Abstract:
A system capable of detecting the hazardous accumulation of ice on the surfaces, engines, instruments and air intakes of aircrafts or other objects of interest. The system consists of an electromagnetic microwave resonator capable of detecting the formation of ice directly where it could cause problems. The sensor could be mounted around the air intake of pitot tubes, static ports, engines intake, engines core, and can be embedded in the aircraft skin. The system uses algorithms based on the variations of the complex dielectric permittivity of water substance with frequency to distinguish the various types of ice from each other and from water.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional application Ser. No. 61/895,038, filed on Oct. 24, 2013. The entire disclosure of the above application is incorporated herein by reference. 
    
    
     FIELD 
     The present disclosure relates to a microwave resonator system capable of detecting the hazardous accumulation of ice on the surfaces, engines, air intakes, pitot tubes, static ports and other components of an aircraft. 
     BACKGROUND AND SUMMARY 
     This section provides background information related to the present disclosure that is not necessarily prior art. This section further provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
     Most current aircraft ice detection systems are based on measurements by ice-collecting probes, not placed directly on the areas where ice accumulation can cause problems. For example, U.S. Pat No. 7,104,502 is for a system capable of detecting the accumulation of ice by measuring changes in the vibration frequency of a strut mounted on the nose cone of an aircraft. The strut contains at least one feature that allows ice to accrete on it at higher rate than in other parts of the aircraft. U.S. Pat. No. 7,370,525 refers to a dual channel inflight system that detects ice accretion on a housing containing a light source, mounted on the aircraft surface. The system illuminates the housing with linearly polarized light. Light conductors with polarization sensitivity aligned to the transmitted light and with polarization sensitivity orthogonal to it acquire the backscattered light. The ratio of the intensities of the light in the two conductors is used to detect the presence of ice. The prior art systems described above detect ice on ice-collecting probes and housings, not directly on the places where ice accumulation can cause problems. Thus, they do not detect ice accumulation where it can be a hazard, such as on the air intake of pitot tubes, static ports, engines, wing surfaces and control surfaces. 
     The aircraft ice detection system of the present teachings comprises an electromagnetic microwave resonator capable of measuring the complex dielectric permittivity of ice accumulated on aircrafts surfaces, air intakes and engines core. In some embodiments, the system contains a multiple frequency microwave resonator, a data processor unit, and interfaces with flight displays and flight systems. 
     The present teachings provide, in part, a system capable of detecting the hazardous accumulation of ice on the surfaces, engines, instruments and air intakes of an aircraft or other objects of interest. Contrary to the previous art, the present system includes an electromagnetic microwave resonator capable of detecting the formation of ice directly where it could cause problems. The microwave resonator sensor can be mounted around the air intake of pitot tubes, static ports, on engines core, and can be embedded in the aircraft skin. The system uses algorithms based on the variations of the complex dielectric permittivity of water substance with frequency to distinguish the various types of ice from each other and from water. The system uses changes in the microwave resonant frequencies, their quality factors, and the transmitted and possibly received power to detect ice and to measure the ice thickness. The system is capable of determining the type and thickness of ice accumulated in the areas of interest as well as the rate of accumulation. In some embodiments, the system uses a dual frequency microwave resonator to distinguish water and the various types of ice from each other. A warning could be given when ice starts to accumulate. A hazards alert could be given when the thickness of the ice accumulated and/or the rate of accumulation reaches pre-established values regarded to be dangerous. 
     Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
         FIG. 1  illustrates the aircraft icing detector system according to the principles of the present teachings, wherein sensors can be placed in critical areas of an aircraft, such as engine inlets, engines core, pitot tubes, elevator skin, wing leading edge and behind ice protected areas where Supercooled Large Droplet Icing (SLD) could cause serious problems. 
         FIG. 2  is a block diagram illustrating an embodiment of the aircraft icing detector system. 
         FIG. 3  illustrates an embodiment of the aircraft icing detector sensor (a hollow microstrip ring resonator) being incorporated into a pitot tube of an aircraft. 
         FIG. 4A  is a front view illustrating an embodiment of the aircraft icing detector sensor (a microstrip ring resonator) according to the principles of the present teachings. 
         FIG. 4B  is a back view illustrating an embodiment of the aircraft icing detector sensor (a microstrip ring resonator) according to the principles of the present teachings. 
         FIG. 4C  is a schematic cross-sectional view illustrating an embodiment of the ice detector sensor sensor (a microstrip ring resonator) of the present teachings. 
         FIG. 4D  is a schematic diagram of the distribution of power with frequency for an unloaded resonator (air) and for the resonator loaded with two types of ice (clear and rime). The resonance frequencies (f i ) are illustrated for the unloaded (air) and loaded resonator with two types of ice (clear and rime). The quality factor (Q d ) is illustrated only for the unloaded (air) resonator. These two parameters (f i  and Q d ) are also strongly affected by the ice thickness. 
         FIG. 5  is a plot showing the real part of the complex dielectric permittivity (ε′) of water and one type of ice. For ice ε′ is approximately constant with frequency, while for water it is much larger and decreases rapidly with frequency at around 10-100 GHz. 
         FIGS. 6A and 6B  are plots showing the imaginary part of the complex dielectric permittivity (ε″) of water and one type of ice. For ice ε″ increases with frequency, while for water it is much larger and decreases rapidly with frequency above around 20 GHz. 
     
    
    
     Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION 
     Example embodiments will now be described more fully with reference to the accompanying drawings. 
     Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail. 
     The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed. 
     When an element or layer is referred to as being “on,” “engaged to,” “connected to,” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to,” “directly connected to,” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     According to the principles of the present teachings, as illustrated in  FIG. 1 , an aircraft icing detector system  10  is provided for detecting ice formation on aircrafts and other objects of interest. In some embodiments, aircraft icing detector system  10  for detecting ice accumulation, the rate of accumulation, the type of ice and the thickness of the ice layer. In some embodiments, aircraft icing detector system  10  can include an ice detector sensor  12 , such as an electromagnetic microwave resonator. In some embodiments, ice detector sensor  12  can be positioned directly at locations that are susceptible to ice formation, critical to flight safety, and/or other areas of interest. By way of non-limiting example, such locations can include the leading edge of wings and other flight surfaces, engines intake areas, engines core, windscreens or other aircraft portals, airspeed measurement systems (such as pitot tubes, static ports, and the like), and other areas where ice accumulation information is desired. Generally, aircraft icing detector system  10  uses variations in the complex dielectric permittivity of water substance (see  FIGS. 5, 6A, 6B ) to detect icing and the type of icing on the areas of interest. 
     In some embodiments, aircraft icing detector system  10  further includes a data processing unit  14  having a central processing unit to receive information from ice detector sensor  12  and determine the complex dielectric permittivity of the detected substance to determine the type of substance as discussed herein. In some embodiments, controller or data processing unit (DPU)  14  can output a control signal that can be routed to a display device  16  to alert a pilot or other user. Additionally, in some embodiments, data processing unit  14  can output a control signal that can be routed to an aircraft control system  18  for activating deicing or anti-icing equipment, output warning or alarms to a user, or activate mediation options. 
     In some embodiments, as illustrated in  FIG. 4 , ice detector sensor  12  can comprise a microstrip ring resonator  20  having an input SMA  22  and an output SMA  24 . Resonator  20  can be disposed on an exterior surface  26  of an aircraft  28  or other surface of interest. Input SMA  22  and output SMA  24  can serve as electrical connection points to receive the signal from a signal-generation circuit and to transmit the signal from ice detector sensor  12  to the data processing unit  14 . In some embodiments, input SMA  22  and output SMA  24  are disposed on an interior surface  28 , opposite exterior surface  26 . As illustrated in  FIG. 4C , ice detector sensor  12  can comprise a layered structure having a ground plate  50 , a microstrip ring resonator  20 , and a substrate  52  disposed therebetween. Ring resonator  20  can define a diameter d and a width of the resonator ring being w s . Ring resonator  20  is where material to be probed or sensed  100  (e.g., ice) will be deposited. 
     In some embodiments, aircraft icing detector system  10  further includes a voltage-controlled oscillator (VCO)  30  used to generate a swept frequency signal ( FIG. 4D ) at each frequency band desired. Control and power supply circuits and digital frequency counters are used to verify the VCO output frequency, wherein said control and power supply circuits and digital frequency counters can be integral with voltage-controlled oscillator  30  or may be incorporated in ice detector sensor  12  and/or data processing unit  14 . Voltage-controlled oscillator  30  outputs a VCO signal that can be amplified and split into two signals. One signal path can feed ice detector sensor  12 , and the other signal can feed a reference. The reference allows the instrument to be calibrated for drifts of the voltage-controlled oscillator  30 , detectors, and amplifiers caused by aging and variations of temperature. This allows accurate measurements of the peak resonant frequency (f i ) and the half-power bandwidth necessary for calculating the quality factor of the resonance (Q d ). 
     In operation, aircraft icing detector system  10  uses changes in the resonant frequency and the quality factor of the oscillator (Q d ) to detect ice and estimate its type and thickness. The fraction of the power transmitted (S 21  is a function of ε′, ε″ and the thickness of the layer of water or ice) and the fraction reflected (S 11 ) by electromagnetic resonators coupled to a transmission line ( FIG. 4 ) depends mostly on the real part of complex dielectric permittivity (ε′) and the thickness of the material in the vicinity of the resonator  20 , in the case of this invention ice accumulated on the surface of the resonator. Thus, measurement of S 21  is sufficient for the implementation of the technique ( FIG. 4D ). 
     In some embodiments, aircraft icing detector system  10  uses multi-frequency resonators similar to the resonator described in  FIGS. 4A, 4B, 4C and 4D  and the algorithm described herein to detect various types of ice and their thickness. 
     The algorithm for detecting the type and the thickness of the ice comprises the following steps (not all sequentially): 
     1. Measure the power of the transmitted signal (S 21 ) as a function of frequency; 
     2. Determine one more resonance frequencies (f i ) and their quality factors (Q d ); 
     3. Use analytical expressions or lookup tables to determine the real part of the complex dielectric permittivity (ε′) at each resonance frequency, and the thickness of the layer of water or ice, based on the value of the transmitted power (S 21 ), resonance frequencies (f i ) and their quality factors (Q d ); 
     4.Use analytical expressions or lookup tables to determine the imaginary part of the complex dielectric permittivity (ε″) at each frequency, and the thickness of the layer of water or ice, based on the value of the power of the transmitted signal (S 21 ), resonance frequencies (f i ) and their quality factors (Q d ); and 
     5. Use analytical expressions or lookup tables based on data similar to that shown in  FIGS. 5, 6A, and 6B  to refine the calculations and confirm or refute the presence of water or ice. 
     The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.