**SMD**

Gowanda designation for surface mount device.

**SMRF**

Gowanda designation for surface mount radio frequency inductors

**SMP**

Gowanda designation for surface mount power chokes

**SMT**

Gowanda designation for surface mount toroid coils

**Saturation**

Maximum density of magnetic flux that can be present in a magnetic material.

**Saturation Current**

The DC bias current flowing through the inductor which causes the inductance to drop by a specified amount from the initial zero DC bias inductance value. Common specified inductance drop percentages include 10% and 20%. It is useful to use the 10% inductance drop value for ferrite cores and 20% for powdered iron cores in energy storage applications.

The cause of the inductance to drop due to the DC bias current is related to the magnetic properties of the core. The core, and some of the space around the core, can only store a given amount of magnetic flux density.

Beyond the maximum flux density point, the permeability of the core is reduced. Thus, the inductance is caused to drop. Core saturation does not apply to “air-core” inductors. (see Incremental Current and Permeability)

**Secondary Current**

Desired output AC current that represents max primary current (AC Ammeter measuring system).

**Secondary Winding**

The winding is the coil where energy is induced from the primary.

**Secondary Voltage**

Required output AC voltage to represent max primary current (AC voltage measuring system).

**Self Leaded**

Inductors that have the internal wire exiting to also form terminals

**Self-Resonant-Frequency (SRF)**

The frequency at which the inductor’s distributed capacitance resonates with the inductance. it is at this frequency that the inductance is equal to the capacitance and they cancel each other. The inductor will act purely resistive with a high impedance at the SRF point.

The distributed capacitance is caused by the turns of wire layered on top of each other and around the core. This capacitance is in parallel to the inductance. At frequencies above the SRF, the capacitive reactance of the parallel combination will become the dominant component.

Also, the Q of the inductor is equal to zero at the SRF point since the inductive reactance is zero. The SRF is specified in MHz and is listed as a minimum value on product data sheets. (also see Distributed Capacitance)

**Shielded Inductor**

An inductor designed for its core to contain a majority of its magnetic field. Some inductor designs are self shielding. Examples of these are magnetic core shapes which include toroids, pot cores and E-cores. Magnetic core shapes such as slug cores and bobbins require the application of a magnetic sleeve or similar method to yield a shielded inductor.

It should be noted that magnetic shielding is a matter of degree. A certain percentage of the magnetic field will escape the core material. This is even applicable for toroidal cores as lower core permeabilities will have higher fringing fields than will high permeability toroidal cores. (see Closed Magnetic Path)

**Sine Waveform**

A signal that varies with time as power the sinusoidal trigonometric function.

**Skin Effect**

Skin effect is the tendency for alternating current (AC) to avoid traveling through the center of a solid conductor. The current is limited to the surface or “skin” of the conductor (to a level called the skin depth). At higher frequencies the skin effect causes the effective resistance of the conductor to increase which reduces the effective cross-section of the conductor.

**Solid Core Type**

Usually round or Toroidal in their shape.

**Split Core Type**

Usually rectangular in shape but may be Toroidal also.

**Square Waveform**

A signal made by switching between two voltages at a constant frequency.

**Step Up Transformer**

When the secondary has a higher voltage than the primary.

**Step Down Transformer**

When the secondary has a lower voltage than the primary.

**Surface Mount**

Components manufactured with solder feet that are soldered to pads on the circuit board providing the mounting and connection to the circuit. Electrical connection is made through soldering the component to these solder pads.