Patent Publication Number: US-7219536-B2

Title: System and method to determine oil quality utilizing a single multi-function surface acoustic wave sensor

Description:
TECHNICAL FIELD 
   Embodiments are generally related to sensing devices and components thereof. Embodiments also relate to oil filter detection. Embodiments additionally relate to bulk acoustic wave (BAW) components and other surface acoustic devices thereof. 
   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, phase and/or amplitude of the wave. 
   Changes in acoustic wave characteristics can be monitored by measuring the frequency, phase characteristics, Q value, insertion loss and input impedance 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. The chemically sensitive coating, however, significantly reduce the Q value, hence the performance of the sensor. In a practical sensor design, the acoustic wave sensor is preferred to be as simple as possible (in electrode configurations, layers of electrode, coatings on top of the electrodes, etc). 
   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. Bulk acoustic wave devices 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 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. 
   Based on the foregoing, it can be appreciated that acoustic wave devices, such as a surface acoustic wave resonator (SAW-R), surface acoustic wave delay line (SAW-DL), surface transverse wave (STW), bulk acoustic wave (BAW), 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 device in an RF powered passive and wireless sensing application. 
   One promising application for micro-sensors involves engine oil quality sensors. Acoustic wave viscosity sensors have been tested in the context of oil quality sensors. While viscosity is a good indicator of many oil quality factors, including low temperature startability, fuel economy, thinning or thickening effects at high/low temperatures, lubricity, and oil film thickness in running automotive engines, viscosity is not an indicator of how much acid is present in engine oil. Such acids can cause a lot of damage to an automotive engine. 
   A certain percentage of engine oil is converted to acids and other unhealthy compounds. Theses acids can attack the engines by etching the engines. The truck automotive industry, for example, currently relies on engine oil&#39;s pH, TBN and TAN as indicators of oil quality, however, such methods do not provide direct indications of precisely how much acid is attacking the engine. Combining a viscosity and corrosivity monitor might provide a technique for solving this problem. Such a method, however, is very costly, time consuming and takes up a great deal of volume. 
   Based on the foregoing, it is believed that what is needed to overcome these problems involves the implementation of an etch rate (corrosivity) monitor in combination with viscosity measurements. It is believed that the oil quality monitoring methods and systems described herein can solve such conventional deficiencies. 
   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 acoustic wave sensing device adapted for oil quality monitoring. 
   It is yet another aspect of the present invention to provide for an acoustic wave device that is coated with a material that is selectively reactive to acids in order to provide an acid etch rate (corrosivity) monitor thereof. 
   It is a further aspect of the present invention to provide for an acoustic wave device that is capable of measuring both the acid etch rate (corrosivity) and viscosity of engine oil. 
   The aforementioned aspects and other objectives and advantages can now be achieved as described herein. A method and system for detecting oil quality is disclosed herein. In general, the quality of engine oil can be determined utilizing an acoustic wave sensor to obtain amplitude/frequency data associated with the engine oil. The etch rate (i.e., acid etch rate or corrosivity) of the engine oil can also be determined based on the frequency data obtained as a result of the frequency measurement utilizing the acoustic wave sensor. The viscosity of the engine oil can additionally be obtained based on a measurement of phase and amplitude obtained from the acoustic wave sensor. The etch rate and the viscosity provide data indicative of the quality of the engine oil. The acoustic wave sensor is coated with a material that selectively reacts to at least one type of an acid in order to provide data indicative of the presence of the acids in the engine oil. 

   
     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 top view of a bulk wave device, which can be implemented in accordance with one embodiment; 
       FIG. 2  illustrates a side view of the bulk wave device depicted in  FIG. 1  in accordance with one embodiment; 
       FIG. 3  illustrates a block diagram of a wireless and passive sensor system that can be implemented in accordance with a preferred embodiment; 
       FIG. 4  illustrates multiple modes that can exist in a wireless oil sensor, in accordance with one embodiment; 
       FIG. 5  illustrates a high-level flow chart of operations depicting logical operational steps that can be implemented in accordance with a preferred embodiment; and 
       FIG. 6  illustrates a pictorial diagram of an oil quality monitoring system that can be implemented in accordance with an alternative 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 top view of a bulk wave device  100 , which can be implemented in accordance with one embodiment.  FIG. 2  illustrates a side view of the bulk wave device  100  depicted in  FIG. 1  in accordance with one embodiment. Note that in  FIGS. 1-2 , identical or similar parts are generally indicated by identical reference numerals. Bulk wave device  100  can be implemented in the context of a multiple function oil quality sensor. Bulk wave device  100  generally comprises two electrodes, including a top electrode  106  and a bottom electrode  107 , which are formed on a piezoelectric substrate  104 . The bulk wave device  100  can be implemented in the context of a sensor chip. The electrodes  106 ,  107  can be round or rectangular, depending upon design considerations. Note that the top electrode  106  can be provided with a top electrode connection  109  that can connect and/or communicate with another component, such as, for example, an antenna. Similarly, bottom electrode  107  can be provided with a bottom electrode connection  111  that can connect and/or communicate with another component, such as an antenna. 
   The bulk wave device  100  illustrated in  FIG. 1  represents only one type of acoustic wave device or acoustic wave sensor that can be adapted for use with the embodiments disclosed herein. It can be appreciated that a variety of other types (e.g., APM, SH-APM, FPW, BAW, SAW-DL, SAW-R, etc.) can be utilized in accordance with the embodiments described herein. Additionally, bulk wave device  100  can be implemented in a variety of shapes (e.g., circular, square, diamond, rectangular, etc) and modes (e.g., fundamental and/or overtones). 
   A reactive coating film  102  depicted in  FIG. 2  can be selected such that a particular species (acids, etc,) to be measured react with the coating  102 , thereby altering the frequency of the bulk wave device  100 . Various reactive coatings can be utilized to implement coating  102 . A change in frequency can be detected and utilized to analyze how fast the metal is being attacked by the acids. Electrode  106  can therefore function as a reactive electrode when covered by coating  102 . Please note that the electrode  106  and reactive film  102  could be the same, depending upon FEM considerations for the whole BAW device and the electrical and chemical properties of the materials used for the electrode  106  and reactive film  102 . Thus, the bulk wave device is generally excited to implement a bulk acoustic mode. Such an excitation, however, can produce a variety of other modes of acoustic wave device  100 . 
   Many modes of vibrations can exist in acoustic wave device  100 . such as, for example, surface acoustic wave (SAW) and bulk acoustic wave (BAW) modes. Unlike, bulk wave device  100 , most acoustic wave devices are designed such that only one mode of vibration is optimized, while other modes are suppressed. Such “undesired” mode(s), however, can be utilized for temperature compensation. Such modes can include, for example, flexural plate mode (FPM), acoustic plate mode, shear-horizontal acoustic plate mode (SH-APM), amplitude plate mode (APM), thickness shear mode (TSM), surface acoustic wave (SAW) mode, bulk acoustic wave mode (BAW), Torsional mode, love wave, leaky surface acoustic wave mode (LSAW), pseudo surface acoustic wave mode (PSAW), transverse mode, surface-skimming mode, surface transverse mode, harmonic modes, and/or overtone modes. Thus, in accordance with embodiments disclosed herein, multiple vibration modes (fundamental and overtones, etc) can be utilized to produce a temperature compensated multiple mode acoustic wave device, such as, bulk wave device  100 . 
   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. Electrodes 106  and  107  can be formed from materials, which are generally divided into three groups. First, electrodes  106 ,  107  can be formed from a metal group material (e.g., Al, Pt, Au, Ag, Rh, Ir, Zr, Cu, Ti, W, Cr, or Ni). Second, electrodes  106 ,  107  can be formed from alloys such as NiCr or CuAI. Third, electrodes  106 ,  107  can be formed from metal-nonmetal compounds (e.g., ceramic electrodes based on TiN, CoSi 2 , or WC). A layer  112  can also be provided between electrode  107  and substrate  104  that functions, for example, as a Cr or Ti adhesion layer. 
   The reactive coating  102  acts as one electrode of the BAW device  100  and need not cover the entire planar surface of the piezoelectric substrate  104 , but may cover only a portion thereof, depending upon design constraints. The size, shape and thickness of the reactive coating  102  determines BAW device  100  parameters such as motional resistance, equivalent circuit capacitance, Q value, spurs, harmonics, etc. This reactive film  102  and electrode  106  can cover part of the planar surface of piezoelectric substrate  104  depending upon FEM design constraints. 
   Because bulk 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 viscosity and corrosivity 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 viscosity, etc. 
     FIG. 3  illustrates a block diagram of a wireless and passive sensor system  300  that can be implemented in accordance with a preferred embodiment. Note that in  FIGS. 1-3 , identical or similar parts or elements are generally indicated by identical reference numerals. Thus, the BAW device  100  depicted in  FIGS. 1-2  functions as an oil quality sensor in accordance with the system  300  illustrated in  FIG. 3 . BAW device  100  can be implemented as an acoustic wave sensor equipped with antennas  108 ,  110 . 
   As indicated by arrow  314  in  FIG. 3 , the surface of BAW device or sensor  100  can be exposed to oil. The acoustic wave sensor or BAW device  100  is excited by energy received through RF communications in order to vibrate in a desired mode(s) and transmit data back to an interrogator  302 , which is equipped with antennas  308 ,  310 . The acoustic wave sensor together with the antenna(s) act as a receiver, sensor and transmitter for system  300 . The antennas  108  and  110  showing in the  FIG. 3  act as transmitter and receiver, they can be the same one but function as both. Same as antennas  308  and  310 . 
     FIG. 4  illustrates multiple modes  400  that can exist in a wireless oil sensor system as described herein. As indicated in  FIG. 4 , example modes  400  can include one or more thickness modes, including fundamental  402 , 3 rd  overtone  404 , and 5 th  overtone  406  modes. An extensional mode  408  is also depicted in  FIG. 4 , along with a face shear mode  410  and a length-width fixture mode  412 . It can be appreciated that one or more of such modes can be adapted for use in accordance with one or more embodiments. Modes  400  depicted in  FIG. 4  can therefore be considered in the implementation of an engine oil quality sensor. 
     FIG. 5  illustrates a high-level flow chart  500  of operations depicting logical operational steps that can be implemented in accordance with a preferred embodiment. As indicated at block  502  of flow chart  500 , the process can be initiated. First, as described at block  504 , an acoustic wave sensor can be coated with a material that reacts to an acid. One example of such an acoustic wave sensor is, for example, BAW device  100  depicted in  FIGS. 1-3 . The methodology described herein with respect to  FIG. 5  can also be implemented in the context of oil quality monitoring system  600  depicted in  FIG. 6  herein. 
   Thus, the acoustic wave or BAW device  100  can be coated with a material that reacts to particular types of acids. Note that the bulk acoustic wave device can be implemented in the context of a wireless sensor (e.g., see antennas  108 ,  110  in  FIG. 3 ). Coating  102  can thus be provided with a material property that is selectively reactive to acids. 
   As depicted thereafter at block  506 , the acoustic wave sensor can come into contact with the engine oil. The sensor can be located, for example, in an oil filter or an internal combustion engine, to monitor the engine oil. Thereafter, as depicted at block  508 , the frequency of the acoustic wave sensor can be measured. Next, as depicted at block  510 , the corrosivity (e.g., etch rate) of the engine oil can be determined, based on the frequency obtained as a result of the frequency measurement utilizing the acoustic wave sensor. 
   Next, as depicted at block  512 , a measurement of phase and amplitude can be obtained from the bulk acoustic wave sensor. Thereafter, as described at block  514 , the phase and amplitude data can be utilized to compile viscosity information associated with the engine oil. Next, as depicted at block  516 , the corrosivity/etch rate and the viscosity are utilized to provide data indicative of the quality of the engine oil. The process can then terminate as indicated at block  518 . 
   By implementing the methodology depicted in  FIG. 5 , a single acoustic wave sensor can be implemented, which is capable of measuring both the etch rate and viscosity of engine oil. The etch rate is obtained through frequency measurement, as depicted at block  508 , and the viscosity information can be obtained through phase and amplitude measurement as depicted at blocks  512  and  514 . The reason the methodology depicted in  FIG. 5  represents an ideal technique for measuring engine oil quality is that frequency is hardly influenced by viscosity and a very slow etch rate will not change the bulk wave phase and amplitude. 
   Note that when the etching electrode is coated with preferred materials simulating engine materials, these coated materials result in a mass loading effect on the base metal layer of the bulk acoustic wave sensing device and the QCM, but the electrical characteristics (R/L/C) are dominated by the base metal layer, the quartz surface roughness, etc. Viscosity appears as vibration resistance and contributes to amplitude changes. The bulk acoustic wave sensor may include, for example, one or more BAW electrodes formed thereon. In such a scenario, all such BAW electrodes can be exposed to the engine oil. 
   Thus, according to the methodology depicted in  FIG. 5 , an acoustic wave sensor can be coated with materials (i.e., or the entire electrode thereof) that are selectively reactive to particular types of acids and which can be utilized as an etch rate monitor and/or acid(s) monitor. The coating materials can be similar to those of engine materials. The most important difference between an acoustic wave device and a conventional wired sensor is that the acoustic wave device can store energy mechanically. Once the acoustic wave device is supplied with a certain amount of energy (e.g., through RF), the device can operation for a time without any active part (e.g., without power supply and/or oscillators). This feature makes it possible for an acoustic wave sensor to be implemented in the context of an RF powered passive and wireless sensing application. 
   Frequency changes of an acoustic wave device in viscosity measurement have been utilized in conventional applications. The frequency changes caused by small changes in viscosity of highly viscous liquids, however, are very small. Also, because of highly viscous loading, the signal from the oscillator is very noisy and the accuracy of conventional measurement systems is very poor. In the embodiments disclosed herein, however, phase and amplitude can be measured wirelessly (e.g., see antennas  108 ,  110 ,  308 ,  310  in  FIG. 3 ). 
   Factors that influence the sensor properties include physical/chemical properties of the coating materials, coating thickness, coating modulus, coating morphology and bonding with the substrate. Such factors relate to coatings  102  described herein. An acoustic wave device is attractive to chemical detection applications because of their good linearity, short response time, small size, ruggedness, high sensitivity, low operating temperature and low power consumption. 
   The materials utilized to implement a coating, such as coating  102 , will affect the sensor&#39;s selectivity. Though perfect selectivity for a single analyte is unattainable except for the biologically-based coating, adequate selectivity for a particular application can be obtained if the potential interferants are known. Coating structures and coating techniques therefore can affect the sensor&#39;s response to acids, and hence contribute to selectivity. 
   Quartz crystal resonators were originally developed for electronic oscillator components. In a typical etch rate monitor, however, the reaction of an acid with a selective thin film coating (e.g., applied to one surface of the crystal) or a reactive electrode can reduce the crystal&#39;s mass and increase its resonant frequency. 
   The frequency of a thickness shear mode (TSM) crystal unit, such as an AT-cut unit, is generally inversely proportional to the thickness of the crystal plate. For example, a typical 5 MHz 3 rd  overtone plate is on the order of 1 million atomic layers thick. The etching of the coating/electrode equivalent to the mass of one atomic layer of quartz changes the frequency by about 1 ppm. Through calculations, one can see that the fundamental mode is 9 times more sensitive than that of the 3 rd  overtone (i.e., see  FIG. 5 ). A 5 MHz AT-cut TSM crystal blank, for example, is about 0.33 mm thick (fundamental). The thickness of the electrodes can be, for example, 0.2 to 0.5 μm. The change in frequency due to coating can therefore be demonstrated by the following formulation: δF=−2.3×10 6  F 2  (δM/A). In this case, the variable or value δF represents the change in frequency due to the coating (Hz), and F represents the frequency of the quartz plate (Hz), δM represents the mass of deposited coating (g), and A represents the area coated (cm 2 ). 
     FIG. 6  illustrates a pictorial diagram of an oil quality monitoring system  600  that can be implemented in accordance with an alternative embodiment. Note that in  FIGS. 1-6 , identical or similar parts or elements are generally indicated by identical reference numerals. System  600  generally includes an oil fitter  601  that includes an oil filter housing or canister  602  and oil filtration media  604 . A gap  606  is centrally located in oil filter  601  through which engine oil flows as indicated by arrows  608  and  609 . An acoustic wave sensor, such as BAW sensing device  100  with antennas  108 ,  110 , can be located within gap  606  and transmit sensor data wirelessly to an RF transmitter/receiver  612 , which may be located elsewhere (e.g. within an automobile cabin, an oil change station, an automotive shop, a home, garage, etc.). Note that RF transmit/receiver  612  generally functions as a wireless interrogator, such as, for example, interrogator  302  depicted in  FIG. 3 . 
   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.