Multiple frequencies from single crystal

A method and an apparatus for ultrasound imaging at different frequencies using a single ultrasound transducer. The transducer has a single characteristic frequency. The method and apparatus involve driving the transducer with pulses having different rise times through different coupling circuits having different impedance characteristics. Between pulses, the same transducer and coupling circuit which were used during the pulse transmission "listen" for echoes from the structure being ultrasonically investigated. It is believed that the combination of different pulses having different rise times and different coupling circuits having different characteristics enhances different ones of the frequencies contained in the Fourier spectrum of the driving pulse and suppresses others. This enables the operator to investigate a structure ultrasonically with a single transducer at different frequencies which illuminate different characteristics of the structure to greatest advantage.