Stacked composite piezoelectric materials for 1.5-D arrays

Composite piezoelectric materials with a 1-3 connectivity are almost ideal for transducer applications where the width-to-thickness aspect ratio of individual elements is in the range of about 0.7 to 10 (the range required for most 1.5-D array applications). The high anisotropy of the composite enhances coupling in the thickness mode but reduces the coupling and damps vibrations in the lateral direction. One major drawback of these composites is that the reduced volume fraction of ceramic results in elements with a low capacitance and high electrical impedance making the small elements difficult to drive. A solution to this drawback is to stack the composite material in n layers and connect the layers in parallel to achieve the n² reduction in electrical impedance. This paper presents a method for making stacked composite material and using them in 1.5-D arrays. This method consists of stacking 2-2 composites with the strips running in the scan-plane of the proposed array and creating the 1-3 structure during array construction by using standard dicing and subdicing techniques of the acoustic stack. Measured results from stacked composites made by both the dice-and-fill and injection mold-and-fill methods are presented and compared. The consequences of misalignment are shown and analyzed. The cost implications for both dice-and-fill and injection mold-and-fill methods are discussed