Non-invasive temperature monitor

A non-invasive temperature monitoring apparatus used in association with a guided wave member that may be for the purpose of sterilization and that is adapted for microwave heating of a substance that is absorptive at microwave frequencies and that is held in some type of container or connector that is transparent at microwave frequencies. The apparatus comprises a length of waveguide. A coupling aperture is defined in the guided wave member. The length of waveguide is supported with one end thereof about the coupling aperture. A microwave radiometer detection circuit is also coupled from the length of waveguide for detecting on a continuing basis the temperature of the substance which is usually liquid being heated by the microwave energy.

BACKGROUND OF THE INVENTION 
The present invention relates in general to a non-invasive technique for 
monitoring the temperature of a material or substance that is absorptive 
at microwave frequencies while being held in a container, connector, bar, 
or the like that is transparent at microwave frequencies. More 
particularly, the non-invasive temperature monitor of the invention may be 
used in association with a microwave sterilizer for providing an accurate 
reading of the temperature of the material or substance being heated which 
in the case of microwave sterilization is typically a liquid, such as 
might be used in continuous ambulatory peritoneal dialysis (CAPD) 
microwave sterilization. Even more particularly, and in accordance with at 
least one embodiment of the present invention, there is provided a 
non-invasive technique for temperature measurement in a microwave 
sterilization apparatus and in which the liquid being sterilized is held 
within a connector means to be heated therein by microwave energy for the 
purpose of sterilization. 
Reference is now made herein to copending application Ser. No. 466,894 
filed Feb. 17, 1983, now U.S. Pat. No. 4,614,514, on a microwave 
sterilizer and assigned to the present assignee herein. This sterilizer is 
described therein as being used for the purpose of sterilizing a coupling 
or connector that intercouples a conduit from a source of liquid such as a 
saline solution to a conduit implanted in the body. The apparatus of this 
sterilizer comprises a guided wave member adapted to enclose the coupling 
or connector and means for heating by excitation of the guided wave member 
to heat an initial charge of the liquid to an elevated temperature for a 
time long enough to destroy bacteria. In this apparatus, it has been 
assumed that the proper sterilization occurs by virtue of the microwave 
power having been applied for a specified period of time. The basic 
problem that has come about is that, because the actual temperature of the 
liquid or solution is not being measured, one cannot be assured that 
sufficient sterilization has taken place. For example, if the microwave 
source is not functioning properly and is say, not putting out the require 
power, then even though the sterilization occcurs for what appears to be a 
sufficient period of time, in fact, sufficient sterilization may not have 
occurred. 
The common technique for measuring temperature is to monitor the surface of 
the container. However, if the container, connector, bar or the like is of 
insulating or semi-insulating material, it will not be possible to obtain 
exact temperature measurements. Also, there will tend to be a thermal lag. 
Accordingly, it is an object of the present invention to provide a 
technique for monitoring the temperature, on a non-invasive basis, of a 
material or substance, usually a liquid, that is absorptive at microwave 
frequencies (also being heated by microwave energy) while being held in a 
container, bag, connector, or the like that is transparent at microwave 
frequencies. 
Another object of the present invention is to provide a non-invasive 
technique for the measurement of temperature of a sterilizing substance 
which is usually a liquid in association with microwave heating of the 
liquid for sterilization purposes. In accordance with the invention, this 
combination of sterilization and temperature detection occurs without any 
interference whereby the heating applied is at a different frequency than 
the detection frequency. 
Another object of the present invention is to provide a non-invasive 
temperature monitor that is of relatively simple construction, adapts 
itself readily to the microwave sterilizer and which can be made in 
miniature size and in which monitoring can occur quite easily so that the 
required temperature for sterilization can be readily achieved. 
Still another object of the present invention is to provide an improved 
means for in particular, the warming of the solutions which are absorptive 
to microwave energy and which are typically contained in plastic bags or 
the like that are transparent to microwave energy. 
A further object of the present invention is to provide a means as set 
forth in the preceding claim and which is in the form of a conformal array 
of elements particularly adapted for heating of relatively large solution 
bags or containers. 
SUMMARY OF THE INVENTION 
To accomplish the foregoing and other objects, features and advantages of 
the invention, there is provided a non-invasive temperature monitoring 
apparatus which is used in association with a guided wave means that may 
comprise part of a microwave sterilizer. This guided wave means is adapted 
for microwave heating of a substance of material, usually a liquid, that 
is absorptive at microwave frequencies and that is held in means, such as 
a container, bag, connector or the like, that is transparent to microwave 
energy. The apparatus of the present invention comprises a length of 
waveguide and means defining a coupling aperture in the guided wave means. 
The length of waveguide is supported with one end thereof about the 
coupling aperture for coupling energy from inside of the guided wave means 
to an opposite end of the length of waveguide. There is also provided a 
microwave radiometer detection circuit and means are provided for coupling 
from the length of waveguide to this detection circuit. The output of the 
detection circuit provides an accurate, high resolution temperature 
display output indicating on a continuous basis the temperature that is 
being detected of the material or substance (usually a liquid) that is 
being heated. The microwave heating is at one frequency and the detection 
is at a higher frequency. For example, the heating may be at 915 MHz while 
the detection may be designed at a frequency of 4.7 GHz. The coupling 
aperture preferably has a cross-sectional area less than the waveguide 
cross-sectional area. Also, the coupling aperture is dimensioned in 
comparison with the guided wave means so as to leave the heating 
characteristics of the guided wave means substantially undisturbed. Also, 
the waveguide is dimensioned to operate as a high pass filter passing the 
higher frequency adn rejecting the lower heating frequency. The waveguide 
is simply designed so as to provide rejection by cut off of the lower 
frequency heating energy. 
In accordance with another embodiment of the present invention, there is 
provided a non-invasive temperature monitoring apparatus used in 
association with a guided wave means in which this guided wave means is of 
generally larger size so as to accommodate a bag or container. In this 
embodiment of the invention, the microwave energy is used for the purpose 
of the warming of solutions absorptive to microwave energy contained in 
the plastic bag or container. The bag or container is transparent to 
microwave energy. In still another embodiment in accordance with the 
present invention there is provided an array of elements that are used in 
association with relatively large volume bags or containers. The array of 
elements may be disposed directly on the bag or container outer surface 
and the array enables heating and warming of materials or solutions 
contained in the bag. The array of elements provides good heat uniformity 
and the arrangement is particularly advantageous in connection with 
materials or solutions that are not good conductors of heat or that are 
not homogeneous.

DETAILED DESCRIPTION 
In FIGS. 1-3 herein, there is shown a technique for non-invasively 
monitoring the temperature of a liquid that is being heated by microwave 
energy for the purpose of sterilization. Thus, there is described herein 
at least part of a CAPD microwave sterilizer such as referred to in 
copending application Ser. No. 466,894 filed Feb. 16, 1983, now U.S. Pat. 
No. 4,614,514. Although the concepts of the invention are described 
primarily in connection with a CAPD microwave sterilizer, it is to be 
noted that the principles may also be applied to any device in which a 
material or substance that is absorptive at microwave frequencies is 
heated while being held in a container, bag, connector or the like that is 
transparent at microwave frequencies. 
Reference may now be made to FIGS. 1-3 which shows a microwave sterilizer 
which is operated from a microwave source 10 which couples to a short 
coaxial cable 12. As noted in FIG. 2, there is also provided a balun 11 
for converting from an unbalanced to a balanced configuration. Also 
depicted in FIG. 2, are the end tuning variable capacitors 14 and 15 for 
providing proper tuning of the guided wave structure. The electrical 
coupling is from capacitors 14 and 15 to conductors 17 and 18, 
respectively. The conductors 17 and 18 form a balanced transmission line 
which may be terminated in either a short circuit or open circuit. In this 
way the transmitter power not absorbed by the liquid initially is 
reflected, or directed back, into the lossy liquid. The loss of the 
structure is adequate to present a proper match to the microwave 
transmitter. 
The microwave source 10 is preferably at a frequency of 950 MHz and 
operates from a typical voltage supply of say 12 volts, allowing safe 
operation from either battery or a low voltage power supply. The output of 
the 915 MHz solid state source is approximately 15 watts. With this low 
power operation, the device is thus compact, efficient, and safe in 
operation. 
FIGS. 2 and 3 show the pivotal heater block 20 and the stationary heater 
block 22. The mechanical motions that are involved provide for the closing 
of the pivotal heater block 20 against the stationary heater block 22 
enclosing the connector 24 which is comprised of the male member 26 and 
the female member 28. FIG. 2 shows the spike 27 of the male member 26 
engaged with the female member 28. FIG. 3 also shows the liquid 30 that is 
being heated within the connector 24 for the purpose of sterilizing the 
connector 24. 
As noted in FIG. 2, the two wire transmission line is comprised of the 
curved conductors 17 and 18. Each of these may be made of stainless steel 
to minimize heat transfer from the liquid. A rotary hinge joint 33 is 
provided to permit the pivotal movement of the heater block 20. Each of 
the heater blocks preferably also includes respective housing members 34 
and 35 and internal insulation 37 and 38. The outer members 34 and 35 may 
be of plastic material and the insulation is adapted to maintain the heat 
concentrated within the connector 24. 
FIGS. 2 and 3 also show the spring 39. This is disposed at the bottom of 
the heater blocks. This is instrumental in providing for an opening 
mechanism to the rotatable heater block 20. In FIG. 2 the end of the male 
spike 27 is shown inside of the female connector with the liquid 
thereabout in readiness for heating. 
Now, in accordance with the present invention and in order to carry out the 
temperature monitoring on a non-invasive basis, there is provided a length 
of waveguide 40 that couples to one of the curved condutors comprising the 
guided wave member used for sterilization purposes. One of the curved 
conductors 17 is mechanically fixed in position and the fixed conductor 
preferably contains or incorporates the temperature sensor. In the 
illustration of FIGS. 1 and 2, the waveguide 40 couples from the curve 
member 17. This coupling of microwave energy to the waveguide 40 for 
temperature sensing is carried out by means of a coupling aperture 42 
through the wall of the conductor 17. The waveguide 40 has its end 44 
suitably secured to the curved conductor 17. This securing may be provided 
by means of a small weld or by some other suitable means of attachment. 
The coupling aperture is preferably uniformly centered relative to the 
waveguide 40. The coupling aperture is sufficiently small so as not to 
disturb the heating characteristics of the curved conductors 17 and 18. 
With regard to the length of the waveguide 40, this should be sufficiently 
long so as to provide a cut off at the lower frequency of 915 KHz. In this 
way the waveguide 40 functions as a high pass filter preventing any 
heating energy from being detected at the radiometer so that the 
radiometer detects only energy associated with the temperature of the 
liquid being sterilized. 
The waveguide 40 is a dielectric filled waveguide. The waveguide thus 
includes a core of a ceramic material such as aluminum oxide with the 
outer boundaries of the waveguide being formed by means of a metallic 
conductive plating on the ceramic. This arrangement is depicted in FIG. 1 
by a small cut out portion showing the plating and the ceramic material. 
In this regard, also note in FIG. 2, the plating 46 and the aluminum oxide 
core 48. 
FIG. 2 also illustrates the coupling from the end 50 of the waveguide 40. 
This includes a connector 52 which is of conventional design coupling by 
way of line 53 to radiometer 54. 
As indicated previously, in the preferred embodiment of the present 
invention, the waveguide 40 is dielectrically filled. The waveguide is 
constructed so as to provide adequate attenuation at the 915 MHz to 
prevent direct coupling of the heating frequency to the sensitive 
receiver. 
In the example given in combination with a microwave sterilizer, it is 
noted that the plastic used in the connector 24 is low loss and therefore 
the radiometer reads primarily only the emission from the liquid contained 
therein. Also, the other curved conductor 18 such as depicted in FIGS. 1 
and 2 functions as a reflector to direct energy back toward the coupling 
aperture which is also desired. This arrangement provides for good signal 
strength allowing the use of a relatively simple radiometer scheme. 
FIG. 4 depicts the microwave radiometer circuit illustrating the waveguide 
coupling device at 60. This is representative of the waveguide 40 depicted 
in FIG. 2. The coupling device connects to the Dicke switch 62. The 
radiometer is preferably of the Dicke switch type utilizing a diode switch 
rather than a ferrite switch. This allows the use of a low cost microwave 
integrated circuit technique for fabrication of the circuit. In one 
version, the diode associated with the Dicke switch 62 may be supported 
across the waveguide 40. As indicated previously, the waveguide itself is 
sufficiently long enough to provide a cut off at the lower frequency of 
915 MHz. 
The output of the Dicke switch 62 couples to the RF amplifier 64. The 
output of the RF amplifier 64 couples to a mixer circuit 66 which also 
receives an output from the local oscillator 68. The output of the mixer 
66 couples by way of the video amplifier 70 to the lock-in amplifier 72. 
There is also provided a low frequency 100 cycle per second switch driver 
74 which is connected in a feedback arrangement for providing control to 
both the lock-in amplifier 72 and the Dicke switch 62. The output of the 
microwave radiometer circuit is taken at the output line 75 from the 
lock-in amplifier 72. For the most part the microwave radiometer circuit 
depicted in FIG. 4 is of conventional design and thus is not discussed in 
detail herein. The operation of this circuit is in substance the same as 
the operation of the circuit depicted in U.S. Pat. No. 4,346,716 also 
owned by the present assignee herein. 
FIG. 5 is a schematic diagram illustrating guided wave conductors 80 and 81 
which may be of larger diameter than the conductors 17 and 18 illustrated 
in FIG. 1. The purpose of the embodiment to FIG. 5 is to illustrate the 
concepts of the invention in association with a bag 83 or the like 
container for containing a material which is usually a substance which is 
absorptive at microwave frequencies and which is being heated within the 
conductors 80 and 81 while being held in the container or bag with the 
container or bag being transparent at microwave frequencies. In the 
embodiment of FIG. 5, it is noted that there is also shown the waveguide 
84 similar to the waveguide 40 of FIG. 2 and the coupling to a radiometer 
86. The construction of the waveguide section 84 and the use of a coupling 
aperture in the conductor 81 may be substantially identical to that 
previously shown and described in connection with FIGS. 1-3. 
The array of elements may be disposed directly on the bag or container 
outer surface and the array enables heating and warming of materials or 
solutions contained in the bag. The array of elements provides good heat 
uniformity and the arrangement is particularly advantageous in connection 
with materials or solutions that are not good conductors of heat or that 
are not homogeneous. 
FIGS. 6 and 7 show the principles of the present invention as applied in 
connection with the heating or warming of a solution contained in a bag or 
container. Typically, this may be a two liter bag such as the bag 88 
illustrated in FIG. 6. The bag 88 may contain a dialysate solution. 
A conformal array of antenna elements 90 are disposed preferably one array 
on each side of the bag. In this connection, FIG. 7 shows element 90A on 
one side and element 90B on the opposite side. FIG. 7 also shows the 
corresponding terminals 91A and 91B. Each of the elements 90 is connected 
in common to one of the terminals as also illustrated in FIG. 6. The 
elements 90 may be deposited on the outer surface of the bag. The elements 
may be refracted onto the bag surface. The array of elements 90 is 
preferably disposed in a manner so as to cover the majority of the surface 
of the container. The elements 90 are also preferably disposed in some 
type of an orderly array so as to provide proper coverage and thus proper 
uniform heating. 
Unlike microwave ovens used for heating, the array shown in FIGS. 6 and 7 
provides for a much more uniform heating pattern. For example, in 
connection with a commercial microwave oven, because of the standing wave 
patterns established therein, there is a need for physically spinning or 
moving the material that is to be heated. The conventional microwave oven 
is far less efficient than the arrangement depicted in FIGS. 6 and 7 
herein because in the microwave oven it is designed to heat a wide variety 
of materials of various sizes and shapes. On the other hand, in accordance 
with the present invention, the array is meant to heat only the solution 
contained within the bag. 
Also, in accordance with the conformal array aspect of the invention 
depicted in FIGS. 6 and 7, much more flexibility is provided. For example, 
the array can be arranged so as to provide a non-uniform heating pattern 
if there would be some reason to heat one portion of the bag more than 
another portion. This might be the case where the bag is divided and 
contains two different types of liquids therein. One may desire to heat 
one of the liquids more than the other and in this connection the 
conformal array adapts itself very well to providing different heating 
patterns or even non-uniform heating patterns if desired. 
It is also noted that all of the elements 90 of each group on each side of 
the bag is coupled out to a single terminal. This is illustrated in FIG. 7 
as terminal 91A for elements on one side of the bag and terminal 91B 
coupling to elements on the opposite side of the bag. FIG. 6 also 
illustrates the electrical interconnections that essentially tie all of 
the elements 90 in common to terminal 91A in FIG. 6. Appropriate microwave 
energy is coupled to terminals 91A and 91B in the same manner as microwave 
energy is applied in connection with the embodiments described earlier. 
Having now described a limited number of embodiments of the present 
invention, it should be apparent to those skilled in the art that numerous 
other embodiments may be contemplated as falling within the scope of this 
invention.