Refractive index matching glass coatings have been applied to mechanically-ground sapphire blanks using a modified glazing technique. The as-fired coatings are optically clear and well adhered, producing coated sapphire windows with up to 88 percent in-line transmittance and excellent optical imaging characteristics. Coated sapphire windows up to 150 x 230 mm in size have been produced, with additional scale-up to at least 300 x 350 mm planned for the near future. Glass-coated sapphire (GCS) can be rapidly polished in a small fraction of the time required for sapphire itself, thereby substantially reducing the cost of transparent armor. Glass-coated sapphire windows are also being evaluated for precision airborne reconnaissance and FLIR systems, to determine the limits, if any, to transmitted wavefront quality. The feasibility of applying index matching glass coatings to sapphire dome shapes has also been demonstrated. Index matching glass has also been used as a bonding material to fabricate actively cooled sapphire windows with internal channels for hypersonic missiles.
Large area sapphire windows have been fabricated by edge-bonding multiple panes. A 4-pane edge-bonded 320 x 410 x 7 mm sapphire window with excellent optical characteristics has been successfully finished. Two different bonding methods were used to build up the 4-pane window blank. Pairs of commercially available EFG sapphire panes were first bonded using a 1500°C bonding process. The bonded pairs were then joined using a 1100°C process. Bond strengths for the two methods are approximately 130 MPa (20 kpsi). Optical finishing was completed using standard methods for sapphire with no significant increase in finishing time caused by the bonds. There are no deleterious optical effects or visible optical distortion due to the bond lines. The edge bonding technology can now produce 600 x 600 mm flat window blanks. Conformal windows have also been produced using the edge bonding method. Very high bond strengths of 250 MPa (37 kpsi) have been attained on smaller samples using an optimized solid ceramic fillet.
Smart materials based on 1-3 piezocomposite transducers, capable of both sensing and actuation, are being developed for active control applications. Large area, low profile SmartPanels, consisting of 1-3 piezocomposite actuators and pressure sensors and net-shape-molded PZT accelerometers, have been fabricated and evaluated for surface mounted boundary control applications. Single layer and two-layer 100 X 100 mm and 250 X 250 mm SmartPanels have been tested for actuator authority, surface displacement uniformity, sensor-actuator coupling, and surface vibration reduction. Single layer SmartPanels have shown broad band 20 dB surface vibration reduction.
Piezocomposite SmartPanels, consisting of 1-3 actuators and pressure sensors and net-shape PZT accelerometers in a large area, low profile panel, have been fabricated and evaluated. Single layer and two-layer 100 x 100 mm and 250 x 250 mm SmartPanels have been tested for actuator authority, surface displacement uniformity, sensor-actuator coupling, and surface vibration reduction. Single layer SmartPanels have demonstrated a broad band 20 dB underwater surface vibration reduction. Current development activities include electronics integration for surface mounted SmartPanels and investigation of SmartPads in hybrid active-passive vibration isolation mounts. SmartPanels draw upon PZT injection molding technology, which is used to produce cost- effective and robust 1-3 piezocomposite materials. The piezocomposites are used extensively for SonoPanel transducers in a number of sensor and actuator applications. SonoPanels are qualified for US Navy applications, based on successful completion of pressure and shock tests, and are available in sizes up to 750 x 750 mm. Applications and performance for SmartPanels and SonoPanels are descried, including multi-element arrays, velocity sensors, and underwater vibration and noise reduction devices.
Piezocomposite SmartPanelsTM, consisting of 1-3 actuators and pressure sensors and net-shape-molded PZT accelerometers in a large area low profile panel, have been fabricated at Materials Systems Inc. and evaluated at the Naval Research Laboratory. Single layer and two-layer 100 X 100 mm SmartPanels have been tested for sensor sensitivities, actuator authority, surface displacement uniformity, and sensor-actuator coupling. Multilayer GRP circuits boards are used both as stiff faceplates and to provide electrical connections and ground planes. The SmartPanel technology has recently been scaled up to 250 X 250 mm devices. SmartPanels draw upon PZT (lead zirconate titanate) ceramic injection molding technology, which is used to produce cost-effective and robust 1-3 piezoelectric ceramic-polymer composite materials. The 1-3 materials are used extensively for SonoPanelTM transducers in a number of sensor and actuator applications. SonoPanels have been qualified for US Navy applications, based on successful completion of pressure and shock tests, and are currently being scaled up from 250 X 250 mm to 750 X 750 mm panels. Several applications for SmartPanels and SonoPanels are described, including conformable transducers, multielement arrays, pressure sensors, and velocity sensors.
A cost-effective technology has been developed for producing 1-3 piezoelectric ceramic/polymer composites for active surface control. SonoPanelTM 1-3 piezocomposite transducers consist of an array of piezoelectric ceramic rods in a polymer matrix. Stiff face plates are bonded to the composite for stress amplification when used as a sensor and to enhance surface response uniformity when used as an actuator. Many piezocomposite design variations have been produced for specific applications. The key technology in SonoPanelTM manufacturing is the PZT ceramic injection molding process. Using this process, an entire array of piezoelectric ceramic rods are molded in one operation using specially designed tooling. Injection molded PZT preforms are formed at a rate of one per minute. Several thousand components with excellent piezoelectric properties and part-to-part reproducibility have been manufactured to date. The piezocomposite fabrication process has been scaled up for low volume manufacturing. More than thirty 250 X 250 mm SonoPanelTM transducers have been produced and evaluated. The transducers show high receiving voltage sensitivity and transmitting voltage response as well as symmetrical beam patterns. Next generation SonoPanelTM transducers, with materials and designs optimized for Navy systems, are under development, including advanced panels for active surface control. The devices incorporate actuators, pressure sensors, and velocity sensors--all made from 1-3 composite materials--into an autonomous smart panel.
This paper describes a fabrication approach for producing high-sensitivity low-cost accelerometers. This approach offers the potential for intrinsically combining accelerometers as a dense array within an actuator. Hence sensing and actuation functions can be combined into one co-formed inexpensive transducer array. Results are presented which show that the combined transducer has predictable properties and is well suited for use in sensing, actuation, and active-control applications.
A manufacturing capability has been established for 1-3 PZT-polymer composite materials and transducers. Uniform arrays of identical PZT rods are formed by a cost-effective ceramic injection molding process. Sintered and poled 1-3 ceramic preforms, containing 361 PZT rods 1.1 mm diameter on a 50 mm square base plate, are arranged to produce 15 or 30 PZT volume percent composite materials with a hard or soft polymeric matrix. More than 2000 identical PZT preforms were produced and more than thirty 250 mm square SonoPanel transducers have been manufactured. The transducers have been found to be well suited for a variety of underwater acoustic applications. Fifteen SonoPanels have been incorporated into a 3 X 5 array as part of a Navy system demonstration.
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