GB2468046A

GB2468046A - Method and Apparatus for Locating an Acoustic Identification Tag

Info

Publication number: GB2468046A
Application number: GB1005136A
Authority: GB
Inventors: Sandip Patel
Original assignee: Individual
Current assignee: Individual
Priority date: 2009-01-23
Filing date: 2010-01-08
Publication date: 2010-08-25
Also published as: GB201005136D0

Abstract

An apparatus comprising an ensonifier or acoustic transmitter 606 configured to ensonify a scene with broadband acoustic signals 614, a plurality of transducers 608 configured to convert acoustic signals 616 received from the scene into non-acoustic signals, at least one timer configured to measure the transit times of acoustic signals between a tag 20 present in the scene and each of the plurality of transducers and a processor 602 configured to determine an approximation of a frequency response of the scene, and to use the approximation of the frequency response of the scene to identify the tag and to calculate the location of the tag on the basis of the transit times.

Description

Tag Identification and Identification Tags

Field of the Invention

This invention relates to the field of tags and tag identification.

Background to the Invention

Computer readable tags have long been used to allow computers easily and efficiently to identify an object. Two such tags are barcodes and Radio Frequency Identification (RFID) tags. Barcodes are optical tags comprising arrangements of relatively dark and light regions. A barcode reader is able to identify a barcode by detecting the reflection of a light source from dark and light regions forming the barcode. RFID tags are usually a combination of an integrated circuit and an antenna. Identification information is stored by the integrated circuit. Following receipt of a signal from an RFID reader, the RFID tag uses the energy of the signal to transmit the information stored by the integrated circuit via the antenna to the RFID reader. Both of these tags are passive in so much as they do not have their own power source.

Summary of the Invention

A first aspect of the invention provides apparatus comprising: an ensonifier configured to ensonify a scene with broadband acoustic signals; a transducer configured to convert acoustic signals received from the scene into non-acoustic signals; and a processor configured to process the non-acoustic signals to determine an approximation of a frequency response of the scene, and to use the approximation of the frequency response of the scene to identify a tag present in the scene.

A second aspect of the invention provides apparatus comprising: a transducer configured to convert acoustic signals received from a scene into non-acoustic signals; and a processor configured to process the non-acoustic signals to determine an approximation of a frequency response of the scene, and to use the approximation of the frequency response of the scene to identify a tag present in the scene.

A third aspect of the invention provides a method comprising: ensonifying a scene with broadband acoustic signals; converting acoustic signals received from the scene into non-acoustic signals; processing the non-acoustic signals to determine an approximation of a frequency response of the scene; and using the approximation of the frequency response of the scene to identify a tag present in the scene.

A fourth aspect of the invention provides a method comprising: receiving a signal representative of a received acoustic signal; processing the signal to determine an approximation of a frequency response of a scene from which the received acoustic signal was received; and processing the approximation of the frequency response in order to identify a tag present in the scene.

A fifth aspect of the invention provides an identification tag comprising a plurality of tubular members each having at least one open end and each having different dimensions and thus different resonant frequencies, for allowing the identification tag to be identified by determination of a frequency response of the identification tag when ensonified.

Brief Description of the Figures

Figure 1 shows an embodiment of an acoustic tag used with embodiments of the invention; Figure 2 shows an alternative embodiment of an acoustic tag used with embodiments of the invention; Figure 3 shows another alternative embodiment of an acoustic tag used with embodiments of the invention; Jo Figure 4 shows another alternative embodiment of an acoustic tag used with embodiments of the invention; Figure 5 shows another alternative embodiment of an acoustic tag used with embodiments of the invention; and Figure 6 is a schematic of an embodiment of an acoustic tag identification system according to aspects of the invention.

Detailed Description of the Embodiments

Figure 1 shows an embodiment of an acoustic identification tag 10. The acoustic identification tag comprises five tubular members 102. It will be understood that the acoustic identification tag 10 may instead comprise a different number of tubular members. The tubular members 102 are cylindrical. It will be understood, however, that tubular members 102 may have a different shape. For example, they may be prismatic.

A first end 104 of each of the tubular members 102 is open. A second end 106 of each of the tubular members 102 is closed. The closed end comprises a rigid surface, the plane of the surface being substantially perpendicular to the longitudinal length of the tubular member. The rigid surface that constitutes the closed end may be integral with the tubular member. The surface may instead be a separate entity, for example, in the form of a cap or a plug. The tubular members 102 are comprised of a solid rigid material. For example, the tubular members 102 may be comprised of metal, glass or plastic. It will be understood, however, that other materials may also be suitable.

Inside each of the tubular members, is an internal hollow region 108. The length L of the internal hollow region 108 is the length of the tubular member 102 minus the thickness of the material that comprises the closed end 106. Each of the tubular members 102 is of a different length.

Acoustic resonance is the tendency of an acoustic system to absorb more energy when the frequency of its oscillations matches the system's natural frequency of vibration (the system's resonance frequency) than is absorbed at other frequencies.

Resonant objects usually have more than one resonance frequency, especially at harmonics of the strongest resonance. The strongest resonance occurs at what can be termed the fundamental frequency. In combination, these frequencies may be described as the "set of resonant frequencies" of an object. A resonant object vibrates easily at its resonance frequencies, and vibrates less strongly at other frequencies. When a resonant object is subjected to a complex excitation signal (i.e. an acoustic signal comprising sound waves at a number of different frequencies) that includes its resonance frequency or frequencies, it oscillates strongly at its resonant frequency or frequencies and comparatively weakly at frequencies that are not at its resonant frequency or frequencies.

When an object oscillates, it emits an acoustic signal. Consequently, when an object is subjected to complex excitation, it emits an acoustic signal. It can be said that the object has an acoustic response. The acoustic response comprises all of the frequencies included in the complex excitation. However, the amplitudes of the component or components of the emitted acoustic signal that correspond to the resonant frequency or frequencies are significantly larger than the components that correspond to off-resonance frequencies.

In the field of acoustics, the tubular members 102, described with reference to Figure 1, are known as closed cylinders (because they have one closed end). A tubular member having an open end at both ends is known as an open cylinder.

The acoustic resonant frequenciesf of air in a closed cylinder at standard atmospheric pressure (100 kPa) are defined by Equation 1, below. The acoustic resonant frequenciesf of air in an open cylinder are defined by Equation 2. mv

f = (Equation 1) 4(L+O.4d) fly f = (Equation 2) 2(L+O.8d) Where: m is a positive integer representing the resonance node (or the harmonic). The resonant frequency of air in a closed cylinder has only odd harmonics. Consequently, m is always odd; v is the speed of sound in air, which is approximately 344m/s at sea level; L is the length of the cylinder in metres; d is the tlianieter of the cylinder in metres; and n is a positive integer representing the resonance node (or the harmonic).

As can be seen from Equation 1, the acoustic resonant frequencies of air in the tubular members 102 are dependent on the length L of the internal holiow region 108 of the tubular member 102. The resonant frequencies of air in the tubular members 102 are dependent also on the internal rUstneter dof the internal holiow regions 108. In the embodiment of Figure 1, each of the internal holiow regions has the same internal tlhtneter a'. Each of the tubular members 108 comprises an internal hollow region 108 of a different length. Consequently, air in each of the tubular members 102 of the acoustic tag 10 of Figure 1 has a resonant frequency different from air in the resonant frequencies of the other tubular members 102.

Alternatively it could be said that each of the tubular members 102 of the acoustic tag 10 of Figure 1 has a resonant frequency different from the resonant frequencies of the other tubular members 102.

In other embodiments, one or more of the rUsnieters d of the tubular members may be different and/or one or more the lengths L may be the same.

When the identification tag of Figure 1 is subjected to an appropriate complex excitation signal, the frequency spectrum of the acoustic response of the tag 10 comprises five distinct peaks, each peak corresponding to one of the five different resonant frequencies. By determining the frequencies of the peaks in the emitted acoustic response, it is possible to determine the identity of the acoustic identification tag. In this way, it is possible to distinguish between two or more different acoustic identification tags (i.e. tags having different frequency spectrums).

This is described in more detail below with reference to Figure 6.

Figure 2 shows an alternative embodiment of an acoustic identification tag 20. The acoustic tag 20 is sinlilsrto that of Figure 1 in that the internal hollow regions 208 of each of the tubular members 202 are of a different length 1, and the internal diameters d of each of internal hollow regions are the same. As such, each of the tubular members 202 has a different resonant frequency. However, unlike in the acoustic identification tag 10 of Figure 1, the overall lengths of the tubular members 202 are the same. This is because each tubular member comprises an internal filled region. The internal filled region 210 may comprise the same material as the main body of the tubular member. Alternatively, the material may be different.

The tubular members 202 may manufactured by filling a portion of the internal hollow region of the hollow tubular member with a volume of filling material to create the filled region 210. Alternatively, the tubular members may be manufactured by drilling or boring solid cylinders to create the hollow regions 208.

The embodiments shown in Figures 1 and 2 comprise "closed" tubular members.

As such, the resonant frequencies of the tubular members are defined by Equation I shown above.

Figure 3 depicts an acoustic identification tag 30 comprising open' tubular members 302. The tubular members comprise an "open end" at each longitudinal end 304. The resonant frequencies of air in the tubular members 302 in Figure 3 are defined by Equation 2 above. Each of the tubular members 302 has the same internal diameter d, but has a different length L. Consequently, each tubular member 302 has a different set of resonant frequencies.

Figure 4 depicts an alternative embodiment of an acoustic identification tag 40 comprising "open" tubular members. The acoustic identification tag 40 comprises plural tubular members 402. Each tubular member is of the same length. Each tubular member 402 comprises an open end 404 at each longitudinal end. Each tubular member 402 includes an aperture 406 in the wall of the tubular member 402.

The aperture acts as a further "open end". As such, the resonant frequency of air in the tubular member is dependent on the distance L between the aperture 406 and a one of the open ends.

The apertures 406 are elliptical. It will be appreciated that differently shaped apertures may also be suitable. Bach of the apertures 406 is located at a different point along the length of its respective tubular member 402. Consequently, each of the tubular members 402 has a different set of resonant frequencies. Unless the aperture is equidistant between the two open ends 404, the tubular member 402 has two different sets of resonant frequencies. This is because the tubular members have two open ends 404, each of which is a different distance L from the aperture 406.

In some embodiments, eight (8) tubular members are provided, each having two resonant frequencies. In these embodiments, the tag 20 provides sixteen (16) resonant frequencies. Using a look-up table, the sixteen frequencies can be used to provide a sixteen bit number relating to the tag. Thus, the tag 20 can provide an identifier that can have a value in the range 3.4 lOexp34, 1niilsr to IPv6 addresses.

In the acoustic identification tags of Figures 1 to 4, the tubular members are aligned linearly, with their longitudinal axes being perpendicular the axis of linear alignment. The longitudinal axes of the tubular members are paraliel to one another.

Figure 5 shows another alternative embodiment of an acoustic identification tag 50.

The acoustic identification tag 50 comprises a plurality of tubular members 502 arranged into a plurality of adjacent layers 504. Bath layer 504 comprises five tubular members 502 aligned linearly, with their longitudinal axes paxaliel to the axis of linear alignment. Bath of the layers is the same as the acoustic identification tag of Figure 2. It will be appreciated that the layers 504 alternatively may be the same as the acoustic identification tags described with reference to Figures 1,3 or 4, or any other suitable form of acoustic identification tag.

Bach of the layers 504 is identical to the other layers 504. Bach of the layers 504 has an 90 degrees different to an adjacent layer 504. As such, if we consider the first layer 504* (the layer depicted at the front of the arrangement of FigureS) to be aligned at 0 degrees, the second layer 504b is aligned at 90 degrees, the third layer 504c is aligned At 180-degrees and the fourth layer 504d is aligned at 270-degrees.

The inclusion of four identical, but differently oriented, layers 504 of tubular members 502 may reduce the influence of extraneous error. This is for two reasons.

The first reason is that the acoustic identification tag 30 comprises four tubular members, instead of just one, at each resonant frequency. Consequently, the intensity of the component of the acoustic response corresponding to that resonant frequency may be four times larger. As such, the component may be more easily distinguishable from background noise and other erroneous signals. Secondly, because the layers have different orientations, if the open ends of one layer are obstructed, thereby adversely affecting the acoustic response of that layer, the acoustic response of at least one of the three other layers may be detected.

The tubular members of the acoustic identification tags shown in Figures 1 to 5 may be secured in any suitable manner. For example, they may be fixed to one another or to an external surface or member using an adhesive.

The lengths of the tubular members may be in the range of 1mm to 3cm. The diameter d of the tubular members may be in the range of 0.1mm to 5mm. The overall dimensions of the main surfaces of the acoustic identification tag may be comparable to the si2e of a standard barcode. It will be appreciated, however, that other dimensions may also be suitable.

Figure 6 illustrates a system 60 for determining the identity of an acoustic identification tag. The system 60 comprises a processor 602, a signal generator 604, a transmitter 606, a receiver 608, an analyser 610, and a memory 612.

The transmitter 606 is configured to provide an acoustic signal 614 to a volume of space containing the acoustic identification tag 20. In other words, the transmitter 606 is arranged to ensonify a scene in which the acoustic identification tag 20 is present. The excitation signal 614 is generated by the signal generator 604 under control of the processor 602.

The excitation signal may comprise a wideband ultrasound signal. The transmitter 606 may be an ultrasound transmitter. Alternatively, the excitation signal may comprise a signal that is swept across the frequency range over a period of time.

Alternatively, the excitation signal may comprise multiple discrete signals, each signal at a different frequency and transmitted at a different time. The frequencies of the discrete signals may be regularly spaced over the entire range of frequencies.

Alternatively, they may be irregularly spaced. Alternatively, the excitation signal may comprise a swept signal, i.e. a signal that commences at a single, relatively low frequency and increases to a single, relatively high frequency over a period of time.

The range of the excitation signal may be, for example, 25 kHz to 100 kHz. It will be understood, however, that a different range of frequencies may instead be used.

The receiver 608 may be an ultrasound receiver. Each of the receiver 608 and the transmitter 606 may comprise a respective ultrasound transducer.

The apparatus 60 is configured to determine the acoustic response of the acoustic identification tag 10. The receiver 608 transforms a detected acoustic response signal 616 into an electrical (i.e. non-acoustic) signal and passes it to the analyser 610. The analyser 610 is configured to analyse the electrical signal to determine the frequency spectrum of the acoustic response signal 616. To this end, the analyser 610 is configured to identify the frequencies of the peaks in the frequency spectrum.

These frequencies constitute at least part of a frequency response of the acoustic identification tag. The frequencies imifring up the frequency response wili be hereafter calied a unique identifying frequency pattern. In order to determine if a frequency peak is present at a particular frequency, the analyser 610 may divide the intensity of the signal at that frequency by the average intensity over the whole signal. If the result surpasses a threshold, the analyser 610 may determine that a peak is present. Any other suitable scheme may instead be used for determining the presence of a peak.

In some embodiments, the tag may comprise more than one tubular member having the same resonant frequency. For example, an acoustic identification tag may -10-comprise two tubular members have a first resonant frequency, and three other tubular members having second, third, and fourth resonant frequencies respectively.

In order to detect the presence of two tubular membets having the first resonant frequency, having identified the frequency peaks the analyser 610 may compare the amplitude of the signal at each of the peak frequencies with the intensity of the signal at the others of the peak frequencies. From this comparison, the analyser 610 may also be able to assign a weighting to each of the frequency peaks. For example the amplitude of the peak corresponding to the first resonant frequency may have approrhmately twice as large an amplitude as that of the other peaks.

Consequently, the frequency corresponding to the first resonant frequency may be assigned a weighting of two and the frequencies corresponding to the second to fourth frequencies may be assigned a weighting of one. In this example, the unique identifying frequency pattern may comprise both the frequencies of each of the peaks, and also their associated weightings.

The analyser 610 is configured to compensate for the atmospheric pressure being significantly different from a pressure at which the tag is normally used. In this way, use of the apparatus 60 at altitude and/or in unusual pressure conditions does not impact the ability of the apparatus correctly to identify a tag with which it is used.

Foliowing its determination, the unique identifying frequency pattern is passed from the analyser 610 to the processor 602. The processor 602 is configured to compare the unique identifying frequency pattern with a database of unique identifying frequency patterns stored in the memory 612. Each unique identifying frequency pattern stored in the database is associated with an identity of an acoustic identification tag. When the processor 602 finds a unique identifying frequency pattern that matches the one received from the analyser 610, the processor 602 retrieves the identity of the acoustic tag from the database. The identity may then be output for use by an operator of the system or for sending over a network etc. The transmitter 606 may include plural acoustic signal generators (not shown). In this case, each generator is configured to ensonify a scene in which the acoustic -11 -identification tag 20 is present. The generators may be at different locations, so as to ensonify the scene from different directions. This reduces the possibility that a tag present in the scene will be prevented from being ensonified by, for example, an object between the tag and an acoustic signal generator. The excitation signal 614 generated by the signal generator 604 under control of the processor 602 may be the same for each of the plural acoustic signal generators. The plural acoustic signal generators may be excited simultaneously, or they may be excited in turn.

The receiver 608 may comprises plural acoustic receiver transducers (not shown).

The acoustic receiver transducers may be at different locations, so as to view the scene from different directions. This reduces the possibility that a tag present in the scene will be prevented from being viewed by, for example, an object between the tag and an acoustic receiver transducer.

Each acoustic receiver transducer transforms a detected acoustic response signal 616 into an electrical (i.e. non-acoustic) signal and passes it to the analyser 610. The analyser 610 is configured to analyse the electrical signals from each of the acoustic receiver transducers in order to determine the frequency spectrum of the acoustic response signal 616.

In other embodiments, plural receivers 608 are spaced apart from one another. In these embodiments, processing of the signals allows determination of the location of the tag 20, in terms of its distance from the transmitter 606 and the direction from the transmitter 606 in which the tag 20 is located.

In one such embodiment, described with reference to Figures 6 and 7, three transceivers 701, 702, 703 are located in a triangular arrangement in a common plane. Each of the transceivers 701-703 is a transmitter 606 and a receiver 608. A timing mechanism (not shown) is operable to measure the difference in time between transmission of a signal (or a part of a signal) and reception of the signal (or the same part of the signal) after it has interacted with the tag 20.

-12 -The first transceiver 701 is place at the centre point of the detector (0, 0 of the x-y axis). The second transceiver 702 is located a distance d along the x axis and the third transceiver 703 is located the same distance d along the y axis.

In operation, the transceivers 701-703 in turn each transmit a short pulse having content at the tag's frequencies, and the timing mechanism determines the transit times of the signals from each transceiver to the tag 20 and back to the originating transceiver. The transit times of signals from the first transceiver 701 are t1, The transit times of signals from the second transceiver 702 are t2, and the transit times of signals from the third transceiver 703 are t3 By using the following equations, the distance from the tag to that transmitter is calculated by the processor 602..

D v*(time/2) where v is the speed of sound Therefore, D2 v*(T1/2), D3 v*(T2/2) and D4 v*(T3/2) Using trilateration equations the processor 602 calculates the relative location of the tag 20: _-n2 2 i2 x1 --_1J3+cl 2d Assuming d-D2<D3<d+D2 -n 2 2 i2

--so 2d

-I 2 2 2 21-� v(D2 -x1 -y1) -13 -In other embodiments, more of fewer transmitters are utilised. In some embodiments one transceiver is provided along with two receivers. In this embodiment, the calculations need to take account of the fact that the signal propagation is from the transceiver via the tag 20 to the receivers (including the receiver of the transceiver).

An exemplary application of the previously described acoustic identification tags and the system 60 for determining their identity will now be described.

An acoustic identification tag according to any of the embodiments described in this specification is incorporated into the packaging of a product offered for sale in a shop. The acoustic identification tag may be used to convey a number of different kinds of information. For example, the tag may be used in the same way as a barcode to allow a vendor's computer system to easily and quickly identify the product. Alternatively or additionally, the acoustic identification tag may convey information identifying the constituent material of the packaging. Different types of information may be included in different resonant frequency ranges. For example, the tubular members of the acoustic identification tag that relate to the identity of the consumable product may have different resonant frequencies in the range of 25 kH2 to 35 kH2, and the tubular members that relate to the constituent material of the packaging may have different resonant frequencies in the range of 40 kH2 to 50 kH2.

When the user purchases the product, the vendor can place the product in a scene that is ensonified with an excitation signal having a range of frequencies of 25 kH2 to 35 kH2. From analysis of the acoustic response emitted from the tag, the vendor's computer system identifies the product by comparison of the unique identifying frequency pattern of the tag with a list of unique identifying frequency patterns relating to each of the consumer products in a vendor's inventory.

The acoustic identification tag is advantageous over the barcode, because the acoustic identification tag is not required to be in the line of sight of the detector.

Consequently, the acoustic identification tag need not be on the exterior of the -14-packaging. This may also save time at the point of sale because no time is required to align a barcode with the detector. Instead, the acoustic identification tag may be detected as it is simply passed through the ensonified scene.

When the user wishes to recycle the packaging of the consumer product, they can place the packaging at a recycling depository along with a number of other items for disposal. The other items may or may not have an acoustic identification tag, and may or may not be made of the same material as the packaging. Prior to recycling, items must be separated into groups, dependent on their constituent material.

Generally, the separation is performed manually, either by the consumer or by staff at the recycling centre. However, when a product includes an acoustic identification tag that identifies its constituent material, the process of separation may be at least partly automated.

Each item is passed sequentially through an ensonified scene, for example on a conveyor belt. The excitation signal may have a of frequency range of 40 kH2 -50 kH2. Consequently, the received acoustic response only includes information relating to constituent material and not information relating to product identity.

Following identification of the constituent material, the item may be automatically passed to a specific location corresponding to its constituent material. When an item does not comprise an acoustic identification tag, the item may be passed to a separate location for manual sorting. It will be understood that when an acoustic identification tag conveys information relating to the constituent material of an item it may be advantageous for the acoustic identification tag to comprise the same material as the item.

It should be realised that the foregoing embodiments are not limiting. Other variations and modifications will be apparent to persons skilled in the art upon reading the present application. Moreover, the disclosure of the present application should be understood to include any novel features or any novel combination of features either explicitly or implicitly disclosed herein or any generalisation thereof and during the prosecution of the present application or of any application derived therefrom, new rlsinis may be formulated to cover any such features and/or combination of such features. -16-

Claims

Claims I. An apparatus comprising: an ensonifier configured to ensonify a scene with broadband acoustic signals; plural transducers configured to convert acoustic signals received from the scene into non-acoustic signals; one or more timers configured to measure transit times of acoustic signals received from the tag at each of the plural transducers; and a processor configured to process the non-acoustic signals from each of the plural transducers to determine an approrhmation of a frequency response of the scene, to use the approrbmation of the frequency response of the scene to identify a tag present in the scene, and to calculate a location of the tag in the scene on the basis of the transit times.
2. An apparatus as rkinied in thin' I, wherein the ensonifier is configured to ensonify the scene with acoustic signals comprising multiple frequencies simultaneously.
3. An apparatus as claimed in r]sin' I, wherein the ensonifier is configured to ensonify the scene with a signal having a frequency that is swept across a bandwidth over a period of time.
4. An apparatus as claimed in r]sini I, wherein the ensonifier is configured to ensonify the scene with a signal comprising a plurality of discrete frequencies at sequential times.
5. An apparatus as rlsinied in any of rlsinis I to 4, wherein the ensonifier comprises plural sources of acoustic signals arranged at different locations.
6. An apparatus as rlsinied in any preceding rlsini, wherein the plural transducers are at different locations, so as to view the scene from different directions.

-17 -
7. An apparatus comprising: plural transducers configured to convert acoustic signals received from a scene into non-acoustic signals; one or more timers configured to measure transit times of acoustic signals received from the tag at each of the plural transducers; and a processor configured to process the non-acoustic signals from each of the plural transducers to determine an approximation of a frequency response of the scene, to use the approximation of the frequency response of the scene to identify a tag present in the scene, and to calculate a location of the tag in the scene on the basis of the transit times.
8. A method comprising: ensonifying a scene with broadband acoustic signals; plural transducers converting acoustic signals received from the scene into non-acoustic signals; measuring transit times of acoustic signals received from the tag at each of the plural transducers; processing the non-acoustic signals from each of the plural transducers to determine an approximation of a frequency response of the scene; using the approximation of the frequency response of the scene to identify a tag present in the scene; and calculating a location of the tag in the scene on the basis of the transit times.
9. A method comprising: receiving signals representative of acoustic signals received from a scene at plural transducers; receiving signals indicative of transit times of the acoustic signals; processing the signals representative of acoustic signals to determine an approximation of a frequency response of the scene; Jo processing the approximation of the frequency response in order to identify a tag present in the scene; and calculating a location of the tag in the scene on the basis of the signals indicative of transit times.