MEMS based worldwide Network/Communications Options

There are three major satellite networks based on MEMS. They are

1. RF-based Satellite Constellation: Probes directly and send discrete data packets to (Low earth orbit) LEO satellite(s) for collection.

2. Mobile Ad hoc Network: Data packets hop through mobile network to be distributed at exfiltration nodes.

3. Hybrid: Combination of the two depending upon probe location and conditions.

Spreading the energy of the communications signal over a wider range of frequencies can be accomplished in a number of different ways. Two of the methods are frequency hopping spread spectrum (FHSS) and direct sequence spread spectrum (DSSS). Both methods use a related but different approach to spread the signal. Ultra-wideband techniques spread the signal over very large frequency ranges. In each case, the key is to make certain that the transmitter and receiver can lock in quickly and synchronize the spreading and dispreading actions.

High frequency communication devices

Advanced information and communication networks are constantly evolving to keep up with the popularity of mobile phones, personal computers, and the Internet. High frequency devices are becoming essential for wireless communications with higher speed and higher capacity to provide greater mobility for users.

a) Monolithic microwave IC (MMIC):

Micro wave communication is a most popular and widely used means of communication especially in the case of cell phones. The very fact that the microwave also travels with almost the same velocity as that of light, made this momentum possible. Microwave can penetrate earths atmosphere without loss and can travel all the way to mars and even further. Normally used microwave frequency range is around 3-300 GHz. And common source used was silicon transistor of 25 GHz as the source. Much more high frequency and compact sources of GaAs (50 GHz) and InP (180 GHz) are replacing the conventional sources currently. Transistors and passive parts are integrated into the same GaAs substrate provides high functionality and high performance in extremely high frequency (EHF), plus miniaturization by function integration. Demand is increasing for MMIC’s in fields of satellite communications, high-speed wireless access, and intelligent transportation systems.

b) Low Noise HEMT (High Electron Mobility Transistor)

Used for BS/CS broadcast reception; meets requirements for lower noise characteristics in a higher frequency for interactive digital satellite broadcasting systems. Lead-less structure provides excellent high frequency characteristics and stable performance.

c) High Power FET (Field Effect Transistor)

Used for transmission of terrestrial microwave communications and satellite communications, plus communications between base stations for cell phones and wireless Internet access. Their high power, high efficiency, and low noise are ideal for applications in base stations for high-speed and high capacity digital information, an expanding market.

Semiconductor lasers

Semiconductor lasers are said to be "the laser of the future". The reasons are: they are compact, they have the potential of mass production, they can be easily integrated, their properties are in rapid improvement, they are becoming more and more powerful and efficient and they have found a widespread use as pumps for solid–state lasers. The majority of semiconductor materials are based on a combination of elements in the third group of the periodic table (such as Al, Ga, In) and the fifth group (such as N, P, As, Sb) hence referred to as the III-V compounds. Examples include GaAs, AlGaAs, InGaAs and InGaAsP alloys. The laser emission wavelengths are normally within 630~1600 nm, but recently InGaN semiconductor lasers were found to generate 410 nm blue light at room temperature.

The semiconductor lasers that can generate blue-green light use materials which are the combination of elements of the second group (such as Cd and Zn) and the sixth group (S, Se). The principle of semiconductor laser is very different from CO2 and The semiconductor materials have valence band V and conduction band C, the energy level of conduction band is Eg (Eg>0) higher than that of valence band. To make things simple, we start our analysis supposing the temperature to be 0 K. It can be proved that the conclusions we draw under 0 K applies to normal temperatures. Semiconductor photon sources come in two major categories laser diodes and light-emitting diodes. Semiconductor lasers are the most basic of the existing laser types. In their simplest form

they consist of a small rectangular slab of semiconductor material with two cleaved facets to act as mirrors. The other facets are destroyed in some way (etched, ground, sawn, ion implanted) in order to avoid spurious laser modes.