Patent Application
20060153739
This invention relates generally to the testing of materials and, more particularly, to methods and apparatus for evaluating material properties of radio frequency (RF) absorbent materials.
At least some known methods used for testing RF absorbent materials use samples that are formed precisely for placement inside a waveguide. Such testing methods are generally not reliable for evaluating highly conductive fillers used with low observable (LO) applications because of gaps that may exist between an outer periphery of the sample and an inner periphery of the waveguide. More specifically, the gaps may introduce unpredictable measurement errors into the test, thus, resulting in inaccurate measurements of RF reflection loss in the waveguide from highly conductive fillers.
Other known free space methods have been used to attempt to characterize conductive fillers. However, such methods generally have the disadvantage of requiring a large sample size.
In one aspect, a system for evaluating a material sample is provided. The system includes a material sample holder including a first flange having an aperture therethrough, a second flange having an aperture therethrough, the first and second flanges configured to frictionally hold a material sample sandwiched therebetween, a waveguide coupled to a first end of each of the first flange and the second flange, each waveguide configured to direct electromagnetic waves through respective apertures, a waveguide adapter communicatively coupled to a second end of each waveguide, and a control unit electrically coupled to the wave source, the control unit configured to control the waveguide adapter to transmit and receive electromagnetic wave signals.
In another aspect, a material sample holder for testing an electromagnetic energy absorbent material is provided. The material sample holder includes a first flange including a face and an aperture therethrough, the first flange is configured to mate to a first surface of a material sample. The material sample holder also includes a second flange including a face and an aperture therethrough, the second flange is configured to mate to a second surface of a material sample, wherein the first and the second flanges are configured to sandwich the material sample such that the face of the first flange engages the first surface and the face of the second flange engages the second surface.
In yet another aspect, a method of evaluating a material sample is provided. The method includes sandwiching a material sample between a transmitting waveguide flange having an aperture therethrough and in communication with a transmitting waveguide, and a receiving waveguide flange having an aperture therethrough and in communication with a receiving waveguide, the apertures are configured to be completely covered by the material sample when the sample is installed between the flanges, emitting an electromagnetic wave through the transmitting waveguide to the material sample, receiving electromagnetic energy from the electromagnetic wave through the sample, and determining a material property of the material sample using the emitted wave and the received energy.
In operation, RF absorbent material sample 113 is sandwiched between flanges 114 and 116 and waveguide assemblies 104 and 106 are assembled such that waveguide adapter 122 is in RF communication with waveguide 118 and waveguide adapter 126 is in RF communication with waveguide 120. Each waveguide adapter 122 and 126 is coupled to respective ports 132 and 136 of control unit 112. As RF energy is transmitted through waveguide 118 toward sample 113, port 136 receives a signal from waveguide adapter 126 proportional to the RF energy that may leak through sample 113. Similarly, RF energy is transmitted through waveguide 120 toward sample 113, port 132 receives a signal from waveguide adapter 122 proportional to the RF energy that may leak through sample 113. Using the received signals, reflection loss measurements may be obtained and when combined with finite element model (FEM) waveguide code, S parameter measurements obtained, may be converted into Rf material properties using a transfer function derived from the FEM analysis.
In the exemplary embodiment, aperture 202 is illustrated as having a rectangular cross-section. It should be understood that this illustration is exemplary only and aperture 202 may be any shape capable of permitting radio frequency material testing system 100 to perform the functions described herein.
A technical effect of the various embodiments of the invention is to automatically determine a reflection loss of a highly conductive sample using a method that facilitates reducing leakage of RF energy past the sample that would otherwise affect the accuracy of the reflection loss evaluation.
The various embodiments or components thereof may be implemented as part of a computer system. The computer system may include a computer, an input device, a display unit and an interface, for example, for accessing the Internet. The computer may include a microprocessor. The microprocessor may be connected to a communication bus. The computer may also include a memory. The memory may include Random Access Memory (RAM) and Read Only Memory (ROM). The computer system further may include a storage device, which may be, but not limited to, a hard disk drive, a solid state drive, and/or a removable storage drive such as a floppy disk drive, or optical disk drive. The storage device can also be other similar means for loading computer programs or other instructions into the computer system.
As used herein, the term “computer” may include any processor-based or microprocessor-based system including systems using microcontrollers, reduced instruction set circuits (RISC), application specific integrated circuits (ASICs), logic circuits, and any other circuit or processor capable of executing the functions described herein. The above examples are exemplary only, and are thus not intended to limit in any way the definition and/or meaning of the term “computer.”
The computer system executes a set of instructions that are stored in one or more storage elements, in order to process input data. The storage elements may also hold data or other information as desired or needed. The storage element may be in the form of an information source or a physical memory element within the processing machine.
The set of instructions may include various commands that instruct the processing machine to perform specific operations such as the processes of the various embodiments of the invention. The set of instructions may be in the form of a software program. The software may be in various forms such as system software or application software. Further, the software may be in the form of a collection of separate programs, a program module within a larger program or a portion of a program module. The software also may include modular programming in the form of object-oriented programming. The processing of input data by the processing machine may be in response to user commands, or in response to results of previous processing, or in response to a request made by another processing machine.
As used herein, the terms “software” and “firmware” are interchangeable, and include any computer program stored in memory for execution by a computer, including RAM memory, ROM memory, EPROM memory, EEPROM memory, and non-volatile RAM (NVRAM) memory. The above memory types are exemplary only, and are thus not limiting as to the types of memory usable for storage of a computer program.
While the present invention is described with reference to RF energy absorbent conductive fillers, numerous other applications are contemplated. It is contemplated that the present invention may be applied to any material evaluation where leakage of a measurement medium past the sample may adversely affect the accuracy of the measurement and subsequent evaluation.
The above-described radio frequency material testing system is a cost-effective and highly reliable means for determining material properties of a sample. The system is configured to receive a sample sandwiched between flanges of a sample holder such that the sample completely covers the flange aperture substantially eliminating the ability of the measurement medium to bypass the sample. Accordingly, the radio frequency material testing system facilitates measuring the material properties of a sample, and in particular conductive filler material, in a cost-effective and reliable manner.
Exemplary embodiments of radio frequency material testing system components are described above in detail. The components are not limited to the specific embodiments described herein, but rather, components of each system may be utilized independently and separately from other components described herein. Each radio frequency material testing system component can also be used in combination with other radio frequency material testing system components.
While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.
