WO2006128830A1

WO2006128830A1 - Temperature sensor

Info

Publication number: WO2006128830A1
Application number: PCT/EP2006/062633
Authority: WO
Inventors: Niels Van Der Laag
Original assignee: Siemens Aktiengesellschaft
Priority date: 2005-05-30
Filing date: 2006-05-26
Publication date: 2006-12-07
Also published as: DE102005024636B3

Abstract

The invention relates to a temperature sensor (1) comprising at least one electric resonant circuit (2) that contains at least one piezoacoustic resonator (10). The latter comprises a first electrode layer (11), at least one additional electrode layer (12) and at least one piezoelectric layer (13) composed of piezoelectric material and positioned between the electrode layers. A resonant circuit frequency of the resonant circuit is dependent on the resonator frequency of the piezoacoustic resonator and the piezoelectric material of the piezoelectric layer in the piezoacoustic resonator contains a langasite. The invention also relates to an assembly consisting of an article (20) and at least one temperature sensor (1) for determining the temperature of the article. The invention further relates to a method for determining a temperature, comprising the following steps: a) emission of an electromagnetic interrogation spectrum; b) filtering the circuit resonant frequency from the interrogation spectrum; c) receipt of the filtered interrogation spectrum; d) determination of the circuit resonant frequency; and e) determination of the temperature from the circuit resonant frequency. The invention enables the temperature of an article, in particular an article that is not easily accessible, to be interrogated in a contactless manner. The article is for example a combustion chamber of a gas turbine or the engine of a motor vehicle.

Description

description

TEMPERATURE SENSOR

The invention relates to a temperature sensor. In addition, an arrangement of the temperature sensor and a product and a method for determining a temperature of the product are indicated.

The temperature of a product or an object is detected, for example, by means of a thermocouple. The thermocouple is a component that consists of two different metals. At an interface between the metals, a temperature-dependent, so-called thermoelectric voltage is generated. This thermoelectric voltage is detected via an electrical line. From the detected thermoelectric voltage, the temperature of the thermocouple is determined by means of an evaluation unit. When the product and the thermocouple are in direct thermal contact with each other, the temperature of the thermocouple corresponds to the temperature of the product. Thus, the temperature of the product can be determined.

To detect the thermoelectric voltage electrical lines are necessary. The lines are usually electrically isolated by means of plastic. Due to the low stability of the plastic, this type of temperature detection in an aggressive environment is unsuitable. The aggressive environment is characterized for example by a high temperature of about 500 ⁰ C and by a presence of reactive gases, such as oxygen.

It is also conceivable that the product and the thermocouple are not in direct, ie in indirect thermal contact. For example, the product emits infrared radiation that is absorbed by the thermocouple. The absorbed Infrared radiation leads to heating of the thermocouple. An amount of heating of the thermocouple depends on an intensity of the infrared radiation emitted by the product and absorbed by the thermocouple. The intensity of infrared radiation emitted by the product depends on the temperature of the product. Thus, the heating of the thermocouple depends on the temperature of the product. A direct relationship can be established between the detectable thermoelectric voltage of the thermocouple and the temperature of the product.

This type of temperature determination is suitable for the case where the product and the thermocouple are in optical contact with each other. This means that the infrared radiation emitted by the product can be absorbed by the thermocouple. This type of temperature determination is unsuitable for products that are optically difficult or difficult to access.

From RC Smythe et. al. "Langasite, Langanite and Langagate Bulk-Wave Y-Cut Resonators", IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, Vol. 47, Iss. 2 (2000), pp. 355-360 is a so-called piezoacoustic resonator A BAW resonator has a capacitor structure with a first electrode layer, a further electrode layer and a piezoelectric layer with piezoelectric material arranged between the electrode layers The piezoelectric material of the known BAW resonator is a langasite Resonator resonance frequency of the resonator depends on the temperature of the resonator A temperature dependence of the resonator frequency was detected in the range of + 5 ⁰ C to + 125 ⁰ C The object of the present invention is to provide a way in which the temperature can be determined in an aggressive environment.

To achieve the object, a temperature sensor is dispensed, comprising at least one electrical resonant circuit having at least one piezoacoustic resonator with a first electrode layer, at least one further electrode layer and at least one arranged between the electrode layers piezoelectric layer with piezoelectric material, wherein an (electromagnetic) resonant circuit resonant frequency of Resonant circuit is dependent on a (acoustic) resonator resonant frequency of the piezoacoustic resonator and the piezoelectric material of the piezoelectric layer of the piezoacoustic resonator has a langasite.

To solve the problem is also an arrangement of a product and at least one such

Temperature sensor specified for determining a temperature of the product.

Finally, to achieve the object, a method for determining a temperature using such a temperature sensor is also specified with the following method steps: a) emitting an electromagnetic interrogation spectrum, b) filtering out the circuit resonance frequency from the interrogation spectrum, c) receiving the filtered interrogation spectrum d) determining of the

Resonant circuit resonant frequency and e) determining the temperature of the resonant circuit resonant frequency.

The basis of the invention is the recognition that resonant piezoacoustic resonators have a temperature-dependent resonator resonant frequency. The temperature dependence is not limited to low temperatures (up to 125 ⁰ C). The temperature dependence of Resonator resonance frequency is observed even at high temperatures, ie at temperatures of 500 ⁰ C to about 1000 ⁰ C and more. Langasite is chemically stable at temperatures. This means that there is no phase transition at these temperatures. In addition, langasite is also inert at these temperatures to a variety of chemicals. For example, there is no reaction with oxygen. Thus, the resonator is suitable for use in an aggressive environment, especially in a very high temperature environment. Characterized in that the resonator is part of the resonant circuit of the temperature sensor and the resonant circuit resonant frequency of the resonant circuit depends on the resonator resonant frequency of the resonator, by determining the resonant circuit resonant frequency of the resonator

Oscillating circuit to be closed to the temperature.

With the help of the temperature sensor, the temperature of an environment of the temperature sensor can be queried. The environment is for example a gas or gas mixture, which is conducted past the resonator of the resonant circuit of the temperature sensor. A heat transfer from the gas or gas mixture to the resonator is effected by convection. It is also conceivable that the resonator is irradiated by infrared radiation emitted by a product. The heat transfer to the resonator takes place by thermal radiation. In particular, the heat transfer from the product to the resonator takes place by heat conduction. In a particular embodiment, therefore, the temperature sensor and the product are in direct thermal contact with each other or be the

Temperature sensor and the product brought into direct thermal contact with each other.

In a preferred embodiment, at least the piezoacoustic resonator of the temperature sensor is eingekappselt. The piezoacoustic resonator is arranged in a (encapsulation) envelope. The envelope acts as a barrier to the gas or gas mixture. This means that the gas or gas mixture is not brought into direct contact with the resonator. There is no mass transfer with the resonator and thus no (chemical) reaction between a material of the resonator and the gas or gas mixture instead. Thus, with the help of the resonator, the temperature can be determined not only at high temperatures, but also in the presence of reactive gases. In addition, with the Einkappselung ensured that the gas or gas mixture can not be adsorbed on the resonator. An adsorption would lead to a change in a mass of the resonator and thus to a change in the resonator resonance frequency. Establishing a clear relationship between the resonator resonance frequency and the temperature would be difficult. The Einkappselung designed such that a heat transfer is possible. This means that the

Enveloping heat conductively connected to the environment and the resonator. The heat is transferred indirectly via the Einkapplselung from the environment to the resonator. For heat transfer by means of infrared radiation, the coating for the infrared radiation is transparent, that is, at least partially permeable.

The resonant circuit resonance frequency of the resonant circuit can in principle be determined by direct electrical contact of an evaluation device with the resonant circuit. The determination of the resonant circuit resonant frequency is cable-bound. Preferably, however, the determination of the resonant circuit resonant frequency is wireless (wireless). The evaluation and the resonant circuit are not in direct, but in indirect electrical contact with each other. Electromagnetic radiation with the resonant circuit resonance frequency is absorbed or emitted by the resonant circuit. By determining the radiated or absorbed electromagnetic radiation is closed to the resonant circuit resonant frequency and thus to the temperature. Preferably, a filter function of the resonant circuit or the piezoacoustic resonator is utilized. It turns off the resonant circuit resonance frequency a given electromagnetic spectrum filtered out. Therefore, in a particular embodiment, the temperature sensor has at least one transmitting device for emitting an electromagnetic interrogation spectrum and at least one receiving device for receiving the

Query spectrum on, wherein the electrical resonant circuit acts as an electromagnetic filter for the resonant circuit resonant frequency and the transmitting device, the resonant circuit and the receiving device are arranged in such a way that with the aid of the resonant circuit, the circuit resonant frequency is at least partially filtered out of the interrogation spectrum and the receiving device filtered query spectrum receives.

For the temperature determination by means of the temperature sensor, it is advantageous if the resonator can be excited to almost undamped resonance vibrations. This means, in particular, that the resonator and the carrier body are mechanically decoupled from one another with respect to the oscillation of the resonator. The resonator and the

Carrier bodies are acoustically decoupled from each other. This is achieved, for example, with the aid of a cavity, which is incorporated in a surface of the carrier body and over which the resonator is arranged. Also conceivable is a spring connection between the resonator and the substrate, as is known, for example, as HU-49-Anorndung in connection with quartz resonators.

The carrier body is any substrate in question. Preferably, the carrier body is a ceramic substrate. A ceramic material of the ceramic substrate is, for example, aluminum oxide (Al 2 O ₃ ) or aluminum nitride (AlN). These materials are characterized by a relatively high thermal conductivity. If the resonator and the product are indirectly connected via the support body with the relatively good heat conductive ceramic materials, there is a rapid heat conduction. The resonator and the product have the same temperature at all times. Thus, at any time, the temperature of the product can be detected very accurately. In addition, the stated ceramic materials show similar good stability against an aggressive environment such as langasite. Thus, the entire structure of resonator and ceramic carrier body is suitable for use in an aggressive environment.

It is particularly advantageous if passive electrical components (components) of the resonant circuit can also be realized with the aid of the substrate. Such components are electrical lines, capacitors or coils. Therefore, the carrier body according to a particular embodiment, a ceramic multi-layer substrate, in the volume of which at least one component of the resonant circuit is integrated.

In a particular embodiment, the carrier body from the group HTCC (High Temperature Cofired Ceramics) - and LTCC (Low Temperature Cofired Ceramics) substrate is selected. For LTCC substrates, the sintering temperature is so low that components made of silver can be integrated in the multilayer body. Silver is particularly suitable for high-frequency applications because of its low losses.

The langasite of the piezoelectric layer may be polycrystalline. For example, the resonator is designed as a thin-film resonator. Individual layers are deposited as thin films (film thickness of a few microns) from the vapor phase. For this purpose, for example, chemical (chemical vapor deposition, CVD)) or physical (Physical Vapor Deposition, PVD) vapor deposition performed. The physical vapor deposition is, for example, sputtering. The langasite single crystals are thereby oriented, that is deposited with a preferred direction.

In a particular embodiment, the langasite is monocrystalline. For producing the resonator, for example, a plate is cut from a larger single crystal of langasite. The single-crystal plate exhibits a plate thickness of 50 .mu.m to 200 .mu.m. Larger or smaller plate thicknesses are also conceivable. A lateral (area) extension of the single-crystal plate is 5.0 mm to 15.0 mm. The lateral extent is for example 10.0 mm. Larger or smaller lateral expansions are also conceivable.

The monocrystalline plate is provided on both sides with electrode material. For example, the electrode material is vapor-deposited. The evaporated

Electrode material forms the electrode layers of the piezoacoustic resonator. The layer thicknesses carried a few nm. A monocrystalline plate of langasite with a layer thickness of 70 microns and vapor deposited on both sides, a few nm thick electrode layers can be excited to acoustic vibrations with a resonator resonant frequency of about 20 MHz.

The electrode material is platinum, for example. Due to its inertness platinum is excellent for

High temperature applications in aggressive environments. Other electrode materials are also conceivable, for example alloys of different metals.

The piezoelectric material is a langasite. The langasite is selected in particular from the group Langasite, Langanat and / or Langatat. The langasite may be a rare earth gallium silicate (langasite), a rare earth gallium niobate (langanate), and rare earth gallium tantalate (langatate). So are langasite group, for example, in addition to langasite (La ₃ Ga ₅ SIOI _4), neodymium langasite (Nd ₃ Ga _S SiO ^) or praseodymium langasite (Pr ₃ Ga _S SiO ^) the Langanat group (eg, La ₃ Ga ₅ , ₅ Nbo, ₅ θi4) and the langatate group (eg La ₃ Ga _S , sTao, ₅ O14). With these materials, the temperature sensor is suitable for applications in a wide temperature range, but especially for applications at temperatures above 600 ^° C. Depending on the application, a single temperature sensor may be sufficient to detect the temperature of the product. It is also conceivable, however, that several temperature sensors are used to detect the temperature of the product. In a particular embodiment of the arrangement, therefore, a plurality of temperature sensors is present. With the aid of the majority of the temperature sensors, an average temperature of the product can be determined. By means of the majority of the temperature sensors, a temperature profile of the product can also be detected.

For example, several temperature sensors are attached to the product. Each of the temperature sensors provides information about the temperature of the product at the appropriate location.

For wireless determination of the temperature, the temperature sensors can each have their own transmitting device and / or each have their own receiving device. According to a particular embodiment of the arrangement, the temperature sensors have a common

Transmitting device and / or a common receiving device. Each transmitting device and each receiving device has an antenna. The transmitting device and the receiving device may have different antenna. According to a particular embodiment, the transmitting and

Receiving devices but at least one common antenna. As a result, a particularly simple and compact construction of the arrangement is realized.

As already mentioned, the temperature sensor is suitable for applications in excess of 600 ^° C. Thus, the temperature sensor is suitable for temperature control of an exhaust gas of a combustion process. For example, the exhaust gas temperature of an incinerator for any fuel can be controlled with the aid of the temperature sensor. The incinerator is, for example, a coal-fired power plant. Also conceivable is a waste incineration plant. With the temperature sensor, not only the temperature of the exhaust gas of a combustion process can be determined. In particular, it is also conceivable to control the temperature of a combustion process itself or the temperature of a combustion process

Product in which the combustion takes place. In a particular embodiment of the arrangement, therefore, the product is a combustion chamber for burning a fuel. In particular, a combustor of a gas turbine is used as the product. Likewise, the combustion chamber a

Be the combustion chamber of a waste incineration plant. In general, the product can be any reaction vessel. One or more chemical reactions take place in the reaction vessel. The chemical reactions are characterized by a certain energy balance (endothermic and exothermic reactions). The temperature sensor becomes the

Temperature control of such reactions used. In addition to the application in the described stationary products, the temperature sensor can also be used in a mobile product, for example in a motor vehicle. With the aid of the temperature sensor, for example, the temperature of an engine of a motor vehicle can be detected.

In summary, the following essential advantages arise with the present invention:

A temperature sensor is specified which can be used in an aggressive environment and especially in the high-temperature range.

The temperature sensor can be used in a wide temperature range and in particular in the temperature range of over 600 ^° C.

- The temperature can be detected contactless.

With reference to several embodiments and the associated figures, the invention will be described in more detail below. The figures are schematic and do not represent true to scale figures.

FIG. 1 shows a piezoacoustic resonator of the temperature sensor.

FIGS. 2A and 2B each show a piezoacoustic resonator on a carrier body.

FIGS. 3A and 3B each show a resonant circuit of FIG

Temperature sensor with piezoacoustic resonator.

Figure 4 shows an arrangement of a product comprising a temperature sensor with transmitting device and receiving device.

The temperature sensor 1 has an electrical resonant circuit 2 with a piezoacoustic resonator 10 with an electrode layer 11, a further electrode layer 12 and a piezoelectric layer 13 arranged between the electrode layers 11 and 12 (FIG. 1). The piezoelectric layer 13 is a single crystal ceramic plate of langasite. The plate has a plate thickness 14 of about 70 μm. A lateral dimension 15 of the plate is about 1.0 mm. The electrode layers 11 and 12 are made of platinum have layer thicknesses of about 5 nm.

For manufacturing the resonator 10, a ceramic plate of a langasite single crystal is cut. This ceramic plate forms the piezoelectric layer 13. On the main surfaces of the ceramic plate, platinum is evaporated to form the electrode layers 11 and 12 of the resonator 10. With the given dimensions, the resonator 10 can be excited to acoustic vibrations with a resonator resonance frequency of about 20 MHz. The resonator 10 is arranged on a carrier body 16 such that the resonator 10 can be excited to almost undamped, acoustic oscillations with the resonator resonant frequency. The resonator 10 and the carrier body 16 are acoustically decoupled from each other. For this purpose, the resonator 10 is arranged above a cavity 161 of the carrier body 16 (FIG. 3A). According to a further embodiment, the resonator 10 is arranged in the cavity 161 of the carrier body 16 (FIG. 3B). As indicated in FIG. 3A, the resonator 10 is arranged in a casing (encapsulation) 19. The sheath 19 ensures that there is no mass transfer to the environment 30 of the resonator 10. The sheath 30 and the substrate 16 form a so-called closed system. The closed system allows only an energy exchange with the environment 30. One

Mass transfer is not possible. The energy exchange is possible via the substrate 16. In an alternative embodiment, a gas for transmitting the energy is arranged in the enclosure 19. The energy exchange takes place via the gas in the envelope and over the substrate.

In a first embodiment, the carrier body 16 is single-layered. The carrier body has a ceramic material. The ceramic material is aluminum oxide. In a further embodiment, the carrier body is multilayered. The carrier body 16 is an LTCC substrate, in whose volume components of the resonant circuit 2 are integrated.

The resonator resonance frequency of the resonator 10 is temperature-dependent. With the aid of the resonator 10, an electrical resonant circuit 2 is realized. Figures 3A and 3B show equivalent circuit diagrams of two possible resonant circuits 20. The resonant circuit 2 each shows a specific resonant circuit resonant frequency. Due to the temperature dependence of the resonator resonance frequency, the resonant circuit resonance frequency is also temperature-dependent. The resonant circuit resonance frequency of the respective resonant circuit 2 is interrogated without contact. The resonant circuit 2 acts as an electromagnetic filter (Figure 4). The resonant circuit 2 is irradiated with electromagnetic radiation of an interrogation spectrum. The

Interrogation spectrum is generated by means of a transmitting device 17. The resonance resonant frequency is at least partially absorbed by the resonant circuit 2. The result is a filtered query spectrum received by a receiving device 18. The transmitting device 17 and the interrogator 18 each have an antenna for transmitting or receiving the interrogation spectrum. Due to the filtered resonant circuit resonant frequency is closed to the temperature of the resonator 10.

With the aid of the temperature sensor 1, the temperature of a product 20 is determined. The product 20 is in thermal contact with the resonator 10 of the resonant circuit 2 of the temperature sensor 1 in such a way that a heat transfer takes place by heat conduction. The product 20 and the

Resonator have the same temperature at any time.

According to a first embodiment, the product is a combustion chamber 21 of a gas turbine, in Figure 4, the combustion chamber 21 is merely indicated. The temperature sensor 1 or the electrical resonant circuit 2 with the piezoacoustic resonator 10 is arranged in the combustion chamber 21 of the gas turbine. The temperature inside the combustion chamber 21 is interrogated without contact.

According to another embodiment, the product is the engine of a motor vehicle. With the help of the temperature sensor, the temperature of the engine is detected.

Claims

claims

1. Temperature sensor (1), comprising at least one electrical resonant circuit (29) with at least one piezoacoustic resonator (10) with a first electrode layer (11), at least one further electrode layer (12) and at least one arranged between the electrode layers (11, 12) piezoelectric layer (13) with piezoelectric material, wherein a resonant circuit resonant frequency of the resonant circuit (2) is dependent on a resonator resonance frequency of the piezoacoustic resonator (10) and the piezoelectric material of the piezoelectric layer (13) of the piezoacoustic resonator (10) is a langasite having.

2. Temperature sensor according to claim 1, wherein at least the piezoacoustic resonator is arranged in a sheath.

3. Temperature sensor according to claim 1 or 2 with at least one transmitting device (17) for emitting an electromagnetic interrogation spectrum and at least one receiving device (18) for receiving the

Query spectrum, wherein the electrical resonant circuit (2) acts as an electromagnetic filter for the resonant circuit resonant frequency and the transmitting device (17), the resonant circuit (12) and the receiving device (18) are arranged in such a way that by means of the resonant circuit (2) the Circuit resonant frequency is at least partially filtered out of the interrogation spectrum and the receiving device (18) receives the filtered interrogation spectrum.

4. Temperature sensor according to one of claims 1 to 3, wherein the resonator (10) in such a way on a carrier body (16). is arranged so that the resonator (10) is excitable to oscillations with the resonator resonant frequency.

5. Temperature sensor according to claim 4, wherein the carrier body 16) is a ceramic multilayer substrate, in whose

Volume at least one component of the resonant circuit (2) is integrated.

6. Temperature sensor according to claim 5, wherein the carrier body (16) from the group HTCC and LTCC substrate is selected.

7. Temperature sensor according to one of claims 1 to 6, wherein the langasite is monocrystalline.

8. Temperature sensor according to one of claims 1 to 7, wherein the langasite is selected from the group langasite, Langanat and / or Langatat.

9. Arrangement of a product (20) and at least one temperature sensor (1) according to one of claims 1 to 8 for determining a temperature of the product.

10. Arrangement according to claim 9, wherein the product (20) and the piezoacoustic resonator (10) of the temperature sensor

(1) are in direct thermal contact with each other.

11. Arrangement according to claim 9 or 10, wherein a plurality of temperature sensors (1) is present.

12. Arrangement according to claim 11, wherein the temperature sensors

(1) have a common transmitting device (17) and / or a common receiving device (18).

13. Arrangement according to one of claims 9 to 12, wherein the product (20) is a chamber (21) and in particular a combustion chamber for burning a fuel.

14. Arrangement according to claim 13, wherein the piezoacoustic resonator (10) of the temperature sensor (1) in the chamber (21) is arranged.

15. A method for determining a temperature below

Use of a temperature sensor according to one of claims 1 to 8 with the following method steps: a) emitting an electromagnetic interrogation spectrum, b) filtering out the circuit resonant frequency from the interrogation spectrum, c) receiving the filtered interrogation spectrum, d) determining the resonant circuit resonant frequency of the resonant circuit and e ) Determining the temperature of the resonant circuit resonant frequency.

A method according to claim 15, wherein a product (20) is brought into thermal contact with the resonator (10) and due to the temperature of the resonator (10) is closed to the temperature of the product (20).

17. The method of claim 16, wherein a combustor of a gas turbine is used as the product.