Quirino Balzano

This Standards paper considers limits of the International Commission on Nonionizing Radiation (ICNIRP) and Institute of Electrical and Electronics Engineers (IEEE C95.1-2019) on “brief exposures” to radiofrequency energy (RF-EMF), that vary significantly within the 6 minute averaging time specified in the limits. This situation arises in two important contexts: exposures from cellular base stations employing Multiple Input Multiple Output (MIMO) antennas with beamforming that sweep beams around the service area, and exposure to pulsed RF-EMF with high peak power but low duty cycle. The ICNIRP and IEEE limits on brief exposures between 6 and 300 GHz are assessed using numerical and analytical solutions to a one-dimensional thermal model of tissue. Analysis is done both for rectangular pulses of RF-EMF (i.e., the step response to a suddenly imposed RF-EMF field), and to impulses of RF-EMF energy. The analysis shows that both sets of guidelines are uneven in the level of protection they offer against excessive transient heating of skin, with the IEEE limits being far more conservative than the ICNIRP limits. The thermal model suggests a simple modification to the pulse fluence limits that provides a more consistent level of protection against excessive temperature increases for pulses of varying duration and frequency. The Standards Paper does not consider possible nonthermal hazards or possible thermoacoustic effects produced by brief but very high amplitude RF-EMF pulses that produce high rates of change of tissue temperature but small temperature increases. The conclusion points to the need for further research and development to establish and refine exposure limits for pulsed RF-EMF.

A theory of surface electromagnetic waves in gradient media exhibiting arbitrary surface gradients of dielectric permittivity and magnetic permeability has been developed. Novel low-loss propagating surface wave solutions have been found in the gradient media in which both dielectric permittivity and magnetic permeability are dominated by their imaginary parts. Several examples of gradient geometries in which the surface wave problem may be solved analytically have been found. Examples of practically useful surface wave geometries spanning from radio communication underwater to UV nanophotonics have been demonstrated.

In this article a portable radio communication system operating in the 30-MHz band and capable of transmitting high-definition live underwater video images is presented. The system operation is based on launching electromagnetic surface waves propagating along the water–air interface using specially designed surface wave antennas. Since the propagation length of the surface electromagnetic waves far exceeds the skin depth of bulk radio waves at the same frequency, this technique is useful for video communication underwater over distances of several meters. This system also appears to be efficient at communicating through the water–air interface, and it may be used for underwater object detection.

A theory of surface electromagnetic waves in gradient media exhibiting arbitrary surface gradients of dielectric permittivity and magnetic permeability has been developed. Novel low‐loss propagating surface wave solutions have been found in the gradient media in which both dielectric permittivity and magnetic permeability are dominated by their imaginary parts. Several examples of gradient geometries in which the surface wave problem may be solved analytically have been found. Examples of practically useful surface wave geometries spanning from radio communication underwater to UV nanophotonics have been demonstrated.

This article discusses the contention in the commented-upon paper that Brillouin precursors generated by 5G New Radio (5G NR) and other cellular systems are a possible cause of tissue damage at deeper layers of tissue than the power penetration depth of the carrier frequency. The original theory for Brillouin precursors from pulsed radiofrequency signals (RF-EMF) and speculation about their possible health effects dates back to the 1990’s and was based on studies of the propagation of very short (nanosecond) ultrawide-bandwidth RF pulses through water. This assumption is not correct for cellular telephone signals due to their narrow bandwidth. The commented-on paper provides no alternative rationale as to why Brillouin effects should cause tissue damage from RF-EMF radiation from cellular and other communications systems. Other inaccuracies in this paper concerning thermal responses of tissue to RF-EMF are also noted.

Underwater radio communication using surface electromagnetic waves propagating along the seawater-air and seawater-sea floor interfaces may provide a promising alternative to commonly used acoustic communication underwater. Here we present a detailed analytical and numerical consideration of TE and TM polarized surface electromagnetic wave properties. The resulting surface waves have propagation constants that permit communication ranges far longer than those of bulk propagation in the lossy media. We demonstrate theoretically and experimentally their ability to carry broadband radio signals over practical communication distances underwater. A 50 MHz radio signal was successfully carried along the sandy seabed over 7 m distance.

While evaluating the near field of dipole antennas, it is noted that different software suites yield values of the electric and the magnetic fields, at the surface of antennas, that can be substantially different, especially at the tips and at the feed gap. The close near field of dipoles has not been yet analysed in detail. An asymptotic expansion method for the near fields at the surface of these antennas has been developed and compared to the computed fields. The results show that the software of the computed field should not use a uniform mesh. The mesh should be much tighter at the metal extremities than in the dipole body. The proposed technique can be used to check complex field computations, producing diverging values, with simple analytical equations.

A portable radio communication system operating in the 30 MHz band and capable of transmitting high-definition live underwater video images is presented. The system operation is based on launching electromagnetic surface waves propagating along water-air interface using specially designed surface wave antennas. Since the propagation length of the surface electromagnetic waves far exceeds the skin depth of bulk radio waves at the same frequency, this technique is useful for video communication underwater over distances of several meters. Also, this system appears to be efficient at communicating through the water-air interface.

This study investigates the absorption of the induced E‐field in homogeneous biological tissue exposed to highly localized field sources in proximity of the body, such as the charged tips of antennas, where E‐field coupling dominates. These conditions are relevant for compliance testing of modern mobile phones where exposure is evaluated at small separation between radiators and the body. We derive an approximation that characterizes the decay of the induced E‐field in the tissue as a function of distance. The absorption is quantified in terms of the local specific absorption rate (SAR) at the tissue surface as a function of the charge at the antenna tip. The approximation is based on the analytical evaluation of the E‐fields of a charged disk under quasi‐static conditions. We validate this approximation using full‐wave simulations of dipoles. We demonstrate that the coupling mechanism of the E‐field is dominated by the perpendicular field component and that wave propagation need not be considered for the characterization of the exposure. The surface SAR decreases approximately with the fourth power of the distance and with the square of the ratio of the permittivities of the tissue and free‐space. The approximation predicts the induced maximum E‐field with an accuracy of better than 1.5 dB. © 2022 Bioelectromagnetics Society.

This commentary, by three authors with an aggregate experience of more than a century in technology and health and safety studies concerning radiofrequency (RF) energy, asks what has been learned over the past 75 years of research on radiofrequency and health, focusing on technologies for exposure assessment and dosimetry. Research programs on health and safety of RF exposure began in the 1950s, initially motivated by occupational health concerns for military personnel, and later to address public concerns about exposures to RF energy from environmental sources and near-field exposures from RF transmitting devices such as mobile phones that are used near the body. While this research largely focused on the biological effects of RF energy, it also led to important improvements in exposure assessment and dosimetry. This work in the aggregate has made RF energy one of the best studied potential technological hazards and represents a productive response by large numbers of scientists and engineers, working in many countries and supported by diverse funding agencies, to the ever rapidly evolving uses of the electromagnetic spectrum. This review comments on present needs of the field, which include raising the quality of dosimetry in many RF bioeffects studies and developing improved exposure/dosimetric techniques for the higher microwave frequencies to be used by forthcoming communications technologies. At present, however, the major uncertainties in dosimetric modeling/exposure assessment are likely to be related to the inherent variability in real-world exposures, rather than imprecision in measurement technologies.