The invention relates to an I-inductor, which represents a passive magnetic component, for high frequency or microwave technology, that is a HF inductor.
Such inductors are known in the transformer field as macroscopic components where they consist of an isotropic magnetically permeable material. They are also known as HF micro-inductors in micro-systems engineering or in integrated circuit designs in xe2x80x9con-diexe2x80x9d construction (on die=disposed on a chip or a substrate), wherein for field-permeated bodies or cores materials with a single-axis, non-axial anisotropy are used in order to be effective also at high frequencies.
By the shape of the magnetically permeated parts, a reduction of the fields leaving the components is achieved which greatly reduces the formation of shielding currents in the support structures of the component or of electromagnetic disturbances in adjacent components. The arrangement of an I-inductor is relatively compact so that parasitic capacities can be kept small. By a suitable conditioning and utilization of surface conductor, arrangements can be provided which reduce the resistance and which improve the grade.
Annular core impedance coils or toroidal micro-inductors are similar in design and in operation. They consist reasonably only of isotopic materials. Magnetic materials with single axis-, in technical terms uni-axial anisotropy, cannot be used. According to the present state of the material science, isotropic magnetic materials are not suitable for the frequency range above 1 GHz [1].
For solenoids or cylindrical coils the same considerations apply. Various embodiments are known in this regard:
In micro-systems engineering, the solenoid is also used as a planar coil, wherein the coil axis extends normal to the substrate. For high frequencies such arrangements are usable in only a limited way since shielding currents are generated in the substrate which reduce the inductivity. These components have a low grade for high frequency applications.
Since the arrangement has a low efficiency particularly in connection with high frequencies, the components are made relatively large which increases also the parasitic capacities. By the use of additional magnetic layers at the front surfaces of the planar coils, the inductivity can-be increased but the frequency limit of the coil is reduced thereby. The quality of the coil can be increased by the use of wide conductor elements in the planar coil but this is possible only to a small extent since, in a planar coil, the required area increases thereby. [II]. Above 0.1 GHz such a design is of no interest because of a pronounced increase of the capacity and eddy current problem. Also, it is only possible with magnetically isotropic materials.
Another group includes solenoids, whose coil axes extend parallel to the substrate. Also, these solenoids are suitable for the high frequency range only under certain conditions because of the excitation of shielding currents in the substrate since the stray field exits at the front surfaces. However, for increasing the inductivity, a core of a material with magnetically non-axial anisotropy may be used [III].
Furthermore, flat conductors are used as inductors. The effectiveness achievable thereby, however, is too low in the frequency range mentioned for technical applications because of the low inductivity. To increase the effectiveness, the conductor can be surrounded by a magnetic material. This solution is already used for macroscopic components with isotropic magnetic materials and is discussed in the literature as micro-inductor application [IV]. Since, in this case for example, the shape anisotropy of these layers is not taken into consideration and the conditions used are highly simplified, an application in microsystems engineering is rather questionable. The arrangement leads to a substantial excitation of shielding currents in the substrate, which complicates an industrial high frequency application. Since there are likely substantial strong fields, this has to be taken into consideration in the design of the surrounding electromagnetic components.
The relevant known state of the art can be summarized as follows:
Annular core impedance coils, which consist of materials with magnetically uniaxial anisotropy, are not effective. Impedance coils consisting of magnetically isotropic materials are not usable for the frequency range under consideration.
Solenoids are not suitable because of the stray fields, which generate shielding circuits and, as a result, cause disturbances in adjacent components.
Flat conductors have too low an inductivity or too high a parasitic capacity.
It is therefore the object of the present invention to provide high power inductors, which are economical and suitable for industrial manufacture.
In an I-conductor for high-frequency or microwave systems, two uniform cores are disposed parallel to each other with a gap therebetween and a coil is disposed on each core in such a way that, when energized by an HF current, a magnetic circuit through the two cores is generated by way of the gap at one end of the arrangement. The magnetic field-forming windings are uniform. As cores, magnetically anisotropic materials may also be used.
Preferably, the material of the bodies or cores is magnetically isotropic or it is uni-directionally or uni-axially magnetically anisotropic.
The geometric relation of the two outer bodies or cores of the arrangement with respect to bodies or cores disposed in between is such that the two outer bodies or cores have the same width and those in between are at least as wide.
Suitable winding techniques and arrangements are the following: the winding comprises a solenoid for each body or core. The turns of a winding form, together with the bodies or cores a web structure. One turn or the turns may consist of a flat conductor, which at each of its ends is provided with a connector structure for an external connection. The turns of the winding may also include band-like rectangular elements, which then may comprise:
two cores which are arranged side-by-side and are evenly trapezoid-shaped, wherein in the gap between the two cores two trapezoidal elements are disposed adjacent each other and are in contact by the two shorter of the two parallel sides of the trapezoid and aligned along the outer longitudinal edges of the bodies/cores and in electrical contact with each other;
more than two cores which are disposed adjacent each other as the elements of a winding on the two outer bodies/cores and are trapezoidal in the same way and rectangular at the inner cores. They are arranged adjacent one another in alignment and are in contact, along the outer edge of the two outer cores, with the longer of the two parallel trapezoidal sides. In the respective gap between the two outer cores and the next adjacent core at the shorter side of the two parallel trapezoidal sides of an element of the winding a rectangular element of the winding with a side of equal length is disposed and is in electrical contact therewith. In the respective gap between the inner cores, two rectangular elements of the winding are disposed adjacent, and in contact with, one another. As a result, the winding elements are disposed fabric-like adjacent one another while maintaining the required minimum distance for isolation. At both ends of a coil a connecting tab is provided for an external connection.
The I-inductor is therefore suitable for high limit frequencies up to 10 GHz with sufficient quality Q less than 500. Expediently, the HF permeability in the direction of the magnetic field axis is disposed in the cores. With the arrangement of the conductor elements and the bodies or layers of magnetic material, the shielding currents are greatly reduced. Since the arrangement is highly compact, also the parasitic capacity is low.
Below, the I-inductor according to the invention will be described in greater detail on the basis of the accompanying drawings.
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