GB1601649A

GB1601649A - Method of detecting substantially non-conductive products

Info

Publication number: GB1601649A
Application number: GB2306778A
Authority: GB
Original assignee: Bekaert NV SA
Current assignee: Bekaert NV SA
Priority date: 1977-11-14
Filing date: 1978-05-26
Publication date: 1981-11-04
Also published as: BE871950A; LU78507A1

Description

(54) METHOD OF DETECTING SUBSTANTIALLY NON-CONDUCTIVE PRODUCTS (71) We, N.V. BEKAERT S.A., a Belgian Body Corporate, of Zwevegem, Belgium, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to a method of detecting and, if desired, locating the position of substantially non-conductive products.

In the case of products made substantially of non-conductive material, electrical methods of detection are not generally possible except where the product is made sufficiently conductive to enable it to be detectable by electrical methods. However, for a great number of products, such as textiles, papers and polymer sheets, the material cannot be rendered conductive without altering its essential nature and appearance.

It is an object of the present invention to provide a method of marking and detecting such products by using a detection method which requires a minimum of conductive material to be introduced in the substantially non-conductive product, and by using such material in a form which renders it particularly detectable by said detection method.

According to one feature of the present invention we provide a method of detecting and if desired locating the position of a product made substantially of a non-conductive material wherein there is included in the said product a conductive material capable, when appropriately disposed, of reflecting and/or attenuating at least a portion of microwave radiation impinging thereon, the said conductive material comprising at least one non-linear conductive filament having a maximum thickness of 50 and/or a non-parallelly orientated array of conductive filaments having a maximum thickness of 50p;; which method comprises irradiating the said product with microwave radiation so that the conductive material reflects and/or attentuates at least a portion of the said radiation, whereby the said product is detected and if desired the position thereof located by means of the reflected and/or attenuated microwave radiation. The product is preferably passed through the microwave radiation.

According to a further feature of the present invention we provide apparatus for carrying out a method as hereinbefore defined, which apparatus comprises means for emitting microwave radiation, means for passing a product through the field of the said microwave radiation, receiving means for receiving microwave radiation attentuated by the passage through the said product and means for measuring the energy level of the microwave radiation received by the said receiving means.

Metallic wire, when it is placed in parallel with the direction of polarization of the electrical field of a microwave beam, acts as a dipole antenna and reflects a considerable amount of radiation energy. Because of the high frequency, the current induced in the wire only runs over the exterior of the wire and the metallic material inside the wire is largely immaterial. The average current density, and consequently the reflection and/or absorption by a certain quantity of wire, will thus increase with an increasing surface to volume ratio.

Very thin wires, having a thickness of 50 or less, preferably less than 15cm, thus produce a maximum degree of reflection and/or attenuation with a minimum quanitity of wire material. Thicker filaments, up to 50 can also be used. The filaments need not necessarily be metallic over their whose cross-section, provided that they have a conductive exterior which renders the filaments conductive.

Thus, a substantially non-conductive product can be rendered detectable by microwaves, without altering the esseítial nature or appearance of the product, by including in at least a part thereof such metallic filamentary material which is capable of reflecting and/or attenuating microwave radiation. It has been found that a continuous length of two centimeters, or even of 1 centimeter, of thin filament produces sufficient reflection, when it is disposed in parallel with the direction of polarization of the electric field of a microwave beam. A more randomly oriented, but larger filament quantity can also produce sufficient reflection, which will then vary as a function of the orientation of the E-field of the microwaves.Also short lengths of a few millimeters can act as dipole antennae and not only reflect a large part of the incident microwave energy, but also attenuate such energy. The conductive filamentary material, when properly oriented with respect to the E-field of an incident microwave beam, thus produces a measurable reflection and/or absorption loss.

The additional attenuation, due to the filamentary material, of the beam passing through the said filamentary material, in addition to the attenuation due to losses in the substantially non-conductive material, is generally at least 0.05 decibel, although this is not an absolute limit, as long as the reflection and absorption losses specifically due to the filamentary material are measurable.

Substantially non-conductive materials for use in the method according to the present invention include textiles and other products. Such materials preferably contain the said filamentary materials in a total amount of less than 1% by weight of the material. The invention is also applicable to sheets of paper or polymer, which sheets include a conductive filamentary material embedded in the paper or polymer. The filamentary material is preferably employed in the form of short fibres of a few millimeters' length.

The filaments in parallel with the direction of the E-field of the emitted radiation reflect the whole or a part of this radiation, and this can be measured in two ways. A receiver can be placed in the radiation beam at the opposite side of the passage through which non-conductive material travels. It receives the radiation and measures its energy level. As soon as the product moves through the radiation beam and the latter impinges the filaments, a part is reflected and the measured energy level decreases, this being the detection signal for the product. It is also possible to place the receiver at a point where it receives a substantial amount of the reflected energy, e.g. in a position to receive the radiation reflected by 1800.

The method according to the present invention is not only applicable for marking the product and detecting its presence, but also for marking and locating the position of the product, e.g. in a cutting or other machine. The product can for example be marked with a number of distinct marking spots or microwave detectable regions by the use of conductive filamentary material, each such region corresponding to a given position. The remainder of the product does not contain any conductive filament. The instrument for measuring the received microwave power will produce a response each time the beam of microwaves strikes a marked portion. The marked portions may be so located in the product that when the product is in a position whereby the filamentary material is capable of reflecting and/or attenuating microwave radiation, it is then and only then irradiated with microwaves.For instance, when the product has an elongated form, such as a band or strip of textile, the marked portions may be located at set distances lengthwise along the product and these marked portions can be used for detecting the progression of the product lengthwise so that the detecting signals can for example serve to stop the belt or to carry out a cutting or other operation at given locations.

When the conductive filamentary material is included to be incorporated in textiles, as well as in other cases, it can be included as part of a textile thread in which thin discontinuous conductive filaments are blended and twisted with discontinuous textile filaments, for example in a proportion of up to 25% by weight of the thread. The thin conductive filamentary material can also be present in the product in the form of one continuous filament.

The filaments represent antenna-lengths and it is preferable to use, as filament material, straight lengths corresponding to the half wavelength, although other lengths which are less tuned to the frequency of the microwaves may produce sufficient reflection and/or attenuation, particularly if the measuring method is very sensitive and very rapid in response. A reflection during less than 20 milliseconds is still detectable.

The thin filaments can be very fine wires of a conductive metal such as stainless steel used in webs for filters. The filaments can be made for example by drawing sheathed bundles of wires covered with a soft material. such as copper, as explained in U.S. Patents Nos.

2.050,298, 2,215,477, 3,029,496 and 3,277,564.

For a better understanding of the present invention, the following embodiments of the method according to the invention will be described with reference to the accompanying drawings in which: Figure 1 illustrates the method according to the invention applied to a textile band.

Figure 2 illustrates the method according to the invention applied to a transport belt.

In Figure la, a textile web in the form of a planar band 4, perpendicular to the plane of the drawing, travels in the direction of arrow 5. In front of the textile web, at a distance of 0.75 centimeter, is located a horn antenna 6, for emitting microwaves, and behind the web 4, at the same distance and on the axis of the emitter antenna 6, is located the horn-antenna 7, for receiving the microwaves emitted by antenna 6. The microwaves are generated in a generator 1 of the Gunn-diode type and transmitted through a variable attenuator 2 towards the emitter antenna 6. The frequency is 9,500 Megaherz. It is necessary to generate microwaves having a wavelength of the same order of magnitude as the length of the metallic filaments which will be used in the marked product, i.e. a wavelength of the order of centimeters, in order to allow the filaments to function as dipole antenna.

The microwaves received by the horn-antenna 7 are transmitted to a crystal-detector 8, the output of of which is connected to a milliammeter 9, or to any other instrument measuring the energy level of the microwaves received by the receiver 7. This milliammeter may if desired be replaced by a relay or any other electronic detector capable of activating operations when a strong attenuation is measured.

The textile web in the form of a flat band 4 and travelling in the direction of arrow 5, is shown in Figure ib. The beam of microwaves emitted by antenna 6 has a rectangular form and traverses the band 4 perpendicularly and inside rectangle 10. The direction of polarization E of the electric field of the microwaves is indicated by the double arrow 11, i.e. in the plane of the band and in the longitudinal direction.

The marking spot to be detected according to the present example is a seam, running transversely over said band, perpendicularly to the longitudinal direction. This seam consists of a thread 15 which runs zigzag along the seam line, in such a way that the major part of the length of the seam thread is in parallel with the longitudinal direction of the band. i.e. with the direction of polarization of the electric field E.

The seam thread used in this example consists of 3 cotton threads, twisted with other threads comprising a metallic filament.

Six types of thread have been used according to Table 1 below: TABLE 1 Type Metric No. of Number and type of Milli the 3 cotton threads comprising amperes threads metallic filament 1 Nm 3() 1 Bekitex H,Nm 54,12%, 8 0.2 2 Nm 30 2 Bekitex H,Nm 54,12%, 8 0.15 3 Nm 30 4 Bekitex H,Nm 54,12%, 8 0.2 4 Nm 30 1 Bekitex L,Nm 54, 3%, 81l 0.3 5 Nm 30 1 Bekitex ,Nm 80, 2% 8 0.2 6 Nm 24 Continuous filament 0.05 thickness 38 In this table, Nm 30 represents the metric number of each of the three cotton threads, i.e.

the number of metres per gram of thread. The thread specified by "Bekitex H" or "Bekitex or or Bekitex" (it should be noted that Bekitex is a registered Trade Mark). is a thread consisting of a blend of synthetic filaments (nylon) and metallic filaments (stainless steel 316 L). the percentage indicates the percentage by weight of metallic filaments. and the thickness of these metallic filaments is indicated in microns.

When the seam 15 arrives in the rectangle 10, the metallic filamentary material in the seam thread being substantially in parallel with the direction of polarization of the electric field. this filamentary material will produce a considerable reflection and the milliammeter 9 measures a substantial reduction of the power received. The values are given in the last column of Table 1, the variable attenuator having been adjusted so that the milliammeter 9 indicated 0.6 milliamperes when the band was between antennae 6 and 7 but the seam 15 being outside rectangle 10 (Figure lb).

In another example. shown in Figure 2a, a conveyor belt 20 is continuouslv passed along an instrument, similar to the one shown in Figure 1. and wherein similar components are indicated by the same reference numerals. The instrument however additionally comprises a receiver horn-antenna 16, placed at the optimal location for receiving the waves reflected by the band, i.e. perpendicularly to the surface of the band and closely adjacent to the emitter antenna 6. This receives antenna 16 is connected to a crystal detector 17, of which the output is connected to a microammeter 18. Because of the great attenuation caused by the conveyor belt 20, the instrument 9 is also a microammeter.

The conveyor belt 20, moving in the direction of arrow 21, is shown in Figure 2b. The beam of microwaves emitted by antenna 6 has the same frequency and perpendicularly traverses belt 20 inside rectangle 23. The distance between antennae 6 and 7 is 2 centimeters. The direction of polarization E of the electric field is indicated by the double arrow 24, i.e. in the plane of the belt and in a transverse direction perpendicular to the longitudinal direction of the belt.

The spot which is to be detected in the present example is a junction between two parts of the belt, where a thread 25 is situated (Figure 2) which traverses the belt in a transverse direction, i.e. parallel with the direction of polarization E. The type of thread used is indicated in the table hereunder: TABLE II Type Number and type of Power Power thread transmitted refle ted 1 1 thread Bekitex H, 7211A 48uA Nm 54, 12%, 8 2 2 parallel threads Bekitex H, 521lA 641lA Nm 54, 12%, 8u When thread 25 enters the rectangle, the metallic filamentary material produces a considerable reflection, and this can be measured by microammeter 18. In the same way, microammeter 9 measures a considerable fall of the received power.When the belt is situated between antennae 6 and 7, but the thread 25 being located outside rectangle 23 (Figure 2b), microammeter 9 indicated a value of 95FA of power transmitted and microammeter 18 measured a value of 27yA of reflected power. However, when the thread 25 is located inside rectangle 23, the microammeter measured the values indicated in Table II. From this one can deduce that in this case the relative variation of the reflected power is greater and that measuring this variation in power provides a more sensitive means of detection.

WHAT WE CLAIM IS: 1. A method of detecting an if desired locating the position of a product made substantially of a non-conductive material wherein there is included in the said product a conductive material capable, when appropriately disposed, of reflecting and/or attenuating at least a portion of microwave radiation impinging thereon, the said conductive material comprising at least one non-linear conductive filament having a maximum thickness of 50eel and/or a non-parallelly orientated array of conductive filaments having a maximum thickness of 501l;; which method comprises irradiating the said product with microwave radiation so that the conductive material reflects and/or attenuates at least a portion of the said radiation, whereby the said product is detected and if desired the position thereof located by means of the reflected and /or attenuated microwave radiation.

2. A method as claimed in claim 1 wherein the said conductive filament is a metal filament having a maximum thickness of 50y.

3. A method as claimed in either of claims 1 and 2 wherein the said conductive material comprises a single continuous non-linear conductive filament having a maximum thickness of 501l.

4. A method as claimed in any one of claims 1 to 3 wherein the said conductive filament has a maximum thickness of 15F 5. A method as claimed in any of the preceding claims wherein the said non-conductive material comprises paper. a textile web or a polymer material.

6. A method as claimed in any of the preceding claims wherein the said product is in the form of a web in which the said conductive material is present in one or more positions along the length of the web.

7. A method as claimed in claim 1 wherein the said conductive material is in the form of

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. indicated by the same reference numerals. The instrument however additionally comprises a receiver horn-antenna 16, placed at the optimal location for receiving the waves reflected by the band, i.e. perpendicularly to the surface of the band and closely adjacent to the emitter antenna 6. This receives antenna 16 is connected to a crystal detector 17, of which the output is connected to a microammeter 18. Because of the great attenuation caused by the conveyor belt 20, the instrument 9 is also a microammeter. The conveyor belt 20, moving in the direction of arrow 21, is shown in Figure 2b. The beam of microwaves emitted by antenna 6 has the same frequency and perpendicularly traverses belt 20 inside rectangle 23. The distance between antennae 6 and 7 is 2 centimeters. The direction of polarization E of the electric field is indicated by the double arrow 24, i.e. in the plane of the belt and in a transverse direction perpendicular to the longitudinal direction of the belt. The spot which is to be detected in the present example is a junction between two parts of the belt, where a thread 25 is situated (Figure 2) which traverses the belt in a transverse direction, i.e. parallel with the direction of polarization E. The type of thread used is indicated in the table hereunder: TABLE II Type Number and type of Power Power thread transmitted refle ted

1 1 thread Bekitex H, 7211A 48uA Nm 54, 12%, 8

2 2 parallel threads Bekitex H, 521lA 641lA Nm 54, 12%, 8u When thread 25 enters the rectangle, the metallic filamentary material produces a considerable reflection, and this can be measured by microammeter 18. In the same way, microammeter 9 measures a considerable fall of the received power.When the belt is situated between antennae 6 and 7, but the thread 25 being located outside rectangle 23 (Figure 2b), microammeter 9 indicated a value of 95FA of power transmitted and microammeter 18 measured a value of 27yA of reflected power. However, when the thread 25 is located inside rectangle 23, the microammeter measured the values indicated in Table II. From this one can deduce that in this case the relative variation of the reflected power is greater and that measuring this variation in power provides a more sensitive means of detection.

4. A method as claimed in any one of claims 1 to 3 wherein the said conductive filament has a maximum thickness of 15F

5. A method as claimed in any of the preceding claims wherein the said non-conductive material comprises paper. a textile web or a polymer material.

a strand or strands of a yarn comprising at least one discontinuous conductive filament blended and twisted with at least one discontinuous textile filament, the conductive filament constituting up to 25% by weight of the total weight of the filaments.

8. A method as claimed in any of the preceding claims wherein the said product is passed through the said microwave radiation.

9. A method as claimed in claim 8 wherein the said filamentary material is located in the said product at one or more distinct positions along the direction of travel of the product.

10. A method as claimed in claim 9 wherein the said product has an elongated form and is moved longitudinally, the said position(s) being located along the length of the product.

11. A method as claimed in any of the preceding claims wherein the reflected microwave radiation is measured.

12. A method as claimed in claim 1 substantially as herein described.

13. A method of detecting and if desired locating the position of a product made substantially of a non-conductive material, substantially as herein described.

14. Apparatus for carrying out a method as claimed in claim 1, which apparatus comprises means for emitting microwave radiation, means for passing a product through the field of the said microwave radiation, receiving means for receiving microwave radiation attenuated by passage through the said product and means for measuring the energy level of the microwave radiation received by the said receiving means.

15. Apparatus as claimed in claim 14 substantially as herein described.