Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
  • G01S13/74—Systems using reradiation of radio waves, e.g. secondary radar systems; Analogous systems
  • G01S13/75—Systems using reradiation of radio waves, e.g. secondary radar systems; Analogous systems using transponders powered from received waves, e.g. using passive transponders, or using passive reflectors
  • G01S13/751—Systems using reradiation of radio waves, e.g. secondary radar systems; Analogous systems using transponders powered from received waves, e.g. using passive transponders, or using passive reflectors wherein the responder or reflector radiates a coded signal
  • G01S13/756—Systems using reradiation of radio waves, e.g. secondary radar systems; Analogous systems using transponders powered from received waves, e.g. using passive transponders, or using passive reflectors wherein the responder or reflector radiates a coded signal using a signal generator for modifying the reflectivity of the reflector
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S1/00—Beacons or beacon systems transmitting signals having a characteristic or characteristics capable of being detected by non-directional receivers and defining directions, positions, or position lines fixed relatively to the beacon transmitters; Receivers co-operating therewith
  • G01S1/72—Beacons or beacon systems transmitting signals having a characteristic or characteristics capable of being detected by non-directional receivers and defining directions, positions, or position lines fixed relatively to the beacon transmitters; Receivers co-operating therewith using ultrasonic, sonic or infrasonic waves
  • G01S1/76—Systems for determining direction or position line
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S1/00—Beacons or beacon systems transmitting signals having a characteristic or characteristics capable of being detected by non-directional receivers and defining directions, positions, or position lines fixed relatively to the beacon transmitters; Receivers co-operating therewith
  • G01S1/72—Beacons or beacon systems transmitting signals having a characteristic or characteristics capable of being detected by non-directional receivers and defining directions, positions, or position lines fixed relatively to the beacon transmitters; Receivers co-operating therewith using ultrasonic, sonic or infrasonic waves
  • G01S1/76—Systems for determining direction or position line
  • G01S1/82—Rotating or oscillating beam beacons defining directions in the plane of rotation or oscillation
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S5/00—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations
  • G01S5/18—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations using ultrasonic, sonic, or infrasonic waves

Definitions

• the present invention relates to the field of locating objects with RFID tags.
• the invention can be used in particular to locate objects in a warehouse or a hangar.
• Radio Frequency Identification technology is currently widely used to list, identify or track all types of objects.
• the infrastructure necessary for the implementation of this technology generally comprises a plurality of RFID tags placed on the objects to be tracked and one or more RFID readers distributed over the reading zone to be covered to interrogate said tags.
• the RFID reader transmits an interrogation signal and the tags receiving this interrogation signal respond by sending a response signal.
• the tags are of different types: passive (no internal source of energy), active (powered by an internal source of energy), semi-passive (battery-powered).
• a passive tag the tag retromodulates the interrogation signal to transmit information.
• the passive tag generally uses the wave (magnetic or electromagnetic) of the interrogation signal to power its on-board electronic circuit.
• the tag includes an RF transmitter and the communication with the interrogator is therefore peer-to-peer.
• This type of tag makes it possible to receive interrogation signals of lower level than the passive tags and to respond to them. It can also have additional functionalities, by a memory, a sensor or a cryptography module.
• the semi-passive tag is a hybrid tag. It communicates with the reader as a passive tag but it has an internal battery that continuously supplies its internal circuit.
• This technology is used not only to identify and list, via their tags, objects present in a given place (warehouse, shed, ...) but also to locate them in this place.
• the tag to be located must also be able to receive the interrogation signals of these three RFID readers and send them back with sufficient power to be received by the three RFID readers; this means that the system must have a dense network of RFID readers;
• tags are passive, their power supply requires the use of high power of emission, leading to multiple reflections, especially in closed environment; these multi-path electromagnetic waves are simultaneously received by a plurality or even all of the RFID readers, significantly reducing the accuracy of tag location.
• An object of the invention is to overcome all or part of the aforementioned drawbacks.
• RFID technology is coupled with sonic and ultrasonic wave technology to locate an RFID tag.
• the ultrasonic waves propagate at frequencies above 20 KHz and that the audible sound frequencies are in the 20 Hz-20 kHz band.
• the sound wave (or acoustic) resulting from the difference of two ultrasonic waves to locate an RFID tag.
• This sound wave is conventionally called a parametric wave. Its main characteristic is to have a directivity of its radiation pattern much higher than that of a classical sound wave or a UHF electromagnetic wave used in RFID. According to the invention, this directivity is used to locate the tags.
• the invention relates to a system for locating at least one object in a predetermined space, said system comprising at least one RFID tag positioned in or on an object to be located in said predetermined space, and an RFID reader capable of transmitting at least one radio frequency interrogation signal for said RFID tag and receiving a radio frequency response signal from said RFID tag.
• the system further comprises at least one ultrasonic generator capable of emitting ultrasound signals of frequencies f1 and f2 in said predetermined space in a given direction, with f1> f2, so as to generate a frequency parametric signal.
• the tag is equipped with an acoustic sensor adapted to pick up the signals of frequency f1-f2, said acoustic sensor being arranged with said RFID tag so as to modify the content or the level of the response signal of the RFID tag when said acoustic sensor receives a frequency signal fl-f2.
• the RFID reader is then able to locate said object in said sound zone when it receives the modified response signal of said RFID tag.
• the directivity of the parametric wave originating from the ultrasonic signals of frequencies fl and f2 to create a sound zone in the predetermined space is present only in this zone of the predetermined space.
• the reception of this parametric wave by the acoustic sensor of a tag then means that this tag is present in this zone.
• this parametric wave causes a modification of the response of the RFID tag.
• This modification may be to attenuate the response signal.
• the response signal may then not be received by the RFID reader.
• This modification can also consist in modifying the content of the response signal, for example by modifying a bit in the response signal.
• the level of the response signal is attenuated when the acoustic sensor receives a sound signal of frequency f1-f2.
• the RFID tag is a passive tag having an RFID chip coupled to a magnetic antenna.
• the acoustic sensor is a capacitive sensor coupled to the magnetic antenna of the tag so as to modify the resonance frequency of the magnetic antenna when said acoustic sensor receives a frequency signal f1-f2.
• the magnetic antenna of the tag is then detuned to receive the interrogation signal and transmit the response signal.
• the response signal retro-modulated by the tag is then attenuated.
• the response signal retro-modulated by the tag is very attenuated, its level may be such that it is below the reception threshold of the reader RFID.
• the RFID reader no longer receives the response signal from the tag and acts as if it had received a modified response signal.
• the tag is then located in the sound zone.
• the RFID tag is an active or semi-passive tag comprising an RFID chip coupled to a magnetic antenna
• the acoustic sensor is a piezoelectric sensor powered by the RFID tag
• the RFID tag is further equipped with a microcontroller powered by the RFID tag and able to write in a register of the RFID chip of said at least one RFID tag.
• the acoustic sensor, the RFID chip and the microcontroller are arranged so that the microcontroller comes to modify the state of the register of the RFID chip when the acoustic sensor receives a frequency signal fl-f2, the state of the register being contained in the signal response of said at least one tag.
• the RFID tag is an active or semi-passive tag comprising an RFID chip coupled to a magnetic antenna and the acoustic sensor is a resistive sensor powered by the tag.
• the resistance varies as a function of the frequency of the acoustic signal picked up so that the acoustic sensor has a first resistance value when the acoustic signal picked up is of frequency f1-f2 and a second resistance value when the acoustic signal picked up is of frequency f1. or f2.
• the acoustic sensor and the RFID chip are arranged so that the RFID chip comes to write in one of its registers a representative state of the value of the resistance of the acoustic sensor, the state of the register being contained in the response signal of said at least one tag.
• the acoustic sensor is a sensor printed on a support of the tag.
• the system further comprises a control circuit coupled to said RFID reader, which control circuit is able to move the position of said at least one ultrasonic generator to move the sound zone.
• the RFID reader can thus locate, zone by zone, the RFID tags present in the predetermined space.
• the system comprises a plurality of ultrasonic generators disposed in or near said predetermined space to scan all of said predetermined space with frequency signals f1-f2.
• each ultrasound generator comprises a plurality of elementary sources of ultrasound distributed over a disk of diameter D.
• the ratio D / ⁇ is greater than 4.7, ⁇ being the wavelength of the signal of frequency f1 or f2.
• the frequencies f 1 and f 2 are between 40 kHz and 200 kHz, preferably between 40 kHz and 100 kHz to limit the attenuation and thus increase the area of sound created.
• the frequency f1-f2 is between 15 kHz and 20 kHz, preferably between 18 kHz and 20 kHz not to be audible by the human ear.
• said ultrasonic signals of frequency f1 and f2 are emitted during one or more time periods of less than 15 ms duration. Within this time, the human ear does not perceive the presence of a sound signal.
• FIG. 1 illustrates the phenomenon of parametric wave generation from ultrasonic waves
• FIG. 2 illustrates the appearance of the parametric wave in a far field
• FIG. 3 is a diagram of a system according to the invention.
• FIG. 4 is an image of an ultrasonic generator of the system of FIG. 3;
• FIG. 5 is a diagram of an RFID tag equipped with an acoustic sensor according to a first embodiment of the invention;
• FIG. 6 shows two curves illustrating the operation of the tag of FIG. 5;
• FIG. 7 is a diagram of an RFID tag equipped with an acoustic sensor according to a second embodiment of the invention.
• FIG. 8 is a diagram of an RFID tag equipped with an acoustic sensor according to a third embodiment of the invention.
• RFID technology is combined with parametric wave technology to locate RFID tags.
• the parametric wave phenomenon is based on the non-linear effects of acoustic wave propagation. This phenomenon has been described for the first time by Westervelt. He was then employed in several fields, particularly for the manufacture of directional loudspeakers.
• Figure 3 schematically shows a system according to the invention.
• the system comprises an RFID reader 10, a plurality of RFID tags 20 placed on objects 2 to be located, an ultrasonic generator 11 and a control circuit 12.
• the objects 2 are present in a predetermined space E .
• RFID tags are active, passive or semi-passive tags.
• the RFID reader 10 is able to transmit a radio frequency interrogation signal I to the tags RFID 20 present in the space E and receive response signals R and R 'from these tags.
• the ultrasonic generator 11 is used to generate the ultrasonic signals of frequency f 1 and ⁇ 2 greater than 20 kHz and a parametric signal of frequency f 1 -2 in a far field in a specific zone, called the sound zone Z (hatched area in FIG. 3). , of space E.
• the frequency fi-Î2 is less than 20 kHz.
• the zone Z extends beyond the near-field limit of the ultrasonic generator 11. The characteristics of this zone depend on the ultrasonic generator 11.
• the ultrasonic generator 11 is a parametric emitter emitting ultrasonic waves having a high directivity.
• the ultrasonic waves of frequencies f 1 and ⁇ 2 are emitted in a given direction to generate in the far field a sound signal in a limited area of the space E.
• This emitter is for example the transmitter AS050A marketed by the Japanese company NICERA.
• This emitter is made from a plurality of piezoelectric transducers disposed relative to one another so as to form a disk of diameter D.
• the sound wave produced by the ultrasonic generator is intended to be picked up by an acoustic sensor.
• each tag 20 is equipped with an acoustic sensor capable of picking up signals of frequency fi-f2.
• This acoustic sensor is coupled to the tag so as to modify or attenuate the response signal of the RFID tag when the latter receives the interrogation signal I from the RFID reader 10.
• the tags present in the zone Z thus return a response signal. modified R 'with respect to the other tags which returns a response signal R.
• the RFID reader 10 can therefore identify, by the response signals R', the tags present in the zone Z and can thus locate the objects 2 present in this zone .
• FIG. 5 illustrates the case of a passive tag 20 provided with a capacitive acoustic sensor 203 for the implementation of the invention.
• the tag 20 includes so a conventional RFID chip 200, a magnetic antenna 201 an electrical antenna 202, dipole type, coupled to the magnetic antenna.
• the capacitive acoustic sensor is connected in parallel with the loop of the magnetic antenna. It is intended to modify the resonance frequency of the tag when it receives a sound signal of frequency f1-f2.
• the natural resonance frequency of the tag thus varies under the effect of the acoustic wave of fl-f2.
• the magnetic loop of the tag has an inductance L0 and a capacitance C0 in the absence of acoustic pressure on the sensor.
• the RFID chip having a Cic capability.
• the resonance frequency F0 of the tag is given by the formula:
• the frequency F0 ' is no longer locked to the frequency F RF i D of the interrogation signals and the response signals.
• This shift of the resonant frequency of the tag's magnetic loop therefore causes attenuation of the response signal returned by the tag.
• This attenuation of the signal of response is represented by a decrease in the reading distance of the tag which passes from dl to d2.
• the level of the response signal R ' may not be sufficient to be received by the RFID reader.
• the reception of the parametric signal by the acoustic sensor thus makes it possible to shift the frequency of the maximum amplitude of the response signal of the tag and thus to attenuate the response signal of the tag.
• the RFID reader in its baseband of its reception circuit.
• the amplitude modulation of the retro-modulated RFID digital signal varies at frequencies between 20 kHz and 40 kHz at a maximum of 640 kHz at the maximum rate chosen for the standard UHF Gen2 RFID communication protocol. If the additional amplitude variation due to the sound pressure is between 3 to 18 kHz, it can be easily separated from the digital communication signals received from the RFID tag by a low-pass filter.
• acoustic sensor 203 can be produced by printing on the flexible support itself of the tag 20.
• the acoustic sensor is a piezoelectric sensor, for example of the MEMS type. These sensors are conventionally used as microphones in mobile phones because of their very small footprint.
• the RFID tag is a semi-passive tag (BAP), equipped for example with the RFID chip EM4325 from MeMarin. It has an output for supplying the acoustic sensor 203 and a microcontroller 204.
• BAP semi-passive tag
• the microcontroller 204 just write information representative of this reception in a register of the chip 200. This register is read when the tag receives the interrogation signal of the RFID reader. Information representative of the state of this register is transmitted to the RFID reader via the response signal.
• the ePC identifier of the TAG RFID can be modified according to whether a sound is detected by the tag.
• the microcontroller can also turn off or wake the tag circuit by a numerical control.
• the microcontroller 204 can produce a DFT (Discrete Fourier Transform) by implementing for example a Goertzel algorithm.
• DFT Discrete Fourier Transform
• This Algorithm is used in the detection of DTMF (Dual Tone Multi Frequency) audible signals used to encode the handset keys in conventional telephony.
• the simple structure of the Goertzel algorithm makes it easy to implement in a small microcontroller requiring a minimum of operation and therefore the lowest power consumption possible. Further simplification is possible by choosing a sampling frequency of the digital analog conversion circuit of the microcontroller four times that of the desired signal. In this particular case, the operations to be performed are even simpler: they are limited to additions and subtractions.
• a 16-bit microcontroller fixed-point operation is sufficient to detect the frequency as long as it is known precisely to about 100Hz. This eliminates ambient and parasitic noise.
• acoustic sensors whose impedance (resistance) varies with the frequency of the signal received.
• the acoustic sensor is powered by the tag which can be passive, active or semi-passive.
• the acoustic sensor is connected between an input and an output of the tag's RFID chip.
• This RFID chip is for example the G2iL + chip of the company NXP.
• the acoustic sensor is for example designed so that its impedance is greater than 20 MOhms when it does not receive a sound signal at the frequency fl2 and it is less than 2 MOhms when it receives one.
• the impedance of the acoustic sensor is greater than 20 MOhms, the voltage at its terminals is high enough for the RFID chip to detect an open circuit. Conversely, if the impedance is less than 2 MOhms, the voltage across the acoustic sensor is below a predetermined voltage threshold and the RFID chip detects a low impedance or a short circuit. At each of these two states corresponds a distinct high or low bit value inscribed in a register of the memory of the chip. This register is read when the tag receives the interrogation signal from the RFID reader. Information representative of the state of this register is transmitted to the RFID reader via the response signal.
• Such an acoustic pressure sensor having an impedance varying according to the sound levels can be envisaged in a printed technique.
• a low pass filter is advantageously added in order to integrate and smooth the low frequency variations of the detected acoustic pressure.
• a mechanical hysteresis maintaining the resistance at a stable value between two alternations of the low frequency acoustic wave is integrated in the sensor. This natural remanence allows the integrated circuit to measure a stable impedance on the scale of the few hundreds of microseconds needed to measure the impedance.
• the control circuit 12 moves in a horizontal or vertical plane the ultrasonic generator 11. It can also move it angularly (rotation around a vertical or horizontal axis). The latter can be positioned in the center of the space E or on one of its sides (as shown in Figure 3). It is the same for the RFID reader 10.
• the frequencies f1 and f2 are preferably between 40 kHz and 100 kHz in order to limit the attenuation and thus increase the zone of sound created.
• the sound signal of frequency f1-f2 is audible if f2 ⁇ 18 kHz.
• the ultrasonic signals f1 and f2 are preferably emitted periodically for a duration of less than 15 msec, below which time the resulting sound signal is not perceived by the human ear.
• the ultrasonic signals are for example emitted every 2 seconds for a period of 15 ms.
• ultrasonic signals are used such that the difference f1-f2 is between 18 kHz and 20 kHz.
• the parametric signal is not audible but remains directive.

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• Engineering & Computer Science (AREA)
• Radar, Positioning & Navigation (AREA)
• Remote Sensing (AREA)
• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Computer Networks & Wireless Communication (AREA)
• Measurement Of Velocity Or Position Using Acoustic Or Ultrasonic Waves (AREA)

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• 2014
  • 2014-10-23 FR FR1460214A patent/FR3027685B1/fr active Active
• 2015
  • 2015-10-23 WO PCT/FR2015/052866 patent/WO2016062982A1/fr active Application Filing
  • 2015-10-23 EP EP15798502.9A patent/EP3210035A1/de not_active Withdrawn
  • 2015-10-23 US US15/521,530 patent/US20180329015A1/en not_active Abandoned

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