Mark Chase

Piezoelectric ceramic hydrostatic sound sensor

A piezoelectric ceramic hydrostatic sound sensor or transducer having highensitivity to hydrostatic pressure is made by placing a flat plastic disc between two flat layers of green ceramic material, compressing and fusing the layers, heating to a first temperature at which the plastic decomposes, leaving a flat void in the ceramic, and heating to a second temperature at which the ceramic sinters. The transducer is provided with electrodes on its top and bottom surfaces. In a further improvement, ceramic particles are provided which are entrapped in the void; they render the sound sensor sensitive to inertial forces. In yet another improvement, the inside walls of the void are coated with a conductive noble metal connected to a terminal wire, whereby an additional electrode is provided for sensing the electromechanical response of the transducer.

High authority, telescoping actuators

A family of high authority actuators was developed at the Naval Research Laboratory. These actuators are based on displacement amplification within a compact, solid state, monolithic piezoelectric actuator, by using a telescoping tube design. In this design, concentric tubes are mechanically connected in series. This gives an effective actuator length that is equal to the sum of the lengths of the individual concentric elements. The high displacement output of this actuator permits efficient coupling of the actuator output into a load of similar impedance, and thereby much greater effective actuator output. Initial prototypes were made of commercially available PZT tubes of three different diameters and wall thickness. These tubes were pulsed through the thickness of the walls and the change in their lengths were used for actuation. Their actuation is therefore making use of the d31 piezoelectric coefficient. Alternatively, electrodes can be applied to the ends of the individual concentric tubes and their lengthwise displacement will subsequently be proportional to the d33 parameter of the material. The tubes were bonded at their ends to alumina plates using epoxy-based adhesive. The displacement obtained from the assembly is close to the sum of those of the three individual tubes at the same applied field. Other parameters such as blocking force and energy densities are also reported. These actuators have applications where high force and simultaneously large displacement are required and space is limited. Potential uses include high end aerospace as well as low tech commercial applications.

PiezogranTM: High sensitivity/low‐cost composites for wide aperture arrays

A shift in US Navy emphasis from blue water to littoral regions has resultled in a need for improved acoustic devices. Wide aperture arrays will be hull‐mounted, thereby making device weight critical. The Naval Research Laboratory has developed a unique, low‐weight composite, transducer design, PiezogranTM, to address this need. Piezograns consist of discrete, polycrystalline piezoelectric‐ceramic elements dispersed in an epoxy matrix between two pressure plates. These plates make a direct mechanical as well as electrical contact to the piezoelectric elements. This design approach uses a 1‐3 composite structure for high‐gain operation with the flexibility of variable element spacing and ceramic volume fraction while achieving both low tooling and fabrication costs. Independent tests of 3.8‐cm diameter PiezogranTM prototypes have yielded high hydrostatic response (dh>150 pC/N) and capacitance of 1.18 nF. Ten‐centimeter‐square array panels have also been assembled and are currently undergoing testing. This ...