Silicon exists in two allotropic forms; brown silicon is a powder, whereas crystalline (metallic) silicon is grey and it is the latter which is more widely used.
SI Engine
An engine whereby the fuel air mixture is compressed in the cylinder and then ignited with an electric spark.
SI Units
The international system of units is based on the seven basic units: Mass, Length, Time, Electric current, Temperature, Amount of substance and Luminous intensity.
A hissing sound produced when pronouncing S and Z.
Silicon Carbide, used extensively as a grinding compound and in abrasive wheels.
Side Branch Orifice
The side branch orifice is an acoustic filter element and behaves as a high pass filter.
Side Cutter
A milling cutter that has cutting teeth on the side as well as on the periphery or circumference.
Side Cutters
A tool like a pair of pliers except the end opposite the handles have sharp edges used to cut wire.
A portion of the energy from a directional antenna, radiated in a direction other than the boresight axis.
Sidereal Year
1 sidereal year = 31.55815x106 seconds
Sidevalve Engine
An internal combustion engine with valves placed in the engine block beside the piston.
Siegbahn, Karl
Swedish physicist who received the Nobel Prize in Physics in 1924 for his work in x-ray spectroscopy.
Siegbahn Unit
A unit of distance used for describing the wavelength of x-rays.
The SI unit of electrical conductance.
Siemens and Halske Thread
German electrical engineering company that later became part of Siemens AG. Siemens & Halske Thread was used in telephones around 1900 AD.
Sieve of Eratosthenes
The algorithm that determines whether a number is prime.
This relates the absorbed dose in human tissue to the effective biological damage of the radiation.
A letter of the Greek alphabet.
Sigma Bonds
A type of covalent bond in which most of the electrons are located in between the nuclei.
The sympol that states whether a number is positive (+) or negative (-). If a sign is not placed immediately before a number, it is taken as positive.
Signal Generator
A circuit that produces a variable and controllable signal.
Signal Ground
The common return or reference point for analog signals.
Signal Processing
Lists all Signal Processing topics in the Encyclopaedia
Signal Processing Books
Lists all Signal Processing Books in the Encyclopaedia
Signal Processing Calculations
Lists all Signal Processing Calculations in the Encyclopaedia
Signal Processing Weblinks
Lists all Signal Processing Weblinks in the Encyclopaedia
Signal to Noise Ratio
The ratio between a recorded signal and spurious background noise.
The two main classification of signals are those that are deterministic and those that are nondeterministic.
Signed Binary Coding
A coding scheme in which the Most Significant Bit represents the sign of a binary number.
Significant Digits
The number of digits to consider when using measuring numbers.
Significant Threshold Shift
A shift in hearing threshold, outside the range of audiometric testing variability.
Signs and Symbols
A list of signs and symbols.
Chemical formula for Silane.


A gas at room temperature, undergoes spontaneous combustion in air without any external ignition.

An acoustic filter element used to reduce sound pressure levels inside a duct.
Silent Mutation
A mutation in a gene that causes no detectable change in the biological characteristics of the gene product.
Another name for Silicon Dioxide.
Silica Fabric
A high performance textile fabric designed for use where severe temperature conditions exist.
Silica Gel
Precipitated silica acid in the form of lustrous granules, especially prepared for absorption of various vapours. Mildly toxic.

Alternative name for Silane.
Exists in two allotropic forms; brown silicon is a powder, whereas crystalline (metallic) silicon is grey and it is the latter which is more widely used.
Silicon Carbide


Used extensively as a grinding compound and in abrasive wheels.

Silicon Controlled Rectifier
A semiconductor device that functions as an electrically controlled switch.
Silicon Dioxide


Known for its hardness since antiquity.

Silicon Hydride
Alternative name for Silane.
Silicon Iron
Adding silicon to low-carbon iron increases both hardness and electrical resistivity.
Silicon Nitride


Excellent thermal shock resistance, ability to withstand high structural loads at high temperatures and superior wear resistance.

Silicon Tetrahydride
Alternative name for Silane.
Protein based material obtained from cocoons of the silkworm.

Sediment particles ranging from 0.004 to 0.06 mm in diameter.
The geological period from 439 million to 409 million years ago.
A pure white metallic element. The best electrical conductor and used in photographic emulsions.
Silver Bromide


Pale yellow insoluble salt used in photography.

Silver Iodide


Yellow crystalline solid.

Silver Nitrate


A white soluble crystalline salt used in marking inks, medicine and chemical analysis.

Silver Oxide Battery
A small, non-rechargeable battery used in devices such as watches and calculators.
Silver Sand
A sand with a very low iron content.
Silver Sulphide


Black or grey-black crystalline solid. The most important ore of silver, known as Argentite.

Silver Zinc Battery
The cathode is a silver screen pasted with silver oxide, the anode is a porous plate of zinc, and the electrolyte is a solution of potassium hydroxide saturated with zinc hydroxide.
Similar Figures
Two geometric figures are similar if their sides are in proportion and all their angles are the same.
Similar Matrices
Matrices A and B are similar if there is a square invertible matrix S such that S-1AS = B.
The relationship between two objects that have exactly the same shape but not necessarily the same size.
Simple Cubic
Of all the elements only polonium crystallizes to a simple cubic structure over a limited temperature range.
Simple Cycle Gas Turbine
Cycle consisting only of compression, combustion and expansion.
Simple Diffusion
The unassisted movement of molecules across a membrane to a region of lower concentration.
Simple Fraction
A fraction whose numerator is an integer of smaller value than its denominator.
Simple Harmonic Motion
A term describing the motion which occurs when a vibrating structure is displaced and experiences a restoring force proportional to its displacement.
Simple Harmonic Quantity
Periodic quantity that is a sinusoidal function of the independent variable.
Simple Mail Transfer Protocol
The original method of transmitting and receiving email on the internet.
Simple Network Management Protocol
A set of standards for communication with devices connected to a TCP/IP network.
Simple Pendulum
The mass hung on a fine wire, displaced from rest and released.
Simple Protein
A protein yielding only amino acids on hydrolysis.
Simple-Range Counting
Range is the difference between two successive reversals. The range is positive when a valley is followed by a peak. The range is negative when a peak is followed by a valley.
Simply Supported
A term used to describe the constraints imposed on a beam, plate or more complex structure by its foundations.
Simultaneity Principle
The principle that all frames of reference will have invariant simultaneity.
Trigonometrical function.
Sinc Function
The function sin of x divided by x.
Trigonometrical function.
Sine Wave
A waveform corresponding to a single-frequency periodic oscillation that can be mathematically represented as a function of amplitude versus angle in which the value of the curve at any point is equal to the sine of that angle.
Sine Wave Inverter
An inverter that produces utility-quality, sine wave power forms.
Single Acoustic Barrier
A single layer acoustic barrier.
Single Bond
When an electron pair is shared by two different elements.
Single Cylinder Engine
The first internal combustion engines were single cylinder designs and mostly stationary engines.
Single Degree of Freedom
A system whose position in space can be completely described by one coordinate.
Single Element Fuse
A fuse having a current responsive element comprising one or more parts with a single fusing characteristic.
Single Ended Input
Analog measurements in which the input′s voltage is measured with respect to ground.
Single Event Level
Also known as Sound Exposure Level, used to describe the amount of noise from an event such as an individual aircraft flyover.
Single Event Noise Exposure Level
The dB(A) level which, if it lasted for one second, would produce the same A-weighted sound energy as the actual event.
Single Line Diagram
A diagram which shows, by means of single lines and graphic symbols, the course of an electric circuit or system of circuits and the component devices or parts used therein.
Single Mode Fibre
Optical fibre supporting only one mode of light propagation.
Single Pole Switch
A switch in which only one circuit is controlled.
Single Shaft Gas Turbine
A gas turbine arrangement in which the compressor and the gas turbine are all coupled to one shaft.
Single Stage Compressor
Compressor having only one compressive step between inlet and outlet.
Single-Ended Input
An analogue input measured with respect to a common ground.
Single-Tube Shock Absorber
A common type of shock absorber with the working cylinder and reservoir contained in one tube.
Singular Matrix
A square matrix A is singular if the equation Ax = 0 has a nonzero solution for x.
Heating a mass of fine particles for a prolonged time below the melting point, usually to cause agglomeration.
A hollow or cavity; a recess or pocket.
Having the form of a sine wave.
Chemical formula for Fused Silica.
Narrow slits in the tread blocks that allow the tread block to flex and so increase grip.
Abbreviation of Serial InfraRed.
Six Degrees of Freedom
An unconstrained mass has six degrees of freedom, 3 translations and 3 rotations.