Ferrite Core Electromagnet

[Aimon Jardine]

Myfinal goal is to generate the strongest magnetic field possible with the minimum amount of current, but for prototyping purposes I used a 0.5mm diameter enamelled copper wire to generate lesser amounts of resistance while varrying the current with my 30V/5A DC power supply.

I know that the magnetic field B is dependent on the permeability of free-space (0), on the permeability of the core material (r) and on the magnetomotive force divided by the length of the coil (NI/l=H).

Thus I started prototyping with what I had under the hand, namely a steel screw and laminated iron plates I cannibalised from an old nokia transformer, needless to say it was a lost cause to search for their B vs H hysteresis curve. In the end I made 3 increasingly powerful magnets, one with the steel screw core, one with a core made of several laminated iron plates and the last and most powerful one with E-shaped laminated iron plates.

But as I said, my goal isn't to generate the most powerful magnetic field possible but rather to find a decent compromise between B and I. Therefore I started looking for other materials online and found these ferrite rods (pdf warning).

These rods are 2.5cm long, have a medium permeability (initial permeability at i=2300) and saturate at about 0.5T which was more or less exactly what I was looking for. Once I got them, I winded 100 turns of copper wire around them. And according to their B vs H curve and this small equation :

I mentioned that I was half-surpised because it was clearly indicated under each graph that all measurements had been done under a 10kHz AC signal, which finally brings us to my questions: first, do lower frequencies affect the permeability of the material or did I just misunderstand the datasheet and second, if the answer to the first question is "yes, lower frequencies affect the permeability of the material", does the datasheet somehow allow us to estimate the impact of these lower frequencies ?

You are using a ferrite rod but you need to consider a closed path in your calculations. To calculate the magnetic flux or flux density you should first think about the closed magnetic circuit. One reluctance (magnetic resistance) of such a magnetic equivalent circuit would be the reluctance of the ferrite rod:$$R_\mathrmm=\fracl\mu A$$To get a closed magnetic circuit, you still have to take the reluctance of the distance through the air into consideration:

Build a closed ring out of the magnet material e.g. Iron and cut a small gap into it, just big enough to fit whatever you want to expose to the field. This maximizes the permeance of the core. A stick bar core has a very bad permeance as explained very nicely by Lars Hankeln.

When winding, consider to use a diameter of conductor that - in the end - will give you a coil resistance that you can drive well with your power source. Usually, that means a winding resistance in the 1 .. 100 Ohm ballpark.

In electronics, a ferrite core is a type of magnetic core made of ferrite on which the windings of electric transformers and other wound components such as inductors are formed. It is used for its properties of high magnetic permeability coupled with low electrical conductivity (which helps prevent eddy currents). Moreover, because of their comparatively low losses at high frequencies, they are extensively used in the cores of RF transformers and inductors in applications such as switched-mode power supplies, and ferrite loopstick antennas for AM radio receivers.

Ferrites are ceramic compounds of the transition metals with oxygen, which are ferrimagnetic but non-conductive. Ferrites that are used in transformer or electromagnetic cores contain iron oxides combined with nickel, zinc, and/or manganese compounds. They have a low coercivity and are called" "soft ferrites" to distinguish them from" "hard ferrites", which have a high coercivity and are used to make ferrite magnets. The low coercivity means the material's magnetization can easily reverse direction while dissipating very little energy (hysteresis losses); at the same time, the material's high resistivity prevents eddy currents in the core, another source of energy loss. The most common soft ferrites are:

As any given blend has a trade-off of maximum usable frequency, versus a higher mu value, within each of these sub-groups, manufacturers produce a comprehensive range of materials for different applications blended to give either a high initial (low frequency) inductance or lower inductance and higher maximum frequency, or for interference suppression ferrites, an extensive frequency range, but often with a very high loss factor (low Q).

It is essential to select the suitable material for the application, as the correct ferrite for a 100 kHz switching supply (high inductance, low loss, low frequency) is quite different from that for an RF transformer or ferrite rod antenna, (high frequency, low loss, but lower inductance), and different again from a suppression ferrite (high loss, broadband)

There are two broad applications for ferrite cores that differ in size and frequency of operation: signal transformers, which are of small size and higher frequencies, and power transformers, which are of large size and lower frequencies. Cores can also be classified by shape, such as toroidal, shell, or cylindrical cores.

The ferrite cores used for signals have a range of applications from 1 kHz to many MHz, perhaps as much as 300 MHz, and have found their main application in electronics, such as in AM radios and RFID tags.

Ferrite rod aerials (or antennas) are a type of small magnetic loop (SML) antenna[3][4] ubiquitous in AM radio broadcast band transistor radios. However, they began to be used in vacuum tube ("valve") radios in the 1950s. They are also helpful in very low frequency (VLF) receivers,[5] and can sometimes give good results over most of the shortwave frequencies (assuming a suitable ferrite is used). They consist of a coil of wire wound around a ferrite rod core (usually several inches longer than the coil). This core effectively concentrates the magnetic field of the radio waves[6] to give a stronger signal than could be obtained by an air core loop antenna of comparable size, although still not as strong as the signal that could be obtained with a good outdoor wire aerial.

Other names include "loopstick antenna", "ferrod", and "ferrite-rod antenna". "Ferroceptor" [7] is an older alternative name for a ferrite rod aerial, mainly used by Philips where the ferrite core would be called a "Ferroxcube" rod (a brand name acquired by Yageo from Philips in the year 2000). The short terms "ferrite rod" or "loop-stick" sometimes refer to the coil-plus-ferrite combination that takes the place of both an external antenna and the radio's first tuned circuit or just the ferrite core itself (the cylindrical rod or flat ferrite slab).

A ferrite core is a type of magnetic material that is commonly used in electronic devices to increase the strength of an electromagnetic field. It is made of a ceramic compound of iron oxide and other metal oxides.

A solenoid is a coil of wire that is used to create a magnetic field when an electric current is passed through it. It is often used in electronic devices to convert electrical energy into mechanical motion.

A ferrite core is placed inside the solenoid and acts as a magnetic amplifier. It concentrates and directs the magnetic field created by the solenoid, making it stronger and increasing its range and effectiveness.

Yes, there are some limitations to using a ferrite core in a solenoid. The size, shape, and material of the core must be carefully chosen to match the specific application. Additionally, the core can only amplify the magnetic field up to a certain point before it becomes saturated and can no longer increase the range.

The best core material for an electromagnet depends on the specific application and desired characteristics. Some common core materials include iron, steel, nickel, and cobalt. Each material has its own unique properties that make it suitable for different purposes.

To choose the best core material for your electromagnet, you should consider factors such as the strength of the magnetic field needed, the desired size and weight of the electromagnet, and the cost of the material. It is also important to consider any potential environmental factors, such as temperature or corrosion, that may affect the performance of the core material.

Iron is a popular choice for core material due to its high magnetic permeability, which allows it to easily magnetize and demagnetize. It is also relatively inexpensive and widely available. Iron cores are also versatile and can be used for a variety of applications.

Yes, it is possible to use multiple core materials for an electromagnet. This is known as a composite core and can provide a combination of the desired characteristics from each material. However, it is important to carefully consider the compatibility and potential effects of combining different core materials.

Choosing the right core material is crucial for optimizing the performance of an electromagnet. A core material with a high magnetic permeability will result in a stronger and more efficient magnetic field. Additionally, selecting a core material that is resistant to factors such as temperature and corrosion can help to improve the longevity and reliability of the electromagnet.

This writing process also causes electricity to be induced into nearby wires. If the new pulse being applied in the X-Y wires is the same as the last applied to that core, the existing field will do nothing, and no induction will result. If the new pulse is in the opposite direction, a pulse will be generated. This is normally picked up in a separate "sense" wire, allowing the system to know whether that core held a 1 or 0. As this readout process requires the core to be written, this process is known as destructive readout, and requires additional circuitry to reset the core to its original value if the process flipped it.

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