Microwaves and Microwave equipment. Essay

The microwave is a type of electromagnetic radiation as X ray, gamma ray, radio wave and ultraviolet radiation, the microwave has a wide range applications including radar and communications, perhaps the best known for many people in cooking is microwave oven. Electromagnetic radiations are transmitted in waves at different wavelength and frequency. This range of wavelengths and frequencies is known by the electromagnetic spectrum (EM spectrum) as shown in figure (1.1). The spectrum is divided into seven regions in order of decreasing wavelength, increasing energy and frequency. The common designations are microwaves, radio waves, ultraviolet (UV), infrared (IR), visible light, X and gamma-rays. Microwaves range in the EM spectrum between infrared light and radio. It is starting about 300 MHz to 300GHz and wavelengths of about 100 centimeters to 1 millimeter, also these values are not definitive. This region is divided into a number of bands as S, C, X, L and K. As appeared in table (1.1) (T. C. Edwards Engalco, 2000)( National Academy Press,1994)( IEEE Standard 521-1984)
A strong and significant core of applications exists for analog signals at microwave frequencies, among them
radars (a very large family with a wide variety of demands and techniques)
point-to-point and point-to-multipoint multichannel radio links ('microwave radio')
satellite communications systems (both fixed and mobile)
cellular (mobile) communications systems - mobiles and infrastructure
cable television (CATV) and associated cable telecommunications
local multimedia distribution services (LMDS)
Millimetre-wave Video Distribution Systems (MVDS)
subspace communications systems (e.g. high-flying aircraft)
microwave transceivers for optical fiber transmission
Wireless Local Area Networks (WLANs)
Microwave instrumentation. (T. C. Edwards Engalco,2000)
1.2 Moisture Constant (MC)
Moisture is the amount of water inside the material and moisture constant measurement in various materials is required in many industrial applications that are why the moisture constant is one of the most important parameters determining quality, it is a key factor to take a decision about the harvest or the storage method. Electromagnetic equipment is widely used for determining the level of water contact in material using different method such as non resonator and resonator methods.
The water content of a material largely affects its complex permittivity, and then the electromagnetic measuring techniques are well suited for testing the moisture constant of hygroscopic materials. Both electromagnetic measurement techniques transmission and reection can be used to estimate the permittivity of the material under test.
Microwave sensors have become more and more common in different areas of industry. A wide range of applications use microwave sensors for measurement of distance, movement, shape, and particle size, and the largest group of applications are depended to measurement of material properties.
Microwave sensors are turned by the interaction between microwaves and material. This interaction may be in the form of refraction, reflection, scattering, absorption, emission, or change of speed and phase. All sensors are depending on some characteristic and measurement which the sensor are based on them, therefore they make them suitable for different applications. (Ebbe Nyfors, 2000).