Extremely Low Frequency (ELF) emissions from power lines have been associated with childhood leukemia. The International Commission fon Non-Ionizing Radiation Protection (ICNIRP
) says “Epidemiological studies on non-ionizing radiation in the low frequency range (50/60 Hz) have consistently shown an increased leukemia risk from magnetic field strengths above 0.3 -0.4 µT.”. Magnetic fields are also measured in units of Gauss. 0.3-0.4 microTesla is equivalent to 3-4 milliGauss (mG).I have a 12 kilovolt (kV) distribution line running along my street about 80 feet from my house. The same power poles also carry 120 V lines.I bought an AlphaLabs TriField 100XE Gauss meter
to measure magnetic field levels in my house. Measurements varied between 3 and 6 mG!
I switched the power off to the house at the main circuit breaker. The readings did not change. With the Gauss meter turned on, walking towards the street, the reading steadily increased and were off the scale (> 100 mG) at the street!The utility company performed measurements inside my house with an EMDEX II
instrument and they varied from 0.5 to 0.8 mG.The Swedish TCO
society has recommended an ELF emission limit of 2-2.5 mG for computer monitors. Computer monitor manufacturers have complied with this limit for over 20 years. The 2.5 mG limit is specified to be measured at a distance from the monitor where the user’s head would be located. The rest of the body would be subject to a lot less emission due to the field falling off as the square of the distance. The limit is also for an adult office worker working 8 hour days, 5 days a week.For children subject to full body power line ELF emission in their home, almost 24/7, the equivalent safety limit would be significantly lower.Like mercury and tobacco smoke, I suspect the only safe level of exposure to ELF emission is zero. So here I describe my experience trying to reduce the ELF field level also known as Electro-Magnetic Fields (EMF) in general, using ELF/EMF cancellation techniques.Measurements
Researching a bit into the discrepancy between the utility company’s instrument and mine , I discovered that the magnetic field in my house was not just at 60Hz – the standard US power line frequency – but also had strong harmonics at 180, 300, 540 and 900 Hz. My AlphaLabs meter reports the total power of all the frequencies from 40Hz – 100 kHz. In other words, it reports the total of the 60, 180, 300, 540 and 900 Hz magnetic fields. However, being an inexpensive instrument, its sensitivity varies with frequency. It is designed to measure only 60Hz fields accurately. For the same strength of 60 and 540 Hz fields, it will report almost 10 times the value for 540Hz than it does for 60Hz. So the readings from this instrument have to be post processed and adjusted in the presence of harmonics. The EMDEX II being a more expensive instrument presumably does not have this drawback and reports the correct value in the presence of harmonics.
As for measuring the harmonics, I used a loop of wire (3ft x 6ft) and connected it to the microphone input of my laptop running Ubuntu. I used jaaa to view the spectrum. It displays the strength of the harmonics at 180, 300, 540 and 900 Hz below.
With cancellation enabled for 180 and 300 Hz jaaa shows the change below.
An analysis using a 3D field solver (LC) showed me that the magnetic field lines 80 feet from the distribution line were almost vertically oriented. So the loop of wire must be oriented horizontally to get the strongest signal from the magnetic field. I used these measurements to perform the adjustments on readings from the AlphaLabs instrument.
A loop of wire carrying a varying electric current produces a varying magnetic field. The wires of the power distribution lines form a loop resulting in magnetic fields that extend more than a 100 ft from the power line. In theory, one can place another loop (call it the cancelling loop) of wire also carrying varying current that can produce a magnetic field of exactly the opposite polarity and cancel the magnetic field inside the cancelling loop. So in theory, if we run a loop of wire around a house and apply the proper varying current through it, the magnetic field inside the house can be cancelled. In practice, complete cancellation can be rarely achieved. In my instance I estimate a cancellation of about 0-25% depending on the area of the house. Higher cancellation is possible, with nearly complete cancellation of some frequencies. However, the field strength near the cancellation wire is too high and becomes counter productive.
The information at this site is provided in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
WARNING: An implementation of the ELF/EMF cancellation system can result in HIGHER magnetic field levels in areas close to the loop of wire used for cancellation.
Care must be taken to ensure that such areas of higher magnetic field are rarely used. Since any system can fail, the EMF cancellation system will also need monitoring to ensure that it is functioning as intended. Improper use or operation can result in MORE DANGER than the original ELF/EMF field.
A laptop or desktop computer with a dual core CPU, audio input and output jacks.
A Linux operating system, preferably Ubuntu. Windows and Mac may also be usable.
Open source audio signal processing software, jack, jack-rack, LADSPA plugins and qjackctl.
An audio amplifier. I used the Logitech z313.
A step down transformer 110VAC to 4.5VAC or similar with the smallest current rating and a 220K ohm resistor.
A few hundred feet of 26 AWG insulated wire (for the cancelling loop).
Some 3.5mm audio jacks to connect the cancelling loop wire and the amplifier to the computer.
The total cost of above components is likely to be less than $600.
High level view of system
Wall outlet -> Transformer -> Computer Mic Input.
Computer audio signal processing.
Computer Headphone output -> Amplifier -> Cancelling loop wire.
For cancellation to work, the cancelling signal should have the exact same frequency and amplitude but opposite phase as the offending signal we are trying to cancel. In practice, the offending signal may have multiple frequencies.
To obtain the exact same frequency, the power line (wall outlet) itself is used as the source. A step down transformer is used to get 4.5V AC from 110V AC. This is fed through a 220K ohm resistor into the microphone input of the computer. The signal level is such that the input amplifier is operating in the non-linear region and results in the signal being clipped. The result is that it creates all the harmonics of the fundamental 60Hz input signal. Audio software filters can be used to pick just one of the frequencies as needed.
In my case the main offending signals were 180, 300 and 540 Hz.
A jack-rack configuration was created for each frequency. In each configuration, an amplifier was used to control amplitude (the Amps gain (dB) slider shown below). An L/C/R delay line was used to control phase (the L delay (ms) slider). Each configuration used a high and a low pass filter to pick the appropriate frequency out of the all the harmonics.
The amplitude and delay values have to be finely tuned manually, while monitoring the jaaa or Gauss meter reading to get optimal cancellation.
Jack-rack configuration for 180 Hz is shown below.
The Jack connection kit was configured to combine the three jack-rack outputs onto the computer’s audio output.
The figure below shows the connections for two frequencies.
Jack set up was as below.
This computer audio output is amplified using an external stereo amplifier to drive the cancelling loop. As I did not want the audio output to play over the sub woofer of the z313 stereo amplifier, I cut the wire driving the sub woofer.
Even though the z313 has 15 and 5W outputs, only the 5W output was needed for my application. A larger house or building may need more drive power.
Cancelling loop placement
Ideally, the cancelling loop would go around the house, 5 ft from the walls and be located ~11 ft above the ground. This will ensure that people are always 5 ft from the wire and avoid the strong field near the cancelling loop wire. In practice, the wire may have to be placed partly inside the house. In that case, it may be best to route the wire along the line where the ceiling meets the wall, on the uppermost floor of the house.
With the ideal cancelling loop, the cancelling signal can be as strong as needed to cancel the field inside the house optimally. In practice, the strength of the signal needs to be adjusted to balance the cancellation and exposure to fields from the cancelling loop itself. When ideal placement is not possible, one may want to prioritize areas of the house where people spend more time. So cancelling wire placement can be chosen to provide maximum cancellation in living rooms and bedrooms.
Since each house is different, it is difficult to specify an optimal placement for the cancelling loop. Some trial and error may be involved.