Place resistor between signal generator and transducter, use scope to monitor signal level across transducer. For transmitter adjust frequency for minimum signal. Measure signal BOTH sides of resistor, you can then work out the current through it, and from that the impedance of the transducer - simple ohms law.
Do the same with the receiver, but adjust for maximum, and use a much higher value resistor - to be honest, there's no real need to measure the receiver!.