Patent Application
20130130362
The present invention relates generally to the monitoring of physical, chemical, and biological properties of various fluids, polymers, and composite thin film materials. As used herein the term “fluid” refers broadly to both liquids and gases composed of one chemical element or compound, and/or mixtures composed of more than one component, including gaseous or liquid solutions, colloids, suspensions, and other heterogeneous phase mixtures. The present invention relates more particularly to the detection, identification, and quantitation of particular chemical or biological species in the sample being measured, and determination of physical properties of the sample such as temperature, pressure, and viscosity, among others; and in particular to apparatus, systems, devices, and methods for monitoring such materials and analyzing the properties thereof using surface acoustic wave technology.
Detecting the presence and measuring the concentration of certain chemical and biological substances is significant in a wide range of applications, including but not limited to industrial process control, agricultural and food production, vehicle condition monitoring, environmental contamination monitoring, and human and veterinary medicine applications such as anesthesia monitoring and clinical diagnostics. Being able to provide real-time information on composition of fluids, and to simultaneously provide physical parameter measurements such as temperature, pressure, flow, and viscosity of the fluid and/or measurements of the surrounding system such as temperature, pressure, and strain, enables optimization of system operation across these disparate applications. Real-time monitoring of the characteristics and properties of thin films, and the interactions of such films with fluids, may also enable tools suitable to study the reaction kinetics of chemical and biological processes necessary for drug discovery and evaluation of efficacy, and a wide range of other fundamental investigations.
Sensors based on surface-launched acoustic wave devices have been developed since the 1980's for application to physical measurements (temperature, pressure, torque, strain, etc.) and to a wide range of chemical and biological detection problems (see, the thirty-five references cited herein). These widely varying devices have utilized several operating modes and corresponding wave propagation modes, including the traditional Rayleigh wave (or Surface Acoustic Wave (SAW)), the surface transverse wave (STW), the surface skimming bulk wave (SSBW), the SSBW that has been guided to the surface via a layer, known as the Love wave, the shear-horizontally polarized acoustic plate mode (SH-APM), the flexural plate wave (FPW) or Lamb wave, the layer guided acoustic plate mode (LG-APM), and the thickness shear mode (TSM) bulk wave (as used in quartz crystal microbalance—QCM devices), and the layer guided shear horizontal acoustic plate mode (LG-SHAPM). A number of different device types have been recognized using these diverse wave modes, including resonators, delay lines, differential delay lines, and reflective delay lines (tag or ID devices). These devices have been operated within a wide range of wired and wireless interrogation system architectures, which have generally been designed specifically to operate with the selected sensor(s). In most cases, wireless interrogation has been applied to physical sensors, and not to biological or chemical sensors. These system architectures include pulsed (dispersive of non-dispersive) radar-like delay measurement systems (Reindl, L. M., et. al., “SAW-Based Radio Sensor Systems,” IEEE Sensors Journal, Vol. 1, No. 1, pp. 69-78, June 2001; U.S. Pat. No. 6,144,332 to Reindl et. al.), Fourier transform measurement systems (Hamsch, M., et. al., “Temperature measurement system and wireless SAW sensors,” IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, Vol. 51, No. 11, pp. 1449-1456, November 2004), and delay line and resonator-based oscillator systems (Buff, W., et. al., “Universal pressure and temperature SAW sensor for wireless applications,” Proceedings of the 1997 IEEE Ultrasonics Symposium, pp. 359-362; Pohl, A., and L. Reindl, “Measurement of physical parameters of car tires using passive SAW sensors,” AMAA 1998, Berlin Germany; U.S. Pat. No. 4,312,228 to Wohltjen). A time-integrating correlator based interrogation system has recently been introduced by the inventors of the present invention (U.S. Pat. No. 7,434,989 to Solie; U.S. Pat. No. 7,268,662 to Hines). The system architecture has usually been selected based on specific device characteristics and application requirements, and generally involves absolute or differential measurements of sensor frequency, phase, delay, amplitude, or power spectral density, and changes in these quantities with exposure, to provide the output sensor measurement. Historically, signal amplitude has only been used as a measurand for devices operated in a wired mode, due to the variation in response amplitude caused by changes in distance between the interrogation system and the sensor(s).
The relative advantages of each wave mode and device type make them suitable for different applications. Rayleigh wave sensors, for instance, involve particle displacements that include a component normal to the substrate surface. When used in a liquid, this component generates a compressional wave in the liquid, causing wave energy to leak into the liquid. This energy leakage results in large attenuation of the Rayleigh wave, often referred to as “damping”. This effect makes Rayleigh waves useful only for gas phase sensing, and not applicable to sensing in the liquid phase. This energy leakage occurs whenever the wave motion in the substrate involves a component of displacement normal to the substrate surface, and the speed of the sound wave in the device is greater than the speed of sound in the liquid (or in the layer coating the device). Certain wave modes, such as flexural plate waves (FPWs), do involve a normal component of displacement, but have wave velocities lower than the speed of sound in the liquid. Leakage therefore does not occur, and FPW devices can operate successfully in liquid environments. Other wave modes that do not involve components of displacement normal to the substrate surface are also operable in both gas and liquid phase. These include Love waves, STW, SH-APM, and LG-APM, LG-SH-APM.
Rayleigh waves coated with polymers have been used extensively for chemical vapor detection. QCM devices have also been applied to characterization of interfacial chemistry in both vapor and liquid environments (Thompson book). In recent years, there has been significant research into the application of STW, APM, FPW, and Love waves to liquid based biosensing (the references listed below represent a small sample of relevant publications).
Love waves are often cited as having the highest possible mass sensitivity (Gizeli, E., Stevenson, A. C., Goddard, N. J., and Lowe, C. R., “A novel Love-plate acoustic sensor utilizing polymer overlayers”, IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, Vol. 39, No. 5, September 1992, pp. 657-659). STW devices have the practical drawback of difficulty of creating a physical interface between the fluid (liquid or gas) sample chamber and the active device surface. In STW devices, the fluid must be constrained to interact with the surface of the device on which the wave is generated and propagates. This involves making a liquid or gas tight contact on the substrate surface without interfering with the generation and propagation of the acoustic wave. FPW, APM, and LG-APM devices, by comparison, have an advantage in that a gas or liquid sample can interact with the back side of the device, leaving the wave generation process (on the front side of the device) unaffected.
Most FPW devices reported have been fabricated using silicon substrates with deposited surface layers with desired properties. The Silicon substrates are then etched away in the region beneath the sensor active region, leaving a membrane consisting of the surface layer only. These layers may be composed of various films, and the backside of the device may be used to allow exposure of the device to liquid samples, while keeping the electrical connections of the device separated from the sample. Typical films consist of a structural component such as silicon nitride (Si3N4), combined with a ground electrode layer (often aluminum), followed by a piezoelectric film layer such as zinc oxide (ZnO), and surface fabricated electrodes (Costello, B. J., Martin, B. A., and White, R. M., “Acoustic plate-wave biosensing”, Proceedings of the IEEE Engineering in Medicine and Biology Society 11th Annual International Conference, 1989). Composite layer thicknesses typically range from around 3 microns to around 6 microns in thickness, and the resulting devices have operating frequencies in the low MHz range.
APM devices, by comparison, have generally been fabricated from plates of piezoelectric materials, often using the thickness of standard wafers. Typical devices may utilize substrates with thickness of 0.5 mm (20 mils). APM devices have been demonstrated on quartz and on high coupling substrates such as lithium niobate. Typical APM devices operate in the low hundred MHz range (Dahint—1997 FCS Immunosensor paper; Dahint, R., Bender, F., and Morhard, F., “Operation of acoustic plate mode immunosensors incomplex biological media”, Anal. Chem. Vol. 71, 1999, pp. 3150-3156; Zimmermann, C., Rebiere, D., Dejous, C., Pistre, J, and Chastaing, E., “Evaluation of Love waves chemical sensors to detect organophosphorous compounds: comparison to SAW and SH-APM devices”, Proceedings of the 2000 IEEE International Frequency Control Symposium, pp. 47-51).
Love wave devices consist of a substrate and a top layer that acts as a guiding layer for the acoustic wave. Generally, the substrate is piezoelectric, such as quartz, and the guiding layer is made of a material with a sound speed lower than the wave speed in the substrate. On quartz, amorphous SiO2 and various polymers (PMMA, etc.) are often utilized as the guiding layer. Standard thickness piezoelectric substrates are generally used, with varying thicknesses of guiding layers based on device design. Fundamental and harmonic device operation have been evaluated, resulting in operating frequencies ranging from roughly 100 MHz to over 300 MHz (Newton—electronic letters 2001 harmonic love wave).
Finally, layer-guided SH-APMs have been identified as shear horizontally polarized waves that occur in a system that consists of a finite substrate covered by a finite guiding layer of slower shear acoustic speed, and are analogous to either Love waves or to SH-APMs, depending on the precise structure of the device under consideration. It has been suggested that these devices will be capable of higher mass sensitivity than other previously identified device structures (McHale, G., Newton, M. I., and Martin, F., “Layer guided shear horizontally polarized acoustic plate modes”, Journal of Applied Physics, Vol. 91, No. 9, 1 May 2002, pp. 5735-5744), and biosensor devices have exploited this high sensitivity (U.S. Pat. No. 7,500,379 to Hines).
Due to the sensitivity of surface-launched acoustic wave sensors to changes in environmental parameters, it has been customary to utilize some sort of reference signal in the sensors or a reference device in the sensor systems. This has been accomplished in various ways. For example, differential delay line devices have been used to eliminate variations in electronic signals common to both delay paths, resulting in sensors that are only sensitive to variations in temperature (U.S. Provisional Patent Applications Nos. 61/512,309, 61/151,884, and 61/512,883 to Hines regarding SAW deposition monitor for ultra-thin films, July 2011 (not yet published); Malocha, D. C., D. Puccio, and D. Gallagher, “Orthogonal Frequency Coding for SAW Device Applications,” Proceedings of the 2004 IEEE International Ultrasonics, Ferroelectrics, and Frequency Control Symposium, Montreal Calif., August 2004; U.S. Pat. No. 6,144,332 to Reindl et. al.). Similarly, pressure sensors have been developed that utilize multiple transducer and/or reflector structures with wave propagation at different orientations on the substrate to provide information about temperature simultaneously with information about pressure, allowing for the unambiguous determination of both parameters using a single sensor device (Malocha, D. C., D. Puccio, and a Gallagher, “Orthogonal Frequency Coding for SAW Device Applications,” Proceedings of the 2004 IEEE International Ultrasonics, Ferroelectrics, and Frequency Control Symposium, Montreal Calif., August 2004; Puccio, D., D. C. Malocha, D. Gallagher, and J. Hines, “SAW Sensors Using Orthogonal Frequency Coding,” Proceedings of the 2004 IEEE International Ultrasonics, Ferroelectrics, and Frequency Control Symposium, Montreal Calif., August 2004; Hines, J. H., NASA Contract Number NNX10CD41P, “Rapid Hydrogen and Methane Sensors for Wireless Leak Detection”, Phase I SBIR Final Report, 29 Jul. 2010; Hines, J. H., NASA Contract Number NNX09CB77C, “Passive Wireless SAW Humidity Sensors and System”, Phase II STTR Final Report, 18 November, 2011). SAW-based chemical vapor sensor systems have historically utilized multiple polymer-coated SAW sensor devices in an array configuration. Polymers were selected for their chemical orthogonality, or their ability to selectively adsorb or absorb chemical vapors of interest. Patterns of vapor responses developed on the multi sensor arrays could then be characterized using pattern recognition techniques. Reference sensors that were hermetically sealed or otherwise protected from exposure to the vapors under test were generally included in the arrays in order to allow for accurate determination of the array response. These arrays were often temperature controlled, either through bulk temperature control of the sensor devices (using under package heating and cooling) or through on-chip heaters incorporated in the sensor devices (Sawtek Inc. internal reports (not published)). These temperature control elements (including on-chip heaters) could be used to thermally ramp sensors and observe the temperature (and thus time) dependent desorption of adsorbed of vapors, providing an additional metric useful for pattern recognition (Sawtek Inc. internal reports (not published)). Prior biosensor devices have generally been used individually or in pairs, where one device serves as a reference device for the pair. In most cases where arrays of sensors have been used in biological and/or chemical sensing, the array has been composed of multiple individual distinct sensor devices along with measurement electronics (the exception being (U.S. Pat. No. 7,500,379 to Hines)). Depending on the system configuration, the measurement electronics may be common (“shared” and used sequentially by all sensors in the array), or multi-channel electronics may be used, allowing the simultaneous (or near-simultaneous) measurement of all array elements.
Prior SAW based RF ID tags and physical sensors (including Malocha, D. C., D. Puccio, and D. Gallagher, “Orthogonal Frequency Coding for SAW Device Applications,” Proceedings of the 2004 IEEE International Ultrasonics, Ferroelectrics, and Frequency Control Symposium, Montreal Calif., August 2004; Puccio, D., D. C. Malocha, D. Gallagher, and J. Hines, “SAW Sensors Using Orthogonal Frequency Coding,” Proceedings of the 2004 IEEE International Ultrasonics, Ferroelectrics, and Frequency Control Symposium, Montreal Calif., August 2004; Hines, J. H., NASA Contract Number NNX10CD41P, “Rapid Hydrogen and Methane Sensors for Wireless Leak Detection”, Phase I SBIR Final Report, 29 Jul. 2010; Hines, J. H., NASA Contract Number NNX09CB77C, “Passive Wireless SAW Humidity Sensors and System”, Phase II STTR Final Report, 18 November, 2011) have utilized various coding techniques to allow identification of individual sensors within multisensor networks. Such sensors have also been accessed primarily via wireless radio frequency (RF) communication techniques. The ability to incorporate unique sensor identification and the potential wireless operation aspect of these sensors has not been exploited for chemical and biological sensing applications in vapors and liquids.
Surface launched acoustic wave chemical and biological sensor device embodiments have historically been intended for use in wired measurement systems, and have not included coding, frequency, or time diversity to generate multiple individually identifiable sensors. The most well known SAW chemical and biological sensor devices also involve absolute or differential measurements of sensor frequency, phase, delay, amplitude, or power spectral density, and changes in these quantities with exposure, to provide the output sensor measurement. Historically, signal amplitude has only been used as a measurand for devices operated in a wired mode, due to the variation in response amplitude caused by changes in distance between the interrogation system and the sensor(s). Typical SAW wireless sensor systems utilized differential frequency measurements, or differential delay measurements (one example of which is in U.S. Pat. No. 6,144,332 to Reindl et. al.).
A detailed description of devices that involve absolute or differential measurements of sensor frequency, phase, delay, and amplitude will not be included herein, as these have been widely reported for two decades in wired and wireless applications. A more detailed discussion of power spectral density based sensors is included in order to address the differences between these sensors and the present invention.
Patents previously issued to the inventors of the current invention teach a SAW-based sensor and system suitable for wired or wireless determination of hydrogen vapor concentration and/or temperature, based on changes in features of the power spectral density (PSD) of the sensor response (see U.S. Pat. No. 7,434,989 to Solie, and U.S. Pat. No. 7,268,662 to Hines). It has been established that SAW devices with three acoustic wave elements including at least one transducer can be constructed to produce two responses that are closely spaced in time, resulting in a train of notches in the frequency domain separated by the inverse of the delay difference in responses, windowed by the bandpass function produced by the SAW transducer and reflector elements.
Proper selection of the device passband (made up of half passbands 120 and 122) and time separation Δt (102) produces a device with one or more nulls in the passband. As the time separation between impulses varies, the string of nulls “accordians” in and out, with the DC end pinned. The sensitivity of the device can be varied by selecting the appropriate separation Δt (102), and by selecting at which null to operate. Nulls farther away from DC move faster for a given change in separation Δt. In addition, for a fixed passband, as the separation Δt (102) varies, the number of nulls in the passband can change. Also, as the relative amplitudes of the two impulses change, the depth and sharpness of the nulls changes. It should be noted that this technique can be extended to utilize multiple passbands rather than simply two window functions as shown in
In practice, the actual notches produced can be significantly sharper and narrower than shown in
Another recent invention utilizes SAW differential delay line devices with equal to significantly differing delays, that when combined with the films being deposited provide measurable changes in device response based on film deposition and properties.
U.S. Provisional Patent Applications Nos. 61/512,309, 61/151,884, and 61/512,883 entitled “SAW deposition monitor for ultra-thin films”, and U.S. Utility patent application Ser. No. 13/485,317 entitled “Surface Acoustic Wave monitor for deposition and analysis of ultra-thin films”, filed previously by one of the inventors of the present invention, teach a thin film deposition monitor device that utilizes changes in the notched PSD response of a device to provide real-time information on the properties of thin films as they are deposited.
The size of the changes observed in the frequency response notches, both in amplitude (i.e. notch depth) and in frequency, are quite large. Notches vary by over 40 dB in depth, and by many MHz in frequency in the simple example shown in
The accompanying drawings, which are incorporated into this specification, illustrate one or more exemplary embodiments of the inventions disclosed herein and, together with the detailed description, serve to explain the principles and exemplary implementations of these inventions. One of skill in the art will understand that the drawings are illustrative only, and that what is depicted therein may be adapted based on the text of the specification and the spirit and scope of the teachings herein.
In the drawings, where like reference numerals refer to like reference in the specification:
It should be understood that this invention is not limited to the particular methodology, protocols, etc., described herein and as such may vary. The terminology used herein is for the purpose of describing particular embodiments only, and is not intended to limit the scope of the present invention, which is defined solely by the claims.
As used herein and in the claims, the singular forms include the plural reference and vice versa unless the context clearly indicates otherwise. Other than in the operating examples, or where otherwise indicated, all numbers expressing quantities used herein should be understood as modified in all instances by the term “about.”
All publications identified are expressly incorporated herein by reference for the purpose of describing and disclosing, for example, the methodologies described in such publications that might be used in connection with the present invention. These publications are provided solely for their disclosure prior to the filing date of the present application. Nothing in this regard should be construed as an admission that the inventors are not entitled to antedate such disclosure by virtue of prior invention or for any other reason. All statements as to the date or representation as to the contents of these documents is based on the information available to the applicants and does not constitute any admission as to the correctness of the dates or contents of these documents.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as those commonly understood to one of ordinary skill in the art to which this invention pertains. Although any known methods, devices, and materials may be used in the practice or testing of the invention, the methods, devices, and materials in this regard are described herein.
Unless stated otherwise, or implicit from context, the following terms and phrases include the meanings provided below. Unless explicitly stated otherwise, or apparent from context, the terms and phrases below do not exclude the meaning that the term or phrase has acquired in the art to which it pertains. The definitions are provided to aid in describing particular embodiments of the aspects described herein, and are not intended to limit the claimed invention, because the scope of the invention is limited only by the claims. Further, unless otherwise required by context, singular terms shall include pluralities and plural terms shall include the singular.
As used herein the term “comprising” or “comprises” is used in reference to compositions, methods, and respective component(s) thereof, that are essential to the invention, yet open to the inclusion of unspecified elements, whether essential or not.
As used herein the term “consisting essentially of” refers to those elements required for a given embodiment. The term permits the presence of additional elements that do not materially affect the basic and novel or functional characteristic(s) of that embodiment of the invention.
The term “consisting of” refers to compositions, methods, and respective components thereof as described herein, which are exclusive of any element not recited in that description of the embodiment.
Other than in the operating examples, or where otherwise indicated, all numbers expressing quantities used herein should be understood as modified in all instances by the term “about” The term “about” when used in connection with percentages may mean ±1%.
The singular terms “a,” “an,” and “the” include plural referents unless context clearly indicates otherwise. Similarly, the word “or” is intended to include “and” unless the context clearly indicates otherwise. Thus for example, references to “the method” includes one or more methods, and/or steps of the type described herein and/or which will become apparent to those persons skilled in the art upon reading this disclosure and so forth.
Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of this disclosure, suitable methods and materials are described below. The term “comprises” means “includes.” The abbreviation, “e.g.” is derived from the Latin exempli gratia, and is used herein to indicate a non-limiting example. Thus, the abbreviation “e.g.” is synonymous with the term “for example.”
To the extent not already indicated, it will be understood by those of ordinary skill in the art that any one of the various embodiments herein described and illustrated may be further modified to incorporate features shown in any of the other embodiments disclosed herein.
The following examples illustrate some embodiments and aspects of the invention. It will be apparent to those skilled in the relevant art that various modifications, additions, substitutions, and the like can be performed without altering the spirit or scope of the invention, and such modifications and variations are encompassed within the scope of the invention as defined in the claims which follow. The following examples do not in any way limit the invention.
According to the present invention, a surface acoustic wave (SAW) based sensor device and system for detecting the presence of and measuring the concentration of chemical and biological analytes in vapor and liquid phase can include inherent temperature compensation, higher sensitivity to surface interactions than conventional surface launched acoustic wave chemical and biological sensor devices, and the capability to operate in a wired mode or in a wireless mode with the ability to measure the distance of the sensor from the wireless transceiver (in addition to measuring temperature and the chemical and/or biological analytes of interest). This device can also monitor changes in state of thin films, including but not limited to sensing glassy to rubbery transitions in polymers, and measurement of the kinetics of chemical and/or biological processes occurring at the surface of the device. Coding (code diversity), time diversity, and frequency diversity can be included in the device structure to enable production of groups of individually identifiable sensor devices capable of operating simultaneously within the field of view of a wireless transceiver. A transceiver circuit can be configured to provide wired or wireless interrogation of the sensor device or group of devices. Wireless operation can utilize the passive nature of these sensors, or can include active components in connection with the sensors to produce active sensor modules powered by either batteries or energy harvesting techniques.
The present invention can utilize a power spectral density (PSD) of a sensor response to determine desired measurement(s) in a manner different from that previously described. The presence, location, and depth of notches in the frequency response are not utilized for measurement in the present invention as was previously described. Rather, the present invention provides device embodiments that can produce PSD signals with amplitudes that change in different portions of the frequency domain response in reaction to variations in measured parameters. At least one reference response can be incorporated in the sensor signal, allowing determination of wireless range (for wireless applications) and temperature, in addition to the other measurements of interest.
Previously demonstrated PSD temperature sensor and chemical/film sensing devices relied on two different acoustic propagation paths with slightly offset delays to produce a reflected sensor filter response that has a notch in one portion of the passband. Movement of this notch in frequency (or changes in the number of notches and notch structure) in response to changes in target parameters was useful as a measurand. In this prior application, changes in attenuation of the SAW sensor response were not a factor, as changes in target parameters produced a change in frequency of the notch, number of notches, or notch structure in the device passband. Chemical and biological sensors for both liquid and vapor phase, however, involve the use of selective coatings that can produce changes in SAW device attenuation (in addition to impacting other performance parameters). The degree of attenuation often increases with increasing interaction with the target analytes of interest, due to increased viscoelasticity, and potentially to modified electrical conductivity of the film. For certain conductive films however, the change in conductivity caused by analyte interaction can cause a decrease in attenuation. Delay (or phase or frequency) also generally changes in these sensors due to the change in velocity, but this effect can be much smaller than the change in attenuation, which can exceed 50 dB.
In order to take advantage of the large changes in attenuation observed for surface launched acoustic wave (SAW) devices coated with selective films, a new SAW sensor structure was developed that can be read by a time integrating correlator transceiver, among other techniques. The basic device structure has a minimum of two acoustic propagation paths, one of which is left bare, and the other of which is coated with a sensitive film suitable to promote interactions with one specific target analyte. The SAW elements (transducers and/or reflectors) used in certain embodiments of these sensors are either tapered, meaning that the electrode spacing varies monotonically laterally across the transducer, with the widest spacing producing the lowest frequency acoustic wave, and the smallest electrode spacing producing the highest frequency wave, or are made up of discrete frequency subtransducers arrayed laterally across the device aperture (a structure referred to as “step-tapered”). Slanted transducers with varying pitch across the passband can also be utilized. For clarity, much of the remainder of this discussion will focus on the use of tapered transducers in embodiments of the present invention, although this is not intended to limit the embodiments or to exclude ordinary untapered transducers and reflectors, dispersive transducers and reflectors, and other structures including those mentioned above.
In the simplest embodiment, shown in
Tapered transducers have been used in high performance wideband SAW filters for decades, but have only recently been applied to SAW sensing (U.S. Pat. No. 7,434,989 to Solie; U.S. Pat. No. 7,268,662 to Hines; U.S. Provisional Patent Applications Nos. 61/512,309, 61/151,884, and 61/512,883 to Hines regarding SAW deposition monitor for ultra-thin films, July 2011 (not yet published)).
The frequency response of one particular set of devices produced according to the present invention by the inventors consists of eight frequency channels, each created in one of the acoustic paths produced by the subtransducers of the tapered transducer. As shown in
Humidity sensors according to the present invention have been demonstrated by the inventors under NASA contract NNX09CB77C. In these sensors, the lower frequency half passband (4 of 8 acoustic channels) was used as a reference response, and the high frequency half passband (the other 4 of 8 acoustic channels) was coated with a humidity sensitive nanostructured LiCl doped TiO2 film. When exposed to increased RH levels, the lower frequency components of the response are unaffected, while the high frequency components are attenuated significantly with increasing humidity levels. A time integrating correlator-based transceiver system developed by the team measures the integrated energy in each half passband of the sensor response, and the ratio of these energies is a measure of the humidity. A combination of code diversity and time diversity was implemented in this sensor system to produce a set of 16 individually identifiable sensors that can function simultaneously in the field of view of the transceiver. Both wired and wireless humidity readings have been demonstrated using this multi-sensor measurement system.
One skilled in the art will recognize that there are a wide range of device embodiments that can be used to implement chemical and/or biological sensor devices according to the present invention. A selection of these device types is shown herein. All of these devices can be implemented in single acoustic track formats, or in multiple acoustic track formats. One or multiple acoustic paths can be used to provide reference signals, and one or multiple acoustic tracks can be used to provide measurements for target analytes. These acoustic tracks can all be at different frequencies, as shown in
The transducers and/or reflectors described thus far are all non-dispersive, and similar embodiments could be envisioned that utilize transducers that are tapered, slanted, stepped tapered, apodized, withdrawal weighted, EWC, UDT, SPUDT, dispersive, and/or waveguide structures. Even reflective array compressor structures could be used to implement such a sensor, although such a device structure would be unnecessarily complex for most applications. All of these techniques could also be used to implement device embodiments using dispersive and harmonic techniques. In addition to implementing an attenuation-based sensor on a single substrate, it is possible to utilize multiple substrates to implement one embodiment of the present invention.
Also, one skilled in the art will recognize that these devices can be implemented on various substrate materials, and can utilize various acoustic wave propagation modes, in order to achieve performance required for specific applications. Performance suitable to measure analytes of interest in vapors and liquids; to monitor changes in thin film polymers, solids, nanostructured materials, and other films; to monitor the kinetics of reactions at the surface or the device or at the interface between an applied surface films and the adjacent environment; and to measure numerous other quantities can be achieved.
Any of a wide range of known coding techniques can be implemented in the transducers and/or reflectors. It would be understood by one versed in the art that simple on-off keying, phase modulation, pulse position modulation, and many other techniques could be used to enhance the number of codes available. The use of multiple delay “slots” within each code reflector nominal delay position is widely used to achieve increased code set size, and the use of multiple pulses per data group is also well known. Frequency diversity, code diversity, time diversity, and other know techniques can be combined to achieve sets of devices with desirable properties. Any of these techniques could be utilized in the aforementioned device embodiments to increase the number of sensors that can work together in a system. Devices utilizing such structures could be useful for RFID tag applications, where more than one deposition monitor is required within a system, and identification of individual devices is desired. In addition, combinations of these techniques may be advantageous in certain circumstances.
These embodiments can be extended to provide multiple acoustic tracks at different frequencies, either on a single die or on multiple die. One or more tracks can be used to provide reference measurements, and in some cases more than two SAW elements may be used in a single track in order to allow extraction of the desired measurement. One or more acoustic tracks can be used with sensitive coatings to measure multiple analytes simultaneously. The transceiver system architecture will be designed to include matched filters for each frequency band used in the sensor device(s).
The simple schematic in
In order to extract information about the film being deposited, it is worthwhile to measure conductive effects as well as effects of mass loading and viscoelasticity, and to separate these effects from one another to the extent possible. Inclusion of a temperature sensor device allows extraction of the effects of temperature, which can be done using the delay of the integral reference track responses, or with separate temperature sensing elements incorporated. Inclusion of multiple differential delay lines, preferably operable in different frequency ranges, with different coating treatments allows separation of conductive effects from those involving mass loading and viscoelasticity.
The example shown in
It would be clear to one skilled in the art that films with properties that vary over time with exposure to certain environments could be used in the present invention to implement monitoring devices. As one concrete example, a corrosion monitor could be constructed that utilizes multiple thin films of the same or different materials deposited on a multichannel device. These films can be designed to corrode at different rates in a given environment, so that the changes observed in acoustic wave propagation in each channel can be correlated to the rate at which a relevant material (such as steel pipe) would corrode. This approach utilizes the films as a sacrificial material, and provides a sequential series of measurements to assess how far corrosion has progressed in the materials of interest. This example also highlights the fact that sensors and monitoring devices according to the present invention can be implemented utilizing reversible, equilibrium chemical or biochemical processes to produce real-time monitors for analytes in the environment of the sensor; or alternatively they can be implemented employing irreversible physical, chemical, biochemical processes to provide alarm or dosimeter-like monitoring devices.
Thus far, all of the embodiments shown have been “single-sided” in that the acoustic wave propagation from only one side of the transducer has been utilized in device operation. This is beneficial in the examples shown due to the delay-coded nature of one of the transducers. The embodiments shown in
It should be noted that
One skilled in the art will recognize that there are a wide range of device embodiments that can be used to implement sensor devices according to the present invention. A selection of these device types has been shown. However, deviations from the examples included herein are within the scope of the present invention. All of these devices can be implemented in single-track formats, or in multiple acoustic track formats. They can be provided with electrical shorting pads in the deposition region(s) or portions thereof and/or the reference acoustic path(s) or portions thereof, if beneficial for the desired application (to separate the electrical effects of the deposited film from the mass loading and viscoelastic properties). These devices can utilize single sided and double sided die, differential delay lines and non-differential delay lines, or a mixture of the two within a single device. Differential delay lines can be implemented in a single or double-sided fashion, and can be extended to provide multiple differential delay signals in a single track (of one or more sides). Any of the devices shown can be implemented as a single die or as multiple separate die, each with one or more of the acoustic reference and/or measurement tracks. If multiple die are used, they may be of the same or different substrate materials and electrode materials. Multiple die may be packaged together, or selected die can preferentially be packaged separately, for example to serve as a hermetically sealed reference device. If implemented in separate devices, the reference device need not necessarily be co-located with the sensing devices.
The transducers and/or reflectors described thus far are all non-dispersive, and similar embodiments could be envisioned that utilize transducers that are tapered, slanted, stepped tapered, apodized, withdrawal weighted, EWC, UDT, SPUDT, dispersive, and/or waveguide structures. All of these techniques could also be used incorporating dispersive and harmonic techniques. For example, use of chirped transducers to provide processing gain may be beneficial, as is widely recognized. Harmonic techniques may be utilized by incorporating nonlinear elements into the device. Alternatively, high frequency SAW signals may be made to interact with SAW elements at the wave frequency and at sub-harmonics of that frequency, depending on the electrode structures used in the SAW elements used.
Also, one skilled in the art will recognize that these devices can be implemented on various substrate materials, and can utilize various acoustic wave propagation modes, in order to achieve performance required for specific applications. Performance to measure deposition of vapors, liquids, polymers, solids, and numerous other quantities can be achieved. Measurement of films deposited at high temperatures can be accomplished using langasite, langanite, langatate, or other substrate capable of operating at high temperatures. In order to measure conductive films, a substrate with high electromechanical coupling coefficient is preferred. Electrodes and busbars of SAW elements can be made from materials appropriate to survive the application environment, including the ability to withstand high or low temperatures, and chemical environments. Measurement of chemical and biological analytes in liquids, or measurement of physical properties of liquids such as viscosity, may benefit from use of a two-sided device such as a FPW or LG-SH-APM device, wherein a two-surfaced die is used. In this case, the electrodes are on one surface of the device (arbitrarily referred to as the “bottom”) while the fluid handling is on the opposite (“top”) surface of the device. Alternate wave modes may be more useful for specific applications.
Any of a wide range of known coding and other diversity techniques can be implemented in the transducers and/or reflectors. It would be understood by one versed in the art that simple on-off keying, phase modulation, pulse position modulation, and many other techniques could be used to enhance the number of codes available. The use of multiple delay “slots” within each code reflector nominal delay position is widely used to achieve increased code set size, and the use of multiple pulses per data group is also well known. Frequency diversity, code diversity, time diversity, and other know techniques can be combined to achieve sets of devices with desirable properties. Any of these techniques could be utilized in the aforementioned device embodiments to increase the number of sensors that can work together in a system with individually identifiable devices. Devices utilizing such structures could be useful for RFID tag sensing applications, where more than one sensor is required within a system, and identification of individual devices is desired. In addition, it would be understood by one skilled in the art that sensor-tag application of the present invention is possible, wherein external sensing devices can be connected to one or more specific SAW elements to measure additional external parameters. Variations in the impedance other properties (voltage, etc.) of the external sensor can then be read through the SAW device. Combination devices that include measurements made with integral sensitive films, in addition to external sensor device loads, are also within the scope of the present invention.
The broad nature of the invention described here are clear, and one skilled in the art will understand that there are a variety of device configurations that can be generated using combinations of one or more of the techniques discussed. The inventions described herein and illustrated in the figures provide device embodiments capable of measuring a wide range of chemical and biological analytes, changes in surface coatings, and reaction kinetics. The present invention can be interrogated using, among other techniques, a preferred time integrating correlator system such as that disclosed above. While some preferred forms and embodiments of the invention have been illustrated and described, it will be apparent to those of ordinary skill in the art that various changes and modification may be made without deviating from the inventive concepts set forth above.
The foregoing description, for purpose of explanation, has been described with reference to specific embodiments. However, the illustrative discussions above are not intended to be exhaustive or to be limiting to the precise forms disclosed. Many modifications and variations are possible in view of the above teachings. The embodiments were chosen and described in order to best explain the principles of the aspects and its practical applications, to thereby enable others skilled in the art to best utilize the aspects and various embodiments with various modifications as are suited to the particular use contemplated.
This application claims the benefit of, and priority to, U.S. provisional application No. 61/561,571, filed on Nov. 18, 2011, herein incorporated by reference in its entirety.
This invention was made with Government support under contract NNX09CB77C awarded by the National Aeronautics and Space Administration (NASA). The Government may have certain rights in the invention.
| Number | Date | Country | |
|---|---|---|---|
| 61561571 | Nov 2011 | US |
