DE7209940U - Magnetometer probe - Google Patents

Description

DR. MÜLLER-BORE DIPL.-INQs CiRU EM NG _; DIPL.-CHEM. DR. DEUFEL DIPL.-CHEM. DR. SCHÖN DIPL.-PHYS. HERTEL

PATENT LAWYERS

P 22 12 610.9-55 _{M # in character L 2} 1/2

Dipl.-Phys. Dr. S. Drosdziok

Titled Magnetometer Probe

The invention relates to a magnetometer probe for measuring small magnetic fields with a core made of magnetizable Material, with a connected to an alternating current source, running parallel to the longitudinal axis of the probe back and forth Conductor for generating an alternating magnetic field at right angles to the magnetic field to be measured and with a the core arranged measuring coil for tapping the measuring signal.

Magnetometer probes for measuring small constant magnetic fields in the range from a few Oersteds (Oe) down are known in the mOe area. These probes work according to the so-called Harmonics method that uses magnetic flux control and represents a special case of parametric amplification. In this case, a highly permeable magnetic material is used Material a saturating magnetic alternating exciter ^ ld (Pumpfeld) exposed. This means that the permeability of the material is modulated with twice the pumping frequency will. As a result, the magnetization caused by the constant field to be measured is also with double the pumping frequency modulated. This results in the measurement signal in the induction coil, which was received by a phase-sensitive detector will. In the case of the known pin probes, the pump and the measuring field parallel. A tube core probe with an orthogonal arrangement of the pump field and the measuring field has also already been proposed the opposite of the pen probe with a parallel arrangement

Dr. Müller-Bor6 Dlpl.-Ing. Groening Dr. Deufel Dr. Schön Dlpl.-Phys, W. Hertel

33 Braunschwelg 8000 Munich 22, Robert-Koch-Strasse 1 5 Cologne 41 (Lindenthal)

Am Bürgerpark8 Telephone (0 89) 29 36 45 Telex 5-22 050 Bachemerstraße 54-56

Tel. (0531) 73887 Telegram address Muebopat Munich Telephone (0221) 417756

Postal check: Cologne I42J Q- & QC ^ / ßiikschareai * A »Main, account no. 2,569,366

3ai * A »MIn,

of the pump field and the measuring field has the main advantage that the useful or measuring signal is separate from the generator background is delivered and consequently this tube core probe also for Measurement of the smallest magnetic fields is suitable. (Fritz Primdahl in "IEEE Transactions on Magnetics", Vol. Mag-6, No. Jun. 2, 1970, pp. 376-385; U.S. Patent 2,856,581)

However, the size of the known probes limits their local resolution to a few mm. The presence of a Relatively large amounts of magnetizable probe material and the scattered pumping field ("with pin probes) interfere with this measuring field in the vicinity of the probe considerably.

Magnetometer probes with an orthogonal field arrangement are also known, in which a core made of magnetic material is provided is, which is also the conductor of the electrical current to generate the excitation field (DT-OS 2 122 420). Of the The conductor core is a straight rod, a U-shaped curved rod and a combination of one Cylinder sleeve with a straight rod arranged concentrically in it, the sleeve and the rod at one end are electrically connected. In all cases the measuring coil is arranged around the conductor core. In this known probe Much of the signal flow is short-circuited in the magnetically unsaturated part of the core, because this is also the excitation conductor is.

The invention is based on the object of a magnetometer probe to create smallest dimensions with significantly higher sensitivity for measuring small magnetic fields, which itself does not change the field to be measured and has a high local resolution with low electrical power requirements.

The solution to this problem is "with a magnetometer probe of the type described at the outset according to the invention achieved in that the core between the back and forth running Head is arranged. The measuring coil looping around the core can also loop around the conductor in whole or in part.

In the magnetometer probe according to the invention, the core is located as a result of the excitation conductor formed separately from the core completely in an area of maximum excitation field. Therefore, the excitation current becomes optimal for the magnetic saturation of the entire core. Furthermore, the magnetic signal flow is fully usable in the measuring coil, whereby the sensitivity of the probe according to the invention becomes extremely high.

In one embodiment of the invention it is provided that the extending part of the conductor coaxially inside the arranged backward running part of the conductor and the core is a cylinder ring arranged between the two conductor parts.

In a production-wise particularly advantageous and extremely Small-sized embodiment of the magnetometer probe according to the invention is provided that the back running part of the conductor consists of a round piece of conductor, on the outside of which is a layer of the core and before or after the core an insulating layer and finally the backward running conductor part of the conductor are applied, the two conductor parts being connected in an electrically conductive manner at the head end of the probe.

Another embodiment of the invention provides that the conductor is a flat conductor and the core and the insulation

Are flat bodies, so that a probe layered from flat bodies is created.

The conductor can consist of a U-shaped folded strip or foil conductor, with an insulating layer inside the U and the core are arranged. A particularly advantageous development of this embodiment of the invention in terms of production provides that the core and the insulating layer are applied as a layer on one side of the flat, ribbon or foil conductor.

In the embodiment of the magnetometer probe referred to as a cylinder probe according to the invention, in which the extending Conductor part coaxially inside the back Conductor part is arranged, occurs outside of the probe no magnetic pumping field and inside is the thin cylinder core magnetized homogeneously in a circular direction. The result is a probe with extremely small dimensions and extraordinary high local resolution.

In the embodiment of the invention referred to as a film probe, in which the two conductor parts are formed by a U-shaped bent ribbon or foil conductor, must because of of the open pumping circuit in terms of a low demagnetization factor the thickness of the magnetic layer must be correspondingly small compared to the width of the probe.

The invention provides a magnetometer probe which, because of its small size and because of the extremely small amount of magnetizable substance is particularly suitable for use in research and industrial testing. Of the The probe's extremely low power requirement makes it particularly suitable for use in battery-operated devices, weather balloons, Sea probes, satellites, etc. are suitable. The small dimensions and the low power requirement of the probe opened up

this is a particularly significant area of application insofar as than the probe is directly connected to the integrated semiconductor circuit technology can be combined. In this way Kan can construct complete magnetic field measuring devices, which consist of the probe, the pump oscillator, the amplifier with phase-sensitive demodulator, etc. and their largest dimension is only about 2 mm.

Exemplary embodiments of the invention are explained with reference to the accompanying drawings. In the. Drawings show:

1 shows, in a greatly enlarged representation, a schematic longitudinal section through what is referred to as a cylinder probe Embodiment of the invention, and

Fig. 2 pine of FIG. 1 corresponding sectional view the embodiment of the invention referred to as a film probe.

The cylinder probe 10 shown in Fig. 1 consists of a straight, round conductor piece L2, which has a connecting wire L1 is fed with alternating current I. On the outside of the part of the conductor that runs towards it Conductor piece L2 is a thin layer of magnetizable material forming a hollow cylindrical core M upset. Around this, in turn, a thin insulating layer S is applied, one on the outside applied back running conductor part IA insulated to the inside. This ladder part L4, its cross section t.twa corresponds to that of the inner conductor part L2, is via a connecting wire L5 to the power source for connected to the circular magnetic pumping field. The inner and outer conductor parts L2, L4- are at the head end

of the probe 10 through a conductive head piece L3 connected with each other. A measuring coil V is arranged around the probe and is electrically insulated from it Outputs are labeled U.

The individual parts of the probe 10 can be composed of prefabricated elements to achieve extremely however, to simplify the manufacture of the probe, it is preferable that the Insulating layer S, the core M and the backward running conductor part IA are applied as layers on the conductor part L2. Of course you can use the core M and the Replace insulating layer S with one another in terms of their sequence.

The current I for the circular magnetic pump field is fed in via the connecting wires L1 and L5 and flows in the leading part L2 via the connection L3 to the backward running, outer conductor part ΊΑ.The result is that outside the probe 10, the magnetic pump field disappears completely. Inside, this pump field magnetizes the thin magnetic layer forming the core M homogeneously in a circular direction.

The constant magnetic field H to be measured is parallel to the Probe 10 directed. The longitudinal magnetization of the core M generated by it and modulated by the pump field is compared with the as an induction coil acting coil W measured with the probe 10 as the core.

When making such a probe, especially when applying the thin magnetic, electrically conductive and insulating layers, can use various methods, such as

II · Il

ζ. B. evaporation in a high vacuum, electroplating, oxidation or painting can be applied. Very small probes with diameters down to about 20 μm can be produced in this way with a length of the probe of about 1 mm, the required pumping current being linear with the diameter of the inner conductor part L2 decreases.

The structure for a typical cylinder probe of this type is shown below

Inner conductor:
Magnetic layer:

Insulating layer: outer conductor layer:

Connection between inner and outer conductor: Connection wires: Dimensions of the probe: Induction coil:

Adjustment of the coil:

Amount of magnetizable probe material:

Beryllium copper, diameter 85 yum 80 Ni / 20 Fe permalloy, electrodeposited, thickness 0.6 Aim Two-component adhesive resin, special curing process, thickness 15 μm Gold, vapor deposition in a high vacuum and galvanic thickening, thickness 25 μm

special soft solder

Copper, soft-soldered, diameter 100 μm, diameter 176.2 μm, length 6 mm, enamel-insulated copper wire with a diameter of 30 μm, 4 layers, a total of 300 turns
not mandatory

8.3 / ig - 0.000 0083 g Π

Because of its small dimensions, the probe can be brought up to about 0.2 mm to objects to be measured. The extremely low one Amount of magnetizable substance (8.3 / ig) changes the Field distribution in the vicinity of the probe is no longer significant.

The disturbance is only about 0.3% of that of an equivalent pen probe.

With a sinusoidal pump current of 250 mA of the frequency of 5 kHz (measuring frequency 10 kHz), a stability and thus detection sensitivity of 0.5 mOe - without stabilization the temperature and the pumping current measured with conventional laboratory equipment - achieved. The required electrical Pump power is around 25 mW.

FIG. 2 shows a variant of the invention, referred to here as a film probe. These foil probes have taken place the round structure of the probe according to FIG. 1 has a flat structure. The parts in FIGS. 1 and 2 corresponding to one another are given the same reference number with the addition of an 'in Fig. 2 denotes.

In the space between two electrically conductive, flat layers, which form the back and forth leading part L2 ', IA' of the conductor, there are two thin layers of magnetizable material and insulating layers S ¹ each forming the core M ', each consisting of only one Layer could exist and are only two-layered here because of the advantageous manufacturing process to be described below. The pump current I flows through the two conductor parts L2 ', LV formed by a conductor foil, so that the core layer M ¹ is magnetized homogeneously transversely to the direction of the current. The insulating layer S ¹ prevents a short circuit in the pump circuit.

The longitudinal magnetic constant field H to be measured in turn supplies a signal voltage tapped at U with twice the pump frequency ^{in the induction coil W 1.}

Since the magnetic pumping circuit is open, one must ensure that in terms of a low demagnetization factor the thickness of the magnetic layers is correspondingly small compared to the width.

A particularly advantageous way of producing a film probe according to FIG. 2 consists in ^{folding a multilayer film consisting of the layers L ', M' and S 1 in a} U-shape and then arranging the induction coil W around this probe 10 '.

In comparison to the cylinder probes according to FIG. 1, the film probes have an open magnetic pump circuit and a lower mechanical stability, but compared to cylinder probes they have the advantage of being easier to manufacture.

The exemplary embodiments chosen here to explain the invention should of course?., not delimit the inventive idea on which the invention is based. Rather, this can also be implemented in a structurally modified embodiment.

Claims (1)

- ίο - Magnetometer probe for measuring small magnetic fields with a core made of magnetizable material, with a conductor that is connected to an alternating current source and running parallel to the longitudinal axis of the probe to generate an alternating magnetic field at right angles to the magnetic field to be measured and with one around the core Measuring coil for tapping the measuring signal, the axis of which runs in the direction of the field to be measured, characterized in that the core (M, M ¹ ) is arranged between the conductor (L2 IA, L2 '- L4') running back and forth.