Patent Description:
This section is intended to introduce the reader to various aspects of art, which may be related to embodiments that are described below. Accordingly, it should be understood, that these statements are to be read in this light.

Radio-frequency identification (RFID) is a generic term for technologies that use radio waves to automatically identify people or objects. An RFID system uses tags, or labels attached to the objects to be identified. Two-way radio transmitter-receivers called interrogators or readers send a signal to the tag and read its response. There are several types of RFID tags, depending on range, size, cost and underlying technology.

RFID tags can be passive, active or battery-assisted (or semi) passive. An active tag has an on-board battery and periodically transmits an ID signal. A battery-assisted passive (BAP) tag has a small battery on board and is activated when in the presence of an RFID reader. A passive tag ls cheaper and smaller because it has no battery, instead, the tag uses the radio energy transmitted by the reader as the power source. However, to operate a passive tag, it must be illuminated with a power level roughly a thousand times stronger than for signal transmission. That makes a difference in interference and in exposure to radiation. The energy conversion is performed by an RF energy harvester generally including an antenna and a rectifier/multiplier tuned to the waves received from the RFID reader.

Tags may either be read-only, having a factory-assigned serial number that is used as a key into a database, or may be read/write, where object-specific data can be written into the tag by the system user. Field programmable tags may be write-once, read-multiple; "blank" tags may be written with an electronic product code by the user.

RFID tags contain at least two parts: an integrated circuit (IC, microchip or chip) for storing and processing information, modulating and demodulating a radio-frequency (RF) signal, collecting DC power from the incident reader signal, and other specialized functions; and an antenna for receiving and transmitting the signal. The tag information is stored in a non-volatile memory. The RFID tags includes either fixed or programmable logic for processing the transmission and sensor data, respectively.

An RFID reader transmits an encoded radio signal to interrogate the tag. The RFID tag receives the message and then responds with its identification and/or other information. This may be only a unique tag serial number, or, may be product-related information such as stock number, lot or batch number, production date, or other specific information. Since tags have individual serial numbers, the RFID system design can discriminate among several tags that might be within the range of the RFID reader and read them simultaneously.

RFID systems may be classified in two major classes operating in different frequency bands. The difference between the two classes is based on the type of physical coupling between the reader and the tag, which could be either magnetic (inductive coupling) or electromagnetic (radiative coupling). Inductive or magnetic coupling (MC) occurs when a varying magnetic field exists between two parallel conductors typically less than a wavelength apart, inducing a change in voltage along the receiving conductor. It generally applies to frequencies up to the Very High Frequency (VHF) range, around <NUM>. In RFID systems based on inductive coupling, the tag gets its energy from the proximately coupled magnetic field and responds by loading its own antenna with different impedances.

Radiative or electromagnetic coupling occurs when the source and the target (or victim) are separated by a large distance, typically more than a wavelength. The source and the target act as radio antennas: the source emits or radiates an electromagnetic wave which propagates across the space in between and is picked up or received by the target. Radiative coupling generally applies to frequencies above <NUM>. In RFID systems based on radiative coupling, the tag gets its energy from the electromagnetic field radiated by the reader and reflects it back, modulating with its own impedances presenting different Radar Cross Section (RCS). RCS is a measure of the ability of a target to reflect radar signals in the direction of the radar receiver.

The coupling nature of the first class (inductive coupling) limits the read range to an order of magnitude of the size of the reader or the tag antenna (generally a few centimeters) while the range of the second class (radiative coupling) could reach up to tens of meters depending on the nature of the tags (passive and active) and its sensitivity. For long range RFID systems operating in the Ultra High Frequency (UHF) band or microwave bands using passive tags, a part of the incoming RF signal (issued from the remote RFID reader and coupled through the tag antenna) is converted to DC for the supply of the chip. Once the chip is activated, the received signal is demodulated by the interface and reflected back (backscattered) modulated by the information stored in the chip memory. The chip activation is the limiting factor of the achievable range of RFID systems using passive tags. Typical ranges of <NUM> meters are currently achievable in Line of Sight (LOS) conditions using state of the art passive tags and readers.

The Electronic Product Code (EPC™) Generation <NUM> (Gen2) air interface protocol defines the physical and logical requirements for an RFID system of interrogators and passive tags, operating in the <NUM> - <NUM> UHF (or also called <NUM>) band. Over the past decade, EPC Gen2 has established itself as the standard for UHF implementations across multiple sectors, and, is at the heart of more and more RFID implementations.

More recently with the explosion of wireless sensors, a new generation of RFID chips compliant with the EPC Gen2 standard has emerged with a power supply input to be connected to a coin-size battery, increasing the device range to several tens of meters. The new devices are not strictly passive, but, may be considered semi-passive devices. However, battery life is not only inconvenient but may also be fatal to the commercial success of these new generation devices due to the complexity and cost of replacing batteries.

While RFID tags are now established as a standard technology for object identification and tracking, some research is aimed towards extending the capability of RFID tags, including passive tags beyond the identification function (RFID beyond ID). Specifically, RFID tags and systems are combining the identification function with a sensing of a physical or biological signal. For many such systems, a sensing module (for example, temperature, pressure, etc.) is coupled to the RFID chip through a secondary wired interface to store/update the sensed data in the memory of the chip.

Document <CIT> describes a small-size pressure sensor device that can perform temperature compensation and that has high reliability. The pressure sensor device includes a pressure-detecting piezoelectric substrate.

Document <CIT> describes a remotely interrogatable passive sensor comprising an antenna and a surface wave resonator including a transducer with inter-digitated electrodes with two ports on the surface of a piezoelectric substrate.

Document <CIT> describes a vibration sensor based on acoustic wave radio frequency identification technology. The surface acoustic wave device includes an antenna and a piezoelectric substrate.

Document <CIT> describes a radio frequency identification label comprising an antenna, the antenna comprising a magnetostrictive material and a piezoelectric material.

Document <CIT> describes a wireless sensor having a detection unit including a vibration sensor, a temperature sensor and a rotation speed sensor. A piezoelectric element is applicable to the sensor.

The proposed apparatus concerns an antenna which is augmented with sensing capability for use in a wireless system. It will be appreciated that the proposed apparatus is not limited to any specific type of device and may be applied to any wireless communication device, such as for example a radio frequency identification device (RFID).

Embodiments are disclosed, described and claimed according to the appended claims.

Some processes implemented by elements of the disclosure may be computer implemented. Accordingly, such elements may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, microcode, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as "circuit", "module" or system. Furthermore, such elements may take the form of a computer program product embodied in any tangible medium of expression having computer usable program code embodied in the medium.

Since elements of the present disclosure can be implemented in software, the present disclosure can be embodied as computer readable code for provision to a programmable apparatus on any suitable carrier medium. A tangible carrier medium may comprise a storage medium such as a floppy disk, a CD-ROM, a hard disk drive, a magnetic tape device or a solid-state memory device and the like. A transient carrier medium may include a signal such as an electrical signal, an optical signal, an acoustic signal, a magnetic signal or an electromagnetic signal, e.g. a microwave or RF signal.

Embodiments of the disclosure will now be described, by way of example only, and with reference to the following drawings in which:.

It should be understood that the drawings are for purposes of illustrating the concepts of the disclosure and is not necessarily the only possible configuration for illustrating the disclosure.

The present disclosure is directed to a radio frequency identification device (RFID) capable of sensing mechanical impact, vibrational energy and/or acoustic signals.

Fundamentally, a passive RFID device acts as an energy harvester. The RF energy harvesting may be performed by an antenna and a rectifier/multiplier tuned to the waves received from the RFID reader. Indeed, a portion of the energy of an incoming RF signal, transmitted by the RFID reader, and coupled through the RFID antenna, may be converted to DC by the rectifier/multiplier for the supply of the RFID chip and is thus not used for the wireless communication link.

<FIG> illustrates a simplified block diagram of an exemplary RFID system <NUM> in accordance with an embodiment of the present disclosure. RFID system <NUM> includes RFID reader device <NUM> and RFID tag device <NUM>. RFID reader device <NUM> includes RFID reader circuit <NUM> coupled to RFID reader antenna <NUM>. RFID tag device <NUM> includes RFID tag circuit <NUM> coupled to RFID tag antenna <NUM>. The RFID tag device <NUM> may be attached to the object to be sensed, using, for example, an adhesive film.

RFID reader device <NUM> generates and modulates a request message in RFID reader circuit <NUM> to create a transmitter signal, and radiates the transmitter signal via electromagnetic waves through antenna <NUM>. RFID tag antenna <NUM> is tuned to receive the waves radiated from RFID reader antenna <NUM>. An antenna is a specialized transducer or converter that converts RF fields into Alternating Current (AC) or vice-versa. RFID tag antenna <NUM> converts electromagnetic fields of the received waves to an electrical signal.

RFID tag device <NUM> draws power from the electrical signal and uses it to power up RFID tag circuit <NUM>. The electrical signal may fully power up the RFID tag circuit <NUM>, in a passive RFID tag, or partially power up the RFID tag circuit <NUM>, in the case of a semi-passive RFID tag. RFID tag circuit <NUM> also receives and demodulates the electrical signal to retrieve the request message. RFID circuit <NUM> then generates and modulates a response message with its identification number(s) and/or other information. The modulated response message is radiated via electromagnetic waves through RFID tag antenna <NUM>.

One of the aspects of passive and semi-passive RFID tags is the method of re-modulating an RFID reader electromagnetic wave via backscattering. Since RFID tags are designed to generally have a reactive (e.g., capacitive) impedance, any incoming electromagnetic wave is reflected (re-radiated) by an antenna to its source. Thus, when RFID reader device <NUM> transmits an electromagnetic wave to RFID tag device <NUM>, the wave is reflected by the RFID tag device <NUM> back toward the RFID reader device <NUM>. Due to this reflective characteristic, RFID tag device <NUM> is able to encode a message by modulating the re-radiated electromagnetic wave. Actual modulation of the wave may occur as a transistor in RFID tag circuit <NUM> rapidly switches between two discrete impedance states. Since each impedance state may have both a resistive and a capacitive characteristic (real and imaginary impedance), the RFID tag device <NUM> may perform both phase and amplitude modulation of the re-radiated signal.

RFID reader device <NUM> may receive the re-radiated waves through RFID reader antenna <NUM> and convert the waves to digital data containing the response message. It is to be understood that RFID reader circuit <NUM> may be any RFID reader circuit or IC well-known to one of ordinary skill in the pertinent art. Likewise, RFID reader antenna <NUM> may be any antenna well-known to one of ordinary skill in the pertinent art, e.g., dipole antennas, loop antennas, inverted-F antennas, monopole antennas, patch or micro-strip antennas, etc..

<FIG> illustrates a simplified block diagram of an exemplary RFID tag device <NUM> in accordance with an embodiment of the present disclosure. RFID tag device <NUM> may be similar to RFID tag device <NUM>. RFID tag device <NUM> includes RFID antenna <NUM>. RFID tag device <NUM> also includes analog front end (AFE) <NUM>, digital processor <NUM> and memory <NUM>, which together are similar to RFID tag circuit <NUM>.

Antenna <NUM> preferably operates in the Ultra High Frequency (UHF) band. Antenna <NUM> is augmented with the capability of sensing any mechanical impact, vibration or acoustic signal. In one aspect of the disclosure, antenna <NUM> is formed on a piezoelectric film. <FIG> shows an exemplary flexible piezoelectric film <NUM> that has a metal layer <NUM> disposed thereon.

<FIG> illustrates a planar view of the metallized piezoelectric film shown in <FIG>. In <FIG>, the metal layer <NUM> is disposed on the piezoelectric film <NUM>. <FIG> illustrates a schematic side view of the metallized piezoelectric film shown in <FIG>. In <FIG>, both sides of the piezoelectric film <NUM> have a metal layer <NUM> disposed thereon. The metal layer that is depicted in <FIG>, has a square shape. However, several topologies and shapes for the antenna are contemplated and are a matter of design choice.

Piezoelectric films typically have a relative permittivity, in the range of <NUM>-<NUM>. Such a relative permittivity allows for smaller antenna sizes in comparison to antennas disposed on conventional substrates. The relative permittivity of conventional substrates is typically in the range of <NUM>-<NUM>. Thus, for example, a substrate having a relative permittivity about four (<NUM>) times higher than a conventional substrate may have antennas with sizes about two (<NUM>) times smaller than those disposed on a conventional substrate with the same performance.

In addition to antenna <NUM> operating in the UHF frequency band, the antenna is also an efficient mechanical to electrical transducer for the detection and/or the acquisition of an impact, vibration or acoustic signal due to its disposition on the piezoelectric film. Suitable examples for the piezoelectric film include polyvinylidene fluoride (PVDF) and copolymers of polyvinylidene fluoride.

AFE <NUM> is coupled to antenna <NUM> and includes rectifier <NUM>, regulator <NUM>, demodulator <NUM>, modulator <NUM> and vibration/impact/acoustic signal integrated circuit <NUM>. Rectifier <NUM> performs the function of rectification/multiplication of the received electrical signal and provides Direct Current (DC) power to regulator <NUM>. An RF energy harvester is built around an RF rectifier which is an electrical circuit that converts RF power from a lower voltage to a higher DC voltage using a network of capacitors and diodes. The RFID antenna <NUM> input is connected to a diode rectifier through a matching network and for given diode characteristics and fixed RF input power, the load is optimized for a maximum RF to DC converter efficiency. As an example, the HSMS-<NUM> family of RF detector diodes from Avago™ is well suited for use in energy harvesting from <NUM> up to <NUM> frequency range.

Regulator <NUM> is coupled to rectifier <NUM> and regulates input power to desired levels by the remaining components of RFID tag device <NUM>, which are coupled to regulator <NUM>. Demodulator <NUM> is coupled to regulator <NUM> and to antenna <NUM> and receives and demodulates the input electrical signal to receive the request message and possibly control signals from the RFID reader (e.g., RF reader device <NUM>). Modulator <NUM> is coupled to regulator <NUM> and to antenna <NUM>, and, modulates a response message including its identification number(s) and/or other information, and possibly control signals. The modulated response message is radiated via electromagnetic waves through RFID tag antenna <NUM>.

Vibration/impact/acoustic signal integrated circuit (IC) <NUM> is coupled to antenna <NUM> and receives sensed mechanical impact, vibration, or acoustic signals therefrom. Vibration/impact/acoustic signal IC <NUM> converts the mechanical, vibrational or acoustic signals to electrical energy, a portion of which may be used for powering, detecting and storing the detected signal information in the memory <NUM> of the chip. The vibration/impact/acoustic signal IC <NUM> preferably includes an amplifier and an Analog-to-Digital circuit (not shown) which are used for post-processing signals from digital processor <NUM> or for storing the information in the memory <NUM>. For example, in the case of impact detection, vibration/impact/acoustic signal integrated circuit <NUM> may be a simple state machine based IC which provides two output states depending on the level of the analog input signal as compared to a programmable threshold value. Alternatively, a battery (not shown) could be used for the power supply of a high-speed Analog-to-Digital convertor (ADC) or a microcontroller when required, while the antenna <NUM> only provides the impact, the vibration or the acoustic signal information to be stored.

Digital processor <NUM> is coupled to regulator <NUM>, demodulator <NUM> and modulator <NUM>. Digital processor <NUM> receives and interprets a digital request message and control signals from demodulator <NUM> and requests identification number(s) and/or other information. Memory <NUM> may be a non-volatile memory, including a read-only memory (ROM) or a read-write memory. Memory <NUM> provides the necessary information to digital processor <NUM> upon request. Digital processor <NUM> may also include the operations of clock management, data encoding (e.g., error correction encoding), data decoding (e.g., error correction decoding), data encryption, data decryption, anti-collusion, etc. Digital processor <NUM> may include a digital logic circuit, including e.g., finite state machine(s) (FSM) and registers. Digital processor <NUM> may include a controller or processor that controls the operation of RFID tag device <NUM>. Digital processor <NUM> may also generate appropriate control signals and send the response message including identification number(s) and/or other information and possibly control signals to modulator <NUM>.

It is to be understood that the various components of RFID tag device <NUM> may be well-known circuits to a person of ordinary skill in the art and will not be described in detail. It is to be understood that other well-known components may be present in RFID tag device <NUM>, e.g., a frequency oscillator. It is to be understood that RFID tag device <NUM> and corresponding RF reader (e.g., RFID reader device <NUM>) may be compliant with at least one RFID standard e.g., the EPC Gen2, the International Standards Organization ISO <NUM> series standards, etc..

According to one or more embodiments of the present disclosure, more than one rectifier/multiplier circuits or RF harvester may be included in RFID tag device <NUM> (not shown), the plurality of rectifiers/multipliers harvesting energy from a plurality of frequency bands.

<FIG> illustrates a flowchart of an exemplary method in accordance with another aspect of the disclosure. In step <NUM>, at least one of vibrational energy, acoustic energy and impact energy is sensed using a piezoelectric substrate configured as an antenna of an integrated circuit. The antenna preferably operating in the UHF frequency band, is an efficient mechanical to electrical transducer for the detection and/or the acquisition of an impact, vibration or acoustic signal due to its disposition on the piezoelectric film. Suitable examples for the piezoelectric film include polyvinylidene fluoride (PVDF) and copolymers of polyvinylidene fluoride.

The sensed at least one of vibration energy, acoustic energy and impact energy is then converted to electrical energy, as depicted in step <NUM>. Vibration/impact/acoustic signal IC converts the mechanical, vibrational or acoustic signals to electrical energy sensed during step <NUM>. A portion of the converted energy is used for storing the detected signal information in a memory. Alternatively, a battery (not shown) could be used for the power supply of a high-speed Analog-to-Digital convertor (ADC) or a microcontroller when required, while the antenna only provides the impact, the vibration or the acoustic signal information to be stored.

It should be understood that the elements shown in the figures may be implemented in various forms of hardware, software or combinations thereof. Preferably, these elements are implemented in a combination of hardware and software on one or more appropriately programmed general-purpose devices, which may include a processor, memory and input/output interfaces. Herein the phrase "coupled" is defined to mean directly connected to or indirectly connected with, through one or more intermediate components. Such intermediate components may include both hardware and software based components.

It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described or shown herein, embody the principles of the disclosure and are included within its scope.

All examples and conditional language recited herein are intended for educational purposes to aid the reader in understanding the principles of the disclosure and the concepts contributed by the inventors to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions.

Thus, for example, it will be appreciated by those skilled in the art that the block diagram presented herein represents conceptual views of illustrative circuitry embodying the principles of the disclosure. Similarly, it will be appreciated that any flow charts, flow diagrams, state transition diagrams, pseudocode and the like represent various processes which may be substantially represented in computer readable media and so executed by a computer or processor, whether or not such computer or processor is explicitly shown.

The functions of the various elements shown in the figures may be provided through the use of dedicated hardware as well as hardware capable of executing software in association with appropriate software. Moreover, explicit use of the term "processor" or "controller" should not be construed to refer exclusively to hardware capable of executing software, and may implicitly include, without limitation, digital signal processor (DSP) hardware, read only memory (ROM) for storing software, random access memory (RAM), and nonvolatile storage.

Claim 1:
A sensor, comprising:
an integrated circuit (<NUM>, <NUM>, <NUM>); and
a piezoelectric substrate (<NUM>);
the piezoelectric substrate (<NUM>) being configured as an antenna (<NUM>) of the integrated circuit (<NUM>, <NUM>, <NUM>);
the antenna (<NUM>) being configured to sense at least one of vibrational energy, acoustic energy and impact energy;
the integrated circuit (<NUM>, <NUM>, <NUM>) being configured to convert said sensed at least one of vibrational energy, acoustic energy and impact energy into electrical energy;
characterized in that:
at least a portion of the converted electrical energy is used for storing detected signal information in a memory (<NUM>) of the integrated circuit (<NUM>, <NUM>, <NUM>).