Comments on "electric current and electric field induced in a human body when exposed to an incident - Microwave Theory and Techniques, IEEE Transactions on

736

IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 49, NO. 4, APRIL 2001

Author’s Reply

Ronold W. P. King

The entire series of comments by Lapin and Guy deals with the spe-

cific absorption rate (SAR). That is, their comments are concerned with

the temperature increase in the body due to microwave irradiation. Nei-

ther of the above papers

makes any claim that the microwave electric

fields to which radio amateur operators are exposed have any signifi-

cant thermal effect. The discussion in Section I of the above paper

2

shows that its concern was directed to the possible effect of microwave

radiation on the replication of cells. Lapin and Guy should study the

first two references in the above paper

2

(repeated here as [1], [2]). After

they have studied them, they may not be quite so sure that “there is ab-

solutely no basis for the conclusion that amateur radio operators are

at any health risk.” The effect of a microwave electric field on cells is

quite different from thermal effects in the body.

EFERENCES

[1] E. Pennisi, “Trigger for centrosome replication found,”

Science

, vol.

283, pp. 770–771, Feb. 1999.

[2] E. H. Hinchcliffe, C. Li, E. A. Thompson, J. L. Maller, and G. Sluder,

“Requirement of Cdk2-cyclin E activity for repeated centrosome repro-

duction in

Xenopus

egg extracts,”

Science

, vol. 283, pp. 851–854, Feb.

1999.

Manuscript received December 21, 2000.

The author is with the Division of Engineering and Applied Sciences, Gordon

McKay Laboratory, Harvard University, Cambridge, MA 02138-2901 USA.

Publisher Item Identifier S 0018-9480(01)02436-X.

R. W. P. King,

IEEE Trans. Microwave Theory Tech.

, vol. 48, no. 9, pp.

1537–1543, Sept. 2000.

R. W. P. King,

IEEE Trans. Microwave Theory Tech.

, vol. 48, no. 11, pp.

2155–2158, Nov. 2000.

Comments on “Electric Current and Electric Field Induced

in a Human Body When Exposed to an

Incident Electric Field Near the

Resonant Frequency”

William B. Bridges

In the above paper,

King calculates the induced current density

and electric field at the surface of a right circular cylinder modeling a

human being in size and composition, when illuminated by a vertical

dipole source 10-m distant with a power of 1 kW at 60 MHz. To quote

from the abstract of the above paper: “Since this frequency range in-

cludes an important amateur radio band of 50–60 MHz and exposure

to electric fields at this frequency has been shown to be hazardous, the

study has a specific motivation.” In his analysis, he derives a resonance

curve for his model human that peaks at 53 MHz. At the conclusion of

his paper, he gives the values of current density and electric field at

the body for his assumed parameters and states: “These values are sig-

nificant and provide a quantitative basis for the statistically observed

increases in malignancies in amateur radio operators.” This latter state-

ment refers to a study by Milham [1] of mortality in a population con-

sisting of men in California and Washington states that were listed by

the Federal Communications Commission (FCC), Washington, DC, as

possessing amateur radio licenses.

I will leave it to others to comment in detail on the merits of King’s

model and the actual biological effects of the current densities and

electric fields he calculates with this model. However, I will make the

following two observations on this matter: When using their transmit-

ters, the great majority of radio amateurs will be seated at a desk typi-

cally covered with metal boxes. Whether such a seated person is well

modeled as a right circular cylinder seems questionable to me. The

second observation is that King cites only microwave studies on mice to

show that electromagnetic radiation causes malignancies. Also, these

studies themselves are widely disputed. He then uses simple dimen-

sional scaling to show that 2.45 GHz for a mouse scales to 100 MHz

for a man. Such a scaling law may be useful in calculating the “res-

onant frequency” for a human subject versus a mouse when treated

as antennas, but such scaling is meaningless when the physics of a

hypothetical carcinogenic process are unknown. Would 100 MHz be

as effective as 2.45 GHz in causing cancer in a cell by this unknown

process? In fact, there is no unequivocal evidence that radiation at ei-

ther frequency causes cancer. Due to the variation of loss tangent with

frequency, 2.45 GHz is much more effective in

cooking

tissue than

100 MHz so that this

known

process does not scale as King proposes.

However, my main objection to King’s conclusions, quoted above in

this paper’s opening paragraph, is in the connection of his analysis to

[1]. First, let us look at the Milham study. Milham obtained the names

of 67 829 amateur radio license holders in the states of Washington and

California from the FCC files whose licenses were in force from Jan-

uary 1, 1979 to June 16, 1984. The death records in these two states

were then searched to obtain 2485 names matching those in the FCC

file. The deaths were sorted into many standardized

International Clas-

sification of Diseases

(ICD-8) categories. A striking result of the study

Manuscript received December 12, 2000.

The author is with the Department of Electrical Engineering, California In-

stitute of Technology, Pasadena, CA 91125-0001 USA.

Publisher Item Identifier S 0018-9480(01)02439-5.

R. W. P. King,

IEEE Trans. Microwave Theory Tech.

, vol. 48, no. 9, pp.

1537–1543, Sept. 2000.

IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 49, NO. 4, APRIL 2001

737

is that, for all causes, the 2485 deceased individuals had an overall mor-

tality rate of 71% of the norm for the U.S. population as a whole. From

this, you might conclude that holding an amateur license is definitely

healthy! (Milham speculates that this is due to a lower rate of cigarette

smoking among radio amateurs, but cites no statistics for this). Some

of his categories also have lower than normal mortality rates: All circu-

latory diseases, all respiratory diseases, all accidents, all cancers (when

grouped together) have mortality rates below 100% of the norm. How-

ever, two of the specific ICD categories had mortality rates exceeding

the norm: Code 202 (other neoplasms of lymphoid tissue) and Code

203 (multiple myeloma) taken together had 43 deaths when only 26.6

would be expected in the normal population, for a mortality rate of

162% of the norm. Milham gives a

significance for this rate,

implying a “one out of 20” probability that it is caused by chance alone.

However, since Milham divided his original data into several different

categories of cancer for analysis, it is much more likely than “one out

of 20” that

at least one

category would exceed the norm by this much

through chance alone. Thus, his 162% rate is not all that convincing

about cause and effect. The proper conclusion from the Milham study

would be that additional statistical studies of these cancers in larger or

different populations of radio amateurs may be warranted. It is inter-

esting that such studies were evidently not undertaken.

Next, let us consider some observations about amateur radio. The

frequency range specifically cited by King, i.e., 50–60 MHz, does, in-

deed include a range assigned to radio amateurs. Before Wold War II

(WW II), it was 56–60 MHz, i.e., the “5 meter band.” In its infinite

wisdom, the FCC changed this assignment to 50–54 MHz, i.e., the

“6 meter band,” following WW II in order to assign TV Channel 2

to 54–60 MHz, thus placing Channel 2 right on top of the harmonics

from all the lower frequency amateur bands and creating endless grief

for amateurs and TV viewers alike! Contrary to the impression given

by King’s statement that 50–60 MHz is “

...

a principal amateur-radio

frequency

...

,” the present 6-m band is arguably one of the least pop-

ular of all the amateur bands between 1.8–460 MHz. It is in only the

last few years (a decade after Milham’s mortality study) that this band

has been included in the popular “made-in-Japan 100 Watt high-fre-

quency transceiver” now used almost universally by amateurs. In the

years before the Milham study, 5- or 6-m gear was home built and low

power. It is likely that only a handful of amateurs the country possessed

a 1-kW 6-m transmitter.

What is the impact of this on the Milham study? Milham could say

nothing about the operating habits of the licensees he studied, beyond

citing a survey of 8895 members of the American Radio Relay League

in 1981 [2] that gave the “average amateur” as a 46 year-old male who

was first licensed in 1963 and spent a total of 6.1 h a week on his hobby.

Certainly nothing regarding whether or not the typical amateur used

a 1-kW transmitter on 50 MHz. Thus, we are reduced to guess work

about the operating habits of the individuals in the Milham study. You

may make your own guesses; as an active radio amateur for 51 years

(licensed 1949 as W6GEB, 1976 as W6FA), mine are as follows: 1% or

fewer ever used 6 or 5 m, 0.1% or fewer used it as a significant part of

their operating time, and fewer than 0.01% ever used 1 kW of power.

If correct, this would put 678, 68, and 7 as the number of amateurs

in the sampled population in these three categories. Thus, the overlap

between King’s physics and Milham’s statistics seems nearly zero.

It is usually not worth the effort to comment on “unwarranted con-

clusions” in the technical literature. If the subject is unimportant, who

cares? If the subject is important, further work will yield the truth. How-

ever, with a subject so “loaded” as electromagnetic radiation and human

health, coupled with a tabloid press that exaggerates dangers, or even

makes up new dangers, the possibility of a headline “Noted Harvard

Professor Proves Amateur Radio Causes Cancer” cannot go unchal-

lenged.

EFERENCES

[1] S. Milham, Jr., “Increased mortality in amateur radio operators due to

lymphatic and hematopoietic malignancies,”

Amer. J. Epidemiol.

, vol.

127, no. 1, pp. 50–54, 1988.

[2] Amer. Radio Relay League,

Amateur Radio Survey 1980; A Look at Ham

Radio as We Enter the Eighties

. Newington, CT: Amer. Radio Relay

League, 1981.

Author’s Reply

Ronold W. P. King

1) The claim that use is made of “simple dimensional scaling to

show that 2.45 GHz for a mouse scales to 100 MHz for a man”

is not correct. It is stated on the right-hand-side column of page

1537 of the above paper:

“

If scaling is assumed to be valid

according to the formulas

r

r

, where

is the frequency,

the half-length, and

the mean radius,

these results could be significant for humans. Specifically, with

100

MHz,

, and

for a man, and

, and

for a rat or mouse, the frequency

2450

MHz gives

100

2450

071

m or 7.1 cm. This is a

reasonable length for a rat or mouse. The validity of such scaling

is examined as part of this study.” Later, on page 1540 at the end

of Section IV of the above paper, it is stated: “An examination of

(3) for

and (27) for

1

(

)

shows that the radius

occurs in

2

and in

1

, not only as

2

as required for frequency scaling.

It follows that

scaling as described in the introduction and as

used by Gandhi [21] is not quantitatively valid in the frequency

range 50–200 MHz.

”

2) The author is grateful to Dr. Bridges for his detailed information

about the Milham study. Actually, it is irrelevant to the analytical

determination of the electric fields and currents induced in the

human body in the 50–200-MHz range. It seemed to provide

an additional motivation for studying this range. However, the

facts should have been looked into more closely or the reference

omitted. Actually, in the more recent detailed study in [1], no

mention is made of the Milham study until the very last sentence

where it is stated: “Although no direct correlation is possible, the

fact that statistical evidence found by Milham [17] indicates an

increase in malignancies in some radio amateur operators over

that of the general population should not be ignored.”

3) Dr. Bridges’ detailed information about frequencies used by am-

ateur radio operators is interesting, but not particularly impor-

tant with reference to the complete analysis in [1] of one actual

amateur radio setup. Reference [1] provides detailed formulas

Manuscript received December 21, 2000.

The author is with the Division of Engineering and Applied Science, Gordon

McKay Laboratory, Harvard University, Cambridge, MA 02138-2901 USA.

Publisher Item Identifier S 0018-9480(01)02435-8.

R. W. P. King,

IEEE Trans. Microwave Theory Tech.

, vol. 48, no. 9, pp.

1537–1543, Sept. 2000.