The concept of phase modes has been known for quite a while. In the mid-thirties, Henri Chireix published [1] and patented [2] the application of phase modes in antenna arrays. Since then, the concept has been widely used in connection with circular arrays (e.g. [3]), multi-arm spiral antennas (e.g. [4]), radio navigation systems (e.g. [5]), etc. The literature within the area is substantial, with many papers published in various journals and conference proceedings.
Prior art search is an extinct art, indeed...
[1] H. Chireix, L'Onde Électrique, Vol. 15, pp. 440-456, 1936. [2] H. Chireix, US Patent No. 2109835, Priority date 7 Jan. 1935, Granted 1 March 1938. [3] H.L. Knudsen, IRE Trans. Antennas Propagat., Vol. AP-4, No.3, pp. 452-472, July 1956. [4] J.E. Webb, US Patent No. 3344425, Priority date 13 June 1966, Granted 26 Sept. 1967. [5] G. Höfgen, US Patent No. 4197542, Priority date 6 April 1977, Granted 8 April 1980. [6] J.R.F. Guy and D.E.N. Davies, IEE Proc., Vol. 130, Pt. H, No.6, pp. 410-414, Oct. 1983.
To my knowledge, no plastic has a "resonance" in the microwave frequency range. Except for heating effects, I doubt there can be any microwave assisted chemistry involved in this. There is too little info in the New Scientist article to assess this, but I doubt this is rocket science...
For the umptieth time: THERE IS NO WATER RESONANCE AT 2.4 GHz!!! Water in its gas phase has a resonance around 22 GHz. Liquid phase water has a very broad resonance, peaking around 10 - 30 GHz (temperature dependent).
OK, let's do some back-of-the-envelope calculation...
The ICNIRP guidelines for EM exposure (see http://www.icnirp.de/documents/emfgdl.pdf) give the following reference levels for general public exposure to time-varying electric and magnetic fields:
Frequency range: 10-400 MHz E-field strength = 28 V/m^2 H-field strength = 0.073 A/m^2 Equivalent plane wave power density Seq = 2 W/m^2
Thus, how large must a sphere be if we spread 100 W over it, and still want to comply with the guidelines? Ans: R = 2m
Of course, we are in the nearfield, and have to do a full CEM simulation or measurement, but this quick result gives a hint on what kind of levels we are talking about. You can read the full ICNIRP paper, but I quote some of the interesting parts here:
At frequencies above 10 MHz, the derived electric and magnetic field strengths were obtained from the whole-body SAR basic restriction using computational and experimental data. In the worst case, the energy coupling reaches a maximum between 20 MHz and several hundred MHz. In this frequency range, the derived reference levels have minimum values. The derived magnetic field strengths were calculated from the electric field strengths by using the far-field relationship between E and H (E/H = 377 ohms). In the near-field, the SAR frequency dependence curves are no longer valid; moreover, the contributions of the electric and magnetic field components have to be considered separately. For a conservative approximation, field exposure levels can be used for near-field assessment since the coupling of energy from the electric or magnetic field contribution cannot exceed the SAR restrictions. For a less conservative assessment, basic restrictions on the whole-body average and local SAR should be used.
Yupp, this is "well known" in antenna and microwave R&D circles. There are many theories, ranging from RF exposure to working odd hours... I have sired four girls vs. zero boys, and even though this is just one data point, the trend is very much obvious in departments I've worked.
BTW, the combination of WiTricity and Pendry looks like a marriage made in heaven -> Metamagical materials and cargo cult electromagnetics go together...
I believe there is a scientific reason for the ISM band being there - I think water has a bit of an absorption peak in the 2.4 GHz region.
For this reason, 2.4 GHz wasn't too hot for long-haul communications due to water vapor in the air, so no one was in a rush to license spectrum for it, and no one fought designating it as an "Industrial, Scientific, Medical" band. (with the primary use in all three of those categories being to take advantage of that water absorption peak for heating.) This is plain wrong. Water vapor has an absorption peak at about 22 GHz. Liquid water has a very broad resonance centered around 10 - 30 GHz (depending on temperature). The ISM frequency band around 2.4 GHz is a trade-off between absorption, penetration depth, uniformity of heating, availabity of cheap sources (magnetrons), and thus just a regulatory thing. There was an alternative band at 905 MHz as well. 2-8 GHz (S- and C-band) is actually optimum for low-noise operation (e.g. deep-space probe comms) due to the absorption loss from atmospheric gases, background radiation, etc being minimum her.
Please stop propagating myths, and please stop labeling junk like this as "informative".
Another example of how the tabloids (Nature & Science) publish things that have been known for ages... There seems to be a trend that you can get anything published there, since the peer review is done by totally clueless physicists who do not know anything about the state of the art.
The concept of making filters by cutting holes in a sheet of metal has been known for ages. Using periodic (or in this case quasiperiodic) metallic patterns is called Frequency Selective Surfaces (FSS). There are numerous books and tons of publications in IEEE transactions, etc. in this area.
I did etched FSS filters for 375 GHz around 1982, and the concept was already pubslished in books by then.
Old stuff. Too many scientists, too much money, too little brain.
My experience of millimeter and submillimeter sources is that the MTBF is rather limited, and this would be even more true for a semi-mobile multi-kW 94 GHz system as the Raytheon Silent Guardian. 4.5 tons of transmitter (and power supply) equipment together with sun, sand, and not-always-so-competent soldiers will be factors to consider...
I have got RF burns during my career from 3,5 MHz, 144 MHz, and 350 GHz transmitters as well as 10 um CO2 lasers, and I can assure you that they can been quite painful! I would go for the CO2 laser if maximizing bang for the bucks... However, there are some Geneva conventions that might be violated, but who cares about signatures on papers nowadays;-)
The countermeasures can be rather low-tech. The wavelength is about 3 mm and thus a metallic wire mesh hood with a mesh size much smaller than this could easily block this (I have tested one of those microwave shielding suits, and yes they work). Water soaked clothes/gloves takes care of the rest of the body. Also you can try carrying around reflectors and hit back at the soldiers. But then they will probably strike back with non-non-lethal weapons. Another obvious weak point is the IR camera in the middle of the reflector. A sniper would easily ruin their day!
Metamaterials and the concept of negative index of refraction are likely the cold fusion equivalents of this decade...
There are several weak points in this whole business of "Harry Potter cloaks" where physicists with little experience in electromagnetics (and even less in radar cross section reduction) go astray. To list but a few points:
Irrelevance of group velocity It has long been known that effects like anomalous dispersion in resonant media can render classical group velocity concepts irrelevant. Several authors seem to lack an understanding of the inherent assumptions when equaling the group velocity with a power or information transfer speed. Thus an interpretation leading to an "equivalent" negative index of refraction can be misleading.
Bandwidth The bandwidth of these materials is inherently small. There is also often a significant loss as well.
Misuse of models The assumption of monochromatic and plane waves interacting with an infinite structure will be like pressing a square peg into a round hole when dealing with some cases. For example, it is well-known that a simplistic plane-wave model is invalid when dealing with lossy materials (apart from normal incidence).
Publications in out-of-field journals It is clear that a lot of the metamaterial material has been published in journals that are outside the typical antenna or microwave area, such as Nature, Science, and Phys. Rev. This could potentially lead to deficient papers slipping through, due to lack of a proper review. An example of something that hopefully would have been curbed in an IEEE journal is a Phys. Rev. paper [*] that showed a transmission vs. frequency plot with a dynamic range of 1600 dB! (The range of scale of the size of the universe compared to the Planck length is dwarfed by this...). There are numerous examples of publications without even the most basic sanity checks performed by the authors and the reviewers. The situation has been bad enough for the microwave field, now it is unfortunately spreading to optical frequencies.
[*] R.W. Ziolkowski and C.-Y. Cheng, "Existence and design of trans-vacuum-speed metamaterials", Phys. Rev. E, 68, 026612, 2003.
Peer review endangered The field of metamaterials has now grown to such a volume that a wholly separate sub-science or "sect" with its own special issues and conferences, etc. has formed. There is an inherent problem with this, since the peer review process will be endangered. The people most knowledgeable within the subject are by definition those that are active within the subject, and fewer outside reviewers will be used after a while.
"Publication by news releases" Several of the groups within this field are heavy on marketing their results as revolutionary. In the present "publish or perish" environment it is very important to secure funding, and gullible grant-givers are abundant...
Even though this regards a US patent, one should remember that there are some differences between US and "the rest of the world" regarding "First to Invent" vs. "First to File", see e.g. http://en.wikipedia.org/wiki/Prior_art Thus the grace period for prior art need not apply universally...
This unfortunately seems to be a case of "cargo cult science". It looks like science, but isn't. I just got hold of the actual paper on arXiv.org, and some comments after quickly browsing through are:
1) It is a purely theoretical study made by a physicist, who evidently has little experience within RF engineering. With such a "simple" concept, why didn't he bother making a quick experiment? (Spoiler warning: Many beatiful theories have been killed at infancy by experiments...)
2) He is assuming totally unrealistic Q-values.
3) He doesn't explain how he will get the RF energy into and out of the resonators. The Q-value of these circuits would load his resonators.
4) He is using ridiculous precision in his results (6 significant digits...)
5) Magnetic coupling between tuned circuits has been known for ages, but then of course cast in its standard EE terminology. Now a physicist has rediscovered it...
6) "Publication by press release". Making exaggerated claims in the media is no substitute for peer review (where the peers are within the correct field).
Yes, of course the basestation can use all timeslots, and average power could be = peak power.
The power from one GSM base station frequency channel is of the order 10 W. A typical three-sector base would have three channels, and would get a total of 22 useful channels. Statistically, the peak use is in the afternoon, when the averaged power is around 20 W. Short periods, maybe for 30 seconds a day or so, all time-slots and channels are used and the average power will be 30 W.
In one survey the number of channels spanned from one to five, where the total average power spanned 1 to 60 W. Thus an average lightbulb would outshine most basestations...
All this would of course be depending on the scenario, but this is roughly the situation. Averaging over 24/7 gives a much lower average power level. Can dig out some references, but they are probably in the deep strata in the heap of reprints under my desk...
>This is totally different; those towers are pumping out huge amounts of >radiation, to try and make sure you can get a strong signal at great >distances. It's not like living inside a nuclear reactor, but its close >enough to be a bad idea.
This is not true. A GSM cell phone puts out maximum 2 W peak (900 MHz band) or 1 W peak (1800 MHz band). The average is 1/8 of this. A base station puts out a few tens of Watts. The power levels cannot be that different since you want a fairly symmetrical link budget.
The antenna elevation pattern of the base station is such that most of it is directed towards the horizon, and less towards the base of the tower. Since the power density (W/m^2) will drop off as the square of the distance, these two factors will cancel in such a way that you essentially get the same power density when moving out from the base station at ground level, at least for several hundred meters.
You will not be nuked from the handset, and certainly not from the base station. The power density from the base station will always be many orders of magnitude below that from the handset...
Since your handset will automatically decrease its power to mW when close to a base station (to save battery time, etc.), the best way to get less exposure is actually to be as close to a base station as possible!
I once attended a conference at JPL in Pasadena. The venue was the von Karman auditorium where they have a full-scale mock-up of one of the Voyagers. I studied this wonderful space probe, especially the attached gramophone record with "sights and sounds" from Planet Earth. However, when I tried to understand the "user's manual", i.e. the plate with a drawing of how to use the record together with the enclosed pick-up/stylus, I was stuck. It didn't make sense at all! The I realized that this was drawn by an *American*, and I am an alien European... The confusion was due to the subtle difference between the US and European standard for presenting different projections of an object on a drawing (first vs. third angle).
The moral of this is that it is very difficult to find universal methods for symbolic transmission of information, since we often use conventions without even thinking about alternate interpretations.
Slashdot Mirror
The concept of phase modes has been known for quite a while.
In the mid-thirties, Henri Chireix published [1] and patented [2] the application of phase
modes in antenna arrays. Since then, the concept has been widely used in
connection with circular arrays (e.g. [3]), multi-arm spiral antennas (e.g. [4]), radio
navigation systems (e.g. [5]), etc. The literature within the area is substantial, with
many papers published in various journals and conference proceedings.
Prior art search is an extinct art, indeed...
[1] H. Chireix, L'Onde Électrique, Vol. 15, pp. 440-456, 1936.
[2] H. Chireix, US Patent No. 2109835, Priority date 7 Jan. 1935, Granted 1 March 1938.
[3] H.L. Knudsen, IRE Trans. Antennas Propagat., Vol. AP-4, No.3, pp. 452-472, July 1956.
[4] J.E. Webb, US Patent No. 3344425, Priority date 13 June 1966, Granted 26 Sept. 1967.
[5] G. Höfgen, US Patent No. 4197542, Priority date 6 April 1977, Granted 8 April 1980.
[6] J.R.F. Guy and D.E.N. Davies, IEE Proc., Vol. 130, Pt. H, No.6, pp. 410-414, Oct. 1983.
To my knowledge, no plastic has a "resonance" in the microwave frequency range. Except for heating effects, I doubt there can be any microwave assisted chemistry involved in this. There is too little info in the New Scientist article to assess this, but I doubt this is rocket science...
For the umptieth time: THERE IS NO WATER RESONANCE AT 2.4 GHz!!! Water in its gas phase has a resonance around 22 GHz. Liquid phase water has a very broad resonance, peaking around 10 - 30 GHz (temperature dependent).
The ICNIRP guidelines for EM exposure (see http://www.icnirp.de/documents/emfgdl.pdf) give the following reference levels for general public exposure to time-varying electric and magnetic fields:
Frequency range: 10-400 MHz
E-field strength = 28 V/m^2
H-field strength = 0.073 A/m^2
Equivalent plane wave power density Seq = 2 W/m^2
Thus, how large must a sphere be if we spread 100 W over it, and still want to comply with the guidelines?
Ans: R = 2m
Of course, we are in the nearfield, and have to do a full CEM simulation or measurement, but this quick result gives a hint on what kind of levels we are talking about. You can read the full ICNIRP paper, but I quote some of the interesting parts here:
Yupp, this is "well known" in antenna and microwave R&D circles. There are many theories, ranging from RF exposure to working odd hours... I have sired four girls vs. zero boys, and even though this is just one data point, the trend is very much obvious in departments I've worked.
BTW, the combination of WiTricity and Pendry looks like a marriage made in heaven -> Metamagical materials and cargo cult electromagnetics go together...
For this reason, 2.4 GHz wasn't too hot for long-haul communications due to water vapor in the air, so no one was in a rush to license spectrum for it, and no one fought designating it as an "Industrial, Scientific, Medical" band. (with the primary use in all three of those categories being to take advantage of that water absorption peak for heating.) This is plain wrong. Water vapor has an absorption peak at about 22 GHz. Liquid water has a very broad resonance centered around 10 - 30 GHz (depending on temperature).
The ISM frequency band around 2.4 GHz is a trade-off between absorption, penetration depth, uniformity of heating, availabity of cheap sources (magnetrons), and thus just a regulatory thing. There was an alternative band at 905 MHz as well.
2-8 GHz (S- and C-band) is actually optimum for low-noise operation (e.g. deep-space probe comms) due to the absorption loss from atmospheric gases, background radiation, etc being minimum her.
Please stop propagating myths, and please stop labeling junk like this as "informative".
Another example of how the tabloids (Nature & Science) publish things that have been known for ages... There seems to be a trend that you can get anything published there, since the peer review is done by totally clueless physicists who do not know anything about the state of the art.
The concept of making filters by cutting holes in a sheet of metal has been known for ages. Using periodic (or in this case quasiperiodic) metallic patterns is called Frequency Selective Surfaces (FSS). There are numerous books and tons of publications in IEEE transactions, etc. in this area.
I did etched FSS filters for 375 GHz around 1982, and the concept was already pubslished in books by then.
Old stuff. Too many scientists, too much money, too little brain.
My experience of millimeter and submillimeter sources is that the MTBF is rather limited, and this would be even more true for a semi-mobile multi-kW 94 GHz system as the Raytheon Silent Guardian. 4.5 tons of transmitter (and power supply) equipment together with sun, sand, and not-always-so-competent soldiers will be factors to consider...
;-)
I have got RF burns during my career from 3,5 MHz, 144 MHz, and 350 GHz transmitters as well as 10 um CO2 lasers, and I can assure you that they can been quite painful! I would go for the CO2 laser if maximizing bang for the bucks... However, there are some Geneva conventions that might be violated, but who cares about signatures on papers nowadays
The countermeasures can be rather low-tech. The wavelength is about 3 mm and thus a metallic wire mesh hood with a mesh size much smaller than this could easily block this (I have tested one of those microwave shielding suits, and yes they work). Water soaked clothes/gloves takes care of the rest of the body. Also you can try carrying around reflectors and hit back at the soldiers. But then they will probably strike back with non-non-lethal weapons. Another obvious weak point is the IR camera in the middle of the reflector. A sniper would easily ruin their day!
http://v3.espacenet.com/textdoc?DB=EPODOC&IDX=US20 07011109&F=0
Metamaterials and the concept of negative index of refraction are likely the cold fusion equivalents of this decade...
There are several weak points in this whole business of "Harry Potter cloaks" where physicists with little experience in electromagnetics (and even less in radar cross section reduction) go astray. To list but a few points:
Irrelevance of group velocity
It has long been known that effects like anomalous dispersion in resonant media can render classical group velocity concepts irrelevant. Several authors seem to lack an understanding of the inherent assumptions when equaling the group velocity with a power or information transfer speed. Thus an interpretation leading to an "equivalent" negative index of refraction can be misleading.
Bandwidth
The bandwidth of these materials is inherently small. There is also often a significant loss as well.
Misuse of models
The assumption of monochromatic and plane waves interacting with an infinite structure will be like pressing a square peg into a round hole when dealing with some cases. For example, it is well-known that a simplistic plane-wave model is invalid when dealing with lossy materials (apart from normal incidence).
Publications in out-of-field journals
It is clear that a lot of the metamaterial material has been published in journals that are outside the typical antenna or microwave area, such as Nature, Science, and Phys. Rev. This could potentially lead to deficient papers slipping through, due to lack of a proper review. An example of something that hopefully would have been curbed in an IEEE journal is a Phys. Rev. paper [*] that showed a transmission vs. frequency plot with a dynamic range of 1600 dB! (The range of scale of the size of the universe compared to the Planck length is dwarfed by this...). There are numerous examples of publications without even the most basic sanity checks performed by the authors and the reviewers. The situation has been bad enough for the microwave field, now it is unfortunately spreading to optical frequencies.
[*] R.W. Ziolkowski and C.-Y. Cheng, "Existence and design of trans-vacuum-speed metamaterials", Phys. Rev. E, 68, 026612, 2003.
Peer review endangered
The field of metamaterials has now grown to such a volume that a wholly separate sub-science or "sect" with its own special issues and conferences, etc. has formed. There is an inherent problem with this, since the peer review process will be endangered. The people most knowledgeable within the subject are by definition those that are active within the subject, and fewer outside reviewers will be used after a while.
"Publication by news releases"
Several of the groups within this field are heavy on marketing their results as revolutionary. In the present "publish or perish" environment it is very important to secure funding, and gullible grant-givers are abundant...
Even though this regards a US patent, one should remember that there are some differences between US and "the rest of the world" regarding "First to Invent" vs. "First to File", see e.g.
http://en.wikipedia.org/wiki/Prior_art
Thus the grace period for prior art need not apply universally...
Just my $0.02...
This unfortunately seems to be a case of "cargo cult science". It looks like science, but isn't. I just got hold of the actual paper on arXiv.org, and some comments after quickly browsing through are:
1) It is a purely theoretical study made by a physicist, who evidently has little experience within RF engineering. With such a "simple" concept, why didn't he bother making a quick experiment? (Spoiler warning: Many beatiful theories have been killed at infancy by experiments...)
2) He is assuming totally unrealistic Q-values.
3) He doesn't explain how he will get the RF energy into and out of the resonators. The Q-value of these circuits would load his resonators.
4) He is using ridiculous precision in his results (6 significant digits...)
5) Magnetic coupling between tuned circuits has been known for ages, but then of course cast in its standard EE terminology. Now a physicist has rediscovered it...
6) "Publication by press release". Making exaggerated claims in the media is no substitute for peer review (where the peers are within the correct field).
Yes, of course the basestation can use all timeslots, and average power could be = peak power.
/ toc.html has a lot of useful info on this topic.
1 857.pdf on power density levels.
The power from one GSM base station frequency channel is of the order 10 W. A typical three-sector base would have three channels, and would get a total of 22 useful channels. Statistically, the peak use is in the afternoon, when the averaged power is around 20 W. Short periods, maybe for 30 seconds a day or so, all time-slots and channels are used and the average power will be 30 W.
In one survey the number of channels spanned from one to five, where the total average power spanned 1 to 60 W. Thus an average lightbulb would outshine most basestations...
All this would of course be depending on the scenario, but this is roughly the situation. Averaging over 24/7 gives a much lower average power level. Can dig out some references, but they are probably in the deep strata in the heap of reprints under my desk...
Moulder's site http://www.mcw.edu/gcrc/cop/cell-phone-health-FAQ
See also for example http://www.ursi.org/Proceedings/ProcGA02/papers/p
>This is totally different; those towers are pumping out huge amounts of >radiation, to try and make sure you can get a strong signal at great >distances. It's not like living inside a nuclear reactor, but its close >enough to be a bad idea.
This is not true. A GSM cell phone puts out maximum 2 W peak (900 MHz band) or 1 W peak (1800 MHz band). The average is 1/8 of this. A base station puts out a few tens of Watts. The power levels cannot be that different since you want a fairly symmetrical link budget.
The antenna elevation pattern of the base station is such that most of it is directed towards the horizon, and less towards the base of the tower. Since the power density (W/m^2) will drop off as the square of the distance, these two factors will cancel in such a way that you essentially get the same power density when moving out from the base station at ground level, at least for several hundred meters.
You will not be nuked from the handset, and certainly not from the base station. The power density from the base station will always be many orders of magnitude below that from the handset...
Since your handset will automatically decrease its power to mW when close to a base station (to save battery time, etc.), the best way to get less exposure is actually to be as close to a base station as possible!
I once attended a conference at JPL in Pasadena. The venue was the von Karman auditorium where they have a full-scale mock-up of one of the Voyagers. I studied this wonderful space probe, especially the attached gramophone record with "sights and sounds" from Planet Earth. However, when I tried to understand the "user's manual", i.e. the plate with a drawing of how to use the record together with the enclosed pick-up/stylus, I was stuck. It didn't make sense at all! The I realized that this was drawn by an *American*, and I am an alien European... The confusion was due to the subtle difference between the US and European standard for presenting different projections of an object on a drawing (first vs. third angle).
/Joakim Johansson (alien from Sweden)
The moral of this is that it is very difficult to find universal methods for symbolic transmission of information, since we often use conventions without even thinking about alternate interpretations.