Conductors sandwich-type

The two basic types of circulators, shown in Fig. 13.91(b) and Fig. 13.91(c), consist ofY-shaped conductors sandwiched between magnetized ferrite discs. The final shape, dimensions, and type of material varies according to frequency of operation, power handling requirements, and the method of coupHng. The distributed constant circulator is the older design it is a broadband device, not quite as efficient in terms of insertion loss and leg-to-leg isolation, and considerably more expensive to produce, but useful in applications where broadband isolation is needed. More common is the lump constant circulator, a less expensive and more efficient but narrow-band design. 

The MCFC membrane electrode assembly (MEA) comprises three layers a porous lithiated NiO cathode structure and a porous Ni/NiCr alloy anode structure, sandwiching an electrolyte matrix (see detail below). To a first approximation, the porous, p-type semiconductor, nickel oxide cathode structure is compatible with the air oxidant, and a good enough electrical conductor. The nickel anode structure, coated with a granular proprietary reform reaction catalyst, is compatible with natural gas fuel and reforming steam, and is an excellent electrical conductor. As usual, the oxygen is the actual cathode and the fuel the anode. Hence the phrase porous electrode structure . 

Solid state detectors consist of three layers, a layer of pure silicon sandwiched between a p-type and an n-type conductor. We recall that an example of an n-type conductor is germanium to which is added P or As, an impurity. The extra electron in the phosphorus or arsenic atoms is thought of as being in an energy level close to the conduction band. These electrons are readily thermally excited into the conduction band increasing the conductivity. A p-type semiconductor may be silicon to which a trivalent element such as boron or aluminum is added as an impurity. This creates holes close to the valence band. Electrons are readily promoted to these holes leaving positive holes in the valence band that provide for a conduction pathway. 

If the vacuum tube is the grandfather, then the transistor is the parent of today s electronic components. Transistors (Figure 1.2) work in basically the same manner as vacuum tubes. A small voltage applied to one pole controls a larger voltage on the other poles. The difference between a transistor and a vacuum tube is that a transistor uses a sandwich of silicon instead of tube filled with gas to do the switching. Silicon falls into a family of elements that are neither conductor nor insulator they re called semiconductors. This type of element will be either a conductor or an insulator depending on some condition. In the case of transistors, an electrical current will cause the silicon to be a conductor. 

Another type of electrochemical analogue memory has been investigated (2, Ul, 42). In this type of device a mixed electronic and Ag conductor is sandwiched between two layers of RbAgl I. ... 

Scanning Spreading Resistance Microscopy (SSRM), like SCM, can provide carrier concentration maps to a spatial resolution of around 2 nm. The sample may be a conductor or a semiconductor. Information is, however, derived by measuring the electrical conductivity or resistivity of a sample sandwiched between an atomically sharp tip and a conductive back plate. This is useful for measuring concentrations of active n- and p-type dopants if present at concentrations greater than lel6 atoms/cm. ... 

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