Ultrasonic transducer interface-circuit for simultaneous transmitting and receiving

In some single transducer ultrasound applications it is useful to be able to receive echo signals during transmitting. Thereby it´s possible to measure short distances of nearby obstacles. However only a few solutions for this problem are described in the literature and none is known to be used in an industrial application. This contribution presents an interface circuit which permits to receive and transmit simultaneously during the steady state of the transducer. Therefore the transducer is connected to a sine-burst generator via a series resistor. A differential amplifier is used to extract the received signal of the signal measured at the transducer. It subtracts a compensation signal, which is similar to the electrical transmitter signal, from the signal measured at the transducer, so only the received signal is left in the measurement. This compensation signal is generated with the generator signal using a phase shifter and a variable gain amplifier. To understand the function and the limits of this approach the theoretical background of the signal separation is described at the beginning of the contribution. Afterwards the used circuit is introduced. Finally the results using this circuit for a burst-echo measurement are presented and discussed.