Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Distributive type parameters
Reexamination Certificate
2001-12-17
2003-08-19
Le, N. (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Distributive type parameters
C324S533000, C324S534000
Reexamination Certificate
active
06608489
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to electronic detection derived from correlating changes in dielectric field strength. More particularly, it applies to systems that detect the presence of certain classes and combinations of material as the material accumulates on a surface, e.g., ice buildup on the surfaces of aircraft.
BACKGROUND
Ice accretion on the wings of fixed-wing and on the rotors of rotary-wing aircraft can have disastrous results. The ice that forms on a wing structure, especially along the leading edge, modifies the aerodynamics of the wing, resulting in decreased lift. In the extreme, this can lead to loss of lift and control of the aircraft and potentially a crash. Ice accumulating elsewhere on the wing and airframe can add significant weight to the aircraft. Several techniques and flight protocols have been developed and are widely used to prevent a plane from becoming ice covered, both in flight and on the ground.
Some, typically larger aircraft, are equipped with in-flight heaters that melt the ice before it can substantially build up on wings or rotor blades. Protocols have been established for permitting or denying flight under weather conditions or into areas where the potential of aircraft icing is high. On the ground, there are deicing protocols and methods that ensure that there is little to no accretion of ice on wings or rotors immediately prior to flight.
An outstanding problem is that it is difficult while in flight or on the ground to determine when ice is building up on the aircraft until a substantial accretion has taken place. By that time, it may be difficult or even too late to take evasive maneuvers or rely on the in-flight deicing capability.
On the ground, it would be useful to monitor the state of wing and airframe coverage by deicing fluid, liquid water or the accretion of ice. Availability of this information can be used to decide when to implement deicing procedures with greater efficiency and economy.
Current icing detectors using radio frequencies (RF) in transmission lines are single point detectors. For example, U.S. Pat. No. 5,695,155
, Resonator Based Surface Condition Sensor
, issued to; MacDonald et al., Dec. 9, 1997, uses multiple microstrip resonators, one for each point, positioned to couple with an RF energized transmission line. The resonators produce amplitude minima in the RF signal, the resonance changing dependent upon the makeup of the dielectric covering the microstrips. By fabricating each microstrip to have a different resonant frequency and knowing where each is installed, the location of material accretion can be identified.
U.S. Pat. No. 5,772,153
, Aircraft Icing Sensors
, issued to Abaunza et al., Jun. 30, 1998, employs complex phase detection circuitry with a parallel electrode “surface gap transmission line” that must be affixed to various locations of interest on a surface, one for each point. In a preferred embodiment the surface gap transmission line is energized with an electric field of varying frequency that is reflected by a ground (conducting) plane upwards into a volume immediately above and between the two electrodes. It determines the makeup of the material on the surface, if any, by detecting phase changes in the RF signal passing down the two electrodes and reflecting upwards from the ground plane and converting these phase changes to “propagation times” to correlate to changes in the square root of the dielectric constant of the media through which the reflected RF signal passes. Temperature data may also be used to provide an unambiguous determination of the material. One embodiment also uses an identical second sensor system as a reference, eliminating the need to determine temperature.
Other ice detectors use acoustics, heat, light, or a combination thereof, e.g., U.S. Pat. No. 5,467,944
, Detector For Indicating Ice Formation on the Wing of an Aircraft
, issued to Luukkala, Nov. 21, 1995 is based on a thread-like or a tape-like transducer, through which an ultrasonic signal is transmitted at one end. The attenuation of a signal passing through the thread is measured with a receiver at the opposite end while the thread is simultaneously being heated such that ice that may surround it melts again, the attenuation thus resuming its initial level. U.S. Pat. No. 5,629,485
, Contaminant Detection System
, issued to Rose et al., May 13, 1997, transmits ultrasonic signals through a surface “skin” and collects data based on propagation of these signals through the skin and the dispersion curves representing natural resonance of the signals on an “unloaded” surface skin. Knowing a priori the response of an “unloaded” skin and a catalog of responses for one that is loaded with a variety of materials, e.g., water, ice, glycol, and combinations thereof, a detector and warning system may be applied to various applications, e.g., buildup of ice on an airframe.
A preferred embodiment of the present invention provides a continuous indication of the presence or absence of a buildup of material on a surface, e.g., liquid water, glycols or ice alone, or mixed phase liquid water, glycols and ice, over large areas of an airframe. Additionally, it has the potential to indicate the presence of at least a pre-specified minimum level of a contaminant on any region of a surface instrumented with a preferred embodiment of the present invention.
SUMMARY
A system is provided for detecting accumulation of types of material, including combinations of types, upon multiple areas of a surface concurrently. In one preferred embodiment, it uses a single long wire conductor having a pre-specified characteristic impedance. At one end of the conductor an energizing source is connected while at the opposite or distal end the conductor is configured to have a “termination impedance” different from the conductor's characteristic impedance. For this embodiment, an electromagnetically conducting ground plane is employed. The ground plane abuts the conductor but is electromagnetically isolated from it. The ground plane may be part of the surface being instrumented if that surface is a good conductor. A second preferred embodiment does not require an adjoining ground plane, but uses another similar conductor run parallel and in the same plane as the single conductor or the single wire configuration. This is useful when the surface comprises a strong dielectric such as fiberglass.
A major part of the system is the sub-system comprising a reflectometer, either a Time Domain Reflectometer, including commercial models, or an FM-CW reflectometer. One function of the reflectometer is to provide the analog signal that energizes the conductor, typically a transmission line. It also processes the reflection of the analog signal from the distal end as well as partial reflections from any dielectric discontinuities present at boundaries indicative of accumulation of material on the surface above the conductor. The processed reflected signal, combined with a portion of the original signal, yields information for decision making.
A number of configurations can be used for the transmission lines, e.g., conducting tape electromagnetically insulated on one side, striplines, electromagnetically insulated wires, coaxial cable, and substrates having at least a dielectric layer and an electromagnetically conducting layer.
The TDR may be fabricated from components. One example uses a generator for providing a pulse of narrow pulsewidth and appropriate repetition frequency; a circulator for coupling the pulsed signals to the conductor and coupling the reflections from the conductor to the TDR; and a processor for processing the signals and displaying results, such as an oscilloscope.
The FM-CW reflectometer may be constructed from the following components: a linear sweep generator for generating the FM-CW analog signal; a circulator for coupling the FM-CW signal to the conductor and the reflected signals from the conductor to the reflectometer; a mixer for combining the reflected signal with a portion of the initial analog signal; a low pass
Ryerson Charles C.
Yankielun Norbert E.
Baugher Jr. Earl H.
Lair Donald M
Le N.
The United States of America as represented by the Secretary of
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