CN112466629A

CN112466629A - High-frequency high-power inductor for MRI gradient power amplifier

Info

Publication number: CN112466629A
Application number: CN202011429405.9A
Authority: CN
Inventors: 徐建; 黄捷
Original assignee: Shanghai Chenguang Medical Technology Co ltd
Current assignee: Shanghai Chenguang Medical Technology Co ltd
Priority date: 2020-12-07
Filing date: 2020-12-07
Publication date: 2021-03-09

Abstract

The invention discloses a high-frequency high-power inductor for an MRI gradient power amplifier, which comprises a power ferrite magnetic core (4), a foil-shaped conductor winding (2) and an amorphous iron core (5); the amorphous iron cores (5) are coaxially arranged at equal intervals to form an amorphous iron core assembly, and two adjacent amorphous iron cores (5) are mutually insulated and provided with iron core air gaps (52); the amorphous iron core component is arranged in an air gap (3) of the power ferrite core (4), and the foil-shaped conductor winding (2) is wound on the power ferrite core (4) and surrounds the outside of the amorphous iron core component. The invention can obviously reduce the scattered magnetic flux of the high-frequency magnetic core coil, thereby reducing the eddy current loss of the copper foil coil conductor, the electromagnetic interference of the surrounding circuit and the circuit loss without increasing the volume of the inductor.

Description

High-frequency high-power inductor for MRI gradient power amplifier

Technical Field

The invention relates to an output filter inductor of a gradient amplifier, in particular to a high-frequency high-power inductor for an MRI gradient power amplifier.

Background

A gradient amplifier is one of the core components of an MRI (Magnetic Resonance Imaging) system, and is responsible for supplying power to gradient coils, so that the gradient coils generate a linearly changing gradient Magnetic field in an Imaging space, thereby changing the Magnetic field in each Imaging area to realize Magnetic field spatial encoding. To obtain high quality images, gradient amplifiers are required to provide high precision, fast varying current pulses to the inductive load. Therefore, very high requirements are placed on the output filter inductance of the gradient amplifier, especially for such high-frequency, large-current and high-power applications. Because the power ferrite has low price, complete material and magnetic core specification, good high-frequency performance, simple process of foil-shaped conductor windings (such as copper foil, aluminum foil and copper-clad aluminum foil), large current-carrying capacity, easy winding and convenient heat dissipation, the inductor formed by the power ferrite magnetic core and the foil-shaped conductor windings is a good choice.

Referring to fig. 1, in a high-frequency and high-power inductor composed of a power ferrite 1 and a foil-shaped conductor winding 2 in the prior art, the saturation magnetic flux density of the power ferrite 1 is low, in order to reduce the volume of the inductor, an air gap 3 of the power ferrite 1 is relatively large, and the larger the air gap 3 is, the larger the proportion of the fringe magnetic flux to the end face magnetic flux is, as shown in fig. 2.

The greater the extent of fringe flux expansion, the more likely it is to cause eddy currents in the copper foil coil conductor near the air gap, reducing the effective cross-sectional area of the conductor, thereby increasing conductor loss, or causing local overheating of the conductor. At the same time, stray flux can also cause electromagnetic interference and circuit loss in surrounding circuits. In order to reduce the influence of the fringing flux, the prior art solutions are: the distance between the foil-shaped conductor winding and the air gap is enlarged, but this also leads to an increased volume of the inductor.

Disclosure of Invention

The invention aims to provide a high-frequency high-power inductor for an MRI gradient power amplifier, which can remarkably reduce the scattered magnetic flux of a high-frequency magnetic core coil by changing a large air gap into a plurality of small air gaps through an amorphous iron core, thereby reducing the eddy current loss of a copper foil coil conductor, the electromagnetic interference of a peripheral circuit and the circuit loss without increasing the volume of the inductor.

The invention is realized by the following steps:

a high-frequency high-power inductor for an MRI gradient power amplifier comprises a power ferrite magnetic core, a foil-shaped conductor winding and an amorphous iron core; the amorphous iron cores are coaxially and equidistantly arranged to form an amorphous iron core assembly, and two adjacent amorphous iron cores are mutually insulated and provided with iron core air gaps; the amorphous core assembly is disposed within the air gap of the power ferrite core, and the foil conductor winding is wound around the power ferrite core and around the outside of the amorphous core assembly.

The area of the first cross section of the power ferrite core at the air gap is larger than that of the second cross section of the amorphous core.

The area S1 of the first cross section is at least 4 times of the area S2 of the second cross section, namely S1 is more than or equal to 4S 2.

The graph projected on the first cross section by the amorphous iron core is a rectangular structure concentrically arranged with the first cross section, and four edges of the graph are respectively arranged in parallel with four edges of the first cross section.

The length of the iron core air gap is less than 3mm, namely d is less than 3 mm.

The length direction of the amorphous iron core component is perpendicular to the magnetic flux cross section of the main magnetic circuit.

Compared with the prior art, the invention has the following beneficial effects:

1. the invention divides the large air gap of the power ferrite magnetic core into a plurality of small air gaps by a plurality of blocky amorphous iron cores which are arranged in series at equal intervals, and can effectively reduce the influence of the edge magnetic flux of the high-frequency and high-power inductor by reducing the size of the air gaps.

2. The cross section of the amorphous iron core adopted by the invention is smaller than that of the power ferrite magnetic core, and under the condition of not increasing the volume of the inductor, the enough distance between the foil-shaped conductor winding and the air gap can be kept, so that the fringe magnetic flux effect near the air gap is greatly weakened.

Drawings

Fig. 1 is a longitudinal sectional view of a high-frequency high-power inductor of the prior art;

FIG. 2 is a magnetic flux distribution plot of a prior art high frequency high power inductor;

FIG. 3 is a longitudinal cross-sectional view of a high frequency high power inductor for an MRI gradient power amplifier of the present invention;

FIG. 4 is a magnetic field line profile of a high frequency high power inductor for an MRI gradient power amplifier of the present invention;

FIG. 5 is a top view of an amorphous core in a high frequency high power inductor for an MRI gradient power amplifier of the present invention;

FIG. 6 is a transverse cross-sectional view of a high frequency high power inductor for an MRI gradient power amplifier of the present invention;

FIG. 7 is a graph of eddy current losses in a copper foil coil caused by fringing magnetic flux in a high frequency high power inductor of the prior art;

FIG. 8 is a graph of eddy current losses in copper foil coils caused by fringing magnetic flux in a high frequency high power inductor for an MRI gradient power amplifier of the present invention.

In the figure, 1 power ferrite, 2 foil conductor winding, 3 air gap, 4 power ferrite core, 41 first cross section, 5 amorphous core, 51 second cross section, 52 core air gap.

Detailed Description

The invention is further described with reference to the following figures and specific examples.

Referring to fig. 3 and 4, a high-frequency high-power inductor for MRI gradient power amplifier includes a power ferrite core 4, a foil-shaped conductor winding 2 and an amorphous iron core 5; the amorphous iron cores 5 are coaxially arranged at equal intervals to form an amorphous iron core assembly, and two adjacent amorphous iron cores 5 are mutually insulated and leave iron core air gaps 52; the amorphous core assembly is arranged in the air gap 3 of the power ferrite core 4, and the foil-shaped conductor winding 2 is wound on the power ferrite core 4 and surrounds the outside of the amorphous core assembly.

Preferably, the power ferrite core 4 is a conventional power ferrite, but has a large air gap 3 for disposing an amorphous core assembly. The amorphous iron core 5 can adopt a block iron-based amorphous magnetic core as a magnetic conductive material.

Referring to fig. 5 and 6, the area of the first cross section 41 of the power ferrite core 4 at the air gap 3 is larger than the area of the second cross section 51 of the amorphous core 5. Since the saturation flux density of the amorphous core 5 is about 4 times that of the power ferrite core 4, it is preferred that the area S1 of the first cross section 41 is at least 4 times the area S2 of the second cross section 51, i.e. S1 ≧ 4 × S2.

The pattern of the amorphous iron core 5 projected on the first cross section 41 is a rectangular structure concentrically arranged with the first cross section 41, and four edges of the pattern are respectively arranged in parallel with four edges of the first cross section 41, that is, the left and right edges of the pattern are parallel with the left and right edges of the first cross section 41, and the distance between the left and right edges of the pattern is a, the front and back edges of the pattern are parallel with the front and back edges of the first cross section 41, and the distance between the front and back edges of the pattern and the front and back edges of the first cross section 41 is b, and the size of the rectangular. The similar patterns arranged concentrically can ensure that the distances from the foil conductor winding 2 to the iron core air gap 52 are equal as much as possible, and avoid the problems of serious eddy current loss or over-high local temperature and the like of the foil conductor winding 2 caused by the fact that the foil conductor winding 2 is too close to the iron core air gap 52.

The length of the iron core air gap 52 is less than 3mm, namely d is less than 3mm, so that the problem that the nearby coil conductor is locally overheated due to the overlarge iron core air gap 52 is avoided.

The length direction of the amorphous iron core component is perpendicular to the magnetic flux cross section of the main magnetic circuit, so that the main magnetic flux passes through the amorphous iron cores 5 which are insulated with each other, and the eddy current resistance is increased by n compared with the prior art²And/2 times, wherein n is the number of the amorphous iron cores 5 insulated from each other, thereby greatly reducing the eddy current loss generated in the magnetic core by the coil.

Example 1:

the length of the air gap 3 of the power ferrite core 4 is 2mm, an amorphous core assembly formed by connecting 12 amorphous cores 5 in series at equal intervals is arranged in the air gap 3, the two adjacent amorphous cores 5 are insulated from each other, and the length d of the core air gap 52 is 2 mm.

The first cross section 41 of the power ferrite core 4 at the air gap 3 and the second cross section 51 of the amorphous core 5 are both rectangular, and the area S1 of the first cross section 41 is 4 × the area S2 of the second cross section 51. The gaps between the left and right edges of the amorphous core 5 and the left and right edges of the power ferrite core 4 are both a, a is 7mm, and the gaps between the front and rear edges of the amorphous core 5 and the front and rear edges of the power ferrite core 4 are both b, b is 7.5 mm.

The edge magnetic flux of the embodiment causes eddy current loss in the copper foil coil as shown in fig. 8 (the core air gap 52 is 2mm), and the magnetic flux of the high-frequency high-power inductor in the prior art causes eddy current loss in the copper foil coil as shown in fig. 7 (the air gap 3 is 22 mm); the edge magnetic flux of the high-frequency high-power inductor adopting the embodiment causes eddy current loss in the copper foil coil to be reduced to 54% of that in the prior art, and meanwhile local overheating of a nearby coil conductor caused by an excessively large air gap can be avoided.

The present invention is not limited to the above embodiments, and any modifications, equivalent replacements, improvements, etc. within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A high-frequency high-power inductor for an MRI gradient power amplifier is characterized in that: comprises a power ferrite magnetic core (4), a foil-shaped conductor winding (2) and an amorphous iron core (5); the amorphous iron cores (5) are coaxially arranged at equal intervals to form an amorphous iron core assembly, and two adjacent amorphous iron cores (5) are mutually insulated and provided with iron core air gaps (52); the amorphous iron core component is arranged in an air gap (3) of the power ferrite core (4), and the foil-shaped conductor winding (2) is wound on the power ferrite core (4) and surrounds the outside of the amorphous iron core component.

2. A high frequency high power inductor for an MRI gradient power amplifier according to claim 1, characterized by: the area of the first cross section (41) of the power ferrite core (4) at the air gap (3) is larger than the area of the second cross section (51) of the amorphous core (5).

3. A high frequency high power inductor for an MRI gradient power amplifier according to claim 1, characterized by: the area S1 of the first cross section (41) is at least 4 times of the area S2 of the second cross section (51), namely S1 is more than or equal to 4S 2.

4. A high frequency high power inductor for an MRI gradient power amplifier according to claim 1, characterized by: the graph of the amorphous iron core (5) projected on the first cross section (41) is a rectangular structure concentrically arranged with the first cross section (41), and four edges of the graph are respectively arranged in parallel with four edges of the first cross section (41).

5. A high frequency high power inductor for an MRI gradient power amplifier according to claim 1, characterized by: the length of the iron core air gap (52) is less than 3mm, namely d is less than 3 mm.

6. A high frequency high power inductor for an MRI gradient power amplifier according to claim 1, characterized by: the length direction of the amorphous iron core component is perpendicular to the magnetic flux cross section of the main magnetic circuit.