Calculating GSM Wavelength in Salt Water

Specific gravity plays no direct role.

The velocity of propagation in seawater is about 1/9 that of free space, so your number should be 33.3cm/9 or about 3.7cm.

You might find this pdf article useful:

On a sunny day (Sun, 12 Oct 2014 22:23:10 +1100) it happened Robert Wade wrote in :

Personally I would no expect 900 MHz RF to work in (conductive) seawater. But I have not tried my cellphone underwater yest for other reasons :-).

depending on saltiness the skindepth into sea water is in the range of

60 mils to 0.2 inches

However, the 'mechanical' energy of launching 900 MHz...you'd get a lot of attenuation compared to 1-10MHz used in ultrasonic scans.

electrical wavelength in free space is around 33.3cm

conductivity of sewater is somewhere beteen 10-100S/m 40? which places the skin depth at around 3 cm, which is so lossy, the term 'wavelength' no longer has much meaning.

However if you're looking at the mechanical energy, do a search in ultrasonice basice, they use 1-10MHz You'll get a lot of attenuation at

900MHz, but not so much attenuation that the meaning of wavelength is still there. From memory, resolution at 2MHz is around 50mils?, or 0.1 to 0.2 inches ?? so 450 times better is a lot better! But do that search, it will show you how the wavelength of mechanical energy is calculated. relates to elasticity and mass/volume is that specific gravity?

plus everything I've seen is related to sqrt() of something else in this stuff.

apologies for vagueness, but been a while, and haven't looked at this stuff in a loooong time.

Bad question. The wavelength (or frequency) of the RF signal does not change when you submerge the cell phone under water. If it did, your cell phone would change frequency/channel/wavelength when submerged and would not be able to communicate.

What does happen is that the velocity of propagation is slowed down by the dielectric properties of the medium (water). This causes delays in transmission lines to increase and antenna lengths to shorten. Free space wavelength (as measured in a vacuum) shortens to become electrical wavelength (as measured in your salt water medium).

Velocity_Factor = 1 / e^-0.5 VF is expressed as a percentage of the speed-o-light. e = dielectric constant or relative permittivity.

The dielectric constant of water varies with temperature and frequency. At 1 GHz and 25C, my guess(tm) is about 60.

VF = 1 / 60^-0.5 = 0.13 Electrical_wavelength = Free_space_wavelength * VF Electrical_wavelength = 33.3 cm * 0.13 = 4.3 cm

Google for "electromagnetic aquametry" or "microwave aquametry" if you want to dig deeper.

Also, GSM, the cellular modulation protocol, has no effect on the velocity of propagation or wavelength and does not change in any manner by immersion in salt water.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

Thank you for your concise explanation.

If I understand correctly then, a structure measuring 4.3cm within a water-filled vessel would be resonated by a 900MHz signal.

What would happen if the vessel itself was a 4.3cm diameter sphere?

The dielectric constant of sea water is around 80. In my OP I confused this with specific gravity, and the 1.4 figure was incorrect anyway. It should be around 1.02.

Robert Wade

Correct. However, the losses created by the very lossy water dielectric would result in a resonator Q that is so low as to be useless. In effect, all the energy in the resonant structure would end up being dissipated by the water. This is one reason why underwater RF communications has such limited range and really only works at very low frequencies (used for submarine communications).

The same thing. The "vessel", which I assume means either a boat or bottle is in itself a structure, which can be resonant. Please note that 33.3 cm would be a full wave resonant cavity, which is not particularly useful. Multiples of 1/4 wavelength tend to be more common.

It would be helpful if you would kindly disclose what you are trying to accomplish, and what you have to work with. Your questions are far too simplistic to supply a specific answer.

The difference in dielectric constant between fresh water and sea water isn't that different. Sea water is about 81, while fresh is about 80. Both vary with temperature and frequency, although not exactly at the same rate. What is radically different is the conductivity. Sea water is about 5 Siemens/meter, while fresh water is about 0.001 S/m. Also see the loss tangent and dissipation factor (and note the frequency at which they're specified).

A resonant cavity is build very much like a coax cable. One of the demonstrations I give at the local radio club meetings is what happens when you fill a length of coaxial cable with water. I cheat a little and clean out the inside of a length of Heliax (all copper) before the test. I then fill it with distilled water. The impedance goes down to about 30 ohms(?), but with proper matching, the loss is about the same as it would be with an air filled length of Heliax. I then drop a "pinch" of salt into the coax cable. The losses climb dramatically. Given enough power, I could probably boil the salt water.

The same thing will happen to your cavity. In fresh or distilled water, the system is a good low loss dielectric and will work just like a cavity resonator, but resonate at a lower frequency. With polluted or salt water, the dielectric will start to dissipate energy and render your resonator rather useless.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

Thanks for the tutorial AND the URLs!

closer to 33.2cm

the specifiy gravity of sea water is about 1.04, but you want the refractive index. which is the square root of the dielectric constant,

probably something like that.

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umop apisdn

Thank you. I will save your replies for future reference.

Just wondering. My Dad expresses concerns about holding a cell phone next to his head. Does the same resonant wavelength principle you described apply to human brain tissue as well? He can't afford to loose any more ;-)

Robert Wade

Now I am a little confused. How does this relate to what Jeff is saying?

Is the wavelength then actually 23.8cm as I originally posted, based upon a refractive index of salt water of 1.4.

Sorry, I confused this with specific gravity in my OP. Possibly leading some people astray.

So what is the _dominant_ determining factor of resonant wavelength for a 900MHz signal when passing through a container of salt water ... dielectric constant, conductivity or refractive index?

Robert Wade

How loose are his brains?

--
Anyone wanting to run for any political office in the US should have to 
have a DD214, and a honorable discharge.

Here's my take on cell phone RF causing brain and CNS cancers.

A better graph: Looks like I need to update the graph. Maybe later. If you want to grind your own graphs, start here:

Note that the incidence rate of new cases of brain and CNS cancers is nearly flat over the 1975 to 2011 range of the data. During this time, cell phone usage increased dramatically starting in about 1995. If there was any causal connection between cell phone use and brain cancer, it would have appeared as a rise in the incidence rate. Instead, it has gone down slightly (caused by improved early diagnostics using positron emission tomography).

Also note that the rubbish about growing young minds being more susceptible to RF isn't true: Most of the new brain cancer cases appear among seniors. Cell phone use by seniors is far less than that of teenagers. Again, if there was a causal relationship, I would expect to see far more cases among the younger, high cell phone use, populations. The bad news is that as a senior, your fathers risk of getting cancer increases with age, which requires no alleged assistance from cell phones.

I hope this helps.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

Yes.

...Dielectric constant can be expressed in complex form, where the imaginary part represents loss (conductivity).

Ideally -- actually, not even ideally, but by definition from theory: n ~= sqrt(e_r). BUT, this is e_r at a given frequency, and in general it varies, even for well behaved materials.

Probably the best behaved examples are materials like polyethylene and teflon, which are simple chemically, and low loss. But even these exhibit atomic and molecular resonances in the IR band.

Water contains anything from rotational resonance in the GHz (I think it's

36GHz, for vapor; of course, it's not going to be exactly the same in liquid form, but still something), to rotational and translational resonances between THz and near IR. Throughout the range, the dielectric constant is changing, from ~80 near DC, to, I think it drops off in the 10s of kHz or maybe it's MHz, due to molecular diffusion phenomena. All the while being somewhat conductive, or if doped with ions, fairly conductive. Which will act to increase |e_r|, but also significantly decrease the transmission length characteristic.

So, figuring out what's going on at any arbitrary frequency isn't very obvious (one of those wonderfully enigmatic aspects of water's physics and chemistry). You might measure it yourself, or find data from someone else who did...

(And by the way, if you consider the complex permittivity of metals, you'll end up with a tranmission length or depth that's oddly similar to the skin depth of that material. Not at all a coincidence, of course!)

Tim

--
Seven Transistor Labs 
Electrical Engineering Consultation 
Website: http://seventransistorlabs.com

As with all "science" the outcome depends partly on who funds the studies and what methodology is used. There is evidence on both sides, which only encourages selective reporting depending on which side of the debate you want to support.

Everyone asserts the other side's research is "flawed". There is also alot of outdated industry propaganda floating around. Like reps who claim there is no evidence of biological effects.

One might ask why manufacturers now advise in their literature to hold the cell phone a few cm's away from the head. Better reception?

The best we can say is that the extent of the problem or the precise mechanisms involved are not well enough understood.

Excerpt from the linked article:

People who started using mobiles as teenagers, and have done so for at least 10 years, were 4.9 times more likely to develop astrocytoma, compared to controls.

Worringly, the comparable figure for cordless home phones - which are very similar to mobiles in terms of radiation emission - was almost as high, at 3.9.

Looking at the whole group, regardless of age of first ise of mobile or cordless phone, they found that usage for more than 10 years increased the risk of all malignant tumours by 30 per cent, and astrocytomas in particular by 40 per cent.

Robert Wade

I did some sonobouy. They use a 6db/octave boost, but I have no idea if that was to compensate the sea water or the hydrophone.

Everyone lies, but that's ok because nobody pays attention.

If a brain cancer victim arrives with their attorney and claims that the cell phone manufacturer is responsible for their brain cancer because they failed to provide suitable warnings, the manufacturer can claim that the user failed to follow the recommendations in the manual.

You can say that about literally any technology, science, disease, or phenomenon. Complete understanding is almost impossible and research continues. Just look at all the areas of research that have not been fully beaten to death. Here's a partial list:

Sure. Presumably before ubiquitous cell phones, people didn't get brain cancer. The big rise in cell phone use started in the early

1990's. Please show me where that increase appears in the statistics: 4.9 times the pre-cell phone rate of about 7.0 cases per 100,000, would be about 35 cases per 100,000. Show me that increase in the general population here:

The typical cordless phone handset transmits at about a 5 milliwatt average power level. The typical cell phone can run up to about 250 milliwatts, but usually operates at a much lower level in strong signal areas to conserve battery power. I'm not 100.0% certain of these numbers and can dig out more accurate numbers if you want.

That probably correct if you don't consider the age of the cell phone user. See graph at: and notice the drastic increase in incidence with increasing age. For example, if I selected a population of 40 to 50 year olds, which have a brain cancer incidence rate of 6.0 per 100,000, and compared it with a group of 50 to 60 year olds, 10 years later, then the incidence rate would increase to 11.0 per 100,000 or almost double the initial rate. What interesting is that it will almost double even if there is no cell phone exposure involved. I'm surprised that they only were able to show an increase of 30-40%. By carefully cherry picking the ages, I can probably produce an 80% increase, without ever involving a cell phone.

Actually, RF exposure does cause physiological effects. When I first got into 2way radio and mobile phones, I had a full head of hair, a steady hand, a positive attitude, and a full bank account. After about 45 years of continuous exposure to various forms of RF, the hair is almost gone, the hand is somewhat shaky, the attitude is depressing, and the bank account is depleted. Obviously, all these symptoms were caused by RF exposure. Correlation is not causation.

I almost forgot the traditional ending tag line: More research is necessary. Send funding.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

Here's the UK numbers for incidence of brain cancer and tumors: The various graphs show much the same lack of a radical increase in brain cancers with the introduction of cell phones, and the radical increase in incidence that accompanies aging. No sign in the graphs of any 490% increase among teenagers using cell phones for 10 years.

I was somewhat off on the tx power of a cordless phone and cell phone.

DECT tx power: 10 mW (250 mW peak) in Europe 4 mW (100 mW peak) in the US

For cell phones: 100 mW avg (2 watt max) for 800/900 MHz band 100 mw avg (1 watt max) for 1900/1800 MHz band

UMTS/3G phones are a bit different: 1 watt - Power Class 1 mobile 500 mW - Power Class 2 mobile 250 mW - Power Class 3 mobile

Bluetooth: 100 mW - Class 1 2.5 mW - Class 2 1 mW - Class 3 The tx power of a cell phone is controlled by the cell site and is usually set for the lowest tx power needed to maintain a minimum BER (bit error rate). If you can get into the "Field Test Mode", you can display that power output: My junk LG VX8300 started out showing about -9dBW (126 mW). After about 30 seconds, the TX power settled down to about -15dBW (32 mW) and stayed there (as long as I didn't move).

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558