EP0855064A4

EP0855064A4 - Remotely powered electronic tag and associated exciter/reader and related method

Info

Publication number: EP0855064A4
Application number: EP96931470A
Authority: EP
Inventors: Ted Geiszler; Larry Fort; George Lauro; Russ Walker; Noel Eberhardt; John Howard Rolin; Sebastian Thomas Kakkanad
Original assignee: Motorola Inc
Current assignee: Motorola Solutions Inc
Priority date: 1995-10-11
Filing date: 1996-09-04
Publication date: 2001-07-18
Also published as: EP1329837A2; CA2234686C; CA2234686A1; CN1101037C; CN1199482A; JPH11513518A; BR9610948A; AU7014496A; JP3909607B2; WO1997014112A1; KR19990064161A; NZ318619A; KR100313691B1; AU700340B2; EP1329837A3; EP0855064A1

Abstract

A portable communication device comprising a first electrostatic antenna element (T1) and a second electrostatic antenna element (T2) and circuitry (43-51) which is coupled to the first antenna element and to the second antenna element and which derives operating power from an electrostatic field in the vicinity of the first and second antenna elements.

Description

REMOTELY POWERED ELECTRONIC TAG AND ASSOCIATED EXCITER/READER AND RELATED METHOD

BACKGRQTΓNP OF THE INVENTION

1. Field of the Invention

The invention relates generally to portable remotely powered communication devices and to systems for powering up and receiving infoπnation from such devices, and more particularly, to such devices and systems that employ electrostatic coupling.

2. Description of the Related Art

Remotely powered electronic devices and related systems for powering up and receiving stored information from such devices are well known. For example, U.S. Patent No. 4,818,855, issued to Mongeon et al., entitled,

Identification System, discloses a remotely powered identification device which derives power from a remote source via one of an electric field or a magnetic field and which transmits stored information back to the source via the other of the electric field or magnetic field. Similarly, U.S. Patent No. 5,009,227, issued to Geiszler et al., entitled, Proximity Detecting Apparatus, discloses a remotely powered device which uses electromagnetic coupling to derive power from a remote source and which uses both electromagnetic and electrostatic coupling to transmit stored data back to the source.

In the earlier systems described above, an electromagnetic mechanism is used to remotely couple the remote device with either one or both of an exciter system and a receiver system. The exciter generates an excitation signal used to power up the device. The receiver receives the signal produced by the remote device. One reason for the use of electromagnetic coupling in prior devices is that it was believed to be more efficient to remotely couple power from an exciter to a device via an electromagnetic field rather than via an electrostatic field. Moreover, it was believed that in order to employ an electrostatic mechanism to couple energy from an exciter to a remote device using a single-plate antenna, relatively high voltage signals were required. However, the ability to emit higher voltage signals for power up often is limited by FCC regulations.

Earlier electromagnetic coupling mechanisms included an oscillator as part ofthe exciter circuitry and coil antennas mounted on both the exciter circuitry and a tag or other article that embodied the device and contained its electronic circuit. For example, in one earlier system, excitation circuitry is connected to a coil antenna which radiates excitation signals that are picked up by a coil antenna mounted on a tag that contains the electronic circuit. The excitation signals energize the electronic circuit which automatically produces an information carrying signal that is transmitted to the receiver using electromagnetic or electrostatic coupling.

An ongoing objective in the development of remote communication devices and associated exciters receivers ofthe general type described above has been to minimize cost and size and to improve efficiency of operation. A problem with the use of electromagnetic coupling between a remote device and either an exciter or a reader has been the additional complexity involved in the manufacture of remote devices that employ a coil antenna. For example, the spiral layout of a typical coil antenna can be more difficult to produce than the simpler layout of an electrostatic antenna which often can be in the form of a straight wire or planar and plate-like. Another problem, explained above, has been the inability to efficiently couple power electrostatically using acceptable voltage levels. As a consequence, electromagnetic coupling generally has been favored over electrostatic coupling.

Thus, there has been a need for a low cost remotely powered communication device that employs electrostatic coupling both for remote power up and for the transmission of information carrying signals. There also has been a need for an improved method and apparatus for coupling electrostatic power up signals to such a device. The present invention meets these needs.

SUMMARY OF THE INVENTION The present invention provides an improved electrostatically coupled communication device and associated methods of operation, methods of manufacture and related exciter/reader systems. In one aspect, the invention provides an electronic communication device which is powered-up by electrostatic signals. The novel device can be relatively inexpensively produced since it employs electrostatic (capacitive) plates for both data transmission and for power-up, and therefore, does not require a magnetic coil.

These and other features and advantages ofthe invention will become more apparent from the following detailed description of presently preferred embodiments in conjunction with the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a block diagram of an exciter/reader and a remotely powered communication device in accordance with a presently preferred embodiment ofthe invention;

Figure 2 is a block diagram of an alternative embodiment of an exciter/reader and a remotely powered communication device in which the device has a dedicated data transmission antenna element;

Figures 3 A-3B illustrate a test set up used to perform voltage measurements (V), across Tl and T2, in which a Tl terminal was connected to ground potential and load resistance values (K_) represented different possible loads attributable to a different possible integrated circuits connected between the Tl and T2 terminals;

Figure 4 A provides a curve which plots voltage across Tl and T2 versus distance away from El and E2 over one inch intervals from 1 inch to 8 inches, where Tl and T2 each is rectangular and measures 4 inches by 5 inches;

Figure 4B provides the actual voltage measurements plotted in Figure 4A;

Figure 5 A provides a curve which plots voltage across Tl and T2 versus distance away from El and E2 over one inch intervals from 1 inch to 8 inches, where Tl and T2 each is rectangular and measures 3 inches by 4 inches;

Figure 5B provides the actual voltage measurements plotted in Figure 5A;

Figure 6 A provides a curve which plots voltage across Tl and T2 versus distance away from El and E2 over one inch intervals from 1 inch to 8 inches, where Tl and T2 each is rectangular and measures 2 inches by 3 inches;

Figure 6B provides the actual voltage measurements plotted in Figure

6A;

Figure 7 A provides a curve which plots voltage across Tl and T2 versus distance away from El and E2 over one inch intervals from 1 inch to 8 inches, where Tl and T2 each is rectangular and measures 0.5 inches by 5 inches; Figure 7B provides the actual voltage measurements plotted in Figure

7A;

Figure 8 A is a top elevation view showing the layout of a presently preferred embodiment ofthe remotely powered communication device of

Figure 1;

Figure 8B is a top elevation view showing the layout of an alternative embodiment ofthe remotely powered communication device of Figure 1;

Figure 8C is a top elevation view showing the layout of a presently preferred embodiment ofthe remotely powered communication device of Figure 2;

Figure 8D is a top elevation view showing the layout of an alternative embodiment ofthe remotely powered communication device of Figure 1 in which no substrate is employed;

Figure 8E is a top elevation view showing the layout of an alternative embodiment ofthe remotely powered communication device of Figure 2 in which no substrate is employed;

Figure 9A-9C are side cross-sectional views ofthe three different constructions ofthe devices of Figures 8 A-C; Figure 10 is a top elevation view of an alternative embodiment of a remotely powered communication device in accordance with the invention which includes two pairs of antenna elements;

Figure 11 is a top elevation view of an alternative embodiment of a remotely powered communication device in accordance with the invention which includes four pairs of antenna elements;

Figures 12A-12B show the device of Figure 8 A in two different orientations relative to a portion of an array of exciter elements;

Figure 13 is a simplified top elevation view of a portion of an array of fixed exciter elements which includes elongated horizontal exciter elements and elongated vertical elements;

Figure 14A-14C are simplified top elevation views of three more alternative configurations of a portion of an array of commutated exciter elements; Figure 14A shows a horizontal configuration; Figure 14B shows a diagonal configuration; and Figure 14C shows a vertical configuration;

Figure 15 is a simplified top elevation view of yet another alternative commutated exciter array configuration in which two parallel stripes of exciter elements are dynamically swept in a circular pattern; and

Figure 16 is a top elevation view of still another alternative commutated exciter array configuration in which the array is bounded by sensors which detect the motion of a communication device across the array. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention comprises a novel remotely powered communication device, an associated exciter/reader system and related methods. The following description is presented to enable any person skilled in the art to make and use the invention. Descriptions of specific applications are provided only as examples. Various modifications to the preferred embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein.

Referring to the illustrative drawings of Figure 1, there is shown a block diagram of an exciter/reader apparatus 30 and a remotely powered communication device 32 in accordance with a presently preferred embodiment ofthe invention. The exciter portion ofthe apparatus 30 produces eleαrostatic signals that are used to power up the device 32. The reader portion ofthe apparatus 30 receives electrostatic communication signals produced by the device 32 once it has been powered up. The device, for example, can serve as an electronic identification card. In one application, for example, when the device 32 is placed in close proximity to the exciter/reader apparatus 30, the exciter sends electrostatic signals that power up the device 32. The device then automatically transmits an electrostatic signal that carries identifying information The reader portion ofthe apparatus 30 receives the identifying signals and determines whether to trigger some aαion such as the opening of a locked door.

The exciter portion ofthe apparatus 30 includes an oscillator 34, which generates a signal at frequency F₀. The oscillator is conneαed to a power amplifier 35 which, in turn, is conneαed to the primary coil 36 of an impedance transformer 37. A secondary coil 38 of the impedance transformer 37 is conneαed in parallel with a capacitor 39. A top terminal ofthe secondary coil 38 is conneαed to a first electrostatic exciter antenna plate El, and a bottom terminal ofthe secondary coil 38 is conneαed to a second electrostatic exciter antenna plate E2. In a present embodiment, the exciter includes a pair of antenna plates that operate as a balanced out of phase pair. In another embodiment described below, the exciter includes an array of balanced out of phase antenna plates. For the sake of simplicity, however, the following description of Figures 1 discusses only two exemplary exciter plates, El and

E2. Alternatively, for example, wire antenna exciter elements or a comb-like structure may be employed instead of antenna plates, for example.

The reader portion ofthe apparatus 30 includes a single-plate electrostatic reader antenna plate Rl conneαed to a receiver 40 which provides input signals to a deteαor 41. An I O processor 42 receives signals from the deteαor 41.

A current embodiment ofthe remotely powered communication device 32 includes first and second electrostatic device antenna plates Tl and T2 which are connected as shown to provide clock A and clock B inputs to a full wave bridge reαifier 43. Note that Tl and T2 are electrically isolated from each other. Alternatively, for example, wire antenna elements can be used instead of plates. A capacitor 44 is conneαed across the V+ and "common" terminals ofthe rectifier 43. The clock B input is also provided to a frequency dividing counter circuit 45. The counter 45 is conneαed to provide address signals to a digital storage device, a read only memory (ROM) 46 in a current embodiment. A modulator circuit, in the illustrative embodiment a biphase modulator implemented as an exclusive-or gate 47, receives clock signals, at frequency F^n, from the counter 45 and data output from the ROM 46. The output of modulator circuit (the exclusive-or gate 47) is provided via diode 48 and resistor 49 to the clock B line.

While the device 32 of the presently preferred embodiment employs biphase modulation, virtually any modulation technique can be used consistent with the invention. For example, PSK, FSK, AM or other modulation schemes can be used as alternatives. Moreover, in the current embodiment, the modulated signal is returned to the clock B input for transmission to the reader via antenna plate T2. However, as an alternative for example, the modulated signal could be provided to a separate antenna element (not shown) for transmission to the reader. An alternate embodiment which includes such a separate data transmission antenna element is discussed below with reference to Figure 2.

In operation, the oscillator 34 of a presently preferred embodiment generates a 4 Megahertz signal which is approximately 2-5 volts peak to peak. The signal is boosted to approximately 20-30 volts peak to peak by the amplifier 35. The impedance transformer 37 further boosts the voltage to approximately 300-400 volts peak to peak. The parallel connected capacitor 39 tunes the transformer circuitry to make it resonant at the oscillator frequency. The signal provided to exciter plate El via the top terminal ofthe secondary coil 38 is balanced and 180° out of phase with the signal provided via the bottom terminal ofthe secondary coil 38 to exciter plate E2. The exciter plates El and E2 produce electrostatic energy, indicated by the arrows, which is used to power-up the communication device 32. It will be appreciated that the desired voltage levels ofthe electric field may depend upon faαors such as the distance over which the exciter is to power-up the device 32. Additionally, the desired voltage levels may, for example, depend upon frequency emission requirements ofthe country in which the exciter will operate. Moreover, certain operations such as writing data into device memory may require more power than other operations such as reading information from device memory.

The eleαrostatic field produced by the exciter elements El and E2 excites voltages on antenna elements Tl and T2. The Tl element is conneαed to provide the clock A input to the full wave bridge rectifier 43, and the T2 element is conneαed to provide the clock B input to the rectifier 43. Tl and T2 are not conneαed directly to each other. The capacitor 44 filters out exciter pulses from the received power up signals to ensure a pure DC output ofthe reαifier. The reαifier provides a V+ DC voltage signal relative to a "common" terminal ofthe rectifier 43. It will be appreciated that a pure D.C. signal is not required. Some ripple in the V+ voltage signal may be acceptable depending upon the implementation ofthe device circuitry. The counter 45 receives the 4 Megahertz clock B signal and provides a set of address signals on lines 50 which are used to address and to set the data rate for the output of data from the ROM 46. The different signals on the different lines 50 are produced by dividing the 4 Megahertz by different values in a manner well known by those skilled in the art. The data rate out ofthe ROM is significandy

It will be understood that although the preferred embodiment uses a 4

Megahertz signal, signals of a different frequency could be used. For example, a 13.56 Megahertz signal or a 37.5 Megahertz signal could be employed.

The counter also provides on line 51 a 2 Megahertz carrier signal which serves as the clock input (or carrier signal input) to the exclusive-or gate 47.

The data output ofthe ROM 46 serves as a data input (or modulation signal input) to the exclusive-or gate 47. The counter, therefore, divides the input frequency by two to provide a carrier signal and sets the data rate of data signals output by the ROM 46 that modulate the carrier. The exclusive-or gate 47 serves as a biphase modulation circuit, and its output is a biphase modulated signal which is provided via diode 48 and resistor 49 to clock B signal line. The biphase signal is injeαed back onto the T2 device element and is eleαrostatically transmitted to the receiver portion ofthe exciter/receiver 30. The role ofthe diode 48 and the resistor 49 is to couple modulated signals back to the clock B input. As explained above, there are numerous other modulation schemes that use different modulation circuits consistent with the invention. Moreover, as explained below with reference to Figure 2 it can be advantageous to employ a third antenna element dedicated to data transmission on a communication device in accordance with the invention

The electrostatic receiver antenna Rl receives the eleαrostatically transmitted signals emitted by device antenna element T2, and provides those received signals to the receiver 40 which amplifies the signals and may convert their frequency to an intermediate frequency for further amplification and bandpass filtering ofthe signals before providing them to the deteαor circuit 41 which deteαs data carried by the received signals. The receiver 40 and the deteαor 41 are well known circuits which need not be described in detail herein. The deteαor 41 provides the data signals to the I O processor 42 which produces an output in a format usable by a host computer (not shown), for example.

The transmission of balanced out of phase electrostatic signals via exciter elements El and E2 couples energy to the device 32 via the device electrostatic antenna elements Tl and T2. When the voltage on exciter element El is at a positive level, for example, the voltage on element E2 is at a negative level. Conversely, when the voltage on exciter element El is at a negative level, the voltage on exciter element E2 is at a positive level. The objeαive is to have the balanced out of phase voltages on El and E2 cause the voltages of device antenna elements Tl and T2 to produce a balanced out of phase relation to each other. The desired result is to always have a voltage potential difference between the device elements, Tl and T2, such that a V+ DC supply voltage source can be produced relative to a "common" potential. In essence, the exciter elements, El and E2, are capacitively coupled to the device elements, Tl and T2. This approach permits power to be more efficiently coupled using eleαrostatic energy.

Moreover, because the exciter antenna elements El and E2 produce eleαrostatic fields that are balanced and out of phase, these fields often tend to cancel each other at farther distances, reducing the risk of exceeding FCC or other regulatory agency emissions limits, for example. As a consequence, the exciter signals often can use higher power up voltage levels.

Instead of using balanced out of phase excitation signals, unbalanced excitation signals can be used as an alternative in accordance with the invention. In particular, for example, a single excitation antenna element could be employed to produce a periodic electrostatic excitation signal. A remotely powered communication device, for example, that was powered up by such an unbalanced signal would include a single antenna element with one terminal conneαed to a clock A input. It is important, however, that such alternative remotely powered communication device be coupled to an external ground potential. Note that for balanced signals there is no need for an external ground connection since a "common" ground is produced using a clock B input and balanced out of phase signals. In such an alternative embodiment, the single power-up element also could be used to transmit and receive data signals as well.

It is desirable for the device 32 to consume relatively little power. Hence, the information carrying signals transmitted by antenna element T2 are relatively low power. The receiver 40 is highly sensitive and capable of extraαing data from the relatively (low power) weak signals transmitted by the device 32.

Note that Tl and T2 are not required to have half wavelength dimensions of a typical eleαromagnetically excited two element antenna. The elements are electrostatically excited, through capacitive coupling, and need not be resonant as required for electromagnetic coupling. The elements can, therefore, be of an arbitrary size sufficient for capacitive (eleαrostatic) coupling. In general, capacitive coupling inαeases with increased antenna area and increased signal frequency. In addition, the device antenna elements need not have a charaαeristic impedance as do resonant antenna elements. The spacing apart ofthe exciter antenna elements El and E2, however, should be well matched to the spacing ofthe device antenna elements Tl and T2 in order to efficiently couple energy from the exciter to the device.

Referring to the illustrative drawing of Figure 2, there is shown a simplified block diagram of an alternative embodiment of a communication device 32" and exciter/reader 30" in accordance with the invention. In virtually all respeαs the alternative device 32" of Figure 2 is identical to the device 32 of Figure 1 except for the addition of a third antenna element (T3) which is used solely for data transmission. Referring to both Figures 1 and 2, the internal circuit conneαions are identical for device 32 and device 32" except that in device 32", neither Tl" nor T2" is conneαed to receive the output ofthe data transmission circuitry. Instead, Tl" and T2" are dedicated to receipt ofthe electrostatic power-up field that emanates from the exciter elements El" and E2". In a current embodiment, Tl" and T2" are conneαed to a bridge circuit 43" and to a counter 45", but there is no connection between the clock A" node or the clock B" node and the output ofthe data modulation circuitry 47".

The data terminal T3 is disposed in a null region between the power-up terminals Tl" and T2". The null position is the place on the device 32" where the power-up fields produced by the exciter elements El" and E2" substantially cancel each other out, and therefore, produce the minimum amount of interference with data signals transmitted by the device 32". When the device 32" is aligned with Tl" and T2" aligned for maximum energy pick-up from exciter elements El" and E2", the data transmission element T3 will experience minimal interference with transmissions to the reader element Rl".

It should be understood that the word "remote" is intended to be a relative term. Depending upon the circumstances, the term, remote, may apply to distances from millimeters to larger ranges. Depending upon faαors such as the voltage level ofthe electrostatic signals radiated by the exciter, the exciter and the device may have to be positioned very close to one another in order to power up the device; or it may be that they can be spaced farther apart and still achieve coupling. The term remote just means that power is coupled over the air from the exciter to the device. It is believed that, in general, increased signal frequency and increased antenna plate area tend to increase the distance over which electrostatic signals can power-up a tag device.

The power-up ofthe integrated circuit device 32 using eleαrostatic fields applied over distances such as those achieved in the experiments described with reference to the tables below, is a suφrising result. In the past, eleαrostatic signals had been used to transmit data from a tag device to a reader device. In prior eleαrostatic data transfers, the data transfer signal often operated at approximately 80% ofthe power level ofthe power-up signal used to power-up the earlier tag device. A typical earlier reader had to be highly sensitive, achieving approximately 80-1 lOdB gain, in order to extract data from a carrier signal. In view ofthe relatively weak eleαrostatic coupling of data signals in earlier tag devices, it is surprising that electrostatic power-up is achieved, in accordance with the present invention, over the distances tested during the experiments. Furthermore, there is no apparent electrical current path between antenna elements Tl and T2. Thus, Tl and T2 would appear to constitute opposite sides of an open circuit. Opposite terminals ofthe bridge circuit 43, therefore, appear to be conneαed to an open circuit. Thus, it is surprising that power-up is achieved in accordance with the present invention since there appears to be an open circuit applied to the bridge circuit.

More specifically, Tl and T2 are conneαed to opposed nodes ofthe bridge circuit 43. Each feeds the same plate of the capacitor 44. Thus, the capacitor plate is a node within the device 32 that is coupled to both Tl and

T2. There is no apparent closed circuit, which includes both Tl and T2, and in which current can flow to cause the voltage across capacitor 44. Nevertheless, a sufficient charge build-up aαoss capacitor 44 results from the application of the electrostatic fields by El and E2 to produce supply voltage V+ relative to common substrate ground.

The exemplary test results illustrated in Figures 3-7 demonstrate that electrostatic coupling, in accordance with the invention, can generate sufficient energy to power-up an integrated circuit device. It will be appreciated that power is proportional to V² R_L Figures 3 A-3B show the test set up used to perform voltage measurements (V) across Tl and T2. The tests were performed on a tag device in which the Tl terminal was conneαed to ground potential. The load resistance values (R_) represent different possible loads attributable to a different possible integrated circuits conneαed between the Tl and T2 terminals. Figure 4A provides a curve which plots voltage across Tl and T2 versus distance away from El and E2 over one inch intervals from 1 inch to 8 inches, where Tl and T2 each is reαangular and measures 4 inches by 5 inches. The table in Figure 4B provides the actual voltage measurements plotted in Figure 4A. The curves and tables in Figures 5A-5B, 6A-6B and 7A- 7B provide similar measurements for Tls and T2s that measure 3" x 4", 2" x 3" and 0.5" x 5", respeαively.

It is believed that the actual power that can be electrostatically coupled in accordance with the invention depends upon distance between the tag device and the exciter, tag device antenna area and signal frequency. An analytical approximation of device behavior has been derived from the empirical results set forth in Figures 3-7 and the supporting specification. The data in Figures 4-

7 were imported into a commercially available computer program known as "Mathematica." Two-dimensional curve fitting was performed in order to find a least squares fit starting with a curve that is similar to the expression for a parallel plate capacitance (C = eA/d). The seleαed starting curve was (V/V J = k * (A, * AJ' /D^d _a D^d _a; where "k" is a constant; "a" is an area exponent; and "d" is a distance exponent.

A derived equation for voltage coupling between from the exciter to the communication device is: Vt/Vx = 0.132586((A_x*A_l)⁰ "/D,,, where

A, = exciter antenna element area

^ = communication device antenna element area

V_d = device voltage

V_x = exciter voltage D_β = distance between device and exciter The use of eleαrostatic coupling both for device power up and for device transmission permits the production of simple and relatively inexpensive remotely powered communication devices. Referring to the illustrative drawing of Figure 8 A, there is shown a top elevation view of a presently preferred embodiment of a remote communication device 32 in accordance with the invention. The device 32 includes a substrate 58, a two element antenna 60, which includes a first element 62 (Tl) and a second element 64 (T2), and an integrated circuit (IC) transponder 66. The antenna element 60 and the IC 66 are mounted on the substrate 58. The entire device 32 can be encapsulated in a protective structure (not shown) such as plastic or other material. The IC contains the device electronics described above. The first and second elements 62 (Tl) and 64 (T2) comprise a conductive patte formed on the substrate. In a current embodiment, the elements 62 and 64 can be electrically conneαed to high impedance terminations to pads on the bottom of the IC 66. Since the device 32 operates as a low current device, high impedance terminations can be employed. The two element antenna 60 and the IC 66 can be electrically conneαed by any of a number of different mechanisms. For example, portions ofthe plates may be soldered to IC pads; or they may be secured to the pads with a conduαive adhesive or by wire conneαions

Referring to the illustrative drawings of Figure 8B, there is shown an alternative embodiment of a remote device 32' with an alternate antenna configuration. The antenna elements 62' and 64' are conneαed to an integrated circuit 66'. The antenna plates and the IC all are disposed on a substrate 58'.

The altemative device 32' operates as described with reference to Figure 1. The antenna elements 62' and 64', however, are disposed such that they are maximally spaced apart. That is, their elongated dimensions are substantially parallel to each other and peφendicular to an axis that extends between them and interseαs the IC. An advantage of this increased spacing ofthe device antenna plates is a reduction ofthe risk of destructive interference between signals emanating from balanced out of phase exciter plates.

As explained in the following paragraphs, the device 32 (32' or 32") can be produced relatively inexpensively because ofthe simple layout and construction ofthe antenna elements 62 and 64. Figures 9A-9C are side cross- seαional drawings of three different constructions ofthe device of Figure 8A (8B or 8C). Referring to all three Figures 9A-9C, the substrate member 58 can be formed from any suitable material having desired charaαeristics such as, strength or flexibility, including paper, electrically insulating tape, polyester, polyethylene, polycarbonate, polypropylene, polypropylene with calcium carbonate (CACO₃) filler, plastic, or acαate for example. The antenna elements 62 and 64 are seieαed from any suitable conduαive material such as copper, aluminum, silver or conduαive ink contaimng copper, aluminum, silver, graphite or other conductive fillers for example. The antenna material can be seieαed based upon faαors such as cost and ease of assembly or construction as well as intended usage. The elements can be produced on the substrate by any suitable process such as deposition, printing or etching. For deposition, any process, such as offset printing or roll printing, whereby a layer of (quasi) conduαive material is deposited on the substrate can be used. For example, photocopying antenna plate pattems on paper or acetate using carbon loaded ink is possible. Also, vapor deposition of antenna pattems on a substrate is possible. Additionally, for instance, copper antenna elements can be produced using printed circuit board (PCB) manufaαuring techniques. There are numerous etching processes such as etched copper, for instance, that can be used to produce antenna pattems on substrates. Furthermore, for example, antenna patterns may be cut from larger sheets of conducting material or hot stamped and adhered to the substrates. The production method can be seieαed based on faαors such as cost, durability and performance ofthe remote device.

As another alternative, for example, a communication device in accordance with the invention may comprise an integrated circuit plus electrostatic antenna elements which are not disposed on a substrate. Referring to the illustrative drawing of Figures 8D and 8E, there are shown communication devices in accordance with the invention, each of which includes an integrated circuit and electrostatic antenna elements. Neither the device of Figure 8D nor the device of Figure 8E, however, is mounted on a substrate. The integrated circuit of Figure 8D is the general type described above in conneαion with Figure 1 and is coupled to two eleαrostatic antenna elements. The integrated circuit of Figure 8E is the general type described above in connection with Figure 2 and is coupled to three eleαrostatic antenna elements. It will be appreciated that a device, like that in Figures 8D or 8E, in which the IC and antenna elements are not disposed on a substrate at the time of manufacture may, nevertheless, be bonded subsequently to a substrate such as paper or plastic in order to ensure mechanical stability.

A feature of electrostatic coupling is the use of relatively low currents and relatively high voltages when compared with eleαromagnαic couphng. An advantage of lower currents is that lower conductivity materials can be used for the device antenna plates. This means that materials that are less costly and/or easier to fabricate into antenna plates often can be employed. This can reduce the cost of remotely powered communication devices produced in accordance with the invention.

The IC 66 may have multiple high impedance terminals or pads 68 that are eleαrically conneαed to the antenna 60. Each ofthe antenna elements 62 and 64 of the antenna eleαrically contaαs a different pad. The two plates are kept electrically isolated from each other. In Figure 9 A, an anisotropic conduαive adhesive 70 such as approximately 40% conduαor filler (gold, silver or copper spheres or perhaps graphite for example) is used for the dual puφoses of securing the IC to the substrate 58 and providing an eleαrical connection between the antenna elements 62 and 64 and the IC pads. The anisotropic conductive adhesive 70 conducting in one direction and nonconductive in a direction approximately peφendicular to the conduαion path. In a present embodiment, it conduαs better along paths in which the adhesive is subjeαed to greater pressure. In Figure 9 A, the anisotropic conductive adhesive is cured under greater pressure in the two narrow regions 72 where it is squeezed between the antenna elements 62 and 64 and the IC pads than in the wider recessed region 74 that separates the two plates between the rest ofthe IC and the substrate. Hence, there is conduction between each pad and the respeαive element adhered to it, but there is little or no conduαion across the recessed region 74 The elements 62 and 64, therefore, are eleαrically isolated from each other. An advantage ofthe use ofthe anisotropic conduαive adhesive 70 is that it need not be applied to the IC pads or to the antenna plates with precision since its conduαivity depends upon applied pressure. Therefore, it can be easier to manufacture devices using the anisotropic conduαive material because the adhesive can be applied to the aαive side of an IC or onto the substrate without the concern about overlapping onto other areas. As long as regions ofthe adhesive that are to be nonconduαing are cured under lower pressure than the conduαive regions, they will remain nonconducting and will not interfere with the isolation ofthe two antenna elements.

In Figure 9B, isotropic conductive adhesive 76 such as is used to secure the IC to the substrate 58 and to create an electrical connection between the antenna elements 62 and 64 and the IC pads 68. An isolation material 78 such as solder mask or nonconductive ink or epoxy, is used to eleαrically isolate different globs ofthe isotropic conductive adhesive 76 used to adhere the different elements 62 and 64 to different pads 68. The isotropic conductive adhesive conduαs equally well in all directions. It must be applied with care so that no conductive path is formed between the two eleαrically isolated antenna plates.

Figure 9C is similar to Figure 9A except that an intermediate layer of paper or other material 80 is bonded over the antenna plate structure; a layer of adhesive 82 is applied to the intermediate layer 80; and a peel and stick layer 84 is apphed over the adhesive layer 82. The device 32 can be adhered or stuck to an object by peeling off the peel and stick layer 84 and pressing the adhesive layer 82 against an objeα to be identified. Thus, an objeα can be easily "tagged" with an inexpensive device which can store eleαronic information about the object.

The object, for example, can be airline luggage. The tag device may have passenger identifying information written into its eleαronic memory during passenger check-in. The device is stuck to the side ofthe luggage to identify its owner. When the owner rαrieves the luggage, he peels off the tag and discards it

As explained above, in operation, the two antenna elements 62 (Tl) and

64 (T2) must be at different voltages in order to power up the device 32. Specifically, electrostatic coupling for power up requires that a voltage differential (between V+ supply and "common") be sα up within the device. In a present embodiment, the voltage differential is established aαoss the two elements 62 and 64 by the balanced out of phase power up signals produced by the exciter. The two antenna elements are conneαed to a rectifier circuit, a full bridge rectifier in the presently preferred embodiment. A DC voltage is produced between V+ and common. In essence, V+ serves as VDD voltage supply, and common serves as substrate ground for the mtegrated circuit ofthe current embodiment.

Referring to the illustrative drawings of Figure 10, there is shown a first altemative embodiment of a remote communication device 190 in accordance with the invention. The device includes two pairs of antenna elements 192 and 194 disposed on a substrate 196 and conneαed to an IC 198 as shown.

Referring to Figure 11, there is shown a second altemative embodiment of a remote communication device 200. The device includes four pairs of antenna elements 202-208 disposed on a substrate 210 and conneαed to an IC 212 as shown.

The manufacture ofthe devices 190 and 200 can be similar to that of the devices of Figures 9 A-C. However, the presence of additional antennas provides greater opportunities for the remote device to align with the exciter plates as will be appreciated from the following discussion. As an alternative to additional device antennas, as explained below, the excitation pattem of an array of exciter plates can be systematically varied in order to produce the greatest likelihood of power up of a remote device regardless of device antenna orientation.

Referring to the illustrative drawings of Figures 12A and 12B, there is shown the device 32 of Figure 3A in two different orientations relative to a portion of an antenna array 86 that can be employed by the exciter/reader apparatus 30. In each of Figures 7A and 7B, the antenna array portion includes a first exciter element 88 (El) and a second exciter element 90 (E2). The exciter elements 88 (El) and 90 (E2) have balanced out of phase power up signals applied to them as described above. It should be appreciated that the following discussion applies to the embodiment of Figures 8B and 8C as well.

In Figure 12 A, the device 32 has its two antenna elements 62 (Tl) and 64 (T2) oriented so that one ofthe two elements, element 62 (Tl), is eleαro¬ statically coupled to the exciter element 88 (El), and the other antenna element 64 (T2) is electrostatically coupled to the second exciter element 90 (E2).

Since remote eleαrostatic coupling is, in essence, capacitive coupling the antenna element 62 (Tl) should be positioned opposite (over) the first exciter element 88 (El) in order for the first exciter element 88 to eleαrostatically couple its voltage to the element 62 (Tl) This positioning is represented in Figure 7A by the curved arrows. Similarly, the device antenna element 64 (T2) should be positioned opposite (over) the second exciter element 90 (E2) to eleαrostatically couple its voltage to element 64 (T2). It will be appreciated, of course, that it is the voltage differential between the two elements 62 (Tl) and 64 (T2) that is important. The voltages on device elements 62 and 64 is dynamic. When the voltage on device element 62 is high, the voltage on device element 64 is low. Thus, it is not essential, for example, that one ofthe two device elements 62 or 64 be at any particular voltage, such as ground potential, for power up to work. Furthermore, while the above explanation speaks in terms of exciter element 88 (El) being coupled to device element 62 (Tl) and exciter element 90 (E2) being coupled to device element 64 (T2), the invention also works with exciter element 88 (El) coupled to device element 64 (T2) and with exciter element 90 (E2) coupled to device element 62 (Tl).

In Figure 12B, the device 32 is shown oriented relative to the portion of the antenna array 86 such that power up will not be successful. Both ofthe device elements 62 (Tl) and 64 (T2) are opposite (over) the same exciter element 90 (E2). As a consequence, a voltage differential is unlikely to be set up between the two elements 62 (Tl) and 64 (T2), and power up is unlikely. Similarly, power up would be impossible if both device elements 62 and 64 were disposed opposite (over) the other exciter element 88 (El) or if both device elements were positioned equally opposite (over) each ofthe exciter elements 88 (El) and 90 (E2). Thus, a challenge in achieving sufficient electrostatic couphng between the device 32 and the exciter/receiver apparatus 30 is to achieve appropriate orientation and positioning ofthe device elements 62 (Tl) and 64 (T2) and the exciter array elements 88 (El) and 90 (E2). It is, therefore, important that shape, dimensions and spacing between device antenna elements be appropriately matched to the shape dimensions and spacing ofthe balanced exciter elements. It is not necessary, however, that device antenna element dimensions be the same as exciter element dimensions. For example, an altemative embodiment (not shown) might employ elongated thin device antenna elements excited by wider exciter elements. It has been found that exciter element sizes and shapes may depend, not only upon the size and shape of remote device antenna elements, but also up on the likely trajeαory of a device as it passes over an array of exciter elements. As explained below, the required device antenna orientation relative to an array of exciter elements, for example, can be achieved dynamically by electronically changing the relative positioning ofthe balanced out of phase exciter elements 88 and 90 within the antenna array 86.

In order to achieve the required orientation of device elements and exciter elements, an exciter antenna array in accordance with the invention may comprise either a fixed array or a commutating array of exciter elements. In a fixed array, the relative phasing of voltage signals applied to different exciter elements is fixed. That is, if two exciter elements have a balanced out of phase relation with each other, then that relationship is fixed. In a commutating array, the phase relationships of voltage signals apphed to different exciter elements can change. In a commutating array, for example, a controller (not shown) determines the phase relation ofthe excitation of different antenna elements. For instance, as explained below, in one configuration two adjacent elements may be in a balanced out of phase relationship. However, at a later time, those two elements may operate in phase with each other. In either the fixed or the commutating case, however, the spacing between exciter elements is matched to the spacing between the device antenna elements of a remote communication device. This spacing ensures maximum eleαrostatic coupling of power from the exciter to the remote device. The illustrative drawmgs of Figure 13 shows a fixed exciter antenna array 100 in accordance with the invention. The array 100 includes a group of elongated horizontal exciter antenna elements 102 and a group of elongated verticai exciter elements 104. Each ofthe horizontal exciter elements is conneαed to either the top or the bottom terminal ofthe secondary coil 38.

Similarly, each ofthe vertical exciter elements is conneαed to either the top or the bottom terminal ofthe secondary coil 38. The horizontal exciter elements on either side of any given horizontal exciter element have a balanced out of phase voltage relationship to the given horizontal exciter element. Likewise, the vertical exciter elements on either side of any given vertical exciter element have a balanced out of phase voltage relationship to the given vertical exciter element. For example, if horizontal exciter elements 106 and 108 are conneαed to the top ofthe secondary coil, then exciter elements 110 and 112 are connected to the bottom ofthe secondary coil. Further, for example, if vertical exciter elements 114 and 116 conneαed to the top ofthe secondary coil, then vertical exciter elements 118 and 120 are conneαed to the bottom of the secondary coil. In a presently preferred embodiment, the spacing between adjacent horizontal exciter elements and between adjacent vertical exciter elements is approximately the same as the spacing between the remotely powered communication device elements.

In operation, a first communication device 32-1 is oriented so that its antenna elements will be opposite adjacent horizontal exciter elements as it moved across the face ofthe antenna array 100 in the direαion ofthe horizontal arrow. Hence, the first device will be oriented for maximal power coupling with the horizontal exciter elements as it horizontally crosses the group of horizontal elements 102 A second device 32-2 is oriented so that its device antenna elements will be opposite adjacent vertical exciter elements as it moves across the face ofthe antenna array 100 in the direction ofthe vertical arrow. Thus, the second device will be oriented for maximal power coupling with the vertical exciter elements as it vertically crosses the group of vertical elements 104.

The drawings of Figure 13 represent only a portion of a larger array in which there are numerous groups, 102 and 104, of horizontal and vertical exciter elements oriented as shown. During intervals when a device 32-1 or 32-2 is disposed for maximal power coupling, the device will power up and transmit information. The illustrated grouping of exciter elements seeks to ensure that at some point as device is moved across the exciter antenna array, the device will have sufficient power coupled to it to power up and become operational.

Referring to the illustrative drawings of Figures 14A-14C, there are shown three different configurations of a single portion of a commutated antenna array 124 in accordance with a current embodiment ofthe invention. Over the course of three time intervals, the array 124 is switched from the horizonal configuration in Figure 14 A, to the diagonal configuration in Figure

14B, and finally, to the vertical configuration in Figure 14C. The array consists of a plurahty of identically shaped (square in the current embodiment) exciter plates that are arranged in symmetrical rows and columns as shown.

In the horizontal configuration shown in Figure 14 A, all ofthe exciter elements in a given horizontal row share the same voltage phase, and the exciter elements in rows adjacent to the given row all share a balanced out of phase voltage relationship to the given row. That is, the exciter elements in rows 126 and 128 are in balanced out of phase relation with the voltage ofthe exciter elements in rows 130 and 132. In the horizontal configuration, the array is optimally configured to couple power to a communication device 32 moving across the array in the direction ofthe horizontal arrow.

In the diagonal configuration shown in Figure 14B, each exciter element in a given row is in a balanced out of phase voltage relation with adjacent exciter elements on either side of it in the same row and with adjacent exciter elements above and below it in the same column. Conversely, each exciter element in a given column is in a balanced out of phase relation with exciter elements above and below it in the same column and with adjacent exciter elements on either side of it in the same row. That is, for example, exciter element 134 is in a balanced out of phase voltage, relation with exciter elements 136 and 138 on either side of it in the same row and with exciter elements 140 and 142 above and below it in the same column. In the diagonal configuration, the array is optimally configured to couple power to a communication device 32 moving diagonally across the array, such as in the direαion ofthe diagonal arrow.

In the vertical configuration shown in Figure 14C, all ofthe exciter elements in a given vertical column share the same voltage phase, and the exciter elements in columns adjacent to the given column all share a balanced and out of phase relationship relative to the voltage ofthe given column. That is, the exciter elements in columns 144 and 146 are in a balanced out of phase relation with the exciter plates in columns 148 and 150. In the vertical configuration, the array is optimally configured to couple power to a communication device 32 moving aαoss the array in the direction ofthe vertical arrow.

Figure 15 illustrates yα another altemative technique for energizing an array of exciter elements. Rather than step through a sequence of horizontal, diagonal and vertical stripes of plates as shown in Figures 14A-14C, a pair of appropriately spaced balanced out of phase stripes 202 and 204 (of individual elements), is swept in a circular pattem aαoss the exciter element array as indicated by the arrows. At some point during the sweep, the antenna elements of a remote device (not shown) disposed sufficiently close to the exciter are likely to be suitably aligned for power up. More specifically, in Figure 15, there is shown a portion of an array 200 of exciter elements. The individual exciter elements ofthe array 200 are energized such that a plurality of individual exciter elements that comprise the two stripes (shaded) 202 and 204 are in phase with each other but out of phase with other individual (unshaded) exciter elements. The orientation ofthe two stripes changes with time, but they remain parallel to each other. Thus, for example, in Figure 15 the stripes 202 and 204 are shown vertically oriented. At other times they will be horizontally oriented, and at still other times they will be diagonally oriented. While a pair of balanced out of phase stripes rotating in a circular motion is shown, it will be appreciated that other dynamically changing exciter element pattems and movements can be practiced consistent with the invention.

The illustrative drawing of Figure 16 depicts yet another approach to energizing an array of exciter elements in accordance with the invention. In the embodiment of Figure 16, the exciter antenna elements are arranged in an array of rows and columns. An array of sensors, such as optical sensors, are disposed about the periphery ofthe array of exciter antenna elements. The sensors deteα the presence and direction of motion of a communication device, such as device "A" (horizontal), "B"(diagonal) or "C" (vertical). In response to sensor deteαion of motion, an array controller (not shown) seleαs an excitation configuration for the array which is likely to couple energy most efficiently to the device as the device passes across the face ofthe array. For example, depending upon the dαeαed motion ofthe device, the optimal array configuration may be a horizontal configuration as illustrated in Figure 14 A, a diagonal configuration as illustrated in Figure 14B, or a vertical configuration as illustrated in Figure 14C.

While particular embodiments ofthe invention have been described in detail herein, it will be appreciated that various modifications can be made to the preferred embodiment without departing from the scope ofthe invention. Thus, the foregoing description is not intended to limit the invention which is defined in the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A portable communication device, comprising:

a first electrostatic antenna element;

a second electrostatic antenna element; and

circuitry which is coupled to the first antenna element and to the second antenna element and which derives operating power through the first and second antenna elements from an electrostatic field in a vicinity of the first and second antenna elements.

2. The device of claim 1 , further comprising a substrate member, and wherein the circuitry is an integrated circuit which is secured to the substrate, and the antenna elements are formed on the substrate such that they are electrically isolated from each other.

3. A portable communication device, comprising:

a first electrostatic antenna element and a second electrostatic antenna element;

an integrated circuit electrically interconnected with the first antenna element and the second antenna element; wherein the integrated circuit includes a power-up circuit which is electrically coupled to the first and second antenna elements and which derives operating power through the first and second antenna elements from electrostatic energy received by the first and second antenna elements;

a memory in which information is stored; and

a signal generation circuit which is powered by the power-up circuit and which generates a carrier signal modulated with information stored in the memory.

4. The device of claim 3, wherein the signal generation circuit is electrically coupled to one of the first and second antenna elements.

5. The device of claim 3, further comprising a third antenna element electrically coupled to the signal generation circuit so as to transmit signals produced by the generation circuit. 6. A method for producing a portable identification device, comprising the steps of:

providing an electrically insulating substrate member,

placing on the substrate member first and second electrostatic antenna elements which are electrically isolated from each other,

securing an integrated circuit, which includes first and second terminals, to the substrate member, and

electrically coupling the first and second terminals to the first and second elements.

7. A method for imparting power to a portable commumcation device having a first and second electrostatic antenna element coupled to circuitry which derives operating power through the first and second antenna elements from an electrostatic field in a vicinity of the first and second antenna elements, comprising d e steps of:

providing first and second electrostatic exciter elements;

generating a balanced out-of-phase electrostatic signal on the first and second exciter elements;

aligning and positioning the antenna elements of me communication device close enough to the exciter elements such that sufficient electrostatic energy is transmitted from the exciter elements to the antenna elements to the circuitry so as to power up the circuitry. 8. A system for communicating with a portable remotely powered communication device having a first and second electrostatic antenna element, an integrated circuit electrically interconnected with the antenna elements and including a power-up circuit electrically coupled to the antenna elements and deriving operating power through the electrostatic energy received by the antenna elements, a memory in which information is stored, and a signal generation circuit powered by the power-up circuit and which generates a carrier signal modulated with infoπnation stored in the memory, comprising:

an exciter circuit which produces respective first and second out-of-phase excitation signals for powering up the device;

first and second electrostatic exciter elements which are respectively coupled to the first and second excitation signals for transmitting signals to the device;

an electrostatic receiver antenna element which receives the modulated carrier signal transmitted by the device; and

a receiver circuit coupled to receive the signal from the receiver antenna element.

9. A system for communicating with a portable remotely powered communication device having a first and second electrostatic antenna element, an integrated circuit electrically interconnected with the antenna elements and including a power-up circuit electrically coupled to die antenna elements and deriving operating power through the electrostatic energy received by the antenna elements, a memory in which information is stored, and a signal generation circuit powered by the power-up circuit and which generates a carrier signal modulated with information stored in the memory, comprising:

an antenna array which includes multiple respective electrostatic exciter antenna element pairs in which, for a respective pair, a respective first exciter antenna element is coupled to receive die first excitation signal produced by the exciter circuit and to transmit the first excitation signal to the device, and a respective second exciter antenna element of such respective pair is coupled to receive the second excitation signal produced by the exciter circuit and to transmit the second excitation signal to the device;

a receiver circuit coupled to receive the signal from the receiver antenna element. 10. A system for communicating with a portable communication device having a first and second electrostatic antenna element, an integrated circuit electrically interconnected with the antenna elements and including a power-up circuit electrically coupled to the antenna elements and deriving operating power through the electrostatic energy received by the antenna elements, comprising:

an exciter circuit which produces respective first and second out-of-phase excitation signals for powering up die communication device;

an antenna array which includes multiple respective electrostatic exciter antenna elements arranged in rows and columns; and

a control circuit which alternatively,

(A) connects exciter antenna elements in a given column to receive one of the first and second excitation signals and connects exciter antenna elements in columns adjacent to such given column to receive die otiier of die first and second excitation signals; or

(B) connects exciter antenna elements in a given row to receive one of the first and second excitation signals and connects exciter antenna elements in rows adjacent to such given row to receive die omer of me first and second excitation signals.