Description

The present invention relates to a measurement method for detection of features in a specimen being a smoking article and/or a smoking articles packaging using THz-waves.

In the smoking article industry it is important to securely identify features in smoking articles or packaging of smoking articles in particular in terms of genuineness to prevent counterfeiting but also in terms of automation of productions processes and electronic devices. The identification must be non-destructive to the smoking article and the packaging and cannot induce or generate any substances into the smoking article or its packaging that could pose a healthrisk to consumers. It is also beneficial if the identification method itself is not harmful to people.

It is therefore the objective of the invention to provide a measurement method and means to securely identify features in a smoking article and/or a smoking articles packaging that take the restrictions given above into account.

The objective of the invention is reached by a measurement method for detection of features in a specimen being a smoking article and/or a smoking articles packaging, wherein the specimen consists of at least a first material and comprises a tag consisting of at least one second material having predetermined optical properties differing from those of the first material in a frequency range between 0.3 and 10 THz, wherein the differing optical properties of the second material comprise a coded information comprised in the tag, comprising the steps: a. generating electro-magnetic waves comprising a frequency between 0.3 and 10 THz with a THz-wave-emitter; b. directing the electro-magnetic waves being an incident signal onto the specimen and onto the tag; c. allowing the electro-magnetic waves of the incident signal to be modulated by the tag due to different interaction with the second material in comparison to the interaction with the first material thereby creating a response signal consisting of at least modulated electro-magnetic waves comprising the coded information from the tag; d. detecting the response signal comprising the modulated electro-magnetic waves, which interacted with the tag, with a THz-wave-detector; e. deriving the coded information from the detected modulated electro-magnetic waves of the response signal.

Electro-magnetic radiation comprising a wavelength between 0.3 and 10 THz, in the following referred to as THz-radiation, can pass through most solid non-conductive materials, which makes it possible to detect features not only on the surface of a specimen but also in its volume. Also THz-radiation has no ionizing effect on matter. Irradiation with THz-radiation is nondestructive to the specimen. Also is not harmful to people, which makes THz-emitters easily integrable into production processes without the necessity to install safety measures for operating personnel. In the given frequency range between 0.3 and 10 THz, the radiation comprises a wavelength between 30 pm and 3 mm, which makes sub mm spatial resolution possible. The THz-wave generator and/or the THz-wave detector may be a photoconductive antenna. Also a heat source may be used as a TH-wave generator.

After generation the electro-magnetic waves are directed onto the specimen. This can either be accomplishes by a direct beam or with additional optical elements, e.g. lenses, mirrors, filters, beam choppers and/or polarizers. For example positive and/or negative magnification systems comprising mirrors and/or lenses can be arranged in the beam path between THz- wave emitter and specimen and/or in the beam path between specimen and THz-wave detector.

By using a tag consisting of a material (second material) having different optical properties in comparison to the material of the specimen (first material) in the THz-regime, the incident signal will be modulated by the tag differently compared to the specimen. The term “differing optical properties” may refer to all types of optical properties like e.g. reflectance, transmittance, absorbance, refractive index, polarizing properties and/or diffraction properties. In this way, the tag will create a different response signal compared to the rest of the specimen. Hence, the overall response signal comprises two differing contributions, one from the tag and one from the rest of the specimen. These two contributions are superimposed on each other and together form the response signal. To ensure proper detection of the tag, the tag preferably comprises a size of 3 mm x 1 mm, more preferred 2 mm x 0.6 mm, most preferred 1 mm x 0.3 mm.

The response signal is then detected by a THz-wave detector. The response signal may either be directed to the detector as a direct beam or with additional optical elements, e.g. lenses, mirrors, filters, beam choppers and/or polarizers. The detector is preferably an intensity detector.

The THz-After detection the response signal is analyzed. By knowing a standard response signal contribution from a specimen without a tag, the contribution of the tag can be identified in the overall response signal.

The differing optical properties comprise a coded information. This means that the response signal carries an information, which is not obtainable just from the response signal itself. More precisely, a decoding is needed to access the information. For example, the tag can be designed in a way that the contributions of the tag and of the rest of the specimen have a certain intensity ratio. Preferably, the contribution of the tag comprises an intensity h being smaller than the contribution of the rest of the specimen comprising an intensity Io. Preferably, the intensities satisfy the equation:

0.3 ■ I ₀ < I ₁ < 0.6 ■ I _o

Even more preferred, they satisfy the equation:

0.4 ■ I ₀ < I ₁ < 0.55 - / ₀

Certain intensity ratios could for example be correlated with specific production dates or product types. With the given method information, which has been incorporated into a smoking article or its packaging by arrangement of the tag, can be accessed in an easy, secure and fast way and the information can afterwards for example be used for automatic routing or alignment in the production site or as a security feature.

It is also conceivable to execute the method according to the invention, when a smoking article is inserted into an electronic device, e.g. when a heat-not-burn stick is inserted into the electronic heating device, or a liquid containing capsule into an electronic cigarette. In this embodiment, the tag can comprise coded information on the product type. With the given method, this information can be obtained from the smoking article by the electronic device and the electronic device may then for example execute a specific smoking or vaping program according to the type of the smoking article. To do so, an THz-imaging system comprising at least one THz-wave emitter and at least one THz-wave detector has to be comprised in the electronic device.

According to another embodiment, an imaging system comprising at least two THz-wave emitters and at least two THz-wave detectors is used, wherein the two THz-wave emitters are arranged orthogonally to each other creating a first and a second incident signal, which comprise propagation directions orthogonal to each other, wherein both incident signals are directed onto the specimen thereby interacting with the specimen creating a first and a second response signal, wherein each response signal is detected by an own THz-wave detector.

With the two orthogonal incident signals, the tag can be irradiated with the THz-radiation regardless of the rotational state of the specimen and/or regardless of the position of the tag. . In this way, the tag is irradiated with the THz-radiation under every circumstances and can thus create a respectively modulated response signal. Preferably, the specimen is fed through a focal point or line of the two incident signals in a feeding direction. Preferably, the specimen is fed through the focal point or line with its center. Preferably, the specimen is arranged parallel to the feeding direction with its longest extent

According to another embodiment, the incident signal is directed from the THz-wave emitter to the specimen with a waveguide and/or the response signal is directed from the specimen to the THz-wave detector with a waveguide.

With the waveguide it is possible to arrange the THz-wave-emitter and -detector independently of the positioning of the specimen. This is particularly relevant if the THz-wave-emitter and - detector have to be integrated into existing production machinery for in-line detection of features. In this way, the measurement method can also be used on existing and already installed and running production machinery via retrofitting. Preferably, polymer-based waveguides are used, more preferred polyethylene (PE) and/or polyethyleneterephtalate (PTFE). Preferably, the core of the waveguide comprises a microstructure. Preferably, subwavelength dielectric fibers are used as a waveguide. Subwavelength dielectric fibers are fibers comprising a diameter which is smaller than the wavelength of the guided wave. Preferably, the waveguide also comprises high-refractive index materials like e.g. TiO ₂ , CaCOs, Mg(OH) ₂ and/or nanowires. Preferably, the waveguide is a flat waveguide.

According to another embodiment, the THz-wave detector comprises an array of 1 - or 2-dimensional detectors having at least 20 detector elements, preferable at least 50 detector elements. With this array arrangement, a measurement with lateral resolution is possible. This is especially advantageous for larger specimens. The tag is also more securely irradiated with THz-radiation and its response is more securely captured. With a higher number of detector elements whereas the detector area remains constant, a higher image resolution is reached. With a 1 -dimensional array, a line detector is obtained. With a 2-dimensional array, a plane or area detector is realized.

The objective of the invention is also reached by a tag arranged on any inner surface of a smoking article or a smoking articles packaging consisting of at least one first material and the tag consisting of at least one second material, wherein the tag is able to modulate electromagnetic waves of an incident signal having a frequency between 0.3 and 10 THz into a response signal by interaction of the second material with electro-magnetic waves of the incident signal. The invention is characterized in that the second material comprises predetermined optical properties differing from those of the first material in the frequency range between 0.3 and 10 THz, wherein the differing optical properties of the second material comprise a coded information comprised in the tag derivable from the tag by the response signal.

Preferably, the second material of the tag is a polymer (e.g. high-density polyethylene (HDPE), polytetrafluoroelthylene (PTFE), polyamide (PA)), a resin, a polymer nanocomposite comprising oxide- or nitride fillers in a polymer matrix, a metal, a semiconductor (e.g. high-resistivity silicon) and/or paper. As already explained above, using a tag consisting of a material (second material) having different optical properties in comparison to the material of the specimen (first material) in the THz-regime, the incident signal will be modulated by the tag differently compared to the specimen. In this way, the tag will create a different response signal compared to the rest of the specimen. Hence, the properties of the tag can be detected with THz-radiation.

The differing optical properties comprise a coded information. For example, the tag can be designed in a way that the contributions of the tag and of the rest of the specimen have a certain intensity ratio when examined with THz-radiation. Certain intensity ratios could for example be correlated with specific production dates or product types. In this way it is possible to use the tag for identifying specimens. This can for example be used for automatic routing in the production site or as a security feature.

According to another embodiment, the tag is a strip of at least the second material. A single strip of the second material is easy to manufacture and easy to integrate both in smoking articles and also in smoking articles packaging. For example can the strip be arranged on any wrapper of a smoking article or between layer of or on top of the material of the smoking articles packaging. The strip may also comprise further material apart from the second material, e.g. for laminating and/or creating a necessary stability of the strip for proper machine handling.

According to another embodiment, the tag comprises a specific shape, preferably a triangular, square, rectangular, round or circular shape. Preferably, the second material portion of the tag comprises this specific shape. The specific shape of the tag can be detected with any THz- wave detector, that allows for a lateral resolution. This can either be achieved with a detector according to the previously illustrated embodiment and a moving specimen, wherein the line detector detects the response signal over time, or by the previously illustrated embodiment of an area detector with or without a moving specimen. With the specific shape, additional information can be stored in the tag. The different specific shapes can for example be correlated with a production information regarding the specimen.

According to another embodiment, the tag comprises multiple pieces of the second material arranged in a pattern. The pattern further increase the amount of data storable in the tag. The pattern can be 1 - or 2-dimensional. A 1 -dimensional pattern could e.g. be a barcode. A 2- dimension pattern could e.g. be a QR-code. According to another embodiment, the tag is arranged in the smoking article or smoking articles packaging overlapping with itself in possible beam paths of incident and/or response signals. This means that the THz-radiation passes the tag twice when the specimen is irradiated with the incident signal. This creates an increased modulation strength. This arrangement can therefore increase the contrast between the modulated and unmodulated parts of the response signal. If this embodiment is combined with the previous embodiment, the pattern, a moireeffect can be generated by the overlapping patterns in the response signal. Such a moirepattern is strongly dependent on the exact positioning of the overlapping patterns with respect to each other. This makes the moire-effect extremely difficult to counterfeit. The combination of the two mentioned embodiments resulting in the overlapping pattern with the moire-effect, is therefore a very powerful security feature.

According to another embodiment, the tag is arranged circumferentially in the smoking article or the smoking articles packaging. This is the most convenient and easiest way of arranging the tag overlapping with itself in possible beam paths of incident and/or response signals.

According to another embodiment, the second material is an ink printed onto any inner surface of the smoking article or the smoking articles packaging. In other words, the tag consists of a printing printed onto any inner surface. An ink is particularly easy to apply. Any known printing method can be applied in this context. Printing the ink on an inner surface of the smoking article means that the ink is not applied on the outer surface of the smoking article or the packaging. This implies that the ink is covered by at least one material layer, when viewed from the outside. This will protect the tag from any external influences. It also can hide the tag in the smoking article or the packaging. This is highly advantageous for anti-counterfeiting features but also in terms of an appealing product design without any visible bar codes or markings. Pref- eralby, with the ink a barcode is printed onto the inner surface thereby forming the tag. Preferably, the ink is deposited on the inner surface having a layer thickness of 5 - 10 pm.

According to another embodiment, the ink comprises a THz-reflective material, preferably a metal, more preferred aluminum or copper or most preferred a conductive carbon component. The term THz-reflective means, that the THz-reflective material comprises a reflectance R for electro-magnetic radiation with a frequency between 0.3 and 10 THz. As an example, the reflectance R is 0.9 < R < 1 with R + T + A = 1 , wherein T is the transmittance and A is the absorptance of the respective material, preferably 0.95 < R < 1 , even more preferred 0.98 < R < 1. The given materials, metal, aluminum, copper or a conductive carbon component are preferred, but any material comprising the describes optical properties and which is safe to use in a smoking article or its packaging may be used. The THz-reflective material may either be the second material or may be comprised in the ink in addition to the second material. In the first case, the THz-reflective material enables the use of the ink to print the tag. In the latter case, the THz-reflective material increases the contrast between the tag and the first material of the smoking article or the smoking articles packaging, which makes the tag easier to detect.

According to another embodiment, the tag further comprises a third material having optical properties in the frequency range between 0.3 and 10 THz which differ from the second and first material. With the third material, the tag becomes more complicated and thus more difficult to replicate, which makes it an effective anti-counterfeit feature. Also the amount of data storable in the tag increases with the addition of a third material. Preferably, the signature to be detected in the response signal could be the ratio S = (l ₂ - 13) / (I2 + I3), wherein l ₂ is the intensity transmitted or reflected by the second material and I3 is the intensity transmitted or reflected by the third material. Preferably, the third material consists of the same basic material as the second material but the third material experienced a process to alter the optical properties of the material, preferably a thermal or UV treatment. Without the knowledge of the exact treatment of the basic material, the resulting response signal, preferably the ratio S, is very difficult to replicate.

According to another embodiment, the tag further comprises a contrast material, preferably a polymer, arranged on the second and/or third material facing away from the surface on which the second and/or third material is arranged. Preferably, the surface on which the second and/or third material is arranged is an inner surface facing towards the center of the smoking article or the smoking articles packaging. In this way, the second and/or third material are irradiated with the incident signal through the material on whose surface they are arranged. Preferably, the contrast material is arranged in the beam path behind the second and/or third material. Preferably, the contrast material is a THz-reflective material. With the reflection at the contrast layer being arranged in the beam path behind the second and/or third material, the incident signal travels through the second and/or third material at least twice. This is similar to the principle of an etalon or optical cavity. This increases the modulation strength of the tag and therefore increases the contrast of the modulated part or the response signal in comparison to the unmodulated part. According to another embodiment, from the outside of the smoking article or smoking articles packaging the tag is invisible to the human eye. Preferably, the tag is also invisible from the outside of the smoking article or smoking articles packaging to infrared light. This can for example be accomplished by arranging the tag on an inner surface of the smoking article or the smoking articles packaging. In alternative, the tag comprises only materials which are invisible to the human eye, e.g. transparent in the visible regime of electro-magnetic radiation, but comprise a reflectance in the THz-regime of electro-magnetic radiation. As a result, the product design is not disturbed by the tag and can be designed independently of the tag.

Further advantages, objectives and features of the present invention will be described, by way of example only, in the following description with reference to the appended figures. In the figures, like components in different embodiments can exhibit the same reference symbols.

The figures show:

Fig. 1 a a schematic view of an imaging system 10 with a smoking article 1 a.

Fig. 1 b a schematic view of an imaging system 10 with a smoking articles packaging

1 b;

Fig. 2 an imaging system 10 with two THz-wave emitters 6a, b and two THz-wave detectors 8a, b;

Fig. 3 an imaging system 10 comprising waveguides 1 1 ;

Fig. 4 an imaging system 10 comprising a detector array 12;

Fig. 5 an enlarged view of a tag 3 arranged in a smoking article 1 a or a smoking articles packaging 1 b;

Fig. 6 different specific shapes of the tag 3;

Fig. 7a, b a tag 3 comprising multiple pieces 4a-d of the second material arranged in a pattern;

Fig. 8 a tag 3 comprising a third material 21 .

Figure 1 a shows an imaging system 10 to execute the measurement method according to at least one embodiment of this invention. The imaging system 10 comprising at least one THz- wave emitter 6 and at least one THz-wave detector 9. Fig. 1 a shows a smoking article 1 a as a specimen 1 being irradiated with electro-magnetic waves 5. The electro-magnetic waves 5 comprise a frequency between 0.3 and 10 THz and are thus also referred to as THz-waves 5. The THz-waves 5 are generated by a THz-wave emitter 6. The generated THz-waves 5 are directed onto the specimen 1 , which in this embodiment is a smoking article 1 a. The THz- waves 5 directed onto the specimen 1 denote an incident signal 7. The specimen 1 comprises at least one first material 2. The specimen 2 also comprises a tag 3. The tag 3 comprises at least one second material 4, which comprises different optical properties in the frequency range between 0.3 and 10 THz in comparison to the first material 2 of the specimen 1 .

The THz-waves 5 of the incident signal 7 interact with the specimen 1 and the tag 3, in particular with the first and second materials 2, 4 of the specimen 1 and the tag 3. Due to the different optical properties in the frequency range between 0.3 and 10 THz, the first and second material 2, 4 will interact differently with the THz-waves 5 of the incident signal. As a result of this different interaction, the THz-waves 5 will be modulated differently by the first and second material 2, 4 respectively, thereby generating modulated THz-waves 5a. The modulated THz- waves 5a comprise the THz-waves 5a modulated by the first material 2 as well as the THz- waves 5a modulated by the second material 4.

The modulated THz-waves form a response signal 8. The response signal 8 is detected by THz-wave detector. After the detection, the response signal 8 is analyzed in order to derive the coded information from the detected modulated THz-waves 5a of the response signal 8. The detected response signal 8 may either be a reflected portion of the modulated THz-waves 5a or a transmitted portion. For most first and second materials 2,4 a reflected as well as a transmitted portion will exist. One of them may of course be very small. This means, that nearly every specimen will generate a first and a second response signal 8a, 8b, wherein in this embodiment the first response signal 8a corresponds to the reflected portion and the second response signal corresponds to a transmitted portion. The positioning of the THz-wave detector 9 therefore depends on which response signal 8, i.e. first 8a or second 8b, is to be measured. It is also possible to use a first and a second THz-wave detector 9a, 9b to measure the first and the second response signal 8a, 8b. Fig. 1 a shows both a first THz-wave detector 9a and also an additional or alternative second TH-wave detector 9b.

Preferably, the specimen is fed though a focal point F of the incident signal in a feeding direction D. Preferably, the beam with at the focal point F is 1 - 4 mm. The feeding may e.g. be done by production machinery of the specimen 1. In this case, the imaging system 10 may be part of a production machinery, handling machinery, packaging machinery or the like. In this way, the specimen is automatically fed through the imaging system 10. Fig. 1 b shows the same imaging system 10 but with a smoking articles packaging 1 b as the specimen 1. All explanations made with reference to fig. 1 a also apply to this embodiment.

Fig. 2 shows an imaging system 10 with two THz-wave emitters 6a, b and two THz-wave detectors 8a, b. The two THz-wave emitters 6a, b are arranged orthogonal to each other. This means, that they generate a first and a second incident signal 7a, b respectively, which comprise propagation directions Pi,P ₂ being orthogonal to each other. The first and second incident signals 7a, b meet in the focal point F. The focal point F is arranged in the specimen 1 , preferably in its center X. This results in a specimen 1 being irradiated with THz-waves 5 from two different, orthogonal directions.

The shown embodiment also comprises two THz-wave detectors 9a, b. In this embodiment, the first THz-wave detector 9a detects a first response signal 8a originating from the first incident signal 7a emitted by the first THz-wave emitter 6a. The second THz-wave detector 9b detects a second response signal 8b originating from the second incident signal 7b emitted by the second THz-wave emitter 6b. The first and second THz-wave detectors may each detect a transmitted portion of the modulated THz-waves 5a or a reflected. Fig. 2 shows a transmission measurement set-up wherein both THz-wave detectors 9a, b respectively measure the transmitted portion of the modulated THz-waves 5a originating from the first and second incident signal 7a, b respectively.

This embodiment is advantageous in particular for specimens 1 having a circular cross section as e.g. smoking articles 1 a may have. With a circular cross section the rotational state of a smoking article 1 a lying on a plane surface is not determined. In other words, the smoking article 1 a does not comprise a preferred orientation when lying on a plane surface. In order to definitely irradiate a non-circumferential tag, which may have an extent in the feeding direction D, 3 in the smoking article 1 a with the THz-waves 5, the two respective THz-wave emitters and detectors 6a, b, 9a, b with orthogonal propagation directions Pi, P ₂ are highly advantageous. Preferably, the tag comprises a thin metal layer. As metal does not transmit THz-waves, the difference between the two response signals 8a, b, will be very large and therefore easy to detect.

Fig. 3 shows an imaging system 10 comprising wave guides 1 1. The set-up of the imaging system 10 basically corresponds to the one shown in fig. 1 . Again THz-waves 5 are generated by a THz-wave emitter 6, directed to the specimen 1 , therein modulated and then detected by the THz-wave detector 9. But in contrast to the embodiment of fig. 1 the incident signal 7 is not directed directly onto the specimen 1 but guided to the specimen 1 by a waveguide 1 1 .

As an alternative to a waveguide, the incident signal 7 may also be directed to the specimen 1 with optical components like e.g. lenses or mirrors. However such optical components have to be oriented very precisely and the open beam path between the respective optical components can easily be blocked. Also the optical components require frequent cleaning, especially if arranged in a smoking article production machinery. Waveguides overcome all these issues and provide reliable guidance of THz-waves 5,5a also along curved beam paths or around corners. They may also comprise a protective coating to make them more robust. Preferably the response signal 8 is also guided by a waveguide to the THz-wave detector 9. In this way, the THz-wave emitter 6 and detector 9 can be arranged freely.

Preferably, each waveguide 1 1 comprise incoupling and/or outcoupling means 27 at their respective ends 1 1 a, b.

Fig. 4 shows a detector array 12. The detector array 12 comprises multiple detector elements 12a-d. Four of these detector elements 12a-d are marked in fig. 4. The detector array 12 shown in fig. 4 comprises further detector elements which are not equipped with reference sings to ensure the clarity of the figure. However, the term “detector elements 12a-d” refers to all detector elements of the detector array 12 including the ones without a reference sign. The detector elements 12a-d are arranged in a line or in a plane resulting in a 1 -dimensional or 2- dimensional arrangement. Preferably, the detector array 12 comprises at least 20 detector elements 12a-d, more preferred at least 50 detector elements 12a-d. Preferably, the detector array 12 comprises 100 detector elements 12a-d and the detector elements 12a-d are arranged in a 10 x 10 matrix. Preferably, the detector array 12 comprises a diameter of 5 mm, 3 mm or even 2 mm.

In this way the response signal 8 can be detected with lateral resolution. In order to irradiate the specimen 1 , preferably along its entire width perpendicular to a feeding direction D, a bundle 23 of parallel THz-waves 5 is directed to the specimen 1 . Preferably, the width b of the bundle 23 equals or exceeds the width w of the specimen 1 . The bundle 23 may be generated directly by the THz-wave emitter 6 or by any optics arranged in the beam path of the incident signal 7. Preferably, the detector array 12 comprises a depth resolution of 20 pm and/or a lateral resolution of 200-300 pm.

Fig. 5 shows an enlarged view of a tag 3 arranged in a smoking article 1 a or a smoking articles packaging 1 b, together referred to as the specimen 1 . The specimen 1 comprises a material layer 24. Preferably, the material layer 24 material layer consists of the first material 2. The material layer 23 comprises an inner surface 13 directed towards the center X of the specimen 1 and an outer surface 14 directed to the adverse side, i.e. the outside of the specimen 1 . The tag 3 is arranged on the inner surface 13 of the material layer 23. In case of the specimen 1 being a smoking articles 1 a, the material layer 23 is preferably a wrapper. Preferably, the tag 3 is arranged in the tobacco rod and/or a filter section and/or an intermediate section of the smoking article 1 a. The tag comprises the second material 4. The material layer 23 can be the outmost layer of the specimen 1 . Alternatively, the material layer 23 is any inner layer arranged in the specimen 1 .

According to one of the previously described embodiments, the tag 3 may comprise a specific shape. Fig. 6 shows a variety of possible shapes of the tag 3. The tag 3 may be a strip 15 or may have a triangular 16, square 17, rectangular 18, round 19 or circular shape 20. The tag 3 comprising such shape may be arranged as depicted in fig. 5, i.e. on the inner surface 13 of a material layer 24 of the specimen 1 . Preferably, a piece of the second material 4 comprises the specific shape and thus forms the tag. In this case, the tag consists of a piece of the second material 4 comprising a specific shape and being arranged on the inner surface 13 of a material layer 24 of the specimen 1 . It is also possible that the tag 3 comprises more than one piece of the second material 4 each comprising a specific shape. The pieces of the second material 4 may all comprise the same specific shape or different shapes. Alternatively, some pieces of the second material 4 of one tag 3 comprise the same specific shape while other pieces of the second material 4 of the same tag 3 comprise a different specific shape.

If the tag 3 comprises more than one piece of the second material 4, the multiple pieces 4a-d are preferably arranged in a pattern, as shown in fig. 7a. In this embodiment, multiple pieces 4a-d each comprising the shape of a stripe 15 are periodically arranged in the tag 3. The tag 3 only occupies a section of the circumference 25 of the specimen 1 , as the lower part of fig. 7a shows in the sectional view. Preferably, all stripes 15 are arranged having the same distance 28 to the neighboring stripe 15. In alternative versions of this embodiment, the stripes may comprise different width 29 and different distances 28 to each other. They may e.g. form a barcode. Also other specific shapes may be arranged in a pattern. E.g. square and/or rectangular shapes may be arranged to form a QR-code. Of course, all other 1 D or 2D code types are also possible. The pattern may be arranged along a circumference of the specimen or parallel to the feeding direction D. In a preferred embodiment, the distance 28 of the stripes 15 and their width 29 is in of the same magnitude as the used THz-wavelength. In this way diffraction effects can be generated in the response signal 8. Preferably, such a diffraction pattern is generated by depositing an array of stripes 15 onto the inner surface 14 of a wrapper, wherein the wrapper preferably consists of paper. Alternatively, the wrapper may be structured, wherein the structures form the diffraction pattern.

Fig. 7b shows the same pattern consisting of multiple pieces 4a-d of the second material 4 as fig. 7a. However, the tag 3 is arranged along the whole circumference 25. This means that the tag 3 is overlapping with itself in possible beam paths B of the incident/response signal 7,8. In other words, the tag 3 is arranged in the specimen 1 in a way, that the THz-waves 5, 5a on their way through the specimen along the beam path B interact with at least two different parts of the same tag 3. The easiest embodiment for this case is a circumferentially arranged tag 3 which is then measured in a transmission set-up, i.e. a straight beam path B. When a tag 3 comprising a pattern overlaps with itself in the beam path B, a moire-effect can be created which further complicates the modulation of the response signal 8. The moire-effect will depend on the width of the stripes 15 and their respective distance to each other and on the optical characteristics, preferably an absorption characteristic, of the second material 4 of the stripes 15. The upper side view of the specimen 1 in fig. 7b schematically shows the resulting crisscrossing overlap in the beam path B of multiple stripes 15 arranged in a pattern around the whole circumference 25 of the specimen 1 .

Fig. 8 shows a tag 3 comprising a third material 21 . In the shown embodiment, the third material 21 forms the tag 3 together with the second material 4. In this way, the tag 3 comprises at least two different materials 4, 21 . The second and third material 4, 21 can be arranged next to each other along the circumference 25 of the specimen 1 , as depicted. Preferably, the second and third material 4, 21 are arranged next to each other on the inner surface 13 of a material layer 24 of the specimen 1 . In alternative to that, the two materials may also be arranged on top of each other along a radial direction R. The embodiment shown in fig. 8 also comprises a contrast material 22. The contrast material 22 is comprised in the tag 3. The contrast material 22 is preferably arranged on the side 26 of the second and/or third material 4, 21 being averted from the incident signal 7 and preferably also from the response signal 8. This averted side 26 is the side of the second or third material 4, 21 facing away from the surface 13 on which the second and/or third material 4, 21 is arranged. The contrast material 22 preferably is a polymer layer. Preferably, the polymer layer comprises a layer thickness of 50 - 11 pm. Preferably, reflection of the THz-waves occurs at the interface 30 between the contrast material 22 and the tag 3. To further enhance the reflection, a reflective layer 31 may be deposited on top of the contrast material 22.

The applicant reserves his right to claim all features disclosed in the application document as being an essential feature of the invention, as long as they are new, individually or in combination, in view of the prior art. Furthermore, it is noted that in the figures features are described, which can be advantageous individually. Someone skilled in the art will directly recognize that a specific feature being disclosed in a figure can be advantageous also without the adoption of further features from this figure. Furthermore, someone skilled in the art will recognize that advantages can evolve from a combination of diverse features being disclosed in one or various figures.

List of reference symbols

1 specimen

1a smoking article

1b packaging

2 first material

3 tag

4 second material

4a-d multiple pieces

5 electro-magnetic waves, THz-waves

5a modulated electro-magnetic waves, modulated THz-waves

6 THz-wave emitter

6a first THz-wave emitter

6b second THz-wave emitter

7 Incident signal

7a first Incident signal

7b second Incident signal

8 Response signal

8a first response signal

8b second response signal

9 THz-wave detector

9a first THz-wave detector

9b second THz-wave detector

10 Imaging system

11 Waveguide 11 a,b ends

12 Detector array 12a-d detector elements

13 inner surface

14 outer surface

15 strip

16 triangular shape

17 square shape

18 rectangular shape 19 round shape

20 circular shape

21 third material

22 contrast material

23 bundle of waves

24 material layer

25 circumference

26 averted side

27 in- /outcoupling means

28 distance

29 width

30 interface

31 reflective layer

D feeding direction

P1 first propagation direction

P2 second propagation direction

B beam path

F focal point

X center of specimen