24-11-2010, 02:08 PM
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ABSTRACT
Typically electronics has been defined in terms of three fundamental elements such as resistors and inductors. These three elements are used to define the four fundamental circuit variables which are electrical current, voltage, charge and magnetic flux. Resistors are used to relate current to voltage, capacitors to relate voltage and charge, and inductor to relate current to magnetic flux, but there was no element which could relate charge to magnetic flux.
To overcome this missing link, scientists came up with a new element called Memristor. These Memristor has the properties of both a memory and a resistor (hence named as Memristor). Memristor is being called as the fourth fundamental component, hence increasing the importance of its innovation.
Its innovators say “Memristor are so significant that it would be mandatory to re-write the existing electronics textbooks”.
INTRODUCTION
Generally when most people think about electronics, they may initially think of products such as cell phones, radios, laptops, computes etc., others, having some electronics background, may think of resistors, capacitors etc., which are the basic components necessary for electronics function. Such basic components are fairly limited in number and each having their own characteristic function.
Memristor theory was formulated and named y Leon Chua in a 1971 paper. Chua strongly believed that a fourth device existed to provide conceptual symmetry with the resistor, inductor and capacitor. This symmetry follows from the description of basic passive circuit elements as defined by a relation between two of the four fundamental circuit variables. A device liking charge and flux (they defined as time integrals of current and voltage), which would be the memristor, was still hypothetical at the time. However, it would be until thirty- seven years later, on April 30, 2008, that a team at HP Labs led by the scientist R. Stanley Williams would announce the discovery of the switching memristor. Based on a thin film of titanium dioxide, it has been presented as an approximately ideal device.
The reason that the memristor is radically different from the other fundamental circuit elements is that, unlike them it carries a memory of its past. When you turn off the voltage to the circuit, the memristor still remembers how much was applied before and for how long. That’s an effect that can’t be duplicated by any circuit combination of resistors, capacitors, and inductors, which is why the memristor qualifies as a fundamental circuit element.
The arrangement of these few fundamental circuit components form the basis of almost all of the electronic devices we use in our everyday life. Thus the discovery of the brand new fundamental circuit element is something not to be taken lightly and has the potential to open the door to a brand new type of electronics. HP already has plans to implement memristor in a new type of non-volatile memory which could eventually replace flash and other memory systems.
NEED FOR MEMRISTOR
A memristor is one of four basic electrical components, joining the resistor, capacitor and inductor. The memristor short for “memory resistor” was first theorized by student Leon Chua in the early 1970s. He developed mathematical equations to represent the memristor, which Chua believed would balance the function of the other three types of circuit elements.
The known three fundamental circuit elements as resistor, capacitor and inductor relates four fundamental circuit variables as electric current, voltage, charge and magnetic flux. In that we were missing one to relate charge to magnetic flux. That is where the need for the fourth fundamental element comes in. This element has been named as memristor.
MEMRISTOR THEORY AND ITS APPLICATIONS
DEFINITION OF MEMRISTOR
“The memristor is formally defined as a two terminal element in which the magnetic flux ф¬¬m between the terminals is a function of the amount of electric charge q that has passed through the device.”
FIGURE 2 : MEMRISTOR SYMBOL
Chua defined the element as a resistor whose resistance level was based on the amount of charge that had passed through the memristor.
MEMRISTANCE
Memristance is a property of an electronic component to retain its resistance level even after power had been shut down or lets if remember (or recall) the last resistance it had before being shut off.
THEROY
Each memristor is characterized by its memristance function describing the charge-dependent rate of change of flux with charge.
Noting from Faraday’s law of induction that magnetic flux is simply the time integral of voltage, and charge is the time integral of current, we may write the more convenient form
It can be inferred from this that memristance is simply charge-dependent resistance i.e.,
This equation reveals that memristance defines a linear relationship between current and voltage, as long as charge does not vary. Of course, nonzero current implies instantaneously varying charge. Alternating current however may reveal the linear dependence in circuit operation by inducing a measurable voltage without net charge movement – as the maximum change in q does not cause much change in M.