A telemetry device comprised of a pill-size ingestible transmitter developed to obtain deep body temperature measurements of a human is described. The device has particular utility in the medical field where deep body temperatures provide an indication of general health

Fryer, T. B.

Pope, J. M.

English

NASA Technical Reports Server

Pope et a]. 
[ 1 11 3,971,362 
[451 July 27, 1976 
1541 MINIATURE INGESTIBLE TELEMETER 
DEVICES TO MEASURE DEEP-BODY 
TEMPERATURE 
1751 inventors: Jack M. Pope; Thomas B. Fryer, 
[ 7 3 ]  Assignee: The United States of America as 
both of Saratoga, Calif. 
represented by the Administrator of 
the National Aeronautics and Space 
Administration, Washington, D.C. 
[ 2 2 ]  Filed: Oct. 27, 1972 
[21] Appl. No.: 301,418 
[52] U.S. CI. ................................ 128/2 P; 128/2 H; 
128/2.1 A 
[ 5  11 Int. CI .............................................. A61B 5/07 
[ 5 8 ]  Field of Search ......... 128/2 H, 2 P, 2 R, 2.1 A, 
128/2.1 R 
1561 References Cited 
UNITED STATES PATENTS 
3,218,638 1 1/1965 Honig .................................. 128/2 P 
3,274,994 9/1966 Sturm ................................. 128/2 H 
3,453,546 711969 Fryer ............................... 128/2.1 A 
3,465,103 9/1969 Lynch .............................. 12812.1 A 
3,719,183 3/1973 Schwartz ............................. 128/2 P 
Primary Examiner-William E. Kamm 
Attorney, Agent, or Firm-Darrell G. Brekke; Armand 
G. Morin; John R. Manning 
ABSTRACT 1571 
A miniature, ingestible and encapsulated telemeter de- 
vice for transmitting information relating to deep-body 
temperature of a subject comprising a battery source 
of power, and a free running multivibrator circuit hav- 
ing fixed biasing means connected to oscillator having 
a predetermined resonant frequency. A thermistor 
having a negative temperature coefficient of resistance 
is connected to the battery and the fixed biasing means 
and is operative to vary the output frequency of the 
multivibrator circuit in proportion to the temperature 
of the thermistor, the oscillator being pulsed into aler- 
nate states of conduction and non-conduction at the 
output frequency of the multivibrator to produce an 
output consisting of bursts of energy at the predeter- 
mined resonant frequency, preferably in the range 88 
- 108 MHz. The time interval between successive 
bursts is proportionate to the deep-body temperature 
of the subject, and the thermistor having a very high 
resistance below a predetermined low temperature to 
cause inactivation of the multivibrator circuit and 
thereby only insignificant battery drain during refrig- 
erated storage. A radiating inductor is connected to 
the output of the oscillator to transmit the bursts to a 
receiver. 
8 Claims, 1 Drawing Figure 
https://ntrs.nasa.gov/search.jsp?R=19760022806 2020-03-20T02:21:42+00:00Z
3,971,362 
3,971,362 
1 
MINIATURE INGESTIBLE TELEMETER DEVICES 
TO MEASURE DEEP-BODY TEMPERATURE 
ORIGIN OF THE INVENTION 
The invention described herein was made by employ- 
ees of the United States Government and may be man- 
ufactured and used by or for the Government for gov- 
crnmental purposes without the payment of any royal- 
ties thereon or therefor. 
BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to a telemetry device compris- 
ing a pill-size ingestible transmitter to obtain deep-body 
temperature measurements of a human or other sub- 
ject. It has particular utility in the medical field wherein 
deep-body temperatures provide an indication of gen- 
eral health. 
2. Description of the Prior Art 
In1 the past, deep-body temperature has been mea- 
sured by hard-wired thermistor ear-probes that must be 
fitted to the subject's ear in intimate contact with the 
ear drum. This places the subject in constant discom- 
fort. Thus, U.S. Pat. No. 3,274,994, Sturm, discloses a 
transmitter inserted into the patient's ear comprising a 
multivibrator controlled by a thermistor, wherein the 
multivibrator is activated when a predetermined tem- 
perature is reached. 
Ingestible transmitters that were first developed were 
primarily blocking-oscillator telemetry devices using a 
single transistor as the active element. These devices 
are simple, but their long-term stability is rather poor 
and their transmission distances are quite limited. More 
complicated, stable and accurate transmitter units were 
later developed for long-term implant. However, these 
units are large and expensive. 
The life of battery-powered telemeters is dependent 
on the size of the battery, and a large battery cannot be 
used if the telemeter is to be ingested. A typical battery 
for ingestible use has a life rating of approximately 
16mAH and cannot be remotely controlled. Therefore 
they constantly draw current from the time the teleme- 
ter device is constructed and imbedded in a capsule for 
ingestion, and must be used immediately if they are to 
have a practicable period of use. 
Passive devices are also known in the art. U.S. Pat. 
No. 3,229,684, Nagumo et al., discloses a passive tele- 
metering device for physiological measurements which 
may include a Colpitts oscillator. A thermistor is uti- 
lized to vary the time constant variation of a base cir- 
cuit to affect the oscillating frequency of the transmit- 
ter, dependent upon the temperature of the thermistor. 
Power is supplied to the device by electromagnetic 
induction from an external source. U.S. Pat. No. 
3,407,363, Kaiser et al., also discloses an external 
power source for a passive implantable FM transmitter, 
as does U.S. Pat. No. 3,231,834, Watanabe, which 
relates to a passive telemetering system wherein the 
transponder response time is proportional to the mea- 
sured variable. 
SUMMARY OF INVENTION 
This invention provides a pill-size ingestible active 
transmitter unit which is relatively simple and inexpen- 
sive. The unit may be refrigerated for storage, and in 
this quiescent state draws an insignificant amount of 
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current from the battery. It is thus not necessary to 
immediately use the unit after construction thereof. 
The unit is imbedded in a capsule for ingestion by the 
subject. The circuitry includes a small battery con- 
nected to energize a multivibrator, buffer amplifier, 
oscillator and radiating inductor. The frequency of the 
multivibrator circuit output is determined by the tem- 
perature of a thermistor which is correspondingly de- 
termined by body temperature of the surrounding am- 
bience. The thermistor has a very high resistance when 
refrigerated and is connected to the battery and the 
biasing circuit of the multivibrator to cause the unit to 
draw an insignificant amount of current when refriger- 
ated. 
When in use, the temperature of the thermistor dc- 
termines the operating frequency of the multivibrator, 
which pulses the oscillator causing it to emit bursts of 
energy at the frequency of operation of the multivibra- 
tor, the time interval between successive bursts being 
proportionate to the thermistor temperature. The en- 
ergy bursts are applied to a radiating inductor to pro- 
vide a corresponding electromagnetic field for trans- 
mission to the receiver. 
A buffer amplifier may be connected between the 
multivibrator and the oscillator to minimize any fre- 
quency modulation of the oscillator which might other- 
wise produce an erroneous temperature indication. 
The oscillator preferably operates in the 88 to 108 
MHz band in order that commercially available FM 
receivers may be utilized. 
BRIEF DESCRIPTION OF THE DRAWINGS 
The FIGURE is an electrical schematic diagram of 
the pill-size, ingestible transmitter according to the 
invention. 
DETAILED DESCRIPTION OF THE INVENTION 
The FIGURE shows a free running multivibrator' 
including complementary transistors T1  and T2, which 
periodically conduct to produce an output having a 
frequency which depends upon their biasing condi- 
tions. Transistor T1  is an NPN transistor with its collec- 
tor being connected through load resistor R2 to the 
positive supply terminal of internal battery power sup- 
ply 10, and its emitter being connected to the negative 
supply terminal thereof. Transistor T2 is a PNP transis- 
tor, with its emitter being connected to the positive 
supply terminal, and its collector being connected 
through load resistor R5 to the negative supply termi- 
nal. The oscillator is basically a two-stage R-C coupled 
amplifier with appropriate feedback connections there- 
between. Resistor R3 is connected in parallel with the 
series connection of resistor R4 and capacitor C2, to 
couple the output of the stage comprising transistor T2 
to the base input of transistor TI. The output of the 
stage comprising transistor T1  is coupled to the base 
input of transistor T2 through the series connection of 
resistor R1 and capacitor C1. The operation of the free 
running oscillator so far described is conventional and 
is therefore not detailed herein. The output frequency 
depends upon the biasing elements connected therebe- 
tween, and specifically resistors R1, R2, and R4, and 
capacitors C1 and C2. 
Thermistor 11 is, however, connected between the 
series connection of basc of transistor T2 and resistor 
R1, and the negative supply terminal. It has a negative 
temperature coefficient and, at a temperature mea- 
sured at 25"C., a very high resistance of approximately 
3,97 1,362 
3 4 
6 megohms. As thc tcmpcrature of thermistor 11 in- buffer amplifier, oscillator, and radiating inductor com- 
creases, its resistancc decreases by a proportionate prises a miniature unit which may be fitted into a size 
amount which causes a corresponding change in the zero (0) gelatin capsule (approximately 10 mm. in 
biasing condition of the multivibrator circuit and con- length and 5 mm. in diameter), and then sealed with 
sequently the output frequency thereof, as explained 5 vinyl-acetate-beeswax and two coatings of silicone rub- 
hereafter. 
In order to drive transistor T2 into conduction, a 
sufficiently negative signal must be applied to its base. 
If the resistance of thermistor 11 is sufficiently high, 
due to a low enough temperature, il sufficiently nega- 
tive signal will not be applied to the base of transistor 
T2 and it will not be driven into conduction. As the 
temperature of thermistor 1 1 increases, its resistance 
decrcases, causing the base of T2 to become morc 
negative with respect to its emitter and driving transis- 
tor T2 into conduction. By complementary multivibra- 
tor action, transistor T2 then drives transistor T1 into 
conduction which causes transistor T2 to conduct even 
more heavily. This regenerative action continues until 
there is no-further increase in conduction in either 20 
transistors T1 or T2. Capacitor C1 then begins to 
charge through Rl ,  R2 and thermistor 11 until it is 
charged positive enough to cause transistor T2 to cease 
conduction. This causes transistor T1 to also cease 
conduction. Capacitor C 1 then starts discharging 25 
through R1 and thermistor 11 until the base of T2 
becomes negative enough to drive transistor T2 into 
conduction again. Regenerative action causes the cycle 
to repeat. Since the discharge path of capacitor C1 
includes thermistor 11, the lower its resistance value, 30 
the faster the discharge rate of capacitor C1, the faster 
the discharge rate of capacitor C1, the faster the rate at 
which transistors T1 and T2 arc driven into conduc- 
tion, and thus the higher the multivibrator frequency. 
Capacitor C2 and R4 control the conduction time of 35 
transistors T 1  and T2 while R 3  limits the base current 
of transistor T1. 
The multivibrator output is applied to a buffer ampli- 
fier comprising PNP transistor T3, through the connec- 
tion of resistor R6 to the base of transistor T3. The 40 
buffer amplifier functions to prevent frequency modu- 
lation of the oscillator which might otherwise produce 
an erroneous temperature indication. The buffer ampli- 
fier output is connected to a conventional Colpitts 
oscillator comprising transistor NPN T4, inductor L1, 45 
capacitors C4 and C5, and resistor R8. The Colpitts 
oscillator is tuned to resonate within the radio fre- 
quency rangc 88 through 108 MHz, in order that con- 
ventional FM receivers may be employed to receive the 
transmitted information. The tuned section of the oscil- 50 
lator comprises tapped inductor L1, and capacitors C4 
and C5. Inductor L1 is tapped to provide appropriate 
impedance matching for radio frequency radiating ele- 
ment L2, connected to the output of the oscillator 
through DC decoupling capacitor C6, and which trans- 5 5  
mits the RF signals to an FM receiver. 
The oscillator is alternately activated and deactivated 
at the output frequency of the multivibrator in response 
to the alternate positive and negative output signals 
therefrom. The oscillator thus periodically emits bursts 60 
of RF energy, with the time interval between bursts 
being inversely proportional to the temperature of the 
thermistor. These bursts are applied to the radiating 
inductor L2 for transmission to the receiver. 
active circuit which has proven accurate to 3. I "C. 
from 35°C. to 45°C. The complete device including 
battery, thermistor controlled multivibrator circuit, 
The described temperature telemeter comprises an 65 
ber; The unit is easily ingcstible and is-capable of being 
held by the  subject for approximately 35 hours, de- 
pending upon diet and activity. Completed units have 
been tested by immersion for 35 hours in a hydrochlo- 
0 ric acid solution of pH 1 at 45°C. to insure the integrity 
of the coatings which prevent the gelatin capsule from 
dissolving. 
Nominal current drain from the battery at body tem- 
perature is 25 microamperes, and the operating life of 
5 the encapsulated device is approximately 600 hours. 
The current drain of encapsulated units can be reduced 
to negligible values by storage at approximately O"C., 
thereby extending the storage time indefinitely. Also 
the transmitter does not require critical-tolerance 
parts. 
Capacitor C7, capacitor C3  and resistor R7 provide 
conventional functions and are therefore not described 
herein. It should be evident that the types of transistors 
shown and described may be changed, and that an 
oscillator other than a Colpitts oscillator may be used 
without departing from the scope of the invention. 
I claim: 
1. A miniature, ingestible telemeter device for trans- 
mitting information relating to deep-body temperature 
of a subject comprising: 
a free-running multivibrator having complementary 
transistors; 
an r-f oscillator having a predetermined resonant 
frequency, said oscillator including an inductor for 
radiating r-f energy; 
a buffer amplifier coupled between said multivibrator 
and said oscillator; 
a battery connected to said multivibrator, said buffer 
amplifier, and said oscillator; 
said free-running multivibrator having temperature- 
sensitive circuit means for turning on and off said 
multivibrator and controlling its output pulse fre- 
quency when in the on state, said temperature-sen- 
sitive circuit means comprising an R-C circuit, said 
R-C circuit being connected to said battery and to 
both of said complementary transistors, said R-C 
circuit including a thermistor; 
means in said multivibrator for turning on said buffer 
amplifier when said complementary transistors are 
conducting; 
means in said buffer amplifier for turning on said 
oscillator when said buffer amplifier is on; 
said multivibrator, said buffer amplifier and said r-f 
oscillator being in an off state and drawing an insig- 
nificant current from said battery when said ther- 
mistor is subjected to or below a predetermined 
temperature which is below the deep-body temper- 
ature of the subject ingesting said telemeter device, 
said free-running multivibrator, said buffer ampli- 
fier, and said r-f oscillator being in an on state 
whenever said thermistor is exposed to a tempera- 
ture above said predetermined temperature, the 
output frequency of said multivibrator being pro- 
portional to the temperature of said thermistor, 
said oscillator generating bursts of r-f energy at the 
output frequency of said multivibrator, the period 
between successive bursts being inversely propor- 
tional to the temperature of said thermistor. 
3,97 1,362 
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2. A telemeter device as claimed in claim 1 wherein 
said free-running multivibrator comprises a PNP tran- 
sistor with a base, collector and emitter, a NPN transis- 
tor with a base. collector and emitter. a first resistor 
said NPN transistor, respectively, and the input of 
said buffer amplifier being connected to said col- 
lector of said NPN transistor. 
3. A telemeter device as claimed in claim 2 wherein 
and a first capacitor connected in series between said 
base of said PNP transistor and said collector of said 
NPN transistor, a second resistor connected between 
said emitter of said PNP transistor and said collector of 
said NPN transistor, said thermistor connected be- 
tween said base of said PNP transistor and said emitter 
of said NPN transistor, a third resistor connected be- 
tween said collector of said PNP transistor and said 
emitter of said NPN transistor, a fourth resistor con- 
nected between said base of said NPN transistor and 
said collector of said PNP transistor, and a fifth resistor 
and a second capacitor connected in series between 
said base of said NPN transistor and said collector of 
said PNP transistor; 
the terminals of said battery being connected to said 
emitter of said PNP transistor and to said emitter of 
said predetermined temperature is 0°C. 
4. A telemeter device as claimed in claim 3 wherein 
the resistance of said thermistor is approximately six 
megohms at 25°C. 
5. A telemeter device as claimed in claim 4 wherein 
l o  the current drain on said battery during said on state is 
6. A telemeter device as claimed in claim I wherein 
7. A telemeter device as claimed in claim 6 wherein 
I 5  the resistance of said thermistor is approximately six 
megohms at at 25°C. 
8. A telemeter device as claimed in claim 7 wherein 
the current drain on said battery during said on state is 
approximately 25 microamperes. 
said predetermined temperature is 0°C. 
20 approximately 25 microamperes. 
* * * * *  
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Miniature ingestible telemeter devices to measure deep-body temperature

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