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Electromagnetic Field Strength Testing and EMF Instruments


Wireless Technology

Wireless communication is an integral part of today’s society with nearly 800 million households worldwide using a WiFi network. In fact, at the end of 2013 there were more wireless mobile devices on Earth than people.

Towns and cities are constantly shrouded in a haze of electromagnetic fields and from the 1st July 2016, employers within EU member states will need to conform to the Electromagnetic Fields (EMF) Directive, protecting their workforce from excessive EMF’s.

Electromagnetic Fields (EMF)

Electromagnetic fields (abbreviated EMF’s) are forever present within our environment, although invisible to the human eye. As the name suggests an electromagnetic field comprises a combination of an electric field and a magnetic field. An electric field is present whenever an electrical appliance is plugged into a voltage outlet for example. However, a magnetic field is only created when this appliance is switched on, i.e., when electrical current flows. EMF’s are generated by natural and artificial occurrences:

  • Natural EMF’s are produced by a build up of electric charge in the atmosphere associated with thunderstorms, whereas the Earth's magnetic field causes a compass needle to orient North-South and is used by birds and fish during migration. Every cell in our body has its own EMF, enabling us to function and keep healthy.
  • Artificial EMF’s are produced by overhead power lines which distribute power throughout the country, whereas higher frequency electromagnetic fields are produced by TV antennas and radio/mobile phone masts in order to transmit data. Innumerable household appliances generate EMF; mobile phones, tablet computers, cordless phones, utility ‘smart’ meters, remote control toys, wireless networks, radar and baby monitors to name a few.

EMF Frequencies and Wavelengths

The main characteristic defining an EMF is its frequency and its resultant wavelength. EMF waves always travel at the speed of 186,282 miles per second; the speed of light. Wave frequency simply denotes the amount of oscillations (or cycles per second), while the wavelength signifies the distance between one wave and the next. Wavelength and frequency are directly related; the higher the frequency the shorter the wavelength. It is very important to realise that there are two main forms of electromagnetic fields - extremely low frequency (ELF) and radio frequency (RF). Extremely low frequency electromagnetic field (ELF-EMF) frequencies range from 1Hz to 300 Hz and have wavelengths ranging between 1,000km and 10,000km in free space. Whereas radio frequency electromagnetic field (RF-EMF) frequencies range between 100 kHz and 300 GHz and have wavelengths ranging between 10mm and 3km in free space. Below is a table which exemplifies the different EMF frequencies along with some typical uses for each band:

Frequency Description Examples
Up to 300Hz Extremely Low Frequency (ELF) Brainwaves, electrical mains supply
300Hz – 3kHz Voice Frequency (VF) Switched mode power supplies, inverters
3kHz – 30kHz Very Low Frequency (VLF) CFL (compact fluorescent lamp)
30kHz – 300kHz Low Frequency (LF) AM radio
300kHz – 3MHz Medium Frequency (MF) AM radio
3MHz – 30MHz High Frequency (HF) CB radio
30MHz – 300MHz Very High Frequency (VHF) RC models, FM radio
300MHz – 3GHz Ultra High Frequency (UHF) TV broadcast, mobile phones, WiFi (-b,-g and –n), microwave ovens
3GHz – 30GHz Super High Frequency (SHF) WiFi (-a and –n), CCTV
30GHz – 300GHz Extremely High Frequency (EHF) Military communication, Medical, Police speed radar


Can EMF’s cause harm?

Our bodies are susceptible to damage depending on the energy level of the EMF. The energy within high power radio frequency EMF’s can be changed to heat by our body tissue composition, leading to burns and cell damage (hence why we test microwaves for harmful emissions). Powerful extremely low frequency EMF’s can cause interference within our nervous system, hence why we may experience muscle contractions associated with electric shock. Low power EMF’s are not considered as harmful as higher power EMF’s. Nevertheless, numerous epidemiologic studies and comprehensive reviews of scientific literature have evaluated possible associations between exposure to ELF-EMF’s and risk of cancer in children. Most of the research has focused on leukaemia and brain tumours, the two most common cancers in children. Studies have examined associations of these cancers with living near power lines, with magnetic fields in the home, and with exposure of parents to high levels of magnetic fields in the workplace. Although the effects of exposure are evaluated as ‘possible’, the evidence has nevertheless prompted the creation of the EMF Directive in EU member states. The majority of technologies that contribute to our constant exposure to low power EMF’s are fairly new. As such, associated long term health issues are still to be made fully apparent.

Measuring EMF’s

Fortunately, it is possible to measure EMF’s with a variety of instruments ranging from simple EMF monitors suitable for home and office use to more advanced high frequency RF monitors, suitable for measuring microwave and radio frequencies. Generally, there are two types of instrument available. The first is an ELF-EMF tester which will measure frequencies up to around 300Hz, whereas the second is an RF-EMF tester can measure up to 8GHz, although some instruments will have ranges suitable for measuring both frequency bands. An ELF-EMF meter can be used to measure the magnetic fields associated with ELF frequencies (for example 50Hz mains power supplies) and these meters will generally give a measurement in milligauss (mG ) or microtesla (μT). An RF-EMF meter will measure far higher frequencies associated with radio, GSM, WiFi and microwave oven leakage detection. An RF-EMF monitor will commonly provide an electric field strength measurement in mV/m, or mW/m2, but some meters will also provide a magnetic field strength indication. EMF meters feature either a single axis or a three axis sensor. Because of the nature of a magnetic field, a sensor will only detect the magnetic field correctly if it is aligned parallel to the field of magnetic flux: Although less expensive, a single axis meter features a single sensor. In order to record a maximum reading, the meter will need to be turned slowly within the magnetic field, which is a time-consuming method of measurement.  Should the meter be turned 90° from the maximum reading, it should read nearly zero, proving that the meter has been inserted perpendicular to the magnetic field.   A three axis meter features three sensors aligning at 90° from each other. This allows for a maximum measurement regardless of how it is inserted into an EMF. Although slightly more expensive, three axis EMF meters are far quicker to operate. Test-meter.co.uk supply a range of EMF meters that are suitable for many applications of electromagnetic field measurement. Whether testing ELF-EMF in the home or office, or perhaps testing power lines for electric field strength, we will be able to supply an instrument fit for purpose. Please see below for a comparison of the models that we supply:

Model Frequency Response Axis Magnetic Field Strength Electric Field Strength Other Features
Extech 480823 EMF/ELF Meter 30Hz - 300Hz (ELF-EMF) Single 200mG and 20μTesla ranges - -
Extech 480846 RF/EMF Meter 10MHz -8GHz (RF-EMF) Three - 108V/m, 286.4mA/m, 30.93W/m2, 3.093W/cm2 Record up to 99 results
Metrix VX0003 EMF Tester 10Hz - 3KHz (ELF-EMF) Single - 100V/m and 2,000V/m -
Metrix VX0100 EMF Tester 5Hz - 100KHz (ELF-EMF) Single - 200V/m and 2,000V/m 3kHz filter
Tenmars TM191 Magnetic Field Tester 30Hz - 300Hz (ELF-EMF) Single 200mG, 2000 mG, 20µTesla ranges - Data and max hold
Tenmars TM195 RF Field Strength Tester 50MHz - 3.5GHz (RF-EMF) Three - 20V/m Record up to 200 results
Tenmars TM192 Magnetic Field Meter 30Hz - 2kHz (ELF-EMF) Three 2000mG and 200μTesla ranges - Data and max hold
Tenmars TM190 EMF/ELF and RF Meter 50MHz - 3.5GHz (RF-EMF) Three 2000mG and 200μTesla ranges 2000V/m, 554W/m2 Colour screen, data hold
Tenmars TM196 RF Field Strength Meter 10MHz - 8GHz (RF-EMF) Three - 11V/m2 and 309.3mW/m2 Memory recall and adjustable calibration factor

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