### 6.1 Overview

The memristor concept has attracted strong attention due to its practical demonstration based on different
technologies like metal/oxide/metal thin-film and spintronic. It has the potential to lead to novel applications
beyond non-volatile memory due to its functional properties, which are not accessible in electronic circuits
combining resistors, capacitors, and inductors. As the fourth fundamental circuit element, the memristor is
potentially suited for a wide range of tasks (Chapter 1). In this Chapter, it is shown how the unique ability
of the memristor to memorize the history of the applied current or voltage leads to novel sensing capabilities
which cannot be achieved by RLC-networks alone. The historic profile of the applied current or voltage
memorized in the memristance change can be revealed instantaneously by keeping track of its
varying resistance. In principle, this storage capability, which is independent of the memristor
material, can reduce the charge (flux)-based capacitance (inductance) sensing to a simple resistance
measurement.

The behavior of the basic electrical circuits are determined by Kirchhoff’s current (KCL) and
voltage (KVL) laws. A resistor relates the voltage and the current by a (linear) relationship
called Ohm’s law. Its resistance, therefore, can be determined by measuring the current and the
voltage simultaneously. Since a capacitor and an inductor relate their voltage and current through
differential equations (Section 2.1.1), the capacitance and the inductance are typically measured
indirectly and their measurement techniques are entirely different from those used for a resistor.
Approaches to measuring and are based on time domain techniques and frequency domain
techniques. For example, in the time domain techniques is calculated by measuring the oscillation
period of a relaxation oscillator [204, 205] or the time required to reach a threshold voltage in a
charge-discharge circuit [206, 207]. In the frequency domain technique an AC signal of a known
frequency is applied to a capacitive divider (CC circuit) or an RC circuit. The magnitude and
the phase of the output signal across the capacitor or the resistor are measured to determine
[208, 209].