COMSOL 6.4 - Glossary of Terms

Glossary of Terms

A sensor that measures acceleration or gravitational force. See also sensor.

A device or mechanism that produces mechanical motion.

See arbitrary Lagrangian–Eulerian method.

arbitrary Lagrangian–Eulerian (ALE) method

A technique to formulate equations in a mixed kinematical description. An ALE referential coordinate system is typically a mix between the material (Lagrangian) and spatial (Eulerian) coordinate systems.

The ratio of the dimensions of a device in different directions, for example, the ratio of height to width. See also lateral aspect ratio and vertical aspect ratio.

A general term for sensor devices that either detect biological substances or use antibodies, enzymes, or other biological molecules in their operation. Biosensors are a subcategory of chemical sensors.

A process by which one substrate is firmly attached to the surface of another.

The sudden collapse or reduction in stiffness of a structure under a critical combination of applied loads.

cantilever beam

A beam with one end fixed and one end free.

capacitive sensor

A sensor that produces a signal due to a change in its capacitance.

The most fundamental stress measure defined as force/deformed area in fixed directions not following the body.

compliance matrix

The inverse of the elasticity matrix. See elasticity matrix.

A MEMS device consisting of interdigitated fingers similar in appearance to two interlocking combs.

constitutive equations

The equations formulating the stress-strain relationship of a material.

Time-dependent material nonlinearity that usually occurs in metals at high temperatures in which the effect of the variation of stress and strain with time is of interest.

Dissipation of energy in a vibrating structure. A common assumption is viscous damping, where the damping is proportional to the velocity. See also Rayleigh damping.

elastic deformation

A nonpermanent deformation that recovers its shape completely upon the release of an applied stress.

elasticity matrix

The matrix D relating strain to stresses:

Model described and solved in a coordinate system that is fixed (spatial). See also Lagrangian and arbitrary Lagrangian–Eulerian method.

frequency-response analysis

An analysis solving for the steady-state response from a harmonic excitation. Typically a frequency sweep is performed, solving for many excitation frequencies.

Green–Lagrange strain

A measure of nonlinear strain used in large-deformation analysis. In a small-strain large rotation analysis, the Green–Lagrange strain corresponds to the engineering strain with the strain values interpreted in the original directions. The Green–Lagrange strain is a natural choice when formulating a problem in the undeformed state.

The strain in a stress-free structure before it is loaded. See also strain and residual strain.

The stress in a nondeformed structure before it is loaded. See also stress and residual stress.

The increase in temperature of a medium as a result of resistance to an electric current flowing through it.

A dimensionless number that provides a measure of how rarefied a gas flow is, in other words, the average distance between the gas molecules compared to the length scale of the flow. The following equation defines the Knudsen number Kn where λ is the mean free path of the molecules and L is a length scale characteristic to the flow.

Model described and solved in a coordinate system that moves with the material. See also Eulerian and arbitrary Lagrangian–Eulerian method.

large deformation

The deformations are so large so the nonlinear effect of the change in geometry or stress stiffening need to be accounted for.

lateral aspect ratio

The ratio of the length of a structure in the plane of a wafer to its width in that plane. See also aspect ratio and vertical aspect ratio.

An acronym for microelectromechanical systems. More generally, MEMS refers to systems, devices, and components with microscale size and in which the physics is not necessarily limited to electrical or mechanical phenomena.

See MEMS.

piezoelectricity

The ability of certain crystalline materials to produce an electric voltage when subjected to mechanical stress (direct piezoelectric effect). Inversely, the material’s ability to change shape when an external voltage is applied (reverse piezoelectric effect).

An assumption on the strain field where all out-of-plane strain components are assumed to be zero.

An assumption on the stress field where all out-of-plane stress components are assumed to be zero.

principle of virtual work

States that the variation in internal strain energy is equal to the work done by external forces.

A predetermined test mass in a measurement device or machine that serves as the reference mass for the quantity to be measured.

Rayleigh damping

A viscous damping model where the damping is proportional to the mass and stiffness through the mass and stiffness damping parameters.

residual strain

Strain remaining in a structure after some operation, for example, the strain resulting from cooling a system after high-temperature bonding. It often appears as the initial strain for any consequent tasks. See also strain and initial strain.

residual stress

Stress remaining in a structure after some operation, for example, stress resulting from cooling a system after high-temperature bonding. It often appears as the initial stress for any consequent tasks. See also stress and initial stress.

second Piola–Kirchhoff stress

Conjugate stress to Green–Lagrange strain used in large deformation analysis.

A device that measures a physical variable such as temperature or pressure and converts it (usually) to an electrical signal.

slide-film damping

The damping effect of a fluid between two solid surfaces when the distance between them is small compared to their area and there is mostly tangential movement (lubrication). Slide-film damping is a type of thin-film damping.

The skew-symmetric part of the velocity gradient tensor.

squeeze-film damping

The damping effect of a fluid between two solid surfaces when the distance between them is small compared to their area and there is mostly normal movement. Squeeze-film damping is a type of thin-film damping.

Relative change in length, a fundamental concept in structural mechanics.

Internal forces in a material. Normal stresses are defined as forces/area normal to a plane, and shear stresses are defined as forces/area in the plane. A fundamental concept in structural mechanics.

thermoelastic damping

When an elastic rod is stretched reversibly and adiabatically its temperature drops. The drop in temperature compensates for the increase in entropy caused by the stress in the rod (since the process is reversible the entropy remains constant). In a general deformation, the strain in a structure is nonuniform and so the temperature changes in a nonuniform manner throughout the structure. The irreversible flow of heat that accompanies these temperature changes result in energy loss and damping of the structure.

thin-film damping

Damping that occurs in a thin channel of fluid (fluid film) between moving structures. See squeeze-film damping and slide-film damping.

A device that converts one type of energy to another. It often refers to a device that responds to a physical parameter and converts it to an electrical signal.

vertical aspect ratio

The ratio of the height of a structure perpendicular to a wafer’s surface to its depth in the wafer’s plane.