Abstract:
A multiple-mode acoustic wave sensor apparatus includes an acoustic wave device comprising a piezoelectric substrate and at least one electrode on the substrate. When such sensor is used in a wireless configuration, a plurality of antennas can be configured on the substrate in association with the acoustic wave device, wherein each antenna among the plurality of antennas is responsive to varying interrogation signals transmitted wirelessly to the plurality of antennas in order to excite multiple frequency modes via at least one interdigital transducer on the substrate and thereby passively detect multiple and varying parameters of a sensed material utilizing the acoustic wave device.

Description:
TECHNICAL FIELD 
   Embodiments are generally related to sensing devices and components thereof. Embodiments additionally relate to surface generated acoustic waves, such as shear horizontal surface acoustic wave (SH-SAW), flexural plate wave (FPW), Love mode, acoustic plate mode (APM), shear horizontal acoustic plate mode (SH-APM), and bulk acoustic waves (BAW), including thickness shear mode, torsional mode, overtone modes, and flexural mode components and devices thereof. Embodiments additionally relate to the wireless transmission of detection data. 
   BACKGROUND OF THE INVENTION 
   Acoustic wave sensors are utilized in a variety of sensing applications, such as, for example, temperature and/or pressure sensing devices and systems. Acoustic wave devices have been in commercial use for over sixty years. Although the telecommunications industry is the largest user of acoustic wave devices, they are also used for chemical vapor detection. Acoustic wave sensors are so named because they use a mechanical, or acoustic, wave as the sensing mechanism. As the acoustic wave propagates through or on the surface of the material, any changes to the characteristics of the propagation path affect the velocity and/or amplitude of the wave. 
   Changes in acoustic wave characteristics can be monitored by measuring the frequency or phase characteristics of the sensor and can then be correlated to the corresponding physical quantity or chemical quantity that is being measured. Virtually all acoustic wave devices and sensors utilize a piezoelectric crystal to generate the acoustic wave. Three mechanisms can contribute to acoustic wave sensor response, i.e., mass-loading, visco-elastic and acousto-electric effect. The mass-loading of chemicals alters the frequency, amplitude, and phase and Q value of such sensors. Most acoustic wave chemical detection sensors, for example, rely on the mass sensitivity of the sensor in conjunction with a chemically selective coating that absorbs the vapors of interest resulting in an increased mass loading of the acoustic wave sensor. 
   Examples of acoustic wave sensors include acoustic wave detection devices, which are utilized to detect the presence of substances, such as chemicals, or environmental conditions such as temperature and pressure. An acoustical or acoustic wave (e.g., SAW/BAW) device acting as a sensor can provide a highly sensitive detection mechanism due to the high sensitivity to surface loading and the low noise, which results from their intrinsic high Q factor. Surface acoustic wave devices are typically fabricated using photolithographic techniques with comb-like interdigital transducers placed on a piezoelectric material. Surface acoustic wave devices may have either a delay line or a resonator configuration. Bulk acoustic wave device are typically fabricated using a vacuum plater, such as those made by CHA, Transat or Saunder. The choice of the electrode materials and the thickness of the electrode are controlled by filament temperature and total heating time. The size and shape of electrodes are defined by proper use of masks. 
   Surface acoustic wave resonator (SAW-R), surface acoustic wave delay line (SAW-DL), surface transverse wave (STW), bulk acoustic wave (BAW), and acoustic plate mode (APM) all can be utilized in various sensing measurement applications. One of the primary differences between an acoustic wave sensor and a conventional sensor is that an acoustic wave can store energy mechanically. Once such a sensor is supplied with a certain amount of energy (e.g., through RF), the sensor can operate for a time without any active part (e.g., without a power supply or oscillator). This feature makes it possible to implement an acoustic wave in an RF powered passive and wireless sensing application. 
   Many sensing applications require measurements of multiple parameters. Multiple or groups of sensors are typically employed in these types of applications. Each sensor is dedicated to a particular measurand. In an application such as, for example, oil quality sensing, many factors (e.g., pH, TAN, TBN, viscosity, particulate, lubricity, temperature, flow, pressure, conductivity, humidity, etc.) can contribute to the quality of oil, and thus it is not practical to configure, for example, ten individual sensors in a sensing package. Thus, it would be advantageous to provide a single sensor that can detect multiple parameters. To date, a single sensor for detecting multiple parameters has not been adequately implemented. It is believed that the embodiments disclosed herein overcome the disadvantages of conventional detection systems through the use of a unique surface acoustic sensing arrangement. 
   BRIEF SUMMARY 
   The following summary is provided to facilitate an understanding of some of the innovative features unique to the embodiments disclosed and is not intended to be a full description. A full appreciation of the various aspects of the embodiments can be gained by taking the entire specification, claims, drawings, and abstract as a whole. 
   It is, therefore, one aspect of the present invention to provide for an improved sensing device. 
   It is another aspect of the present invention to provide for an improved acoustic wave sensing device 
   It is yet another aspect of the present invention to provide for a wireless and passive multiple mode acoustic wave sensor. 
   The aforementioned aspects and other objectives and advantages can now be achieved as described herein. A wireless and passive multiple-mode acoustic wave sensor apparatus is disclosed, which includes an acoustic wave device comprising a piezoelectric substrate and at least one interdigital transducer formed as an electrode on the piezoelectric substrate. A plurality of antennas can be configured on the piezoelectric substrate in association with the acoustic wave device, wherein each antenna among the plurality of antennas is responsive to varying interrogation signals transmitted wirelessly to the plurality of antennas in order to excite multiple frequency modes via at least one interdigital transducer on the piezoelectric substrate and thereby passively detect multiple and varying parameters of a sensed material utilizing the acoustic wave device. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying figures, in which like reference numerals refer to identical or functionally-similar elements throughout the separate views and which are incorporated in and form a part of the specification, further illustrate the embodiments and, together with the detailed description, serve to explain the embodiments disclosed herein. 
       FIG. 1  illustrates a perspective view of an interdigital surface wave device, which can be implemented in accordance with one embodiment; 
       FIG. 2  illustrates a cross-sectional view along line A-A of the interdigital surface wave device depicted in  FIG. 1 , in accordance with one embodiment; 
       FIG. 3  illustrates a perspective view of an interdigital surface wave device, which can be implemented in accordance with one or more embodiments; 
       FIG. 4  illustrates a cross-sectional view along line A-A of the interdigital surface wave device depicted in  FIG. 3 , in accordance with one embodiment; 
       FIG. 5  illustrates multiple modes that can exist in sensor, in accordance with a preferred embodiment; 
       FIG. 6  illustrates a graph depicting fundamental and 3 rd  overtone temperature characteristics of an SC-cut crystal, which can be adapted for temperature compensation applications, in accordance with one embodiment; 
       FIG. 7  illustrates a wired dual mode oscillator that can be adapted for use in association with acoustic wave device, in accordance with a preferred embodiment; and 
       FIG. 8  illustrates a block diagram of a wireless and passive multiple-mode acoustic wave sensing system that can be implemented in accordance with a preferred embodiment. 
   

   DETAILED DESCRIPTION 
   The particular values and configurations discussed in these non-limiting examples can be varied and are cited merely to illustrate at least one embodiment and are not intended to limit the scope thereof. 
     FIG. 1  illustrates a perspective view of an acoustic wave device  100 , which can be implemented in accordance with one embodiment. Acoustic wave device  100  generally includes one or more interdigital transducers (IDT)  106  formed on a piezoelectric substrate  104 . The acoustic wave device  100  can be implemented in the context of a sensor chip. Interdigital transducer  106  can be configured in the form of an electrode, depending upon design considerations. 
   Note that the acoustic wave device  100  represents only one type of acoustic wave device that can be adapted for use with the embodiments disclosed herein. It can be appreciated that a variety of other types (e.g., SH-SAW, BAW, APM, SH-APM, FPW, SH-SAW-DL, SH-SAW-R, etc.) can be utilized in accordance with the embodiments described herein. Additionally, acoustic wave device  100  can be implemented in a variety of shapes and sizes. 
     FIG. 2  illustrates a cross-sectional view along line A-A of the acoustic wave device  100  depicted in  FIG. 1 , in accordance with one embodiment of the present invention. Piezoelectric substrate  104  can be formed from a variety of substrate materials, such as, for example, quartz, lithium niobate (LiNbO 3 ), lithium tantalite (LiTaO 3 ), Li 2 B 4 O 7 , GaPO 4 , langasite (La 3 Ga 5 SiO 14 ), ZnO, and/or epitaxially grown nitrides such as Al, Ga or Ln, to name a few. Interdigital transducer  106  can be formed from materials, which are generally divided into three groups. First, interdigital transducer  106  can be formed from a metal group material (e.g., Al, Pt, Au, Rh, Ir Cu, Ti, W, Cr, or Ni). Second, interdigital transducer  106  can be formed from alloys such as NiCr or CuAl. Third, interdigital transducer  106  can be formed from metal-nonmetal compounds (e.g., ceramic electrodes based on TiN, CoSi 2 , or WC). 
   The coating  102  need not cover the entire planar surface of the piezoelectric substrate  104 , but can cover only a portion thereof, depending upon design constraints. Coating  102  can function as a guiding layer, which is shown in greater detail herein with respect to  FIG. 5 . Selective coating  102  can cover interdigital transducer  106  and the entire planar surface of piezoelectric substrate  104 . Because acoustic wave device  100  functions as a multiple mode sensing device, excited multiple modes thereof generally occupy the same volume of piezoelectric material. Multiple modes excitation allows separations of temperature change effects from pressure change effects. The multi-mode response can be represented by multiple mode equations, which can be solved to separate the response due to the temperature and pressure. 
     FIG. 3  illustrates a perspective view of an acoustic wave device  300 , which can be implemented in accordance with an embodiment. The configuration depicted in  FIGS. 3-4  is similar to that illustrated in  FIGS. 1-2 , with the addition of an antenna  308 , which is connected to and disposed above a wireless excitation component  310  (i.e., shown in  FIG. 4 ). Acoustic wave device  300  generally includes an interdigital transducer  306  formed on a piezoelectric substrate  304 . 
   Acoustic wave device  300  can therefore function as an interdigital surface wave device, and one, in particular, which utilizes surface-skimming bulk wave techniques. Interdigital transducer  306  can be configured in the form of an electrode. A coating  302  can be selected such that a particular species to be measured is absorbed by the coating  302 , thereby altering the acoustic properties of the acoustic wave device  300 . Various selective coatings can be utilized to implement coating  302 . 
   A change in acoustic properties can be detected and utilized to identify or detect the substance or species absorbed and/or adsorbed by the coating  302 . Thus, coating  302  can be excited via wireless means to implement a surface acoustical model. Thus, antenna  308  and wireless excitation component  310  can be utilized to excite multiple modes, thereby allowing separation of temperature change effects from pressure change effects. Such an excitation can produce a variety of other modes of acoustic wave device  300 . 
     FIG. 4  illustrates a cross-sectional view along line A-A of the acoustic wave device  300  depicted in  FIG. 3 , in accordance with one embodiment of the present invention. Thus, antenna  308  is shown in  FIG. 4  disposed above coating  302  and connected to wireless excitation component  310 , which can be formed within an area of coating  302 . Similar to the configuration of  FIG. 2 , Piezoelectric substrate  304  can be formed from a variety of substrate materials, such as, for example, quartz, lithium niobate (LiNbO 3 ), lithium tantalite (LiTaO 3 ), Li 2 B 4 O 7 , GaPO 4 , langasite (La 3 Ga 5 SiO 14 ), ZnO, and/or epitaxially grown nitrides such as Al, Ga or Ln, to name a few. 
   Interdigital transducer  306  can be formed from materials, which are generally divided into three groups. First, interdigital transducer  106  can be formed from a metal group material (e.g., Al, Pt, Au, Rh, Ir Cu, Ti, W, Cr, or Ni). Second, interdigital transducer  106  can be formed from alloys such as NiCr or CuAl. Third, interdigital transducer  306  can be formed from metal-nonmetal compounds (e.g., ceramic electrodes based on TiN, CoSi 2 , or WC). Thus, the electrode formed from interdigital transducer can comprise a material formed from at least one of the following types of material groups: metals, alloys, or metal-nonmetal compounds. 
     FIG. 5  illustrates multiple modes  500  that can exist in a wireless sensor as described herein. As indicated in  FIG. 5 , example modes  500  can include one or more thickness modes, including fundamental  502 , 3rd overtone  504 , and 5th overtone  506  modes. An extensional mode  508  is also depicted in  FIG. 5 , along with a face shear mode  510  and a length-width fixture mode  512 . It can be appreciated that one or more of such modes can be adapted for use in accordance with one or more embodiments. 
     FIG. 6  illustrates a graph  600  depicting fundamental and 3rd overtone temperature characteristics of an SC-cut crystal, which can be adapted for temperature compensation applications, in accordance with one embodiment. Note that in  FIGS. 5-6 , identical or similar parts or elements are generally indicated by identical reference numerals. Thus, graph  600  depicts a curve depicting data representative of 3rd overtone frequency mode  504  and a curve depicting data representative of fundamental frequency mode  502 . Note that as utilized herein the terms “frequency mode” and “mode” may be utilized interchangeably to refer to the same phenomena. Graph  600  plots data indicative of a change in frequency over a frequency (y-axis  608 ) versus a change in temperature (x-axis  610 ). Graph  600  further illustrates the approximate location  606  representing the Intersection of modes  502  and  504 . Based on the data indicated in graph  600 , multiple modes can therefore be utilized to accomplish frequency compensation applications. 
     FIG. 7  illustrates a wired dual mode oscillator  700  that can be adapted for use in association with acoustic wave device  100  or  300 , in accordance with a preferred embodiment. Note that in  FIGS. 1-8 , identical or similar parts or elements are generally indicated by identical reference numerals. Thus, acoustic wave device  100  or  300  can be utilized in association with the oscillator  700  depicted in  FIG. 7 . The dual mode oscillator  700  is generally composed of acoustic wave device  100 ,  300 , which can transmit a signal  701  to a transistor  708  having an input connected to an input of an amplifier  704  and an input of an amplifier  706 . 
   The output from amplifier  704  is fed to impedance  710 . The output from amplifier  706  is fed to an impedance  712 . The output from transistor  708  is connected to both impedance  710  and impedance  712 . Output  713  from amplifier  704  and impedance  710  is fed to a frequency multiplier  714 , while output  715  from impedance  712  and amplifier  706  is fed to a mixer  716 . 
     FIG. 8  illustrates a block diagram of a wireless and passive multiple-mode acoustic wave sensing system  800  that can be implemented in accordance with a preferred embodiment. In general, system  800  incorporates the use of acoustic wave device  100  or  300 . A reader unit  806  can transmit excitation signals  804  to a plurality of antennas  802  and  803  associated and connected to acoustic wave device  100 ,  300 . Note that reader unit  806  can be further composed of one or more sub-units, identified in  FIG. 8 . For example, reader unit  806  can be composed of an RF (Radio Frequency) transmitter/receiver component, a DSP (Digital Signal Processor), and a PC (Personal Computer). Reader unit  806  can be implemented, in some embodiments, as a radar device or radar unit, depending upon design considerations. 
   Antenna  802 , for example, can be utilized to receive signals that excite a fundamental frequency mode  502 , while antenna  803  can be utilized to receive signals that excite a 3 rd  overtone frequency mode  504 , depending upon design considerations. It is important to note that although  FIG. 8  illustrates antennas dedicated to particular frequency modes, such as 3 rd  overtone frequency mode  504  and fundamental frequency mode  502 , a variety of other types of frequency modes can be implemented accordingly. 
   The different excitation modes can be controlled by interrogation electronics (IE) associated with reader unit  806  by providing one or more input signals  804  that possess different frequencies and/or power levels. For example, some excitation modes may possess a higher impedance and may require a higher power level to be excited, hence, the electronics depicted in  FIG. 7 . In some cases, the acoustic wave sensing device  100 ,  300  may be optimized or configured so that some predetermined modes can be more easily excited, while suppressing other modes. This may be accomplished in a number of ways, including for example, selecting appropriate design parameters such as electrode thickness, IDT aperture, finger widths and/or spacing of the interdigital transducer(s), the piezoelectric material used, the cut angle of the substrate materials, the orientation of the interdigital transducer(s) relative to the crystalline planes in the piezoelectric material, and so forth. 
   A variety of acoustic modes may propagate in a piezoelectric half-space, including bulk waves and surface waves. For example, in an interdigital surface (SAW) device design, the substrate materials and crystal orientation can be selected such that that the only surface wave that can be excited is a Rayleigh wave. Other modes of excitation, however, are always present. 
   Such multiple acoustical modes include, for example, a surface acoustic wave (SAW) mode, shear-horizontal surface acoustic wave (SH-SAW) mode, a pseudo surface acoustic wave (PSAW) mode, and a leak surface acoustic wave (LSAW) mode. Such multiple frequency modes can also include one or more of the following types of modes: flexural plate mode (FPM), acoustic plate shear-horizontal acoustic plate mode (SH-APM), amplitude plate mode (APM), thickness shear mode (TSM), bulk acoustic wave (BAW) mode, transverse mode, surface skimming mode, surface transverse mode, harmonic mode and overtone mode. Note that the multiple frequency modes can be excited through said acoustic wave device to permit a separation of temperature change effects from physical and chemical measurand change effects thereof including pressure, torque, viscosity, density, corrosivity, conductivity, pH, flow, a lubricity, a turbidity, a humidity, a particulate concentration, a total base number, and a total acid number. 
   In a wireless configuration, such as that of system  800  depicted in  FIG. 8 , multiple modes can be excited by the interrogation via reader unit  806  in accordance with a preferred embodiment. Multiple modes excitation allows for the separation of temperature change effects from the pressure change effect. Note that in the particular example illustrated in  FIG. 8 , the 3 rd  overtone is usually about three times the frequency of the fundamental overtone. Thus, the length of antenna  803 , for example, may be ⅓, ⅔, 4/3 or 8/3 of the length of the fundamental mode antenna  802 , depending upon design considerations. 
     FIGS. 1-8  generally illustrate a sensor design that utilizes multiple modes of a piezoelectric device. Thus, one sensor is utilized to obtain multiple parameters. Multiple modes excitation allows for the separation of one parameter from another (or others). The multi-mode response can be represented by multiple equations, which can be solved to separate the response due to different measurand. In some cases, interrogation electronics (e.g., see reader unit  806 ) can be adapted to excite multiple modes in the acoustic wave device  100 ,  300 . This may be accomplished, for example, by transmitting an appropriate input or power signal to the acoustic wave device  100 ,  300 . In some cases, a surface acoustic wave (SAW) mode, shear-horizontal surface acoustic wave (SH-SAW) mode, a pseudo surface acoustic wave (PSAW) mode, and a leak surface acoustic wave (LSAW) mode may be the easiest types of modes to excite, but as indicated herein, other types of modes may also be excited. 
   It will be appreciated that variations of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also that various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.