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Wireless Worries Overshadow Triumphs of RF Research

A leading expert in radio-frequency dosimetry dissects distress over 5G—and the differences between exposure and dosage

7 min read
smart phone emitting different colored light beams
John Lamb/Getty Images

Kenneth R. Foster has decades of experience researching radio frequency (RF) radiation and its effects on biological systems. And now he’s coauthored a recent survey on the subject with two other researchers—Marvin Ziskin and Quirino Balzano. Collectively, the three of them (all IEEE Life Fellows) have more than a century of experience on the subject.

The survey, published in February in the International Journal of Environmental Research and Public Health, looks at the last 75 years of research into RF exposure assessment and dosimetry. In it the coauthors detail how far the field has advanced and why they believe it to be a scientific success story.

IEEE Spectrum carried out its conversation with Foster, a professor emeritus at the University of Pennsylvania, by email. We wanted to find out more about why RF exposure assessment research has been such a success, what makes RF dosimetry so difficult, and why public worries about health and wireless radiation never seem to go away.

For those who aren’t familiar with the distinction, what’s the difference between exposure and dose?

Kenneth Foster: In the context of RF safety, exposure refers to the fields outside the body, while dose refers to energy absorbed within body tissues. Both are very important for a host of applications—medical treatments, occupational health, and safety studies for consumer electronics, for example.

“For a good review of 5G bioeffects studies, see [Ken] Karipidis’s article that found ‘no confirmed evidence that low-level RF fields above 6 gigahertz such as those used by the 5G network are hazardous to human health.’ ”
—Kenneth R. Foster, University of Pennsylvania

In your opinion, is exposure assessment a solved problem?

Foster: Measuring RF fields in free space is not a problem. The real problem that arises in some situations is the highly variable nature of RF exposure. For example, a number of scientists are surveying levels of RF fields in the environment, to address the public’s health concerns. Not an easy task, given the multitude of RF sources in the environment and the rapid falloff of RF fields from any source. Accurately characterizing an individual’s exposure to RF fields is a real challenge, at least for the handful of scientists trying to do that.

When you and your coauthors wrote your IJERPH article, was your goal to point out the success of exposure-assessment research and the challenges of dosimetry?

Foster: Our goal was to point out the remarkable progress over the years in exposure-assessment research, which has added a lot of clarity to studies on biological effects of RF fields and enabled major advances in medical technology.

By just how much has the instrumentation in these fields improved? Can you give me a sense of what tools you had available to you at the beginning of your career, for example, versus what’s available now? And how has improved instrumentation contributed to the success of exposure assessment?

Foster: The instrumentation for measurement of RF fields in health and safety studies has become smaller and more capable. Decades ago, who would have imagined that commercial field meters would be available that are rugged enough to take to a work site, able to measure RF fields strong enough to pose occupational hazards but also sensitive enough to measure weak fields from distant antennas? And at the same time, determine the precise spectrum of a signal to identify its source?

What about when wireless technologies move into new frequency bands—millimeter and terahertz waves for cellular, for example, or the 6-gigahertz band for Wi-Fi?

Foster: The problem again relates to the complexity of exposure situations, not instrumentation. For example, high-band 5G cellular base stations transmit multiple beams that move around in space. That makes it difficult to quantify exposure to people near cellular base stations, to verify that exposures are within safety limits (as they almost invariably are).

“I am personally more concerned about possible effects of excessive screen time on child development and privacy issues.”
—Kenneth R. Foster, University of Pennsylvania

If exposure assessment is a solved problem, what makes the jump to accurate dosimetry so difficult? What makes the first so much simpler than the latter?

Foster: Dosimetry is much more challenging than exposure assessment. You generally cannot stick an RF probe into someone’s body. There are many reasons you might need that information, such as in hyperthermia treatments for cancer therapy, where tissue must be heated to precisely specified levels. Too little heating and there is no therapeutic benefit, too much and you burn the patient.

Can you tell me more about the ways in which dosimetry is done today? What’s the next best thing, if you can’t stick a probe into someone’s body?

Foster: For many purposes, using the good old RF meter to measure fields in air is okay. That is certainly the case with occupational-safety work, where you need to measure the RF fields incident on a worker’s body. For clinical hyperthermia, you may still need to skewer the patient with thermal probes but computational dosimetry greatly improves the accuracy of measuring thermal dose and has led to important advances in the technique. For RF bioeffects studies—for example, using antennas placed against an animal—it is crucial to know how much RF energy is absorbed in the body and where it goes. You can’t just wave a cellphone in front of the animal as the exposure source (but some investigators do just that). For some major studies, such as the recent National Toxicology Program study in rats exposed for their lifetimes to RF energy, there is no real alternative to computational dosimetry.

Why do you think there’s so much persistent worry about wireless radiation, to the extent people will measure the levels in their homes?

Foster: Risk perception is a complicated business. Wireless radiation has characteristics that tend to raise peoples’ concerns. You can’t see it, there is no immediate connection between exposure and the kinds of effects that some people worry about, people tend to confuse RF energy (which is nonionizing, meaning that its photons are too weak to break chemical bonds) with ionizing radiation such as X-rays (which are truly dangerous). Some people believe that they are “hypersensitive” to wireless radiation, despite the inability of scientists to demonstrate such sensitivity in properly blinded and controlled studies. Some people feel threatened by the immense number of antennas that are popping up everywhere for wireless communications. The scientific literature contains many reports of varying quality and relevance to health and one can fish through this literature and put together a frightening story. And a few scientists think that there really may be health problems (although health agencies find little to concern them but say that “more research” is needed).The list goes on.

Exposure assessment plays some role in this. Consumers can buy cheap but very sensitive RF detectors and survey their environments for RF signals, of which there are many. Some of these devices emit “clicks” when measuring RF pulses from devices such as Wi-Fi access points, and sound for all the world like a Geiger counter at a nuclear reactor. Frightening. Some RF meters are also sold for hunting ghosts, but that is a different application.

Last year, the British Medical Journal published a call to halt 5G rollouts until the technology’s safety could be determined. What do you make of these kinds of calls? Do you think they help inform the portion of the public that is concerned about the health effects of RF exposure, or cause more confusion?

Foster: You refer to an opinion piece by [epidemiologist John] Frank, much of which I disagree with. Most health agencies that have reviewed the science simply call for more research, but at least one—the Health Council of the Netherlands—has called for a moratorium on rollout of high-band 5G until more safety studies are done. Such recommendations are surely concerning to the public (even though HCN also considered it unlikely that any health problems existed).

In his piece, Frank writes that “an emerging preponderance of laboratory studies indicating RF-EMFs’ [radiofrequency electromagnetic fields] disruptive biological effects.” Here is the problem: There are thousands of RF bioeffects studies in the literature that vary widely in endpoint, relevance to health, study quality, and exposure level. Most of them report some kind of effect, over all frequencies and at all exposure levels. However most of the studies have significant risk of bias (inadequate dosimetry, lack of blinding, small size, and so on) and many are inconsistent with other studies. The “emerging preponderance of studies” means little with respect to this murky literature. Frank should have relied on more careful reviews by health agencies. These consistently fail to find clear evidence for adverse effects of environmental RF fields.

Frank complains about inconsistencies in public discussion of “5G”—but he makes the same error, referring to 5G without reference to the frequency band. In fact, low and midband 5G operates at frequencies close to present cellular bands and would seem to present no new exposure issues. High-band 5G operates just below the millimeter-wave range which begins at 30 gigahertz. Fewer bioeffects studies have been done in that frequency range, but the energy hardly penetrates the skin and health agencies have not expressed concern about its safety at ordinary exposure levels.

Frank is not specific about what studies he wants done before rolling out “5G,” whatever he means by that. The [U.S. Federal Communications Commission] requires licensees to comply with its exposure limits, which are similar to those of most other countries. There is no precedent for requiring new RF technologies to be directly assessed for RF health effects before approval, which would require a potentially endless series of studies. If the FCC limits are unsafe they should be changed.

For a good review of 5G bio-effects studies see [Ken] Karipidis’s article that found “no confirmed evidence that low-level RF fields above 6 GHz such as those used by the 5G network are hazardous to human health.” The review also called for more research.

So that’s what’s needed at this time? More research?

The scientific literature is uneven, but so far health agencies have not found clear evidence for health hazards from environmental RF fields. But to be sure, the scientific literature on bioeffects of millimeter waves is relatively sparse, with maybe 100 studies, and very mixed in quality.

Governments have made a lot of money selling spectrum for 5G communications, and should invest some of that in high quality health studies, particularly for high-band 5G. I am personally more concerned about possible effects of excessive screen time on child development and privacy issues.

Are there ways in which dosimetry efforts are improving? If so, what are some of the most interesting or promising examples?

Foster: Probably the major advance has been in computational dosimetry, with the introduction of the finite difference time domain (FDTD) method and numerical models of the body based on high-resolution medical images. This allows very precise calculation of the absorption of RF energy in the body from any source. Computational dosimetry has given new life to established medical treatments such as hyperthermia for treatment of cancer, and has facilitated the development of improved MRI imaging systems and many other medical technologies.

The Conversation (0)

Metamaterials Could Solve One of 6G’s Big Problems

There’s plenty of bandwidth available if we use reconfigurable intelligent surfaces

12 min read
An illustration depicting cellphone users at street level in a city, with wireless signals reaching them via reflecting surfaces.

Ground level in a typical urban canyon, shielded by tall buildings, will be inaccessible to some 6G frequencies. Deft placement of reconfigurable intelligent surfaces [yellow] will enable the signals to pervade these areas.

Chris Philpot

For all the tumultuous revolution in wireless technology over the past several decades, there have been a couple of constants. One is the overcrowding of radio bands, and the other is the move to escape that congestion by exploiting higher and higher frequencies. And today, as engineers roll out 5G and plan for 6G wireless, they find themselves at a crossroads: After years of designing superefficient transmitters and receivers, and of compensating for the signal losses at the end points of a radio channel, they’re beginning to realize that they are approaching the practical limits of transmitter and receiver efficiency. From now on, to get high performance as we go to higher frequencies, we will need to engineer the wireless channel itself. But how can we possibly engineer and control a wireless environment, which is determined by a host of factors, many of them random and therefore unpredictable?

Perhaps the most promising solution, right now, is to use reconfigurable intelligent surfaces. These are planar structures typically ranging in size from about 100 square centimeters to about 5 square meters or more, depending on the frequency and other factors. These surfaces use advanced substances called metamaterials to reflect and refract electromagnetic waves. Thin two-dimensional metamaterials, known as metasurfaces, can be designed to sense the local electromagnetic environment and tune the wave’s key properties, such as its amplitude, phase, and polarization, as the wave is reflected or refracted by the surface. So as the waves fall on such a surface, it can alter the incident waves’ direction so as to strengthen the channel. In fact, these metasurfaces can be programmed to make these changes dynamically, reconfiguring the signal in real time in response to changes in the wireless channel. Think of reconfigurable intelligent surfaces as the next evolution of the repeater concept.

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