QCW is pleased to present a glossary of specialized terminology for electromechanical/mechatronic transducers/actuators.

• Aging Rate. Aging is the attempted return of a piezoelectric ceramic to its state prior to polarization. The rate at which aging occurs increases with voltage, stress, strain, and temperature. The aging rate of terfenol-d is zero.
  
  
• Anisotropy. The physical properties of some materials depend on the direction in which they are measured. These materials are also known as "oriented" materials.
  
  
• Blocked Electrical Impedance. For an electromechanical transducer, the blocked electrical impedance is the complex ratio of the voltage divided by the current at the electrical terminals with the mechanical terminals constrained from moving. Motional impedance summed with blocked electrical impedance equals total impedance.
  
  
• Breakdown. An electrical discharge through insulation.
  
  
• Breakdown Voltage. The voltage at which a breakdown occurs between two conductors.
  
  
• Curie Temperature. The temperature above which magnetostrictive or piezoelectric phenomena are lost. Since magnetostriction is an atomic phenomenon, magnetostriction fully returns upon cooling. Passing its Curie point returns the polarized, distorted crystal structure of a piezoelectric ceramic to its original, undistorted state, rendering it inert at any temperature.
  
  
• Dielectric Strength. The voltage which an insulating material can withstand before breakdown occurs, usually expressed as a voltage gradient such as volts per unit length.
  
  
• Driving Point Impedance. For an electromechanical transducer, the driving point impedance is the electrical impedance presented by the transducer electric input terminals in the absence of any signal applied to the output mechanical terminals.
  
  
• Eddy Current or Foucalt Current. A current resembling a vortex motion that is induced in a continuum of conducting material by a time-varying magnetic field.
  
  
• Ferromagnetic. A ferromagnetic material is attracted to a magnetic field. The amount of attraction is limited by saturation of the material.
  
  
• Flux Density. The total number of flux lines passing perpendicularly through a given area.
  
  
• Flux Line. The unit of magnetic field in the CGS system of measurement. One flux line is called one maxwell. Flux lines exit the north pole and return to the south pole.
  
  
• Flux Linkage. Magnetic flux links to (threads through) a coil when the flux passes at a time rate through the coil conductors, inducing a voltage.
  
  
• Hard Magnetic Material. A material which, once magnetized, tends to resist demagnetization. All permanent magnet materials are considered "hard." The TbDyFe alloy is a soft magnetic material.
  
  
• Hard PZT Material. A piezoelectric ceramic material that is not easily poled or depoled except at elevated temperatures.
  
  
• Hysteresis. A portion of the response of a device or system where a change in input does not produce a change in output.
  
  
• Impedance. When measured across a pair of terminals, impedance is the sum of the responses of energy dissipating and energy storage elements within a device or system.
  
  
• Joule Effect. The Joule effect is the term for the change in length of a ferromagnetic material along the axis of the applied magnetic field, when this field is changed.
  
  
• Leakage Flux. That part of a magnetic field outside the intended magnetic path.
  
  
• Magnetic Anisotropy. In certain crystalline materials, magnetization prefers to lie along certain crystal directions, called easy directions of magnetization. Work is required to point the magnetization away from these easy directions. Hard directions of magnetization are associated with a maximum of the anisotropic energy.
  
  
• Magnetic Domain. That small region within a magnetic material featuring a uniform magnetization direction.
  
  
• Magnetic Field Intensity / Magnetic Field Strength / Magnetizing Force. A consequence of the flow of electric current, be that through a solenoid coil or the small currents in a permanent magnet.
  
  
• Magnetic Flux Density / Magnetic Induction. Magnetic flux density is magnetic field intensity per unit normal to that field.
  
  
• Magnetic Permeability. Magnetic permeability is a property of the specific substance through which the magnetic field passes. The permeability of a material is a measure of the degree to which the material can be magnetized, or the ease with which magnetic flux density can be induced in the presence of an external magnetic field.
  
  
• Magnetic Saturation. A material is said to be magnetically saturated when the slope of magnetic flux density per unit magnetic field intensity equals the permeability of free space.
  
  
• Magnetomechanical Coupling Coefficient. A dimensionless number defined as the square root of (mechanical energy stored per cycle / magnetic energy stored per cycle).
  
  
• Magnetostriction. Production of mechanical strain in proportion to an applied magnetic field. Magnetostriction occurs in ferromagnetic materials when domains are forced into alignment by an external energy source. Caused by bond distortion, due to interactions of magnetic moments in adjacent domains - if repulsive, the material expands. Very large magnetostriction is possible in rare earth metals and alloys, due to exceptionally high magnetic moments associated with unpaired 4f electrons. The highest known values occur in pure rare earths but only at cryogenic temperatures. The word magnetostriction originates from the words magnetic and constriction.
  
  
• Motional Impedance. For an electromechanical transducer, motional impedance is that part of the electrical impedance due to mechanical motion. Motional impedance summed with blocked electrical impedance equals total impedance.
  
  
• Piezoelectric Ceramic. A ceramic in which the crystals possess large electric dipole moments that can be aligned in an electric field and maintain that alignment below the Curie temperature.
  
  
• Poling. Aligning electric dipoles within a piezoelectric element is dubbed "poling." Poling a piezoelectric ceramic element increases the dimension between poling electrodes and decreases the dimensions parallel to the electrodes.
  
  
• Transducer. A device (or medium) that converts energy from one form to another.