Let’s explain several Basic concepts in EMF Measurement: frequency, sampling rate, duty cycle, measuring over time and frequency, exposure load and other topics
Frequency
Electromagnetic radiation sources can be divided into 2 frequency types, low frequency (ELF Magnetic and Electric fields from power line, power transformers) and high frequency (RF from DECT, Mobile phone, microwave). Some meters can measure both types, some can measure only one.
Read more about Electromagnetic Radiation (EMF/EMR) source by frequencies:
https://www.norad4u.com/emf-sources/elf-emf-sources/
https://www.norad4u.com/emf-sources/rf-sources/
Read more about Electromagnetic Radiation (EMF/EMR) measurement: https://www.norad4u.com/monitor
Read more about home use meters: https://www.norad4u.com/measure/home-use-emf-emr-elf-rf-meters-and-detectors/
The house we live in and the EMF sources inside it, RF and ELF
Meters’ sampling rate
When the radiation level is changing rapidly and when most modern RF signals are based on fast/short pulses (like in some digital radiation sources, 3G and 2G mobile phones, WiFi routers, DECT phones and etc.) it is very important (actually a must) to use electromagnetic radiation meters with a high sampling rate(at least 1000/sec). If the sampling rate is low, for example once or twice a second, like in some simple and professional meters, the measurement outcome of will be very low as the meter did not see all the peaks and pulses of the radiation that were active during the full second (as many of these peaks and pulses are few microSeconds, or milliSeconds).
For example, if you try to measure the radiation emitted from a WIFI router with RF meters that measure the radiation once or twice a second, the slow RF meter would probably not be able to even detect the radiation coming out from the router as the router transmit a “I am Hear” bicon signal only 2% of the second (10 transmissions of about 2 mSec each). While the router emits/transmit high peaks of RF radiation at least 10 times a seconds, a slow meter will most likely show 0mW/m2. This is why I usually use electromagnetic radiation meters with the highest possible sampling rate, higher than 1000/sec, most of the time 5000/half a second, as the CORNET ED88TPLUS does).
Average measurements
In some cases, it is the custom to make an average out of the levels of radiation that were measured. It is recommended (but not a must) to make a note of the minimum and maximum values that were measured as well. When only average outcomes are reported it will usually mean that the picture revealed by the report will be very partial and limited since the peaks and high values that were measured in some of the time were averaged by low and even zero values that were measured most of the time. In most cases, I don’t use the average in my measurements. Instead, I try to get a clear and full picture and try to understand what causes high peak levels. When the measurement is changing all the time, I write down the Max, Min and the level the meter showed most of the time.
There are several types of Average in EMF measurement:
All Average – Average of all the sampled levels over a small period of time (in the CORNET ED88TPLUS it is an average of 5000 samples over half a second). This measurement should give you a glimpse of the Duty Cycle of the signal measured.
PEAK Average – Average of only the peaks (each peak out of 5000 samples per 0.5 second) over a longer time lap( in the CORNET ED88TPLUS it is over 15 seconds).
Duty Cycle
Duty Cycle is measured in %. It marks the parentage of the second the signal (RF signal) was present. In case of AM and FM broadcast, the duty cycle is usually 100%. In the case of cellphone towers, the duty cycle is usually between 20%-80% depending on the traffic. In the case of WIFI, DECT, UMTS, and CDMA cell phones, Bluetooth devices and many more modern RF signals, most of the time the duty cycle is lower than 10%. A single with low duty cycle will be noticeable only by a meter with a very high sampling rate.
The ratio between the peak value and the average measured value can give some clue about the duty cycle. A high ratio, for example Peak=1mW/m2 (peak value over 5000 samples over 0.5 a second) and Average=0.001mW/m2 (done over the same 5000 samples) will mean low duty cycle (like WIFI). A low ratio, for example, Peak=1mW/m2 and Average=0.8mW/m2 will mean a high duty cycle(like from a cellular tower).
Regarding the possible biological effect of RF radiation, I think that also low duty cycle signals, like for example WIFI, have the ability to effect and disturber biological systems. These effects can result in health issues. Therefore I don’t take lightly low duty cycle signals. I actually look at law duty cycle signals at the same severity as high duty cycle signals.
Measuring over long periods of time
When the Radiation levels are changing throughout the day there is a need to measure them during all the hours of the day, sometimes for several days. In most cases when this is the need, you have to use electromagnetic radiation meters that have the option to Record/monitor the radiation levels through the day and night and to store all the results in an internal memory or a computer. Then you can review, examine and process the measurement. The most recommended meters for this operation are meters that can be connected to a PC for data acquisition, extraction, real-time and offline analysis and display of all the information gathered during the measurement (like the CORNET ED88TPLUS and the ENV RD10.
If you don’t have a meter with a logger or a PC connection, you can always video record the meter’s display, and later review the recording (on a PC, smartphone or video camera).
When it is not possible to use a logger, you should take the measurements again and again in different hours and days until the radiation pattern over time is understood.
Multi-frequency and multiple sources of measurements
Please note that most of the High-frequency electromagnetic radiation meters that I encountered to date (both professional and simple) are not able to measure multiple frequencies and multiple radiation sources correctly (mobile, WIFI, cellular antennas, cordless phones, etc.). This limitation is due to the difficulty of measuring and summing up all the radiation levels, from all the directions and in all the frequencies. Therefore the measurement of radiation sources that emit RF radiation in several frequencies (eg: WIFI, mobile phone antennas mailman third or cellular) and/or measuring several radiation sources please around you at once, may not be accurate and the results will generally be lower than the radiation levels in reality. It does not mean that all EMF meters are not good. It simply means they are limited and that the outcome is almost always partial. The EMF meters are a good way to “see” the EMF radiation, a tool that exposes radiation sources and to understand how to shield and how to reduce your exposure. The only way to measure multi-frequency and the multi-source environment is by using a very fast spectrum analyzer. The only way of measuring several EMF sources that are around you, with an EMF meter, is to measure each one of them by its own, and then calculate it all together.
Safety standard and exposure levels recommendations
Since the EMF safety standard around the world are very poor and based on the ICNIRP standards which are based only on short term acetic effect and don’t cover any long term biological effect, we can’t trust them to protect us from chronic exposure. What you need to do is to read about the health risk, about standards in countries around the world and decide for yourself to which level are you willing to be exposed to, and to expose your loved ones. In order to make the process easier, we created a page on this site about standards and our recommendations. In general, we always recommend being exposed to as low as possible EMF radiation, to track and find the source of the radiation and to fix the problem.
Press here to read more about safety standard and out recommendations…
Our recommendations
As far as exposure to EMF radiation is concerned, EHS people that are exposed to EMF will feel pain and suffer from symptoms. Therefore EHS people should try to reduce their exposure to the absolute minimum possible. For people who are not EHS (yet) it is recommended to reduce the exposure load as much as possible.
For RF, we consider levels higher than 0.04mW/m2 too high for nonEHS people( for EHS it sho pore pore uld be closed to 0.0005mW/m2).
For ELF Magnetic field, we consider everything higher than 2mG to be problematic.
For ELF Electric Field, we consider everything higher to 10V/m to be a problem.
Assessment of the Exposure Load
Exposure load should be assessed based on several elements, some are measurable and some should be based on knowledge and understanding of the EMF subject and “big picture”. The elements are:
- Number of signals on the frequency span, and number of sources around you
- The level-strength of the signals
- The exposure time
The number of signals could be measured only by using a spectrum analyzer. This equipment is expensive and is rarely used in EMF safety surveys. So usually we will use our knowledge of EMF and RF to guess if there are only a few signals over the frequency, or many (such in the case of exposure to a cellphone tower).
The level of the radiation can be roughly measured (only ” roughly ” because of the multi-source, low duty cycle, and multi-frequency issues, please see above) using EMF meters.
The time of exposure can be easily assessed in most cases, for example, in front of a cell tower, the exposure is 24X7.
Example, a Cell Tower Va a Cell phone measurements
Let’s take for example the exposure of a person to EMF radiation from a mobile phone. The phone can emit several frequencies (RF) while transmitting. In addition, it will emit some levels of ELF. We don’t have control over the number of frequencies emitted, but we should take that into consideration while assessing the exposure load (and while doing the measurement). The radiation level can be partially and roughly measured using an EMF meter, just keep in mind that you are not measuring all of it. The radiation exposure level can be minimized by using the phone in an open environment (not in elevators, trains, cars or indoors) where the reception is better and where the phone will emit less RF radiation. In addition, using the speakerphone function or a wired earpiece will reduce the exposure even more. The time of exposure can be easily assessed and reduced by keeping the conversation short and to the point.
In the case of a mobile phone mast in front of your house, the number of signals can reach hundreds or thousands, in several different frequency bands and we can not control it. The level of the radiation will be seen at first look as not a lot (compared to other sources of RF) but keep in mind that you are not measuring all of it(see above “Multi frequencies” and “Multiple sources”) and that the duty cycle is high. In this case, the radiation exposure level can be controlled by using RF protection measures and choosing the location of where you sleep, work and sitting area where the radiation level is at minimum levels. The exposure time, in this case, is 24 hours (or as much as you stay in front of the mast). We sometimes have partial control over the time we spend near or across the mobile phone mast. In some cases, you can choose to leave the area, in some cases, for example, if you live or work in this area it is less of a possibility.
If in the 2 examples above, a measurement from a simple cellphone, and a cell tower, the meter will show the same number (say 10 mW/m2), it is not the same exposure. In the case of the cell tower, there are more signals over the frequency span. In addition, the exposure from the phone is localized on the area of the body it is most close to, while the exposure from a cell tower is full body. In addition, the Duty cycle of the cell tower is usually much higher than of the cell phone. Therefore we can assume that the cell tower exposure of 10mW/m2 is usually higher than the exposure to 10mW/m2 from a cell phone.
More relevant to RF measurements
Exposure load assessment is more relevant to RF since in RF there are lots of signals and since more RF communication standards are based on “spectrum spread” and “frequency hopping” which means that a single device can generate several, or many, signals. In ELF most of the radiation is on the 50-60Hz.
But in ELF exposure, it can also be possible in case there are several sources around you or in case some of them emits also other frequencies than 50-60Hz.