Immittance

Immittance is a term used in physics and engineering to collectively describe two related complex quantities: impedance (Z) and admittance (Y). These quantities are fundamental in the study of electrical circuits, acoustics, and other fields where waves and oscillations are of interest. Immittance is used to characterize how easily a system can be driven by an external source of energy. In electrical engineering, it helps in understanding how electrical circuits behave under various conditions. In acoustics, it is used to describe how sound waves interact with different materials and interfaces.

Definition

The term immittance is a portmanteau of impedance and admittance. Impedance is a measure of how much a device resists the flow of an alternating current (AC) at a given frequency, while admittance is the measure of how easily an alternating current flows through a device. Mathematically, impedance (Z) is the complex ratio of the voltage to the current in an AC circuit, expressed as Z = V/I, where V is the voltage and I is the current. Admittance (Y) is the reciprocal of impedance, Y = 1/Z = I/V.

Types of Immittance

There are two main types of immittance:

• Impedance (Z): Represents the opposition that a circuit presents to the flow of alternating current. It is a complex number that consists of a real part (resistance) and an imaginary part (reactance).
• Admittance (Y): Represents how easily alternating current flows through a circuit. It is also a complex number, consisting of a real part (conductance) and an imaginary part (susceptance).

Applications

Immittance concepts are widely used in various fields, including:

• Electrical Engineering: For designing and analyzing circuits, especially in the context of AC power systems and signal processing.
• Acoustics: In the study of sound transmission and reflection at interfaces between different media.
• Telecommunications: For the design of filters, amplifiers, and antennas.
• Biomedical Engineering: In bioimpedance analysis for measuring body composition and other physiological parameters.

Measurement

Measuring immittance involves determining the impedance or admittance of a system. This can be done using instruments like the impedance analyzer or network analyzer. The measurement can provide valuable information about the system's characteristics, such as resonance frequencies, quality factors, and energy storage capabilities.

Impedance and Admittance in Parallel and Series Circuits

In electrical circuits, the total impedance or admittance depends on whether components are connected in series or parallel.

• In a series connection, impedances add up, while admittances in parallel add up.
• Conversely, in a parallel connection, admittances add up, while impedances in series add up.

See Also

• Electrical resistance and conductance
• Capacitance
• Inductance
• Resonance
• Wave propagation