21-01-2012, 02:02 PM
Electrical Impedance Tomography
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To begin with, the word tomography can be explained with reference to ‘tomo’ and
‘graphy’; ‘tomo’ originates from the Greek word ‘tomos’ which means section or slice,
and ‘graphy’ refers to representation. Hence tomography refers to any method which
involves reconstruction of the internal structural information within an object mathematically from a series of projections.
The projection here is the visual information probed using an emanation which are physical processes involved. These include physical processes such as radiation, wave motion, static field, electric current etc. which are used to study an object from outside.Medical tomography primarily uses X-ray absorption, magnetic resonance, positron emission, and sound waves (ultrasound) as the emanation. Nonmedical area of application and research use ultrasound and many different frequencies of electromagnetic spectrum such as microwaves, gamma rays etc. for probing the visual information.
Magnetic Amplifiers
A magnetic amplifier is a device which controls the power delivered from an a.c. source by employing a controllable non linear reactive elements or circuit generally interposed in series with the load. The power required to control the reactive element or circuit is made for less than the amount of power controlled; and hence power amplification is achieved. The non-linear reactive element is a saturable reactor. When used in a combination with a set of high-grade rectifiers, it exhibits power amplification properties in the sense that small changes in control power result in considerable changes in output power. The basic component of a magnetic amplifier, as mentioned above, is the saturable reactor. It consists of a laminated core of some magnetic material. The hysteresis loop of the reactor core is a narrow and steep one. A schematic diagram of a simple saturable core reactor with control winding and a.c. winding wound on two limbs. The control winding having a number of turns, Na.c. is fed with d.c. supply. By varying the control current, it is possible to largely vary the degree of saturation of the core. The other winding, called the a.c. winding or gate winding having a number of turns,Na.c. is fed from an a.c. source, the load being connected in series with it.
Low Power Wireless Sensor Network
Wireless distributed microsensor systems will enable fault tolerant monitoring and control of a variety of applications. Due to the large number of microsensor nodes that may be deployed and the long required system lifetimes, replacing the battery is not an option.
