## 2 Origins in Medicine  
A century ago (1920) the first commercial radio station, KDKA, began broadcasting in Pittsburgh, sparking a revolution in the dissemination of information and entertainment directly to the public via radiofrequency signals [3]. The need to assess human exposure to RF energy gained importance with the advent of RF diathermy, which was first developed commercially by the General Electric Company (Schenectady, NY, USA) and Siemens (Erlangen, Germany) in the 1920s and subsequently widely adopted in physical medicine for therapeutic heating of tissue [4].  
Early pioneers in bioelectromagnetics, including [PERSON] (1915-2005) and [PERSON] (1928-2014), began their research careers investigating therapeutic uses of RF energy. [PERSON] did his doctoral, and later habilitation, research on electrical properties of tissue at radiofrequencies under the prominent radiation biologist [PERSON] (1893-1974), who had become interested in therapeutic applications of RF energy. After the war, [PERSON] was brought to the U.S. by the Navy and established a laboratory at the U.S. Naval Base in Philadelphia (1947). In 1950 he took an appointment in the Department of Physical Medicine at the University of Pennsylvania. He soon (1952) received a secondary appointment in the engineering school, where he remained for the remainder of his career [5].  
Originally trained as a radar engineer, [PERSON] began his academic career in the Department of Physical Medicine and Rehabilitation at the University of Washington, which was led by [PERSON] (1921-2006), a distinguished physiatrist with special interest in diathermy. [PERSON] maintained that appointment for many years, but took an adjunct appointment in the electrical engineering department as well as, at the university's Center for Bioengineering. As head of the Bioelectromagnetics Research Laboratory, he maintained a longstanding research program on the bioeffects of RF energy.  
Occupational safety concerns became a growing motivation for RF bioeffects studies. By the early 1950s, the US Department of Defense (DoD) had in operation a large number of high-power RF transmitters including communications and radar systems, with many shipboard transmitters operating in close proximity to personnel. Concerned about possible occupational hazards of such systems, DoD set up the Tri-Services Program (1956-1960), which funded RF bioeffects studies by prominent investigators at ten academic centers, including [PERSON]'s laboratory. The studies were small but overall were carefully done, with due attention to dosimetry within the capabilities available at the time.  
However, as one review put it, 'the art of microwave dosimetry was just emerging' [6]. Methods available at the time could provide only limited information about the distribution of absorbed energy in the exposed animal, and temperature control was often a problem. [PERSON]'s research focused on biophysical mechanisms of the interaction of RF fields with tissue and the dielectric properties of biological materials. [PERSON] and his colleagues pursued more applied topics. Starting in the early 1970s, he and his student, [PERSON] (now a senior leader in bioelectromagnetics and RF standards setting) carried out a series of animal studies that, even by present-day standards, stand out for high quality exposure assessment. Their technical advances include thermographic imaging of split, scaled-down models of the human body [7] to determine patterns of RF absorption within the body. [PERSON] was apparently the first to use the term specific absorption rate (SAR) in his PhD. thesis in 1975 [8].