Product having a sensor and a surface acoustic wave element, as well as a method and arrangement for determining a measurement variable, which corresponds to a reactance, by a sensor

Abstract

An electrical-technical product has a sensor ( 1 ) through which can be supplied a measured variable corresponding to a reactive resistance within a range of measurement, a matching network ( 2 ) and a surface acoustic wave (SAW) element in which the sensor is connected via the matching network ( 2 ) to a first reflector of the SAW element ( 3 ), and the first reflector ( 4 ) forms a resonator with the matching network ( 2 ) and the sensor ( 1 ). The resonator for one value of the measured variable within the range of measurement, is tuned to an acoustic surface wave on the surface wave element ( 3 ), in view of a reflection of the surface wave propagating at the first reflector ( 4 ). The resonance is determined by a maximum reflectivity of the first reflector ( 4 ).

1 . A product having a sensor ( 1 ), by means of which a measurement variable which corresponds to a reactance and which is within a measurement range can be supplied, having a matching network ( 2 ) and having a surface acoustic wave element ( 3 ), with the sensor ( 1 ) being connected via the matching network ( 2 ) to a first reflector ( 4 ) in the surface acoustic wave element ( 3 ), and the first reflector ( 4 ) together with the matching network ( 2 ) and the sensor ( 1 ) forming a resonator, characterized in that, for a value of the measurement variable within the measurement range, the resonator has a resonance with respect to a reflection of a surface acoustic wave, which propagates on the surface acoustic wave element ( 3 ), on the first reflector ( 4 ).  
     
     
         2 . The product as claimed in  claim 1 , in which the resonance is governed by the maximum reflectivity of the first reflector ( 4 ).  
     
     
         3 . The product as claimed in one of the preceding claims, in which the resonance is unique within the measurement range.  
     
     
         4 . The product as claimed in one of the preceding claims, in which the measurement variable is a capacitance.  
     
     
         5 . The product as claimed in  claim 4 , in which the matching network ( 2 ) is an inductance ( 2 ) connected in series with the sensor ( 1 ).  
     
     
         6 . The product as claimed in one of the preceding claims, in which the surface acoustic wave element ( 3 ) has a second reflector ( 5 ).  
     
     
         7 . The product as claimed in  claim 6 , in which the second resonator ( 5 ) is not switched.  
     
     
         8 . The product as claimed in one of the preceding claims, in which the surface acoustic wave element ( 3 ) has an electroacoustic transducer ( 6 ), to which an antenna ( 7 ) is connected.  
     
     
         9 . A method for determining a measurement variable, which corresponds to a reactance, within a measurement range by a sensor ( 1 ), which is connected via a matching network ( 2 ) to a first reflector ( 4 ) in a surface acoustic wave element ( 3 ), and which, together with the first reflector ( 4 ) and the matching network ( 2 ), forms a resonator, which resonator has, for a value of the measurement variable within the measurement range, a resonance with respect to a reflection of a surface acoustic wave, which propagates on the surface acoustic wave element ( 3 ), on the first reflector ( 4 ), comprising the following steps: 
 a) production of a surface acoustic wave which propagates on the surface acoustic wave element ( 3 );    b) production of a first reflected acoustic wave by reflection of the surface acoustic wave on the first reflector ( 4 );    c) reception of the first reflected surface acoustic wave; and    d) determination of the measurement variable from a phase of the first reflected surface acoustic wave.    
     
     
         10 . The method as claimed in  claim 9 , in which the surface acoustic wave is converted from an incoming electromagnetic signal and the reflected surface acoustic wave to an outgoing electromagnetic signal, and the measurement variable is determined from the outgoing electromagnetic signal.  
     
     
         11 . The method as claimed in  claim 10 , in which the incoming signal is received via an antenna ( 7 ), and the outgoing signal is transmitted via the antenna ( 7 ).  
     
     
         12 . The method as claimed in one of  claims 9  to  11 , in which a second reflected surface acoustic wave is produced by reflection of the surface acoustic wave on a second reflector ( 5 ) in the surface acoustic wave element ( 3 ), the second reflected surface acoustic wave is likewise received, and the measurement variable is determined from a phase difference between the first and the second reflected surface acoustic waves.  
     
     
         13 . An arrangement for determining a measurement variable, which corresponds to a reactance, within a measurement range by a sensor ( 1 ), which is connected via a matching network ( 2 ) to a first reflector ( 4 ) in a surface acoustic wave element ( 3 ), and which, together with the first reflector ( 4 ) and the matching network ( 2 ), forms a resonator, which resonator has, for a value of the measurement variable within the measurement range, a resonance with respect to a reflection of a surface acoustic wave, which propagates on the surface acoustic wave element ( 3 ), on the first reflector ( 4 ), comprising means ( 6 ,  7 ,  8 ) for: 
 a) production of a surface acoustic surface wave which propagates on the surface acoustic wave element ( 3 );    b) production of a first reflected surface acoustic wave produced by reflection of the surface acoustic wave on the first reflector ( 4 ); and    c) determination of the measurement variable from a phase of the first reflected surface acoustic wave.    
     
     
         14 . The arrangement as claimed in  claim 13 , in which the means ( 6 ,  7 ,  8 ) comprise an electroacoustic transducer ( 6 ) on the surface acoustic wave element ( 3 ), an antenna ( 7 ) connected to it, and an evaluation appliance ( 8 ) which is mechanically separate from the sensor ( 1 ) and from the surface acoustic wave element ( 3 ).  
     
     
         15 . The arrangement as claimed in  claim 14 , in which the evaluation appliance ( 8 ) has a transceiver ( 9 ) for producing an incoming electromagnetic signal, which is to be transmitted to the antenna ( 7 ) and is to be converted by the transducer ( 6 ), and for receiving an outgoing electromagnetic signal, which is converted by the transducer ( 6 ), and has a phase discriminator ( 10 ) for determining the measurement variable.