# US 2013/0278357 A1 · Maximally flat frequency coded (mffc) passive wireless saw rfid tags and sensors > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2013/0278357 A1 - Document ID: US20130278357A1 - Status: Published application - Kind: A1 - Application number: 13/653,391 - Filed: 2012-10-16 - Published: 2013-10-24 - Earliest claimed: 2011-10-16 - Assignees: Mnemonics, Inc. - Applicants: Mnemonics, Inc. - Inventors: Donald Mark Haines - Web page: https://patentgrep.com/patent/US20130278357A1 ## CPC - H03H 9/64: using surface acoustic waves - H03H 9/642: {SAW transducers details for remote interrogation systems, e.g. surface acoustic wave transducers details for ID-tags (remote interrogation systems per se G06K7/10009, G01S13/74)} - H03H: IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS (waveguides, resonators, lines or other devices of the waveguide type H01P) ## Abstract A surface acoustic wave device responsive to an interrogation signal for producing a return signal. The surface acoustic wave device comprises an antenna for receiving the interrogation signal, a piezoelectric substrate, one or more frequency-selective reflective arrays disposed on the piezoelectric substrate, an interdigital transducer for launching an incident surface acoustic wave on the substrate in response to the interrogation signal, the incident surface acoustic wave propagating to the one or more frequency-selective reflective arrays, a reflected surface acoustic wave reflected from each one of the reflective arrays, the interdigital transducer receiving the reflected surface acoustic waves, and the return signal, responsive to each reflected surface acoustic waves. ## Claims ### Claim 1 A surface acoustic wave device responsive to an interrogation signal for producing a return signal, the surface acoustic wave device comprising: an antenna for receiving the interrogation signal; a piezoelectric substrate; one or more frequency-selective reflective arrays disposed on the piezoelectric substrate; an interdigital transducer for launching an incident surface acoustic wave on the substrate in response to the interrogation signal, the incident surface acoustic wave propagating to the one or more frequency-selective reflective arrays; a reflected surface acoustic wave reflected from each one of the reflective arrays; the interdigital transducer receiving the reflected surface acoustic waves; and the return signal, responsive to each reflected surface acoustic waves. ### Claim 2 (depends on 1) The surface acoustic wave device of claim 1 wherein a frequency difference Δf between a frequency of the reflected surface acoustic wave reflected from a first frequency-selective reflective array and the reflected surface acoustic wave reflected from a second reflective array is selected to minimize amplitude ripple in a power spectrum of the return signal. ### Claim 3 (depends on 2) The surface acoustic wave device of claim 2 wherein the frequency difference Δf is selected such that the power spectra of the reflected surface acoustic wave from each of the frequency-selective reflective arrays overlap at a frequency at about a half power value. ### Claim 4 (depends on 1) The surface acoustic wave device of claim 1 wherein the return signal exhibits a maximally flat magnitude as a function of frequency. ### Claim 5 (depends on 1) The surface acoustic wave device of claim 1 wherein each of the frequency selective reflective arrays is amplitude weighted with a predetermined window function that modifies the amplitude of the incident surface acoustic wave such that an impulse response of each frequency-selective reflective arrays is an amplitude weighted RF pulse and the window function defines the shape of a pulse envelope. ### Claim 6 (depends on 1) The surface acoustic wave device of claim 1 wherein each of the frequency selective reflective arrays comprises a plurality of reflector elements, and wherein a spacing between each one of the plurality of reflector elements determines a frequency of the reflected surface acoustic wave from each of the reflective arrays. ### Claim 7 (depends on 1) The surface acoustic wave device of claim 1 wherein a peak frequency response of each frequency-selective reflective array is spaced by a frequency difference that causes a response spectrum of each reflective array to intersect the response spectrum of a next reflective array at about a half power point of both spectra, such that the combined power spectrum of all the reflective arrays is maximally flat. ### Claim 8 (depends on 1) The surface acoustic wave device of claim 1 wherein a power spectrum associated with each successive frequency chip in a set of maximally flat frequency coded code chips, and therefore the power spectrum of the reflective array of the SAW device, intersects the power spectrum of the next higher array at about a −3 dBc point of each chip's spectrum. ### Claim 9 (depends on 1) The surface acoustic wave device of claim 1 wherein each frequency-selective reflective array has a center frequency and the reflective arrays are disposed on the substrate in order of lowest to highest center frequency or from highest to lowest center frequency. ### Claim 10 (depends on 1) The surface acoustic wave device of claim 1 wherein a time delay gap between each successive frequency selective reflective array is selective. ### Claim 11 (depends on 10) The surface acoustic wave device of claim 10 wherein a time delay gap between each successive frequency selective reflective array is about zero. ### Claim 12 (depends on 1) The surface acoustic wave device of claim 1 wherein each of the frequency selective reflective arrays comprises a plurality of reflector elements, and wherein a spacing between each one of the plurality of reflector elements determines a frequency of the reflected surface acoustic wave from each of the reflective arrays and wherein each one of the frequency selective reflective arrays exhibits a different frequency of the reflected surface acoustic wave. ### Claim 13 A surface acoustic wave device responsive to an interrogation signal for producing a return signal, the surface acoustic wave device comprising: an antenna for receiving the interrogation signal; a piezoelectric substrate; one or more frequency selective reflective arrays formed on the piezoelectric substrate; a first interdigital transducer responsive to the interrogation signal for launching a surface acoustic wave on the substrate responsive thereto, the surface acoustic wave propagating to the one or more frequency selective reflective arrays; a second interdigital transducer; a reflected surface acoustic wave reflected from each one of the frequency-selective reflective arrays to the second interdigital transducer; and the second interdigital transducer producing the return signal responsive to each reflected surface acoustic wave. ### Claim 14 (depends on 1) The surface acoustic wave device of claim 1 wherein each one of the one or more frequency-selective reflective arrays provides a reflected signal such that a composite signal responsive to each of the reflected signals exhibits one or more of a desired frequency, phase, time delay and amplitude. ### Claim 15 A surface acoustic wave system comprising a plurality of surface acoustic wave devices, each surface acoustic wave device comprising a an antenna for receiving the interrogation signal; a piezoelectric substrate; one or more frequency-selective reflective arrays disposed on the piezoelectric substrate; an interdigital transducer for launching a surface acoustic wave on the substrate, the surface acoustic wave propagating to the one or more frequency-selective reflective arrays; a reflected surface acoustic wave reflected from each one of the frequency-selective reflective arrays; the interdigital transducer receiving each of the reflected surface acoustic waves; the return signal, responsive to each reflected surface acoustic wave, formed at the interdigital transducer array; and wherein each one of the plurality of surface acoustic wave devices has an impulse response with a different delay path to a first reflective array of each one of the plurality of surface acoustic wave devices, thereby shifting an impulse response of each one of the plurality of surface acoustic wave devices by a different increment of time. ### Claim 16 (depends on 15) The surface acoustic wave system of claim 15 wherein each one of the plurality of surface acoustic wave devices exhibits a code chip set that differs from the other surface acoustic wave devices in the system according to one or more of frequency, phase, amplitude and time delay. ### Claim 17 (depends on 15) The surface acoustic wave system of claim 15 wherein each one of the plurality of surface acoustic wave devices of the system exhibits a different impulse response. ### Claim 18 (depends on 15) The surface acoustic wave system of claim 15 wherein a sequence of code chips, with one code chip embodied in each selective-frequency reflective array of each one of the plurality of surface acoustic wave devices is selected to minimize interference from other ones of the plurality of surface acoustic wave devices. ### Claim 19 (depends on 18) The surface acoustic wave system of claim 18 wherein the interference is minimized by avoiding producing a return signal from a first one of the plurality of surface acoustic wave devices of a same or adjacent frequency at about a same time as a return signal from a second one of the plurality of surface acoustic wave devices.