Introducing Brillouin Precursors

Microwave Radiation Runs Deep

Original article here.

When a very fast pulse of radiation enters the human body, it generates a burst of energy that can travel much deeper than predicted by conventional models. This induced radiation pulse, known as a Brillouin precursor, is at the heart of the continuing conflict over the U.S. Air Force’s (USAF) PAVE PAWS phased array radar on Cape Cod.

Brillouin precursors can also be formed by ultrawideband radiation and, in the near future, by high-speed data signals. Dr. Richard Albanese, a researcher at Brooks Air Force Base in San Antonio, is concerned that the radiation from the PAVE PAWS radar entails widespread human exposure to Brillouin precursors.

In a May 23, 2000, letter to the Massachusetts Department of Public Health (MDPH), Albanese warned that this type of phased array radiation has never been tested. He has been working on Brillouin precursors for over 15 years. The National Academy of Sciences–National Research Council has initiated a study to evaluate Albanese’s theories at the request of Senator Edward Kennedy (D-MA), with funding from the USAF.

Pulses of radiofrequency microwave (RF/MW) radiation must have extremely short rise times or very rapid changes in phase in order to create Brillouin precursors on entering “lossy” materials like soil, water or living tissue. (Materials that absorb radiation are called lossy.) Once generated, the new pulses propagate without significant attenuation.

Brillouin precursors present both an advantage and a potential hazard.

“They are useful for imaging because they penetrate materials that conventional radar signals do not,” explains Dr. Kurt Oughstun, who has long studied the dynamics of RF/MW pulses and has collaborated with Albanese for many years. “On the other hand, it may not be a good thing to have signals that penetrate deep into human beings.”

Oughstun began investigating Brillouin precursors while a doctoral student at the University of Rochester, NY. At that time, no one hought that they were very significant, he says, but his doctoral research suggested otherwise. Oughstun now believes that Brillouin precursors can be the dominant component of some types of RF/MW pulses traveling through human tissue. These ideas have prompted some skeptical, even derisive, reactions. Such “strange pulse effects,” Dr. Robert Adair of Yale University in New Haven, CT, told Oughstun in a caustic letter last December, “simply don’t exist.”

Oughstun is unfazed.

“I find it odd,” he told Microwave News, “that the USAF is pushing to develop technologies that use signals that penetrate different materials, while they are ignoring the fact that these signals will also penetrate the human body.”

While Oughstun has received numerous grants from the USAF’s Office of Scientific Research, his work appears to be ignored—or dismissed—by the USAF departments responsible for radiation safety. Albanese told Microwave News that he decided to go public after discovering that a 1999 report prepared for the MDPH by a panel of four experts ignored Brillouin pulses and the entire issue of phasing.

Does USAF Have Secret Health Studies on Phased Array Radiation?

Tensions Surface at NAS–NRC Meeting on PAVE PAWS Radar

“I want to know the effects that the PAVE PAWS radar is having in my community,” Richard Judge, an elected official from Cape Cod, MA, told the newly constituted committee of the National Academy of Sciences–National Research Council (NAS–NRC) that is investigating the possible health effects of the U.S. Air Force (USAF) radar. “We need to know why the rates of disease are higher in our community.”

“We were told that there are no studies of phased array radiation, but we now believe that’s not true,” Judge charged at the panel’s first meeting on March 15 in Washington. “We would like to see the [USAF’s] electromagnetic safety program, which is classified.”

Before Judge spoke, Jimmy Dishner, the executive director of the PAVE PAWS project, emphasized that he and the USAF treat any allegation that the radar might be harming the people it is designed to protect “very seriously.” In a series of presentations, USAF officials said that there is no evidence to suggest that the radar is responsible for any health problems on the cape. “There is no plausible reason to believe that PAVE PAWS is a unique RF energy source from the point of view of the human body or any biological entity,” said Dr. Johnathan Kiel of Brooks Air Force Base (AFB) in San Antonio. None of the USAF presentations mentioned any classified health data.

Then, Dr. Richard Albanese addressed the committee over a speakerphone from San Antonio. Albanese, a career USAF researcher who reports to Kiel, is the individual most responsible for the new NAS–NRC study. Close to two years ago, he wrote to the Massachusetts Department of Public Health warning that the potential effects of the PAVE PAWS radiation are “completely unexplored”. Albanese said that he is “particularly concerned about brain tumors” in the communities near the radar installation. “There are simply no published data sets for phased arrays,” Albanese told the committee. As he repeatedly emphasized the word “published,” it became apparent that there are reports classified secret that are not available without a security clearance.

Once, while explaining the biological importance of phasing, Albanese cut himself off and said that any further discussion would have to take place in “another setting.

Asked after the meeting about the stark contrast between his concerns and the literature reviews presented by members of the USAF team, Albanese told Microwave News that, “There are two distinct tracks. There is a two-world situation at work.”

The tension over secret information nearly boiled over when Judge sought to give the NAS–NRC staff copies of two of Albanese’s papers, which had been obtained by Charles Kleekamp, a retired engineer who serves as a technical advisor to citizen activists on the Cape. The equations in the papers were garbled, however, prompting NAS–NRC’s Dr. Rick Jostes to say that he would request original copies from the USAF.

Judge said that he was skeptical that the USAF would supply the papers and insisted that Jostes accept his copies, which he eventually did. Kleekamp said that it had taken him a year to obtain the two papers. Albanese told Microwave News that the papers do not contain classified material. He explained that the USAF could nevertheless limit access to them. “Because they do not conform to USAF policy, they are able to stop them from open distribution,” he said. On April 25, the USAF will hold a classified briefing in San Antonio for those members of the NAS–NRC panel with security clearances:

  • Dr. Larry Anderson of Battelle Labs in Richland, WA
  • Dr. Robert Hansen, an RF consulting engineer based in Tarzana, CA.
  • Dr. Evan Douple, the NAS–NRC study director, also has a clearance.
  • Albanese himself has a “top secret” clearance.

Brillouin Precursors 101 with Professor Kurt Oughstun

Dr. Kurt Oughstun is a professor of electrical engineering and mathematics at the University of Vermont, Burlington. He has done extensive work on the propagation of extremely short electromagnetic pulses through different types of materials, and has collaborated with USAF’s Dr. Richard Albanese for over 15 years. Oughstun is the author of more than 50 published papers, as well as the textbook Electromagnetic Pulse Propagation in Causal Dielectrics with G.C. Sherman (Berlin: Springer-Verlag, 1994).

A list of Oughstun’s publications is available on his home page, He is on the editorial board of IEEE Transactions on Antennas and Propagation. The USAF has long supported his research, with no restrictions on what he can publish or present at meetings. In fact, he does not have a security clearance for access to classified information. Oughstun spoke with Microwave News in March.

MWN: Do you agree with Dr. Albanese that the radiation emitted by a phased array radar system is different from other sources of RF/MW radiation or from an ordinary radar?

KO: Yes, I do. Our research has shown that the electromagnetic field radiated from an antenna system like PAVE PAWS can penetrate much deeper into the human body than the radiation from a conventional radar. Let me explain why: In a phased array system like PAVE PAWS, several individual antennas radiate pulses in a specified time sequence. Within the main beam of the radar, these pulses are typically separated by short time intervals. In the side lobes outside the main beam, however, the time intervals between the various pulses will be different and the assembly of pulses can overlap each other in such a way that they may produce an extremely rapid change in phase in the electromagnetic field.

MWN: What happens when the phase changes very rapidly?

KO: The most important effect is that the radiation no longer decays exponentially in lossy materials such as water, foliage and biological tissue. In these cases, most of the RF energy is absorbed within a few centimeters. But our research shows that if a change in phase is sufficiently rapid, a quasi-static field known as a Brillouin precursor is generated when the radiation penetrates the human body. This special type of wavefield was first described by the French physicist Leon Brillouin in 1914. We have found that pulses that produce a Brillouin precursor can deliver a significant fraction of their energy deep into the tissue—much more so than can pulses from a conventional radar.1

MWN: If the phased-array radiation is deposited deeper into the human body, what can it do when it gets there?

KO: The Brillouin precursor field is totally different from the RF/MW radiation addressed in ANSI/IEEE exposure standards. In his 1994 paper2 Dr. Richard Albanese described four potential mechanisms for biological tissue damage due to a Brillouin precursor. These are changes in the conformation of molecules, changes in the rates of chemical reactions, effects on membranes and thermal damage. In my opinion, the most serious may be the membrane effects. A single Brillouin precursor can open small channels through the cell membrane because, as it passes through the membrane, it can induce a significant change in electrostatic potential across that membrane.

MWN: One of the contentious effects of microwave radiation is leakage through the blood-brain barrier. Do you think that PAVE PAWS radiation may be more likely to induce such leakage?

KO: Published laboratory results have demonstrated that low-intensity electromagnetic radiation modifies the blood-brain barrier in laboratory animals. Additional work has shown that electromagnetic pulses with the same average power but different pulse characteristics result in different barrier permeabilities. Because the PAVE PAWS system can produce a sequence of Brillouin precursors in the brain — each precursor opening small channels through the cell membrane — radiation from the PAVE PAWS system may indeed be more likely to induce such leakage.

MWN: Are Brillouin precursors unique to PAVE PAWS radiation?

KO: No—not at all.

MWN: What other real-world radiation sources could they be associated with?

KO: As data transmission rates continue to increase, wireless communication systems will approach closer to and may, at some time in the not-too-distant future, exceed the conditions necessary to produce Brillouin precursors in living tissue.

MWN: The FCC recently authorized certain types of ultrawideband (UWB) signals—for example, for imaging and for short-range communications Could these signals, as well as other types of UWB, generate Brillouin precursors?

KO: Yes. In fact, some of the UWB imaging technologies being developed are based on Brillouin precursors. In the past few years, I have been modeling the behavior of Brillouin precursors in substances like soil and vegetation for the USAF. They are ideal for locating objects hidden underground or beneath a tree canopy because they can penetrate through substances that absorb conventional radar, and then reflect off any metal surface that may be hidden underneath.

MWN: Why do you think that these ideas have prompted such skepticism among some who work on RF/MW bioeffects?

KO: Two reasons immediately come to mind. First of all, it has been long assumed that the adverse effects of electromagnetic radiation on living beings are primarily thermal in nature. Any nonthermal effects are assumed to be comparatively insignificant. Because of this assumption, RF Microwave radiation exposure guidelines have been established based solely on thermal effects. Entire industries that use RF/MW technologies support these RF Microwave radiation exposure guidelines. Naturally, they will resist any changes prompted by the recognition of nonthermal effects. [Note: these are commercial guidelines; they have never been health and safety guidelines].

MWN: What is the other reason?

KO: The most widely accepted view of pulse dispersion is based upon the so-called group velocity approximation. Because of its inherent simplicity, many researchers have embraced this approximation without paying much, if any, attention to its accuracy. But this approximation breaks down for pulses with short rise times.

MWN: What is the group velocity approximation?

KO: It is based on the idea that the carrier frequency of the pulse dominates the behavior of the pulse. Other frequencies that are present when the pulse enters a lossy material are assumed to be negligible in comparison. But in reality, the Brillouin precursors can become the dominant field.3

MWN: Give us an example of what happens to short-rise-time pulses with a 430MHz carrier frequency traveling through simulated brain tissue.

KO: The group velocity approximation predicts that the pulses decay very quickly. But if you take into account the Brillouin precursors, you see that the strength of the signal is 78 times greater at a depth of 50 cm. (See figure below.)

MWN: But our brains aren’t that big. Do Brillouin pulses still matter?

KO: Yes, because the pulses are repeatedly reflected back and forth inside the skull cavity, resulting in an effectively long propagation distance, as well as in several hot spots due to beam focusing.

MWN: Dr. Robert Adair is perhaps your and Dr. Albanese’s harshest critic. How do you respond to his contention that such “strange” pulse effects “simply don’t exist”?

KO: Dr. Adair’s statement is simply wrong. Our research program is mathematically rigorous and we present a physically correct theoretical description of the dynamics of extremely short pulses. The work began at the University of Rochester in the 1970s and continues today at the Computational Electromagnetics Laboratory at the University of Vermont, where I work.

MWN: We still don’t understand how Adair, a physicist with a chair at Yale University, could say that these ideas are outlandish. Are they that esoteric?

KO: I can only guess what any person says or believes. Perhaps it is because the math used to model the behavior of Brillouin precursors — which is known as asymptotic analysis — can be very complicated. In fact, the famous Norwegian mathematician N.H. Abel is said to have called it “the invention of the devil.” But the asymptotic description of pulse behavior has been completely verified by independent numerical solutions and by carefully designed experiments. In spite of this incontrovertible evidence, many researchers continue to cling to the group velocity description.

MWN: Has a Brillouin precursor ever been experimentally observed in tissue?

KO: I have not seen any lab results, but I believe that the USAF has sponsored experiments that have shown Brillouin precursors in tissue. If so, the results have not been published. I do know that researchers working under contract for the USAF have observed a beautiful Brillouin precursor in water. These experimental results were reported in 1988 by Richard Smith in “Dispersive Pulse Propagation: First Experiments,” which may be found at the Defense Technical Information Center. But here again, these important results have not been published in the open literature.

MWN: Why not? KO: These experiments require some highly sophisticated technology and the USAF may be reluctant to discuss it in public. More significantly, it may also be that these results raise several health and safety issues that the USAF is unable — or perhaps even unwilling to address at this time. To be sure, our current guidelines for exposure to pulsed electromagnetic radiation have failed to consider these critical factors.

  1. K. Oughstun, “Noninstantaneous, Finite Rise-Time Effects on the Precursor Field Formation in Linear Dispersive Pulse Propagation,” Journal of the Optical Society of America A, 12, pp.1715-1729, 1995; P. Smith and K. Oughstun, “Electromagnetic Energy Dissipation and Propagation of an Ultrawideband Plane Wave Pulse in a Causally Dispersive Dielectric,” Radio Science, 33, pp.14891504, November-December 1998. 

  2. R. Albanese et al., “Ultrashort Electromagnetic Signals: Biophysical Questions, Safety Issues and Medical Opportunities,” Aviation, Space and Environmental Medicine, 65 (Supplement), pp.A116-A120, May 1994. 

  3. H. Xiao and K. Oughstun, “Failure of the Group Velocity Description for Ultrawideband Pulse Propagation in a Double Resonance Lorentz Model Dielectric,” Journal of the Optical Society of America B, 16, pp.1773-1785, 1999