Method of Providing Ultrasound Electrical Impedance Matching Circuits

This invention pertains to electrical circuits, and, in particular, to a method of providing an ultrasound electrical impedance matching circuit which incorporates the use of a computer software program to accomplish this goal.

There have been a number of attempts to design systems to match and evaluate ultrasonic system characteristics. The reason an ultrasound system is such a problem is that the return signal is transmitted over the same coaxial cable as the receive signal. The receive signal is 120 dB down from the transmitted signal. This means that maintaining the lowest possible attenuation during the transmission of the received signal from the acoustic medium of the transducer to the electrical medium of the system controller is imperative. The tuning circuits calculated by the matching software make this goal attainable. This is a desirable goal in order to make the ultrasound system perform more accurately and thereby give better results in its designated uses. What has not been accomplished is a system that will provide the best impedance matching of a transducer to a fixed single ultrasound cable impedance and with different ultrasound system receiver transmitter impedance elements with inductors and capacitors. All components--transducer, cable, rectifier, transmitter--have different impedances and the software will select the electrical matching component to provide the best two way voltage transfer. Another element that has not been accomplished is the design of a system which will select the nearest commercially available components and will display a schematic of the closest matching network circuit. No current systems are available that specialize in medical ultrasound system matching and also allow for the incorporation of characteristic data from a microminature coaxial cable.

Clearly, it is desirable for a method for producing ultrasound electrical impedance matching circuits which is simple to use and, at the same time, be very accurate and effective. It is also a worthwhile purpose to produce a program that will permit the user to use experimental or theoretical data to be selected when inputting parameters from the cable impedance or loss information, from the transducer impedance data, and the system generator and or receiver impedance data. An object of this invention is to provide a method that provides the user with a simple and easy installation of the program with no external pieces in order for it function. It is an object of this invention to set forth an improved method of providing ultrasound electrical impedance tuning circuits thus improving signal to noise ratio, bandwidth and two way voltage transfer which avoids the disadvantages, limitations, above-recited, obtained from other circuit matching systems.

Particularly, it is the object of this invention to set forth a method of providing ultrasound electrical impedance matching circuits, for use in order to evaluate the effectiveness of the operating circuit, comprising the steps of storing in a software package an electrical model of an ultrasound in the transmitting mode which gives values to the system generator output voltage, the system output impedance, the transducer input impedance, the voltage at the transducer and the cable system; storing in a software package an electrical model of an ultrasound system in the receiving mode which gives values to the impedance of the receiver, the transmitter transducer output impedance, the transducer's induced output voltage, the voltage at the receiver and the cabling system; modeling the transducer and the transmitting/receiving switch; cable; determining the design frequency impedance; determining the end to insert the matching network; transforming the transducer or transmitting/receiving switch to the other end of the transmission line; calculating the matching network based upon the fixed and rotated impedance; inserting the matching network into the ultrasound system and simulating and evaluating the ultrasound system.

Further objects and features of this invention will become more apparent by reference to the following description taken in conjunction with the accompanying figure, in which:

FIG. 1 is a schematic view of the ultrasound system in the transmitting mode;

FIG. 2 is a schematic view of the ultrasound system in the receiving mode;

FIG. 3 is a schematic view of the matching network being inserted into the ultrasound system in the receiving mode;

FIG. 4 is a schematic view of the matching network being inserted into the ultrasound system in the transmitting mode;

FIG. 5 is a block diagram of the novel software program;

FIG. 6 is a graphical representation of the voltage transfer of the system;

FIG. 7 is a graphical representation of the impulse response of the system; and

FIG. 8 is a graphical representation of the convolution response of the system.

As shown in the figures, the novel method of providing ultrasound electrical impedance matching circuits allows the operator to be able to use the software that is capable of designing a one or two component circuit that will tune the impedance of a transducer to an ultrasound cable and system receiver elements and, at the same time, automatically select the nearest commercially available components and displays a schematic of the matching network circuit. As shown in figures one and two, the software program has modeled the ultrasound system in the transmitting mode with the system generator output voltage being given the value Vg, the system output impedance being given the value Zg, the ultrasound cabling system being labeled the cable, the transducer electrical impedance given the value X1 and the voltage at the transducer given the value Vx. The modeling of the ultrasound system in the receiving mode with the receiver impedance is given the value Zr, the transducer electrical impedance given the value X1, the transducer's induced voltage given the value Vx, the voltage at the receiver given the value Vr and the ultrasound cabling system being labeled cable. These parameters can be derived from the lumped element networks, piezoelectric analysis or from impedance values measured with an impedance analyzer test equipment.

The program uses the concepts of transmission line theory which measures the physical length of the transmission line, the input impedance at some frequency with the line open and the input impedance at the frequency with the line short circuited. The transmitting/receiving switch cable and transducer can be modeled at either the system or transducer interface connectors. The design frequency impedances are determined and the end into which to insert the matching network is determined. The transducer or transmitting/receiving switch impedance is transformed to the other end of the transmission line. The matching network is calculated based upon the reactance of the fixed and rotated impedances and the matching network is inserted into the ultrasound system as shown in FIG. 3 (the receiving mode) and FIG. 4 (the transmitting mode). In those schematics, m1 is the parallel inductor network and n1 and n2 are inductor and capacitor of a PI network. The software designs a tuning circuit based upon the impedance matching and maximum voltage transfer and uses the capacitance of the cable to design the PI network to have only two instead of three components.

The software program uses a number of parameters such as design frequency, cable and transducer impedance list, piezoelectric parameters, system transmitting/receiving elements, the length of the cable, and the network type. The software processes the input parameters into a matching network to design for maximum power and voltage transfer across a wide frequency band. The output parameters of the software are the schematics shown and the plots of a two way voltage transfer (which is defined as the voltage of the receiver divided by the voltage of the generator and is closer to zero when the tuning network is utilized), the signal to noise ratio of the received signal, the two way impulse response of the ultrasound system (defined as the inverse fourier transform of the voltage transfer function), cable and transducer electrical port and the convolution of the system response with a real stimulus (defined as the convolution of the system impulse response with a given input stimulus function) as shown in FIGS. 6, 7 and 8. One of the advantages of the software system is its ability to compare the system response with the tuning network versus without the tuning network.

Among the future embodiments of the novel method and means is the capability to be able to have an electronic bulletin board delivery system version of the novel software. An outline of the software operating instructions is presented below to clarify the functions of the software. ##SPC1##

While we have described our invention in connection with specific embodiments thereof, it is clearly to be understood that this is done only by way of example and not as a limitation to the scope of our invention as set forth in the objects thereof and in the appended claims.