Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2001-06-25
2002-09-24
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S31300R, C310S31300R, C340S572100, C342S051000
Reexamination Certificate
active
06455979
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a coded surface acoustic wave component which can be interrogated by a radio, as is known in principle from the prior art (see U.S. Pat. Nos. 4,263,595, and 5,469,170, 1995 IEEE Ultrasonics Symp., pages 117-120, and International Patent Disclosures WO 96/14589, WO 97/42519, and WO 97/26555).
In terms of its physical configuration, a surface acoustic wave component contains a substrate wafer formed from a piezoelectric material or a material with a piezoelectric coating. At least one interdigital structure is disposed as a piezoelectric transducer on or in its surface/coating having the piezoelectric characteristic. When the structure elements of the transducer are electrically excited appropriately, the transducer results in an acoustic wave, which is generally referred to as a surface acoustic wave, being produced in the surface of the substrate. The surface acoustic wave has a movement direction/form there that is governed, as is known, by the interdigital structure. Such a structure defines a main wave propagation direction in the plane of the surface.
In a manner corresponding to a surface acoustic wave component which can be interrogated by radio, the surface acoustic wave in the component can be excited by the transducer being excited/fed by radio. To this end, the transducer is equipped with an appropriate antenna for radio reception and, generally, also for radio return transmission of a response signal from the transducer to a receiver. A separate transducer with an antenna can also be provided for the interrogation signal.
The interrogation signal is transmitted by a transmitter which can transmit with a minimum bandwidth which can be predetermined. The radio signal transmission can be carried out using, for example, an apparatus that can use thermal and/or mechanical energy to produce a radio-frequency pulse with the aid, for example, of a nonlinear electronic component, like a radio path. Details of this are known.
The receiver which is provided for the radio response signal transmitted back from the component must be configured, as is known, particularly in terms of its bandwidth to satisfy the requirements of the system operating with the surface acoustic wave component.
In the case of surface acoustic wave components which are used for identification, it is necessary to ensure that a received signal can be uniquely associated, as a response signal, with a predetermined surface acoustic wave component which is appropriately individually coded for this purpose, where a system contains a number of such components which can be interrogated but are coded differently from one another, and/or where other signals are received which arrive in the system receiver in some other way.
It is thus known and normal practice for such surface acoustic wave components which can be interrogated by radio to be provided with respective individual coding, which makes it possible to distinguish the individual components from one another uniquely in the respective received signal within a large number of such surface acoustic wave components contained in the system.
First of all, two examples should be cited of the application options for such coded surface acoustic wave components that can be interrogated by radio. One of these examples is for such a surface acoustic wave component with coding to be fitted, for example, to an object that can be identified in an appropriate manner by the component or its coding. Such components are also known as ID tags. Another example is where the surface acoustic wave component has the additional characteristic, or is equipped with such an additional characteristic, as a sensor for, for example, measuring a temperature, a force variable and/or other physical, chemical or such like state variables. Such applications and refinements of a surface acoustic wave component relating to them are known.
Various principles are possible for producing a coded radio response signal from an interrogation signal. One example is to provide reflector elements for the coding, which are disposed such that they are managed in a known manner to the configuration of the already mentioned interdigital structure of the transducer. Such reflector elements are generally strip elements, which are provided on/in the surface of the substrate wafer in the path of the main wave propagation direction of the surface acoustic wave. As a further example for code elements and instead of such the reflector elements, resonators can also be assigned to the transducer or transducers, and they will also be described further below.
An individual reflector element produces a surface acoustic wave component response signal that is shifted in time with respect to the interrogation signal, that is to say with respect to the transmitted pulse. A component which, instead of this, is provided with resonators produces a response signal at an appropriate specific (resonant) frequency. A respective large number of reflectors disposed in different positions (with respect to one another and with respect to the transducer) produce a corresponding large number of pulse response signals shifted differently in time, with the mutual time shifts being dependent on the positions of the relevant reflectors with respect to one another. A corresponding situation applies to the various response resonant frequencies for a respective number of different resonators provided for different frequencies.
The response signal to be produced by the surface acoustic wave component in response to a radio interrogation signal is thus, in the case of reflectors, an additive superimposition of response signal elements offset in time with respect to one another or, in the case of resonators, an additive superimposition of a correspondingly large number of sinusoidal, limited-time (generally exponentially decaying) response signal elements at frequencies which differ from one another. A respective surface acoustic wave component is normally identified by determining the reception times corresponding to the selected positions of the individual reflectors in the relevant component. The resonator principle results in amplitudes in the received spectrum at frequency support points that correspond to the selected resonant frequencies of the individual resonators. The coding or the impressed code of a relevant reflector-coded surface acoustic wave component thus physically/structurally contains coded positioning of the individual reflectors that are provided, with respect to a reference reflector element or with respect to the position of the transducer on the surface of the substrate wafer. When resonators are used for coding, the various resonant frequencies, which are provided in a selective manner, of the individual resonators result in the code impressed on the respective component.
One problem that is associated with this is that the structure resolution of the associated measurement system is always limited. In this case, structure resolution refers to the capability of the system (in this case essentially containing the transmitter, the surface acoustic wave component and the receiver) to identify two reflection or resonant response signal elements from two reflectors disposed immediately adjacent to one another on the substrate wafer or from two resonators with immediately adjacent resonant frequencies, as being two response signal elements, which are separated from one another, in each case. In systems with time measurement (reflectors), the time structure resolution (&Dgr;t) is inversely proportional to the spectral bandwidth B used for the system/the measurement, that is to say &Dgr;t is proportional to 1/B.
In a system using frequency measurements (resonators), the relationships are in principle analogous, that is to say, in this case, the structure resolution, &Dgr;f is in this case based on the quality of the system, that is to say it is inversely proportional to the time duration t of the measurement signals (&Dgr;f is proportional to 1/
Reindl Leonhard
Schmidt Frank
Sczesny Oliver
Vossiek Martin
Dougherty Thomas M.
Greenberg Laurence A.
Locher Ralph E.
Siemens Aktiengesellschaft
Stemer Werner H.
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