The sonar systems that are used by many of the world’s navies contain ceramic materials, as they offer solutions where high acoustic transmission properties are required in low frequency environments. Morgan Advanced Materials is now able to provide products that are operable at extremely low depths, and which are able to continue to work even in the most severe bath thermal conditions, where water temperature falls as water depth increases.
To produce low frequency active sonar, Morgan currently manufactures a range of ‘stave’ components, assembled together to create large ceramic rings and used as underwater projector transducers. To combat size restrictions, electrodes are positioned between each ceramic segment, with the segments then poled around the circumference. This arrangement is also known as a segmented construction and allows for very large rings to be constructed, although careful control of the tolerance is necessary to obtain a well-consolidated assembly with uniform joints.
Ceramic stave components are available from Morgan Advanced Materials in a combination of lengths and widths, ranging from 10mm to 165mm, with thicknesses ranging from 10mm to 40mm. They can be manufactured to specific a range of angular specifications allowing for large diameter assembled rings to be created. Larger or smaller sized staves outside these dimensions can also be created.
Various additional geometries are available with a choice of specially machined notch grooves to allow easier integration and soldering of connecting wiring and customized angle apertures to manufacture substantially larger diameter and lower frequency transducers. In addition, Morgan offers stave sub-assemblies and pre-stressing of stave sub-assemblies complete with a range of insulated flexible wire terminals.
Suitable materials for sonar transducers include PZT400 and PZT800 series piezoelectric formulations, which are both considered as ‘hard’ materials and therefore suitable for underwater naval operations. These piezoelectric formulations ensure low dielectric and mechanical losses in the transducer for optimum acoustic output and efficiency. Multi-element piezoelectric rings are used to ensure that the coupling coefficient of the transducer is substantially higher than for the single monolith piece ring with radial poling. When driven to high power, the joints and ceramic are subjected to high levels of tensile stress, therefore some level of pre-stress is necessary to lower the rate of expansion. This is achieved through a customized process of circumferentially compressing the ring, and consolidating the whole assembly in epoxy resin.
Free flooded rings are one type of efficient transducer benefiting from this manufacturing technology. This transducer is simply a radiator, which provides omni-directional coverage from the axis of the ring. Free flooded rings provide numerous benefits such as high power handling, low mechanical quality factor and virtually no performance changes due to hydrostatic pressure.
According to Frederic Pimparel, Technical Manager for Morgan Advanced Materials, “We work closely with our clients in the defence and security industries to listen and really understand their challenges. The launch of the stave shaped component range reflects our commitment to radical innovation and to bringing to life the products that our clients want and need. We believe that this ethos to work for our customers is what allows us to retain our position as leader in the design and manufacture of electro-ceramic products for the security and defence markets.”