AC Magnetics

Magnetic Fields and Magnetic material properties can be measured for, and used with… either or both  AC or DC applications. [1]Resulting magnetic measurements can be used to characterize magnetic fields and magnetic materials for different uses. In many cases, AC magnetic measurements provide important property data that supplements DC magnetic data.

ARkival uses the newest technologies 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 material properties. All probes, Tesla meters, and Magnetometers focus on the measurement of magnetic flux (Moment) associated with magnetized samples and associated fields.

In the DC magnetometer data, the relationship between the applied field and the resulting magnetic flux (Moment) is the parameter called ‘permeability’, the equivalent measurement parameter with an AC magnetometer (susceptibility meter) is called “susceptibility’.

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

[1] AC and DC magnetic fields differ in their sources. AC magnetic fields are produced by an alternating electric current that changes direction, have polarity-designation and magnetic field magnitudes that change with time, while a DC field is constant both in magnitude and polarity (direction). DC magnetic fields are typically generated from earth sourced, natural material Magnets or DC electrical circuits whereas  AC magnetic fields are for the most part, all derived from human-designed electrical circuitry.

AC Magnetic Field Measurements

ARkival Technology has developed a fast and accurate measurement means for 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 now possible with calibrated accuracy referenced to standardized sources and calibration materials[2]. 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.

[2] NIST Standard Reference materials and Helmholtz coil technology

AC Magnetic Material Measurements

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

Adding Complexity To The Data Mix

The AC material measurement has the potential to measure very small AC magnetic fields, and the AC property measurement can also provide material data with simultaneous AC frequency reporting and material-related losses.

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. The AC loss factor is reported as complex data.

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 ranges.

AC Measurement Data

Susceptibility, the focus of AC magnetometry measurements…

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 AC magnetic 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 (VSM) magnetometer[3]

[3]  Low frequency, Field induced AC magnetic moments typically follow the slope of the DC, B-H curve. The slope parameter reported as AC “susceptibility” and in DC terminology, reported as “permeability”.

Typical AC Measurements

Susceptibility & AC Loss Factor

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:


Frequency Response

Critical Temperatures

Critical Current Density

Eddy Currents

The AC magnetic susceptibility can be also used to study magnetic relaxation

Susceptibility is used to characterize magnetic materials such as ferrites, Sendusts (FeSiAl materials),  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.

About Eddy Currents (AC or DC losses)

Eddy currents are a cause of energy loss in many AC devices and their component materials. In DC devices, eddy current loss and hysteresis loss occur as Iron losses and are called core losses or magnetic losses.

Eddy currents have no direction and continually circulate in different conducting materials having ‘suitable’ cross sections for their presence. The magnetic flux (Moment) generated by the circular current motion generates an emf in the associated conducting surface and creates energy loss. Most important, Eddy currents typically dissipate their energy in the form of heat.

To reduce eddy current losses, wires are divided into separate strands and magnetic circuit components and shielding materials made from separate material sheets insulated from each other. The layer division into sheets placed at right angles to the direction of the eddy currents restricts the eddy current paths and reduces eddy-current losses. ARkival can perform eddy currents measurements and material analysis.

AC Services & Applications

AC Measurement of magnetic Fields and material properties

Measurements of AC Susceptibility & material losses

Material measurements of Ferrites, Sendusts and Ferromagnetic materials

Measurements of AC Absorbing and Deflecting materials

Measurements of zero field environments using mu-metal and shielding materials

Measurement of magnetic fields at different AC frequencies

Measurement of eddy-currents and temperature loss

Confirmation of 1D, 2D or 3D static or dynamic magnetic fields

Measurement of interactive fields AC magnetic field and DC magnets

Calibration of magnetic sensors

Calibrations of Hall effect magnetic measurement devices

Certification of Zero-Tesla Fields for AC Magnetic shielding

Measurements & Calibrations of AC magnetic fields and sources

Measurements of zero field environments by mu-metal and materials shielding the earth’s magnetic field

Physical Measurement & Mapping confirmation of magnetic solutions done by FEM analysis

Measurements of transformers, standard cylinder coils and flat coil devices

Measurements of induced fields in remote charging and control devices

Measurement of Contactless identification devices (e.g., RFID)

Measurements of zero field environments by mu-metal and materials shielding the earth’s magnetic field

Testing of remotely activated, magnetic devices

Magnetic field measurements of spintronic devices

Measurement of Magnetic nano particle transport in fluid carriers