Feature of Far Infrared Radiation : An Overview of Its Biomedical Application

(1)

MEMOIRS OF SHONAN

INST]TUTE OP TECHNOLOGV

VoL 28,No,1,1994

Feature

of

FarInfraredRadiation

-An

_Overview

_of

_Its

BiomedicalApplication-TadashiFusE*

and

Masao

TAKi**

This

_paper

_presents

an overview of

the

biomedical

applications of

far

infrared

radiatien.

Far

infrared

radiation of

5-30

micrometer wavelengths

is

dealt

with

in

the

case of

the

applications utilizing

incoherent

radiation, and wavelengths

longer

than

about

30

rnicrometers are

taken

as

the

object of

interest

when spectroscopic technology

is

concemed.

First,

_penetration

of

far

infrared

radiation

into

biolegical

tissues

is

described

which

is

the

basis

for

the

biomedical

applications of

far

infrared

radiation.

Second,

the

biomedical

application utilizing

thermaL

effects of

far

infrared

radiation;

temperature

measurement,

infrared

thermography

and

_physical

therapy.

is

reviewed.

Third,

far

infrared

spectroscopy and related

_technology

are examined.

From

the

spectroscopic point of view,

millimeter waves and microwaves are also considered, especially when extremely

large

molecules of

the

biological

bodies

are concerned,

Finally,

_possibility

of nenthermal effects of

far

infrared

radiation

to

the

biological

bodies

is

investigated

based

on a

theoretical

model

_proposed

by

H. FrOhlich.

1. Introduction

When

one

discusses

far

infrared

radiation,

it

is

necessary

to

define

the

range of wavelengths of

far

infrared

because

various

definitions

of

far

infrared

exist.

The

wavelengths of so called

far

infrared

range

from

about

25

micrometers

through

1

millimeter.

It

is

over

this

range

that

the

rotation spectra appear

in

molecules of

great

interest

to

the

discipline

of spectroscopy.

0n

the

other

hand,

it

extends

down

to

about

5

micrometers

in

those

applications which utilize

the

energy of

far

infrared

radiation such as

infrared

heating.

For

further

information

about

the

classification

of

far

infrared

radia-tion

in

terms

of wavelengths, refer

to

refer-encei},

Further,

in

this

latter

case,

the

actual

wave-lengths

of

interest

are not

longer

than

about

30 micrometers

because

the

emitted

energy

of

the

radiation

is

decreasing

sharply

beyond

30 mi-crometers.

Thus

the

term

far

infrared

is

actual-ly

used

to

denote

different

wavelength ranges

separately corresponding

to

far

infrared

spec-*

_{asfi]le]ijiSP}

_tyma,

**

_{MRas.iZrt\I7zz}

SIZut

₅

_al

_lO

n

₁₂

_H･xr!Ltit

troscopy

or

far

infrared

heating.

So

we

discuss

far

infrared

radiation

here

according

to

each

definition

explained

above.

That

is,

when

we

deal

with

far

infrared

in-coherent radiation, wavelengths of

5 through

30 micrometers

are

taken

as

the

wavelength

range

for

discussion.

When,

however,

we

deal

with

far

infrared

spectroscopy or

far

infrared

technology

utilizing coherent radiation,

wave-lengths

longer

than

about

30

micrometers are

taken

as

the

object of

interest

Furthermore,

from

the

viewpoint

of

continu-ity

in

the

nature of

_coherent

_radiation,

when

we

deal

with

the

technology

utilizing coherent

radiation, millimeter waves and microwaves

will also

be

_properly

included.

According

to

this

classification,

the

biomedical

applications

of

the

C02

laser,

whose wavelengths are

1O's

of

micrometers, are excluded.

This

subject

is

to

be

discussed

specifically

by

other experts.

2. Penetration

of

Far

Infrared

Radiation

into

Biological

Tissue

An

important

basic

knowledge

required

to

discuss

the

biomedical

applications of

far

infra-red radiation

is

the

_penetration

characteristics

(2)

maMIRFrt7keee

ag

28 g

ag

1 e

10-=: 10,taEti-loiklitrHltg loug:Eei( 10p- 100vn 1an 10"r- 100nt- 1" 10-V-VELEHCTII

Fig.

1. Attenuation

coeMcient of

biological

tissues.

T=::es::zats-Figure

1 shows

the

attenuation coefficient of

biological

tissue

to

electromagnetic radiation

ranging

from

radiowaves

through

infrared

radiation2].

An

incident

plane

electromagnetic

wave

_passing

into

the

material

is

regarded,

in

most

cases,

as

attenuating

exponentially

as

it

proceeds.

Although

various expressions

have

been

employed

to

express

the

_quantity

of

the

attenuation

depending

on

the

wavelengths,

here

in

Figure

1,

the

attenuation

characteris-tics

are

presented

in

terms

of

the

attenuation

coeMcient,

in

dB/cm.

The

_penetration

depths,

which are

defined

by

the

distance

where

the

energy of

the

incident

radiation

is

decreased

to

e-i with respect

to

the

value at

the

surface, are

also

shown

in

Figure

1,

Because

the

biological

tissues

contain a

large

arnount

of

water

which absorbs

far

infrared

radiation strongly,

the

transparency

of

the

bio-logieal

tissues

to

far

infrared

radiation

is

very

low

as

shown

in

Figure

1. Consequently,

most

of

the

incident

far

infrared

radiation

passing

into

the

biological

tissue

is

absorbed

in

the

vicinity of

it's

surface.

Although

some

biolog-ical

tissues

with

less

water content show a

slightly

higher

transparency,

the

values of

the

penetration

depth

for

dehydrated

biological

tissues

are

no

more

than

three

times

larger

at

the

most

than

those

at

their

natural

state,

Judging

from

these

facts,

it

is

reasonable

that

the

present

biomedical

applications of

far

in-frared

radiation

have

been

those

taking

advan-tage

of

their

strong absorption characteristics,

and very

few

biomedical

other characteristics of

far

infrared

radiation

have

been

seen

in

the

case

of

in

vivo

so

far.

3. Applications

of

Far

Infrared

Radiation

to

Biomedical

Engineering

TemPerature

Measurements

and

in,frared

71hermograPhy:

The

energy

distribution

of

the

radiation emitted

frorn

a

black

body

at room

temperature,

including

the

human

body

tem-perature,

shows a

_peak

around

1O

micrometers

in

wavelength.

The

biological

tissues

also

show

large

values

of

the

radiation

coefficients

at

those

temperatures

as well as

large

values of

absorption

coefficients,

and

the

measurements

on

the

temperatures

of

the

human

body

sur-face

have

been

widely

_practiced

utilizing

these

characteristics.

The

value of

1.0 for

the

radia-tion

coefficient

of

the

skin

surface

has

been

frequently

_quoted

according

to

Hardy3L

It

has,

however,

been

_pointed

out

that

Hardy's

method

of

measurement

was

incorrect

and

it

is

said

that

the

actual value

is

slightly smaller

than

1.04).

This

fact

can

be

a

_problem

in

those

(3)

tempera-Eeature

of

Jinr

1}ofrared

Radiation

ture

of

the

body

surface

is

needed.

Thermography

which supplies valuable

clin-ical

information

is

one of

the

most

firmly

estab-lished

technologies

among

the

medical

applica-tions

of

infrared

radiation.

It

is

a

tool

for

obtaining

the

temperature

distribution

image,

which

is

formed

by

two-dimensional

scanning

over

the

body

surface using radiation

ther-mometers.

It

takes

about

1

second

to

accom-plish

one

frame

of

the

image

by

means of

the

existing optical scanning

technique.

Recently

the

SPRIT

detector

has

been

developed

which

detects

pixels

on a scanning

line

in

parallel

and

which shortens

the

time

to

complete an

image

to

about

1/30

second.

As

a consequence, a

high

speed version of

time

series

images

of

the

tem-perature

distribution

on

the

surface of

the

human

body

has

become

feasible,

and

has

been

recognized

as

a

new

tool

for

the

measurement

of

_{physiological}

functions5L

Those

methods measuring

body

tempera-tures

by

means

of

detecting

the

heat

radiated

from

the

body

surface

take

advantage of

the

high

emissivity of

biological

tissues,

which

means a

high

absorption

in

the

biological

tis-sues as well,

This,

conversely,

implies

that

the

temperature

measurements

by

means of

this

method are

limitted

to

knowing

only

the

sur-face

temperature

of

skin,

and

information

about

the

temperatures

at

the

deep

_parts

of a

body

cannot

be

given.

So,

another

technique,

which

is

also

based

on

the

principle

of

radiation measurements,

is

used

for

temperature

measurements on

the

deep

_part

of a

body.

This

uses microwaves

whose wavelengths are

far

longer

than

far

in-frared

radiation6).

Rhysicat

Therupy

utitizing

har

infra7ed

Radia-tion:

A

thermal

therapy

using

infrared

radia-tion

has

long

been

practiced

which

helps

to

ease

pains

or

to

promote

blood

circulation.

In

many cases

infrared

Iamps,

which

_get

their

infrared

radiation

by

eliminating

the

visible

components

from

the

emitted

light

from

ther-mal

lamps,

have

been

used as

the

infrared

radi-ator.

In

those

cases

the

wavelength of

the

infrared

radiation

is

centered around

1

mi-crometer.

On

the

other

hand,

comparatively

low

tem-perature

heaters

whose surfaces are coated

by

ceramics

with

high

emissivity

for

far

infrared

have

also

corne

to

be

employed recently.

Al-though

favorable

effects of

far

infrared

heating

on

human

bidoes

have,

sometimes.

been

em-phasized

by

some

_{practitioners,}

their

mecha-nisms,

however,

have

not

been

clarified.

Since

the

absorption of

far

infrared

radiatien

is

ex-tremely

strong

in

biological

tissue

as

stated

in

section

2,

most

of

the

energy

of

the

incident

far

infrared

radiation

is

dissipated

near

the

skin,

say within some

100

micrometers

in

depth

from

the

surface.

Therefore

_a

doctrine

_of

"penetrability

of

far

infrared

radiation

in

the

human

body",

which

has

after

been

em-phasized

by

some

_people

in

the

field

of

thermo-therapy,

is

not

due

to

the

_penetration

of

far

infrared

radiation

itselL

However,

far

infrared

thermotherapy

has

a

feature

in

its

high

conversion

efficiency

from

the

electromagnetic

energy

to

heat

energy

in

the

biological

tissues,

The

far

infrared

thermo-therapy

also

has

an advantage over

the

exist-ing

infrared

thermotherapy

in

terms

of

uni-forrnity

of

heating

which results

from

the

fact

that

it

makes

the

size of

the

light

source

larger

in

order

to

_produce

the

necessary amount of

illuminance.

In

contrast

to

this

method, a

device

which

heats

the

deep

part

of

the

human

body

using

infrared

lamps

equipped with a

O.9-1.2

mi-crometer

bandpass

filter

is

commercially

avail-able.

This

near

infrared

version of

thermo-therapy

has

_quite

opposite

features

to

far

infra-red version

in

that

it

heats

the

deep

_parts

of

the

human

body

suppressing erythema caused

by

the

temperature

rise at

the

skin surface, since

near

infrared

radiation with wavelengths of

O.9-1.2

micrometers

has

an

extremely

high

penetrability

into

the

human

body7).

In

this

case,

the

_ground

for

adopting near

infrared

radiation as a means of

heating

is

clear.

Although,

it

has

not

been

clarified

which

is

preferable

as a means of

heating,

far

infrared

or

near

infrared,

the

result of a

_study

_comparing

the

heat

sensitivity of

the

human

body

to

near

(4)

meetIrv)it#eet

ag

28 g

ee

1 _e

Matsui8).

According

to

these

results,

man

is

likely

to

feel

more "heat

with

_pain"

when

ex-posed

to

infrared

radiation

(1.5-4.8

micrometer

and

6-20

micrometer

wavelength>

than

when

exposed

to

near

infrared

radiation

(O.72-2,7

micrometer

wavelength)

under

the

same

amount of

illuminance.

As

Matsui

commented,

near

infrared

radiation

has

high

reflectability

as well as

high

_{penetrability,}

therefore

the

net

energy

absorbed

by

a

human

body

is

small.

These

characteristics are

_partly

refiected

in

these

results.

So,

in

discussion

of

the

biological

effects of

infrared

radiation,

it

is

necessary

to

compare

far

infrared

radiation

with

near

infra-red radiation

in

terms

of

their

_{physiological}

effects,

as

well

as

their

sense

of

warmth

at

equal values of specific absorption rate.

Besides

thermal

applicators

which

use

far

infrared

heaters,

a

textile

sheet coated with

ceramics

of

high

far

infrared

emissivity

has

also

been

tested

for

therapeutic

applications.

In

this

case no

heaters

are

involved.

Although

it

has

been

reported

that

the

device

was

effec-tive

in

maintaining warmth,

its

scientific

basis

has

not

_yet

been

illustrated.

In

short,

although

far

infrared

technology

has

come

to

be

introduced

into

various

branches

of medical application9).

clear

illustra-tions

have

not

been

_given

a$

to

what

is

the

crucial

_point

for

each medical application of

the

far

infrared

radiation.

This

is

_partly

due

to

the

fact

that

little

analytical

investigation

on

the

effects of

far

infrared

radiation

on

biologi-cal

bodies

has

been

made

based

on

the

theory

of

heat,

Assessment

of

far

infrared

thermal

therapeutics

should

_properly

be

made on

the

above

mentioned

_ground$.

4. Biomedical

Applications

of

Far

Infrared

Radiation

in

Terrns

of

Spectroscopy

har

infrared

SPectroscopy:

The

far

infrared

region of wavelengths

longer

than

about

30

micrometers

is

where

the

molecular retation

spectra are observed,

This

wavelength region

also coincides with

that

of

the

skeletal

vibra-tions

of

the

biological

macro-molecules.

There-fore,

far

infrared

radiation

is

important

in

the

spectroscopic study of

the

structure of

DNA

and

proteins

which

_play

important

roles

in

biological

bodies,

However,

far

infrared

spec-troscopy,

even

by

means of

the

highsensitive

Fourie

transform

spectroscopy,

has

not

been

able

to

_provide

sufficient

informatien

to

con-tribute

to

biomedical

engineering except

for

some

basic

research,

This

is

because

far

infra-red radiation

is

strongly absorbed

in

the

water

contained

in

the

biological

tissue$,

and also

because

the

spectroscopic experiments need an

amount of specimen which

is

not available

from

the

biological

tissues,

The

extremely

high

cost

of

the

experimental

apparatus

for

far

infrared

spectroscopy

_may

_also

have

impeded

the

spectroscopic experiments.

Raman

spectroscopy

is

considered

to

be

more useful

to

_obtain

information

in

_the

far

infrared

region

from

biological

tissues

than

is

common spectroscopy

by

means

of

the

direct

use

of

the

far

infrared

radiation.

Thus,

_present

spectroscopic researches

on

biological

materi-als

have

been

made mainly

by

means

of

the

low

oscillating

frequency

Raman

spectroscopy

excited

by

visible

light.

Considering

the

_strong

absorption

of

far

infrared

radiation

in

water,

it

is

clear

that

this

method

is

superior

to

common

spectroscopy

for

the

biological

materials

which,

in

most cases. contain

large

amounts of

water.

The

longitudinal

acoustic modes are

ob-served

in

the

macro molecular chains

by

means

of

Raman

spectroscopy.

Since

the

Raman

scat-tering

frequencies

are

inversely

_proportional

to

the

length

of

the

ma ¢ro molecular chains,

the

Raman

scattering

frequencies

observed

in

extremely

large

molecules of

the

biological

bodies

range not

_only

over

_the

far

infrared

region

but

also extend

to

rnillimeter waves and

microwaves.

For

example,

it

has

been

es-timated

that

the

Raman

scattering

frequency

in

a

long

macro molecular chain such as

the

DNA

molecules would

be

6GHz

(O.2cm-i>tOL

Therefore,

from

the

spectroscopic

_point

of

view,

far

infrared

radiation can

be

reasonably

considered alongside millimeter waves and

mi-crowaves.

The

photon

energy of

far

infrared

radiation

(5)

mole-Eeatute

_of

thr

Icbared

Radiation

cules of

biological

material and also

less

than

the

thermal

agitation energy at room and

body

temperature.

Therefore,

along with

_the

strong

absorption

of

far

infrared

radiation

in

biologi-cal

tissue,

there

exists

a continuity

in

nature

among

the

radiation at

these

wavelengths,

Ac-cordingly, when

investigating

the

biological

effects of

far

infrared

radiation

in

terms

_of

spectroscopy,

it

should

be

natural

to

consider

wavelengths

beyond

1

millimeter and up

to

the

mlcrowave reglon,

Although

the

present

state of art of

far

infra-red spectroscopy

for

clinical applications

is

far

from

promising,

it

is

considered

that

its

impor-tance

to

basic

research will

_grow.

Ilossibildy

_of

IVbnthermat

Efacts:

Although,

apart

from

basic

research,

far

infrared

radia-tion

has

not

been

intreduced

into

clinical

appli-cations as

far

as we

know,

the

interaction

be-tween

the

in

this

region

and

biological

bodies

is

attracting

inter-est.

This

is

_on

the

_ground

_of

_the

safety

prob-lems

the

effect of electromagnetic

radiation

on

biological

bodies,

These

safety

problems

have

been

pointed

out

from

various

fieldsii).

The

biological

effects of electromagnetic

ra-diation

have

been

discussed

by

classifying

them

into

two

categories, namely,

the

thermal

effects and

the

nonthermal effects.

The

ther-mal effects are

the

ones arising

from

the

tem-perature

rise

caused

by

absorption

of

the

elec-tromagnetic

energy

in

biological

bodies,

while

the

nonthermal effects are

the

ones

developed

directly

by

the

electromagnetic

field.

A

theoretical

model

_proposed

by

H. Fr6hlich

has

been

well

known

since

the

1960's

and

which attempts

to

describe

the

mechanisms

_of

the

nonthermal effect of

the

electromagnetic

field

at

frequencies

from

submillimeter waves,

the

longest

wavelength region of

far

infrared

radiation,

through

microwavesi2).

This

theoret-ical

model

is

summarised as

follows:

Coherent

oscillations exist

in

biological

bodies,

and

they

have

a nonlinear

interaction

between

them

which

_plays

an

important

role

in

controlling

the

function

of

the

cells.

This

is

through

the

intervention

of

the

energy

transfar

between

the

large

number of

tion

modes

in

_proteins

and

_the

biological

membranes.

Fr6hlich

has

derived

the

following

conse-quences:

1)

The

oscillations

have

a metastable

_state

with strong electric

_{polarization.}

2)

In

the

case

that

energy

is

applied

to

them,

the

oscillations concentrate on a

specific mode and an excitation with a

macroscopic order

takes

_place,

3)

A

long

distance

interaction

between

the

oscillation modes of

identical

frequency

exlsts.

Fr6hlich,

based

on

these

consequences,

has

also

_predicted

that

ranging

from

far

infrared

radiation

through

microwaves

has

nonthermal effects on

biologi-cal

bodies.

Among

the

early experiments with regard

to

this

theory

is

a study

made

by

Webb

et

al.

This

has

been

well

known

and

has

shown

that

the

Raman

shift

lines

with

law

wave number

(

tr

40

cm-i) are observed only at a

_paticular

stage of

development

of

the

synchronized active cells

ofE coli

bacteria.

Their

study

has

also shown

that

the

ratio

R

of

the

intensities

of anti-Stokes and

Stokes

Raman

shift

lines

of

124cm-i

and

ef

118cm-i

of

active

EL

coti.

B. bacten'a

would

be

measured and

found

to

be

R21.0

which

is

far

above

the

thermal

equilibrium value.

This

implies

that

the

biological

system was excited

strongly above

thermal

excitationi3),

Many

researches with regard

to

Fr6hlich

model

followed

Webb

et al.'s

and a symposium

on

the

subject was

held

in

1982i`L

Arnong

the

results of

those

studies,

the

experiments

con-ducted

by

Grundler

et al, are noted as a very

good

agreement with

FrOhlich

model.

They

have

reported

that

the

growth

rate of

_yeast

cultures was strongly enhanced or suppressed

under

the

influence

of millirneter waves

in

the

vicinity of

42GHz

according sharply

to

fre-quency

deviations

of only

8MHzi5),

Despite

their

experiments

being

carried

out extremely

carefully

in

order

_to

_avoid

artifacts,

Furia

et aL

repeated

the

experiment and reported

_quite

(6)

mamr*gv<%Eg

eg

2s

g

eg

1e

problem

of nonthermal effects of millimeter

waves on

the

_growth

rate

of

yeast

cultures

has

not

_yet

been

brought

to

_a

conclusioni7).

Several

studies on

the

effect of

the

electro-magnetic radiation on

the

functions

of

biologi-cal membranes

have

been

reported and

indi-cate

the

_possible

influence

of

the

electromag-netic radiation on

the

_phase

transformation

of

the

biological

membranes and conformation of

proteinsi8)･i9L20}.

It

is

noted

that

all of

these

researches were carried out

_paying

attention

to

the

temperature

dependent

characteristics

of

the

function

of enzymes and

the

permeability

of

the

biological

membranes.

If

the

electromag-netic radiation should

_produce

_physical

effects

on

the

functions

of

the

biological

membranes,

then

_possible

application of electromagnetic

radiation

to

controlling

the

function

of

the

membranes would

be

expected.

Many

researches on

the

nonthermal

_effects

of

the

electromagnetic

radiation on

biological

bodies

have

been

conducted at relatively

long

wavelengths

_up

to

the

microwave region,

This

is

due

to

the

needs arising

from

the

safety

problems

associated with

electromagnetic

compatibility.

Readily

available

instrumenta-tion

at

the

high

frequency

region

_up

to

micro-waves may

also

be

another reason

for

much of

the

research.

However,

in

reference

to

the

Fr6hlich

rnodel,

the

shorter wavelength

reg-ions

such as millimeter waves and

far

infrared

radiation are of

interest

in

terms

of

the

interac-tien

between

the

electromagnetic

radiation

and

biological

bodies

in

association with

the

skeletal vibrations

in

the

biological

molecules.

No

hard

experiments on

the

effects of

far

infrared

radiation on

biological

bodies

has

been

reported, except

for

a

few2}.

In

order

to

open a new

_phase

in

the

application of

far

infrared

radiation

to

biomedical

engineering,

further

basic

investigation

about

the

interac-tion

between

far

infrared

radiation and

biolog-ical

bodies

is

necessary,

5. Con

¢

ludingRemark

With

regard

to

the

applications of

far

infra-red radiation

to

biomedical

engineering,

the

tendency

to

consider

biomedical

applications

utilizing

thermal

effects of

far

infrared

radia-tion,

and

the

possibility

of

biomedical

ap-plications

in

terms

of

spectroscopy

has

been

reviewed.

In

short,

the

_present

state of

this

discipline

is

_premature

in

terms

of

basic

knowl-edge except

for

some

particular

technology,

In

other words,

it

may

be

said

that

the

far

infrared

region

has

so

far

been

exceptionally neglected

throughout

the

entire wavelength

band

of

elec-tromagnetic

radiation.

However,

the

technolo-gy

which

fi11s

up

the

_gap

between

light

and

microwaves

is

making

remarkable

_progress

and so

it

is

anticipated

that

the

application of

far

infrared

radiation

to

biornedical

engineer-ing

will

be

materialized step

by

step.

References

1)

1986

Joint

National

Convention

Record

of

tutions

of

Electric,

Information

and related

gineers,

part

2 (1986),

25-49

(in

Japanese),

2}

T. Fuse

and

M,

Taki,

Paper

of

Tech.

Group

on

Application

ef

Light

and

Visual

Sence,

I.E.E.

Japan.

LAV-87-l

(1987)

(in

Japanese).

3)

J.

D. Hardy

and

C. Mushenheim,

J,

Clinical

Invest.

13 {1934),

817-831.

4)

T. Togqwa,

BME,

2,

3{1988),

156-160

{in

nese).

5)

L

Fujimasa,

BME,

2.

3 (1988),

180-184

_(in

nese),

6)

S. Mizushina,

BME,

2,

3 (1988),

171-174

{in

anese),

7>

T. Arai,

O

plus

E,

70 <1985),

94-101

<in

nese).

8)

M. Matsui,J,

Japan

So.

of

Infrared

Sc,

and

Tech.

12 (1987),

18-26

(in

Japanese).

9)

Kogyogijutsu-kai,

Up-to-date

Technology

of

Far

Infrared

Application

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(in

Japanese).

10)

M. TsuboL

Kagakuno

Ryoiki

(Chemical

Field),

139-Ex,

(1983),

119-134

(in

Japanese).

11)

The

Ministry

of

Post

and

Telecommunications,

Report

of

Study

on

Electromagnetic

rnent around

Establishments

utilizing

magnetic

Waves

(1987)

(in

Japanese).

12)

H,

FrOhlich,

Advances

in

Electron

Phys.

53 (1981),

85-152,

13)

S. J,

Webb,

et at.

Phys.

Let.

69A

(1979),

408. 14)

tations

in

Biological

Systems

{1983),

Verlag.

(7)

Aeature

of

har

inhared

Radiation

16)

L. Furia,

et al,,

IEEE

Trans,

BME,

BME-33

{1986),

993-999.

17)

S.

M. Motzkin,

IEEE

Ninth

Anual

Conf.

Eng.

in

Med.

and

Bio.

Soc.

(1987},

446-447,

18)

M

Taki,

et at.

9th

Int'1

Conf.

on

Infrared

and

Millimeter

Waves

(1984),

24-25,

19)

J.

W. Allis,

et al.

Bioelectromagnetics,

3 (1987L

203-212.

20)

R,

P. Liburdy

and