Metrology Glossary: Impedance

What Is Impedance?

Impedance represents the overall resistance that electric current encounters within an alternating current (AC) circuit. This electrical property includes two fundamental components: resistance and reactance. Resistance signifies the opposition that current faces when flowing through a direct current (DC) circuit, primarily caused by the material’s inherent resistance to electron flow. In contrast, reactance embodies the opposition encountered in an AC circuit, arising from the interplay of inductors and capacitors. This opposition is not purely resistive; it has a dynamic, oscillatory nature. Impedance, as a complex quantity, incorporates both of these elements, providing a comprehensive characterization of the challenges faced by current as it navigates the intricacies of electrical circuits.

Why Is Impedance Important?

Circuit Analysis and Design:

Predicting Current Flow: Impedance governs the magnitude of current that a circuit will experience under a given applied voltage. This is fundamental in circuit design and analysis, ensuring that components are appropriately dimensioned to achieve the desired circuit functionality.
Matching Impedances: Efficient power transfer among disparate circuit components is ensured through impedance matching. For example, precise impedance matching in audio equipment is crucial to prevent signal loss or distortion.
Filtering Signals: The frequency-dependent characteristics of reactance allows circuits to sift through unwanted frequencies. Impedance analysis aids in creating filters that can selectively permit or obstruct specific frequency bands.
Tuning Resonant Circuits: In devices like radio receivers and tuned circuits, impedance plays an important role in achieving resonance, allowing the circuit to effectively amplify signals at designated frequencies.

Material Characterization:

Measuring Conductivity: Impedance measurements serve to characterize the electrical conductivity of diverse materials, offering insights into their composition and properties. This is applied in fields such as soil analysis, corrosion monitoring, and ensuring food quality.
Monitoring Biological Systems: Bioimpedance analysis gauges the impedance of biological tissues, finding applications in medical contexts like body composition analysis, disease diagnosis, and the continuous monitoring of vital signs.