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AC Magnetic Fields

AC Magnetics

AC magnetic measurements provide important property data that supplements DC magnetic data. Low AC field frequency results in an induced AC moment that follows the slope of the DC, B-H/ Hystersis loop curve. A typical reported parameter is AC “susceptibility” and in DC magnetics terminology, reported as the sample permeability.

ARkival uses the newest technology and probes for magnetic field measurements (InAs and GaAs Hall Sensor probes, 2 Dex probes and ARkival’s miniature coil probes) for all AC and DC magnetic measurements. ARkival also employs precision DC magnetometers and AC susceptometers for measuring magnetic materials properties. All probe and meter devices focus on the measurement of magnetic flux (Moment) associated with magnetized samples and fields.

The resulting combination of both AC and DC material properties as reported parameters provides an ideal “fingerprint” of any material and its potential use for different magnetic product applications.

AC Magnetic Field Measurements

ARkival Technology has developed a fast and accurate measurement means for measuring AC magnetic fields and their corresponding AC frequencies in/for magnetic devices. Using both precision Hall probe and Miniature Coil probe access, AC field measurements are made with calibrated accuracy referenced to standardized sources and calibration materials. AC Field measurements can be performed in either 1D,  2D or 3D modes at specific measurement location(s) or over larger areal regions of interest by employing either precision manual testing or automated robotic testing, both with and without optional magnetic field mapping technology.

ARkival’s focus on the accurate measurement of AC material properties uses precision magnetometers that typically limits the material sample size to “small” rather than “large” . In many cases, test samples must be prepared for analysis and sample preparation options are discussed with clients prior to measurement.

High frequency Data

In sample measurements, the AC magnetic moment data derived from the AC applied field does not follow the DC magnetization curve for the same sample due to interactive, dynamic effects within the sample. In high AC frequency applications, the AC magnetization of the sample lags the applied field (driving field). In measurement, the AC ‘lagging effect’ is termed an AC loss factor and is one of the more important parameters associated with AC magnetic material measurements and their applications.

AC Susceptibility measurements can be focused and localized while ‘Wide-band’ AC susceptibility measurements can also be made on samples whereby the resulting data employs an integrated reporting method for material property analysis over large frequency range. The AC material measurement can measure and report very small AC magnetic fields, and the AC property measurement can also provide material data with simultaneous AC frequency reporting.

AC Measurement Data

In AC magnetic measurements, where an AC field is applied to a sample and the resulting AC magnetic moment is measured, the resulting data is an important tool for characterizing magnetic materials. Because the induced sample’s magnetic  moment is time-dependent in the AC mode, resulting measurements yield information about magnetization dynamics which are not obtained in DC measurements.

Low to Mid-frequency Data

Low frequency measurement data is typically related to DC magnetometry results where the resulting magnetic moment of the sample follows the traditional DC magnetic, B-H curve measured with a DC magnetometer

Typical AC measurements are

  • Susceptibility vs. temperature,
  • Susceptibility vs. driving frequency,
  • Susceptibility vs. DC field offset,
  • Susceptibility vs. AC field amplitude, and frequency measurements.
  • Susceptibility vs induced magnetization in secondary coils.

Basic physical properties from the AC data are

  • Resistivity,
  • Critical temperatures,
  • Critical current density,
  • Frequency response

Susceptibility is used to characterize magnetic materials such as ferrites, Sendusts,  semiconductors, superconductors and other magnetic materials where surface barriers and effects of granularity are of performance interest. The importance of correlating the AC susceptibility data with the materials’ intrinsic structure, is of interest for many applications, when AC magnetic data is combined with ARkival’s Atomic Force Microscopy (AFM) measurements.

Eddy Current measurements are also possible with reference standard(s)