RF safety considerations for LPD 433 devices.
The specs state that in LPD band (433MHz) it operates at a maximum ERP of 10mW. ( http://www.google.gr/url?sa=t&rct=j&...YXPyPw&cad=rja )
This is the main reason I switched from the PMR (500mW) I previously owned, to LPD (10mW).
I was wondering how safe should this LPD be considered, if operating at something like 10cm from the head?
Now, I know cell phones and wifi are much more "dangerous" if you are close and part of that is the much higher frequency, so please do not say "you use a cell phone, why considering about RF safety of LPDs?" Let's focus on these devices alone.
Of course, a comparison to a cell phone (with hands-free) and a DECT phone, would be helpful, as an estimation.
I just wonder how safe these low power LPDs are at just 10mW at 433MHz for adults and babies in close proximity when transmitting and receiving (LO leakage)?
The standard safety level is 10 mW/cm^2, it would be impossible to get your 433 MHZ power to be focussed down to 2cm^2. It would be a easier at 2..4 GHZ.
Frank
That was very helpful Frank, thank you!
This safety level of 10mW/cm^2 is for all frequencies the same? I guess that as the frequency goes down, this maximum level increases.
Do you refer to the 433MHz on this level?
At much lower frequencies, like MF, the spec. changes to 100V/m. I am not sure of the cross over (change) frequency, the spec. was based on the heating effects of the induced power. Interestingly, the Russians used to use 1mW/cm^2, what do they know that we do not? from memory it was reported that they had seen cellular growth disturbed at this power level. This spec was true for UHF TV 421-866 MHZ and higher. It comes into effect when you have small aerials or dishes (low cm^2) and high power which is true for radar and broadcast TV. I wonder if you can then use the RMS power of the radar rather then the peak? as it 1% of peak power rather then 18% in UHF analogue TV.
Frank
So as far as I can figure out from your description, the mostly isotropic antenna (antenna is a coil of wire) of such LPDs transmitting at 10mW is not likely to reach significantly or overcome this limit. Is that right?
I personally would have not worries about using such a thing for hours a day. the power is so little, and the frequency is pretty low, to the dielectric heating would not be so bad.
It is surprizing to think that. Especially, in an era where lots are heard about cell phone and dect cordless phones radiation.
As said part of that, is the very much higher frequency and more power output of these devices.
Do other members have also an oppinion on that issue about these LPDs?
It would be interesting to hear what do you estimate.
With "radiation" is it assumed what is called EM radiation, occurring mainly natural but also manmade.
Wavelengths of interest are from a few times of earth diameter down to short UV(100nm).
"Heard" is poor knowledge. A basic course in radio technology can give better insight.
There exist no serious research result that shows anything else then a heating effect when a EM wave is absorbed in human body or absorbed in anything else.
It is not likely that it will ever come any proof of anything else as it would be just as sensational as saying that there exists effects which not requiring energy to happen, which would violate physical laws.
How EM waves behaves are well-known and follow strictly mathematical laws, with minimum space for personal estimations.
Even if EM-waves are a assumed to be ether or waves with or without a photon mass is practical result the same.
Currently accepted basic energy unit for EM waves is Joule.
One definition for 1J is when an electric current of one Ampere passes through a resistance of one Ohm for one Second.
So far very basic, but to calculate if an EM-wave can be harmful for the easiest affected particle in human body, an electron, do we need two more parameters.
It is Planck constant and Einsteins first relativity theory. Then can we calculate what physical effect that would happen if an EM wave would pass our body.
Extreme cases are also easy to calculate. If 100% of energy of an EM-wave would pass our body, without any absorption, would nothing at all happen inside the body, as no effect can happen without energy.
Opposite, absorption is almost 100% for frequencies above 2 GHz. At 2.5 GHz is typical attenuation through a human torso around 100 dB, which is almost total absorption.
Still, even at very high frequencies can some waves pass through human body.
As example, pointing a strong flashlight inside your hand palm and most of its energy will be absorbed but a small amount of light can visible be seen passing through the hand.
Lower frequencies will pass human body more easily. Reason is same as for any radio-receiver, our biggest antenna, actual body length, is too ineffective due to the length of emitted wavelength.
If any energy should be absorbed, must something act as receiving antenna. If it not exist any antenna, will no physical reaction happen and the EM wave will either pass without any attenuation or be reflected.
For lower frequencies then visible light, such as 2.5 GHz emitted from a microwave oven is it mainly long chains of albumin in skin and flesh that act as antennas. Pure fat have low amount albumin and is less good as antenna.
Often assumed is that it is water in body that act as antenna/absorber but water is a relative poor absorber at 2.5 GHz. A glass of pour water in microwave oven will be heated, but same wave must pass several times, reflecting against walls as only minor amount of energy is absorbed each time.
At lower frequencies then 2.5 GHz, already at 1 GHz can much more of an EM wave pass deeper in human body or even pass through thinner body parts.
At 100 MHz will most of an EM wave pass a human body with minimal absorption.
Instead do human body at these lower frequencies start acting as an electric conductor. As an example, if touching an FM receiver with poor antenna, can reception be improved, as human body then acts as an extender of antenna => conductor, but some absorptions for same freq. can also occur if body is placed between transmitter and receiver.
At frequencies such as AM at a few MHz, is human body an even better conductor but body is then too short to be able to act as an antenna of value. These EM waves will therefore pass a human body with almost no attenuation at all => less heating effect.
If a lossless conductor surface size relative wavelength is big enough will it reflect EM waves, without any absorption.
Whatever frequency, human body is never a effective reflector but at 1THz and upward do it reflect a bit better, and at frequencies for visible light do human skin, very wavelength depending, either reflect or absorb waves.
If reflection or absorption will occur for a particular wavelength is depending on size and structure of molecules in our skin.
As these structures in skin antennas varies in size between different people will some people seems to have different skin color.
What we sees as skin color is a result of amount of wide band of emitted white light that either is reflected or absorbed by skin. A painted wall may look to have a red color, and it is then because all other colors are absorbed by wall, but red is reflected.
High levels of EM waves may cause burning wounds but nothing else from medical view.
What actually happening is that EM waves causes electrons in our body to increase its vibration. This effect is measured as an increased temperature.
Concentrated levels of EM waves radiated from a strong source can be seen as a lot of streamed photons. A single photon can not create changes in a atom in human body such that an electron can be moved from its position, because of amount of energy in the photon that it would require not is possible until at very high frequencies which starts above low UV-light. UV light of higher frequencies can emit photons with such high energy-level that it can move an electron out of its normal position. This kind of radiation of UV-light is a known reason for skin cancer.
If a single photon not can move an electron, does it not change anything from chemical or medical view, except for a minor vibration in electron due to the collision.
If there are a lot of photons bombarding the electron doesn't change anything as it is the individual mass of each photon relative the electron that counts.
It is called the photoelectric effect.
Formula from about.com:
hν = W + E
where
h is Planck's constant
ν is the frequency of the incident photon
W is the work function, which is the minimum energy required to remove an electron from its electron layer.
Assume that you is worried about body heating due absorption of EM energy emitted from surrounding radio transmitters.
The good news is that human body has inbuilt a lot of temperature sensors reacting on minimal temperature changes. Less then 0.1 degree change of internal body temperature is easily detected by these sensors and starts a lot reactions to compensate for that.
If too hot blood, and it will flow nearer skin for better cooling. Increase skin moisture is another trick to increase cooling effect.
If opposite if temperature is too low, will body increase energy burning, reduce blood circulation and concentrate blood to circulate around vital organs. Whiter fingers is a visible sign of this.
Our dominating EM wave source is the sun. Radiates with about 1kW/squaremeter a sunny day. Human body expose about that size when unshaded. Most of that energy is absorbed but for a limited time can human body compensate an still keep same internal temperature.
A typical indoor light source is about 60W resulting in ~1W/squaremeter depending on size and shape of the room.
A cellphone does effect human body less due to its lower frequencies and less power lesvel.
Amount of energy absorbed when a cellphone is transmitting at full power is about one tenth compared to the energy absorbed from the lamp, for a typical talk position.
It assumes then that the phone is held close to body so that at least 50% of its energy is absorbed in human body.
Main radiators of EM waves in a house are typical heating elements and stove. Radiation from these are easy detectable as heat in human cells and radiation levels can be rather high.
We can even detect direction of a such heatsource from long distance by using our heat sensors.
At body local strong radiation sources can for example be a bed-lamp, if placed so close to your head, that you can feel the increased heat when light is on.
Returning to cellphones, main part of its radiation is already inside phone converted to heat due to electric losses. A big amount of loss is due to the background lightning of the screen.
Some phones can become real hot when surfing, and even worse if phone is held near head, and outer part of phone mostly is covered by a hand, as hand then will act as heat isolator, so that there not is any natural way for this heat to be exchanged to surrounding cooler air.
Remaining heat absorber is then the human body that is holding the phone.
Main frequency emitted from phone is infrared wavelength and a minor amount around 1-2 GHz. Peak power in GHz range is 2 Watt but average power is less then 10mW if reception not is too bad.
It is likely that audio amplifier in the phone consumes/emits similar amount of power during a phone-call.
Total can a modern phone emit up to 10W when in heavy use.
Human body need a lot of radiation that it can absorb, it will else die within minutes. If environment is colder then body temperature must heat be created inside body as compensation and protection suh a thick clothes can stop heat leaking from body to the colder environment.
Earth acts both as radiator and absorber keeping temperature (radiation) in a comfortable level even at night. Partly can we compensate living in colder areas by internally in our body increase creation of radiation by eating/burning more food.
Improve our radiation reflectors (clothes) is another alternative to gain some heat.
Keeping an active cellphone near body is another way to keep warmer, even if it is a marginal effect. Human body can receive or emit max around 1kW. It occurs when receiving sunshine or emit that amount of effect due to heavy work during short periods.
In rest is emitted effect around 100W.
Radiation from a cellphone will not make any bigger difference in total sum of radiation sources needed to keep body alive
A cellphone have a frequency range that have less possible photon-energy then visible light.
Human body length and internal structures makes it less effected by lower frequencies. This is bad if our body needs more heat, as we hardly can be heated by sitting near an AM radio station.
If you want to avoid EM-waves, is cellphone adding marginal amount compared to other surrounding sources, but do not use bed-lamp as it is magnitudes more powerful. Avoid any heat-source including earth/sun.
Actually, only way way to avoid radiation from sun, direct or indirect, is to travel real long away in space. Hiding in shadow of a atmosphere-less planet is almost as good. Effective temperature is then just a few degrees above 0K.
Temperature is a way to measure amount of EM radiation. Without EM-radiation is temperature 0K.
Whatever level of radiation/temperature your body need to keep alive, a cellphone will add very marginal amount of radiation.
A cellphone will shorten many lives due to environment impact when produced and recycled.
Not to forget, traffic accidents caused by people that think that they only partial need to concentrate on driving a car, while texting or checking email.
A link about required level of photon energy to kick an electron
Recommended book:Modern physics for scientist and engineers.
A dubious claim because there are "tons" of serious research articles describing specific observations of apparently "non-thermal" biological effects of electromagnetic waves. The interpretation of the experimental results must not necessarily be correct, but we should at least accept that "non-thermal effects" is a big research topic.
Personally, I tend to believe that (rare) reports about hypersensitive people who can "feel" the radiation of mobile phone towers in their neighborhood are no fake. It's imaginable that the pulsed GSM signal is demodulated by cell membranes and the pulse frequency is well in the range of regular nerve impulses.
Fortunately most people like me don't sense GSM signals, except for getting a warm ear during a long mobile phone call. And referring to the original question, I completely agree that effects of low power radio are most likely negligible.
You refer to low power radio in general (independent if it is wifi or gsm/dect), or these LPD 433MHz 10mW devices on question?
Ps. From internet search I see that there are not only thermal effects as E Kafeman well explained (thanks), but other effects, including neural effects on "sensitive" people, biological non-thermal effects and also every-day effects such as accidents caused from cell phone talk and social effects (everyone in front of a mobile phone). Hey, why doesn't anyone refer to this weird (polarized?smooth looking?) light comming out of the LCD screens?
Most researches I have seen concern thermal and biological effects, that is why I focus on these.
I am trying to replace the cell phone as much as I can in everyday life, with these LPD. I know it is not the same, but with hybrid technologies (using internet for long range backbone and LPDs for clients) some things might be possible.
Thermal effects due to RF radiation poses a certain amount of stress on the body due to the thermoregulatory systems attempt to maintain equilibrium. If the thermoregulatory system of the human body cannot cope the temperature will rise and cell death will occur above 41.6oC. Special care needs to be taken for body parts with less blood circulation such as the eyes and the testes.
A thermal effects due to RF radiation are less well understood and there are suggestions that these do occur at levels below the thermal hazard levels. They may not necessarily constitute a health hazard because the effects disappear when the radiation is removed.
It is generally accepted that health problems start to occur if the radiated power absorbed is greater than 4W/kg of the human body weight. Allowing for a safety factor of ten, a specific absorption rate (SAR) of 0.4W/kg is normally used as a limit on the working level. For a person weighing 60kg, the total limit for uniformly absorbed power is 24W. This corresponds to a power flux density (PFD) of 10W/m2 if the person has an effective aperture of 2.5m2. This limit would be applicable at whole body resonance, away from resonance this limit can be relaxed.
Whole Body resonance is fR=114MHz/h ( h is height in meters)
Cell resonance is another matter.
Some researchers are more concerned with the non-ionizing damage.
Like cooking meat, dont' continue using a device if you feel heat. The eyes are the most sensitive and tuning an open lid 100W VHF transmitter will cause blood shot eyes, which will accelerate cataracts.
Even IR heat is caterogenic.
Really, the discussion is endless if we take RF radiation as a whole.
That is why I focused this thread on the 433MHz LPD (10mW ERP) devices and how they could propose a hazard, if operated relatively close to the body.
I put in the conversation the cell phones and the dect and wifi devices, just as a measure of comparison to these LPD devices, nothing more.
So I would like to focus your oppinions aboud these specific devices.
Non thermal effect, is when no energy is absorbed => It will make no difference if the EM wave exist or not from atomic view.
A not so weak longterm thermal effect is ongoing inside our bodies as we are constantly emitting 100 Watt of radiation, or more.
From http://www.who.int/peh-emf/about/Wha...en/index3.html
"Concerns about other so-called non-thermal effects arising from exposure to mobile phone frequencies have also been raised. These include suggestions of subtle effects on cells that could have an effect on cancer development. Effects on electrically excitable tissues that may influence the function of the brain and nervous tissue have also been hypothesized. However, the overall evidence available to date does not suggest that the use of mobile phones has any detrimental effect on human health."
From same source:
In the area of biological effects and medical applications of non-ionizing radiation approximately 25,000 articles have been published over the past 30 years. Despite the feeling of some people that more research needs to be done, scientific knowledge in this area is now more extensive than for most chemicals. Based on a recent in-depth review of the scientific literature, the WHO concluded that current evidence does not confirm the existence of any health consequences from exposure to low level electromagnetic fields.
There was an offer from John Randi (not any longer as he have retired), 1 million dollar to a person that was able to feel the radiation from a cellular phone or PC screen (tube) in a blind test where such equipment was turned on or off or any else paranormal sensitivity. He still have his money.
I think reason that so few did take the chance winning a lot of money, is that most of them know that this kind of problem is just a smaller part of total problem related to these kind of equipment where stress is a big part.
There is also an almost opposite problem today, when people becomes a nervous wreck if they not is able to check email or Facebook every five minutes.
If holding a flashlight against ear for a few minutes and you will feel same amount of heat. Actually, you can do the same with a inactive headphone as the ear in it self is emitting a lot of heat, if the brain need cooling.
From scientific view is there not anything special with these low power devices. It is quite simple, less energy, less effect, if it is related to known physic.
Something more diluted resulting in stronger effect, have I only heard about related to homeopathy pills and that is just cheap snake oil.
Power level for these small transmitters are below what to expect from normal daylight and there is no secret modulation scheme that can interact with your brain as it would require cells able to react to this specific frequency. Interesting if it was possible, as it would make it possible to create biological tissue behaving as fast electric transistors.
Long time ago was it a rumor that it was possible to receive and demodulate AM with aid of amalgam and saliva in a tooth, and several people reported that they did suffer from this.
Assumption was that amalgam surface should act as a nonlinear band gap related to another electric potential in mouth.
No real cases was registered, but technically is it not seen as absolute impossible even if result probably would very weak as it must exist some kind of band-gap between amalgam and another good conductor covered with oxide or rust so it becomes a relative frequency nonlinear circuit.
I think you are right on this. Try it, hold a flashlight nead your ear for prolonged time and you will feel the heat. I think that if you could be able to feel the heat that has as a source the EM waves of the phone, this would be VERY bad and you would really see the effects quite immediatelly or after a few hour.
Yes I am aware of that, as said I put the cell phones in the discussion to get a measure or comparison between these LPDs and the cell phones. To put it the other way, how many times less dangerous should such an LPD considered (estimation)? They are 10mW (ERP) of continuous power output and at a frequency at least two times less than the lowest band of the cell phones.
Or what is the danger compared to? A hair dryer close to the head? A wall switching power supply (althought lower Freq, but pulsed)? A mains line close to your bed in sleeptime? FM broadcast transmitters in your area? Or what?
Just for comparison...
I think this might relate more to the "mind control" signals, some believe to have been used on people. Obviously There is no such modulation scheme here, I do not refer to this case.
I read somewhere that playing high resolution games with your netbook placed in your lap could damage your descendants 100 times more than is doing a mobile phone situated in the same place.
That's a nice tautology, but not what the term "non-thermal effect" usually means. I'm sure you won't describe the process of receiving a weak radio signal by it's thermal effect, although there's surely energy absorbed.
I think is almost self-explanatory that "non-thermal" means an interaction, where the temperature rise is so low (e.g. mK or even μK) that we can safely exclude that possible effects are caused by heating. We could say the same about a sensitive RF receiver.
I don't actually know if non-thermal effects might involve health risks. In my personal dealing with low power RF up to a few W, I'm mostly careless, but I don't impose this rating to other people.
I fear that our generation won't get complete and final knowledge about this problem. In so far it's a matter of precaution to consider the possibility of non-thermal effects in RF emission regulations, as at least some countries do.
Dipping balls in almost boiling water is a very old known way of temporary birth control.
To much dipping and it may be permanent.
What type of equipment that is more dangerous then another from radiation view, I do not know. As all handheld equipment I know about only adds minor to body heating effect relative be indoor, outdoor.
Covering head with a woollen cap will probably affect heating balance more then any cellphone is able to.
personally do I prefer to make longer calls in a phone that not becomes to hot, but many modern phones consumes a lot of power, and thus becomes warm.
My current phone becomes so hot that it not is comfortable to hold it close at ear after 10-15 minutes.
Yes, expression non-thermal is used a bit mis-leading in these circles as a description that better can be described as a non measurable thermal effect.
As thermal effect is the only thing a EM wave create in biological tissue when an photon emits kinetic energy to an electron, what do then remain, if non-thermal? I do not believe in something from nothing.
If EM wave is very weak, it becomes a weak thermal source drowning in many other thermal sources affecting an atom inside a body.
It becomes a hay-straw in a hay-stack and it is corny to trying to identify if that straw is more harmful then other straws.
Compare with neutrinos which are passing through our body in trillions every second. If not hitting an electron will it pass without any attenuation.
However do it sometimes collide with an electron. Do not happen so often, it can be calculated that a collision will occur once every 3000 light-years. If it does, will a it increase electron kinetic temperature with less then a millionth of a degree. Nothing I worry about, but it is also a hay-straw in total hay-stack.
Replacing one single MacDonald meal with a long walk, one single time in your lifetime, will prolong your life more then trying to avoid non-thermal heating effects during your whole life.
I couldn't agree more.
All this rubbish some of us eat, are more dangerous than what we are trying to avoid in this thread. However, it is not bad to be aware of some things. Most act in addition to others, sometimes all these "additions" make the difference in a healthy body or not. Of course it may depend on the strength and defense of each human organism. After all the things one reads on the net, it feels to me and to the young children nearby, more safe to have something that transmits at 10mW on UHF, rather than higher power on microwaves. But I am not expert on the topic of biological effects of RF. I know, the best is not to use it at all, but if it has anegligible effect, why not have the convenience?
Hey, now I got another idea, why not using this old CB band (27MHz) for home comms? The much larger wavelength should propose very little danger, wouldn't it?