sensor. In particular, the known temperature value is provided by an external control device. In particular, the known temperature value is a temperature value stored in a database.

In one embodiment, the excitation signal is generated in correlation to a temperature value measured by a temperature sensor.

In particular, the temperature sensor is integrated into the ultrasonic transducer.

In particular, the temperature sensor is located outside the ultrasonic transducer.

In one embodiment, the excitation signal is generated in correlation to a temperature value stored in a database.

In particular, the database is integrated into the ultrasound transducer.

In particular, the database is located outside the ultrasound transducer.

In particular, the temperature value stored in the database corresponds to a temperature value according to a weather forecast for a current point in time at a current geographical location.

In particular, the temperature value stored in the database corresponds to a temperature value measured by a weather station, in particular for the current geographical location and the current time.

In particular, the temperature value stored in the database corresponds to a temperature value averaged over a certain period of time from statistically determined temperature values for a specific date, which corresponds to a current date, for the current geographical location.

In particular, the ultrasonic transducer comprises a device which is designed to determine the current geographical location of the ultrasonic transducer.

The use of NLFM excitation signals for an ultrasonic transducer offers the advantage that the NLFM excitation signal can be adapted according to the transfer function of the ultrasonic transducer. This results in an echo signal reflected by an object that has a significantly larger amplitude than an echo signal using an LFM excitation signal.

Due to the increased amplitude of the echo signal, after filtering out noise caused by electronic components, a significantly improved filter output signal with a higher amplitude is obtained, so that the object reflecting the transmitted signal can be located much more precisely.

This is particularly advantageous in road traffic, where an object is located and, if necessary, identified by means of an ultrasonic transducer that uses excitation signals in the kHz range and uses air as a transmission medium.

Further advantageous embodiments, features and functions of the invention are explained in connection with the examples shown in the figures.

• 1 schematische Darstellung einer Verwendung NLFM-Anregungssignale für einen Ultraschallwandler;
• 2 Signalformen für LFM-Signale und NLFM-Signale in einem Betrieb eines Ultraschallwandlers für eine Bandweite von 4kHz
  1. A) Anregungssignale im Vergleich zur Übertragungsfunktion des Ultraschallwandlers;
  2. B) zeitliche Frequenz-Änderung der Anregungssignale;
  3. C) Filter-Ausgangssignale für ein LFM-Anregungssignal und ein NLFM-Anregungssignal im Vergleich
• 3 Signalformen für LFM-Signale und NLFM-Signale in einem Betrieb eines Ultraschallwandlers für eine Bandweite von 12kHz
  1. A) Anregungssignale im Vergleich zur Übertragungsfunktion des Ultraschallwandlers;
  2. B) zeitliche Frequenz-Änderung der Anregungssignale;
  3. C) Filter-Ausgangssignale für ein LFM-Anregungssignal und ein NLFM-Anregungssignal im Vergleich
• 4 schematische Darstellung einer temperaturabhängigen Anpassung von NLFM-Anregungssignalen zur Verwendung für einen Ultraschallwandler;
• 5 Übertragungsfunktionen und Signalformen für NLFM-Signale in einem Betrieb eines Ultraschallwandlers für verschiedenen Temperaturen des Übertragungsmediums
  1. A) NLFM-Anregungssignale im Vergleich zur Übertragungsfunktion des Ultraschallwandlers;
  2. B) zeitliche Frequenz-Änderung der NLFM-Anregungssignale;
  3. C) Filter-Ausgangssignale für die jeweiligen NLFM-Anregungssignale im Vergleich

This shows:

• 1 schematic representation of a use of NLFM excitation signals for an ultrasonic transducer;
• 2 Waveforms for LFM signals and NLFM signals in an ultrasonic transducer operation for a bandwidth of 4kHz
  1. A) Excitation signals compared to the transfer function of the ultrasonic transducer;
  2. B) temporal frequency change of the excitation signals;
  3. C) Filter output signals for an LFM excitation signal and an NLFM excitation signal in comparison
• 3 Waveforms for LFM signals and NLFM signals in an ultrasonic transducer operation for a bandwidth of 12kHz
  1. A) Excitation signals compared to the transfer function of the ultrasonic transducer;
  2. B) temporal frequency change of the excitation signals;
  3. C) Filter output signals for an LFM excitation signal and an NLFM excitation signal in comparison
• 4 schematic representation of a temperature-dependent adaptation of NLFM excitation signals for use in an ultrasonic transducer;
• 5 Transfer functions and waveforms for NLFM signals in an ultrasonic transducer operation for different temperatures of the transmission medium
  1. A) NLFM excitation signals compared to the transfer function of the ultrasonic transducer;
  2. B) temporal frequency change of the NLFM excitation signals;
  3. C) Filter output signals for the respective NLFM excitation signals in comparison

1 shows a schematic representation of a use of nonlinear frequency modulated (NLFM) excitation signals I for an ultrasonic transducer 100.

The NLFM excitation signal I provides the transmitter 101 of the ultrasonic transducer 100 with a voltage according to which the transmitter 101 transmits a transmission signal II. The transmission signal II transmitted by the transmitter 101 is an NLFM chirp signal.

The chirp signal sent as transmission signal II is in particular a burst signal. A burst signal is a signal of a certain temporally predetermined length, also called burst length.

The transmission signal II is thus an NLFM chirp signal with a certain predetermined burst length.

The transmitted signal II is reflected by an object 200.

A receiver 102 of the ultrasonic transducer 100 receives the echo signal III reflected from the object 200.

The receiver 102 amplifies the received echo signal III, in particular in analog form.

In addition, the receiver 102 samples the received echo signal III. The receiver 102 then demodulates the received echo signal III.

The receiver 102 then sends the processed echo signal III as a received signal IV to a filter 103.

The received signal IV contains noise caused by the electronics of the receiver 102. This noise is therefore device-specific and follows a known time-dependent function, so that the filter 103 can filter out the noise from the received signal IV on the basis of this known function.

After filtering, the filter output signal V of the filter 103 is used for further processing to locate the object 200 and, if necessary, to identify the type of object 200.

In the 1 In the embodiment shown, the filter 103 is arranged outside the ultrasonic transducer 100. However, the filter 103 can also be integrated in the ultrasonic transducer 100.

2 and 3 show in comparison the signal curves for a linear frequency modulated chirp signal (dashed line) and for a nonlinear frequency modulated chirp signal (dotted line) in function as an excitation signal of an ultrasonic transducer for a frequency range from 30kHz to 50kHz.

In 2 The bandwidth of the transfer function of the ultrasonic transducer is 4kHz.

In 3 The bandwidth of the transfer function of the ultrasonic transducer is 12kHz.

In both examples, the maximum value of the bell-shaped transfer function is at a frequency of 40kHz.

2A and 3A show an LFM chirp excitation signal (dashed line) and an NLFM chirp excitation signal (dotted line), as well as the bell-shaped transfer function of the ultrasonic transducer.

In 2A The bell-shaped transfer function of the ultrasonic transducer has a steeply rising edge in the range from 35kHz to its maximum at 40kHz.

The LFM excitation signal has a steep rising edge at a frequency of approximately 35kHz to 37.5kHz, whereby the amplitude of the LFM excitation signal in this frequency range has a higher value than the amplitude of the transfer function.

The bell-shaped transfer function of the ultrasonic transducer has a steeply falling edge from its maximum at 40kHz to a frequency of about 45kHz.

The LFM excitation signal has a steeply falling edge at a frequency of approximately 42.5 kHz to 45 kHz, whereby the amplitude of the LFM excitation signal in this frequency range also has a higher value than the amplitude of the transfer function.

In a middle frequency range of 37.5kHz to 42.5kHz, where the transfer function has its maximum, the LFM excitation signal has a mean amplitude which is much lower than the amplitude of the transfer function.

Thus, the portion of the LFM excitation signal that overlaps with the transfer function of the ultrasonic transducer is much smaller than the LFM excitation signal.

Excitation of the ultrasonic transducer with the LFM excitation signal is therefore not very effective, especially since the amplitude of the LFM excitation signal in the maximum range of the transfer function is significantly lower than the amplitude of the transfer function.

The NLFM excitation signal is narrower than the LFM excitation signal and has a significantly higher maximum amplitude than the LFM excitation signal.
When looking at the adjusted NLFM excitation signal, it can be seen that the NLFM excitation signal matches the transfer function of the ultrasonic transducer well. The rising and falling edges, as well as the maxima of the NLFM excitation signal and the transfer function, are almost on top of each other in a frequency range of about 37 kHz to 43 kHz, so that when the ultrasonic transducer is excited using the adjusted NLFM excitation signal, there are negligible losses.

These differences between the LFM excitation signal and the NLFM excitation signal compared to the transfer function of the ultrasonic transducer can be 3A (Bandwidth of the transfer function 12kHz) can be seen even more clearly.

2 B and 3B show the change in the frequency of the 2A or. 3A shown LFM excitation signal and NLFM excitation signal in relation to the temporal length of the respective excitation signal.

The frequency of the LFM excitation signal increases linearly over time.

The frequency of the NLFM excitation signal also increases over time, but not in a constant linear manner like the LFM excitation signal.

2C and 3C show the corresponding filter output signals for an LFM excitation signal and NLFM excitation signal and a transfer function corresponding 2A or. 3A .

The dotted line represents the corresponding filter output signal to the NLFM excitation signal. The dashed line represents the corresponding filter output signal to the LFM excitation signal.

The filter output signal corresponding to the NLFM excitation signal (dotted line) has a significantly higher amplitude than the filter output signal corresponding to the LFM excitation signal (dashed line).

The significantly higher amplitude of the filter output signal corresponding to the NLFM excitation signal enables more precise location and/or detection of objects at which a transmission signal sent by the ultrasonic transducer is reflected.

Using NLFM excitation signals to excite an ultrasonic transducer is therefore significantly more effective than using LFM excitation signals to excite the ultrasonic transducer.

The NLFM excitation signal can be a sinusoidal NLFM chirp signal or a square wave NLFM chirp signal.

Since the amplitude of a chirp signal does not carry any information, but only the time-varying phase, there is no informal difference whether the NLFM excitation signal is a sinusoidal NLFM chirp signal or a square-wave NLFM chirp signal whose phase changes in the same way over time.

4 shows a schematic representation of a temperature-dependent adaptation of NLFM excitation signals I for use in an ultrasonic transducer 100, as in 1 shown.

The transfer function of the ultrasonic transducer 100 changes with the temperature of the air serving as the transmission medium.

Thus, it may happen that an NLFM chirp excitation signal adapted to a transfer function at room temperature (approx. 20°C) leads to a filter output signal of inferior quality if the temperature of the air serving as the transmission medium deviates from a temperature corresponding to room temperature.

The temperature-dependent adaptation of the NLFM excitation signal I is carried out with the aid of a temperature sensor 104 and/or with the aid of a database 105.

The temperature sensor 104 is configured to detect a temperature value for the air that serves as a transmission medium of the ultrasonic transducer 100.

The transfer function H(f,T) of the ultrasonic transducer is calculated using the temperature value determined by the temperature sensor 104.

The NLFM excitation signal I is then adjusted according to the transfer function of the ultrasonic transducer 100 calculated for the measured temperature.

Alternatively, the temperature adjustment of the NLFM excitation signal I can be carried out using a temperature value stored in the database 105.

This stored temperature value may be a temperature value according to a current weather forecast for the current location of the ultrasonic transducer.

Alternatively, the stored temperature value may be a statistical temperature value corresponding to an average value, in particular an arithmetic mean value, for an air temperature in correlation with a time and a location, wherein the time and the location correspond to the current time and the current location of the ultrasonic transducer.

For example, if the ultrasonic transducer is used on January 1st, the database 105 calculates an average of all temperature values stored for January 1st for the current location.

In particular, the database 105 is connected to the temperature sensor 104. In particular, a current temperature value measured by the temperature sensor 104 is stored in the database 105 together with the associated location and the associated date and in particular with the associated time.

In particular, GPS coordinates of the location of the ultrasonic transducer are determined to detect the current location of the ultrasonic transducer.

5A shows the transfer function of an ultrasonic transducer for different temperatures of the ambient air, which serves as the transmission medium, as well as the spectra for the respective temperature-dependent transfer function adapted NLFM excitation signals for exciting the ultrasonic transducer.

The shape and amplitude of the transfer function of the ultrasonic transducer varies greatly depending on the temperature of the air serving as the transmission medium.

The higher the temperature of the ambient air of the ultrasonic transducer, the lower the amplitude and wider the bandwidth of the transfer function of the ultrasonic transducer.

Accordingly, the NLFM excitation signal must be adapted to the transfer function changed by the ambient temperature in order to avoid large losses in effectiveness.

5B shows the modulation frequencies for the 5A NLFM excitation signal spectra shown.
The higher the temperature of the ambient air of the ultrasonic transducer, the more the modulation frequency must increase over time so that the corresponding NLFM excitation signal is ideally adapted to the transfer function for the corresponding temperature.

5C shows the corresponding filter output signals for the 5A NLFM excitation signal spectra shown.

Like the amplitudes of the NLFM excitation signals, the amplitude of the corresponding filter output signal also decreases with increasing temperature.

However, while the width of the signal spectra of the NLFM excitation signals increases with increasing air temperature, the width of the corresponding filter output signal decreases with increasing air temperature.

This results in a clear filter output signal for each temperature of the ambient air of the ultrasonic transducer, which can be easily filtered out from a noise signal.

List of reference symbols

100

Ultrasonic transducer

101

Channel

102

Recipient

103

filter

104

Temperature sensor

105

Database

200

Object

I

Excitation signal

II

Transmission signal

III

Echo signal

IV

Reception signal

V

Filter output signal

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions.

Cited non-patent literature

• Pollakovsky et al. al (IEEE Transactions on ultrasonics, ferroelectrics, and frequency control, Vol.41, No.5, Sep. 1994 [0014]

Claims (14)

Use of non-linear frequency-modulated excitation signals (I) for an ultrasonic transducer (100) comprising a transmitter (101) and a receiver (102), wherein the transmitter (101) is designed to receive the non-linear frequency-modulated excitation signal (I) and to transmit a transmission signal (II) in accordance with the excitation signal (I), wherein the transmission signal (II) is a burst signal with a specific temporal burst length, wherein the transmission signal (II) has a mean frequency, which mean frequency lies in a frequency range between 20 kHz and 200 kHz, in particular in a frequency range between 30 kHz and 60 kHz, wherein a frequency response of the transmission signal (II) transmitted by the transmitter (101) corresponds to a frequency response of the ultrasonic transducer (100), and wherein air serves as the transmission medium for the operation of the ultrasonic transducer (100). Use according to Claim 1 , characterized in that the burst signal has the form of a chirp signal. Use in accordance with any of the Claims 1 until 2 , characterized in that the receiver (102) is adapted to receive an echo signal (III) reflected by an object (200). Use according to one of the preceding claims, characterized in that the receiver (102) is arranged to send a received signal (IV) to a filter (103). Use according to Claim 4 , characterized in that the filter (103) is adapted to receive and filter the received signal (IV), wherein the filter (103) is adapted to take into account a phase response of the ultrasonic transducer (100). Use in accordance with any of the Claims 4 until 5 , characterized in that the filter (103) is arranged to send a filter output signal (V), wherein the filter output signal (V) comprises the filtered received signal (IV). Use according to one of the preceding claims, characterized in that the ultrasonic transducer (100) is excited with an impulse response of the ultrasonic transducer (100). Use according to one of the preceding claims, characterized in that the excitation signal (I) has any voltage values, in particular has only two voltage levels. Use according to one of the preceding claims, characterized in that a transfer function H(f) of the ultrasonic transducer (100) is measured and that the excitation signal (I) is non-linearly frequency modulated in correlation with the transfer function of the ultrasonic transducer (100). Use according to one of the preceding claims, characterized in that the excitation signal (I) with the transfer function H(f) of the ultrasonic transducer (100) is $$x_r\left(t\right)=siGn\left(\text{sin}\left(2\pi {\displaystyle {\int }_0^t\frac{1}{2\pi }}{\left[{\displaystyle {\int }_0^e{C}_1}{|H\left(v\right)|}^{2}dv+C_2\right]}^{-1}d\tau \right)\right)$$

where 0≤t≤T _Chirp , and where T _Chirp corresponds to a temporal duration of the excitation signal. Use according to one of the preceding claims, characterized in that a filter function F(f) of the filter (103) is determined by the complex conjugation $$F\left(e\right)=\left(X\left(e\right)H\left(e\right)\right)*$$

where X(f) corresponds to the Fourier transform of the excitation signal x _r (t), and where H(f) corresponds to the transfer function of the ultrasonic transducer (100). Method for adapting a non-linear frequency-modulated excitation signal (I) for use in operating an ultrasonic transducer (100) according to one of the preceding claims as a function of a temperature of a transmission medium of the ultrasonic transducer, wherein the excitation signal (I) is generated in accordance with a temperature-dependent transfer function H(f,T) of the ultrasonic transducer (100). Procedure according to Claim 12 , characterized in that the excitation signal (I) is generated in correlation to a temperature value measured by means of a temperature sensor (104). Procedure according to one of the Claims 12 until 13 , characterized in that the excitation signal (I) is generated in correlation to a temperature value stored in a database (105).

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