DE102019107600B4 - Antenna arrangement - Google Patents

Abstract

The invention, which relates to an antenna arrangement (1), is based on the object of specifying an antenna arrangement (1) which meets small installation space requirements, with which an improvement in the transmission properties is achieved, especially in the near field, and which can be produced easily and at reduced costs. This object is achieved in terms of the arrangement in that the antenna arrangement (1) is a planar antenna arrangement (1) that in the antenna arrangement (1) a first conductive layer (2), a first substrate (5) and a second conductive layer in a sequence (3), a second substrate (6) and a third conductive layer (4) are arranged so that the conductive layers (2, 3, 4) only partially extend over the surfaces of the substrates (5, 6) that a via (7) is arranged between the second conductive layer (3) and the third conductive layer (4) and that a connection (8) is arranged on the first conductive layer (2).

Description

The invention relates to an antenna arrangement which is arranged in a pacemaker capsule or in a capsule implanted in a body of a living being, the antenna arrangement being arranged for wireless transmission of data.

Cardiac pacemakers or cardiac pacemaker capsules are known from the prior art as devices which are used in the event of malfunctions of the heart such as, for example, a heartbeat frequency that is too low or cardiac arrhythmias or cardiac dysfunction. Cardiac pacemakers are electronic pulse generators, which usually generate regular electrical pulses to stimulate or excite a heart muscle, whereby when a pulse is generated using appropriately arranged electrodes, a targeted contraction of a heart muscle to be stimulated occurs in the area of the electrode. Thus, for example, cardiac pacemakers can be used in the treatment of patients in whom the rhythm of the heartbeats is to be corrected.

Cardiac pacemakers, which work without connections or cables to transmit data, are a very specific application area of innovative medical product research, which has become more and more important in recent years.

Such cardiac pacemakers with wireless transmission of data are, for example, implanted deep into the human tissue in the area of the heart and are intended to enable a wireless exchange of data with an associated external device. In addition, it is desirable that such cardiac pacemakers also enable wireless transmission of data with other implanted arrangements such as capsules arranged in the body or body tissue of a patient directly in the heart chamber.

In this context, these implanted arrangements such as capsules are understood to mean both arrangements implanted near the skin surface and arrangements implanted deeper in the body or body tissue.

In order to enable wireless transmission of data to and from a cardiac pacemaker, such cardiac pacemakers have an antenna arrangement with an antenna, which must meet special requirements.

In order to achieve successful and stable transmission of data or communication between a pacemaker and another implanted capsule or an external device and to extend the life of the battery in the pacemaker, a highly efficient implanted antenna is necessary.

The challenges in the development of such antennas include miniaturization, the reduction of the profile and the reduction of the losses that arise in wireless communication, particularly through human body tissue.

Due to the restricted installation space of a cardiac pacemaker or the restricted volume of a capsule to be implanted, the dimensions or the diameter of such antennas must be less than 6 mm. In addition, the profile of the antenna should have a small height so that more space remains for the battery required to operate the pacemaker and other functionally necessary elements of a pacemaker.

Another problem is the improvement of the radiation efficiency of such antennas, since a large part of the power radiated by the antenna is absorbed by the human body tissue surrounding the pacemaker capsule.

So-called magnetic antennas are known from the prior art, in which the magnetic component of the electromagnetic field is used to generate the electromagnetic waves. Such magnetic antennas are suitable, for example, as receiving antennas within rooms, because the magnetic fields used to transmit information are significantly less disturbed than the electric fields.

The smaller the circumference of the magnetic antenna in relation to the wavelength λ of the transmission or reception frequency used to transmit information, the greater the effect of the magnetic component of the magnetic antenna on its electrical component.

Antennas in which the circumference is 0.3 to 0.1 times the wavelength λ are referred to as electromagnetic antennas, and antennas in which the circumference is less than 0.1 times the wavelength λ are referred to as magnetic antennas or magnetic antennas designated.

These magnetic antennas enable a compact and space-saving design, with the disadvantage that the efficiency to be achieved decreases with the reduction in size of the magnetic antennas. As a result, prior art magnetic antennas are mostly unsuitable for broadcast purposes.

The antennas known from the prior art mostly have sizes that are too large to be used in increasingly smaller pacemaker capsules or other capsules to be implanted. In addition, the known antennas have a poor transmission coefficient, especially when used in human body tissue.

In addition, the use of antennas of this type, which have a low degree of efficiency, would place greater demands on the battery power, which leads to a shortening of the service life of a cardiac pacemaker and possibly to a reduction in the reliability of the cardiac pacemaker.

A general and implantable medical device (IMD) is known from US 2010/0 109 966 A1. In particular, the present invention relates to a telemetry antenna suitable for use in medical devices. The object to be solved is to specify a telemetry antenna which has improved transmission properties and is smaller.

To achieve this object, a telemetry antenna for an implantable medical device is specified which comprises at least one antenna conductor which is formed on a dielectric layer. Furthermore, a plurality of discrete dielectric layers, which are arranged above the antenna conductor, are provided, on which further antenna conductors are arranged.

From the US 8,983,618 B2 an antenna for an implantable medical device (IMD) is known. The object to be achieved is to provide an antenna for an implantable medical device which has improved transmission properties.

As a solution, it is proposed that the antenna contain a monolithic structure which consists of several discrete dielectric layers. The antenna includes antenna sections formed in different layers of the monolithic structure with conductive vias formed to extend across the dielectric layers to provide a conductive path between the antenna sections formed on different layers to form an antenna, which extends over several vertical layers. The dielectric layers can comprise layers of ceramic material that can be fired together with the antenna to form a hermetically sealed monolithic antenna structure. The antenna embedded in the monolithic structure can be arranged in such a way that it has a substantially spiral, helical, fractal, meandering or planar serpentine spiral shape.

Based on this prior art, there is a need for an improved antenna assembly for a pacemaker capsule or other implantable capsule.

The object of the invention now consists in specifying an antenna arrangement which satisfies small installation space requirements and with which an improvement in the transmission properties is achieved. In addition, the antenna arrangement should be simple to manufacture and at reduced costs. The aim is to improve the transmission properties in particular in the near field of the antenna.

The object is achieved by an arrangement with the features according to claim 1 of the independent claim. Further developments are in the dependent claims 2 to 4 specified.

It is provided that a magnetic antenna is used in the antenna arrangement. An optimized magnetic antenna of this type has a higher radiation efficiency in human body tissue than an electrical antenna. Thus, on the one hand, an improvement in the quality of wireless communication through the human body tissue can be achieved and, on the other hand, the energy required for communication can be reduced, which results in an increase in the operating time of the pacemaker capsule.

There is also provision for this magnetic antenna to be designed in a miniaturized size and with a small height.

It is provided that the antenna of the antenna arrangement is designed as a planar antenna or planar antenna. In the invention, a planar electrically coupled loop antenna (PECLA; planar electrically coupling loop antenna) is proposed for wireless communication, for example in pacemaker capsules or other implanted capsules.

An electrical coupling structure is used in the signal transmission within the antenna arrangement in order to improve the real part of the impedance of the antenna and to provide a capacitance so that the size of the antenna can be reduced. It is also provided that the current path on the antenna is circular, for example. The term circular does not necessarily mean a course of the antenna arrangement along an imaginary circular path with a constant radius. According to the present In accordance with the invention, other circular current paths can also be considered, for example an elliptical shape or a shape approximating to a rectangle or a shape of an unclosed figure of eight and many other shapes which allow a circular or approximately circular current flow in the antenna arrangement.

It is also provided that the circular current path of the antenna is not designed completely but only as a circular ring sector.

The low height in its design of the antenna arrangement is achieved in that the antenna is manufactured using standard printed circuit board technology (PCB). The use of such technology also enables inexpensive mass production.

In addition, such a flat and planar antenna arrangement on a two-layer printed circuit board can be easily integrated into a transceiver arrangement in a pacemaker capsule. The low height of the antenna arrangement leaves more space, for example for the battery, in the pacemaker capsule. A flat and planar antenna arrangement of this type on a three-layer or multi-layer circuit board is also possible.

The use of the antenna arrangement according to the invention is intended for communication in the near field.

A distinction is made in the spatial areas of an antenna arrangement, for example, between the terms near field, far field and the transition field between the near field and the far field, the boundaries between the individual spatial areas being dependent on the wavelength λ.

For antennas that are shorter or smaller than half the wavelength λ of the radiation they emit, the far and near regional boundaries are defined in terms of a ratio between the distance r from the antenna arrangement to the wavelength λ of the radiation emitted.

For such an antenna arrangement, the near field is the region within a radius r «λ, while the far field is the region for which r» 2λ applies. The transition zone is thus defined as the area between r = λ and r = 2λ.

For the MICS band (MSCI; Medical Implant Communication Service), which is usually used for communication with pacemaker capsules, for example, which can be used in a frequency band from 401 MHz to 406 MHz, the effective wavelength in the human body or body tissue is at an exemplary frequency from 403.5 MHz 91.6 mm, so that the near field area has a radius of about 91.6 mm.

This means that when a magnetic antenna or a magnetic dipole is used as an antenna in the near field of about 91.6 mm, a high magnetic field strength for communication between a pacemaker capsule and an external device or for communication between one pacemaker capsule and another is implanted Capsule is available.

For the ISM band (ISM; Industrial, Scientific and Medical Band) used in industry, science and medicine, the effective wavelength in the human body or body tissue at an exemplary frequency of 2.45 GHz is 16.3 mm, so that the Near field has a radius of about 16.3 mm.

• 1: eine Schnittdarstellung der erfindungsgemäßen planaren Antennenanordnung in einer dreilagigen Ausführung,
• 2: eine Prinzipdarstellung der erfindungsgemäßen planaren Antennenanordnung in einer dreidimensionalen Ansicht der Anordnung nach 1,
• 3: eine Prinzipdarstellung einer planaren Antennenanordnung in einer zweilagigen Ausführung und
• 4: ein Ersatzschaltbild der Antennenanordnung.

The previously explained features and advantages of this invention can be better understood and assessed after careful study of the following detailed description of the preferred, non-limiting example embodiments of the invention with the accompanying drawings, which show:

• 1 : a sectional view of the planar antenna arrangement according to the invention in a three-layer design,
• 2 : a schematic representation of the planar antenna arrangement according to the invention in a three-dimensional view of the arrangement according to FIG 1 ,
• 3 : a schematic representation of a planar antenna arrangement in a two-layer design and
• 4th : an equivalent circuit diagram of the antenna arrangement.

The 1 shows a sectional view of the planar antenna arrangement according to the invention 1 in a three-layer design.

The antenna arrangement 1 has a first electrically conductive layer 2 which extends at least partially over a first surface of a first substrate 5 extends. On one of the first surfaces of the first substrate 5 opposite second surface of the first substrate 5 is a second conductive layer 3 arranged. This second conductive layer too 3 can only partially extend over the second surface of the first substrate 5 extend.

To the second conductive layer 3 adjacent is a second substrate 6th arranged, which is parallel to the first substrate 5 extends so that a first surface of a second substrate 6th on the second conductive layer 3 is applied. The second substrate 6th has a second surface opposite its first surface on the surface of which a third conductive layer 4th is arranged.

In order to enable the antenna arrangement to work in a corresponding manner, a through-hole connection is provided 7th to arrange which the second electrically conductive layer 3 with the third electrically conductive layer 4th electrically conductive connects.

It is also provided that a coupling to the first electrically conductive layer 2 by means of a connection 8th is made possible, the connection 8th is designed such that it passes through the plane of the second electrically conductive layer 3 and the plane of the third electrically conductive layer 4th runs electrically isolated. Via this connection 8th the feed takes place in the antenna arrangement 1 .

In the 2 is a schematic diagram of the planar antenna arrangement according to the invention 1 in a three-dimensional view of the arrangement 1 shown.

A first conductive layer embodied as a section of a ring, that is to say a sector of a circle, can be seen 2 . In the example of 2 covers the circular sector of the first conductive layer 2 about a quarter of the entire ring or circle, the exact size of this section by appropriate dimensioning of the antenna arrangement 1 is determined.

Separated from this first conductive layer 2 through the first substrate 5 is under the first substrate 5 the second conductive layer 3 shown, which is also designed as a circular sector. This second conductive layer 3 forms a circular current path for the antenna. Through the opening of the circular sector or the circular current path in the second conductive layer 3 a first capacity is formed.

In the 2 is under the second conductive layer 3 the second substrate 6th shown. A person skilled in the art will also understand the connection together with the 1 clearly visible.

In the 2 is under the second substrate 6th the third conductive layer 4th shown, which also does not form a completely closed ring and thus a circular sector. The plated-through hole can also be seen 7th which is the second conductive layer 3 with the third conductive layer 4th electrically conductive connects. The one for feeding the antenna arrangement can also be seen 1 used connection 8th which only applies to the first conductive layer 2 is conductively connected. Between the first conductive layer 2 and the second conductive layer 3 Another capacity develops.

The antenna arrangement according to the invention 1 , also referred to as a planar electrically coupled loop antenna, hereinafter referred to as PECLA for short, (PECLA; planar electrically coupling loop antenna) is very advantageously produced by means of standard printed circuit board technology (PCB).

The top copper layer of a three-layer printed circuit board, for example, is the first conductive layer 2 This forms an open transmission line with low impedance that connects to the feed probe, the connector 8th connected is. The middle copper layer of the three-layer circuit board provides the second conductive layer 3 ready, which forms a short-circuited high-impedance transmission line. The second conductive layer 3 is about the via 7th to the lower copper layer and thus the third conductive layer 4th connected to the three-layer circuit board. The second conductive layer 3 is made by capacitive coupling from the top first conductive layer 2 fed.

The first substrate 5 has a low relative permittivity ε, for example in the range between 2 and 4, in particular around 3, and a large thickness, for example in the range between 0.2 mm and 0.3 mm, in particular around 0.254 mm (10 mil), around the ohmic Losses and the stored energy in the antenna arrangement 1 to minimize. The height of the first conductive layer 2 , the thickness of the first substrate 5 and the permittivity of the first substrate 5 are for scaling the input impedance of the antenna arrangement 1 responsible.

The capacitance that develops between the second conductive layer 3 and the third conductive layer 4th can be the size of the antenna arrangement 1 minimize. Hence the second substrate 6th with a high relative permittivity, for example in the range between 9 and 11, in particular about 10.2, and a small thickness, for example in the range between 0.1 mm and 0.2 mm, in particular 0.127 mm (5mil). Due to the three-layer structure of the antenna arrangement shown 1 the antenna can be easily adjusted to an impedance of around 50 ohms.

The radiation part of the antenna arrangement 1 is the second conductive layer 3 , which is designed as a "loop" or a circular ring sector, where the Antenna array diameter 1 is smaller than λ / 4 and where the radiation field of the antenna arrangement 1 can be approximated as a magnetic Hertzian dipole.

For the short-distance communication scenario of a deeply implanted pacemaker capsule, the radiation field of the magnetic Hertzian dipole has a lower electric field density than the electric dipole in the near field, which implies that the absorbed power in the near field, i.e. in the human tissue directly surrounding the pacemaker capsule, is lower, so that the transmission coefficient of the antenna arrangement 1 is improved.

The working principle of the antenna arrangement according to the invention 1 (PECLA) is not completely different from other antenna arrangements known from the prior art, such as one from [1] Akbarpour, A., & Chamaani, S. (2017) “Dual-band electrically coupled loop antenna for implant applications” IET Microwaves , Antennas & Propagation, 11 (7), 1020-1023 known antenna arrangement or from [2] Manteghi, M. (2013) "Electrically coupled loop antenna as a dual for the planar inverted-f antenna" Microwave and Optical Technology Letters, 55 (6), 1409-1412 known antenna arrangement.

The disadvantages of these known antenna arrangements are, on the one hand, the insufficiently small design of such antennas and, on the other hand, the increased effort involved in producing such antennas using micromachining systems, which must have sufficient accuracy.

These disadvantages are caused by the antenna arrangement according to the invention 1 overcome because the planar designed electrically coupled loop antenna according to the invention 1 (PECLA) can be manufactured by means of a multilayer printed circuit board technology. This results in both miniaturization and high machining accuracy of the antenna arrangement 1 as well as inexpensive mass production possible.

The planar structure of the antenna array 1 reduces the antenna volume required. For example, the dimensions and volume of the MICS tape ECLA proposed in [1] without a lumped capacitor are 14.3 mm x 13 mm x 15 mm and 2788.5 mm ³ .

In contrast to this, the dimensions of the antenna arrangement are 1 only 12 mm x 12 mm x 0.4 mm and the volume is thus reduced to 57.6 mm ³ , which corresponds to about 1/50 of the volume of ECLA in [1].

In addition, the planar structure facilitates the antenna assembly 1 the integration in the pacemaker capsule and saves space, which increases the space requirement of the battery and other functionally necessary components with the limited volume of the pacemaker capsule. The electrical components of the pacemaker capsule are usually positioned as a stacked structure, so that the planar antenna arrangement 1 a pacemaker capsule can be placed in the upper or lower area.

The 3 shows a schematic diagram of a planar antenna arrangement 1 in a two-layer design with a coupling capacitor shown 9 .

About the structure of an antenna array 1 To simplify (PECLA), only a two-layer arrangement of the elements of an antenna arrangement is required 1 shown on a two-layer circuit board or the like, with only a first substrate 5 is needed.

Here is the lower copper layer of a printed circuit board, i.e. the second conductive layer 3 , designed as an open transmission line and is connected to the positive part of a coaxial cable over which the antenna arrangement 1 is connected to a transmit-receive arrangement. The connection of the coaxial cable to the antenna arrangement 1 is in the 3 not shown.

The top copper layer of the circuit board, i.e. the first conductive layer 2 , is a short-circuited transmission line that connects to the negative part of the coaxial cable.

The first conductive layer 2 is made by capacitive coupling from the second conductive layer 3 powered, with between the first conductive layer 2 and the second conductive layer 3 the first substrate 5 is arranged.

The layer thickness of the first conductive layer 2 and the second conductive layer 3 , the thickness and the permittivity of the first substrate 5 affect the real part of the input impedance Zin 10 the antenna arrangement 1 . The input impedance Zin 10 the antenna arrangement 1 can be set by appropriate dimensioning and material selection.

A coupling capacitor is provided 9 on the first conductive layer 2 to arrange.

By arranging a coupling capacitor 9 becomes the size of an antenna array 1 scaled down. In addition, by means of the coupling capacitor 9 the imaginary part of the input impedance can be adjusted so influenced.

By means of a two-layer antenna arrangement 1 the structure is simplified and the requirement in a manufacturing process is reduced. In particular, the coupling capacitor used leads 9 to a reduction in the size of the antenna arrangement 1 .

In the 4th is an equivalent circuit diagram of the antenna arrangement 1 shown. The 4th shows the input impedance Zin 10 . This input impedance Zin 10 results according to: $$Z_{in}={\mathrm{R.}}_{in}+j{X}_{in}=\left({\mathrm{R.}}_r+{\mathrm{R.}}_{\mathrm{L.}}\right)+j\omega \left({\mathrm{L.}}_{\mathrm{A.}}+{\mathrm{L.}}_i-{\mathrm{C.}}_r\right)$$

Here R _{r is} the radiation resistance 11 , R _{L is} the loss resistance 12 , L _{A is} a loop inductance 13th , L _{i is} an inductance of the loop conductor 14th and C _r a capacitance 15th a parallel capacitor.

In the first embodiment of the antenna arrangement 1 according to 1 and 2 by means of a three-layer printed circuit board, the capacitance C _{r is} 15 between the second conductive layer 3 and the third conductive layer 4th educated.

In the second embodiment of the antenna arrangement 1 according to the 3 by means of a two-layer printed circuit board, the capacitance C _{r is} 15 through the coupling capacitor 9 educated.

As already mentioned, the coupling between the feed head and the loop line can increase the real part of the impedance, so that the dimensions of the feed head and loop line, i.e. the size of their respective circular ring sectors, change in order to set a radiation resistance R _r of about 50 ohms.

Such an antenna arrangement according to the invention 1 can also be used, for example, in the area of medical probes, which are used, for example, in medical examinations or therapy in areas of the body that are difficult to access.

List of reference symbols

1

Antenna arrangement

2

first conductive layer (top layer)

3

second conductive layer (middle layer)

4th

third conductive layer (bottom layer)

5

first substrate

6th

second substrate

7th

Plated through hole (via)

8th

Connection (feeding probe)

9

Coupling capacitor

10

Input impedance Z _in

11

Radiation resistance R _r

12

Loss resistance R _L

13

Loop inductance L _A

14th

Inductance of the loop conductor L _i

15th

Capacity C _r

Claims (4)

Antenna arrangement (1) which is arranged in a pacemaker capsule or a capsule implanted in a body of a living being, the antenna arrangement being arranged for wireless transmission of data, the antenna arrangement (1) being a planar antenna arrangement (1), wherein in the Antenna arrangement (1) a first conductive layer (2), a first substrate (5), a second conductive layer (3), a second substrate (6) and a third conductive layer (4) are arranged in a sequence and wherein the conductive layers (2, 3, 4) only partially extend over the surfaces of the substrates (5, 6), characterized in that a through-contact (7) only between the second conductive layer (3) and the radiation part of the antenna arrangement (1) forming the third conductive layer (4) is arranged and that a connection (8) is arranged on the first conductive layer (2) for feeding in such a way that the connection (8) through the level ne of the second electrically conductive layer (3) and the plane of the third electrically conductive layer (4) is electrically insulated. Antenna arrangement (1) according to Claim 1 , characterized in that the conductive layers (2, 3, 4) which only partially extend over the surfaces of the substrates (5, 6) are arranged in the form of circular ring sectors. Antenna arrangement (1) according to Claim 1 or 2 , characterized in that the connection (8) is arranged through the first and the second substrate (5, 6) and through the second conductive layer (3) and the third conductive layer (4) so as to be plugged in and isolated from them. Antenna arrangement (1) according to one of the Claims 1 to 3 , characterized in that the first substrate (5), the second substrate (6) and the conductive layers (2, 3, 4) are arranged in a multilayer printed circuit board.

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