RF radiation effects on humans
Under optimal conditions electromagnetic microwaves only involve appliances or instruments, like antennas and transmitters. This usually involves low level RF fields that pose no health threat. However under certain circumstances interaction with the human body is inevitable such as in MRI scanners (Magnetic Resonance Imaging) or diathermy. Overexposure to RF radiation can heat tissue and damage it over time when tissue absorbs the energy in the body. In general this heating of tissue is the biggest influence of radio frequency radiation concerning health. The main factors that matter here are the intensity, duration, frequency, distance and shielding to the exposure. In most circumstances this is not a problem, but when there are implants in the tissue (metal plates or pacemakers for example) these can heat up or the electromagnetic field can interfere with its function. Also certain parts of the body have difficulty transmitting heat out of their system making them vulnerable to overheating and sustaining actual damage as a result of it. The reproductive system of men and the lenses of eyes are examples of body parts that are prone to this type of heat damage.
Ranges for effect
For microwave frequency radiation to have an effect on the body it should emit in the 150 MHz to 1 GHz range. In this range heat is absorbed in the deeper parts of the body. At oscillations higher than 10 GHz the heat is mainly concentrated on the outer skin. For comparison, visible light operates in the 400 THz to 800 THz range and this is, as we know from experience, absorbed by the skin. Also the intensity should be regarded. Under 1 mW/cm2 thermal effect and extremely minimal and improbable. 1-10 mW/cm2 is considered medium intensity, it’s a weak effect, but definitely noticeable. For high intensity one should be exposed to RF levels higher than 10 mW/cm2. From this point it’s noticeable that heat is forming in the tissue.
Controlling RF stray radiation
When RF devices are active a lot of electromagnetic radiation will scatter and might end up in places where you don’t want it. Controlling any risks and minimizing stray radiation is an important consideration in setting up any facility that works with RF devices. Shielding is a way of controlling leaking RF and microwave radiation. On the other hand shielding also prevents noise from slipping in and interfering with experiments, procedures and tests.
Shielding can be applied in three ways: reflection, internal reflection and absorption. The latter technique can be accomplished by placing pyramidal polystyrene spikes in the workplace. The varying frequency spectra that can be absorbed range from 30 MHz to 1 GHz with hybrid EMC absorbers and up to 40 GHz with ferrite tiles. Combined with fiberglass epoxy walkway absorbers a complete room can be sealed off to prevent RF radiation from leaking out or entering. DMAS is specialized in producing these various RF and microwave absorbers.