GB2260413A

GB2260413A - Monitoring magnetic fields

Info

Publication number: GB2260413A
Application number: GB9121637A
Authority: GB
Inventors: Mohammad Javad Birjandi
Original assignee: Individual
Current assignee: Individual
Priority date: 1991-10-11
Filing date: 1991-10-11
Publication date: 1993-04-14
Anticipated expiration: 2011-10-11
Also published as: GB9121637D0; GB2260413B

Abstract

Apparatus for monitoring the strengths of alternating magnetic fields or magnetic field components of non-ionising. near-field radiations at radiofrequency and microwave frequencies comprises a search coil having a magnetic core (a) and a winding (d) of conducting wire, paint or spray, an output being taken via twisted wires (h) and a differential amplifier (i). The search coil may include a Faraday shield (f). Three coils may provide three-dimensional sensing (Figure 4 not shown). <IMAGE>

Description

Search Coil for Detecting Nagnetic Field Components I Nohannad Javad Birjandi of 88 Stockethill Court, Aberdeen, AB2 5UQ, Scotland, Great Britain, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be perforned, to be particularly described in and by the following statement: This invention relates to provision of the radical means by which the quality or dosisetry or strength or distribution patterns of non-ionising, near field (in particular) radiations (particularly at radiofrequency and microwave frequencies) nay be assessed very accurately using highly sensitive, of any desired dimensions -small or miniature in particular-, magnetic material based search coils.

Previous approaches are: large and/or based on conventional methods, less sensitive, less reliable, and conprise different constituents and/or employ different configurations.

It is an object of the present invention to introduce small or miniature magnetic material based search coils with enhanced sensitivity, accuracy, reliability, and resolution (and/or angular definition) that provide improvements in the means which assist in determining the quality or dosimetry or strength or distribution patterns of nonionising radiation Embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings and diagrams, in which: figure 1 is perspective view of the claimed, prototype invention -conprising a plurality of components-, providing a novel approach for detecting or sensing magnetic field conponents.

figure 2 is cross sectional view of the prototype invention -of figure 1- clained herein.

figure 3 schematically depicts a possible faraday shield, part of the invention clained herein, for cancelling the electric field components.

figure 4 schematically depicts a possible arrangement of a number of search coils (of figure 1, part of the invention clained herein) for construction of: eg. two or three (or more, whether mutually perpendicular or otherwise, as desired) dimensional search coils.

With reference to figures 1 and 2, a search coil, capable of detecting or sensing magnetic fields or magnetic field conponents, is invented and provides, by a novel approach, inproved means which assist in determining the quality or dosi metry or strength or distribution patterns of the said fields or field conponents.

The said search coil, being one approach for achieving the invention clained herein, conprises, partly, a small (eg. as small as 5 mm or even less) or miniature cylindrical (or any other desired shape) nagnetic material a which has: length 1, inner and outer diameters b and c respectively, electronagnetic characteristics, frequency-range -or frequency- of response, and perneability, all as -reasonably and/or possiblydesired.

A single turn, or plurality of turns -with any desired winding pitch-, of reasonably desired winding(s) of: - a bare or laninated, sheathed or unsheathed wire (or conductor, or wires or conductors) d with a desired -preferably small- dianeter n; or - conducting material d, eg. conducting paint or spray -of reasonably desired thickness-, preferably protected (eg. sandwiched between two -or more- insulating layers -eg. insulating paint or spray of reasonably desired thickness-) furnishes the circunference of the said magnetic material a -part of the invention declared hereabove- in a helical -or other reasonably desired- fashion.

The ends of (or other desired supposedly appro- priate points along the length of) the winding(s) discussed in the preceding sentence, preferably abiding by the declarations made for the nature and the conditions of their appropriate winding(s), are twisted tightly (or otherwise as desired), and guided to the end (or ends, as desired) of the length of the search coil eg. as shown in figure 1.The said ends are then fed: to a differential operational amplifier i (or to any other electronic conponents, filters, etc, as desired; or bypassedl as desired), and then, eventually, either via niniature plugs or via hard connection or by any other desired approaches -not necessarily via direct contact- to an appropriate, preferably small or miniature, cable k (eg. a coaxial or a balanced cable, or otherwise as desired) which, depending on the frequency of operation, at sone stage along its length (or possibly before or after the cable length), is preferably connected to a 50 ohm feed through m.

A preferably thin insulating layer e of any desired dielectric naterial is painted -or sprayed, or wrapped around, or otherwise as desired- over the winding(s) d (as desired, depending on the configuration adopted) eg. as shown in figures 1 and 2.

With reference to figures 1, 2, and 3, a desired faraday shield f surrounds the search coil components discussed hereabove. The said shield is, preferably, a continuous, thin (or as desired), cylindrical, conducting current sheet (of any desired naterial) with overlapping (but not in direct contact) ends; or, it maybe in the forn of electric dipoles f (whether painted, sprayed, made from thin wires, or otherwise as desired) e9. as shown in figure 3; or otherwise, it maybe designed as reasonably (and/or possibly) desired. The said shield Is duly grounded, or is shorted to one end of (or a supposedly appropriate point along the length of) the hereabove clained conductor(s) d (depending on the configuration adopted) which is eventually grounded, as desired.

With reference to figures 1 and 2, an insulating layer g -of any reasonably (and/or possibly) desired nature and thickness- may be used to protect the hereabove clained search coil -or its constituent components from accidental danage.

With reference to figure 4, a plurality of the hereabove claimed search coils may be arranged or nounted, either nutually orthogonal or as desired, to give rise to two or three (or more, as desired) dimensional nagnetic naterial based search coils.

The search coil(s) claimed hereabove may be used to provide the input to any desired probe(s) whose frequency or frequency-range of response (or operation) covers the frequency or frequency-range of interest.

Nodifications may be incorporated without departing from the scope of the invention. Some exanples are incorporated hereabove.

Claims

WEAT I CLAIM IS:

1, Apparatus for monitoring the strength of an alternating magnetic field at or In the vicinity of a chosen point In space, consisting of a solenoidal coil of conducting wire, and/or a solenoidal coil of conducting material (for example, conducting paint or spray), of either one turn or a plurality of turns, and containing a core of ferromagnetic or ferrimagnetic material whose primary purpose is to enhance the voltage induced In the coil by the said alternating magnetic field.

2. A coil as claimed in claim 1, in which the core of ferromagnetic or ferrimagnetic material is a carefully shaped and oriented cylinder, enabling the induced voltage to respond accurately to the component of the alternating magnetic field along the axis of The said cylinder, while not responding to wagnetic field components perpendicular to the Sdld axis.

3. A coil as claimed in any one of claims 1 to 2, in which, two, or a plurality of, tightly twisted wires are used so as to minimise any additional voltages induced in the cable(s) by the alternating nagnetic field.

4. A coil as claimed in any one of claims 1 to 3, in which the coil is electrically connected to a voltage-monitoring apparatus by means of cable consisting of a pair of, or a plurality of, tightly twisted wires, such that any additional voltages induced in the cable by the alternating magnetic field are minimised.

5. A coil as claimed in any one of claims 1 to 3, in which the- coil Is electrically connected to a voltage-onitoring apparatus by leans of a coaxial cable consisting of concentric inner and outer conductors, such that any additional voltages induced in the cable by the alternating magnetic field are minimised.

6. A coil as clailed in any one of claims 1 to 3, in which communication exists between the coil and a voltage- (or other suitable) monitoring apparatus either immediately or ultimately, by means of remote control.

7. A coil as claimed in any one of claims 1 to 6, in which the assembly is surrounded by an electrically conducting "Faraday Cage" shield designed to shield the coil from any alternating electric fields present in its environment while being transparent to the alternating magnetic field being monitored. An example design of such a shield is illustrated in Pigure 3. The metal of the shield would normally be connected to the outer conductor of the coaxial cable of claim 5.

8. Apparatus consisting of a plurality of coils as claimed in any one of claims 1 to 7 in close proximity, having their axes aligned along predetermined or chosen directions, with each coil connected to a voltage- (or other suitable) monitoring apparatus as claimed hereinbefore, such that simultaneous measurements may be made of more than one directional magnetic field component. It would normally be necessary to post on the coils in such a group (or in such a plurality) in such a manner that the mutual inductance between any pair of coils is zero, to ensure Independent measurements.

9. A coil substantially as hereinbefore described with reference to Figures 1 to 2.

10. A coil substantially as hereinbefore described with reference to Figures 1 to 2 and modified by Figures 3 and/or 4.