WO2013159815A1

WO2013159815A1 - Heating of dielectric loads

Info

Publication number: WO2013159815A1
Application number: PCT/EP2012/057552
Authority: WO
Inventors: Pierre Westin; Lars Ekemar
Original assignee: Antrad Medical Ab
Priority date: 2012-04-25
Filing date: 2012-04-25
Publication date: 2013-10-31

Abstract

A dielectric load (115) is heated from an initial temperature level to a desired final temperature level by using alternating electromagnetic energy from an energy source (130), which energy ineludes a predefined set of spectral components. A cavity (140) contains the dielectric load (115), and an antenna (150) transmits an electromagnetic field through the dielectric load (115). Mechanical processing means (160) cause a relative movement between the dielectric load (115) and the at least one antenna (150), thus varying a spatial relationship between the alternating electromagnetic field and the dielectric load (115). As a result, the electromagnetic energy is distributed relatively evenly in the dielectric load (115). Sensor means (171, 173) register at least one parameter (ml, m2, m3) indicative of a temperature level of the dielectric load (115); and based thereon, a control unit (180) produces a power control signal (P_CTRL) controlling an amount of energy transmitted through the dielectric load (115).

Description

Heating of Dielectric Loads

THE BACKGROU ND OF THE I NVENTION AND PRIOR ART

The present invention relates generally to elevating the temperature of delicate substances in a precise and speedy manner, such as thawing of frozen blood plasma or stem cells; or warming up blood cells. More particularly the invention relates to an apparatus according to the preamble of claim 1 . The invention also relates to a method according to the preamble of claim 9, a computer program according to claim 15 and a computer pro- gram product according to claim 16.

Heating , or thawing , a cooled/frozen substance to a desired temperature is not always a trivial task. In both food processing and health care, there are many examples of demanding heating processes. For example thawing blood plasma or warming up red blood cells requires specific attention . To maintain adequate quality during storage, bags of blood plasma or red blood cells are cooled , typically to around -30 °C and +4 °C respectively. When the blood substances are to be used in a patient they must have a temperature matching that of a human being , i .e. around +37 °C. Since blood su bstances are often needed in with short notice, a speedy heating/thawing process is wanted . Nevertheless, the substances must also attain a homogenous final temperature. This may be complicated to achieve, inter alia because the substances as such may be somewhat inhomoge- neous/irregular, and/or they have been frozen in a slightly irregular manner. In worst case, some areas of a blood substance may reach temperatures above +45 °C before the coldest areas thereof have been heated up to +37 °C. This is unacceptable because in such a case the substance risks being partially dena- tured , and must be discarded .

It may also be difficult to determine a cooled/frozen su bstance's initial temperature with sufficient accuracy. Consequently, the exact amount of energy required to heat the substance to the desired final temperature cannot be established . Most measure- ment methods have problems measuring temperature levels be- low -30 °C. Thus, if for example a frozen su bstance having an initial temperature around -120 °C is to be thawed to room temperature, there is a high risk that some areas of the substance are either under- or overheated . Stem cells are biological subs- tances that may be subjected to such a thawing process in connection with retrieval from storage.

The above-mentioned biological substances are dielectric materials, which can be regarded as dielectric loads having a dielectric constant, ε, and a dissipation factor, tan (δ). The dielectric load (i .e. the su bstance) may be heated by means of electromagnetic energy transmitted from one or more antennas. In the prior art solutions, the dielectric load is preferably surrounded by a medium (normally a viscous dielectric material , e.g . water) that is adapted to equalize the electromagnetic field . As a result, when electromagnetic energy is transmitted through the field equalizing medium and the dielectric load , the electromagnetic field becomes essentially homogenous, and the dielectric load is heated very evenly. Here, it is advantageous if the field equalizing medium has approximately the same dielectric constant, ε, as the dielectric load , however a relatively low dissipation factor, tan (δ) (compared to the dielectric load ). Due to the low dissipation factor, tan (δ), the equalizing medium is heated insignificantly.

Dielectric heating of a conductive medium is caused by induced electric currents in the medium . If conductivity is poor, or the frequency is high , then dielectric heating is the dominant mechanism of loss of energy from the electromagnetic field into the medium. For dielectric heating , the generated power density per volume, P, may be described by: P = E²-f-c-tan (δ) [W] where E is the electric field strength [V/m] ,

f is the frequency [Hz] ,

ε is the dielectric constant (influencing the imaginary component of a system impedance), and tan (δ) is the dissipation factor (influencing the real component of a system impedance).

The dissipation factor, tan (δ), is a measure for the ability of a dielectric material to convert radio frequency electromagnetic field energy into heat.

GB 599 935 reveals a method for heating a dielectric body evenly by high-frequency electric fields, where the dielectric body is embedded , at least partially, in at least one insulating medium of equal or greater dielectric constant or loss-factor. The medium may be liquid , a fine powder, e.g . ceramic, or a plastic. The method may be used for therapy in connection with diathermy.

WO 2002/054833 discloses a solution to the problem with the overheating of perishable dielectric matters. Dielectric matters are warmed and/or heated by being placed in oscillating electro- magnetic fields generated at frequencies being below 900 MHz between capacitor discs or in cavities.

SE 534 837 descri bes a method and a devise for equalizing warming processes in dielectric loads using electromagnetic fields at frequencies below 900 MHz. Here, the load is surrounded by a field equalizing material , and the load and the electromagnetic field are moved relative to one another.

PROBLEMS ASSOCIATED WITH TH E PRI OR ART

Hence, efficient solutions are known for heating dielectric loads quickly and evenly. However, there is yet no solution , which minimizes the risk that the desired final temperature level is not exceeded .

SUM MARY OF TH E I NVENTION

The object of the present invention is therefore to provide a solution , which enables quick and yet safe heating of a dielectric load , for instance containing a biologic substance.

According to one aspect of the invention , the object is achieved by the initially described apparatus, wherein the apparatus contains at least one sensor means configured to register at least one parameter indicative of a temperature level of the dielectric load . A control unit in the apparatus is configured to receive the at least one registered parameter; and based thereon , produce a control signal arranged to control an amount of electromagnetic energy transmitted through the dielectric load .

This apparatus is advantageous because the effect of the dielectric heating is verified , and appropriate measures can be ta- ken to control the final temperature to the desired level .

According to one embodiment of this aspect of the invention , the apparatus includes a flexible container inside the cavity. The flexi ble container is configured to hold a medium that is adapted to equalize the alternating electromagnetic field . The flexible container, in turn , has an inner cavity surrounded by the equalizing medium. The inner cavity is configured to hold the dielectric load . Hence, the electromagnetic field is made relatively homogenous in the dielectric load , and as a result, the heating thereof becomes even . According to another embodiment of this aspect of the invention , the at least one registered parameter represents: a volume of the dielectric load , a dielectric constant of the load , a dissipation factor of the load and/or an impedance contri bution of the load imposed by the volume of the dielectric load . Namely, these pa- rameters are all relevant indicators of the temperature in a dielectric load , either alone or in various combinations with one another.

According to yet another embodiment of this aspect of the invention , the control unit is specifically configured to derive a temperature level of the dielectric load from the at least one registered parameter, and compare the derived temperature level with the desired final temperature level . The control unit is then configured produce the control signal , so that the temperature level of the dielectric load is estimated to level out on the desi- red final temperature level . Thereby, the control unit may apply a relatively straightforward algorithm to control the electromagnetic energy transmitted through the dielectric load .

According to still another embodiment of this aspect of the invention , the control unit is configured to receive the at least one registered parameter at repeated occasions. In response thereto, the control unit is configured to update the control signal , aiming for the desired final temperature level . Naturally, such repeated (or continuous) control vouches for improved precision in the final temperature level of the dielectric load . According to a further embodiment of this aspect of the invention , the at least one antenna is enclosed by the cavity, and the cavity, in turn , has a screening for minimizing the amount of electromagnetic energy leaking out from the cavity. This increases the efficiency of the heating process and improves the chances of controlling the temperature level accurately.

According to another embodiment of this aspect of the invention , the predefined set of spectral components exclusively contains spectral components below 900 MHz, and further preferably below 300 MHz. Namely, the comparatively long wavelengths as- sociated with these frequencies have good penetration properties, and are less inclined to cause so-called hotspots in the dielectric load , than for example the commercial frequency 2 450 MHz. Therefore, the proposed low-frequency type of electromagnetic energy is particularly useful when heating sensitive dialect- ric loads, such as biological substances.

According to another aspect of the invention , the object is achieved by the method described initially, wherein at least one parameter is registered being indicative of a temperature level of the dielectric load . Based on the at least one registered parameter, an amount of energy transmitted through the dielectric load is controlled . The advantages of this method , as well as the preferred embodiments thereof, are apparent from the discussion hereinabove with reference to the proposed apparatus.

According to a further aspect of the invention the object is achieved by a computer program loadable into the internal me- mory of a computer, comprising software for controlling the above proposed method when said program is run on a computer.

According to another aspect of the invention the object is achieved by a computer program product, having a program recorded thereon , where the program is to make a computer control the above proposed method .

BRI EF DESCRI PTION OF THE DRAWI NGS

The present invention is now to be explained more closely by means of embodiments, which are disclosed as examples, and with reference to the attached drawings.

Figure 1 shows a block diagram over an apparatus according to one embodiment of the invention , and

Figure 2 shows a flow diagram illustrating the general method according to the invention . DESCRI PTION OF EMBOD I MENTS OF THE I NVENTION

We refer initially to Figure 1 , which shows an apparatus for heating a dielectric load 1 1 5 according to one embodiment of the invention . The dielectric load 1 15 has an initial temperature level and shall be heated/thawed to a desired final temperature level . To this aim , the apparatus includes: an energy source 130, an impedance matching unit 135, a cavity 140, at least one antenna 150 (one of which is shown in Figure 1 ), mechanical processing means 160, one or more sensor means 1 71 ; 1 73 and a control unit 180. A return connection GND is arranged between the cavity 140 and the energy source 130 to close the circuit.

The energy source 130 is configured to generate alternating electromagnetic energy including a predefined set of spectral components, say up to 300 MHz or 900 MHz.

The cavity 140 is configured to contain the dielectric load 1 15 during heating thereof, and each of the at least one antenna 150 is configured to receive an alternating electric current from the energy source 130, and transmit an electromagnetic field through the dielectric load 1 15 when contained in the cavity 140.

The mechanical processing means 160 is configured to cause a relative movement between the dielectric load 1 1 5 and the at least one antenna 1 50. As a result of such movements, the spa- tial relationship between the alternating electromagnetic field and the dielectric load 1 1 5 varies over time, and the dielectric load 1 1 5 is heated comparatively evenly. The mechanical processing means 160 may include a main member 163 configured to act mechanically on the dielectric load 1 1 5, a pushing rod 165 and an actuator 167. A first end of the pushing rod 1 65 is here connected to the main member 1 63 and a second end of the pushing rod 165 engages the actuator 167. Thereby, in response to a signal M PC from the control unit 180, the actuator 167 may cause the dielectric load 1 1 5 move relative to the at least one antenna 150 via for example linear movements along a symmetry axis of the pushing rod 165.

The impedance matching unit 135 is configured to enable an adaption of the overall impedance of the system to a desired value. Here, the system includes the energy source 1 30, the impe- dance matching unit 135, the at least one antenna 150, the dielectric load 1 15, the cavity 140 and the return connection GND. As will be discussed below, the system may also include a flexible container 1 10 and a field equalizing medium 125. In any case, the impedance matching unit 135 is configured to produce a signal m2 indicative of its own contri bution to the overall system impedance. The control unit 180 is configured to produce an impedance control signal Z_CTRL _> which causes an adjustment of the impedance matching unit 135, so that the overall system impedance attains a desired value. Since the im- pedance contribution of the dielectric load 1 1 5 varies depending on its temperature, and the remaining circuit elements 140, 150 and GND ( 1 10, 125) are presumed to have constant impedance, the signal m2 produced by the impedance matching unit 135 is indicative of the dielectric load's 1 15 temperature. Each of the at least one sensor means 1 71 and 1 73 is configured to register at least one parameter m l and m3 respectively indicative of a temperature level of the dielectric load 1 15.

According to embodiments of the invention , the registered parameters m 1 /m3 may represent: a direct temperature measure of the dielectric load 1 1 5, a volume of the dielectric load 1 15, a dielectric constant of the load 1 1 5, and/or a dissipation factor of the load 1 15. The direct temperature measure may be obtained via a first probe 1 71 (e.g . including a sensor for registering infra-red-light properties). The volume of the dielectric load 1 15 may either be measured directly (i .e. mechanically), or indirectly (e.g . via impedance measurements). Thus, a second probe 1 73 may be configured to provide a direct or indirect volume measure of the dielectric load 1 15. Different parameters m 1 /m3 may be suitable to use depending on the specific properties of the dielectric load 1 15, for example if the dielectric load 1 1 5 contains red blood cells, blood plasma or stem cells.

In addition to receiving the signal m2 and producing the signals Z_CTRL and MPC, the control unit 180 may therefore be configured to receive the at least one registered parameter m 1 /m3. Based on the at least one registered parameter m 1 /m3, the control unit 180 is configured to produce a power control signal P_CTRL , which , in turn , is arranged to control an amount of electromagnetic energy transmitted through the dielectric load 1 15. Preferably, the control unit 180 is configured to derive a temperature level of the dielectric load 1 1 5 from the at least one registered parameter m l , m2 and/or m3, and compare the derived temperature level with the desired final temperature level . Depending on the temperature conditions reflected by the at least one registered parameter m l , m2 and/or m3, further electromagnetic energy can be injected into the dielectric load 1 1 5 if deemed necessary.

In short, the control unit 1 80 is configured to produce the power control signal P_CTRL , SO that the temperature level of the dialectic load 1 15 is estimated to level out on the desired final temperature level . In practice, this means that, if it is estimated that further heating is required , the control unit 1 80 produces such a power control signal P_CTRL that an amount of energy is injected into the dielectric load 1 15, which amount of energy is calculated to be sufficient, however not excessive, to reach the desired final temperature level of the dielectric load .

Especially if the span between the current temperature level and the desired final temperature level is relatively wide, it may be difficult to, in one go; calculate the exact amount of energy to add . Therefore, an iterative process may be advantageous to apply. To this aim , according to one embodiment of the invention , the control unit 180 is configured to receive the at least one registered parameter m l , m2 and/or m3 at repeated occasions, or even continuously, and in response thereto produce an updated power control signal P _CTRL -

The parameters m l , m2 and/or m3 may either be registered continuously and in parallel with transmitting electromagnetic ener- gy through the dielectric load 1 15, or during appropriate intermissions, such as when no electromagnetic energy is transmitted and/or when there is an interruption in the mechanical processing of the dielectric load 1 15.

According to one embodiment of the invention , a flexi ble contai- ner 1 10 is included inside the cavity 140. The flexi ble container 1 1 0 is configured to hold a field equalizing medium 125 (e.g . water), i .e. a medium that is adapted to equalize the alternating electromagnetic field generated by the at least one antenna 150. The flexible container 1 1 0 also has an inner cavity surrounded by the field equalizing medium 125, which inner cavity is configured to hold the dielectric load 1 15. Hence, the dielectric load 1 1 5 can be completely surrounded by the field equalizing medium 1 25 when located inside the cavity 140. Preferably, for efficiency reasons, there shall be as little spacing as possible bet- ween the field equalizing medium 125 and the dielectric load 1 15.

According to one embodiment of the invention , the at least one antenna 150 is enclosed by the cavity 140. The cavity 140 comprises a screening (e.g . a so-called Faraday cage) configured to minimize the amount of electromagnetic energy leaking out from the cavity 140. This arrangement increases the efficiency of the electromagnetic energy transmitted from the at least one antenna 150. The resulting relatively low losses also improve the chances of controlling the temperature level more accurately. The above-described heating procedure, which is implemented by the control unit 180, is preferably controlled by a computer program loaded into a memory M of the control unit 180, or an external memory unit accessible by the control unit 180 (not shown). The computer program , in turn , contains software for controlling the steps of the procedure when the program is run on the control unit 180.

In order to sum up, the general method of heating a dielectric load from an initial temperature level to a desired final temperature level according to the invention will be described below with reference to the flow diagram in figure 2.

In a first step 210, a dielectric load is heated by transmitting an amount of electromagnetic energy from an antenna there through while causing a relative movement between the dialectic load and the antenna, so as to vary a spatial relationship between the dielectric load and the alternating electromagnetic field . Preferably, the dielectric load is also surrounded by a medium adapted to equalize the alternating electromagnetic field . Thereby, the electromagnetic energy is distri buted relatively evenly in the dielectric load . In a step 220, during or after transmitting the electromagnetic energy through the dielectric load , one or more registered parameters are received . The parameters are indicative of a temperature level of the dielectric load . I n a step 230, a current temperature level is then derived ; where after, in a step 240, this tem- perature is compared with the desired final temperature level . Based on said comparison , a step 250 checks whether or not further heating is deemed to be required in order to level out the temperature of the dielectric load on the desired level .

If, in step 250, it is found that no more heating is needed , the procedure ends. Otherwise, the procedure loops back to step 210 for further heating .

The process steps, as well as any sub-sequence of steps, described with reference to the figure 2 above may be controlled by means of a programmed computer apparatus. Moreover, although the embodiments of the invention described above with reference to the drawings comprise computer apparatus and processes performed in computer apparatus, the invention thus also extends to computer programs, particularly computer programs on or in a carrier, adapted for putting the invention into practice. The prog- ram may be in the form of source code; object code, a code intermediate source and object code such as in partially compiled form, or in any other form suitable for use in the implementation of the process according to the invention. The carrier may be any entity or device capable of carrying the program. For example, the carrier may comprise a storage medium, such as a Flash memory, a ROM (Read Only Memory), for example a CD (Compact Disc) or a semiconductor ROM, an EPROM (Erasable Programmable Read-Only Memory), an EEPROM (Electrically Erasable Programmable Read-Only Memory), or a magnetic recording medium, for example a floppy disc or hard disc. Further, the carrier may be a transmissible carrier such as an electrical or optical signal , which may be conveyed via electrical or optical cable or by radio or by other means. When the program is embodied in a signal , which may be conveyed , directly by a cable or other device or means, the carrier may be constituted by such cable or device or means. Alternatively, the carrier may be an integrated circuit in which the program is embedded, the integrated circuit being adapted for performing, or for use in the performance of, the relevant processes.

The invention is not restricted to the described embodiments in the figures, but may be varied freely within the scope of the claims.

Claims

1 . An apparatus for heating a dielectric load (1 1 5) from an initial temperature level to a desired final temperature level , the apparatus comprising :

an energy source (1 30) configured to generate alternating electromagnetic energy including a predefined set of spectral components,

a cavity (140) configured to contain the dielectric load (1 1 5) during heating thereof,

at least one antenna (150) configured to receive an alternating electric current from the energy source (130) and transmit an electromagnetic field through the dielectric load (1 1 5) when contained in the cavity (140), and

mechanical processing means (160) configured to cause a relative movement between the dielectric load (1 1 5) and the at least one antenna (150), thus varying a spatial relationship between the alternating electromagnetic field and the dielectric load (1 15), characterized in that

the apparatus comprises at least one sensor means (135, 1 71 , 1 73) configured to register at least one parameter (m l , m2 , m3) indicative of a temperature level of the dielectric load (1 15), and

a control unit (180) configured to receive the at least one registered parameter (m l , m2 , m3), and based thereon , produce a power control signal (P_CTRL ) arranged to control an amount of electromagnetic energy transmitted through the dielectric load (1 15).

2. The apparatus according to claim 1 , comprising a flexible container (1 1 0) inside the cavity (140), the flexible container (1 10) being configured to hold a medium (1 25) adapted to equalize the alternating electromagnetic field , the flexible container (1 10) having an inner cavity surrounded by the said medium, the inner cavity being configured to hold the dielectric load (1 15).

3. The apparatus according to any one of the preceding claims, wherein the at least one registered parameter (m l , m2 , m3) represents at least one of: a volume of the dielectric load (1 15), a dielectric constant of the dielectric load (1 15), a dissipation factor of the dielectric load (1 1 5) and an impedance contri bution of the load dielectric (1 1 5) imposed by the volume of the dielectric load ( 1 15).

4. The apparatus according to any one of the preceding claims, wherein the control unit (1 80) is configured to:

derive a temperature level of the dielectric load (1 1 5) from the at least one registered parameter (m l , m2 , m3),

compare the derived temperature level with the desired final temperature level , and

produce the power control signal (P _CTRL) SO that the temperature level of the dielectric load (1 1 5) is estimated to level out on the desired final temperature level .

5. The apparatus according to any one of the preceding claims, wherein the control unit (1 80) is configured to:

receive the at least one registered parameter (m l , m2, m3) at repeated occasions, and in response thereto

update the power control signal (P _CTRL ) -

6. The apparatus according to any one of the preceding claims, wherein the at least one antenna (150) is enclosed by the cavity (140), and the cavity (140) comprises a screening configured to minimize the amount of electromagnetic energy leaking out from the cavity (140).

7. The apparatus according to any one of the preceding claims, wherein the predefined set of spectral components exclusively contains spectral components below 900 MHz.

8. The apparatus according to any one of claims 1 to 7, wherein the predefined set of spectral components exclusively contains spectral components below 300 MHz.

9. A method of heating a dielectric load (1 1 5) from an initial temperature level to a desired final temperature level , the method comprising : generating, via an energy source (130), an alternating electromagnetic field including a predefined set of spectral components,

transmitting, via at least one antenna (150), energy from the energy source (130) through the dielectric load (115) while contained in a cavity (140), and

causing a relative movement between the dielectric load (115) and the at least one antenna (150), thus varying a spatial relationship between the dielectric load (115) and the alternating electromagnetic field,

characterized by the method comprising

registering at least one parameter (ml, m2, m3) indicative of a temperature level of the dielectric load (115), and

controlling an amount of electromagnetic energy transmit- ted through the dielectric load (115) based on the at least one registered parameter (ml, m2, m3).

10. The method according to claim 9, wherein the at least one registered parameter (ml, m2, m3) represents at least one of: a volume of the dielectric load (115), a dielectric constant of the load (115), a dissipation factor of the load (115) and an impedance contribution of the load dielectric (115) imposed by the volume of the dielectric load (115).

11. The method according to any one of claims 9 or 10, comprising:

deriving a temperature level of the dielectric load (115) from the at least one registered parameter (ml, m2, m3),

comparing the derived temperature level with the desired final temperature level, and

producing the power control signal (P_CTRL) SO that the tem- perature level of the dielectric load (115) is estimated to level out on the desired final temperature level.

12. The method according to any one of claims 9 to 11, comprising:

receiving the at least one registered parameter (ml, m2, m3) at repeated occasions, and in response thereto updating the power control signal (P _CTRL ) -

13. The method according to any one of claims 9 to 1 2, wherein the predefined set of spectral components exclusively contains spectral components below 900 MHz.

14. The method according to any one of claims 9 to 1 2, wherein the predefined set of spectral components exclusively contains spectral components below 300 MHz.

15. A computer program loadable into the internal memory (M) of a computer, comprising software for controlling the steps of any of the claims 9 to 14 when said program is run on the computer.

16. A computer program product, having a program recorded thereon , where the program is to make a computer control the steps of any of the claims 9 to 14.