Method of producing a magnetic field sensor, and sensor with a sensor wire press-fitted into spaced-apart conductors

A method of producing a magnetic field sensor, whose sensor element is formed by at least one piece of wire comprising amorphous or nanocrystalline ferromagnetic material, whose electrical impedance is dependent on the magnetic field. The piece of wire is connected by an electrical terminal of nonferromagnetic metal. The ends of the at least one piece of wire are press-fitted into two spaced-apart conductors of nonferromagnetic metal, in particular copper.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to a method of producing a magnetic field sensor, 
whose sensor element is formed by at least one piece of wire comprising 
amorphous or nanocrystalline ferromagnetic material, whose electrical 
impedance depends on a magnetic field, the piece of wire being provided 
with electrically conductive terminals of nonferromagnetic metal. The 
invention further relates to magnetic field sensors produced by this 
method. 
2. Description of the Related Art 
Prior art magnetic field sensors include a piece of wire made of an 
amorphous, ferromagnetic material, whose electrical impedance is 
magnetic-field-dependent. Because of this property, it is possible to 
detect the intensity of a magnetic field by measuring the current flowing 
through the sensor element. Such magnetic field sensors are used for 
instance to scan magnetically coded data carriers, which have a plurality 
of magnetic dipoles located close together. There is a need to be able to 
detect each of the thus-generated individual magnetic fields separately, 
so as to be able to pick up the information from the data carrier. Since 
the individual magnetic fields are thus very close together, there is a 
need to embody the sensor element with very short lengths, for instance on 
the order of magnitude of about 100 .mu.m, so that the desired local 
resolution can be attained. 
In the production of such magnetic field sensors, however, the problem 
arises that sensor elements made from an amorphous or nanocrystalline wire 
material with the aforementioned dimensions can be electrically connected 
by soldering only with difficulty if at all. Magnetic field sensors with 
very short effective lengths thus cannot be produced by conventional 
methods. 
It has become known from Japanese patent disclosure JP 08-323 479A to 
connect sensor elements formed of amorphous material to the electrical 
terminals by means of resistance welding. It is disadvantageous, in that 
process, that resistance welding destroys or damages the amorphous 
structure of the sensor elements, thereby destroying or affecting the 
magnetic field dependency of the sensor elements. 
SUMMARY OF THE INVENTION 
It is accordingly an object of the invention to provide a method of 
producing a magnetic field sensor, which overcomes the above-mentioned 
disadvantages of the prior art devices and methods of this general type 
and which allows the production of magnetic field sensors with very short 
effective lengths. 
With the foregoing and other objects in view there is provided, in 
accordance with the invention, an improved method of producing a magnetic 
field sensor, wherein a sensor element is formed from at least one piece 
of wire of amorphous or nanocrystalline ferromagnetic material, the 
electrical impedance of which is magnetic-field-dependent, and the piece 
of wire is provided with electrical terminals of nonferromagnetic metal. 
The improvement comprises the step of: 
press-fitting the ends of the at least one piece of wire into two 
spaced-apart electrical conductors of nonferromagnetic metal. 
In other words, the objects of the invention are attained in that the ends 
of the at least one piece of wire are press-fitted into two spaced-apart 
electrical conductors of nonferromagnetic metal, in particular copper. The 
spacing between the two conductors from one another defines the effective 
length of the sensor element. 
In accordance with an added feature of the invention, the at least one 
piece of wire, after being press-fitted into the conductors of 
nonferromagnetic metal, is additionally joined to the metal by welding, in 
particular by high-energy beams, such as laser beams. It is also 
expedient, after the at least one piece of wire is press-fitted into the 
two electrical conductors, to cut off its ends by means of high-energy 
beams, especially laser beams, or by severing welding. The reason for this 
is that these ends can influence the magnetic fields and thereby change 
the outcome and accuracy of the detection. 
In a preferred embodiment, the ends of a straight piece of wire produced 
from amorphous or nanocrystalline ferromagnetic material are press-fitted 
into two spaced-apart electrical conductors of nonferromagnetic metal. As 
an alternative to this, a piece of wire is bent approximately into a U, 
and its two legs are slipped onto a plate of electrically insulating 
material, both sides of which are provided with coatings of an 
electrically conductive nonferromagnetic metal, in particular copper, and 
press-fitted into the coatings. 
By means of both these methods, very short effective lengths of the sensor 
element can be achieved. 
In accordance with again another feature of the invention, the piece of 
wire produced from amorphous or nanocrystalline ferromagnetic material is 
embodied in a meandering shape, and its two ends are press-fitted into 
conductors of nonferromagnetic metal that are electrically separated from 
one another. The ends of two pieces of wire of ferromagnetic, electrical 
material, which form an angle with one another, in particular an angle of 
90.degree., can also be press-fitted into spaced-apart conductors of 
nonferromagnetic metal, in particular copper. As a result, magnetic field 
sensors are created by which variously oriented magnetic fields can be 
detected in a linear motion, without changing the angular position of the 
sensor. 
With the above and other objects in view there is also provided a magnetic 
field sensor produced by the above-noted method. The sensor comprises: 
a sensor element formed from at least one piece of wire of amorphous or 
nanocrystalline ferromagnetic material, the at least one piece of wire 
having two ends; 
the wire having an electrical impedance which depends on a magnetic field; 
and 
two spaced-apart electrical conductors of nonferro-magnetic metal, the ends 
of the at least one piece of wire being press-fitted into the two 
spaced-apart electrical conductors of nonferromagnetic metal, such as 
copper. 
In accordance with again a further feature of the invention, the piece of 
wire is substantially U-shaped with two legs, and the conductors are 
defined by coatings on two sides of an electrically insulating plate, and 
wherein the two legs are press-fitted into the coatings of the plate. 
In accordance with another feature of the invention, the piece of wire has 
a meandering shape. 
In accordance with a concomitant feature of the invention, the at least one 
piece of wire is one of two pieces of wire of amorphous or 
nanocrystalline, ferromagnetic material, with ends enclosing a given angle 
with one another. 
Other features which are considered as characteristic for the invention are 
set forth in the appended claims. 
Although the invention is illustrated and described herein as embodied in a 
method of producing magnetic field sensors and field sensors produced 
thereby, it is nevertheless not intended to be limited to the details 
shown, since various modifications and structural changes may be made 
therein without departing from the spirit of the invention and within the 
scope and range of equivalents of the claims. 
The construction and method of operation of the invention, however, 
together with additional objects and advantages thereof will be best 
understood from the following description of specific embodiments when 
read in connection with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to the figures of the drawing in detail and first, 
particularly, to FIG. 1 thereof, there is seen a plate 1 made from 
fiber-glass-reinforced epoxy resin, and which has an electrically 
conductive coating of a nonferromagnetic metal, such as copper, with a 
thickness of 35 .mu.m. Two electrically conductive contact faces 2 and 3 
are separated from one another, by means of a conventional etching 
technique. Electrical conductors 12 and 13 are connected to the contact 
faces 2 and 3 in the usual way, such as by soldering. The contact faces 2 
and 3 are embodied with two lugs 21 and 31, which are spaced apart from 
one another by approximately 100 .mu.m. A piece of wire 4 made of 
amorphous or nanocrystalline ferromagnetic material and having a thickness 
of about 35 .mu.m is press-fitted into these lugs 21 and 31. As a result, 
the wire 4 is mechanically and electrically joined to the lugs 21 and 31. 
Press-fitting is possible because the nonferromagnetic metal is 
substantially softer than the material from which the piece of wire 4 is 
made. 
Thereafter, the ends 41 and 42 of the piece of wire 4 that protrude past 
the lugs are cut off along the lines A--A and B--B by laser beam or by 
sever welding. This is necessary, since these ends affect the magnetic 
field, which would otherewise render the measurement incorrect. The 
effective length of the sensor element formed by the piece of wire 4 is 
determined by the spacing of the two lugs 21 and 31 from one another. 
By this method, it is thus possible to produce magnetic field sensors in 
which the effective lengths of the sensor elements have very slight 
values, and thus even magnetic fields generated by magnetic dipoles 
located close together can be detected. High resolution of a magnetically 
coded data carrier is thereby made possible, for example. With such a 
magnetic field sensor, it is also possible to detect the rotational angles 
of gear wheels or stepping motors. 
In FIG. 1a, a magnetic field sensor is shown in which the sensor element 
has a different embodiment. Once again, electrical contact faces 2a and 3a 
of non-ferromagnetic metal coatings, especially of copper, are located on 
a supporting plate 1. Conductors 12 and 13 are soldered to them. The two 
ends of a meandering sensor element 4a (formed of amorphous or 
nanocrystalline, ferromagnetic material) are press-fitted into the two 
contact faces 2a and 3a, thereby joining the ends and the faces 
mechanically and electrically. One of the terminals, which intersects the 
sensor element, must be insulated from the sensor element 4a. This 
configuration of the sensor element 4a increases its effective length 
multiple times, without thereby increasing the actual length of the sensor 
element 4a to any appreciable degree. As a result, the sensitivity of the 
sensor element is increased substantially. 
In addition, by means of such a sensor element, variously oriented magnetic 
fields can be detected by means of a linear motion, without requiring any 
change in the angular position of the magnetic field sensor. Thus magnetic 
fields oriented in various directions can be detected when the magnetic 
field sensor moves in a single direction. 
In FIG. 1b, a magnetic field sensor is shown that is embodied with two 
sensor elements. Here four contact faces 2b, 3b, 2c and 3c of a 
nonferromagnetic metal coating, in particular copper, are located on a 
supporting plate 1; the electrical terminal lines 12 and 13 and 12a and 
13a are soldered to one side of these faces while on the other, the 
respective ends of two sensors 4b and 4c, which are made of amorphous or 
nanocrystalline ferromagnetic material and intersect one another at a 
right angle, are press-fitted into the contact faces. By means of this 
kind of magnetic field sensor, directionally independent measurements can 
also be made, or magnetic fields can be detected in two dimensions. 
A second production method for a magnetic field sensor will now be 
described with reference to FIG. 2: 
The plate 20 is formed of an electrically nonconductive material, and it is 
provided on its top and bottom sides with respective electrically 
conductive coatings 22 and 23 of a nonferromagnetic electrical metal, such 
as copper. A substantially U-bent sensor element 5 of amorphous or 
nanocrystalline ferromagnetic material is placed on the plate in such a 
way that its two legs 52 and 53 are press-fitted into the coatings 22 and 
23. As a result, the sensor element is mechanically and electrically 
joined to the supporting plate 20. For magnetic fields created by very 
small magnetic dipoles, the length of the crosspiece 51 of the sensor 
element determines the length of the dipole, and the effective length of 
the sensor element is determined by the length of this crosspiece 51. 
The press-fitting of the sensor elements, made of amorphous or 
nanocrystalline ferromagnetic wire material, into the nonferromagnetic 
contact faces can be effected for instance with a polished platelet of 
aluminum oxide ceramic. 
By cutting off the ends of the pieces of wire press-fitted into the metal 
contact surfaces by means of high-energy beams or by severing welding, 
there is thus no attendant damage to the structure of the pieces of wire, 
since good heat dissipation is effected by means of the terminal faces. 
Magnetic field sensors made in this way can also be integrated into 
electrical circuits.