WO2007025589A1

WO2007025589A1 - Temperature sensor

Info

Publication number: WO2007025589A1
Application number: PCT/EP2006/006230
Authority: WO
Inventors: Udo Weimar; Nicolae Barsan; Michael Wandel
Original assignee: Eberhard Karls Universität Tübingen
Priority date: 2005-09-01
Filing date: 2006-06-28
Publication date: 2007-03-08
Also published as: DE102005041495A1; EP1929261A1

Abstract

In a temperature sensor (10) which is suitable for being fixed to or on objects of all types, at least two spaced-apart electrodes (14, 16) and at least one material layer (18) are arranged on a substrate (12). The material layer (18) is formed between the electrodes (14, 16), wherein the material layer changes as a function of the temperature acting on the material layer (18) or is enriched in different form between the electrodes (14, 16). The temperature sensor (10) does not require an energy source and material changes in the material layer (18) can be measured via the electrodes (14, 16).

Description

temperature sensor

Description

The invention relates to a temperature sensor which can be attached to any objects and over the permanently detectable whether heat has been supplied to an object beyond a certain level.

Today, it is important for many items to know whether they have been treated, ie packaged, stored, transported, on their way from production to use, and that their original quality and expected effects have not been damaged. The influence of temperature is critical to the quality and / or performance of many products, so it is of the utmost interest of a user to know whether the product provided to him has been treated to be temperature safe on the way from production to use. Many foods experience a deterioration in quality due to inadmissible heat input, drugs may be effective, and precision components may lose their dimensional accuracy. It is therefore important, especially for bulk goods, to know whether the individual product has been professionally treated before it is used for its intended purpose. The object of the invention is to develop a temperature sensor which is simple to produce in large numbers, can be constructed inexpensively, is permanently functional, is easy to install on any objects, has a certain flexibility with respect to assembly and does not require its own energy source.

According to the invention, the object is achieved with a temperature sensor which has at least two spaced-apart electrodes and at least one material layer on a substrate, and wherein material from the material layer accumulates between the electrodes on the substrate as a function of the temperature acting on the material layer and / or changed.

The temperature sensor according to the invention has the significant advantage that it does not require any specific materials for the substrate or the necessary material layer. It is only important that one can perform a capacitance measurement and / or resistance measurement via the electrodes and that at a temperature change or certain amount of heat supply, which is not desired for the selected product, the material layer then undergoes a capacitive change and / or electrical resistance change measurably. The change in capacitance and / or resistance is irreversible, so that it can be permanently proven whether the product provided with the temperature sensor according to the invention was exposed to an impermissible quantity of heat input. If, for example, an elevated material layer of wax is formed in the middle between the electrodes, and if the material layer is selected such that it changes in the temperature range which is impermissible for the product, then the capacitance of the material layer between the electrodes or the electrical resistance also changes, if the Material layer is electrically conductive. If the change is linked to the temperature, its temperature value is to be detected, it can always be permanently demonstrated by means of a measurement whether the product was exposed to an unintended temperature by comparing the reference capacitance with the measured capacitance or by comparing measured electrical resistance values with one another.

Since the temperature sensor assembly does not require an energy source, temperature changes on a product provided with the temperature sensor can be permanently detected and the time limit of the measurement verification depends solely on the durability of the materials used to construct the temperature sensor.

It is particularly advantageous if the enrichment and / or the change in the material layer can be adjusted by exceeding the melting point of the material layer. This has the advantage that material layers of which the melting point is known are applied to the substrate of the temperature sensor and, for example, an object exceeds a critical temperature and the melting point of the material layer likewise corresponds to this critical temperature, then the material layer becomes the aggregate state at this temperature and thus also their capacitive properties and their electrically conductive behavior. If this changed behavior or the changed properties is measured, then the degree of heat input into an article or its temperature load can be detected by performing a measurement on the temperature sensor according to the invention before a heat load and after a heat load. If the measured values are the same or lie within an allowed fluctuation range, then the article provided with the temperature sensor according to the invention has not undergone any inadmissible supply of heat. Are those to be compared? The measurements are significantly different, it can be said with certainty that the tested item was exposed to an impermissible heat.

It is advantageous if a wax from one of the following substances or from a combination of the following substances is used as the material layer. These are substances whose melting point is between -33 ° and + 60 °. Combinations of the substances specified here are also conceivable, so that melting points of substance combinations can be produced which lie between the values indicated. The substances listed in the table below are only a selection and other substances can be selected which have, for example, by themselves a waxy behavior or which are additionally incorporated in base waxes or are.

Temoeratursensorik with Memorveffekt

In order to refine the states to be measured, to which an object equipped with the temperature sensor was exposed, several electrodes or electrode pairs are provided on the substrate. Different distances between the electrodes can be used to determine different heat quantity feeds.

It is also advantageous if, in the case of more than two electrodes, at least one electrode has an extension of different length compared to the other electrodes formed on the substrate and / or if electrode pairs are arranged on the substrate in a series and / or parallel connection. This increases the possibilities of the measurements to be carried out. Valuations about the temperature load of an object can be given more differentiated.

If the thickness of the material layer is changed, the capacitive or electrically conductive behavior of the material layer used can also be changed.

The substrate of the temperature sensor according to the invention is preferably selected from glass or ceramic, if the temperature sensor according to the invention is to be used in an aggressive medium or in an aggressive atmosphere. However, the substrate can also be a plastic carrier or a plastic film or other flexible materials can also be selected as carrier material for the material layer and the electrodes.

If the electrodes and the material layer are designed to be flexible, for example by a plastic film that forms the substrate, then the temperature sensor according to the invention can also be mounted on curved surfaces in a simple manner. Thus, the temperature sensor can always be attached to an object where it is needed. Changes in the material layer in the temperature sensor according to the invention can be measured particularly easily if measuring surfaces for contacting a measuring and / or reading device are formed on the electrodes.

In a further embodiment of the invention, the material layer flows on the substrate in an aggregate state change of the material layer due to capillary forces in at least one formed on the substrate riser and at least one electrode is provided along both longitudinal and on both sides of the riser to the riser. If the temperature sensor is formed with riser tubes, into which a liquid material layer can flow, it is also possible to make a statement about the duration of the heat supply or the temperature radiation onto the temperature sensor. Namely, the riser pipes are made differently in cross-sectional diameter, the capillary forces acting in the riser tubes are different. In a narrow standpipe, liquid inflows or changes are stronger and faster to recognize than in risers with larger diameters. If electrodes are arranged in the riser pipes at comparable heights on both sides of the riser pipes and if only the diameters of the riser pipes differ, the condition may occur that one or the other riser pipe is loaded with liquid and another riser tube still exhibits the original initial capacity behavior during a measurement ,

In another embodiment of the temperature sensor according to the invention, an electrically conductive metal powder and / or metallic particles can be mixed into the material layer, which are provided in the functional state of the temperature sensor locally without heat supply and limited to the surface on the substrate After the heat supply under the change of the state of aggregation of the material layer, the metal powder or the metallic particles with the liquid material layer are uniformly distributed between the electrodes. In this case, the law of entropy is used, which remains minimally the same in a closed system but normally increases. This is especially the case with a temperature increase and with a heat supply. If the binding of the metallic particles or the electrically conductive particles by the liquefaction of the wax given by the particles are locally bound, so the particles distribute evenly between the electrodes and there may be a change in capacitance in the material layer or a modified electrical Conductive behavior of the material layer can be measured. If the product provided with the temperature sensor is cooled again, the electrically conductive particles are locally bound in the metal layer and fixed there. Due to the change of state or due to the local place changes of the particles, evidence can also be provided staggered in time whether a product was exposed to an inadmissible heat supply or to an impermissible temperature load.

If, in a further embodiment of the invention, a self-adhesive coating is applied to the substrate on the surfaces diametrical to the electrodes, then the temperature sensor according to the invention can be permanently attached to a product which is to be temperature-monitored.

If the electrically conductive particles are plastics, carbons or else the metallic metallic particles can be magnetized, then the

Particles in a predetermined distribution in the material layer of the temperature sensor then held over a magnetic strip if the temperature sensor should be exposed to an inadmissible temperature during storage or transport.

Furthermore, the temperature sensor according to the invention can be used in an RFID element and also integrated there. If the known technology of radio frequency identification is used, data can also be read from the temperature sensor without contact and without visual contact, and they can be stored accordingly.

With regard to a method, the invention is achieved for producing a temperature sensor with subsequent production steps.

First, electrodes are applied to a substrate of glass, ceramic, plastic or plastic film. Subsequently, in a second step, the electrodes are embedded in a material layer of wax, consisting of the substances of Table 1 or of combinations of substances from Table 1, and then the material layer is cured in a production mold of the temperature sensor. In another embodiment, electrically conductive particles made of plastic, metal or carbon are introduced into the liquid or viscous wax layer in a third step, and also aligned locally. Subsequently, the material layer is cured. If such method steps are used, the temperature sensor according to the invention can be manufactured in a simple and cost-effective manner. If electrically conductive and magnetizable particles are used in the material layer, they can be aligned with an electromagnet. Likewise, it is also conceivable to bring the electrically conductive or magnetisable particles onto a material layer by means of an adhesive tape provided with metallic particles, by surface-depositing these particles stick to the tape. When the metal layer melts, the particles are transferred in the desired manner into the material layer. If the particles have been introduced into the liquid or viscous material layer, then this material layer is cured. The particles are then fixed locally in the material layer.

The temperature sensor according to the invention will be described in subsequent embodiments. The illustrations shown in the figures are highly schematic and not to scale. The temperature sensor according to the invention can be made very thin and also with respect to its total thickness very thin, by using components in film thickness for all process steps.

It shows:

Fig. 1 is a plan view of a temperature sensor with a material layer having two electrodes on a substrate;

2 shows a temperature sensor according to the invention in the ready state with a material layer in which electrically conductive particles are embedded;

3 shows a temperature sensor according to the invention in the activated state in which the material layer has liquefied.

4 shows a further embodiment of a temperature sensor according to the invention with three electrodes;

5 shows a further embodiment of a temperature sensor according to the invention with riser tubes; and 6 shows the layer structure of a temperature sensor according to the invention.

1 shows a temperature sensor 10 with a substrate 12, to which a first electrode 14 is applied. The first electrode 14 has a first measuring surface 15. Spaced apart from the first electrode 14, a second electrode 16 is arranged on the substrate, on which a second measuring surface 17 is formed. The first and second electrodes 14, 16 are embedded in a material layer 18. The first and second measuring surfaces 15, 17 are freely accessible to a reading device on the temperature sensor 10, so that capacitive changes in the material layer or changes in the electrical resistance of the material layer 18 can be measured via the electrodes 14, 16. The material layer 18 is selected at the temperature sensor 10 to be tuned to a critical temperature of an article to which the temperature sensor 10 is attached. If the critical temperature on the object is exceeded, the capacitive behavior or the electrical behavior of the material layer 18 changes permanently. Time offset can thus be measured via the electrodes 14, 16, the different capacitive behavior or a differential resistance. If reference output values and measured values are different, this is the proof that the product provided with the temperature sensor 10 was exposed to an inadmissible heat input or temperature radiation.

2 shows a temperature sensor 20 with a substrate 22, on which a first electrode 24 with a first measuring surface 25 is arranged. Locally spaced a second electrode 26 is arranged with a second measuring surface 27 on the substrate 22. The electrodes 24, 26 are embedded in a material layer and in the region of an electrode 26 metallic particles 29 are arranged. The metallic particles 29 are fixed in a waxy material layer 28 because the material layer 28 is solid and cured in the state shown in FIG. The response of the temperature sensor 20 may be adjusted over a distance 29 'by embedding the metallic particle concentration at different distances from the first electrode 24. When the material layer 28 melts, the metallic particles 29 can move in the liquid material layer 28, following the findings of entropy, and a distribution, as shown by way of example in FIG. 3, arises. The state changes of the material layer 28 and the different distribution of the metallic particles 29 can be detected via the measuring surfaces 25, 27 via a change in resistance.

In Fig. 3, a current flow is possible between the electrodes 24, 26.

4 shows a further embodiment of a temperature sensor 30 having a substrate 32 and a first electrode 34 with a first measuring surface 35, a second electrode 36 and a second measuring surface 37, as they are embedded in a material layer 38. Metallic particles 39 are concentrated at the second electrode 36 in the hardened material layer 38 incorporated. A third electrode 41 with a third measuring surface 42 is likewise embedded in the material layer 38. If electrically conductive state changes between the electrodes 36, 41 on the one hand and 36, 34 on the other hand are measured, the duration of a heat input into the temperature sensor 30 can also be detected via the temperature sensor 30.

Fig. 5 shows a further embodiment of an inventive

Temperature sensor 50 with a substrate 52, on which electrode pairs 54, 55, 56, 57 and electrode pairs 58, 59 are arranged. On the

Substrate 52 is formed a material layer 61, which in a Aggregate state change from the solid to the liquid form in risers 63, 65, 67 can flow. The inflow of the liquefied material layer 61 via capillary forces. A change in capacitance 69 can be used to ascertain whether a layer of material in liquefied form has flowed into the riser pipes 63, 65, 67 into the region of the electrode pairs and possibly has solidified there again.

FIG. 6 shows the production of a temperature sensor 70 according to the invention with a substrate 72, on which electrodes 74, 76 are embedded, which are embedded in a material layer 78. Electrically conductive particles 79 made of metal, plastic or carbon are identified by the reference numeral 79. If the particles 79 are magnetizable, they can be aligned via magnets within the material layer 78 as long as the material layer 78 has not yet cured.

On a Peltier element 81, a film-like substrate 72 is placed. On this substrate 72, the electrodes 74, 76 are brought. If the material layer 78 is applied in liquid phase to the substrate and the electrodes 74, 76, then the particles 79 can be locally positioned on the substrate 72 via an electromagnet. After positioning, the material layer 78 is cured and the temperature sensor can be used as described according to the invention.

In a temperature sensor 10, which is suitable for attachment to or on objects of all kinds, at least two spaced-apart electrodes 14, 16 and at least one material layer 18 are arranged on a substrate 12. The material layer 18 is formed between the electrodes 14, 16, wherein the material layer 18 changes depending on the temperature acting on the material layer 18 or it accumulates in different Form between the electrodes 14, 16 at. The temperature sensor 10 does not require an energy source and material changes of the material layer 18 can be measured via the electrodes 14, 16.

Claims

P atentansor ü che

A temperature sensor (10; 20; 30; 50; 70) for mounting on or on objects of all kinds, the temperature sensor (10; 20; 30; 50; 70) being mounted on a substrate (12; 22; 32; 52; 72 ) at least two spaced apart

Electrodes (14, 16; 24, 26; 34, 36, 41; 54, 55, 56, 57, 58, 59; 74, 76) and at least one layer of material (18; 28; 38; 61; 78), and wherein between the electrodes (14, 16; 24, 26; 34, 36, 41; 54, 55, 56, 57, 58, 59; 74, 76) on the substrate (12; 22; 32; 52; 72) Material from the

Material layer (18; 28; 38; 61; 78) depending on the temperature on the material layer (18; 28; 38; 61; 78) acting temperature enriched and / or changed.

2. Temperature sensor according to claim 1, characterized in that the enrichment and / or the change of the material layer (18; 28; 38; 61; 78) by exceeding the melting point of the material layer (18; 28; 38; 61; 78) established.

3. Temperature sensor according to claim 1 or 2, characterized in that the material layer (18; 28; 38; 61; 78) is a wax of one of the following substances or of a combination of the following or other comparable substances 1,1,1-trichloroethane

nitromethane

DL-limonene o-xylene 1-octene

glycol

cycloheptane

nonanol

1-chloronaphthalene cyclohexane

cyclo Dean

Cyclononane p-xylene

Cyclooctane 1,2,4-trichlorobenzene

acetophenone

heptadecane

heptane

Cyclohexanone tert-butanol

2-Hexandecanol

1,2,3-trichlorobenzene

hexanediol

is provided.

4. Temperature sensor according to one of claims 1 to 3, characterized in that a plurality of electrodes (34, 36, 41) or electrode pairs (54, 55, 56, 57, 58, 59) on the substrate (32, 52) are provided.

5. Temperature sensor according to one of claims 1 to 4, characterized in that the length of the spacing of the electrodes (14, 16; 24, 26; 34, 36, 41) on the substrate (12; 22; 32) is variable.

6. Temperature sensor according to claim 4 or 5, characterized in that with more than two electrodes (34, 36, 41) at least one electrode (41) has a different length extension compared to the other on the substrate (32) formed electrodes (34 , 36), and / or in the case of electrode pairs (54, 55, 56, 57, 58, 59) the electrode pairs (54, 55, 56, 57, 58, 59) on the substrate (52) in a series and / or parallel connection are arranged.

7. Temperature sensor according to one of claims 1 to 6, characterized in that the thickness of the material layer (18; 28; 38; 61; 78) is variable.

8. Temperature sensor according to one of claims 1 to 7, characterized in that the substrate (12; 22; 32; 52; 72) consists of glass, ceramic, plastic, a plastic film or of another flexible material.

9. Temperature sensor according to claim 8, characterized in that the electrodes (14, 16) and the material layer (18) in a substrate (12) made of plastic film or of another material are flexible.

10. Temperature sensor according to one of claims 1 to 9, characterized in that at the electrodes (14, 16, 24, 26, 34, 36, 41) measuring surfaces (15, 17, 25, 27, 35, 37, 42) for Contacting with a measuring and / or reading device are provided.

11. Temperature sensor according to one of claims 1 to 10, characterized in that in the material layer (61) on the substrate (52) during aggregate state change of the material terialschicht (61) due to Kapiliarkräften in at least one on the substrate (52) formed riser (63, 65, 67) flows in and at least one electrode (54, 55, 56, 57, 58, 59) respectively along and on both sides of the riser pipe (63, 65, 67) is provided.

12. Temperature sensor according to one of claims 1 to 11, characterized in that in the material layer (28; 38; 78) electrically conductive metal powder and / or metallic particles (29; 39; 79) are introduced, which in the ready state of the Temperature sensor (20; 30; 70) without

Heat supply locally and in the surface limited to the substrate (22; 32; 72) are provided and that after the heat supply with the change of state of aggregation of the material layer (28; 38; 78) the metal powder or particles (29; ) with the material layer

(28, 38, 78) are distributed between the electrodes (24, 26, 34, 36, 41, 74, 76).

13. Temperature sensor according to one of claims 1 to 12, characterized in that the substrate (12; 22; 32; 52; 72) has a self-adhesive coating on the surface diametrical to the electrodes.

14. Temperature sensor according to claim 12 or 13, characterized in that the metal powder and / or the metallic particles (29; 39; 79) are magnetizable.

15. Temperature sensor according to claim 14, characterized in that on the material layer (28; 38; 78) a magnetic strip is provided removable.

16. Temperature sensor according to one of claims 1 to 15, characterized in that the temperature sensor (10, 20;

30; 50; 70) is integrated in an RFID element.

17. Manufacturing method of a temperature sensor (70) with the following manufacturing steps:

a) application of electrodes (74, 76) on a substrate (72) made of glass, ceramic, plastic, plastic film;

b) embedding the electrodes (74, 76) in a material layer (78) made of wax consisting of substances according to claim 3; c) curing the liquid or viscous wax after step b) or previously introducing and local alignment of metal powder and / or metallic particles (79) in the still viscous or liquid wax and subsequent curing of the waxy material layer (78).

18. The method according to claim 17, characterized in that the alignment of the metal powder and / or the metallic particles (79) with an electromagnet (82).

19. The method according to claim 17, characterized in that the introduction of the metal powder and / or the metallic particles (79) into the material layer (78) via a wetted with the metal powder and / or the metallic particles (79) adhesive tape, the at Melting the material layer (78) the metal powder or the metallic particles (79) to the material layer (78) emits.