High strength edge bonds between individual sapphire components have been developed as a means to produce affordable large area windows. Several bonding methods have been demonstrated, with bond fracture strengths ranging from 100-200 MPa. When polished, the bonded windows show excellent transmittance with no degradation in transmitted wavefront quality. The bonding processes have recently been scaled up to 355mm wide, 10mm thick bond lines and multipane windows. Using singly-curved sapphire components for the individual panes, doubly-curved bonded sapphire components have also been produced and polished with excellent results. The edge bonding approach shows promise for fabricating affordable sapphire windows up to 750mm diameter. In addition, recent developments with index-matching glass coatings show the feasibility of substantial cost reductions in optical finishing of sapphire windows, particularly for transparent armor.
With the objective of producing affordable large area windows, high strength edge bonds between individual sapphire components have been developed. Several bonding methods have been demonstrated, with bond fracture strengths ranging from 100 - 200 MPa. The directed energy process, which yields the strongest bonds, has produced bonded sapphire components 600 mm long and 3 mm thick with a 75 mm wide bond line. When polished, the bonded windows show no degradation in transmittance or transmitted wavefront quality. The processes have recently been scaled up to 355 m wide, 10 mm thick bonds lines and multipane window blanks. In addition, doubly-curved bonded sapphire components have been produced and polished with excellent results, using singly curved sapphire components for the individual panes. The edge bonding approaches shows promise for fabricating affordable sapphire windows up to 750 mm diameter.
High strength edge bonds have been achieved between individual sapphire components, showing promise for fabricating window blanks up to 600 mm diameter or larger in size. Several bonding methods were investigated, with a directed-energy diffusion-bonding method yielding components with bond fracture strengths of 200 MPa. Bonded sapphire components 600 mm long and 3 mm thick with a 75 mm wide bond line have been produced. When polished, the bonded windows show no degradation in transmittance or transmitted wavefront quality. Process scale up to larger bonds lines is planned. Mechanical and optical characterizations of sub- scale edge-bonded sapphire windows are presented.
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.
A process is presented for fabricating titanium doped silica aerogels. Aerogels were produced by the hydrolysis of TEOS and titanium isopropoxide in ethanol and then supercritically dried in a nitrogen overpressure. A detailed study of gelling and annealing was performed to minimize shrinkage and produce dried gels with densities less than 10% of ordinary glass. Lightweighted structures with densities between 0.16 g/cm3 and 0.06 g/cm3 were produced.
Close attention to crystal growth parameters and characterization of the crystal's thermal environment during growth has led to improvement in the crystal structure of EFG grown dome blanks. These near net shape 80 mm sapphire blanks have been fabricated to produce high quality finished domes. New measurements of the coefficient of thermal expansion (CTE), thermal conductivity, optical scatter, rain erosion and the thermal coefficient of refractive index (dn/dT) as a function of wavelength have been performed and the data are presented.
A polishing process for fabricating high-quality optical sapphire windows is presented. This process was successfully used to produce very high aspect ratio, as high as 1500:1, sapphire windows for use in optical imaging systems. During the development of the process as unusual print-through phenomenon was discussed. This replication of surface features on the blocking bodies, such as bumps or grooves, onto the polished window surface produced distortion in the final wavefront and degraded window performance. A method of bonding smaller, thick sapphire panes into a larger optical window is also presented. A glass fritting process utilizing two different temperature frits is discussed. The optical errors encountered during fritting which contribute to the optical error budget and methods for minimizing their effect on the wavefront of the final window are also reviewed. An 8' diameter X 0.435' optical sapphire window was produced using this fritting technology.
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