Data processing: vehicles – navigation – and relative location – Relative location
Reexamination Certificate
2002-07-22
2003-08-26
Nguyen, Tan Q. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Relative location
C701S217000, C342S357490
Reexamination Certificate
active
06611758
ABSTRACT:
FIELD OF THE INVENTION
A The present invention relates to method and apparatus for determining a location within an environment, and more particularly to a system which derives information from a plurality of passive devices, each having a predetermined location and communicating insufficient information to define the predetermined location.
BACKGROUND OF THE INVENTION
A known radio frequency passive acoustic transponder system provides a radio-frequency surface acoustic wave on a piezoelectric substrate which interacts with elements on the substrate to produce an individualized complex waveform response to an interrogation signal. The code space for these devices may be, for example, 2
16
codes, or more, allowing a large number of transponders to be produced without code reuse. These devices consist of a piezoelectric substrate on which a metallized conductor pattern is formed, for example by a typical microphotolithography process, with a minimum feature size of, for example, one micron, and appropriate antennas and mechanical enclosures. The acoustic wave mode is often a surface acoustic wave (e.g. a Rayleigh wave), although acoustic wave devices operating with different wave types are known.
The known transponder devices thus include a surface acoustic wave device, in which an identification code is presented as a characteristic time-domain delay pattern in signal retransmitted from the transponder. Typical systems generally require that the signal emitted from an exciting antenna be non-stationary with respect to a signal received from the tag. This ensures that the reflected signal pattern is easily distinguished from the emitted signal during the entire duration of the retransmitted signal return, representing a plurality of internal states of the transponder, allowing analysis of the various delay components within the device.
In such a device, received RF energy is transduced onto a piezoelectric substrate as an acoustic wave with a first interdigital electrode system, from whence it travels through the substrate, interacting with reflector, delay or resonant/frequency selective elements in the path of the acoustic wave, resulting in specific known electro-acoustic interactions. A portion of the acoustic wave energy is ultimately received an interdigital electrode system and retransmitted. The retransmitted signal thus represents a complex delay and attenuation pattern function of the emitted signal, and a receiver is provided which analyzes the delay and perturbation pattern to characterize the system which produced it: thus identifying the device.
These devices do not require a semiconductor memory nor external electrical energy storage system, e.g., battery or capacitor, to operate. The propagation velocity of an acoustic wave in such a surface acoustic wave device is slow as compared to the free space propagation velocity of a radio wave. Thus, the time for transmission between the radio frequency interrogation system and the transponder is typically short as compared to the acoustic delay intrinsic to the device, so that an allowable rate of the interrogation frequency change is based on the delay characteristics within the transponder. The interrogation frequency is controlled to change by a sufficient amount so that the shortest possible delay path of a return signal may be distinguished from the simultaneous interrogation frequency, and so that all of the relevant delays are unambiguously received for analysis. Further, the interrogation frequency should not return to the same frequency before a maximum delay period, thus preventing ambiguity or aliasing. Generally, such systems are interrogated with a pulse transmitter or chirp frequency system.
Systems for interrogating a passive transponder employing acoustic wave devices, carrying amplitude and/or phase-encoded information are disclosed in, for example, U.S. Pat. Nos. 4,059,831; 4,484,160; 4,604,623; 4,605,929; 4,620,191; 4,623,890; 4,625,207; 4,625,208; 4,703,327; 4,724,443; 4,725,841; 4,734,698; 4,737,789; 4,737,790; 4,951,057; 5,095,240; and 5,182,570, expressly incorporated herein by reference. Other passive interrogator label systems are disclosed in the U.S. Pat. Nos. 3,273,146; 3,706,094; 3,755,803; and 4,058,217.
In its simplest form, the acoustic transponder systems disclosed in these patents include a radio frequency transmitter capable of transmitting RF pulses of electromagnetic energy. These pulses are received at the antenna of a passive transponder and applied to a piezoelectric “launch” transducer adapted to convert the electrical energy received from the antenna into acoustic wave energy in the piezoelectric material. Upon receipt of an electrical signal corresponding to the RF interrogation wave, an acoustic wave is generated within the piezoelectric material and transmitted along a defined acoustic path. This acoustic wave may be modified along its path, such as by reflection, attenuation, variable delay (phase shift), and interaction with other transducers or resonators.
When an acoustic wave pulse is reconverted into an electrical signal, it is supplied to an antenna on the transponder and transmitted as RF electromagnetic energy. The signal may be reflected back along its incident path, and thus a single antenna and transducer may be provided, for both receiving and emitting Radio Frequency energy. This energy is received at a receiver and decoder, typically at or near the same location as the interrogating transmitter, and the information contained in this response to an interrogation signal is decoded. Designs are known, with unitary and separate receiving and transmitting antennas, which may be at the same frequency or harmonically related, and having the same or different polarization.
In systems of this general type, the information code associated with and which identifies the passive transponder is built into the transponder at the time that the metallization pattern is finally defined on the substrate of piezoelectric material. This metallization also typically defines the antenna coupling, launch transducers, acoustic pathways and information code elements, e.g., reflectors. Thus, the information code in this case is non-volatile and permanent. The information is present in the return signal as a set of characteristic perturbations of the interrogation signal, such as a specific complex delay pattern and attenuation characteristics. In the case of a transponder tag having launch transducers and a variable pattern of reflective elements, the number of possible codes is N×2
M
where N is the number of acoustic waves launched by the transducers (path multiplicity) and M is the number of reflective element positions for each transducer (codespace complexity). Thus, with four launch transducers each emitting two acoustic waves (forward and backward) (N=8), and a potential set of eight (M=8) variable reflective elements in each acoustic path, the number of differently coded transducers is 2048. Therefore, for a largenumber of potential codes, it is necessary to provide a large number of launch transducers and/or a large number of reflective elements. However, efficiency is lost with increasing complexity, and a large number of distinct acoustic waves reduces the signal strength of the signal encoding the information in each. Therefore, the transponder design is a tradeoff between device codespace complexity and efficiency.
Typically, the sets of reflective elements in each path form a group having a composite transfer function, while each group, representing different acoustic paths, has a different characteristic timing, allowing the various group responses to be distinguished.
The transponder tag thus typically includes a multiplicity of “signal conditioning elements”, i.e., delay elements, reflectors, and/or amplitude modulators, which are coupled to receive the first signal from a transponder antenna. Each signal conditioning element provides an intermediate signal having a known delay and a known amplitude modification to the acoustic wave interacting wit
Milde & Hoffberg LLP
Nguyen Tan Q.
X-Cyte Inc.
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