Method for signal transmission between an ultrasonic transducer and ultrasonic electronics, and associated arrangement

Abstract

Method for signal transmission between an ultrasonic transducer (1) and an ultrasonic electronics unit (2), in which transmitting signals (4) for the ultrasonic transducer (1) are generated and received signals (5) from the ultrasonic transducer (1) are recorded and / or processed, wherein - the signal transmission takes place via a cable connection (7) which has at least one pair of conductors and a shield for the pair of conductors, - the transmit signals (4) asymmetrically over both conductors of the wire pair with the shield as return conductor and - the received signals (5) are transmitted symmetrically over both wires of the same wire pair.

Description

Technical application area

[0001] The present invention relates to a method for signal transmission between an ultrasonic transducer and an ultrasonic electronics unit, in which transmission signals for the ultrasonic transducer are generated and reception signals from the ultrasonic transducer are recorded and / or processed. The invention also relates to an arrangement comprising at least one ultrasonic transducer and at least one ultrasonic electronics unit, which uses the method for signal transmission.

[0002] Ultrasonic transducers convert electrical energy into acoustic energy and vice versa. In technical and medical applications, they generate directed sound waves (transmission) and, after interacting with the medium through which the sound passes, convert them back into electrical signals (reception) and record them. The recorded signals are then evaluated using various methods. This principle underlies, for example, ultrasonic testing in non-destructive materials testing (NDT) and modern sonography for medical diagnostics.

[0003] Due to sound attenuation and low conversion efficiency, the received signals are several orders of magnitude smaller than the transmitted signals. Piezoelectric transducers or electromagnetic transducers (EMATs), commonly used for ultrasonic conversion, generate sound with an electrical transmitter, transmitting signals from 50 to 1000 V. However, only signals in the range from µV to approximately 1 V are received.

[0004] Ultrasonic electronics and ultrasonic transducers are typically separated and connected by cables. The ultrasonic electronics generates the transmitted signals, and the received signals are recorded and / or processed. Due to the different signal characteristics of transmitted and received signals, high demands are placed on the cable connection between the ultrasonic electronics and the ultrasonic transducer, depending on the application. The transmitted signals are transmitted to the ultrasonic transducer at high voltages, high currents, and fast rise times (< 10 ns for sound frequencies in the MHz range), while the received signals are transmitted from the transducer to the electronics at low signal amplitudes, thus requiring high immunity to line- and field-coupled interference.The cable connection must often also meet high mechanical requirements, particularly with regard to the cable diameter and robustness against stress such as bending, torsion or chemicals.

[0005] The mechanical requirements are largely determined by the specific application. For example, the cables in automated ultrasonic testing systems for non-destructive materials testing are subject to constant movement, are often up to 20 meters long, and are generally located in harsh environments with sources of electrical interference, such as time-controlled servo motors. In medical applications, however, the handling and thickness of the cables are paramount. State of the art

[0006] In most state-of-the-art applications, the connection between the ultrasonic electronics and the ultrasonic transducers is currently made via coaxial cables. Fig. Figure 1 shows, as an example, a schematic representation of the ultrasonic transducer 1 of a piezo single-element probe connected to an ultrasonic electronics system 2, connected via a coaxial cable 3. The outer conductor of the coaxial cable 3 serves as a return conductor and simultaneously as a shield for the inner conductor. The transmitted signal 4 and the received signal 5 are each transmitted via the inner conductor of the coaxial cable 3. For this purpose, the ultrasonic electronics system 2 has a device 6 for separating the transmitted signal and the received signal, which are routed via different circuit components (TX: transmitter, RX: receiver).

[0007] However, the use of coaxial cables for transmit and receive signals has numerous disadvantages. For example, the inner conductor is only protected from interference fields and waves by the shielding attenuation of the outer conductor. The outer conductor simultaneously carries the current of the sensitive measurement signal and coupled interference currents for dissipation. To dissipate interference, it must usually be connected at both ends to the housing of the ultrasound device containing the ultrasound electronics and the probe housing containing the ultrasound transducer, which can result in compensating currents. Furthermore, depending on the dielectric, coaxial cables are sensitive to mechanical stress such as bending and torsion. Movements can cause capacitance changes and thus also interference signals.

[0008] Some of these disadvantages can be overcome by using triaxial cables, where a second outer shield provides shielding and the inner shield serves only as a return conductor for the signal. However, the resulting increased diameter makes the cable more sensitive to mechanical stress such as bending and torsion, especially for use in test systems with travel paths in drag chains or on robot arms.

[0009] US 6,277,077 B1 discloses a medical catheter with an ultrasound transducer in which the transmit and receive signals are transmitted symmetrically between the ultrasound transducer and the ultrasound electronics via a twisted pair of wires. US 2014 / 0269206 A1 also describes an arrangement comprising an ultrasound transducer and ultrasound electronics in which the signal transmission of both the transmit and receive signals occurs symmetrically via a twisted pair of wires. However, the pair of wires is not protected from interference fields and waves. The symmetrical feed of the transmit signals also requires a more complex high-voltage transmitter than the transmission via a coaxial cable described above.

[0010] US Patent No. 7,791,254 B1 describes a method and arrangement for signal transmission between an ultrasonic transducer and ultrasonic electronics, in which the transmission of the transmit signals and the receive signals takes place on different lines of a cable bundle. The receive signals are transmitted symmetrically via a pair of wires, while a coaxial cable is used for the transmission of the transmit signal. For the transmission of the receive signals, a preamplifier is additionally used in the probe, which amplifies the receive signals from the ultrasonic transducer and then transmits them symmetrically.

[0011] WO 2019 / 180094 A1 discloses a method for signal transmission between an ultrasonic transducer and ultrasonic electronics, in which the signal is transmitted via a cable connection comprising, among other things, a wire pair and a shield for the wire pair. The received signals are transmitted symmetrically via the wire pair, while the transmitted signal is transmitted via a separate line of the cable connection.

[0012] DE 196 13 311 A1 describes an ultrasonic flow measuring device in which each ultrasonic transducer is decoupled from the control and evaluation device by means of a transmitter.

[0013] DE 197 01 334 C2 describes an ultrasonic transducer arrangement in which decoupling between the transmit and receive signals takes place via a center tap of a transformer. Description of the invention

[0014] The object of the present invention is to provide a method for signal transmission between an ultrasonic transducer and ultrasonic electronics as well as an associated arrangement in which the cable connection between the ultrasonic transducer and the ultrasonic electronics has a lower sensitivity to mechanical stress than coaxial cables and yet a transmission of the received signals with high interference immunity is achieved.

[0015] The object is achieved by the method and the arrangement according to patent claims 1 and 10. Advantageous embodiments of the method and the arrangement are the subject of the dependent patent claims or can be derived from the following description and the exemplary embodiments.

[0016] In the proposed method, signals are transmitted via a cable connection that has at least one symmetrical wire pair and a shield for the wire pair. The transmitted signals are transmitted asymmetrically via both wires of the wire pair, with the shield serving as the return conductor. The received signals, in contrast, are transmitted symmetrically via both wires of the same wire pair. Symmetrical transmission means that the portion of the received signal transmitted via one wire of the wire pair has the opposite polarity to the portion (of the same amplitude) of the received signal transmitted via the other wire of the wire pair (differential transmission). In asymmetrical transmission of transmitted signals, both signal components transmitted via the wire pair have the same polarity. In symmetrical transmission, inductively and capacitively coupled interference has the same effect on both wires.By calculating the difference between the two signal components on the receiver side, the interference signals can then be eliminated. The two wires of the wire pair are symmetrical, meaning they have identical electrical properties. Additionally, the wires can be twisted against each other.

[0017] The proposed method uses a connection via shielded cables with a single wire pair, with the transmission of transmit and receive signals taking place in different modes. The receive signals are transmitted symmetrically, while the transmit signals are transmitted asymmetrically in parallel, with the shield serving as the return conductor. The transmit and receive signals run over the same wire pair. The wire pair can be individually twisted (twisted pair) or present in another configuration within the cable, such as a star-quad. The method can also be used with multi-element transducers (ultrasonic transducer arrays), in which case a corresponding number of wire pairs can be used in one cable or even several cables with corresponding wire pairs.

[0018] With the proposed method and the associated arrangement, reduced sensitivity to external interference fields and waves is achieved compared to coaxial cables through the symmetrical signal transmission of the received signals in addition to shielding. Using a shielded pair of wires instead of a coaxial cable also results in reduced sensitivity to mechanical stress, as such cables are better suited for highly flexible applications such as drag chains and robot arms. Unlike coaxial cables, multi-core shielded cables generally do not have a solid dielectric, which can be sensitive to mechanical stress and increases the cable diameter. Instead, the individual wires are only insulated from each other by a thin sheath.By utilizing symmetrical signal transmission for the receive signals and asymmetrical transmission for the transmit signals on a shielded wire pair, different characteristic impedances are advantageously achieved in the transmit and receive directions. Typical line impedances for symmetrical signals on wire pairs are in the range of approximately 80 to 120 Ω. When connected directly to the wire pair, the ultrasonic transducer is subjected to less electrical load than with coaxial cables with 50 to 75 Ω. In the transmit direction, however, the wires are connected in parallel and operated asymmetrically against the shield, which serves as the return conductor. The resulting line impedance for this mode is usually less than half the symmetrical impedance, typically 30 to 50 Ω, so that more power can be transmitted in the transmit direction at the same voltage.The proposed method and the associated arrangement also provide the possibility of impedance matching and amplification of the received signals on the ultrasonic transducer side.

[0019] At the ends of the transmission path, i.e., the cable connection between the ultrasonic electronics and the ultrasonic transducer, depending on the transducer type and ultrasonic electronics, circuits are required to separate the transmitted and received signals and / or to mode-match them, i.e., to balance / debalance them. Debalance refers to the combining of the symmetrically transmitted signal components, which compensates for or eliminates any interference fields and waves affecting the cable connection. This usually involves calculating the difference between the two symmetrical signal components. The circuits for separation and / or mode-matching can be implemented actively or passively and can also simultaneously include impedance matching and signal amplification. They can be located in the housing of the ultrasonic transducer or probe and in the housing for the ultrasonic electronics.Alternatively, these circuits can also be installed upstream and downstream in separate housings, so that existing conventional ultrasound devices and ultrasound probes can be adapted.

[0020] In an advantageous embodiment, the received signals are each balanced via a transformer on the ultrasonic transducer and / or debalanced or combined via a transformer in the ultrasonic electronics. Impedance matching can then also be achieved via the winding ratios of the transformers. With such a configuration, the transmitted signal can be fed in or tapped off via a center tap of the transformer. In other embodiments, the decoupling between the transmitted and received signals can also be achieved via suitable diode circuits.

[0021] In a further embodiment, the desymmetrization of the received signals on the ultrasonic electronics side is carried out by a differential amplifier.

[0022] The ultrasonic transmitting and receiving arrangement designed to carry out the method accordingly comprises at least one ultrasonic transducer and at least one ultrasonic electronics unit in which transmit signals for the ultrasonic transducer are generated and receive signals from the ultrasonic transducer are recorded and / or processed. The cable connection for signal transmission between the ultrasonic transducer and the ultrasonic electronics unit comprises at least one wire pair and a shield for the wire pair. Circuits are then provided on the ultrasonic transducer and ultrasonic electronics sides through which the transmit signals are transmitted asymmetrically via both wires of the wire pair, with the shield as the return conductor, and the receive signals are transmitted symmetrically via both wires of the wire pair. The circuits are designed to separate the transmit and receive signals and / or to carry out mode matching.For this purpose, they can be designed in accordance with the advantageous embodiments of the method described above.

[0023] The proposed method and associated arrangement can be used, for example, for non-destructive material testing, technical sensor technology (fill level, flow, wall thickness, distance sensors, etc.) or for medical ultrasound applications. Short description of the drawings

[0024] The proposed method and the associated arrangement are explained in more detail below using exemplary embodiments in conjunction with the drawings. Herein: Fig. 1 a schematic representation of the signal transmission between ultrasonic electronics and ultrasonic transducer according to the prior art; Fig. 2 a schematic representation of the proposed method for signal transmission between ultrasonic electronics and ultrasonic transducer; Fig. 3 a schematic representation of a method not according to the invention for signal transmission between ultrasonic electronics and ultrasonic transducer; Fig. 4 an exemplary embodiment of the proposed arrangement for signal transmission via a single wire pair; Fig. 5 shows a further exemplary embodiment of the proposed arrangement for signal transmission via a single wire pair; and Fig. 6 shows a further exemplary embodiment of the proposed arrangement for signal transmission via a single wire pair. Ways to implement the invention

[0025] The proposed method uses a shielded pair of wires for signal transmission between the ultrasonic electronics and the ultrasonic transducer. The transmission of the transmit signal and the receive signal takes place via the same pair of wires.

[0026] Fig. Figure 2 shows a schematic diagram of the arrangement for signal transmission via a common wire pair. The figure shows the ultrasonic electronics 2 on the left and the ultrasonic transducer 1 on the right. A shielded wire pair 7 is used for signal transmission, as shown in the Fig. 2 is shown schematically. The ultrasonic electronics 2 has amplifiers for the transmit and receive signals as well as a device 6 for separating the transmit and receive signals. This device 6 splits the transmit signal 4 asymmetrically between both wires of the wire pair, as shown schematically in the upper part of the Fig. 2. The received signal 5, however, is distributed symmetrically to both wires of the wire pair by a symmetrizing circuit 8, as shown in the lower part of the Fig. 2 is shown schematically. This circuit 8 for balancing the received signal also includes a circuit for separating the transmitted and received signals. The device 6 for separating the transmitted and received signals in the ultrasonic electronics 2 also includes a circuit section that debalances the two symmetrically arriving received signal components, usually by forming a difference.

[0027] A method not according to the invention and an associated arrangement is shown schematically in Fig. 3. In this case, a shielded cable 9 with two pairs of wires is used for the connection, as indicated in the figure. The upper pair of wires carries the transmit signals 4, and the lower pair of wires carries the receive signals 5. The transmit signals 4 are again transmitted asymmetrically, while the receive signals 5 are transmitted symmetrically, as shown in the upper and lower parts of the Fig. 3. In this example, the unbalancing of the received signals 5 in the ultrasonic electronics 2 is achieved via a differential amplifier, while the distribution of the transmitted signals 4 between the two wires of the upper wire pair is achieved by simple branching. On the ultrasonic transducer 1 side, a circuit 8 is required to balance the received signals 5 and to separate the transmitted and received signals.

[0028] The circuits on the ultrasonic electronics 2 side and on the ultrasonic transducer 1 side, which are required for balancing / debalancing and for separating the transmit and receive signals, can be implemented in various ways. The following examples show different possibilities, but these are only examples. Those skilled in the art can also find other circuit variants that fulfill the functions required here.

[0029] In the example of Fig. 4, transmit and receive signals are transmitted via a single wire pair. An additional circuit is mounted on the ultrasound device 10, which generates the transmit signal and records or processes the receive signal. This circuit serves, on the one hand, to separate the transmit and receive signals and, on the other hand, to debalance the receive signal transmitted via the wires. On the side of the ultrasonic transducer 1, an additional circuit is provided for balancing the receive signal and separating the transmit and receive signals. The transmit signal is coupled into both wires in common mode via the diodes and is also coupled out via diodes on the transducer side. In this and the following examples, purely negative transmit pulses are assumed, as in the Fig. 2 and Fig. 3 were schematically indicated. Bipolar transmit signals can also be used with anti-parallel connected diodes or components with a comparable current-voltage characteristic, such as bipolar TVS diodes. The diodes have low resistance for the transmit signals, and high resistance for the receive signals. The breakdown or forward voltage determines the maximum possible voltage of the receive signals. The receive signals are balanced at the converter with a transformer and converted back into an asymmetrical signal on the opposite side. The winding ratios of the two coils of the transformer on the ultrasound device 10 side can be used to match the impedance between the line and the device resistance (usually 50 or 75 Ω). The resistance between ultrasonic transducer 1 and the transformer separates it from the high transmit voltages and simultaneously represents a load for the transmit signals, whereby the transformer usually goes into magnetic saturation.In the present and subsequent examples, a piezoelectric transducer is shown as ultrasonic transducer 1. However, the method and the circuits shown work for all transducer types in which the transmitted signals have significantly higher amplitudes than the received signals.

[0030] Fig. Figure 5 shows another example of a possible configuration of the proposed arrangement for transmitting transmit and receive signals via a single wire pair. Here, too, the receive signals are de-balanced or balanced via suitable transformers on the side of the ultrasound device 10 and on the side of the ultrasound transducer 1. However, the coupling and decoupling of the transmit signals takes place via a center tap on the transformers, as shown in the Fig. 5. The decoupling on the side of the ultrasonic transducer 1 is again achieved via corresponding diodes.

[0031] Fig. Figure 6 shows another embodiment of the proposed arrangement. The desymmetrization of the received signals on the side of the ultrasound device 10 is not performed via a transformer in this example, but rather by a differential amplifier. The separation of the transmitted and received signals is performed as in the design of the Fig.3. The series resistors in conjunction with the clamp diodes at the inputs protect the differential amplifier from the transmitted signals. On the ultrasonic transducer 1 side, mode separation is achieved by a diode network, shown here again as an example for negative transmitted voltages. During transmission, all diodes are low-impedance due to the forward voltage being exceeded, and the transmitted voltage is switched from both wires to one transducer pole. The other transducer pole is grounded by anti-parallel diodes that are also switched to ground. In the received signal, the diodes are high-impedance for signals below the forward voltage. Ultrasonic transducer 1, now floating relative to ground, feeds the signal symmetrically into the cable or wire pair via two resistors. List of reference symbols 1 ultrasonic transducer 2 Ultrasonic electronics 3 coaxial cables 4 Transmission signal 5 Reception signal 6 Device for separating transmit and receive signals 7 shielded cable with wire pair 8 Circuit for balancing and separation 9 shielded cable with two wire pairs 10 Ultrasound device

Claims

[1] Method for signal transmission between an ultrasonic transducer (1) and an ultrasonic electronics unit (2), in which transmission signals (4) for the ultrasonic transducer (1) are generated and reception signals (5) from the ultrasonic transducer (1) are recorded and / or processed, in which - the signal transmission takes place via a cable connection (7) which has at least one wire pair and a shield for the wire pair, - the transmission signals (4) asymmetrically over both wires of the wire pair with the shielding as the return conductor and - the received signals (5) are transmitted symmetrically via both wires of the same wire pair. [2] Method according to claim 1, characterized by that a cable connection (7, 9) is used in which the wire pair is twisted. [3] Method according to claim 1 or 2, characterized by that the received signals (5) are symmetrical via a transformer on the ultrasonic transducer (1). [4] Method according to claim 1 or 2, characterized by that the received signals (5) are symmetrical via a fully differential amplifier on the ultrasonic transducer (1). [5] Method according to one of claims 1 to 4, characterized by that the received signals (5) are combined via a transformer in the ultrasonic electronics (2). [6] Method according to claim 3 or 5, characterized by that impedance matching is achieved via a winding ratio of the transformer. [7] Method according to one of claims 3, 5 or 6, characterized by that a decoupling between the transmit and receive signals (4, 5) is achieved by the transmit signal (4) being fed in or tapped off via a center tap of the transformer. [8] Method according to one of claims 1 to 4, characterized by that the received signals (5) are combined via a differential amplifier in the ultrasonic electronics (2). [9] Method according to one of claims 1 to 8, characterized by that decoupling between transmit and receive signals occurs via diodes. [10] Ultrasonic transmitting and receiving arrangement with at least one ultrasonic transducer (1) and at least one ultrasonic electronics unit (2), in which transmitting signals (4) for the ultrasonic transducer (1) are generated and receiving signals (5) from the ultrasonic transducer (1) are recorded and / or processed, and a cable connection (7) for signal transmission between the ultrasonic transducer (1) and the ultrasonic electronics unit (2), in which the cable connection (7) has at least one wire pair and a shield for the wire pair, and circuits are provided by which the transmitting signals (4) are transmitted asymmetrically via both wires of the wire pair with the shield as a return conductor and the receiving signals (5) are transmitted symmetrically via both wires of the same wire pair.

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