DE102010013665A1 - Safety element for increasing falsification protection of e.g. banknotes, has thermoacoustic vibration generator, which is attached on safety document and outputs vibration energy during coupling electrical power - Google Patents

Abstract

The element has a thermoacoustic vibration generator (2) i.e. carbon nanotube thin film loudspeaker, which is attached on a safety document i.e. banknote (1), and outputs vibration energy during coupling electrical power. The generator is connected with an electric circuit, which is attached on the safety document. The electric circuit consists of a receiver for electromagnetic energy. The receiver outputs the electrical power to the generator during irradiation of the electromagnetic energy, which is produced by an external transmitter, and outputs the vibration energy.

Description

The invention relates to a security element for increasing the protection against counterfeiting of security documents such as banknotes, securities, identity cards, credit cards, debit cards or the like.

Security documents are provided with security elements for security, which allow a verification of the authenticity of the object and at the same time serve as protection against unauthorized reproduction. Furthermore, security elements often produce a highly visible visual impression, which is why such security elements are used in addition to their function as securing means sometimes even as decorative elements for such media or for their packaging. A security element can be embedded in such security documents, for example in a banknote or in a chip card, or designed as a self-supporting transfer element, for example as a patch or as a label, which after its production on a data carrier or other object to be secured, for example over a window area of the Disk, is applied.

A security document with a security element in the form of a loudspeaker is off WO 2004/090800 A2 known. In this case, the security document consists of a contactless data carrier with an antenna and a chip, data being arranged on the data carrier which can be transmitted to a reading device via an antenna-based data transmission channel. In this case, acoustic information can be reproduced, these being produced by a conventional loudspeaker of the prior art, for example a piezoelectric loudspeaker.

Disadvantage of conventional speakers of the prior art is that they have too large a thickness, are too inflexible and usually not transparent. As a result, they are susceptible to deformation and damage and also rely on the vibration characteristics of the substrate. Such conventional loudspeakers of the prior art are, for example, piezoelectric sound transducers, wherein ceramic piezoelectric transducers are not yet ready for market mechanically, and plastic-based piezoelectric transducers are not yet ready for market. Other common loudspeakers of the prior art are so-called "flat flexible loudspeakers" (FFL), which, however, have a complex, multi-layered structure in the form of a laminate and with a thickness of about 200 μm too thick for use on or in security documents are. Furthermore, the membrane of an FFL must be able to oscillate freely in order to generate sound waves.

The invention is therefore the object of developing a generic security element such that the disadvantages of the prior art, the protection against counterfeiting further increases and the recognizability of counterfeits is improved.

This object is solved by the features of the independent claims. Further developments of the invention are the subject of the dependent claims.

According to the invention, the security element consists of at least one thermoacoustic vibration exciter, which is applied to the security document and emits vibration energy when coupled in by electrical energy.

The mode of action of a thermoacoustic vibration exciter is based on the thermoacoustic effect. In the thermoacoustic effect, either thermal energy of a material is converted into vibrational energy of the medium adjacent to the material, in the case of a gaseous medium adjacent to the material, in sound energy or sound waves, or vice versa, vibration energy of the surrounding medium into thermal energy. In the latter case, the vibrations of the surrounding medium cause pressure changes, which result in immediate thermodynamic changes of state. Thus, temperature waves or inhomogeneous temperature distributions at limiting contact surfaces stimulate acoustic waves. In principle, the thermoacoustic effect is an energy conversion from thermal to acoustic energy.

The phenomenon of the thermoacoustic effect was already discovered at the end of the 19th century and applied to the so-called "thermophone" (see for example Preece, 1879-1880, Braun et. al. 1898 ). In these embodiments, sound waves were generated by heating a thin metal foil by applying an alternating current.

The generation of vibrational energy in the thermoacoustic effect can be explained as follows: By applying an alternating current to a thin electrical conductor, periodic heating of the thin electrical conductor takes place. This periodic heating results in temperature waves being delivered to the surrounding medium. The thermal expansion and contraction of these conductor layers and the adjacent gases then determines the amplitude of the vibrational energy.

Preferably, the thermoacoustic vibration exciter vibrational energy in the form of airborne sound, d. H. in the form of oscillations or pressure fluctuations of the surrounding gaseous medium or the surrounding air. In this case, the thermoacoustic vibration exciter acts as a thermoacoustic speaker. Of course, a release of vibration energy in the form of structure-borne noise is possible, the thermoacoustic vibration exciter passes its vibrations to a solid, which is positively connected with him.

The prerequisite for an efficient thermoacoustic effect is a very thin conductor layer, for example for platinum conductor layers, having a layer thickness of less than 700 nm, with a specific heat capacity of less than 800 J / (kg.K), preferably of about 500 J / (kg. K), as well as a suitable material capable of generating vibration energy of preferably audible or detectable amplitude or audible volume.

The thermoacoustic vibration exciter is preferably designed as a carbon nanotube or carbon nanotube (CNT) loudspeaker and particularly preferably as a carbon nanotube thin-film loudspeaker. Carbonnanotube (CNT) or carbon nanotube thin film loudspeakers are known in the art, for example L. Xiao et al., "Flexible, Stretchable, Transparent Carbon Nanotube Thin Film Loudspeakers, Nano Letters, vol. 8, no. 12, 2008, pp. 4539-4545 , the publication of which is fully incorporated in this application. Carbonnanotube (CNT) or Carbonnanotube thin-film loudspeakers use periodic heating of the CNT layer by heating with alternating currents. A CNT layer preferably consists of a multiplicity of carbon nanotubes arranged in parallel, each carbon nanotube having a diameter of approximately 10 nm. A carbon nanotube (CNT) or carbon nanotube thin film loudspeaker may be constructed of one or more of these CNT layers. This has the consequence that the sound waves or the associated pressure oscillation is not generated by a vibrating membrane, as is the case for example in conventional speakers, but by a temperature oscillation.

CNT thin film layers have the following advantageous properties: they are transparent, i. H. have a transmission of at least 80% of the incident light, so that they are also suitable for banknotes with openings or windows, they are stretchable, they can take up to 200% of the original dimensions, they are flexible, the thermoacoustic effect works in All dimensions and shapes, they can be applied to all materials, including on insulators, and they have layer thicknesses in the range of 10 nm to 100 nm.

Furthermore, the substrate of the security document and any wrinkles or damages of the CNT thin film layer scarcely affect the generation of sound energy. Thus, even embossing of the substrate is particularly advantageous even with already applied CNT thin-film loudspeaker possible.

The thermoacoustic vibration exciter is preferably applied to a carrier material, in particular a film strip, a patch, a BOPP or PET film, a metallized film strip or a hologram strip. Here, the thermoacoustic vibration exciter is applied to the carrier material and this in a transfer or lamination process on the substrate of the security document. Following this, further printing or individualization processes can take place, such as intaglio printing, screen printing, letterpress printing or laser marking.

Alternatively, the thermoacoustic vibration exciter is applied directly to the substrate of the security document.

The substrate of the security document is particularly preferably made of paper made of cotton fibers, as used, for example, for banknotes. By a two-sided coating or lamination, each with a plastic film results in a security paper, as in DE 102 43 653 A9 is described, the disclosure of which is fully incorporated in this regard in this invention.

Preferably, the substrate of the security document may also be made of paper of other natural fibers, also preferably of synthetic fibers, d. H. a mixture of natural and synthetic fibers or also preferably consist of at least one plastic film, which consist for example of a polymer. Further preferably, the substrate consists of a combination of at least two superimposed and interconnected different substrates, a so-called hybrid, for example a combination of plastic film-paper-plastic film, d. H. a substrate of paper is covered on either side by a plastic film, or paper plastic film paper, d. H. a substrate made of a plastic film is covered on each of its two sides by a paper substrate.

In a preferred embodiment, the thermoacoustic vibration exciter is connected to an electrical circuit which is applied to the security document.

Here, in a first preferred embodiment, the electrical circuit at least from a receiver for electromagnetic energy, wherein the receiver emits electrical energy to the thermoacoustic vibration exciter upon irradiation of electromagnetic energy, which is generated by an external transmitter and emits this vibration energy. The coupling of vibration signals into the thermoacoustic loudspeaker thus takes place externally or outside the security document.

• – Bei einem Carbonnanotube(CNT)- oder Carbonnanotube-Dünnfilm-Lautsprecher durch direkte galvanische Kontaktierung. Da die CNT-Schicht selbst leitfähig ist, kann sie zur Überprüfung der Echtheit an mindestens zwei Stellen elektrisch kontaktiert werden. Dies kann z. B. durch Klemmen oder Rollen geschehen, die selbst leitfähig sind und mit dem Frequenzgenerator verbunden sind.
• – Durch Kontaktierung mit leitfähiger Farbe: um die galvanischen Kontaktierungsstellen räumlich vom Ort der Erzeugung der Schwingungssignale zu trennen, können leitfähige Druckfarben, z. B. auf Metall-(Silber etc.) oder Polymerbasis (Polyanilin, Polythiophen etc.) verwendet werden. Dies kann z. B. aus designtechnischen Gründen wünschenswert sein, oder helfen, den Teil des Sicherheitsdokuments, der die Schwingungsenergie erzeugt, außerhalb der Verifikationsvorrichtung zu halten, während die galvanische Kontaktierung im Inneren stattfindet.
• – Durch eine Kombination mit berührungsloser Einkopplung: bei einer Senderfrequenz im Bereich der Hörfrequenzen (10 Hz–20 kHz) besteht eine weitere Möglichkeit darin, das Schwingungssignal berührungslos einzukoppeln. Dazu strahlt im einfachsten Fall ein externer Sender ein elektromagnetisches Signal geeigneter Frequenz und Stärke aus. Ein Empfänger, der beispielsweise in Form einer gedruckten Antenne auf dem Sicherheitsdokument ausgeführt ist, ist mit dem thermoakustischen Schwingungserreger verbunden, nimmt die Energie auf und wandelt die elektromagnetischen Schwingungen in detektierbare bzw. hörbare Signale um. Falls eine Senderfrequenz mit einer Frequenz von mehr als 20 kHz verwendet werden soll, kann diese z. B. als Trägersignal für eine aus dem Stand der Technik bekannte Amplitudenmodulation eingesetzt werden.

For example, in this external coupling of the vibration signal is a vibration generator, such as a frequency generator, outside the security document, eg. B. in a device for verification of authenticity. Various ways are provided for transmitting the vibration signals to the thermoacoustic vibration exciter:

• - For a carbon nanotube (CNT) or carbon nanotube thin-film loudspeaker by direct galvanic contacting. Since the CNT layer itself is conductive, it can be electrically contacted in at least two places to verify the authenticity. This can be z. B. done by clamping or rolling, which are themselves conductive and are connected to the frequency generator.
• - By contacting with conductive paint: to physically separate the galvanic Kontaktierungsstellen from the location of the generation of the vibration signals, conductive inks, z. B. on metal (silver, etc.) or polymer base (polyaniline, polythiophene, etc.) can be used. This can be z. B. be desirable for design reasons, or help to keep the part of the security document that generates the vibration energy outside of the verification device, while the galvanic contacting takes place inside.
• - By a combination with non-contact coupling: at a transmitter frequency in the range of the audio frequencies (10 Hz-20 kHz) is another way to couple the vibration signal contactless. In the simplest case, an external transmitter radiates an electromagnetic signal of suitable frequency and strength. A receiver, for example in the form of a printed antenna on the security document, is connected to the thermoacoustic vibration exciter, absorbs the energy and converts the electromagnetic oscillations into detectable or audible signals. If a station frequency with a frequency of more than 20 kHz is to be used, this z. B. be used as a carrier signal for a well-known from the prior art amplitude modulation.

In a second preferred embodiment, the electrical circuit consists of at least one source of electrical energy and a switch, wherein upon actuation of the switch, the source of electrical energy is connected to the thermoacoustic vibrator and emits this vibrational energy. Here, the generation of the vibration energy is performed on the security document itself. For example, there is generally enough space on chip cards to accommodate a small vibration generator together with a voltage source, or a microcontroller itself can provide this function. The essential components are in addition to the thermoacoustic vibration exciter still an oscillator, connecting tracks and a voltage source. The latter can be located both on the banknote and externally. As the vibration generator, an astable multivibrator or any other suitable oscillator can be used.

Another preferred embodiment is a combination with thermochromic inks / pigments known in the art. If no alternating current is applied to the thermoacoustic vibration exciter, but the polarity of the applied voltage is kept constant for a long time, the thermoacoustic vibration exciter heats up due to its ohmic resistance. If, for example, the thermoacoustic vibration generator is at least partially overprinted with a thermochromic color or if it is at least partially arranged above a thermochromic color, then the thermoacoustic effect can be made visible to the human eye. The result is an optical / acoustic combination feature, wherein upon application of a suitable alternating voltage or an alternating field, a characteristic vibration signal and when applying a DC voltage, a color change is produced.

The security element according to the invention is also suitable for machine processing. Specially for this purpose, frequencies of the radiated vibration energy outside of the audible or perceptible frequency range can be used, which are detectable by sensors.

Security documents within the meaning of the present invention are in particular banknotes, stocks, bonds, certificates, vouchers, checks, high-quality admission tickets, but also other papers which are subject to forgery such as passports or other identification documents, and also card-shaped documents Data carriers, in particular chip cards, as well as product security elements, such as labels, seals, packaging and the like. The term "security document" also includes non-executable precursors of such data carriers which, for example in the case of security paper, are present in virtually endless form and are processed further at a later time.

Reference to the following embodiments and the additional figures, the advantages of the invention will be explained. The embodiments represent preferred embodiments, to which, however, the invention should not be limited in any way. Furthermore, the representations in the figures of better understanding are highly schematized and do not reflect the realities. In particular, the proportions shown in the figures do not correspond to the conditions present in reality and serve exclusively to improve the clarity. Furthermore, the embodiments described in the following exemplary embodiments are reduced to the essential core information for the sake of clarity. In the practical implementation much more complex patterns or images can be used.

In detail, the figures show schematically a security document with a security feature according to the invention and in this case

1 with direct coupling of electrical energy by means of galvanic contacting,

2 when electrical energy is coupled in by means of galvanic contacting via printed conductive layers, the contacting taking place within a verification device while the generation of vibrational energy takes place outside the verification device,

3 for non-contact coupling of vibration signals in the security feature.

1 shows a security feature according to the invention in the form of a thermoacoustic vibration exciter 2 on a banknote 1 , Electrical energy is turned into the thermoacoustic vibrator 2 directly by galvanic contacting via an electrical supply line 4 and an electrical drain 5 coupled. Is the thermoacoustic vibration exciter 2 Carried out as a carbon nanotube (CNT) or carbon nanotube thin film speaker, it can be directly electrically contacted at two or more locations to verify authenticity since the CNT layer forming the carbon nanotube (CNT) or carbon nanotube thin film speaker , itself is electrically conductive. This can be z. B. done by clamping or rolling, which are designed to be conductive and with a frequency generator 3 are connected.

2 shows a security feature according to the invention in the form of a thermoacoustic vibration exciter 2 on a banknote 1 when coupling electrical energy by means of galvanic contacting via an inlet and outlet 6 . 7 in the form of two printed conductive layers. Here, the contacting takes place within a verification device 8th instead, while generating vibration signals in a frequency generator 3 takes place with the verification device 8th via an electrical supply and discharge 9 connected is. The printed conductive layers can be made of conductive inks, z. For example, on metal (silver, etc.) or polymer base (polyaniline, polythiophene, etc.) or from hybrid materials such as composites of conductive polymers and inorganic materials.

3 shows a security feature according to the invention in the form of a thermoacoustic vibration exciter 2 on a banknote 1 for non-contact coupling of the vibration signals in the security feature. In addition an external transmitter radiates 11 an electromagnetic signal of suitable frequency and strength. A receiver 10 , which may for example be embodied as a printed antenna and is arranged on or in the security document, picks up the vibration signals and passes them to the thermoacoustic vibration exciter 2 which then converts the electromagnetic oscillations into audible or perceptible signals.

LIST OF REFERENCE NUMBERS

1

bill

2

thermoacoustic vibration exciter

3

frequency generator

4

Electrical supply

5

electrical discharge

6, 7

electrical supply or discharge

8th

verification device

9

electrical supply or discharge

10

receiver

11

transmitter

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 2004/090800 A2 [0003]
• DE 10243653 A9 [0018]

Cited non-patent literature

• Preece, 1879-1880, Braun et. al. 1898 [0009]
• L. Xiao et al., "Flexible, Stretchable, Transparent Carbon Nanotube Thin Film Loudspeakers, Nano Letters, vol. 8, no. 12, 2008, pp. 4539-4545 [0013]

Claims (6)

Security element for increasing the protection against counterfeiting of security documents, such as banknotes, securities, identity cards, credit cards, debit cards or the like, characterized in that the security element consists of at least one thermoacoustic vibration exciter, which is applied to the security document and emits vibration energy when coupled in electrical energy , A security element according to claim 1, characterized in that the thermoacoustic vibration exciter is connected to an electrical circuit which is applied to the security document. A security element according to claim 2, characterized in that the electrical circuit consists of at least one receiver for electromagnetic energy, wherein the receiver emits electrical energy to the thermoacoustic vibration exciter upon irradiation of electromagnetic energy, which is generated by an external transmitter and emits this vibration energy. Safety element according to claim 2, characterized in that the electrical circuit consists of at least one source of electrical energy and a switch, wherein upon actuation of the switch, the source of electrical energy is connected to the thermoacoustic vibration exciter and this emits vibration energy. Security element according to at least one of the preceding claims, characterized in that the thermoacoustic vibration generator emits vibration energy in the form of airborne sound and / or structure-borne noise. A security element according to at least one of the preceding claims, characterized in that the thermoacoustic vibration exciter is a carbon nanotube (CNT) speaker, preferably a carbon nanotube thin-film loudspeaker.

Images