| 摘要 |
<p>Ultrasound bulk wave transducers and bulk wave transducer arrays for wide band or multi frequency band operation, in which the bulk wave is radiated from a front surface and the transducer is mounted on a backing material with sufficiently high absorption that reflected waves in the backing material can be neglected. The transducer is formed of layers that include a high impedance section comprised of at least one piezoelectric layer covered with electrodes to form an electric port, and at least one additional elastic layer, with all of the layers of the high impedance section having substantially the same characteristic impedance to yield negligible reflection between the layers. The transducer further includes a load matching section comprised of a set of eleastic layers for impedance matching between the high impedance section and the load material and, optionally, impedance matching layers between the high impedance section and the backing material for shaping the transducer frequency response. For multiband operation, the high impedance section includes multiple piezoelectric layers covered with electrodes to form multiple electric ports that can further be combined by electric parallel, anti-parallel, serial, or anti-serial galvanic coupling to form electric ports with selected frequency transfer functions. Each electric port may be connected to separate electronic transceiver systems to obtain, through selection of drive signals on individual ports, selectable electric parallel, anti-parallel, serial, or anti-serial coupling of the ports in transmit mode, enabling transmission of ultrasound pulses with multi-band frequency components. In receive mode, signals from the individual electric ports can be combined after isolation amplifiers in a filter-combination unit to obtain composite electric ports with extreme wide-band transfer functions and multi-band transfer functions covering a range from a 1st to a 4th harmonic band.</p> |
