Crystal pickup

The last volume of this miniseries, 21, Part D, covers device applications, including solar cells, electrophotography, image pickup tubes, field effect transistors (FETs) and FET-addressed liquid crystal display panels, solid state image sensors, charge-coupled devices, optical recording, visible light... 

The main types of SiOj used in indu.siry are high-purity a-quanz, vimeous silica, silica gel. fumed silica and diaiomaceous eanh. The most important application of quartz is as a piezoelectric material (p. 58) it is used in crystal oscillators and filters for frequency control and modulation, and in electromechanical devices such as transducers and pickups tens of millions of such devices are made each year. There is insufficient natural quartz of adequate purity so it must be synthesized by hydrothermal growth of a s crystal using dilute aqueous NaOH and vitreous SiOy at 4(I0°C and... 

Properties Hazen 150 color thinnable with ether esters, aromatics, alcohols dilutable with ketones, esters dens. 0.9 g/cm (20 C) vise. 12,000 03000 mPa-s-(23 C) 25 01% NV Toxicology Harmful avoid skin/eye contact, inh. of vapors Precaution Highly flamm. take precautions against electrostatic pickup Storage 6 mos min. shelf life when stored in sealed containers below 30C may crystallize below 5 C heat to 30 C max. and homogenize before use... 

Currently, quartz is often utilized in accelerometers. Due to their high piezoelectric voltage coefficient lithium sulfate and tourmaline are often applied in commercial hydrophones especially to measure shock and pressure waves. Rochelle salt can be found in acoustic pickups and special devices to measure acoustic pressure. Due to their long-term stable piezoelectric properties natural crystals are in particular perfect for sensor applications where the monitoring of a quantity has to be made over long periods [85]. 

Certain polymers, such as polyvinylidene fluoride (PVDF) and polyvinyl fluoride (PVF), possess special properties in the film form, caileApiezoelectricity and pyroelectricity. Piezoelectricity is electric polarization of a film produced by mechanical strain in some crystals. The polarization is proportional to the amount of strain and changes sign with it. The reverse is true and an electrical polarization induces a mechanical strain in piezoelectric sensors. Pyroelectricity is electric polarization of a film induced by thermal absorption in some polymer crystals. The induced polarization is proportional to the level of thermal change. These properties can be used in the manufacture of transducers, microphones, loudspeakers, pressure gauges, pickup heads, hydrophones, motion sensors, and other devices from biaxially oriented PVDF films. Table 13.37 gives the properties of a piezoelectric film of polyvinylidene fluoride. 

This is a hard tough material made by the acetylation of cellulose. It is sensitive to moisture pickup and is dimensionally unstable. It is resistant to weak acids and alkalies but is decomposed by strong ones. Both the triacetate and the secondary cellulose acetate give crystal clear films with high gas and water vapour permeabilities. 

Siveras is the brand name of Toray s liquid crystal polymer range. Siveias finds uses in coimectors, sensors and other electronic components and CD pickup parts, and in cop5dng machine and fax components in office and audiovisual equipment. 

---