Hi Maurice van Bussel ,

generally, the answer is yes. I feel the crucial parameter is the frequency of the EM field, dependent on the distribution of the particles:

If the particles are in electrically conducting contact to their neighbours, i. e. if the powder forms a bulk of material, with an extent of some cm or more, a frequency as low as 50 Hz would be enough (higher frequencies, as in induction hobs, might by preferable). If the particles are isolated from each other and embedded in a medium with relatively low conductivity, you will need a frequency in the microwave range (e.g. 2.5 Ghz).

An example for the latter case is the approach (as far as I know still in a laboratory stage) to apply locally restricted hyperthermia to cancer tissue by introducing and magnetically guiding ferromagnetic particles to the affected area first, and then by applying a microwave field. If I understand correctly, this kind of heating is based neither on eddy currents nor on hysteresis but on causing an oscillating movement of the magnetized particles.

PS I just realized that your particles are rather large. The ones used in medical applications are in the nm range. So, I guess heating by vibration will be weaker resp. your field has to be stronger or the frequency lower. If a stronger field is an option depends on the application, of course.

Fundamentally, this is feasible. you should establish the right frequency and the heating method but this mainly driven by the applications and the scale of your load etc. we have performed some successful trials here at Nottingham, if you provide further details so we can discuss it further.

Yes you can heat iron powder in an AC magnetic field .Of course in case the individual particles where insolated from each other, it would not work very well at low frequencies ; but at high frequencies stuff like that is called carbonly iron and can be a rather effective microwave absorber. But if you take just normal iron filings it depends very much on their state of surface oxidation which has an impact on the highly nonlinear contact resistance. BTW stuff like this was used in the VERY early days of radio engineering (around 1900) as a kind of RF rectifier (early diode) and it was also applied in the very first RADAR (Hülsmeyers "telemobiloscope" 1904; IEEE milestone plaque inaugurated last year in Cologne)) and named "coherer" since those particles tend to stick together (cohere) and require regular gently tapping.

Hi, thanks you all for responding.

I am testing a ceramic tile that contains a mix of iron and copper particles that I based on the following study: https://www.mdpi.com/2076-3417/9/5/970/pdf.

This mix of iron, copper and silica is painted onto a ceramic tile and then fired at 900 degrees Celsius. Then it is placed on an induction hob of 24.4 kHz and a setting of 300W. This however, does not heat the metal particles. As the above mentioned study does nearly the same thing, I do not understand why my version does not work.

Could this be caused by the frequency or the mix of metal that I am using?

Hi Maurice van Bussel ,

please excuse the following question:

If you are using a common domestic hob, did you verify that the iron in your mix is sufficient to trigger the "pot recognition" gadget (which would switch off the coil otherwise)?

If the tile was recognized, the first possible reason for results different from the published ones which comes to mind is: The electronics of some hobs measure voltage at and current through the coil and provide feedback control in order to account for pots with uneven base etc.; other hobs lack feedback control. So with a setting of 300 W and a poor "pot", with feedback control the coil could be operated with parameters providing 2 kW for "good pots", for example, and without feedback control just with standard parameters for 300 W. Unfortunately, this feature is not documented in user's manuals, so one has to rely on detailed test reports or on the schematics if available.

Generally, the main purpose of the iron is to increase the magnetic flux B and hence curl E = d B / d t, while most of the eddy current will flow through the copper particles, provided they are in contact with each other. If possible I would try to measure the electrical resistance of the fired mix, and look what an increased proportion of copper would do.

Hi Joerg Fricke

Thanks for your reaction.

I tested the tile on a domestic and professional induction hob as well as with a laboratory setup with a coil measuring the inductance and capacitance with and without the tile.

The domestic hob was bypassed using a ring of 0.05 mm thick steel foil. The ring of foil did heat up however the iron and copper particles in the glaze that did not touch the steel foil ring did not heat. With the professional induction hob, the pan detection was turned off and the output power was recorded. When placing a tile on the induction hob there was no difference in output power, thus no heat production in the glaze.

The laboratory setup provided similar results. It showed that without the tile above the coil the coil gave a certain value for inductance and capacitance. Placing the tile above the coil did not change these values. The coil and the tile are not electrically linked. The laboratory setup was tested with 100kHz and 200kHz, but with a very low power supply.

Is it possible that for the particles to heat, due to an oscillating movement, the frequency or power should be extremely high (10-100Mhz and more then a 1000W)?

Hi Katrib Juliano ,

As mentioned above, I am testing a ceramic tile with a glaze of 20wt% Iron, 56wt% of Copper and 24wt% of Glaze and additives. With a commercial and domestic induction hob of around 25 kHz and varying output power it does not show any electrical couple. Even with a 100kHz and 200kHz it does not show promising results.

I am wondering about the trials and results at the university of Nottingham. Is there a way that you can share some information regarding your tests?