Patent ID: 6645150
Filing Date: 2003-11-11
Classification: B06B,G10K,H04R

Abstract:
An ultrasound bulk wave transducer for transmission and reception of ultrasound pulses in one of a wide band and multiple bands of frequencies, where the ultrasound is radiated from a front face of the transducer and in a thickness direction normal to the radiating front face, comprising:a high impedance section composed of multiple, stacked layers with at least one piezoelectric layer and at least one additional elastic layer, the at least one piezoelectric layer having a front face and a back face that are covered with conducting electrodes to form two connections for at least one electric layer port, the layers having characteristic impedances so close to each other that the total thickness of the high impedance section defines the thickness resonance frequencies of the high impedance section with open electric ports of the piezoelectric layers, a back face of the high impedance section being acoustically connected to a backing material and optionally through a back impedance matching section comprised of a stack of at least one elastic layer, the backing material having a sufficiently large acoustic absorption that reflected waves in the backing material can be neglected, a front face of the high impedance section being acoustically connected to a load material through a load matching section composed of a set of elastic layers, the characteristic impedance of the layers of the load matching section lying between that of the high impedance section and of the load material with monotonously falling values from the high impedance section towards the load material, and at least one electric layer port being used for electro-acoustic coupling to vibrations of the transducer radiating front face at frequencies at which the thickness of the high impedance section is substantially larger than half a wave length.