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Ferrites for sensor applicatons – design and properties


Common exploited properties of Ferrites
Forming fields
Shaping ferrites
Contacting coils
Permeability μ changes with
frequency | temperature
air gap | excitation level
DC bias/magnetic fields | mechanical forces
What do you need?
Wireless power and data transfer
Less common exploited properties of Ferrites

Properties and applications of Ferrites 1

  • “collecting” and shaping of magnetic fields
    ➤ sensors, antennas, transponders
  • Increasing “inertia” of electric current
    ➤ chokes, noise suppression, filters, delay lines
  • Increase magnetic coupling of conductors
    ➤ transformers, converters, storage chokes,
    impedance matching

Antennas and Sensors



Metal detection and recognition

source: IFM

Inductive proximity switch: 
Directing and focussing magnetic field


Non destructive Material testing: 

  • Material sorting (e.g. Coin recognition)
  • Material thickness (e.g. Coin recognition)
  • Crack detection and depth determination
  • Imaging of material faults

Dry pressing of ferrites


Cross-section through a sintered pot core


pressed part before sintering


powder column in the mould before pressing



 uneven densification
➤ strains and cracks,
particularly at the lines
where portions of
different thicknesses meet

Crack formation in pressed ferrites


Density differences during powder pressing
➤ differing densification in thinner and thicker
areas of the part can cause
crack formation at the intersections



Examples for injection molded parts


Isotropic 3D-cube antenna 9x9x9mm

  • monolytic, hollow ferrite
  • high Q-factor, high sensitivity
  • reduction in material and weight


smallest customer specific designs

  • wall thickness ≥ 0,22mm,
  • volume ≥ 1mm3
  • tolerances down to +-1%


SMD transponder coils

  • high Q-factor, high sensitivity
  • high reliabilty in vibration und drop tests

Ferrite production at NEOSID

mixing oxides main components Fe Mn Ni Zn
pre sintering homogenization and formation of the ferrite structure
milling creating a very fine powder
compounding mixing ferrite powder and binder
injection moulding 1 to 28 cavities
barrel finishing rounding edges, removing flash
sintering in air or under controlled oxygen concentration
annealing establishing an optimum domain structure
grinding tight tolerance, flat surface, round, thread grinding, CNC milling of prototypes
coating e.g. parylene, self-locking screw cores, metallization
Inspection electrical, geometrical

Contacting Technologies


Wire wound terminal


Metal pin terminal


Metallized core terminal

Common competitors Metallisations



Dipping in silverpaste, burning in and plating

➤ low quality factor caused by eddy currents in end faces

➤ Nickel-Zink-Ferrite only


single layer PVD

selective deposition of e.g. silver

➤ poor adhesion

➤ dissolves during soldering, does not withstand thermocompression

Metallisation from NEOSID


3-layer PVD
selective deposition of 3 layers where whished for, no burning in

➤ reduction of eddy currents

➤ works on Manganese- and Nickel-Zink-Ferrite

➤ good adhesion

➤ withstands soldering and thermocompression


automated 100 % optical inspection


Soft magnetic Ferrites


  • μi from 10 to 2.000
  • high Q between 0 and 100 MHz
  • large electrical resistance
  • higher Tc
  • sintering in air


  • μi from 700 to 20.000
  • high Q between 0 and 1 MHz
  • small electrical resistance
  • lower Tc
  • sintering under controlled atmosphere only

Influence of Frequency


μ‘ = permeability
μ‘‘ = losses

Q = μ‘/μ‘‘

For lower losses (higher Q) at higher frequencies chose lower μ material

Influence of Temperature


Medium and small μi

  • Very small temperature drift


High μ

  • Almost linear temperature drift
    (can be compensated)

Very high μ materials


Very unstable μ
 troublesome compensation


Sources: TDK-Catalogue

Only for very low
frequency applications

Influence of air gap


Air gap: Fraction of magnetic path not
running in ferrite material

μeff vs. % air gap for varying μi


Sensing Coils are mainly open magnetic circuits
with a large air gaps (≈ 50% for a pot core).

source: IFM

The larger the air gap, the less difference in μeff
remains between high and medium μ materials.

Influence of excitation level


Initial permeability μi is
μ measured at low excitation
levels (B < 0,5 mT)

μa changes at high excitation

With open magnetic circuits
μeff << μa

B = μeff*μo*H is rather small
and sensors usually work in
stable μ regime

Influence of DC-Bias and external Fields

Inductivity of transponder-Coil vs. DC-Current

Permeability decreases with
application of

  • DC-bias
  • external magnetic fields


ferrites stay stable up to a certain
level and than drop quite fast

Higher μ ferrites suffer earlier

Composites PFS4 and PFS9
drop earlier but slower

Composite Material PFS3 is
extremely stable
up to > 1000 mT

Impact of strong magnetic fields and excessive mechanical force

3 ferrite material classes

NiZn-ferrites F2a to F100b

  • Some impact, extremely slow recovery
  • complete recovery can be reached only through thermal annealing
  • a-Types (like F2a) are less sensitive


MnZn-ferrites F02 and F08

  • impact, but fast recovery


NiZn-ferrites F1ib, F1is, F5is and Composite Materials

  • hardly any impact


Composite materials

  • Hardly any impact
  • distributed air gap ➤ lower permeability
  • Saturation flux density > 1000 mT for PFS3
  • Tighter mechanical tolerances
  • Easy to machine

What do you need ?

High Q value at your frequency

  • wide range of ferrite materials F02 to F100
  • number in name gives maximum frequency in MHz
    for which high Q is still achieved (02 is 0.2 MHz)


Excelent temperature stability

  • materials F2 to F100 are your choice


High temperature applications

  • Materials with Curie Temperature ranging
    from 150 to 600 °C are available


Highest excitation levels
Large DC-Bias or strong external magnetic fields

  • PFS3 will do your job


Temporary Magnetic or mechanical stress

  • F1ib does not remember the torture


Smallest sizes, Customized shapes
Complicated geometries, Design for automation

  • Ceramic Injection Moulding of ferrites
    turns your vision into products


Contacting Pads, Shielding
Thermal compression of wire ends

  • Selective metallization of ferrites serves your needs


Medical applications

  • Parylene coating gives you coverage


You do not like cables and plugs

  • Wireless data and power transfer gets rid of cables

Wireless power and data transfer

Rotating scanner system






Energy transfer from primary to secondary side.

Bi-directional data transfer


Properties and applications of Ferrites 2

Less common thought of properties of soft magnetic ferrites:

  • Magnetostriction
    ➤ Ultrasonic actuators and sensors, “invisible speakers”
  • Lossy interaction with fields from MHz to some GHz
    ➤ Inductive Heating, selective microwave heating
  • Colour and magnetics
    ➤ Copier powder
  • DC-Magnetization
    ➤ Switchable mechanical forces



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