Passive interrogator label system with a surface acoustic wave transponder operating at its third harmonic and having increased bandwidth
First Claim
1. In an interrogation system having means for producing an interrogating signal in a prescribed frequency range and a passive transponder for transmitting a reply signal containing encoded information in response to the receipt of said interrogating signal, said transponder comprising:
- (a) a substrate having a substrate surface, said substrate being capable of propagating acoustic waves on said surface along a plurality of paths of travel;
(b) at least one transducer arranged on said surface for converting between electrical energy and surface acoustic wave (SAW) energy which propagates on said surface along said paths of travel, said transducer having its fundamental, resonant frequency fo =f/n, where f is a frequency within said prescribed range and n is an odd integer;
said transducer comprising an interdigital finger structure, with adjacent, parallel fingers spaced apart by a distance λ
0 /2, each finger being split into two parallel, electrically connected finger elements, each being spaced apart by a distance of λ
0 /4 and having a width of approximately λ
0 /8, where λ
is the SAW wavelength on said surface at said fundamental frequency f0 ;
adjacent ones of said fingers being electrically connected at their opposite ends, respectively, to form a plurality of finger pairs, each pair being capable of converting between electrical energy and SAW energy;
said transducer having a sufficient number of finger pairs to convert at least approximately 40% of the supplied energy into another form of energy; and
said transducer having a bandwidth of at least said prescribed frequency range;
(c) a plurality of acoustic wave reflectors arranged on said surface along said paths of travel for reflecting said SAW energy back toward said transducer; and
(d) circuit means electrically connected to said opposite ends, respectively, of said finger pairs in said transducer, for supplying said interrogating signal to said transducer and for receiving said reply signal from said transducer.
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Accused Products
Abstract
A "passive interrogator label system" (PILS) is disclosed with passive, SAW transponders which are capable of receiving an interrogation signal, processing this signal and transmitting a reply signal that is derived from the interrogation signal and contains encoded information. The SAW transducers employed in the transponders are operated at their third harmonic and comprise split fingers which reduce SAW reflections. These transducers are also shaped to increase their bandwidth and to reduce their capacitance. The bus bars connecting the transducers are formed of double thickness to reduce ohmic resistance losses and these bus bars as well as the transponder phase delay pads have two levels of serrations on their edges to substantially cancel reflections. SAW reflectors in the transponder are provided with shorts between successive fingers to reduce ohmic resistance losses and to render them less susceptible to fabrication errors.
65 Citations
19 Claims
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1. In an interrogation system having means for producing an interrogating signal in a prescribed frequency range and a passive transponder for transmitting a reply signal containing encoded information in response to the receipt of said interrogating signal, said transponder comprising:
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(a) a substrate having a substrate surface, said substrate being capable of propagating acoustic waves on said surface along a plurality of paths of travel; (b) at least one transducer arranged on said surface for converting between electrical energy and surface acoustic wave (SAW) energy which propagates on said surface along said paths of travel, said transducer having its fundamental, resonant frequency fo =f/n, where f is a frequency within said prescribed range and n is an odd integer;
said transducer comprising an interdigital finger structure, with adjacent, parallel fingers spaced apart by a distance λ
0 /2, each finger being split into two parallel, electrically connected finger elements, each being spaced apart by a distance of λ
0 /4 and having a width of approximately λ
0 /8, where λ
is the SAW wavelength on said surface at said fundamental frequency f0 ;
adjacent ones of said fingers being electrically connected at their opposite ends, respectively, to form a plurality of finger pairs, each pair being capable of converting between electrical energy and SAW energy;
said transducer having a sufficient number of finger pairs to convert at least approximately 40% of the supplied energy into another form of energy; and
said transducer having a bandwidth of at least said prescribed frequency range;(c) a plurality of acoustic wave reflectors arranged on said surface along said paths of travel for reflecting said SAW energy back toward said transducer; and (d) circuit means electrically connected to said opposite ends, respectively, of said finger pairs in said transducer, for supplying said interrogating signal to said transducer and for receiving said reply signal from said transducer. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19)
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Specification