WO2008145478A2 - Tunable inductive component and use of the component - Google Patents

Abstract

The invention relates to a tunable inductive component (100) comprising at least one ceramic multi-layer body (1) having at least one ferrite layer (2) having ferritic material and at least one coil (7) integrated in the volume of the multi-layer body. A permeability of the ferrite layer is dependent on a mechanical stress acting on the ferrite layer, the coil being integrated in the volume of the multi-layer body such that an inductivity of the coil is dependent on the permeability of the ferrite layer, and a means (3, 4, 10, 11) for transferring the mechanical stress to the ferrite layer is provided, so that the permeability of the ferrite layer can be adjusted. The means for transferring the mechanical stress is, for example, an integrated piezo-element (34). The tunable inductive component is used in filter or oscillator circuits. The component can also be used as a pressure sensor.

Description

description

Tunable inductor and use of the device

The invention relates to a tunable inductive component. In addition, a use of the device is specified.

In an electronic circuit of power electronics or high-frequency technology, inductive components in combination with capacitive components play an important role. The electronic circuit is for example a resonant circuit, a frequency filter, an impedance matching network or a charge pump.

Such an electronic circuit can be optimally designed with a fixed value of the inductive and the capacitive components only for a limited frequency range (fixed frequency characteristic). An electronic circuit with variable

Frequency characteristic would be welcome but only for cost reasons.

There are circuit elements with tunable electrical characteristics. Such a circuit element is for example a tunable (controllable) inductance (variometer). Such a variometer consists, for example, of two nested cylindrical coils connected in series one behind the other. A coil has a wire winding. The wire winding has a number of turns of an electrical conductor for generating a magnetic flux by means of the current flowing in the electrical conductor. The wire winding also serves to generate a voltage by changing the magnetic induction in the wire winding.

The inner of the two coils can be rotatably mounted, for example. A maximum of total induction is achieved when the winding planes of the turns of the two coils are parallel and be flowed in the same direction from the stream. If, however, the currents flow in opposite directions with such an arrangement of the coils, the resulting inductance of the coils cancel each other out. The total induction assumes a minimum value. Likewise, relative coaxial displacement of both coils would entail a change in overall induction.

An alternative variometer consists of cylindrical coils, inside each of which a core of ferromagnetic core material is arranged. A core of a coil serves to increase the magnetic induction. The ferromagnetic core material has, as for example in a ferrite, a high permeability. Alternatively, the ferromagnetic core material is electrically conductive. This core material is a metal such as copper and aluminum. By axial movement of the cores, the magnetic flux is increased or decreased.

With respect to ferrites, it is known from H. Meuche, D. Lange, AH Nguyen, "The Impact of Pressure on Ferrite", EPCOS Components 3/2005, pp. 35-38, that the permeability of ferrites is controlled by a mechanical impact on the ferrite Voltage (pressure) is dependent.

The above-described embodiments of the variometer have limited suitability for miniaturization due to the use of macroscopic mechanical components necessary for the axial movement of the coils or cores.

The object of the present invention is to provide a compact, tunable inductive component which is suitable for miniaturization.

To achieve the object, a tunable inductive component is specified, comprising at least one ceramic multilayer body having at least one ferrite layer with ferritic material and at least one coil integrated in the volume of the multilayer body. There is one Permeability of the ferrite layer as a function of a mechanical stress acting on the ferrite layer, the coil integrated in the volume of the multilayer body such that an inductance of the coil is dependent on the permeability of the ferrite layer and a means for transmitting the mechanical stress to the ferrite layer, so that the permeability of the ferrite layer can be adjusted.

By utilizing the effect of the pressure dependence of the permeability of ferrites, the inductance of the device is varied. The following relationship is exploited (see H. Meuche et al.):

_{μ (} a) = * °> (1)

\ + kσμ (0)

6 mean the mechanical stress (pressure), μ (0) the permeability at no mechanical stress. Behind k hides a material-specific size. At a pressure of some 10 MPa, the change μ (6) -μ (0) of the permeability of the ferrite layer may be some 10%.

The ferrite layer acts as a ferrite core of the coil. The ferromagnetic core essentially influences the magnetic

Flow of the coil. Compared with a coil of the same type, which is in the air, the inductance is higher in a first approximation by the factor of the permeability of the ferrite layer. A decrease in the permeability of the ferrite layer thus causes a proportional decrease in the inductance of the coil and vice versa. With the invention, a compact, integrated, tunable inductive component is accessible. The integration leads to a high degree of miniaturization. The basic structure allows the electrical tuning of single or coupled coils, as they are eg in a transformer. As a result, inductors and the transmission behavior of transformers can be controlled. According to a particular embodiment, the coil is embedded in the ferrite layer. The coil may be partially or completely embedded in the ferrite layer. It is also conceivable that the coil is embedded in several ferrite layers. This type of arrangement ensures that the ferrite layer acts as the ferrite core of the coil and that the above-described correlation occurs between external pressure on the ferrite layer and the inductance of the coil.

It is particularly advantageous to embed the coil tension-free. This means that a variation in the permeability of the ferritic material can be fully exploited.

The ferrite is for example an oxide ceramic with the general empirical formula M ¹¹ Fe ¹ ^ ₂ O ₄ (or M ¹¹ O-Fe ₂ O ₃ ). M ¹¹ is a divalent metal, for example cobalt or iron. In particular, the ferrite has at least one selected from the group manganese and / or zinc metal. The ferrite is a MnZn ferrite. Ferrites in general and MnZn-ferrites in the

Specifically, in the stress-free state (6 = 0 MPa), special ones show a high permeability μ (0) in the range from 100 to 1000.

Various components or techniques can be used to transfer the mechanical stress to the ferritic material or to the ferrite layer of the ceramic multilayer body. For example, material having different coefficients of thermal expansion is processed in the multilayer body. By increasing the temperature, it comes to a tension and thus to build up a pressure. If it is ensured that this pressure can act on the ferrite layer, this leads, as described above, to a change in the permeability of the ferrite layer and thus to a change in the inductance Kitchen sink.

In a particular embodiment, the means for transmitting the mechanical stress on at least one piezoelectric element. One Piezoelectric element consists of a piezoelectrically active layer and on both sides of the piezoelectrically active layer attached electrode layers. In particular, the piezoelectric active layer has piezoceramic material (piezoceramic). By electrical activation of the electrode layers, an electric field is coupled into the piezoelectrically active layer. Due to the electric field, there is an expansion change of the piezoelectric layer. If now the piezoelectric element is connected to the ferrite layer in such a way that the expansion change of the piezoelectric layer is transmitted as pressure to the ferrite layer, then a pressure is built up in the ferrite layer which leads to a change of the permeability. It is conceivable that the ferrite layer is clamped between a piezoelectric element and an abutment. By controlling the piezoelectric element, the pressure is built up. Likewise, the ferrite layer can be arranged or clamped with the coil between two piezo elements.

The piezoelectric element or the piezoelectric elements are designed such that a pressure necessary for changing the permeability can be built up on the ferrite layer. For this purpose, a plurality of stacked piezo elements is provided. A multilayer actuator is used. In a multilayer actuator many piezo elements are stacked on top of each other. The multilayer actuator is for example in a

Co-firing (co-sintering) process made of stacked green ceramic sheets printed with electrode material. Such a multilayer actuator is particularly suitable for the construction and for the transmission of high pressures.

The piezoelectric element or the means for transmitting the mechanical stress to the ferrite layer can be arranged externally to the ceramic multilayer body. Preferably, however, in addition to the coil and the means for transmitting the mechanical

Voltage integrated in the multilayer body. Preferably, therefore, the means for transmitting the mechanical stress in the volume of the multilayer body is integrated. The means for transmitting is integrative component of the multilayer body. The means for transmitting the mechanical stress can be partially or completely integrated in the multilayer body. This embodiment is suitable, for example, when the ferrite layer is arranged between two piezo elements with piezoceramic.

According to another embodiment, only one piezoelectric element is part of the ceramic multilayer body. Here an external abutment is provided. This external

Abutment can be formed by a housing of the multilayer body. The housing is designed and connected to the multi-layer body, that within the ferrite layer of the necessary mechanical pressure can be established, for example by electrical control of the integrated piezoelectric element. In a particular embodiment, therefore, the means for transmitting the mechanical stress on a housing of the multilayer body. The housing acts as a pressure housing.

Various technologies for the production of ceramic multilayer bodies can be used to integrate the various components. Particularly suitable is the LTCC (LoW Temperature Cofired Ceramics) technology, with the help of low-melting and highly electrically conductive metals such as silver or copper for the integration of electrical

Components are used in a co-firing process. In a particular embodiment, therefore, at least one layer of the multilayer body has glass-ceramic. Glass ceramic is suitable for a low sealing temperature. For example, the vitrification temperature is below 900 ⁰ C. Preferably, the entire laminate of glass ceramic layers having established. The multilayer body is manufactured in LTCC technology. This can also be provided for the case of an integrated piezoelectric element. Here, the piezoelectrically active ceramic layer also has glass ceramic. However, other ceramic multilayer technologies are also conceivable, for example HTCC (High Temperature Cofired Ceramics). This can, for example, with regard to the integration of the piezoelectric element be beneficial. Piezoceramic materials such as lead zirconate titanate (PZT) are sintered at higher temperatures above 1100 ° C.

The tunable inductive component is used everywhere where inductances are used in a wide range of control. Therefore, the device is used in particular in an electrical circuit, which is selected from the group filter circuit and oscillator circuit. The tunable inductor can be widely used in frequency agile systems. Likewise, with the inductive component, a circuit element accessible, which can be used as a hardware component in the concept Software Defined Radio, SDR.

In addition, the inductive component is used in particular as a pressure sensor. For this purpose, the described pressure-induction correlation is used. Depending on the external pressure, the permeability of the ferrite layer and thus the induction of the coil change. It is merely ensured that the external pressure can act on the ferrite layer. An application of the inductive component as a temperature sensor is also conceivable. In this case, occur by the use of materials with different thermal expansion coefficients in the ceramic multilayer body as a function of temperature mechanical stresses that are transmitted to the ferrite layer and thus lead to a change in the permeability of the ferrite layer.

In summary, the following advantages of the invention should be emphasized:

- The tunable inductor is compact and contains no mechanical moving components. This is particularly true when using piezoelectric elements that are integrated in the multilayer body. - The inductive component is miniaturized, since the coil can be integrated planar, for example by means of LTCC technology between ferrite layers and piezoelectrically active layers can also be integrated by co-sintering or subsequently mounted externally on the multilayer body.

- High permeability ferrites such as MnZn compounds allow a high initial inductance in the de-energized state and thus a wide tuning range.

- When using the inductive component as a pressure sensor, a high bursting pressure is achieved, since instead of the pressure-dependent movement of a thin membrane, the pressure-dependent permeability of a relatively thick ferrite layer is measured.

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

Figures 1 and 2 each show a section of a tunable inductive component with a ceramic multilayer body in the lateral cross-section.

FIG. 3 shows a section of a tunable inductive component with a multilayer ceramic body in a lateral cross-section, which is used as a pressure sensor.

FIG. 4 shows the dependence of the inductance of two coils, each of which is integrated separately in a ceramic multilayer body, on an external pressure.

Example 1 :

The tunable inductive component 100 is a monolithically integrated with piezo elements 3 and 4 variometer, consisting of a ceramic multilayer body 1 with magnetically active Ferrite layers 2 and piezoelectric active layers 3c and 4c. The piezoelectric elements act as means for transmitting mechanical stress to the ferrite layers. The ferrite layers comprise MnZn ferrite, the ferrite layers having a relative permeability of, for example, 500.

An electrical control voltage for deflecting the piezoelectric elements can be applied via the respective electrode layers 3a, 3b, 4a and 4b arranged on both sides of the piezoelectrically active layers. In this case, the inner electrode layers 3b and 4a for the purpose of better mechanical connection of the layers 2, 3c and 4c need not necessarily be designed over a large area, but may contain openings.

In the ferrite layers is about the vertical

Through holes 5a and 6a with the outer contact surfaces 5b and 6b a contactable coil (line member) 7 embedded. The contact surfaces 8 and 9 are used to supply the control voltage for the electrode layers of the piezoelectric elements, wherein for reasons of symmetry 3a and 4b and 3b and 4a are advantageously at the same electrical potential. As a result of the piezoelectric effect, the piezoelectrically active layers 3c and 4c are subjected to mechanical stress, which they partly transfer to them due to the monolithic integration with the ferrite layers, so that the magnetic permeability in the vicinity of the coil 7 decreases and consequently the inductance of the coil decreases.

In a further, not shown embodiment, a plurality of laterally or vertically adjacent and magnetically coupled coils are integrated between the ferrite layers 2, the coupling coefficient can also vote on the pressure dependence of the permeability of the ferrite layers.

In a further embodiment, which is likewise not shown here, individual or a plurality of piezoelectric elements or piezoelectrically active layers are interposed internally integrated into the ferrite layers. In this way, upon actuation of the electrode layers of these piezoelectric elements, local mechanical stresses are introduced into the ferrite layers.

Example 2:

An alternative embodiment provides, instead of the piezoelectric elements as means for transmitting the mechanical stress, simple, thermally stressed dielectric layers in combination with the ferrite layers. It can in

Depending on the thickness of the dielectric layers relative to the thickness of the ferrite layers, mechanical stresses in the ferrite of well over 100 MPa occur, eg 160 MPa (1600 bar) with an observed decrease in permeability of 90% from 500 to 50 and consequently with a decrease inductance from 2 μH to 0.2 μH at 180 μm dielectric thickness and 810 μm ferrite thickness. The constant k (see equation 1) was determined to be k = 10 ^"4 MPa ^{" 1} .

Example 3:

In a further embodiment, in comparison to example 1, the lower piezoelectric element 4 has been omitted and replaced by an all-sided pressure housing 10. Thereby, it is no longer necessary that the upper piezoelectric element 3 for the

Transmission of the mechanical stress on the ferrite layers 2 monolithically integrated with these in the ceramic multilayer body. Rather, it may be a separate element which is placed together with the ceramic body 1 in the pressure housing before it is closed by a lid. For operation as a variometer, the lower electrode layer 3b is electrically biased relative to the pressure housing 10 by means of the through-connection 9. According to the prior art piezoelectric ceramics can at suppressed change in length of a few prints kN / cm or produce some 100 bar ^2, for example, 400 bar in the conventional piezoelectric actuators for automotive fuel injectors. The stress in the ferrite can also be increased structurally slightly by two to three times, if the cross section of the piezoelectric actuator correspondingly larger than that of the ferrite counterpart is selected. Accordingly, the effects described above in the range of 1000 bar can also be achieved in this design.

Example 4:

Instead, the housing 10 is sealed at the top by a flexible membrane 11, which exerts pressure on the ferrite layers 2 either directly or via mechanical intermediate elements or force translations under external load. A pressure equalization takes place on the unloaded side via the channel 12. The resulting change in the inductance of the coil 7 is a measure of the external pressure. The element thus operates as a pressure sensor.

With an embodiment realized according to FIG. 3, the feasibility of the invention could be demonstrated. The tunable inductive component consists of the ceramic multilayer body 1 with integrated coil 7. Der

Multi-layer body is manufactured using the LTCC technology. The multi-layer body is clamped together with a force transducer (strain gauges) in a vice so that the force exerted on the multi-layer body force is measured independently. For known area of the

Thus, the multilayer body can be calculated for the pressure and correlated directly with the observed change in the inductance of the integrated coil. For two coils of different size, the dependencies of the inductances shown in FIG. 4 result from the external pressure. The respective measuring points and the adaptation curves can be seen. For the fitting curves the material constant k = 3x k = 10 ^{~ 4} MPa ^{"1 was} used, resulting in a reduction of the inductances by 25% at 6 = 20 MPa (200 bar).

Claims

claims 1. Tunable inductor (100) comprising - At least one ceramic multilayer body (1) having at least one ferrite layer (2) with ferritic material and - At least one integrated in the volume of the multilayer body coil (7), wherein a permeability of the ferrite layer is dependent on a mechanical stress which acts on the ferrite layer, the coil is integrated in the volume of the multilayer body such that an inductance of the coil depends on the permeability of the ferrite layer, and - There is a means (3, 4, 10, 11) for transmitting the mechanical stress on the ferrite layer, so that the permeability of the ferrite layer can be adjusted. 2. The component according to claim 1, wherein the coil is embedded in the ferrite layer. 3. The component according to claim 2, wherein the coil is embedded stress-free. The device of any one of claims 1 to 3, wherein the ferritic material comprises a MnZn compound. 5. The component according to one of claims 1 to 4, wherein the means for transmitting the mechanical stress at least one piezoelectric element (3, 4). 6. The component according to one of claims 1 to 5, wherein the means for transmitting the mechanical stress in the volume of the multilayer body is integrated. 7. The component according to one of claims 1 to 6, wherein the means for transmitting the mechanical stress comprises a housing (10) of the multilayer body. 8. The component according to one of claims 1 to 7, wherein the at least one layer of the multilayer body has glass ceramic. 9. The device of claim 8, wherein the multilayer body is manufactured in LTCC technology. 10. Use of the component according to one of claims 1 to 9 in an electrical circuit which is selected from the group filter circuit or oscillator circuit. 11. Use of the component according to one of claims 1 to 9 as a pressure sensor.