Elastance

Electrical elastance is the inverse of capacitance. The SI unit of elastance is the inverse farad (F^-1).

The term elastance was coined by Oliver Heaviside through the analogy of a capacitor as a spring. It is not widely used by electrical and electronic engineers. The value of capacitors is invariably specified in units of capacitance rather than inverse capacitance. However, it is used in theoretical work in network analysis and has some niche applications at microwave frequencies.

The term is used for analogous quantities in some other energy domains. It maps to stiffness in the mechanical domain, and is the inverse of compliance in the fluid flow domain, especially in physiology. It is also the name of the generalised quantitiy in bond graph analysis and other schemes analysing systems across multiple domains.

The definition of capacitance (C) is the charge (Q) stored per unit voltage (V).

Elastance (S) is the reciprocal of capacitance, thus,

Expressing the values of capacitors as elastance is not done much by practical electrical engineers, although it is sometimes convenient for capacitors in series. The total elastance is simply the sum of the individual elastances in that case. However, it is used by network theorists in their analysis. One advantage is that an increase in elastance increases impedance. This is in the same direction as the other two basic passive elements, resistance and inductance. An example of the use of elastance can be found in the work of Wilhelm Cauer. On his path to founding network synthesis he formed the loop matrix A,

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