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Friday, 24 May 2013

Microwave tunnel diodes

Tunnel diodes can be used in microwave applications. Quantum tunneling theory is used to explain the tunneling phenomenon that take place in tunnel diodes.  Tunneling phenomenon is actually a majority carrier effect. Some of the advantages of tunnel diodes are low cost, less weight, high speed, low noise, high peak current to valley current ratio and low power operations. These parameters make tunnel diodes ideal candidate in applications like microwave amplification and microwave oscillation. The tunnel diode is a p-n junction semiconductor diode with negative resistance. Tunnel effect is responsible for this negative resistance. Heavy doping is employed during the construction of tunnel diodes. In tunnel diodes, Fermi level lie inside the valence band in p-region and inside the conduction band in n-region. While using for amplifier applications, tunnel diodes are connected either in parallel or in series with a resistive load. Another common practice is connecting tunnel diode to a microwave circulator.

Monday, 20 May 2013

Leaf springs

A spring is the component of a vehicle which serves the purpose of absorbing the shock developed while it is in motion. There are two varieties here. They are tension spring and compression spring. In a tension spring load is connected to one end leading to tension (extension). In a compression spring, the loading results in compression. Leaf springs are specially designed springs which are mounted on vehicles for suspension purposes.  A number of leaf springs bound by a nut and bolt arrangement is widely preferred in vehicles. Commonly used configuration is semi elliptical. On the application of load, friction is developed between the leaf plates. A casing around the leaf plate prevents the accumulation of dust and grit materials. To reduce friction, a lubricant, preferably grease with graphite is applied between the plates. To facilitate bending and springing, one plate is allowed to slide against another.