RU2451290C1 - Method of reading closed documents - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: microscopic ultrasonic "scanning" is performed over a paper medium with the text or graphic information of interest which is protected coatings which are not transparent in the visible range, with further display of the information of interest on a personal computer display, wherein the layer of interest in the paper medium is "scanned" with pulses of linearly frequency-modulated ultrasonic vibrations with a high value of the product of the spectrum width of such a pulsed signal with its duration value, and signals passing through the "scanned" paper medium and received by a piezoelectric sensor undergo spectral-time "compression" in a matched filter on a dispersive delay line, after which the obtained ultra-short radio pulse, after its amplification and amplitude detection, undergoes threshold base limiting, the limiting threshold of which is automatically set based on the control signal from a personal computer so as to eliminate noise signals, after which the obtained useful pulse signals are compared on amplitude with a reference signal, the value of which is determined from the response signal from a threshold device, corresponding to those areas of the paper medium which are known not contain elements of text or graphic information in the layer of the paper medium of interest, but contain a quasi-uniform protective coating, wherein the selected acoustic receiving-transmitting optical system has short focal distance which ensures minimum dimensions of the Airy disc in the combined focal plane of both acoustic lenses, which is combined with the plane of the layer of the paper medium of interest.

EFFECT: high accuracy of reading closed documents.

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Description

The invention relates to the fields of electroacoustics and radio engineering and can be used as a method for recording inhomogeneities of the internal structures of opaque objects, for example, for reading paper documents protected by a special coating, including for reading lottery tickets without breaking protective layers, which the acquirer must correctly erase.

Lottery games are the essence of deception of those who take part in them, since the probability of a big win (apartments in Moscow, cars) is disappearing small, and the lottery organizers receive fabulous dividends, moreover, legally. In order to counter the organizers legal extortion of money from the population, this technical solution proposes a way to read closed documents on paper - lottery tickets.

In addition to the specified purpose of the application, the claimed method can find application in forensics and other fields of knowledge, for example, for reconstruction of the topology of integrated circuits without violating their integrity.

A known method of registering text or images on paper based on the use of scanners associated with personal computers. In this case, the scanner point-by-point transmits to the personal computer information on the luminosity of each scanned point on the surface of the paper medium illuminated by the light of a special lamp. Registration takes place from the visible surface of the paper medium, which is visible directly to the eye. It is not possible to read information from paper media coated with a film opaque to light radiation.

Known methods and devices for recording internal inhomogeneities of an object that is opaque to the visible wavelength range, which use the "sounding" of such objects by ultrasonic vibrations, followed by visualization of the received information in the visible wavelength range [1-11].

The closest technical solution (prototype) with respect to the claimed one is ultrasound microscopes of scanning raster type [12, 13], containing a piezoelectric transducer emitting an ultrasonic wave, coupled through a sound duct to a collecting acoustic lens, which collects ultrasound waves into a small focus in a subsequent sound duct. . Such an acoustic lens may be a spherical recess in the sound duct at the interface with the immersion fluid. The sample is placed in the focal plane of the acoustic lens and moved in this plane along two orthogonal coordinate axes of this plane using a special scanning device. Ultrasonic radiation after interaction with the object is collected by a second spherical acoustic lens, the design of which is similar to the first, and a second piezoelectric transducer is excited through the sound pipe, at the output of which an electric signal is generated with the frequency of ultrasonic vibrations of the generator, exciting ultrasonic vibrations in the first transducer. This signal controls the brightness of the electron beam of the display, in which the scan is synchronized with the movement of the scanning device with the sample placed in it. At the same time, an acoustic image appears on the display screen, which is determined by the distribution of its physical properties (elasticity, density, viscosity, thickness, anisotropy, etc.) along the sample. Other ultrasound microscopes [14] operating in the “reflection” mode and devices for visualizing internal inhomogeneities opaque to the visible wavelength range of objects are also known [15].

A disadvantage of the known method (and the device implementing it) is the reduced reliability of the correct reconstruction of text or image on paper, hidden by a film or a special coating, opaque to the visible wavelength range, associated with large noise components arising from the presence of other inhomogeneities in adjacent layers of paper - text and drawing on the outer parts of this medium, as it actually takes place, for example, on lottery tickets. The low signal-to-noise ratio during visualization on the display of a personal computer of the text or picture being studied only in the layer of paper carrier of interest makes it difficult to read it correctly.

The specified disadvantage is eliminated in the claimed method, explained by the device implementing the method.

The aim of the invention is to increase the reliability of reading closed documents by increasing the signal-to-noise ratio in the process of information visualization.

The specified objective of the invention is achieved in a method for reading closed documents based on microscopic ultrasound “sounding” of a paper medium with text or graphic information of interest, protected by opaque coatings for the visible wavelength range and various kinds of interfering texts and drawings on the outer parts of the paper medium, with subsequent visualization of interest information on the display of a personal computer, as well as on scanning paper media relative to the focal spot growing acoustic optics operating in the “pass through” mode, with the transfer to the computer of the current coordinates of the scanned zones of the paper medium, characterized in that the “sounding” of the layer of interest on the paper medium is carried out by pulsed linear-frequency-modulated ultrasonic vibrations with a large value of the product of the spectrum width of such a pulse signal by the value of its duration, and the signals received by the piezoelectric sensor passing through the “sounding” paper medium are subjected to time-wise “compression” in a matched filter on the dispersion delay line, then the obtained ultrashort radio pulse after amplification and amplitude detection is subjected to a minimum threshold limit, the limit threshold in which is automatically set by the control signal from a personal computer so that interference signals are cut off, after which the received useful pulse signals are compared in terms of amplitudes with a reference signal, the value of which is determined by the signal response from the threshold properties corresponding to those areas of the paper medium that obviously do not contain elements of text or graphic information in the layer of paper of interest, but contain a quasihomogeneous protective coating, and the acoustic transmitting and receiving optics are selected as short-focus, ensuring the minimum size of the Airy disk in the combined focal plane of both acoustic lenses , which is combined with the plane of the layer of interest of the paper medium.

Achieving the stated objective of the invention in the claimed method is explained, firstly, through the use of short-focus acoustic optics, which maximally concentrates the density of ultrasonic radiation on the layer of paper of interest, and secondly, due to the use of the method of spectral temporal “compression” of linear frequency-modulated (LFM) periodically following ultrasonic coherent radio pulses via a dispersive delay line (DLA) with the large base value B = ΔFτ _AND ≥1000, where ΔF = f _MAX -f _MIN - cn strip width ktra chirped signal, τ _I - duration of the impulse response DLA (pulse duration LFM), f _MAX and f _MIN - the upper and lower frequency chirp rf pulse, which significantly increases the signal / noise ratio at the output of the threshold device, that is, increases the probability of correct detection useful information for a given probability of false alarms created by interference - interfering text and a pattern on the outer surfaces of the paper medium, the granularity of the protective coating, the shot noise of the radio signal amplifiers. The use of a reference response signal at the output of a threshold device and its comparison (subtraction) with response signals obtained by “sounding” the elements of a text or a picture of interest when they are combined with an Airy disk of acoustic optics during scanning of paper media also increases the reliability of reconstruction of the extracted information from secure paper.

The inventive method is implemented by a device, a diagram of which is shown in Fig. 1 and contains the following elements and blocks:

1 - a generator of linear-frequency-modulated (HLFM) oscillations,

2 - clock generator (GSI),

3 - the first ultrasonic transducer (transmitting channel),

4 - the first acoustic lens,

5 - investigated opaque to light waves object,

6 - flat stand (in the coordinate system XY),

7 - the second acoustic lens,

8 - second ultrasonic transducer (receiving channel),

9 - a bellows with mechanical scanning elements along the XYZ coordinates,

10 - the case of the ultrasonic module of the microscope disassembled,

11 - immersion fluid filling the housing 10 and protected from leakage from the latter by a bellows 9,

12 - depth scanning device (SG), moving elements 3, 4, 7 and 8 along the Z coordinate, orthogonal to the plane of the stand 6, mechanical connections of the moved elements for simplicity are not shown in Fig. 1,

13 - mechanical two-coordinate scanning device (DSU),

14 - personal computer with a display,

15 is a broadband amplifier,

16 - controlled by a personal computer 14 attenuator,

17 - matched filter on the dispersion delay line (DLZ),

18 - loss-compensating low-noise broadband amplifier,

19 is an amplitude detector,

20 - threshold device (minimum limiter with threshold U _OGR *),

21 is a unit for detecting heterogeneity of an object that is opaque to light waves.

Figure 2 shows plots of short sync pulses from GSI 2, LFM signals generated in HFM 1, and a pulse sequence (bottom of Fig. 2) that determines the duration τ _{AND of} periodically following LFM signals with a period T _AND . The frequency of the LFM signals falls linearly from the value f _MAX to the value f _MIN as a function of time t.

Figure 3 shows an enlarged view of one high-frequency chirp pulse with a frequency band ΔF = f _MAX -f _MIN .

Figure 4 shows the interaction of the LFM signals generated at the output of a personal computer-controlled attenuator 16 — line A and at the output of the second ultrasonic transducer 8 — direct B, with a matched filter at DLZ 17. The constant time delay between the indicated LFM pulses is Δt and is determined by the delay of the LFM of ultrasonic (US) vibrations inside the housing of the ultrasonic module 10 with immersion liquid 11.

Figures 5 and 6 show the pulsed responses from the output of DLZ 17 with their amplification at 18 and amplitude detection at 19 for a given threshold U _OGR of 20 exceeding the noise level for the two compared situations - when probing by ultrasonic vibrations of this zone of the studied object 5 in the absence of heterogeneity in this zone (Fig. 5) and in the presence of heterogeneity in this zone (Fig. 6). In this case, the heterogeneity is either strongly absorbing or strongly reflecting, which reduces the amplitude of the ultrasonic vibrations arriving at the second ultrasonic transducer 8. In the first case, the amplitudes of the responses arriving at the inputs of the broadband amplifier 15 are equalized by the attenuator 16 controlled from the personal computer to the value U ₁ in the initial state, and in the second case, the amplitude of the signal from the second ultrasonic transducer 8 decreases, which reduces the pulse to a value of V ₂ <U ₁ . The values of U ₁ and U ₂ have a small scatter, indicated in Figs. 5 and 6 by two close dashed lines.

Figures 7 and 8 show the results of the operation of the recording unit for the inhomogeneity of the object 5, which is opaque for light waves. In the absence of heterogeneity in the considered area of object 5 (Fig. 7), the response of the unit ΔU _{1 is} significantly lower than a certain threshold level U _OGR *, and in the presence of heterogeneity in this zone, the response ΔU _{2 of the} block is significantly higher than this threshold. These responses are encoded respectively in the values of zero and one in binary code and act on the information input of the personal computer 14.

Consider the action of this device according to the claimed method in relation to its other possible application - reconstruction of the topology of integrated circuits (including multi-layer) in a plastic case without destroying such circuits, as is now done when copying foreign circuits.

Under the influence of short pulses periodically following with a period of T _AND (see the top in Fig. 2), linear-frequency-modulated pulsed oscillations are formed in GLFM 2 from GLI 1, the form of which is shown in Figs. 2 and 3, having a duration of _And and a spectrum with width ΔF = f _MAX -f _MIN . The product of these quantities is called the signal base B = ΔFτ _AND >> 1, and such signals are called complex. These radio pulses are fed to the input of the first ultrasonic transducer 3, forming a plane ultrasonic wave propagating in the immersion liquid 11 in the module housing. This wave is focused by the first acoustic lens 3 into a point zone inside the studied object 5 (the focal plane in Fig. 1 is shown by a dashed line parallel to the plane of the stand 6). The size of the focused spot is d = 2.44λF / D, where λ = V / f is the ultrasonic wavelength inside the studied object 5, V is the propagation velocity of the frequency oscillations f, D is the diameter, and F is the focal length of the first acoustic lens 4. So, if V = 2000 m / s, f = 1 GHz (10 ⁹ Hz), then λ≈5 μm (5.10 ^-6 m), provided that the acoustic lens is short-focus, for example, at D = F. This determines the high resolution of the microscope along the XY plane.

The short focus of the first acoustic lens 4 provides a strong divergence of the ultrasonic flow outside the focal plane of this lens, which positively affects the increase in signal / noise response in the second ultrasonic transducer 8, while the noise is generated from other possible inhomogeneities of the studied object 5 in its other layers parallel to the plane of the stand 6.

The transmitted ultrasound radiation after the object under study 5 is again focused by the second acoustic lens 7, which forms a plane ultrasonic wave acting on the second ultrasonic transducer 8. The amplitude of the broadband ultrasound signal varies depending on the presence or absence of heterogeneity in the studied zone inside the object 5, in particular and mainly, in the combined focal planes of the first and second acoustic lenses 4 and 7. If the inhomogeneity is strongly absorbing (air bubble), then the intensity of the ultrasonic wave incident on Ora ultrasound transducer 8, falls. If the heterogeneity is highly reflective (when an ultrasound spot in the focal plane hits the metal surface of a gold strip conductor in the microcircuit), the result will be the same - a decrease in the intensity of the transmitted ultrasound wave. These circumstances are used in the work of the microscope.

In the initial state, the test object is mounted on a flat substrate 6 so that the focal spot falls on the material inside the test object 5, NOT CONTAINING any heterogeneity when the signal at the output of the second ultrasonic transducer 8 is maximum. At the same time, using a personal computer 14, the controlled attenuator 16 is automatically adjusted so that the signal at its output (at the second input of the broadband amplifier 15) is aligned with the response amplitude of the threshold device 20 (as can be seen in Fig. 5), which minimizes the difference of the response signals ΔU ₁ . After such adjustment of the device, the test object is scanned on the stand plane 6 at the XY coordinates using DSU 13 and along the depth of the plane of the first and second acoustic lenses 3 and 7 using SG 12 under the influence of control signals from the bi-directional outputs of the personal computer 14. These inputs and outputs set the microshifts of the investigated object along the XYZ coordinate axes, and also read the readings of the shift sensors to transfer them to the personal computer 14. When the focal spot falls on the inhomogeneity inside the studied the object, the coordinates of which are set by the signals of the shift sensors DSU 13 and SG 12, at the output of the threshold device there are response signals of substantially different amplitudes, and their difference ΔU ₂ >> ΔU ₁ , calculated in the block 21 for recording the inhomogeneity of the object under study, which is opaque to light waves and exceeding some set threshold U _OGR *, which is transmitted by a code combination to a personal computer as information about heterogeneity. The code signal may contain a multi-valued binary set (instead of the information “Yes” or “No”), with the help of which the degree of heterogeneity (shades of gray level) is estimated. A code combination for heterogeneity is generated in the registration unit 21, and the connection of the output of this unit with a personal computer is shown in Fig. 1 by a curly arrow.

The LFM signals from the second ultrasonic transducer 8 and the controlled attenuator 16 after their linear amplification in a broadband amplifier (summing) 15 are fed to a matched filter on the DLZ 17 having a passband ΔF and a pulse characteristic duration τ _AND , in which spectral-time “compression” is performed signal, as a result of which two short response pulses with a duration of τ _OUT = 1 / ΔF are formed at the DLZ output. So, if the DLS has parameters τ _И = 95 μs and ΔF = 100 MHz (DLS with the base B = 9500), then τ _OUT = 10 ns. In this case, the chasing frequency of the LFM pulses can be set equal to F _И = 1 / Т _И = 10 kHz (the duty cycle of these pulses is σ = Т _И / τ _И = 1,053. The use of spectral-time “compression” of the LFM signals in DLZ allows, as is known, increase the signal-to-noise ratio at the input of the threshold device 20 by a square root of a number equal to the base of the signal matched in the DL, i.e., the signal-to-noise ratio S / N = (9500) ^1/2 = 97.5 (about 40 dB in voltage).

The threshold restriction level U _OGR in the threshold device 20 is selected according to the criterion of providing a given probability of correct detection at a given acceptable probability of false alarms. The use of DLZ processing contributes to the solution of this problem in an optimal way.

Data on the properties of the inhomogeneity and its coordinates inside the object under study 5 are transmitted in the form of a binary code to the inputs of the personal computer 14 and are accumulated in its database, which allows the layered dislocation of the inhomogeneities to be displayed on the display screen inside this object. The number of scanning steps is determined by the geometry of the test sample and the focal spot area d. If, for example, it is necessary to reconstruct the topology of the compounds in a layer of a multilayer microcircuit in a plastic case measuring 20 × 20 mm in size (along a gallium arsenide crystal), then with a focal spot diameter of 5 μm, the number of scanning steps along XY coordinates is of the order of 4000 × 4000 = 16 * 10 ⁶ . In this case, the scanning time of one full layer of such a microcircuit will be T _{SCAN .-- 1} = 16 * 10 ^{6/10 4} = 1600 s = 26 min 40 sec, while the scanning speed is 50 mm / s. Taking into account the preliminary tuning of the microscope, removing the topology of one layer of a microcircuit with a crystal size of 20 × 20 mm ² requires an average of half an hour. Registration of the topology of a layer or its individual part can be repeated many times with subsequent statistical averaging of the results, which will further increase the accuracy of registration at the cost of time loss.

Preliminary automatic tuning of the microscope (tuning of the controlled attenuator 16) is carried out by a personal computer 14 (from its first output) according to the signals ΔU ₁ , which, as a result of the adjustment of the attenuator 16, are minimized with a possible spread ΔU ₁ <U _OGR *, as can be seen in Fig. 7.

The information transmitted by the binary code to the personal computer 14 from the registration unit 21 is reset when the specified code is averaged over the number of measurement repeats at each scan step by the clock signals from the clock generator 2. The reception of the code by the personal computer is confirmed by the transmission of the corresponding signal from the personal computer to the block registration 21. The synchronization of the personal computer is also carried out by applying to its input clock pulses from the second output of the sync generator roimpulsov 2.

Consideration of the electronic structure of the recording unit 21 is omitted due to the obviousness of the functions performed by this unit (the subtraction of the amplitude of the current impulse responses from the amplitude of the reference, statistical averaging, if provided, encoding of the results of calculations) is beyond the scope of this application. The program of work of a personal computer and its algorithm are also beyond the scope of this application and can be easily compiled by specialist programmers. Using this program, you can either perform a line-by-line scanning of the object under study without the accumulation procedure, or with one that, in the latter case, further improves the accuracy of reconstruction of the printed circuit pattern in this layer of the microcircuit, or when information is accumulated only in any particular area, which it is especially important in relation to the removal of topology in microcircuits with its various elements and their connections. The larger the number of information accumulations used with its subsequent statistical averaging, the longer it takes to complete the recognition process.

Scanning of the studied object (including the lottery ticket) can be carried out according to various schemes, which include line-return scanning or spiral-circular. It can be intermittently stepping or continuous. In addition, the sample can be fixed in a scanning device with the possibility of its rotation by 90 and 180 ° with the subsequent correct superposition of the obtained images and their statistical averaging, which also helps to increase the reliability of the result. These operations of correct image overlay are easily carried out programmatically in a personal computer.

In the case of recognition of text in lottery tickets, the task of reliably obtaining information is much easier, since they usually only contain letters known from the Russian alphabet and Arabic numbers in the form of a combination of straight or curved lines of a given width and thickness. The immersion liquid used in the microscope should not interact aggressively with paper media (lottery ticket) in any way, preserving its integrity. Mercury that can be easily melted at a temperature of + 27 ° C metal - gallium and other non-wetting liquids can be recommended as such an immersion liquid, and the lottery organizers will not be able to make any complaints about the quality of the lottery ticket to the “lucky” one. An ultrasonic wave of comparatively low intensity will in no way affect the integrity of the means of protection provided for the lottery ticket, which is an important factor when the organizers of the lottery check the fact of unauthorized actions of its owner. That is why weak ultrasonic radiation in the form of chirp signals is then subjected to spectral-time “compression”, which significantly increases the signal-to-noise ratio, which justifies the use of this processing method in the claimed method.

It is important to note that a further increase in the resolution and reliability of the recognition results obtained when implementing the proposed method can be achieved by increasing the average frequency of the probing ultrasonic radiation, since this determines the reduction in the length of the ultrasonic wave and, consequently, the diameter of the Airy disk in the focal plane of the speaker system, however, it leads to an additional increase in the time of full registration. There is information about the operation of ultrasound microscopes with frequencies of the order of two or more gigahertz.

In addition, it is advisable to use acoustic lenses (or acoustic lens assemblies in order to reduce various kinds of aberrations) with a large aperture and small focal length, so that the ratio F / D <1, which also helps to increase the resolution of the system.

Literature

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2. Ahmed M., Van K., Miderell A. Holography and its use in acoustoscopy. Per. with the English., "TIIER", 1979, t.67, p.25.

3. Zuykova N.V., Light V.D. About one optical method for reconstructing the acoustic hologram of a point source located in an inhomogeneous waveguide. “Acoust. Journal ", 1981, v. 27, p. 513.

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5. Mataushek I. Ultrasonic technology. Per. with it., M., 1962.

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Sources of Patent Information

DE 3835886, 04/28/1990 CA 2012951, 09.25.1990. RU 2112969 C1, 06/10/1998 RU 2011194 C1, 04/15/1994.

Claims (1)

A way to read closed documents, based on microscopic ultrasound “sounding” of a paper medium with text or graphic information of interest, protected by opaque coatings for the visible wavelength range and various kinds of interfering texts and drawings on the outer parts of the paper medium, followed by visualization of the information of interest on the personal computer display as well as on scanning paper media relative to the focal spot of forming acoustic optics operating “pass through” mode, with transferring to the computer the current coordinates of the scanned zones of the paper medium, characterized in that the “sounding” of the layer of interest on the paper medium is carried out by pulsed linear-frequency-modulated ultrasonic vibrations with a large value of the product of the spectrum width of such a pulse signal by its value durations, and the signals received by the piezoelectric sensor passing through the “sounding” paper medium are subjected to spectral-time “compression” in a consistent filter on the dispersion delay line, after which the obtained ultrashort radio pulse after amplification and amplitude detection is subjected to a minimum threshold limit, the limit threshold in which is automatically set by the control signal from a personal computer so that interference signals are cut off, after which the obtained useful pulse signals are compared by amplitudes with a reference signal, the value of which is determined by the signal response from the threshold device corresponding to those zones b important media, which obviously do not contain elements of text or graphic information in the layer of paper media of interest, but contain a quasihomogeneous protective coating, and the acoustic transmit-receive optics are selected as short-focus, ensuring the minimum size of the Airy disk in the combined focal plane of both acoustic lenses, which is combined with the plane layer of paper of interest.

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