Multiplexing surface acoustic wave sensors with delay line coding
A multiplexing surface acoustic wave (SAW) device for simultaneous excitation of SAW sensors or simultaneous sensing of multiple analytes, targets or bio-agents is described. The device includes a plurality of SAW sensors arranged in an array. Each sensor has a delay line and each of the delay lines are different in length. The sensors of the multiplexing SAW device are excited simultaneously to generate an array of surface acoustic waves propagating along the delay lines of each SAW sensor. Because the length of each delay line is different for each SAW sensor, the propagation time of the surface acoustic waves varies in based at least in part on the length variation. A compressed pulse train can be generated with a specific time delay according to the length difference of delay lines, and phase or other information of the compressed pulse can be extracted.
1 . A surface acoustic wave (SAW) device, comprising:
a piezoelectric substrate; and
a plurality of SAW sensors attached to the piezoelectric substrate and arranged on a surface of the piezoelectric substrate, the plurality of SAW sensors including
a first SAW sensor comprising a first delay line configured to propagate a first surface acoustic wave,
wherein the first SAW sensor comprises a transducer positioned on the substrate and a first reflector and a second reflector, each positioned on the substrate opposite the transducer,
wherein the transducer transmits the first surface acoustic wave along the first delay line, and the transducer receives the first surface acoustic wave after the first surface acoustic wave reflects off at least one of the first and second reflectors and propagates along the first delay line twice,
wherein the first delay line comprises a guiding layer on the first delay line that confines propagation of the first surface acoustic wave and a sensitive layer on the guiding layer of the first delay line of each of the plurality of SAW sensors,
wherein the guiding layer comprises at least one of a polymer, SiO 2 , or ZnO, and the sensitive layer attaches to or reacts with at least one analyte, and
wherein the guiding layer extends along at least a portion of the first delay line;
a second SAW sensor comprising a second delay line configured to propagate a second surface acoustic wave, wherein the second SAW sensor comprises a second transducer positioned on the substrate, wherein a length of the first delay line is greater than a length of the second delay line,
wherein each of the plurality of SAW sensors is configured to simultaneously receive an excitation signal; and
one or more processors in communication with each of the plurality of SAW sensors, the one or more processors configured to generate a receiving signal based on a signal received from the plurality of SAW sensors,
wherein the receiving signal comprises a compressed pulse train having a plurality of pulses, each pulse corresponding to a respective one of the plurality of SAW sensors.
2 . The SAW device of claim 1 , wherein the first reflector is positioned farther from the transducer than the second reflector along the first delay line.
3 . The SAW device of claim 2 , wherein the first reflector is configured to reflect a surface acoustic wave having a first frequency and the second reflector is configured to reflect a surface acoustic wave having a second frequency.
4 . The SAW device of claim 1 , wherein the first SAW sensor comprises a first pair of electrical contacts and the second SAW sensor comprises a second pair of electrical contacts, and wherein the first and second pairs of electrical contacts are electrically connected.
5 . The SAW device of claim 1 , wherein each of the plurality of SAW sensors is electrically connected to a common electrical connection configured to deliver the excitation signal simultaneously to each of the plurality of SAW sensors.
6 . The SAW device of claim 5 , wherein the excitation signal includes at least one of a pulse voltage, a sinusoidal electrical signal, frequency modulation, linear frequency modulation, hyperbolic frequency modulation, orthogonal frequency coding, random modulation, continuous phase modulation, frequency shift key, multi-frequency shift key, phase shift key, wavelet modulation, or a wideband frequency signal.
7 . The SAW device of claim 1 , wherein a timing of each pulse of the compressed pulse train is based at least in part on a length of the delay line of the corresponding SAW sensor.
8 . The SAW device of claim 7 , wherein the one or more processors are further configured to determine, monitor, or identify the at least one analyte based at least in part on the receiving signal.
9 . The SAW device of claim 8 , wherein the one or more processors are configured to determine, monitor, or identify the at least one analyte by detecting a variance in amplitude, phase, frequency, or time-delay between at least two of a pulse corresponding to an excitation signal, a pulse corresponding to the first SAW sensor, or a pulse corresponding to the second SAW sensor.
10 . The SAW device of claim 7 , wherein the one or more processors generate the compressed pulse train by correlating a received signal with a reference signal corresponding to the excitation signal.
11 . The SAW device of claim 10 , wherein the one or more processors are configured to determine a concentration of the at least one analyte based on a ratio of an amplitude of a first pulse of the compressed pulse train corresponding to the first SAW sensor, to an amplitude of a second pulse of the compressed pulse train corresponding to the second SAW sensor.
12 . The SAW device of claim 11 , wherein the first pulse and the second pulse are separated in time by an amount based at least in part on a difference between the length of the first delay line and the length of the second delay line.
13 . The SAW device of claim 10 , wherein the plurality of pulses of the compressed pulse train comprises a pulse corresponding to the excitation signal.
14 . The sensor of claim 1 , wherein the piezoelectric substrate comprises at least one of 36° Y quartz, 36° YX lithium tantalite, langasite, langatate, langanite, lead zirconate titanate, cadmium sulfide, berlinite, lithium iodate, lithium tetraborate, or bismuth germanium oxide.
15 . The sensor of claim 1 , wherein the piezoelectric substrate comprises a piezoelectric crystal layer, comprising a thickness greater than a Love Wave penetration depth on a non-piezoelectric substrate.
16 . The sensor of claim 1 , further comprising a detector for measuring a phase response of surface acoustic waves as a function of the at least one analyte added to the sensitive layer, wherein the sensitive layer comprises a biologically sensitive interface for capturing analytes from a liquid medium or a chemically sensitive interface for absorbing analytes from a liquid medium.
17 . The sensor of claim 1 , wherein the first surface acoustic wave corresponding to the first SAW sensor comprises a frequency greater than 100 MHz.