Acoustic Emission
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Transient elastic waves within a material due to localised stress release. Acoustic Emission (AE) events can occur rapidly when materials begin to fail. AE events commonly studied include the extension of a fatigue crack, or fibre breakage in composite materials. AE is related to an irreversible release of energy, and can be generated from sources not involving material failure including friction, cavitation and impact.
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Artificial Photosynthesis
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A chemical process that replicates the natural process of photosynthesis, a process that converts sunlight, water, and carbon dioxide into carbohydrates and oxygen. The term is commonly used to refer to any scheme for capturing and storing the energy from sunlight in the chemical bonds of a fuel
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Barkhausen Effect
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Noise in the magnetic output of a ferromagnet when the magnetising force applied to it is changed. It is caused by rapid changes of size of magnetic domains (similarly magnetically oriented atoms in ferromagnetic materials).
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Biot-Savart Effect
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The generation of a magnetic field by a steady current i.e. an unchanging continual flow of charges (for example through a wire).
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Bragg Diffraction
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Diffraction from a three dimensional periodic structure such as atoms in a crystal. It is similar to what occurs when waves are scattered from a diffraction grating. Bragg diffraction is a consequence of interference between waves reflecting from different crystal planes.
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Bridgman Effect
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(or internal Peltier effect) A phenomenon that occurs when an electric current passes through an anisotropic crystal - there is an absorption or liberation of heat because of the non-uniformity in current distribution
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Bubble
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A globule of one substance in another, usually gas in a liquid. Due to the Marangoni effect, bubbles may remain intact when they reach the surface of the immersive substance.
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Bubble have low inertia and their movement can indicates the presence of fields, such as electric fields, air movement etc.
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Cat's-whisker Detector
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A thin wire that lightly touches a semiconducting crystal to make an imperfect contact-junction detector in a crystal radio. It is a relatively primitive and unstable metal-semiconductor point-contact junction forming a Schottky barrier diode.
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Catapult Effect
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A current passing through two wires connected by a loose wire in a magnetic field causes the loose wire to be catapulted horizontally away from the magnetic field due to the magnetic forces acting in the wires and in the magnetic field itself.
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Cherenkov Effect
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Electromagnetic radiation emitted when a charged particle (such as a electron) passes through an insulator at a speed greater than the speed of light in that medium.
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Cherenkov radiation is used to detect high-energy charged particles. In pool-type nuclear reactors, the intensity of Cherenkov radiation is related to the frequency of the fission events that produce high-energy electrons, and hence is a measure of the intensity of the reaction.
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Concentrated Photovoltaics
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Concentrated photovoltaic systems focus a large amount of sunlight onto a small area of solar photovoltaic materials to generate electricity. Unlike traditional, more conventional flat panel systems, CPV systems are often much less expensive to produce, because the concentration allows for the production of a much smaller area of solar cells.
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Converse Piezoelectric Effect
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Materials exhibiting the direct piezoelectric effect (the production of electricity when stress is applied) also exhibit the converse piezoelectric effect (the production of stress and/or strain when an electric field is applied). For example, lead zirconate titanate crystals will exhibit a maximum shape change of about 0.1% of the original dimension.
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Corbino Effect
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A phenomenon similar to the Hall effect, but a disk-shaped metal sample plane of the disk, produces a 'circular' current through the disk.
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Coulomb's Law
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The magnitude of the electrostatic force between two point electric charges is directly proportional to the product of the magnitudes of each charge and inversely proportional to the square of the distance between the charges.
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Crookes Radiometer
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(also known as the light mill) Consists of an airtight glass bulb, containing a partial vacuum. Inside are a set of vanes which are mounted on a spindle. The vanes rotate when exposed to light, with faster rotation for more intense light, providing a quantitative measurement of electromagnetic radiation intensity.
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Curie Point (ferromagnetic)
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The Curie point of a ferromagnetic material is the temperature above which it loses its characteristic ferromagnetic ability
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The change in ferromagnetic properties of a material as it changes temperature can be used to detect heat (or absence of heat)
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Dielectric Heating
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(also known as electronic heating, RF heating, high-frequency heating) The phenomenon in which radiowave or microwave electromagnetic radiation heats a dielectric material, especially as caused by dipole rotation.
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Dielectric Permittivity
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The measure of how much resistance is encountered when forming an electric field in a medium. In other words, permittivity is a measure of how an electric field affects, and is affected by, a dielectric medium. Permittivity is determined by the ability of a material to polarize in response to the field, and thereby reduce the total electric field inside the material. Thus, permittivity relates to a material's ability to transmit (or 'permit') an electric field.
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Diffraction
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Various phenomena which occur when a wave encounters an obstacle. It is described as the apparent bending of waves around small obstacles and the spreading out of waves past small openings. Very similar effects are observed when there is an alteration in the properties of the medium in which the wave is travelling, for example a variation in refractive index for light waves or in acoustic impedance for sound waves and these can also be referred to as diffraction effects.
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Echo
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A reflection of sound, arriving at the listener some time after the direct sound. Typical examples are the echo produced by the bottom of a well, by a building, or by the walls of an enclosed room. A true echo is a single reflection of the sound source. The time delay is the extra distance divided by the speed of sound.
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Eddy Currents
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An electrical phenomenon caused when a conductor is exposed to a changing magnetic field due to relative motion of the field source and conductor; or due to variations of the field with time. This can cause eddys of circulating current within the conductor which create electromagnets with magnetic fields that opposes the change of the magnetic field.
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For example, electromechanical induction electric meter.
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Electret
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An Electret is a dielectric material that has a quasi-permanent electric charge or dipole polarisation. An electret generates internal and external electric fields, and is the electrostatic equivalent of a permanent magnet.
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For example, electrets can be used in microphones to convert sound vibrations into an electric signal.
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Electric Field
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The space surrounding an electric charge or in the presence of a time-varying magnetic field has a property called an electric field (that can also be equated to electric flux density). This electric field exerts a force on other electrically charged objects.
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Electric Sonic Amplitude
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Occurs in colloids, emulsions and other heterogeneous fluids under the influence of an oscillating electric field. This field moves particles relative to the liquid, which generates ultrasound.
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Electric Spark
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A type of electrostatic discharge that occurs when an electric field creates an ionized electrically conductive channel in air producing a brief emission of light and sound. A spark is formed when the electric field strength exceeds the dielectric field strength of air. This causes an increase in the number of free electrons and ions in the air, temporarily causing the air to become an electrical conductor through dielectric breakdown.
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Electro-Optic Effects
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A change in the optical properties of a material in response to an electric field that varies slowly compared with the frequency of light. The term encompasses a number of distinct phenomena, which can be subdivided into a) change of the absorption (electroabsorption, Franz-Keldysh effect, Quantum-confined Stark effect, electro-chromatic effect) and b) change of the refractive index(Pockels effect, Kerr Effect, electro-gyration)
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Electroactive Polymer
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(or EAP) A polymer that exhibits a change in size or shape when stimulated by an electric field. The most common applications of this type of material are in actuators and sensors. A typical characteristic property of an EAP is that it will undergo a large amount of deformation while sustaining large forces.
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Electrohydrodynamics
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Includes the following types of particle and fluid transport mechanisms:Electrophoresis, electrokinesis, dielectrophoresis, electro-osmosis, and electrorotation. In general, the phenomena relate to the direct conversion of electrical energy into kinetic energy, and vice versa.
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Electroluminescence
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An optical phenomenon and electrical phenomenon in which a material emits light in response to an electric current passed through it, or to a strong electric field.
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Electromagnet
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A type of magnet whose magnetic field is produced by the flow of electric current. The magnetic field disappears when the current ceases. Electromagnets are very widely used as components of other electrical devices, such as motors, generators, relays, loudspeakers, hard disks, MRI machines, scientific instruments, and magnetic separation equipment, as well as being employed as industrial lifting electromagnets for picking up and moving heavy iron objects like scrap iron.
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Electromagnetic Induction
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The generation of electromotive force (EMF) in a current-carrying conductor exposed to a changing magnetic field
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For example, electromechanical induction electric meter.
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Electromechanical Film
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A thin membrane whose thickness is related to an electric voltage. It can be used as a pressure sensor, microphone, or a speaker. It can also convert electrical energy to vibration, functioning as an actuator.
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Electron Paramagnetic Resonance
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(EPR) or electron spin resonance (ESR) spectroscopy is a technique for studying chemical species that have one or more unpaired electrons, such as organic and inorganic free radicals or inorganic complexes possessing a transition metal ion. The basic physical concepts of EPR are analogous to those of nuclear magnetic resonance (NMR), but it is electron spins that are excited instead of spins of atomic nuclei
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Electropermanent Magnet
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A type of magnet which consists of both an electromagnet and a dual material permanent magnet, in which the magnetic field produced by the electromagnet is used to change the magnetisation of the permanent magnet. Allows creating controllable permanent magnets where the magnetic effect can be maintained without requiring a continuous supply of electrical energy.
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Electrostatic Induction
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A redistribution of electrical charge in an object, caused by the influence of nearby charges. Electrostatic generators, such as the Wimshurst machine, the Van de Graaff generator and the electrophorus, use this principle. Electrostatic induction should not be confused with electromagnetic induction; both are often referred to as 'induction'.
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Faraday Effect
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An interaction between light and a magnetic field in a dielectric material. The rotation of the plane of polarisation is proportional to the intensity of the component of the magnetic field in the direction of the beam of light.
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Faraday Wave
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(or Faraday Ripples) Nonlinear standing waves that appear on liquids enclosed by a vibrating receptacle. When the vibration frequency exceeds a critical value, the flat hydrostatic surface becomes unstable. The waves can take the form of stripes, close-packed hexagons, or even squares or quasiperiodic patterns.
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Feedback
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A circular causal process whereby some proportion of a system's output is returned (fed back) to the input. This is often used to control the dynamic behavior of the system.
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Ferromagnetic Powder
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Ferromagnetic material in a powdered or finely divided form. Ferromagnetic materials (such as iron) form permanent magnets and/or exhibit strong interactions with magnets. Ferromagnetic materials lose their ferromagnetic properties above a characteristic temperature (the Curie Point).
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For example: iron filings may be used to visualise a magnetic field (which may have been generated in response to an electric current or other effect)
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Filter (electronic)
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Electronic circuits which perform signal processing functions, specifically intended to remove unwanted signal components and/or enhance wanted ones.
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Filter (optical)
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Optical filters selectively transmits light having certain properties (often, a particular range of wavelengths, that is, range of colours of light), while blocking the remainder. Optical filters, generally, belong to one of two categories. The simplest, physically, is the absorptive filter, while the latter category, that of interference or dichroic filters, can be quite complex.
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Fluorescence
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Fluorescence is a luminescence that is mostly found as an optical phenomenon in cold bodies, in which the molecular absorption of a photon triggers the emission of a photon with a longer (less energetic) wavelength. The energy difference between the absorbed and emitted photons ends up as molecular rotations, vibrations or heat. Sometimes the absorbed photon is in the ultraviolet range, and the emitted light is in the visible range.
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By detection of flourescence resulting from the field to be detected.
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Focusing
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The gathering of wavefronts of a wave (e.g. radiation) into a spherical or cylindical shape. Focusing of light is used in optics, however focusing can be applied to any radiation or wave.
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Fresnel Lens
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A lens using less material compared to a conventional spherical lens by breaking the lens into a set of concentric annular sections. For each of these, the overall thickness of the lens is decreased, breaking the continuous surface of a standard lens into a set of surfaces of the same curvature, with discontinuities between them. This reduces the thickness (and weight and volume) of the lens, at the expense of reducing the imaging quality.
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Galvanometer
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An analog electromechanical transducer that produces a rotary deflection, through a limited arc, in response to electric current flowing through its coil.
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Hall Effect
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The potential difference (Hall voltage) on the opposite sides of an electrical conductor through which there is an electric current, created by a magnetic field applied perpendicularly to the current.
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Heterodyne
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In radio and signal processing, heterodyning is the generation of new frequencies by mixing, or multiplying, two oscillating waveforms. It is useful for modulation and demodulation of signals, or placing information of interest into a useful frequency range.
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Homodyne Detection
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A method of detecting frequency-modulated radiation by non-linear mixing with radiation of a reference frequency, the same principle as for heterodyne detection.
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Hooke's Law
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Hooke's law of elasticity is an approximation that states that the extension of a spring is in direct proportion with the load added to it as long as this load does not exceed the elastic limit. Materials for which Hooke's law is a useful approximation are known as linear-elastic or 'Hookean' materials.
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Force can be detected by the change in length of an object upon which the force acts.
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Image Processing
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Processing of images using mathematical operations by using any form of signal processing for which the input is an image, a series of images, or a video, such as a photograph or video frame The output of image processing may be either an image or a set of characteristics or parameters related to the image.
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Induction Heating
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The process of heating an electrically conducting object (usually a metal) by electromagnetic induction, where eddy currents are generated within the metal and resistance leads to Joule heating of the metal.
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Inductor
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A passive electrical component that can store energy in a magnetic field created by the electric current passing through it. Typically an inductor is a conducting wire shaped as a coil, the loops helping to create a strong magnetic field inside the coil due to Ampere's Law. Due to the time-varying magnetic field inside the coil, a voltage is induced, according to Faraday's law of electromagnetic induction, which by Lenz's Law opposes the change in current that created it.
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Infrared Radiation
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Infrared (IR) radiation is electromagnetic radiation whose wavelength is longer than that of visible light (400-700 nm), but shorter than that of terahertz radiation (3-300 µm) and microwaves (~30,000 µm). Infrared radiation spans roughly three orders of magnitude (750 nm and 1000 µm).
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Interference
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The addition (superposition) of two or more waves that result in a new wave pattern. As most commonly used, the term interference usually refers to the interaction of waves which are correlated or coherent with each other, either because they come from the same source or because they have the same or nearly the same frequency.
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For example, through constructive interference with a reference field.
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Intumescent Materials
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An intumescent is a substance which swells as a result of heat exposure, thus increasing in volume, and decreasing in density. Intumescents are typically used in passive fire protection.
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Josephson Effect
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The phenomenon of current flow across two weakly coupled superconductors, separated by a very thin insulating barrier.
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Joule Heating
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The process by which the passage of an electric current through a conductor releases heat. Heat generated is a function of current, resistance and time. Also known as the Joule-Lenz effect, Ohmic heating or resitive heating.
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Laser Microphone
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A surveillance device that uses a laser beam to detect sound vibrations in a distant object. The laser beam is reflected off the object and returns to a receiver that converts the beam to an audio signal.
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Where the field is causing an object to vibrate.
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Lens
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An optical device with perfect or approximate axial symmetry which transmits and refracts light, converging or diverging the beam.
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Light Emitting Diode
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A semiconductor diode that emits light when an electric current is applied in the forward direction of the device, as in the simple LED circuit. The effect is a form of electroluminescence where incoherent and narrow-spectrum light is emitted from the p-n junction in a solid state material.
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LEDs can also be used as photodiodes.
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Liquid Crystals
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Substances that exhibit a phase of matter that has properties between those of a conventional liquid, and those of a solid crystal.
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Lyot Filter
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A type of optical filter that uses birefringence to produce a narrow passband of transmitted wavelengths
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Maggi-Righi-Leduc Effect
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Changes in thermal conductivity when placing a conductor in a magnetic field.
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Magnetic Field
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A vector field which surrounds magnets and electric currents, and is detected by the force it exerts on moving electric charges and on magnetic materials. When placed in a magnetic field, magnetic dipoles tend to align their axes parallel to the magnetic field. Magnetic fields also have their own energy with an energy density proportional to the square of the field intensity.
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Magnetic Shape Memory
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Magnetic shape memory (MSM) alloys, or ferromagnetic shape memory alloys (FSMA), are ferromagnetic materials exhibiting large changes in shape and size under the influence of an applied magnetic field due to martensitic phase transformation.
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For a magnetic field.
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Magneto-Optic Effects
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A number of phenomena in which an electromagnetic wave propagates through a medium that has been altered by the presence of a quasistatic magnetic field. Includes the Faraday Effect and the Magneto-Optic Kerr Effect.
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Magneto-Optic Kerr Effect
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(MOKE) Light reflected from a magnetised surface can change in both polarisation and reflectivity. Identical to the Faraday effect except that the magneto-optical Kerr effect is a measurement of the reflected light, while the Faraday effect is a measurement of the transmitted light. Both effects result from the off-diagonal components of the dielectric tensor e.
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Magnetoelastic Effects
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A group of effects including Magnetostriction (or Joule Magnetostriction), Delta-E Effect, Wiedemann Effect, Magnetovolume Effect, and their Inverses: Villari Effect, Delta-E Effect, Matteucci Effect and the Nagaoka-Honda Effect.
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Magnetohydrodynamic Effect
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A magnetic field can induce currents in a moving conductive fluid, which create forces on the fluid, and also change the magnetic field itself.
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Magnetoresistance
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The change of electrical resistance of a material when an external magnetic field is applied. Also called ordinary magnetoresistance (OMR).
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Magnetostriction
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A property of ferromagnetic materials that causes them to change their shape or dimensions during the process of magnetisation. The variation of material's magnetisation due to the applied magnetic field changes the magnetostrictive strain until reaching its saturation value. This effect can cause losses due to frictional heating in susceptible ferromagnetic cores.
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Magnetovolume Effect
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One of a group of Magnetoelastic Effects. Volume change due to magnetisation (most evident near the Curie temperature)
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In the case of a magnetic field.
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Metastability
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A general scientific concept which describes states of delicate equilibrium. A system is in a metastable state when it is in equilibrium (not changing with time) but is susceptible to fall into lower-energy states with only slight interaction. It is analogous to being at the bottom of a small valley when there is a deeper valley close by
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The 'tipping' of a metastable system into a lower energy state in response to a small stimulus could be used to make a senstive detector.
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Mirage (photothermal deflection)
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A naturally occurring optical phenomenon in which light rays are bent to produce a displaced image of distant objects or the sky.
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For example, the detection of heat.
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Nanocomposite
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A multiphase solid material where one of the phases has one, two or three dimensions of less than 100 nanometers (nm), or structures having nano-scale repeat distances between the different phases that make up the material. Can include porous media, colloids, gels and copolymers, but is more usually taken to mean the solid combination of a bulk matrix and nano-dimensional phase(s).
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Ohm's Law
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Ohm's law states that the current through a conductor between two points is directly proportional to the potential difference or voltage across the two points, and inversely proportional to the resistance between them.
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Parasitic Capacitance
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An unavoidable and usually unwanted capacitance between the parts of an electronic component or circuit because of their proximity to each other.
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Particle Image Velocimetry
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An optical method of flow visualisation used to obtain instantaneous velocity measurements and related properties in fluids. The fluid is seeded with tracer particles which, for sufficiently small particles, are assumed to faithfully follow the flow dynamics. The fluid with entrained particles is illuminated so that particles are visible. The motion of the seeding particles is used to calculate speed and direction (the velocity field) of the flow being studied.
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Peltier Effect
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Heat is evolved or absorbed at the junction of two dissimilar metals carrying a small current, depending upon the direction of the current. One of a number of thermoelectric effects (See Seebeck Effect and Thompson Effect).
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In the case of an electical field by observing the resulting Peltier Effect
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Phosphorescence
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A specific type of photoluminescence related to fluorescence. Unlike fluorescence, a phosphorescent material does not immediately re-emit the radiation it absorbs.
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The energy of the detected field is emitted as a detectible field (e.g. light)
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Photo-oxidation
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Oxidation facilitated radiant energy such as UV or artificial light. This process is often the most significant component of weather degradation of polymers.
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By observing or detecting the degradation due to photo-oxidation of a substance exposed to light or other radaition.
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Photoacoustic Effect
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The formation of sound waves, following light absorption in a material sample. Most generally, electromagnetic radiation of any kind can give rise to a photoacoustic effect. This includes the whole range of electromagnetic frequencies, from gamma radiation and x-rays to microwave and radio.
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Photochromism
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The reversible transformation of a chemical species between two forms by the absorption of electromagnetic radiation, where the two forms have different absorption spectra. Trivially, this can be described as a reversible change of colour upon exposure to light.
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Photoconductivity
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An optical and electrical phenomenon in which a material becomes more electrically conductive due to the absorption of electromagnetic radiation such as visible light, ultraviolet light, infrared light, or gamma radiation.
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Photodissociation
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A chemical reaction in which a chemical compound is broken down by photons. Any photon with sufficient energy can affect the chemical bonds of a chemical compound. Since a photon's energy is inversely proportional to its wavelength, electromagnetic waves with the energy of visible light or higher, such as ultraviolet light, x-rays and gamma rays are usually involved in such reactions.
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By detecting the products of photodissociation.
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Photoelectric Effect
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The emission of electrons from matter (metals and non-metallic solids, liquids or gases) as a consequence of their absorption of energy from electromagnetic radiation of very short wavelength, such as visible or ultraviolet light.
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Photography
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The process, activity and art of creating still pictures by recording radiation on a radiation-sensitive medium, such as a photographic film, or electronic image sensors.
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Photoionisation
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The physical process in which an incident photon ejects one or more electrons from an atom, ion or molecule. This is essentially the same process that occurs with the photoelectric effect with metals. In the case of a gas, the term photoionisation is more common.
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Photoluminescence
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A process in which a substance absorbs photons (electromagnetic radiation) and then re-radiates photons. Quantum mechanically, this can be described as an excitation to a higher energy state and then a return to a lower energy state accompanied by the emission of a photon. One of many forms of luminescence (light emission) and is distinguished by photoexcitation (excitation by photons).
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Photon Sieve
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A device for focusing light using diffraction and interference. It consists of a flat sheet of material full of pinholes that are arranged in a pattern which is similar to the rings in a Fresnel zone plate, but a sieve brings light to much sharper focus than a zone plate.
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The same photon sieve will focus light of many wavelengths to different foci, which means they can also be used to detect or extract specific wavelengths.
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Photopolymerisation
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Polymerisation induced by exposure to light or UV radiation.
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Photovoltaic Effect
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The creation of a voltage (or a corresponding electric current) in a material upon exposure to light. Though directly related to the photoelectric effect, the two processes are different and should be distinguished. In the photoelectric effect, electrons are ejected from a material's surface upon exposure to radiation of sufficient energy. The photovoltaic effect is different in that the generated electrons are transferred between different bands (i.e. from the valence to conduction bands) within the material, resulting in the buildup of a voltage between two electrodes.
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Piezomagnetism
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A phenomenon observed in some antiferromagnetic crystals. It is characterised by a linear coupling between the system's magnetic polarisation and mechanical strain. In a piezomagnetic, one may induce a spontaneous magnetic moment by applying physical stress, or a physical deformation by applying a magnetic field. Piezomagnetism differs from the related property of magnetostriction.
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Piezoresistive Effect
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The changing electrical resistivity of a semiconductor due to applied mechanical stress.
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Plenoptic Camera
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(also called a light-field camera) A camera that uses a microlens array to capture 4D light field information about a scene. Such light field information can be used to improve the solution of computer graphics and vision-related problems.
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Polarisation
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A property of waves that describes the orientation of their oscillations. For transverse waves such as many electromagnetic waves, it describes the orientation of the oscillations in the plane perpendicular to the wave's direction of travel. The oscillations may be oriented in a single direction (linear polarisation), or the oscillation direction may rotate as the wave travels (circular or elliptical polarisation).
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Pool-Frenkel Effect
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(or Frenkel-Poole emission) A means by which an electrical insulator can conduct electricity in the presence of a large electric field.
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Purkinje effect
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The tendency for the peak luminance sensitivity of the human eye to shift toward the blue end of the color spectrum at low illumination levels.This effect introduces a difference in color contrast under different levels of illumination.
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Pyroelectric Effect
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The ability of certain materials to generate an electrical potential when they are heated or cooled. As a result of this change in temperature, positive and negative charges move to opposite ends through migration (i.e. the material becomes polarized) and hence, an electrical potential is established.
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Radiation Pressure
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The pressure exerted upon any surface exposed to electromagnetic radiation. If absorbed, the pressure is the power flux density divided by the speed of light. If the radiation is totally reflected, the radiation pressure is doubled.
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Rayleigh Scattering
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The elastic scattering of light or other electromagnetic radiation by particles much smaller than the wavelength of the light.
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Rectenna
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A special type of antenna that is used to convert electromagnetic energy into direct current electricity
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Refraction
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The change in direction of a wave due to a change in its speed. This is most commonly observed when a wave passes from one medium to another at any angle other than 90° or 0°. Refraction of light is the most commonly observed phenomenon, but any type of wave can refract when it interacts with a medium, for example when sound waves pass from one medium into another or when water waves move into water of a different depth.
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Relay
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An electrical switch that opens and closes under the control of another electrical circuit. In the original form, the switch is operated by an electromagnet to open or close one or many sets of contacts. Because a relay is able to control an output circuit of higher power than the input circuit, it can be considered to be, in a broad sense, a form of an electrical amplifier.
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Resonance
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The tendency of a system to oscillate with larger amplitude at some frequencies than at others. These are known as the system's resonant frequencies. At these frequencies, even small periodic driving forces can produce large amplitude oscillations, because the system stores vibrational energy.
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Reverberation
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The persistence of sound in a particular space after the original sound is removed. A reverberation, or reverb, is created when a sound is produced in an enclosed space causing a large number of echoes to build up and then slowly decay as the sound is absorbed by the walls and air.This is most noticeable when the sound source stops but the reflections continue, decreasing in amplitude, until they can no longer be heard.
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Rubber Band Thermodynamics
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Stretching a rubber band will cause it to release heat, while releasing it after it has been stretched will lead it to absorb heat, causing its surroundings to become cooler. Heating causes a rubber band to contract, and cooling causes expansion.
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In the case of detection of heat.
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Scattering
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A general physical process where some forms of radiation, such as light, sound, or moving particles, are forced to deviate from a straight trajectory by one or more localized non-uniformities in the medium through which they pass (includes deviation of reflected radiation from the angle predicted by the law of reflection).
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Scintillation
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A flash of light produced in a transparent material by an ionization event.
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Second Harmonic Generation
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(or frequency doubling) A nonlinear optical process, in which photons interacting with a nonlinear material are effectively combined to form new photons with twice the energy, and therefore twice the frequency and half the wavelength of the initial photons.
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In situations where the doubled frequency is easier to detect than the original frequency.
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Seebeck Effect
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The conversion of temperature differences directly into electricity. A thermoelectric EMF (voltage), is created in the presence of a temperature difference between two different metals or semiconductors. This causes a continuous current in the conductors if they form a circuit.
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Shadow
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An area where direct light (or other radiation) from a source cannot reach due to obstruction by an object. The cross section of a shadow is a two-dimensional silhouette, or reverse projection of the object blocking the light (or radiation).
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By observation of a cast shadow.
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Shadowgraph
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An optical method that reveals non-uniformities in transparent media like air, water, or glass. In principle, we cannot directly see a difference in temperature, a different gas, or a shock wave in the transparent air. However, these disturbances refract light rays, so they can cast shadows. The plume of hot air rising from a fire, for example, can be seen by way of its shadow cast upon a nearby surface by the uniform sunlight.
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Shunt
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In electronics, a shunt is a device which allows electric current to pass around another point in the circuit.
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Smoke
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A collection of airborne solid and liquid particulates and gases emitted when a material undergoes combustion or pyrolysis, together with the quantity of air that is entrained or otherwise mixed into the mass.
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Energy (such as light) may be attenuated or diffracted by smoke.
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Spatial Filter
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An optical device which uses the principles of Fourier optics to alter the structure of a beam of coherent light or other electromagnetic radiation.
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Spirit Level
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An instrument designed to indicate whether a surface is horizontal.
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In the case of a gravity field.
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Spray
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When a liquid is dispersed as a stream of droplets (atomisation), it is called a spray. Spray nozzles are used to achieve two primary functions: increase liquid surface area to enhance evaporation, or distribute a liquid over an area.
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Stroboscopic Effect
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A visual phenomenon caused by aliasing that occurs when continuous motion is represented by a series of short or instantaneous samples. It occurs when the view of a moving object is represented by a series of short samples as distinct from a continuous view, and the moving object is in rotational or other cyclic motion at a rate close to the sampling rate.
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In the case of a modulated field.
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Thermal Hall Effect
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The thermal analog of the Hall effect, i.e. a thermal gradient is produced across a solid instead of an electric field. When a magnetic field is applied, an orthogonal temperature gradient develops. For conductors, a significant portion of the thermal current is carried by the electrons. In particular, the Righi-Leduc Effect describes the heat flow resulting from a perpendicular temperature gradient and vice versa, and the Maggi-Righi-Leduc effect describes changes in thermal conductivity when placing a conductor in a magnetic field.
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Thermal Shock
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Cracking as a result of rapid temperature change. Thermal shock occurs when a thermal gradient causes different parts of an object to expand by different amounts. This differential expansion can be understood in terms of stress or of strain, equivalently. At some point, this stress overcomes the strength of the material, causing a crack to form. If nothing stops this crack from propagating through the material, it will cause the object's structure to fail.
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Thermionic Energy Conversion
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The direct production of electric power from heat by thermionic electron emission
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Thermistor
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A type of resistor whose resistance varies significantly with temperature, more so than in standard resistors.
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Thermochromic Paint
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A paint based on colour-changing pigments. It involves the use of liquid crystals or leuco dye technology. After absorbing a certain amount of light or heat, the crystallic or molecular structure of the pigment reversibly changes in such a way that it absorbs and emits light at a different wavelength than at lower temperatures.
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In the case of a thermal field or one that results in temperature change, such as light absorbed by a surface.
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Thermochromism
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The ability of substance to change color due to a change in temperature. Thermochromism is one of several types of chromism. The two basic approaches are based on liquid crystals and leuco dyes.
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In the case of a thermal field or one that results in temperature change, such as light absorbed by a surface.
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Thermocouple
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A junction between two different metals that produces a voltage related to a temperature difference. Thermocouples are a widely used type of temperature sensor for measurement and control and can also be used to convert heat into electricity.
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Thermography
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Thermal imaging cameras detect radiation in the infrared range of the electromagnetic spectrum (roughly 9000-14,000 nanometers or 9-14 µm) and produce images of that radiation, called thermograms.
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Thermoluminescence
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A form of luminescence that is exhibited by certain crystalline materials, such as some minerals, when previously absorbed energy from electromagnetic radiation or other ionizing radiation is re-emitted as light upon heating of the material. This phenomenon is distinct from that of black body radiation.
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Detection of a thermal field, or detection of a previous exposure to an electromagnetic fied.
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Thermopile
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An electronic device that converts thermal energy into electrical energy. It is composed of several thermocouples connected usually in series or, less commonly, in parallel.
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In particular, a thermal field.
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Tidal Force
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A situation in which a body or material (for example, tidal water, or the Moon) is mainly under the gravitational influence of a second body (for example, the Earth), but is also perturbed by the gravitational effects of a third body (for example, by the Moon in the case of tidal water, or by the Sun in the case of the Moon).
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In the case of a gravity field.
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Total Internal Reflection
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An optical phenomenon that occurs when a ray of light strikes a medium boundary at an angle larger than a particular critical angle with respect to the normal to the surface. If the refractive index is lower on the other side of the boundary, no light can pass through and all of the light is reflected. The critical angle is the angle of incidence above which the total internal reflection occurs.
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Townsend Discharge
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A gas ionization process where an initially very small amount of free electrons, accelerated by a sufficiently strong electric field, give rise to electrical conduction through a gas by avalanche multiplication: when the number of free charges drops or the electric field weakens, the phenomena ceases.
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Avalanche multiplication during Townsend discharge is naturally used in gas phototubes, to amplify the photoelectric charge generated by incident radiation (visible light or not) on the cathode
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Vibrating String
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A vibrating string produces a sound whose frequency in most cases is constant. Therefore, since frequency characterizes the pitch, the sound produced is a constant note. Vibrating strings are the basis of any string instrument like guitar, cello, or piano.
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Voigt Effect
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A magneto-optical phenomenon whereby the polarisation of light may be rotated when passed through a vapour cell immersed in a magnetic field directed perpendicular to the beam direction.
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Weak Point
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Explotation of a natural or deliberately introduced weak point in a system or structure. For example: an electrical fuse or a shear pin.
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The energy of the field to be detected is sufficient to cuase a weak point to change state.
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Wiedemann Effect
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A magnetoelastic effect. The twisting of a magnetic material when a helical magnetic field is applied to it.
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Wiegand Effect
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Generation of electrical pulses when a specially processed wire is moved in a magnetic field. The wire has two distinct magnetic regions that react differently to the magnetic field: the shell requires a strong magnetic field to reverse its magnetic polarity, whereas the core will revert under weaker field conditions. The polarity of the wire shifts very rapidly, generating strong, short (~10 µs) electrical pulses without additional external power.
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In the case of a magnetic field.
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Yarkovsky Effect
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A force acting on a rotating body in space caused by the anisotropic emission of thermal photons, which carry momentum. It is usually considered in relation to meteoroids or small asteroids (about 10 cm to 10 km in diameter), as its influence is most significant for these bodies.
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Zeeman Effect
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The splitting of a spectral line into several components in the presence of a static magnetic field. The Zeeman effect is very important in applications such as nuclear magnetic resonance spectroscopy, electron spin resonance spectroscopy, magnetic resonance imaging (MRI) and Mössbauer spectroscopy. It may also be utilised to improve accuracy in Atomic absorption spectroscopy.
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In the case of a magnetic field.
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Zone Plate
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A device used to focus electromagnetic ratiation (including light), using diffraction instead of refraction. It consists of a set of radially symmetric rings which alternate between opaque and transparent. Incident radiation diffracts around the opaque zones which can be spaced so that the diffracted radiation constructively interferes at a desired focus, creating an image there.
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The same zone plate will focus light of many wavelengths to different foci, which means they can also be used to detect or extract specific wavelengths.
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