DE102009025463A1 - Assembly for determining sonic speeds and distances in e.g. fluid media, using ultrasound of ultrasonic imaging system, has evaluation unit determining variable sonic speed by determining parameters of point reflector at various locations - Google Patents

Abstract

The assembly (10) has a transmission signal generator (1) generating an electrical transmission signal on a channel (14). A transceiver switch (2) provides communication between transmission and receiving signals. Controlled elements (31-33) of an ultrasonic transducer (3) transmit ultrasonic waves into a detected medium (4). An evaluation unit (8) determines an average sonic speed in the medium to a point reflector (5) and distance of the reflector from the transducer, and determines a variable sonic speed by determining reflector's parameters at various locations. An independent claim is also included for a method for determining variable sonic speeds and distances in media using ultrasound.

Description

The invention relates to an arrangement and a method for determining layer thicknesses and sound velocities in media with the aid of ultrasound, comprising a transmission signal generator which generates electrical transmission signals on n ≥ 1 channels, an ultrasonic transducer with m ≥ 1 elements, which receives the transmission signals from the transmission signal generator and whose driven elements transmit an ultrasonic wave into the medium having one or more layers, the ultrasonic transducer receiving the reflected ultrasonic wave and converting it into received electrical signals, a gain unit receiving and amplifying the received electrical signals, a receiving unit receiving the amplified received signals of an analogue Digital conversion for training digital signals supplies, as well as an evaluation that includes the digital signals from the recording unit in the evaluation.

Measurements by means of ultrasound are performed on the one hand to detect defects, to measure layer thicknesses or to visualize structures in technical areas or in medicine, such as tissue structures and organ boundaries. The speed of sound is assumed to be given.

On the other hand, the speed of sound is also of particular interest because it is an important parameter for a solid or liquid substance. The knowledge of the speed of sound is the prerequisite for an accurate topography and layer thickness determination for the individual layers. It can also provide unknown material parameters for hidden, inaccessible structures.

Conventional technical measuring methods, however, require knowledge of the length of the sound propagation path for measuring the speed of sound. For this purpose, either an external reference reflector or a receiving transducer to place at a predetermined position. In practice, however, this is not always possible, especially if there is a lack of space for the measurement setup, if chemically aggressive liquids are present or the destruction of the measurement object with respect to solids is imminent.

A determination of the speed of sound at unknown layer thickness is practically impossible or only possible with great effort. Mechanically, the spatially resolved determination of the speed of sound is only possible with accessible layers or with optical methods only with transparent layers.

A method for determining the layer thickness and the speed of sound in a tube by means of ultrasonic pulses is in the document US 2002134159 described in which the data for calculating the speed of sound and the layer thickness of a series of transmitted and reflected ultrasonic waves are determined, wherein at least one of the waves is transmitted without presence of the measurement object in the transmission path.

A device and a method for calibration and ultrasonic measurement of cylindrical test specimens is in the document DE 50 305 421 T described, wherein a plurality of parameters of the test pattern are determined simultaneously. There is the determination of several sound propagation times for several distances in the calibration unit and the current speed of sound of the water by means of an optical or mechanical distance determination.

The invention has for its object to provide an arrangement and a method for determining layer thicknesses and sound velocities in media using ultrasound, which are designed so suitable that both the structure-related and the evaluation-related effort for sound velocity determination and layer thicknesses in the media is reduced , In particular, external reference reflectors should be saved. Furthermore, the accuracy of the determination of the speed of sound is to be increased.

The object is solved by the features of claims 1 and 8.

The arrangement for determining layer thicknesses and sound velocities in media using ultrasound consists of
a transmission signal generator which generates electrical transmission signals on n ≥ 1 channels,
an ultrasonic transducer having m ≥ 1 elements, which receives the transmission signals from the transmission signal generator and whose driven elements transmits an ultrasonic wave into the medium having one or more layers, the ultrasonic transducer receiving the reflected ultrasonic wave and converting it into electrical reception signals, and
an amplification unit that receives and amplifies the received electrical signals,
a receiving unit that supplies the amplified received signals to an analog-to-digital conversion to form digital signals,
and an evaluation unit which incorporates the digital signals from the recording unit into the evaluation,
wherein according to the characterizing part of patent claim 1
in the central region of the ultrasound transducer there is a central receiving element which receives the reflected ultrasonic waves in the element present there, which transmits the electrical received signals generated in it to the amplification unit,
the transmission signal generator focuses the resulting ultrasonic focus stepwise along the axis of the ultrasonic transducer onto individual focus points F _i solely by electronic focusing or in conjunction with the recording unit by means of a synthetic focusing;
a calibration unit is present, either by simulation calculation or by measurement using the recording unit, the reflected sound on the central receiving element for the ultrasonic transducer used in the following measurements with the corresponding element arrangement for a calibration medium W with the calibration wall as a reflector at a distance a _2W for the different _Focusing points F _iW determines, as a function of the electronic focusing, determines the electronic focus adjustment for the maximum Fok and by varying the distance a _2W , a _3W , a _4W , ... the interface and repetition of the process calibration curves for the different layer thicknesses of the calibration medium in front of the calibration wall, and
the recording unit measures the sound propagation time between the front boundary surface and the rear boundary surface of the layer to be examined, and registers the reflected signal on the central reception element when the focus point F _{i is moved} along the axis for the respective focus point, from which the sound pressure amplitude for the central reception element is determined for each focal point and so on determined sound pressure amplitudes are represented as a function of focusing in the form of sound pressure amplitude curves, and
the evaluation unit determines the local maxima and minima from the sound pressure amplitude curve determined by measurement, determines the equivalent distance of the reflective boundary surface with respect to the calibration medium W from the calibration curves, from the sound propagation time measured by the recording unit relative to the rear boundary surface of the layer to be examined of the medium and the determined equivalent layer thickness with respect to the calibration medium W determines the speed of sound c _Med in the layer to be examined and its layer thickness a _Med .

In the ultrasonic transducer, the central receiving element for detecting the reflected sound is provided, wherein the dimensions - diameter, side length - of the central receiving element in the order of magnitude of an ultrasonic wavelength λ with respect to the medium.

For a single-element ultrasonic transducer with the central receiving element or for a planar or prefocused multi-element ultrasonic transducer with the central receiving element, the change of focus points can be done alone or in addition by mechanical displacement of the ultrasonic transducer in the axial direction, wherein the ultrasonic transducer with a displacement device in combination stands, which shifts the ultrasonic transducer along the axis to move the focal point.

The calibration unit can either by simulation calculations for the ultrasonic transducer used or by measurements using the recording unit, the reflected signal on the central _{receiving element} for the calibration _medium W with a fixed calibration _wall as a reflector at a distance a _iW for different focus points F _1W , F _2W , F _3W .. ., which are realized by electronic focusing or by synthetic focusing when using time delay regimes V ₁ , V ₂ , V ₃ ..., determine the reflected sound on the central receiving element, as a function of the electronic focusing, determine the focus setting for the local maximum and by varying the distance a _1W , a _2W , a _3W ... of the calibration wall and repeating the process, provide calibration curves for the different layer thicknesses of the calibration medium W in front of the calibration wall. The distance between the calibration wall and the ultrasound transducer corresponds to the thickness of the calibration medium in the case of the calibration medium when there is direct contact between the calibration medium and the element (s) of the ultrasound transducer.

The ultrasonic transducer may be in the form of a ring element arrangement in which at least one annular element is optionally additionally subdivided into sectors to detect an inclination of the ultrasonic transducer with respect to the interface so as to be adjusted.

• – der Laufzeit des Ultraschalls im Medium und
• – der materialbedingten Verschiebung der Fokuspunkte F_i, gemessen durch schrittweise Fokussierung und Bestimmung der Echosignal-Kurve als Funktion der Fokussierung.

The invention thus includes a measuring principle for the simultaneous determination of layer thickness a _Med and speed of sound c _Med in at least one medium by means of ultrasound by the detection of two independent measured variables:

• - the duration of ultrasound in the medium and
• The material-related displacement of the focus points F _i , measured by stepwise focusing and determination of the echo signal curve as a function of the focusing.

By exploiting the exact knowledge of sound propagation time and sound field, additional information about the respective medium of a layer or multiple layers can be obtained which could only be determined by introducing reference bodies at a predetermined position according to the prior art.

The following method steps according to the invention are completed in detail using the aforementioned arrangement, in particular with the central receiving element as part of the element located in the central area of the ultrasonic transducer according to the characterizing part of claim 8:

A. Gradual focusing:

The transmit signal generator focused solely by electronic focusing or in conjunction with the recording unit by a synthetic focusing the resulting ultrasonic focus gradually along the axis of the ultrasonic transducer to individual focus points F _i , which are located either before, on and behind the rear interface of the layer to be examined.

B. Calibration:

Before the evaluation can be determined either by simulation calculation or by measuring the reflected sound from a calibration wall, which is generated by the transducers used for the following measurements on the central receiving element for different focus points F _i , represented as a function of electronic focusing and electronic focus adjustment can be determined for the maximum, which can be created by varying the Kalibrierwandabstandes and by repeating the process calibration curves for the different media layer thicknesses in front of the calibration.

C. Recording:

A recording unit measures the sound transit time between the front boundary surface and the rear boundary surface of the layer to be examined with unknown layer thickness and sound velocity. Due to the stepwise displacement of the electronic focus point along the axis of the ultrasonic transducer, the reflected signal is registered on the central receiving element for the respective focal point. From this, the sound pressure amplitude for the central receiving element is determined for each focal point and the sound pressure amplitude curve thus determined for the central receiving element is displayed as a function of the focusing.

D. Evaluation:

An evaluation unit determines the local maxima and minima in the determined sound pressure amplitude curve and determines therefrom the electronic focus adjustment for the maximum. From the determined focusing, the equivalent distance of the reflecting interface with respect to the medium to be examined is determined with the aid of the calibration curves, wherein the sound velocity c _Med . From the measured sound transit time t between the front interface and the rear interface of the layer to be examined and the determined equivalent layer thickness with respect to the calibration medium be determined in the layer to be examined and their layer thickness a _Med .

Said calibration wall can be a solid wall.

• – dass sie die gleichzeitige referenzlose Bestimmung von Schichtdicke a_Med und der mittleren Schallgeschwindigkeit c_Med in einer zu untersuchenden Schicht bei geschichteten fluiden oder soliden Medien ermöglicht,
• – dass die Erfindung die Bildgebung durch die Kenntnis der tatsächlich auftretenden Schallgeschwindigkeit verbessert, wodurch eine bessere Topographie, genauere Ortsbestimmung der Lage von Einschlüssen und eine genauere Dickenbestimmung möglich sind, und
• – dass die Erfindung die Bestimmung von Materialparametern bei verdeckten, unzugänglichen Strukturen möglich macht.

The advantages of the invention are

• That it allows the simultaneous reference-less determination of layer thickness a _Med and the mean speed of sound c _Med in a layer to be examined in the case of layered fluid or solid media,
• That the invention improves the imaging by the knowledge of the actually occurring speed of sound, whereby a better topography, more accurate location of the location of inclusions and a more accurate thickness determination are possible, and
• - That the invention makes the determination of material parameters in covert, inaccessible structures possible.

• – geschichtete Festkörper mit einer Bestimmung der Schichtdicken a_Med und Schallgeschwindigkeiten c_Med in den einzelnen Schichten, insbesondere Schichtdicken im Innern sowie verdeckte Schichten,
• – geschichtete durchsichtige oder undurchsichtige Flüssigkeiten.

With the arrangement according to the invention and the associated method, the following media can be measured:

• Layered solids with a determination of the layer thicknesses a _Med and sonic velocities c _Med in the individual layers, in particular layer thicknesses in the interior, as well as hidden layers,
• - Layered transparent or opaque liquids.

• – eine Schichtdickenbestimmung bei verdeckten Strukturen ohne Kenntnis der Schallgeschwindigkeit,
• – eine zerstörungsfreie Bestimmung von Materialparametern und deren örtlichen Veränderungen in einer Schicht oder in mehreren Schichten,
• – Informationen über Eigenschaften der Schicht (bei Geweben: Einlagerungen, Gewebeart, Tumorgewebe, Beobachtung degenerativer Entwicklungen in Geweben; bei Festkörpern; Materialparameter wie z. B. Dichte, E-Modul, Flüssigkeiten; Dichte, Viskosität) mittels der Parameter (Schallgeschwindigkeit, Schichtdicke).

The following special fields of application can be specified:

• A layer thickness determination in hidden structures without knowledge of the speed of sound,
• - a non-destructive determination of material parameters and their local changes in one or more layers,
• - Information about properties of the layer (for tissues: inclusions, tissue type, tumor tissue, observation of degenerative developments in tissues, for solids, material parameters such as density, modulus of elasticity, liquids, density, viscosity) by means of the parameters (speed of sound, layer thickness ).

Further developments and advantageous embodiments of the invention are specified in further subclaims.

The invention will be explained in more detail by means of exemplary embodiments by means of several drawings.

Show it:

1 an inventive arrangement for determining layer thicknesses and sound velocities in media using ultrasound, wherein

1a a schematic representation of the arrangement with a central receiving element,

1b an enlarged view of the ultrasonic transducer medium assembly with the central receiving element according to 1a .

1c a schematic representation of the arrangement with a central receiving element for calibration and

1d an enlarged schematic representation of the arrangement with a central receiving element for calibration after 1c
demonstrate,

2 Sound pressure amplitudes as a function of the electronic focus point, which represent calibration curves for the central receiving element, wherein

2a the amplitude of the sound reflected from the calibration wall on the central receiving element for the medium of water as a function of electronic focus for a large ultrasonic transducer with a diameter d = 12 mm, a frequency of 3 MHz and a thickness of the water layer with a _W = 13 mm and a _W = 10 mm, and

2 B the amplitude of the sound reflected from the calibration wall on the central receiving element for the medium of water as a function of electronic focus for a small ultrasonic transducer with a diameter d = 11 mm, a frequency of 3 MHz and a thickness of the water layer with a _W = 10 mm
show, and

3 Sound pressure amplitudes as a function of the electronic focus point for multilayer media for a large ultrasonic transducer, wherein

3a the reflected amplitude from the back boundary of a fabric layer with a layer thickness of 5 mm after a water feed of 5 mm,

3b the reflected amplitude from the rear interface of a fabric layer with a layer thickness of 8 mm after a water flow of 5 mm and

3c the reflected amplitude from the rear interface of a Plexiglas layer with a layer thickness of 5 mm after a water supply of 5 mm
demonstrate.

The following are the 1a . 1b . 1c and 1d considered together.

• – einem Sendesignalgenerator 1, der auf drei Kanälen 11 elektrische Sendesignale erzeugt,
• – einem Ultraschallwandler 2 mit drei Elementen 21, 22, 23, der die Signale vom Sendesignalgenerator 1 erhält und dessen angesteuerte Elemente 21, 22, 23 Ultraschallwellen in das Medium 3 mit den beiden Schichten 31, 32 sendet, wobei der Ultraschallwandler 2 reflektierte Ultraschallwellen empfängt und in elektrische Empfangssignale wandelt,
• – einer Verstärkungseinheit 5, die die elektrischen Empfangssignale erhält und verstärkt,
• – einer Aufnahmeeinheit 6, die die verstärkten Empfangssignale einer Analog-Digital-Wandlung zur Ausbildung digitaler Signale zuführt, sowie
• – einer Auswerteeinheit 8, die die digitalen Signale aus der Aufnahmeeinheit 6 in die Auswertung einbezieht.

In the 1a and 1b is a schematic arrangement 10 for determining layer thicknesses and sound velocities in the medium 3 with the layers 31 . 32 shown with the help of ultrasound, the arrangement 10 consists

• A transmission signal generator 1 that on three channels 11 generates electrical transmission signals,
• - an ultrasonic transducer 2 with three elements 21 . 22 . 23 receiving the signals from the transmit signal generator 1 receives and its driven elements 21 . 22 . 23 Ultrasonic waves in the medium 3 with the two layers 31 . 32 sends, with the ultrasonic transducer 2 receives reflected ultrasonic waves and converts them into received electrical signals,
• - an amplification unit 5 that receives and amplifies the received electrical signals,
• - a recording unit 6 , which supplies the amplified received signals to an analog-to-digital conversion to form digital signals, as well as
• - an evaluation unit 8th receiving the digital signals from the recording unit 6 included in the evaluation.

According to the invention is located in the central region of the ultrasonic transducer 2 in the existing element there 21 a central receiving element receiving the reflected ultrasonic waves 4 receiving the electrical reception signals generated in it to the amplification unit 5 the transmit signal generator forwards and focuses 1 solely by electronic focusing or in conjunction with the recording unit 6 through a synthetic focusing the emerging ultrasonic focus gradually along the axis 12 of the ultrasonic transducer 2 to individual focus points F ₁ , F ₂ , F ₃ ,
wherein a calibration unit 7 is present, either by simulation calculation or by measurement using the recording unit 6 the reflected sound on the central receiving element 4 for the ultrasonic transducer used in the following measurements 2 with predetermined element arrangement for a calibration medium W 31 with a fixed calibration wall 9 as reflector at a distance a _W for the different electronic focus points F _iW determined, as in 1c and 1d is shown, and represents as a function of the electronic focusing, determines the electronic focus adjustment for the maximum and by varying the distance a _1W , a _2W , a _3W , ... the calibration 9 and repetition of the procedure Calibration curves for the different layer thicknesses of the calibration medium W 31 in front of the calibration wall 9 delivers, and
the receiving unit 6 for the first shift 31 the sound transit time t ₃₁ between its front interface G1 and its rear interface G2 and / or for the second layer 32 measures the sound transit time t ₃₂ between its front interface G2 and its rear interface G3, and upon displacement of the electronic focal point along the axis 12 for the respective focal point F ₁ , F ₂ , F _3, the reflected signal on the central receiving element 4 registers, from which the sound pressure amplitude for the central receiving element 4 determined for each focal point F ₁ , F ₂ , F ₃ and the sound pressure amplitude thus determined is shown as a function of focusing in the form of sound pressure amplitude curves, as in the 2a . 2 B for the calibration medium W 31 and in the 3a . 3b and 3c is shown for other media layers, and
wherein the evaluation unit 8th determine the local maxima and minima from the sound pressure amplitude curve determined by measurement, and from this, with the aid of the calibration curves, determine the equivalent distance a _{W of} the respective reflective interface G2 or G3 with respect to the calibration medium W. 31 determined from the of the recording unit 6 measured sound transit time t ₃₁ , t ₃₂ between the respective front boundary surface G1, G2 and the respective rear boundary surface G2, G3 in the layer to be examined 31 or 32 and the determined equivalent layer thickness a _W with respect to the calibration medium W 31 the speed of sound c _Med31 , c _Med32 in the layer to be examined 31 or 32 and whose layer thickness a _Med31 , a _{Med32 are} determined.

In the ultrasonic transducer 2 is the central receiving element for receiving the reflected ultrasonic waves 4 provided for determining the sound pressure amplitude curve, wherein the dimensions - diameter d _Z , side length - of the central receiving element 4 in the range of an ultrasonic wavelength with respect to the medium 3 lie.

The simultaneous measurement of the speed of sound c _Med31 , c _Med32 and layer thickness a _Med31 , c _Med32 is based on the determination of the sound propagation time t ₃₁ , t ₃₂ and the sound pressure amplitude curves determined by varying the focus points F ₁ , F ₂ , F ₃ .

In a point-shaped reflector according to the prior art results in variation of the focus points F _i, a maximum in the reflected signal when the point-shaped reflector is in the focal point, which is given by the sound pressure maximum. It results in the reflection of an extended Interface the maximum in the reflected signal only when the focal point F _{i is placed} at a distance of a few millimeters after the interface.

Overcoming this disadvantage, the distance of the reflecting interface can be determined by measurement with a small receiver in the form of the central receiving element introduced according to the invention 4 determine. When representing the received sound pressure amplitude as a function of the electronic focus point, local maxima and minima can be determined at focus points in the vicinity of the reflective boundary surface, which maxima and minima can be used to determine the layer thickness a _Med ( 2 . 3 ). The recorded sound pressure amplitude curves can also be influenced by the geometry and the frequency of the transmitting elements 21 . 22 . 23 depend.

In the 1c specified calibration unit 7 can be a computing unit 71 for calculating the calibration curves and / or a measuring unit 72 to determine the calibration curves.

The operation of the arrangement 10 is accompanied by the following procedure:
In the method for determining layer thicknesses a _Med and sound velocities c _Med in the medium 3 with the layers 31 . 32 with the help of ultrasound are using the arrangement 10 the following steps A, B, C, D realized:

A. Gradual focusing:

A transmission signal generator 1 focused alone or in collaboration with a recording unit 6 the resulting ultrasound stepwise along the axis 12 of the ultrasonic transducer 2 to individual focus points F ₁ , F ₂ , F ₃ , which optionally before, on and behind the rear interface G2 or G3 of the layer to be examined 31 or 32 are placed, with the respective front boundary surfaces G1 and G2.

B. Calibration:

Before the evaluation is either by simulation calculation or by measuring the of a fixed calibration wall 9 reflected sound according to 1c and 1d , that of the ultrasonic transducer used for the following measurements 2 is generated on the central receiving element 4 determined for different focus points F _1W , F _2W , F _3W and shown as a function of electronic focusing and determines the electronic focus adjustment for the maximum, wherein by varying the distance a _1W , a _2W , a _{3W of} the calibration 9 and by repeating the process calibration curves for the different layer thicknesses a _{W of} the calibration medium W 31 in front of the calibration wall 9 to be created.

C. Recording:

A recording unit 6 measures z. B. in the case of a layer to be examined 31 the sound transit time t ₃₁ between the front interface G1 and the rear interface G2 of the layer 31 with the layer thickness a _Med to be determined and with the speed of sound c _Med to be determined, wherein the stepwise displacement of the focal point F ₁ , F ₂ , F ₃ along the axis 12 for the respective focal point F ₁ , F ₂ , F _3, the reflected signal on the central receiving element 4 is registered, from which the sound pressure amplitude for the central receiving element 4 for each focal point F ₁ , F ₂ , F ₃ determined and the thus determined sound pressure amplitudes for the central receiving element 4 be presented as a function of electronic focusing, as in the 3 is shown.

D. Evaluation:

An evaluation unit 8th establishes the local maxima and minima in the determined sound pressure amplitude curve and, using the calibration curves, determines therefrom the equivalent distance a _{W of} the reflecting interface 9 with respect to the calibration medium W 31 and wherein from the measured sound transit time t between the front boundary surface G1 and the rear boundary surface G2 of the layer to be examined 31 and the determined equivalent layer thickness a _W with respect to the calibration medium W 31 the speed of sound c _Med31 in the layer to be examined 31 and whose layer thickness a _{Med31 are} determined.

For a single element ultrasonic transducer with the central receiving element 4 or for an unfocused or prefocused multi-element ultrasonic transducer having the central receiving element 4 may be the change of the distance of the focus points F _i from the ultrasonic transducer alone or additionally by mechanical displacement of the ultrasonic transducer 2 in the direction of its axis 12 take place, wherein the ultrasound transducer 2 with a displacement device (not shown) may be in communication, the ultrasonic transducer 2 along the axis 12 moves to move the focus point.

wobei a_W der aus der Fokussierung ermittelte äquivalente Schichtdickenabstand bezüglich des Kalibriermediums W 31, c_W die Schallgeschwindigkeit im Kalibriermedium W, VL die Schichtdicke des Vorlaufs bezogen auf das Kalibriermedium W 31 und t = t₃₁ die einfache Schalllaufzeit zwischen vorderer Grenzfläche G1 und hinterer Grenzfläche G2 der zu ersten Schicht 31 und t = t₃₂ die einfache Schalllaufzeit zwischen vorderer Grenzfläche G2 und hinterer Grenzfläche G3 der zweiten Schicht 32 sind.For a medium 3 with two layers to be examined 31 . 32 the determination of the speed of sound c _Med31 , c _Med32 and the layer thickness a _Med31 , a _Med32 in the individual layers takes place 31 . 32 successively from the ultrasonic transducer 2 nearest layer 31 in itself, whereby the equations (III) and (IV) apply to the calculation of the speed of sound c _Med and the layer thickness a _Med in both cases

where a _{W is} the determined from the focusing equivalent layer thickness distance with respect to the calibration medium W 31 , c _W the speed of sound in the calibration medium W, VL the layer thickness of the flow relative to the calibration medium W 31 and t = t ₃₁ the simple sound transit time between the front interface G1 and the rear interface G2 of the first layer 31 and t = t ₃₂ the simple sound transit time between front interface G2 and rear interface G3 of the second layer 32 are.

• a) eine elektronische Sendefokussierung des Ultraschalls durch eine dem Zeitverzögerungsregime V₁, V₂, V₃, ... entsprechende zeitversetzte Ansteuerung der drei Einzelwandlerelemente 21, 22, 23 derart realisiert wird, dass die von den Einzelwandlerelementen 21, 22, 23 ausgehenden Ultraschallwellen sich in den Fokuspunkten F₁, F₂, F₃ ... konstruktiv überlagern, d. h. z. B. mit dem Zeitverzögerungsregime V₁ wird der Fokuspunkt F₁ im zu untersuchenden Medium und der Fokuspunkt F_iW im Kalibriermedium W 31 erzeugt, oder
• b) eine synthetische Fokussierung des Ultraschalls durch Aufnahme des von jedem einzelnen Element 21, 22, 23 auf dem Zentralempfangselement 4 erzeugten Echosignals und anschließender Überlagerung der Echosignale entsprechend dem Zeitverzögerungsregime V₁, V₂, V₃, ... realisiert wird.

When focusing, the change of the distance of the focus points F _i from the ultrasonic transducer by one of the following steps, wherein

• a) an electronic transmission focusing of the ultrasound by a time delay regime V ₁ , V ₂ , V ₃ , ... corresponding time-offset control of the three individual transducer elements 21 . 22 . 23 is realized such that the of the individual transducer elements 21 . 22 . 23 Outgoing ultrasonic waves in the focus points F ₁ , F ₂ , F ₃ ... constructively overlap, ie, for example, with the time delay regime V ₁ , the focus point F ₁ in the medium to be examined and the focus point F _iW in the calibration medium W 31 generated, or
• b) a synthetic focusing of the ultrasound by picking up the from each individual element 21 . 22 . 23 on the central receiving element 4 generated echo signal and subsequent superposition of the echo signals according to the time delay regime V ₁ , V ₂ , V ₃ , ... is realized.

In the following examples, the simultaneous determination of the layer thickness a _Med and the speed of sound c _Med becomes an ultrasonic transducer 2 used with a ring element arrangement. For this, first calibration curves, as in 2 shown, calculated. In the calculation, it is assumed that in a water bath at a defined distance parallel to the transmitting elements 21 . 22 . 23 a thick plate 9 is located as a calibration wall, in which no reflection from the plate back wall arrives at the receiving elements during the observation period. By electronic focusing or by synthetic focusing, the focal point F ₁ , F ₂ , F ₃ along the axes 12 in front, on and behind the front reflective surface of the plate 9 placed and a sound pressure amplitude curve with respect to the central receiving element 4 - a small central receiver in the area of the axis 12 - certainly.

The electronic focusing is performed directly by a time-delayed control of the elements with delay times corresponding to the respective time delay regime.

In synthetic focusing, with all transmitting elements 21 . 22 . 23 one at a time, the individual reflected signals from the central receiving element 4 registered and the individual signals for the individual transmission elements 21 . 22 . 23 out of phase according to the respective time delay regime superimposed.

The process is for different distances of the plate 9 from the transmitting elements 21 . 22 . 23 repeated.

Table 1 shows the relationship between layer thickness a _W and electronic focus Fok at the local maximum in the sound pressure amplitude curves for the calibration medium water 31 , Table 1 Distance a _{W of} the plate 9 in water Electronic focusing Fok at local maximum 10 mm 10.5 mm = M10 13 mm 12 mm = M13

This results in the two sound pressure amplitude curves in 2 for a wall distance a _W of 10 mm and 13 mm, wherein the wall distance a _W equal to the layer thickness of the calibration medium W 31 represents when applied to the ultrasonic transducer 2 immediately the layer of the calibration medium W 31 followed. The comparison of 2a and 2 B shows the dependence of the curve on the geometry of the transmitting elements 21 (inner central element), 22 (middle element), 23 (outer element) of the ultrasonic transducer 2 ,

In the 2a and 2 B Recorded calibration curves show in front of and behind the reflective wall 9 a local minimum. The local maximum does not agree exactly with the focal point that was read, but because the distance a _{W of} the plate is in the calibration calculations or measurements 9 from the transmitting elements 21 . 22 . 23 is predetermined, the electronic focus Fok at the maximum of a water layer thickness a _W (= distance of the wall 9 from the ultrasonic transducer 2 for medium water W 31 ) assign. With a diameter d = 12 mm of the ultrasonic transducer 2 and at a distance a _W = 13 mm, the maximum M13 at an electronic focus Fok = 12 mm and at a distance a _W = 10 mm, the maximum M10 at Fok = 10.5 mm, as in 2a is shown. In 2 B the diameter d = 11 mm of the ultrasonic transducer 2 and the local maximum M10 is at Fok = 9 mm.

If at a shift 32 of a different medium with layer thickness a _Med32 to be determined and sound velocity c _Med32 to be determined is focused stepwise and a sound pressure amplitude curve is recorded as a function of the electronic focusing, a similar sound pressure amplitude curve results as in water. Again, local maxima and minima occur. When the focus is read at the local maximum and compared to the calibration curves for water, the calibration curve for water can be selected at which a local maximum occurs at the same focusing and same time delay regime in water.

wobei a für den Abstand bzw. die Schichtdicke, c für die Schallgeschwindigkeit und der Index W für das Kalibriermedium Wasser 31 und Med für das zu untersuchende Medium in der Schicht 32 stehen.That is, it becomes the layer to be examined 32 an equivalent water layer _thickness assigned a _W. This depends on the layer thickness a _{Med32 of} the layer to be determined 32 via the equation (I) together:

where a is the distance or the layer thickness, c for the speed of sound and the index W for the calibration medium water 31 and Med for the medium to be examined in the layer 32 stand.

wobei t_Med die gemessene einfache Schalllaufzeit in der zu untersuchenden Schicht 32 ist.A second information is obtained from the sound transit time t _Med according to equation (II)

where t _{Med is} the measured simple sound propagation time in the layer to be examined 32 is.

Equations (I) and (II) allow the layer thickness a _Med and the speed of sound c _{Med of} the layer to be determined 32 determine.

Is it a multi-layered medium? 3 , z. B. a two-layered with the unknown layers 31 and 32 as in the 1a and 1b shown, so are in the direction of the ultrasonic transducer 2 the layer thicknesses a _Med31 , a _Med32 and the velocities c _Med31 , c _{Med32 are} determined. The equations (I) and (II) go for a two-layered system 31 . 32 into equations (III) and (IV)

VL stands for advance.

If equation (IV) is used in equation (III), an equation (V) results for calculating the speed of sound c _{Med of} the medium in each slice to be examined 31 and 32

3a shows the recorded sound pressure amplitude curve of a tissue layer to be examined (actual values: sound velocity c _Med of c = 1620 m / s and a layer thickness a _Med of 5 mm) after a water flow VL of 5 mm. It is assumed that the layer thickness a _Med and the speed of sound c _{Med are} not predetermined. In the measurement, the sound transit time t for the simple running path between the front interface G2 and the rear interface G3 of the layer to be examined 32 determines t = 3.09 · 10 ^-6 s and ^records the sound pressure amplitude curve by stepwise focusing.

The sound pressure on the central receiving element 4 as a function of electronic focusing is in 3a shown. The position of the local maximum MG5 for Fok = 10.9 mm is taken. This results in a layer thickness with respect to water of a _W = 10.8 mm by interpolation of the values in Table 1. According to equation (V), this results in a speed c _Med of 1649 m / s and a layer thickness a _Med of 5.1 mm.

In the 3b recorded sound pressure amplitude curve for a fabric layer (8 mm thickness, c = 1620 m / s) with a water flow of 5 mm has a local maximum MG8 at Fok = 12.5 mm. For the speed of sound c _Med is 1653 m / s and a layer thickness c _Med of 8.17 mm.

The recorded sound pressure amplitude curve in 3c for a plexiglass layer (5 mm thickness, c = 2730 m / s) with a water flow VL of 5 mm, the local maximum MP5 at Fok = 12.7 mm. For the speed of sound c _Med , c = 2775 m / s and a layer thickness a _Med of 5.11 mm.

LIST OF REFERENCE NUMBERS

1

Transmission signal generator

2

ultrasound transducer

21

inner central element

22

middle element

23

outer element

3

medium

31

first medium

31

W-calibration

32

second medium

4

Central receiving element in the central element

5

amplification unit

6

recording unit

7

calibration

71

measuring unit

72

computer unit

8th

evaluation

9

Kalibrierwand

10

inventive arrangement

11

channels

12

Axis of the ultrasonic transducer

F _i

focus point

F _iW

Focus point on calibration

Fok

electronic focusing

V _i

Time Delay regime

W

calibration

VL

leader

a _w

Layer thickness with respect to the calibration medium

a _med

Layer thickness of the medium to be examined

d

Diameter of the ultrasonic transducer

d _Z

Diameter of the central receiving element

c _W

Speed of sound of the calibration medium

c _med

Speed of sound of the medium to be examined

t

Time

G1

interface

G2

interface

G3

interface

M

local maximum

MG

Local maximum of a sound pressure amplitude curve for a tissue layer

MP

local maximum of a sound pressure amplitude curve for a Plexiglas layer

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been 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 assumes no liability for any errors or omissions.

Cited patent literature

• US 2002134159 [0006]
• DE 50305421 T [0007]

Claims (11)

Arrangement ( 10 ) for determining layer thicknesses and sound velocities in media ( 3 ; 31 . 32 ) with the aid of ultrasound, consisting of - a transmission signal generator ( 1 ), on n ≥ 1 channels ( 11 ) generates electrical transmission signals, - an ultrasonic transducer ( 2 ) with m ≥ 1 elements ( 21 . 22 . 23 ), which transmits the transmission signals from the transmission signal generator ( 1 ) and whose driven elements ( 21 . 22 . 23 ) the ultrasonic waves into the medium ( 3 ) with one or more layers ( 31 . 32 ), wherein the ultrasonic transducer ( 2 ) receives the reflected ultrasonic waves and converts them into received electrical signals, and - an amplification unit ( 5 ) receiving and amplifying the received electrical signals, - a recording unit ( 6 ), which supplies the amplified received signals to an analog-digital conversion for the purpose of forming digital signals, and - an evaluation unit ( 8th ), which receives the digital signals from the recording unit ( 6 ) in the evaluation, characterized in that in the central region of the ultrasonic transducer ( 2 ) in the element ( 21 ) a received the reflected ultrasonic waves central receiving element ( 4 ), which receives the electrical received signals generated in it to the amplification unit 5 forwards the transmit signal generator ( 1 ) by electronic focusing alone or in collaboration with the recording unit ( 6 ) by means of a synthetic focusing the resulting ultrasonic focus stepwise along the axis ( 12 ) of the ultrasonic transducer ( 2 ) focuses on individual focus points (F _i ) that a calibration unit ( 7 . 71 . 72 ), either by simulation calculation or by measurement using the recording unit ( 6 ) the reflected ultrasound on the central receiving element ( 4 ) for the ultrasonic transducer used in the following measurements ( 2 ) with a predetermined element arrangement for a calibration medium W ( 31 ) with a fixed calibration wall ( 9 ) is determined as a reflector at a distance (a _W ) for the different focus points (F _iW ) and represents a function of the focusing, the electronic focus setting for the maximum is determined and by varying the distance (a _iW ) of the calibration _wall ( 9 ) and repetition of the procedure Calibration curves for the different layer thicknesses of the calibration medium W ( 31 ) in front of the calibration wall ( 9 ) and that the recording unit ( 6 ) the sound transit time (t) between the front interface (G1, G2) and the rear interface (G2, G3) of the layer to be examined ( 31 . 32 ) and with displacement of the focal point (F _i ) along the axis ( 12 ) for the respective focal point (F _i ) the reflected signal on the central receiving element ( 4 ), from which the sound pressure amplitude for the central receiving element ( 4 ) is determined for each focal point (F _i ) and the sound pressure amplitude thus determined is represented as a function of the focusing in the form of a sound pressure amplitude curve, and in that the evaluation unit ( 8th ) determines the local maxima and minima from the sound pressure amplitude curve determined by measurement, from which, with the aid of the calibration curves, the equivalent distance of the reflective boundary surface with respect to the calibration medium W (see FIG. 31 ) from which the recording unit ( 6 ) measured sound transit time (t ₃₁ , t ₃₂ ) between the front interface (G1, G2) and the rear interface (G2, G3) of the layer to be examined ( 31 . 32 ) and the determined equivalent layer thickness with respect to the calibration medium W ( 31 ) the speed of sound (c _Med31 , c _Med32 ) in the layer to be examined ( 31 . 32 ) and their layer thickness (a _Med31 , a _Med32 ) are determined. Arrangement according to claim 1, characterized in that the central receiving element ( 4 ) is provided for the determination of sound pressure amplitude curves, wherein the dimensions - diameter d _Z , side length - of the central receiving element ( 4 ) in the range of an ultrasonic wavelength with respect to the medium ( 3 ) lie. Arrangement according to claim 1, characterized in that the ultrasonic transducer ( 2 ) is designed as a ring element arrangement or as a matrix arrangement or as a linear arrangement, so that an electronic focusing or a synthetic focusing is possible. Arrangement according to claim 1, characterized in that for coupling the ultrasound into the medium ( 3 ) optionally a liquid flow (FVL) is used. Arrangement according to claim 3, characterized in that for a single element ultrasonic transducer with the central receiving element ( 4 ) or for an unfocused or prefocused multi-element ultrasound transducer with the central receiving element ( 4 ) the change of the focus points (F _i ) alone or in addition by mechanical displacement of the ultrasonic transducer ( 2 ) in the direction of the axis ( 12 ), wherein the ultrasonic transducer ( 2 ) is in communication with a displacement device, the ultrasonic transducer ( 2 ) along the axis ( 12 ) to focus on the focus points. Arrangement according to claim 1, characterized in that the calibration unit ( 7 . 71 . 72 ) either by simulation calculations for the ultrasonic transducer used ( 2 ) or by measurements the reflected signal on the central receiving element 4 for the calibration medium W ( 31 ) with a fixed calibration wall ( 9 ) is determined as a reflector at a distance (a _1W ) for different foci with the focus points (F ₁ , F ₂ , F ₃ , ...), as a function of focusing, determines the electronic focus setting or the synthetic focus setting for the local maximum and by varying the distance (a _1W , a _2W , a _3W ) of the calibration wall ( 9 ) and repetition of the procedure Calibration curves for the different layer thicknesses (a _W, ) of the calibration medium W ( 31 ) in front of the calibration wall ( 9 ). Arrangement according to claim 3, characterized in that the ultrasonic transducer ( 2 ) in the form of a ring element arrangement, in which at least one annular element is additionally subdivided into sectors, or is additionally received by means of additional ultrasound transducers intended for reception in order to detect an inclined position of the ultrasound transducer ( 2 ) with respect to the interface (G1, G2, G3) and thus to adjust. Method for determining layer thicknesses and sound velocities in media ( 3 ; 31 . 32 ) using ultrasound, using an array ( 10 ) according to claim 1, comprising the following steps: A. Stepwise focusing: a transmission signal generator ( 1 ) focuses alone or in collaboration with a recording unit ( 6 ) stepwise along the axis ( 12 ) of the ultrasonic transducer ( 2 ) to individual focus points (F _i ), which optionally before, on and behind the rear interface (G2, G3) of the layer to be examined ( 31 . 32 ), where (G1) and (G2) respectively the front boundary surfaces of the layers ( 31 . 32 ) are. B. Calibration: Before the evaluation is carried out either by simulation calculation or by measurement of the by a fixed calibration wall ( 9 ) reflected sound from the ultrasonic transducer used for the following measurements ( 3 ) is generated on a central receiving element ( 4 ) is determined for different focus points (F _i ) and represented as a function of the electronic focusing and determines the electronic focus adjustment for the maximum, wherein by varying the distance of the calibration wall ( 9 ) and by repeating the process calibration curves for the different layer thicknesses (a _W ) of the calibration medium W ( 31 ) in front of the calibration wall ( 9 ) to be created. C. Recording: A recording unit ( 6 ) measures the sound transit time (t ₃₁ , t ₃₂ ) between the front boundary surface (G1, G2) and the rear boundary surface (G2, G3) of the layer to be investigated ( 31 . 32 ) with the layer thickness to be determined (a _Med ) and with the speed of sound to be determined (c _Med ), wherein a stepwise displacement of the focal point (F _i ) along the axis ( 12 ) for the respective focal point (F _i ) the reflected signal on the central receiving element ( 4 ), from which the sound pressure amplitude for the central receiving element ( 4 ) is determined for each focal point (F _i ) and the sound pressure amplitude thus determined for the central receiving element ( 4 ) as a function of focusing. D. Evaluation: An evaluation unit ( 8th ) determines the local maxima and minima in the determined sound pressure amplitude curve and determines therefrom, with the aid of the calibration curves, the equivalent distance of the reflecting interface with respect to the calibration medium W (FIG. 31 ) and wherein from the measured sound transit time (t ₃₁ , t ₃₂ ) between the front boundary surface (G1, G2) and the rear boundary surface (G2, G3) of the layer to be investigated ( 31 . 32 ) and the determined equivalent layer thickness (a _W ) with respect to the calibration medium W ( 31 ) the speed of sound (c _Med31 , c _Med32 ) in the layer to be examined ( 31 . 32 ) and their layer thickness (a _Med31 , a _Med32 ) are determined. A method according to claim 8, characterized in that in a multilayer medium ( 31 . 32 ) the determination of the speed of sound (c _Med31 , c _Med32 ) and the layer thickness (a _Med31 , a _Med32 ) in the individual layers ( 31 . 32 ) successively from the ultrasonic transducer ( 2 ) takes place next to the next layer, whereby the equations (III) and (IV) apply to the calculation of the speed of sound (c _Med ) and the layer thickness (a _Med )

where a _{w is} the equivalent layer thickness distance determined from the focusing with respect to the calibration medium W (FIG. 31 ), c _{W is} the speed of sound in the calibration medium W ( 31 ), VL the layer thickness of the flow relative to the calibration medium W ( 31 ) and t is the simple sound transit time between the front interface (G1, G2) and the rear interface (G2, G3) of the layer to be examined ( 31 . 32 ) are. A method according to claim 8, characterized in that during the focusing, the change of the focus points (F _i ) by one of the following steps a) by an electronic transmission focusing of the ultrasound by a time delay regime (V ₁ , V ₂ , V ₃ ) corresponding time-delayed control m individual transducer elements ( 21 . 22 . 23 ) such that the of the individual transducer elements ( 21 . 22 . 23 ) outgoing ultrasonic waves superimpose constructively in the focal points (F ₁ , F ₂ , F ₃ ), or b) by a synthetic focusing of the ultrasound by recording the signal from each individual transducer element ( 21 . 22 . 23 ) on the central receiving element ( 4 ) generated echo signal and subsequent superposition of the echo signals in accordance with the time delay regime (V ₁ , V ₂ , V ₃ ) can be realized. A method according to claim 8, characterized in that the accuracy after rough determination of the speed of sound (c _med ) by using the calibration medium W ( 31 ) is increased at a speed of sound (c _W ) similar to the roughly determined speed of sound (c _Med ).

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