S glossary entries

The S–N curve is a graphical representation of the relationship between the applied cyclic stress amplitude S and the number of cycles to failure N for a material tested under controlled fatigue loading conditions.

The sampling theorem states that an ideal band-limited signal can be reconstructed exactly from uniformly spaced samples when the sampling frequency is greater than twice the signal bandwidth.

Scattering is the redistribution of waves, particles, or radiation when they interact with matter, geometry, defects, or boundaries.

A screw thread is a helical ridge on a cylindrical or conical surface used for fastening, adjustment, sealing, or converting rotation into linear motion.

Seakeeping is the ability of a vessel or floating system to remain safe, controllable, and useful in real sea conditions.

The Seebeck effect is the generation of an electromotive force when a temperature difference exists along a conductor, semiconductor, or thermoelectric junction.

A semiconductor is a material with controllable electrical conductivity between that of a conductor and an insulator.

The sensitivity function is the closed-loop transfer function from a disturbance (or reference) to the tracking error, quantifying how effectively the feedback loop rejects disturbances at each frequency.

Shear modulus is the elastic stiffness that relates shear stress to shear strain in the linear elastic range.

Ship draft is the vertical distance from the waterline to the lowest hull or keel reference used for a vessel condition.

Ship trim is the difference between forward and aft draft, indicating whether a vessel sits bow-down, stern-down, or even-keel.

Signal-to-noise ratio is the ratio between desired signal power and noise power over a specified bandwidth and measurement condition.

A solder joint is a metallurgical connection that bonds component terminations to pads, wires, or terminals while providing electrical and mechanical continuity.

A stability margin is a quantitative measure of the distance between the operating point of a feedback control system and the boundary of instability, expressed in terms of allowable gain increase (gain margin) or allowable phase lag (phase margin).

State of charge is the fraction of stored energy remaining in a battery or storage device relative to its rated or reference capacity.

A state-space model represents a dynamic system through state variables, inputs, outputs, and equations that describe how the state evolves over time.

Sterilization is a validated process used to achieve a required microbial safety state for a product, material, package, or process boundary.

Stormwater runoff is rainfall or snowmelt that flows over surfaces or through drainage systems rather than infiltrating, evaporating, or being stored locally.

A strain gauge is a sensor that converts mechanical strain into a small change in electrical resistance.

Stress is the internal force per unit area that develops inside a material when it is subjected to external loads, displacements, or thermal effects.

Stress concentration is the local amplification of stress that occurs in the vicinity of geometric discontinuities — holes, notches, fillets, grooves, threads, keyways, or weld toes — where the smooth flow of internal forces is disrupted.

The stress tensor is a second-order symmetric tensor that completely characterises the stress state at a point inside a deformable body, specifying the normal and shear stresses acting on every possible internal surface through that point.

Surge impedance is the characteristic impedance seen by a travelling electromagnetic wave on a line before reflections from terminations return.