https://seca.freeforums.net/thread/314/emc-rfi-on-cables
Magnetic shield using Metal shields for reducing radiated magnet field and magnet field susceptibility has been known about for many years and is used in many common place items.
A Magnetic shielded power cable will radiated about 80% less magnetic flux field than an unshielded power cable.
EWA have combine the EMC shield or Faraday cage with magnetic shielding to reduce radiated field and reduce the risk to the cable susceptibility to outside interference over a bigger bandwidth.
And by using a flexible magnetic materials make the cable much more useful than is presently available at the time of writing this document.
Note:- Fe,Ni,Co plastic mix is patented by me for TQ, unfortunately these material when used with plastic like PVC can a do destroy the tool use to draw the cable and make it very brittle and unusable.
EWA however have developed a complex compound not using these Metals to produce a magnetic plastic mix. But this also put considerable wear on the tools needed to draw the cable, so with a costly tool we have achieved what I wanted to do with TQ but with the added advantage of controlling the maximum flux density.
Fig 1:01 Below shows the magnetic fields concentrically around the conductor.
Consider a current in a straight wire of infinite length.
The magnetic field lines are concentric circles in a planes perpendicular to the wire.
The magnitude of the magnetic field at distance R from the centre of the wire is:-
B =
The magnetic field strength is proportional to the current and inversely proportional to the distance from the centre of the conductor.
The magnetic field vector in tangential to the circular magnetic field lines and directed according to Fleming’s Right Hand Rule.
Faraday shielding as shown above will only work with radiated field and not magnetic shielding.
To calculate the size of the faraday shield material the material used could be copper, tin plated copper silver, silver plated copper or any good conductor.
Thus choice of the material depends on the whole environment conditions as with the insulation materials.
As can be seen the shield is woven braided conductor.
Coverage should not be lower than 85%, the angle of the braid should be 20° to 40° for a diameter of 15.2mm and up to and beyond 40°for diameter above 15.2mm.
Percentage coverage K can be calculated from the following
K= (2F-F2)*100
F=NPd/Sin a
A = Tan-1(2?(D+2d)P/C)
F= fill space, K=Percentage cover,N=Number of wires per carrier.P=pick/inch, d=dia of braid wire,a= angle of braid,D= dia of cable under shield, C=number of carriers.
Shield effectiveness is expressed in dB for a single shield of copper it is about 40dB at 85% coverage. And is about 45dB for 90% but using two layer of shield we can get as high as 60dB. And with the EWA interconnect cables we do this.
With variable currents this can change constantly causing micro-phonic noise and induced current absorption and distortion of the signal. The other problem here as a signal cable within a Faraday shielded cable this will cause fluctuations in capacitance with the movement of the conductor relative to the shield and thus change the impedance of the cable and it frequency bandwidth produce time relative distortion linked to amplitude of that signal AM and FM modulation and phase angle errors.
This signal “Wire Modulation” can be caused by internal and external sources. With a magnetic shield the effect is reduced with added bonuses.
But using current designs of material in common use the cable is non flexible and fixed and very costly and making it not possible to be used in all applicable applications.
Here is one construction solution to this problem below.
As can be seen from the above diagram the magnet field is held close and within the magnetic material, thus reduces internal and external influence of the magnetic field increase the information accuracy.
Simulation of this effect on signal are shown below.
Now the same simulation was also done on a magnetic shielded cable.
Due to the increased coupling the inductor value also increase.
As can be seen the amplitude and phase now follow the input much closer.
This combination performs as common mode choke and RFI,EMC and magnetic field shield.
This also could be used with paired cable in applications such as loud speaker cables.
This will reduce magnetic radiation and interference to other electronic or electrical installations.
The magnetic coupling also helps the signal with common mode rejection to the source and load.
On Keyboards reduce the detection of passwords, secure information etc.
On USB cables to eliminate the coupling and stealing of data from the USB cable normal radiation from RFI.
The reduction of RFI from the power cables to computer systems.
Ethernet cables, Screen data cables i.e. HDMI etc
With the Shield coil deactivated the signal within the magnetic shield will have a limited protection, but by energizing the coil with DC or AC will increase the magnetic flux in 90° to the induced magnetic field induced by the signal. This will restrict the possible detection of the signal due to radiation EMC, RFI.
With the Coil Shield on stray magnetic field will be absorbed.
Effective area of magnet path Ae= (Σƒ/A)/( Σƒ/A²)
A= area will depend on the length of the magnetic shield and the diameter and the wall thickness.
The permeability will depend on the concentration of the magnet dust or particles in both planes at 90° to each along the length and around the toridal.
µ= (1/µ0)x(B/H) so the inductance factor will give L= µ · c ·N² · 10⁻⁹
In most case the turns will only be 1
Al = L/N² in nH
But must be considered an open ended rod of magnetic material.
The magnetic saturation must also be considered this will be controlled by the coil, turns and current in the coil as Amp/Turns and the length.
Oscilloscope/Spectrum Analyzer Vellerman PCSGU250
EWA Balance Amplifier, Z = 100, G= 100, BW DC – 15MHz
EWA Rotating Magnet.
Set Up
The Unit under test was first tested to see the effects of the rotating magnetic field over the inner conductor. One end was plugged into the non inverting input and the other into the inverting input with the Faraday shield connected to ground.
The first test was using the standard cable.
The next test was with the flexible magnetic shielding.
The next test was to see the effects on the spectrum of noise/interference.
Again the first test was using standard Competition cable.
Comparing this result with the cable covered with flexible magnetic shielding.
The next test is to ground the inverting input of the Balance amp and short circuit one end of the cables under test. This will show the common mode effect of the flexible magnetic shield.
First the Competition standard cable.
Next the Flexible magnetic shielded cable.
The test is now done to show the spectrum on interference.
First the standard cable.
And then the magnetic shielded cable.
As the magnet field rotational frequencies increase the better the reduction in interference.
More tests are being done again on our cable with 25%, 50%, and 80% mix and not as above with just 10%.
I will post these results in later date.
18/6/2021
To get you started here is the TQ UB spec.
Cable Specification
Resistance/Metre/Pair 18mΩ
Inductance/Metre/Pair (common mode) 25nH
Capacitance/Metre Between Pairs 2nF
Capacitance/Metre Between Conducting Pairs 4pF
Maximum Continues Current 11Amps
Breakdown Voltage/Metre Between Pairs >2500VAC
Breakdown Voltage/Metre Between Conducting Pairs >5000VAC
Maximum Working Temperature 150°C
Recommended Frequency Range (DC) 10Hz – 250KHz
Recommended Maximum Power Amp Load @ 8Ω 450WRMS
Recommended Maximum Power Amp Load @ 4Ω 950WRMS
Lose in Cable @ 11Amps/Metre 2.7Wmax
Cable Width max 13mm
Cable Thickness max 1.7mm
Conductors are Litz Inductively matched to length each pair.
At 60 Hz, the skin depth of a copper wire is about 8 mm. At 60 kHz, the skin depth of copper is about 0.254 mm. At 6 MHz, the skin depth is about 25.4 µm. Round conductors larger than a few skin depths don't conduct much current near their axis, so that material isn't used effectively. This causes a lose in detail and due to differences in Power/Frequency can cause phase changes producing error in depth of sound. Ordinary twisted conductor do not act like Litz as they conduct on there un-insulated surface to produce a solid conduct, only allowing the possibility to conduct more current as size increases, thus giving a larger diameter and solving the problem with brute force not science or thought. And large diameter wire increases the cost of raw materials and the wastes of money.
Please also note as the diameter increases and the gap stay relatively small the capacitance also is increasing reducing the bandwidth and having the opposite response to your need, not counting the fact of the wasted power to charge and discharge this capacitor as the amplifier swing its output voltage following the audio, this often cause another undesirable effect the amplifier become unstable and burnout in the worst case scenario.
- Without scribbles download from above.
Electromagnetic shielding is common place and is used in signal and power cables. And will help to reduce EMC and RFI and is normally only useful from about 100KHz and above. It has little or no effect on magnetic interference as produced by electro mechanical devices such as motors, electromechanical transducers and transformers devices.Magnetic shield using Metal shields for reducing radiated magnet field and magnet field susceptibility has been known about for many years and is used in many common place items.
A Magnetic shielded power cable will radiated about 80% less magnetic flux field than an unshielded power cable.
EWA have combine the EMC shield or Faraday cage with magnetic shielding to reduce radiated field and reduce the risk to the cable susceptibility to outside interference over a bigger bandwidth.
And by using a flexible magnetic materials make the cable much more useful than is presently available at the time of writing this document.
Note:- Fe,Ni,Co plastic mix is patented by me for TQ, unfortunately these material when used with plastic like PVC can a do destroy the tool use to draw the cable and make it very brittle and unusable.
EWA however have developed a complex compound not using these Metals to produce a magnetic plastic mix. But this also put considerable wear on the tools needed to draw the cable, so with a costly tool we have achieved what I wanted to do with TQ but with the added advantage of controlling the maximum flux density.
Fig 1:01 Below shows the magnetic fields concentrically around the conductor.
Consider a current in a straight wire of infinite length.
The magnetic field lines are concentric circles in a planes perpendicular to the wire.
The magnitude of the magnetic field at distance R from the centre of the wire is:-
B =
The magnetic field strength is proportional to the current and inversely proportional to the distance from the centre of the conductor.
The magnetic field vector in tangential to the circular magnetic field lines and directed according to Fleming’s Right Hand Rule.
Faraday shielding as shown above will only work with radiated field and not magnetic shielding.
To calculate the size of the faraday shield material the material used could be copper, tin plated copper silver, silver plated copper or any good conductor.
Thus choice of the material depends on the whole environment conditions as with the insulation materials.
As can be seen the shield is woven braided conductor.
Coverage should not be lower than 85%, the angle of the braid should be 20° to 40° for a diameter of 15.2mm and up to and beyond 40°for diameter above 15.2mm.
Percentage coverage K can be calculated from the following
K= (2F-F2)*100
F=NPd/Sin a
A = Tan-1(2?(D+2d)P/C)
F= fill space, K=Percentage cover,N=Number of wires per carrier.P=pick/inch, d=dia of braid wire,a= angle of braid,D= dia of cable under shield, C=number of carriers.
Shield effectiveness is expressed in dB for a single shield of copper it is about 40dB at 85% coverage. And is about 45dB for 90% but using two layer of shield we can get as high as 60dB. And with the EWA interconnect cables we do this.
Magnetic Shielding
As can be seen from the above currents in two wires can attract or repel dependant on the direction of current flow with respect of each other.
With variable currents this can change constantly causing micro-phonic noise and induced current absorption and distortion of the signal. The other problem here as a signal cable within a Faraday shielded cable this will cause fluctuations in capacitance with the movement of the conductor relative to the shield and thus change the impedance of the cable and it frequency bandwidth produce time relative distortion linked to amplitude of that signal AM and FM modulation and phase angle errors.
This signal “Wire Modulation” can be caused by internal and external sources. With a magnetic shield the effect is reduced with added bonuses.
But using current designs of material in common use the cable is non flexible and fixed and very costly and making it not possible to be used in all applicable applications.
Solution to Magnetic Shielding
By using a flexible material heavily loaded with magnetic dust or particles, we have reduced the effects of radiated and absorption of magnetic interference on signal and power cables.Here is one construction solution to this problem below.
As can be seen from the above diagram the magnet field is held close and within the magnetic material, thus reduces internal and external influence of the magnetic field increase the information accuracy.
Simulation of this effect on signal are shown below.
A one metre length of cable is shown above, the Magnetic coupling without magnetic shielding and a coupling factor to illustrate this.
This is a 20KHz sin wave the green trace is the input and the blue is the output.Now the same simulation was also done on a magnetic shielded cable.
Due to the increased coupling the inductor value also increase.
The outer insulation (red), filler insulation (blue), Faraday shield (light blue), filler insulation (blue), Magnetic flexible shield (red), filler mixed (blue) with three conductors (labelled) .This combination performs as common mode choke and RFI,EMC and magnetic field shield.
This also could be used with paired cable in applications such as loud speaker cables.
This will reduce magnetic radiation and interference to other electronic or electrical installations.
The magnetic coupling also helps the signal with common mode rejection to the source and load.
Flexible Magnetics and Digital
Flexible Magnetic Shielded Cables in the Use with secured computer data transfer.On Keyboards reduce the detection of passwords, secure information etc.
On USB cables to eliminate the coupling and stealing of data from the USB cable normal radiation from RFI.
The reduction of RFI from the power cables to computer systems.
Ethernet cables, Screen data cables i.e. HDMI etc
Forced Shielding
With the Shield coil deactivated the signal within the magnetic shield will have a limited protection, but by energizing the coil with DC or AC will increase the magnetic flux in 90° to the induced magnetic field induced by the signal. This will restrict the possible detection of the signal due to radiation EMC, RFI.
With the Coil Shield on stray magnetic field will be absorbed.
Cross section of flexible magnetic cable magnet sheild.
Effective area of magnet path Ae= (Σƒ/A)/( Σƒ/A²)
A= area will depend on the length of the magnetic shield and the diameter and the wall thickness.
The permeability will depend on the concentration of the magnet dust or particles in both planes at 90° to each along the length and around the toridal.
µ= (1/µ0)x(B/H) so the inductance factor will give L= µ · c ·N² · 10⁻⁹
In most case the turns will only be 1
Al = L/N² in nH
With Active Magnetic Shield
The magnetic length will depend on the concentration of the magnet dust or particles and the length of the flexible magnetic material and it permeability µ.But must be considered an open ended rod of magnetic material.
The magnetic saturation must also be considered this will be controlled by the coil, turns and current in the coil as Amp/Turns and the length.
Test Results Using A Now Standard Cable and Shielded EWA Cable
The test equipment used:-Oscilloscope/Spectrum Analyzer Vellerman PCSGU250
EWA Balance Amplifier, Z = 100, G= 100, BW DC – 15MHz
EWA Rotating Magnet.
Set Up
The Unit under test was first tested to see the effects of the rotating magnetic field over the inner conductor. One end was plugged into the non inverting input and the other into the inverting input with the Faraday shield connected to ground.
With a distance set for all test at 100mm from the centre of the rotating magnet.The first test was using the standard cable.
Has can be seen the signal detected was 0.79mV RMS.The next test was with the flexible magnetic shielding.
Has can be seen the signal detected was 0.44mV RMS a reduction of 3dB with a 4.05Hz north south rotation the reduction could not be achieved using Faraday shielding alone.The next test was to see the effects on the spectrum of noise/interference.
Again the first test was using standard Competition cable.
Note the 19.23Hz FundamentalComparing this result with the cable covered with flexible magnetic shielding.
We see that the Fundamental is reduced 6db and the harmonic and the floor background levels are all reduced.The next test is to ground the inverting input of the Balance amp and short circuit one end of the cables under test. This will show the common mode effect of the flexible magnetic shield.
First the Competition standard cable.
Note the signal is now 9.64mV RMSNext the Flexible magnetic shielded cable.
As can be clearly seen the voltage is now reduced to 3.46mV RMS nearly 10dB.The test is now done to show the spectrum on interference.
First the standard cable.
Again the back ground noise is reduced and the high harmonics.As the magnet field rotational frequencies increase the better the reduction in interference.
More tests are being done again on our cable with 25%, 50%, and 80% mix and not as above with just 10%.
I will post these results in later date.
18/6/2021
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