Glossary

Aging Rate

• Polarizing certain ceramics gives them the property of being piezoelectric. Aging is the spontaneous attempt of the piezoelectric ceramic to change back to its original, unpolarized state. Aging rate is affected by temperature, voltage, stress, and strain.

Anisotropy

• Some physical properties of some substances depend on the direction in which the properties are measured, a phenomenon termed anisotropy. The material may also be known as "oriented."

Apparent Power

• Product of r.m.s. voltage and r.m.s. current. In an AC circuit with reactive components, this is not equal to the dissipated power, but an uncompensated power supply must nevertheless supply it.

Bimorph

• A shape change material, when bonded to either an inert material or a shape change material of opposite polarity, with the bond parallel to the axis of the shape change(s), will cause the assembly to bend when excited due to differential expansion.

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. Blocked electrical impedance summed with motional impedance equals total impedance.

Capacitor

• Pair of conductors separated by a dielectric medium. Capacitors pass AC currents, resist DC currents, and store energy in the form of an electric field.

Coefficient of Coupling or Coupling Factor

• The square root of the ratio of output energy stored per cycle to the input energy stored per cycle.

Coherence

• A measure of the amount of linear and time-invariant dependence of an output signal on the input signal.

Core Loss

• Power dissipated when any conductor, particularly a ferromagnetic core, is subject to a time-varying magnetic field.

Creep

• After a step change in applied voltage, piezoelectric materials undergo a short term dimensional stabilization.

Curie Point or Curie Temperature

• The phenomena of ferromagnetism and piezoelectricity occur below a characteristic material temperature called the Curie temperature.

d33 Constant

• Ratio of elastic strain to incident electromagnetic field.

d*33 Constant

• Ratio of electromagnetic output to incident elastic field.

Demagnetization

• Partial or complete removal of residual magnetism from an object.

Demagnetization Curve

• Second or fourth quadrants of a major hysteresis loop.

Depole

• The opposite of poling.

Dielectric

• (1) Any insulating medium which permits electrostatic attraction and repulsion to take place across it between two conductors. (2) From a dielectric medium, energy needed to establish an electric field is recoverable in whole or in part as electric energy.

Dielectric Absorption

• Accumulation of electric charges within a dielectric material subject to an electric field.

Dielectric Breakdown

• Voltage at which an electrical failure or insulation breakthrough occurs.

Dielectric Constant

• A measure of the degree to which the material can be polarized, or the ease with which electric intensity can be induced in the presence of an electric displacement vector. Ratio of the permittivity of a material to that of free space.

Dielectric Strength

• The voltage which a given thickness of insulating material can withstand before breakdown occurs.

Dipole

• Magnetic dipoles may be thought of as small bar magnets composed of north and south poles. Within a magnetic field, the force of the field exerts a torque that tends to orient a dipole with the field itself. Electric dipoles behave similarly in an electric field.

Dissipation Factor or Loss Angle or Tan "Delta"

• A measure of the electrical losses in a material. It is the ratio of effective resistance to effective reactance or the angle by which an incident field leads its effect on the material.

Distortion

• An undesired waveform change produced by system non-linearities.

Drift

• An undesired change in a characteristic over a period of time.

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.

Dynamic Range

• Ratio of the largest signal a system can process to the smallest signal it can reliably resolve.

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.

Electrostriction

• Material strain is proportional to the square of an applied electric field.

Equivalent Series Resistance (ESR)

• The reciprocal of the product of circular frequency, capacitance, and dissipation factor in a piezoelectric ceramic.

Ferromagnetic

• Hysteretic material the permeability of which depends on the magnitude of an applied magnetizing force.

Gyrator

• Changes a through-variable (such as current or velocity) into an across-variable (such as voltage or force) and an across-variable into a through-variable. Examples are gyroscopes, Hall generators, and magnetostrictive shape change materials.

Hard Magnetic Materials

• Materials used to make permanent magnets because they resist demagnetization.

Hard PZT Material

• Piezoelectric ceramic material with a Curie temperature above 300 °C. Not easily poled or depoled except at elevated temperatures.

Hysteresis

• Difference between output at a given input, when traversing in one direction, and output at the same input when traversing in the other direction.

Impedance

• Vector sum of resistance and reactance of a dynamic system, as measured across a pair of terminals.

Inductor

• Generally, a coil of wire. Inductors pass DC currents, resist AC currents, and store energy in the form of a magnetic field.

Joule Magnetostriction

• Dimensional changes induced in a ferromagnetic material by a magnetic field. Source of hum in electrical transformers.

Leakage Factor

• Ratio between magnetic flux at magnet neutral section and average air gap flux.

Leakage Flux

• Magnetic field outside the useful or intended magnetic circuit.

Lenz's Law

• Direction of current induced in a conductor, by any change in the relation between the conductor and a magnetic field, opposes by its own magnetic field the action tending to induce the current.

Line of Electric Force

• An electric line of force starts at a positive electric charge and ends at a negative electric charge.

Line of Magnetic Force or Flux Line

• A magnetic line of force starts at a north magnetic pole and ends at a south magnetic pole.

Magnetic Domains

• Approximately grain-sized magnetic dipoles which determine the magnetic characteristics of a magnetic material.

Magnetic Field Intensity or Magnetic Field Strength or Magnetizing Force

• Measure of the ability of an electric current or permanent magnet to induce a magnetic field. Quantified by the number of lines of magnetic force intersecting unit area normal to the field.

Magnetic Flux

• One weber is the magnetic flux which, linking (threading through) a circuit of one turn, induces in that circuit a voltage of one volt as the flux is reduced to zero at a uniform rate in one second.

Magnetic Flux Density or Magnetic Induction

• Total number of magnetic flux lines passing perpendicularly through a given area.

Magnetic Flux linkage

• One magnetic flux line linking (threading through) one inductor winding turn.

Magnetic Permeability

• 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 Poles

• Magnetic poles occur where the magnetization vector is normal to the surface. A toroid has no magnetic poles.

Magnetization

• Magnetic moment per unit volume. A vector quantity, it is the magnetic analog of the polarization in a dielectric.

Magnetomotive Force

• Line integral of magnetic field intensity between any two points. Force that tends to produce a magnetic field and is the magnetic analog to electromotive force.

Maximum Energy Product

• The maximum product of magnetic induction and magnetic field intensity which is found on the demagnetization curve.

Motional Impedance

• For an electro-mechanical transducer, motional impedance is that part of the electrical impedance due to mechanical motion. Motional impedance summed with blocked electrical impedance equals total impedance.

Natural Frequency, Resonance

• Condition in an underdamped dynamic system in which the vector sum of the reactances is zero, generally resulting in maximum system amplitude per unit input energy.

Non-Linearity

• The difference between the y-value at a specified x-value and the corresponding point on a straight line between the two end points of interest.

Nyquist Plot

• Graph of real versus imaginary spectral components.

Piezoelectric Effect

• When subject to an electric field, certain ceramic crystals expand along one axis and contract along others. Correspondingly, the reciprocal effect is for compression of these crystals to generate an electrostatic voltage across the crystal.

PMN

• Lead magnesium niobate. Electrostrictive ceramic.

PMN-PT

• Lead magnesium niobate - lead titanate. Electrostrictive ceramic.

Poling

• Process of aligning electric dipoles within a piezoelectric ceramic. The directions of the electrical and mechanical axes depend upon the direction of the original polarizing field. Poled elements exhibit a permanent (except for aging) positive strain in the direction between the poling electrodes and a permanent (except for aging) negative strain in the other directions.

Power Factor

• Ratio of true power to apparent power.

PZT

• A registered trademark of Clevite Corporation to identify a family of lead zirconate -- lead titanate compositions. It has become a common acronym for all piezoelectric ceramics.

Q

• Ratio of peak energy stored per cycle divided by total dissipation in a radian period. High Q dynamic systems exhibit longer rise and delay times.

Reactance

• Opposition to AC power flow caused by a circuit's inductance or capacitance. Reactance does not dissipate power, unlike resistance, but it changes the phase angle between alternating voltage and alternating current. Reactance is the imaginary part of impedance.

Reluctance

• For a given magnetomotive force in a magnetic circuit, reluctance is the property that determines the total magnetic flux. Reluctance is the magnetic analog of electrical resistance.

Saturation

• Condition in which a further increase in an independent parameter produces no increase in the dependent parameter.

Skin Depth or Depth of Penetration

• In an electrical conductor, an incident electromagnetic wave is irreversibly diffused to 1/e of its surface value at skin depth "delta."

Soft PZT Material

• Piezoelectric ceramic material with a Curie temperature less than 200°C. A strong electric field will easily pole and depole a soft PZT at room temperature.

Stationary or Standing Waves

• Stationary or standing waves are produced in a medium by the simultaneous transmission, in opposite directions, of two similar wave motions. Fixed points of minimum amplitude are called nodes. A segment extends from one node to the next. An antinode or loop is the point of maximum amplitude between two nodes.

Susceptance

• The imaginary part of admittance.

Symmetry, Reciprocity

• In a symmetric or reciprocal dynamic system, the source and point of observation may be interchanged without affecting the result, provided that the source impedance equals the observing apparatus impedance.

Transducer

• A device (or medium) that converts energy from one form to another.

Transduction Coefficients Tem And Tme

• In an electro-mechanical transducer, Tem is the voltage appearing in the electrical network per unit velocity in the mechanical network. Tme is the force acting in the mechanical network per unit current in the electrical network.

Villari Effect

• In the presence of a magnetic field, the magnetization of a magnetostrictive material changes when its stress state is changed by external means.

Wertheim Effect

• A wire, made of a magnetostrictive material and placed in a longitudinal magnetic field, will generate a transient voltage difference between the ends of the wire when twisted.

Wiedemann Effect

• A wire, made of a magnetostrictive material and placed in a longitudinal magnetic field, will twist when a current flows through the wire. Correspondingly, such a wire will be axially magnetized when twisted while carrying a current.

Wiegand Effect

• A patented cold-working of a thin wire of Vicalloy causes the wire to have different internal and surface crystal structures. This corresponds to a large hysteresis loop. The Wiegand wire generates pulses in response to excitation from an alternating magnetic field of sufficient magnitude.