WO2001063964A2

WO2001063964A2 - Induction loop

Info

Publication number: WO2001063964A2
Application number: PCT/FI2001/000177
Authority: WO
Inventors: Kari Repo
Original assignee: Benefon Oyj
Priority date: 2000-02-25
Filing date: 2001-02-21
Publication date: 2001-08-30
Also published as: WO2001063964A3; WO2001063964B1; FI20000442A; FI20000442A0; AU4072701A

Abstract

An induction loop for the earpiece of a mobile phone, for example. According to the invention, induction is provided by planar conductor spirals (1, 2), which are arranged in at least two layers (3, 4) and connected in series, the direction of rotation of which on the different layers (3, 4) being the same.

Description

Induction loop

The object of the present invention is an induction loop.

In traditional hearing aids, induction is achieved by wire loops, the most significant disadvantages of which include, among others, poor productivity and inte- grability.

The object of the present invention is to provide a new kind of induction loop, for example, for a hearing aid or the earpiece, with or without a cord, of a mobile phone, radio, CD or tape player or the like, where induction loop can be used to eliminate or at least decrease the disadvantages of the traditional solutions.

The objective of the invention is accomplished by an induction loop, the characteristic features of which are presented in the appended array of claims.

Thus, the invention is based on a new, inventive basic idea that induction is provided by using the multilayer circuit board technology so that the induction loop is implemented by planar conductor spirals, which are connected in series and arranged in at least two layers, while the direction of rotation remains the same to optimise the magnetic field created.

The following advantages could be mentioned when comparing the invention with the traditional wire loop:

1. As one conductor spiral comprises several cycles, the structural height of the induction spiral according to the invention can be made low. 2. The planar conductor spiral according to the invention is easy to produce, so that the need for handwork is minimized and a mechanically durable coil is obtained, facilitating the production process and handling. 3. As the planar conductor spiral is obtained, when so desired, as a by-product from the circuit board of some other product, the cost-effectiveness of the conductor spiral according to the invention is good. It is possible to directly shape the circuit board to correspond to the end product. 4. The frequency response of the conductor spiral according to the invention is good - the minor inductance of the spiral enables an undistorted broadband frequency response.

5. As the small number of the planar spiral cycles enables good immunity to the connection of electromagnetic interference, the conductor spiral according to the invention has high immunity to interference.

6. Various surface-mounted devices can easily be connected directly to the circuit board.

7. The conductor spiral according to the invention is easy to integrate directly to the circuit board in different applications. 8. The surface finish of the circuit board and the conductor spiral on it can be achieved by simply painting, for example.

In the following, the invention is described with the aid of one of its embodiments considered preferable and with reference to the appended drawing, in which:

FIG. 1 shows the conductor spiral structure according to the embodiment of the invention considered preferable, and

FIG. 2 illustrates the frequency response of the conductor spiral structure of the preferred embodiment of the invention.

The preferred embodiment of the invention according to the one presented in the figure of the drawing comprises a first planar conductor spiral 1 having several cycles or loops, however at least two, and a second planar conductor spiral 2 similarly comprising several cycles or loops, however, at least two. Each conductor spiral 1 and 2 is produced, by using the circuit board technology, in its own layer, which is preferably formed by a circuit board 3 and 4 respectively. According to the invention, the conductor spirals 1 and 2 are connected in series and arranged in at least two superimposed layers of circuit boards 3 and 4. The invention is characterized in that the direction of rotation of the conductor spirals 1 and 2 is the same, so that it is possible to optimise the intensity of the magnetic field created.

As illustrated in the drawing, to provide the planar conductor spiral, it is preferable that on the upper layer 3, which comprises the first planar conductor spiral 1, the radius of curvature of the conductor spiral 1 continuously decreases, beginning from the outermost conductor cycle of the first conductor spiral 1 and ending at the innermost conductor cycle of the first conductor spiral 1, which is connected in series with the second planar conductor spiral 2 on the lower layer 4, the radius of curvature of the second conductor spiral 2, which for its part, continuously expands, beginning from the innermost conductor cycle of the second conductor spi- ral 2 and ending at the outermost conductor cycle of the second conductor spiral 2. One advantage of such a two-layer solution or a multiplex solution of the planar conductor spirals 1, 2 is that both the current input 5 and the current output 6 of the conductor spirals 1, 2 connected in series are, outside the conductor spiral 1, 2, possibly even close to the edge of the circuit board 3, 4. As the conductor spirals 1 and 2 are connected in series, the direction of rotation of the current remains the same from the current input 5 through the planar conductor spirals 1 and 2 to the current output 6, and the superimposed planar conductor spirals 1 and 2 intensify the magnetic field generated.

According to an alternative example of application of the invention, instead of the continuously increasing and/or decreasing radius of curvature of the conductor spiral's conductor cycles, the conductor spiral can also be built so that each cycle of the conductor spiral comprises straight portions, and the straight portions are joined by angular portions, which are preferably rounded and connect the straight portions with one another at right angles. According to the invention, to intensify the magnetic field, for example, the number of layers of the planar conductor spirals can preferably be increased in multiples of two layers, so that the connection in series of the conductor spirals and the inputs 5 and the outputs 6 can be carried out without problems. Naturally, the two- layer structure of the planar conductor spirals can also be increased by one planar conductor spiral layer implemented in the circuit board at a time, i.e., by forming a lamellar structure with an odd number of layers. Thus, in such a multilayer structure, either the current input 5 or output 6 is outside the conductor spiral 1 or 2 and, correspondingly, either the current output 6 or input 5 is inside the conductor spiral 1 or 2, in which case electric insulation may be needed.

Testing one induction loop according to the invention, which constituted part of the earpiece of a mobile phone, yielded the following results: 1. Electrical properties: - DC resistance 7.25 Ω

- Impedance (1 kHz) 7.34 Ω

- Inductance 0.24 mH

- Input (V) 100 niA/m to generate a magnetic field 21.4 mV

- Input (W) 100 mA/m to generate a magnetic field 6 x 10^"3 W 2. The frequency response illustrated in Fig. 2:

- The solid line indicates the response that was used to achieve a 100 mA/m magnetic field

- The dashed line + 20 dB and

- The line of dots - 20 db.

The invention is described above by only using one of its embodiments considered preferable. Naturally, this is not to limit the invention to apply to only one such individual embodiment. Accordingly, as is well known by those skilled in the art, many alternative solutions and variations are possible within the appended array of claims that define the inventive idea. It should be noted in particular that the conductor spiral does not have to be a spiral formed by elliptical or quadrangular cycles, because any shape of a planar spiral can be used to generate a magnetic field to achieve the object of the invention.

Claims

1. An induction loop, characterized in that induction is provided by planar conductor spirals (1, 2), which as connected in series are arranged on at least two lay- ers (3, 4), and the direction of rotation of which on the different layers (3, 4) is the same.

2. An induction loop according to Claim 1, characterized in that the planar conductor spirals (1, 2) are implemented in the layers (3, 4) by a multilayer circuit board technology.

3. An induction loop according to Claim 1 and/or 2, characterized in that an input (5) and an output (6) of the planar conductor spirals (1, 2) are outside the conductor spiral (1, 2).

4. An induction loop according to Claim 3, characterized in that the multilayer solution of the planar conductor spirals (1, 2) comprises an even number of layers.

5. An induction loop according to Claim 1 and/or 2, characterized in that the current input (5) or output (6) of the planar conductor spirals (1, 2) is outside the conductor spirals (1, 2).

6. An induction loop according to Claim 5, characterized in that the multilayer solution of the planar conductor spirals (1, 2) comprises an odd number of layers.

7. An induction loop according to any of Claims 1 to 6, characterized in that on the upper layer (3) of two superimposed layers (3, 4), where there is a first planar conductor spiral (1), the radius of curvature of the conductor spiral (1) decreases continuously, beginning from the outermost conductor cycle of the first conductor spiral (1) and ending at the innermost conductor cycle of the first conductor spiral (!)•

8. An induction loop according to any of Claims 1 to 7, characterized in that on the lower layer (4) of two superimposed layers (3, 4), which comprises a second planar conductor spiral (2), the radius of curvature of the second conductor spiral (2) increases continuously, beginning from the innermost conductor cycle of the second conductor spiral (2) and ending at the outermost conductor cycle of the second conductor spiral 2.

9. An induction loop according to Claim 1 and/or 2, characterized in that each cycle of the conductor spiral (1, 2) comprises straight portions, and the straight portions are connected by angular portions, which are preferably rounded and used to connect the straight portions with one another preferably at right angles.

10. An induction loop according to any of the preceding Claims 1 to 9, characterized in that each conductor spiral (1, 2) comprises at least two cycles or loops.