The present invention relates generally to systems and methods for evaluating a material through measurements of transmitted energy. More particularly, the present invention relates to systems and methods for calibration of a material characterization system that is based on measured electromagnetic waves.
Evaluation methods and apparatuses exist within various industries for characterizing electrical and physical properties of a material. Certain properties of a material may be determined by measuring the response of the material to electromagnetic waves impinging upon it, in terms of transmissivity, reflectivity, and absorptivity. In general, the characterization of a sample layer of material is based on a measurement of the electromagnetic scattering parameters of such layer as compared to the corresponding set of electromagnetic scattering parameters, using the same set up, of a layer of reference material used for calibration. Thus, two sets of measurements are performed requiring a set up as identical as possible to avoid characterization inaccuracies.
Accordingly, the performance and reliability of a material characterization system depends on the accuracy and repeatability of a set of measurements conducted to calibrate such system. In particular, the characterization of single-layer and multilayer materials by means of electromagnetic waves heavily relies on an accurate calibration of the scattering parameters of the system.
More specifically, a universal calibration method and apparatus to determine a characteristic of certain materials by means of radio frequency sensors have been addressed in the prior art, as described in U.S. Pat. No. 6,691,563 to Trabelsi et al. However, this method is primarily aimed to determine a universal calibration equation exclusively for estimating the level of moisture content of a material at a given time, based on experimental data.
Typically, instead of determining a status or a certain characteristic of a material at a given time, the goal of a material characterization system is to determine a set of properties of the material, such as those derived from a measurement of the transmissivity, reflectivity, and absorptivity of the material. This set of properties includes surface resistivity, ohmic conductivity, dissipation loss, complex magnetic permeability, and complex dielectric permittivity, in addition to thickness, density, homogeneity, and manufacturing defects, such as the presence of voids or undesired particles either during or after production of the material.
Currently, there is no well-established method of deterministically calibrating a material characterization system accurately by measuring and recording a single set of calibration data. Usually, because the accuracy of the material characterization system critically depends on having a set up as identical as possible for both calibration and characterization measurements, it is required that the sample under test and a reference material have the same thickness. In many cases, this might be difficult or impossible to achieve, particularly where the thickness of the sample under test is in the order of hundreds of microns. Also, preparing a reference layer identical to a sample layer might result in an inefficient and lengthy process. In addition, having a set of samples with a number of thicknesses to cover the range of possible samples to be characterized might be impractical or impose severe limitations to the material characterization system and its users.
As a result, users of a material characterization system typically experience inaccurate, lengthy, and inefficient calibration and characterization processes. On the one hand, different positioning or setups during the measurements of the reference material and the evaluation of the sample under test may largely compromise the accuracy of the characterization. Variations in position may be caused by a number of factors, including a lack of accurate control or not fine enough resolution of the positioning system, thickness variations of the measured materials, and fluttering and displacement of the material to be characterized.
On the other hand, the need to set up and measure a different reference material every time that a sample under test is changed or its thickness varies, involves a lengthier process and practical inconveniences that may severely impair the use of the material characterization system and build up to a highly inefficient characterization process. Each of these aspects is subject to uncertainties that make it difficult to create an accurate characterization of a material.
Previous efforts have been made to use electromagnetic waves in assisting with the calibration of a system to measure one or more properties of a material, as described in U.S. Pat. No. 6,754,543 to Wold and U.S. Pat. App. No. 20020075006 by Goldfine et al. However, these efforts have faced certain challenges and limitations. In particular, attempts made to characterize thin layers of material where thickness variations in the order of tens of microns may affect a measurement. Likewise, in a production environment, quality control of the material may be limited to measurements of a few samples because the time involved in evaluating the material may make prohibitive measuring the whole production. A major challenge is that in a production line, fluttering and displacement of a thin film of a material from a baseline position is typically unavoidable. Therefore, a characterization of a material may, as a result, be impractical and very challenging.
Thus, there remains a need in the art for methods and apparatuses capable of providing the means to accurately and effectively calibrate a material characterization system, through measurements of electromagnetic waves, that avoid the problems of prior art methods and devices.
An improved method and apparatus to set up measurements for collecting data to calibrate a material characterization system are disclosed herein. One or more aspects of exemplary embodiments provide advantages while avoiding disadvantages of the prior art. The method and apparatus are operative to set up multiple configurations for measuring and recording a specific characteristic response of the system for each configuration, using electromagnetic waves. The apparatus is designed to enable the system to measure and record the position of a reference material and a set of calibration data for such reference material, while positioned at locations that correspond to a range of possible thicknesses or fluttering during measurements of a sample that the system is capable of characterizing. As a result, a sample under test having a specific thickness and measured at a particular position can be readily calibrated analytically or by using reference data previously recorded with the same set up.
The method of setting up multiple configurations for data collection to calibrate a material characterization system, using electromagnetic waves, includes the steps of attaching a supporting structure to a material characterization system to be calibrated and measuring and recording the S11 and S22 scattering parameters corresponding to a first reference material at different positions. The method further includes the steps of replacing the first reference material with a second reference material and measuring and recording the S12 or S21 scattering parameter, while maintaining the same mechanical set up at such different positions. The method also includes removing the supporting structure, as required, from the material characterization system.
The apparatus includes one or more structures configured and positioned to accurately set up a reference material at a plurality of positions to be measured by a material characterization system. By recording the measured characteristic response of such known reference material at these known plurality of positions, it is possible to calibrate and compare the corresponding response of a material to be characterized, having the same set up.
Accordingly, the collection of a set of calibration data for each possible position, corresponding to the different thicknesses or fluttering during measurements of a sample of a material to be characterized, allows a single calibration of the material characterization system. The minimum difference in distance among any two of these positions defines the distance resolution of the calibration. The apparatus may include technology to enable a distance resolution in the order of 10 microns.
As a result, the apparatus increases the accuracy of the positions at which the calibration data is collected. In addition, there is no need to measure a set of calibration data every time a material characterization measurement is performed, as is typically done using standard techniques. This is particularly important where evaluation of multiple samples of a material are required or in a production line where a material characterization system is used to monitor the quality of a material under production.
Thus, by enabling the collection of calibration data only once, at accurate positions, with a low distance resolution, the method and apparatus are capable of significantly improving both the calibration and the overall material characterization processes, as compared to standard techniques.
The numerous advantages of the present invention may be better understood by those skilled in the art by reference to the accompanying drawings in which:
The following description is of a method and one or more particular embodiments of an apparatus, set out to enable one to practice an implementation of the invention, and is not intended to limit the preferred embodiment, but to serve as a particular example thereof. Those skilled in the art should appreciate that they may readily use the conception and specific embodiments disclosed as a basis for modifying or designing other methods and systems for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent assemblies do not depart from the spirit and scope of the invention in its broadest form.
Once a sample layer of material under test is placed on the module tray of the calibrated material characterization system, the thickness and position of the sample can be measured using the measurement tool used during the calibration process. Therefore, the position of the sample will be within 10 microns, or as determined in step 120, of two positions of the recorded calibration data. Therefore, the S11, S22, and S12 or S21 measured data corresponding to these two positions can be used to accurately characterize the sample layer of the material under test.
Those skilled in the art will recognize that the steps above indicated can be correspondingly adjusted for specific material characterization system configurations. In particular, the steps to complete the calibration measurements of the S12 or S21 parameter can be performed before the calibration measurements of the S11 and S22 parameters. Likewise, the use, position, and function of the bottom or top trays of the two-stacked-tray structure may be altered or switched depending on the particular material characterization system to be calibrated. Also, those skilled in the art will realize that other type of reference materials may be used to perform S11, S22, and S12 or S21 measurements using the same reference material, including one or a combination of more than one of a transparent conductive material, a nanowire or a copper mesh, metamaterials, and nanomaterials.
In accordance with certain aspects of an embodiment of the invention,
In particular,
Thus, in a preferred configuration, apparatus 50 comprises one or more distance sensors 32a and 32b to measure the location of a first reference material 51 with respect to bottom tray 54, probe 26, probe 29 or any other reference point at each calibration measurement position. Distance sensors 32a or 32b may include a laser sensor, an acoustic sensor, and a measurement tool either installed as part of or added-on to the material characterization system.
More specifically,
In reference to
Additionally, each extension arm 58a, 58b, 58c, and 58d inserts into a corresponding circular through-hole 55a, 55b, 55c, and 55d on top tray 56. Preferably, the diameter of each circular through-hole 55a, 55b, 55c, and 55d of top tray 56 is just large enough to allow top tray 56 to slide along extension arms 58a, 58b, 58c, and 58d, while maintaining mechanical stability during motion and during measurements at fixed positions. Those skilled in the art will recognize that other methods may be implemented for a stable mechanical guidance of top tray 56. For instance, a different number of extension arms, preferably two or more, may be used. Alternatively, a semicircular dent in two or more sides of top tray 56 may be used to fit an extension arm as described above.
In a preferred configuration, and in reference to
Therefore, when step motors 52a, 52b, 52c, and 52d actuate, corresponding actuation arms 59a, 59b, 59c, and 59d may cause top tray 56 to move up or down, or equivalently away from or closer to bottom tray 54 at certain step increments. In other words, actuation arms 59a, 59b, 59c, and 59d use bottom tray 54 as an anchor to push up top tray 56 away from the bottom tray 54 from a position in which top tray 56 and bottom tray 54 are at the closest distance. Preferably, step motors 52a, 52b, 52c, and 52d move top tray 56 in increments as small as 10 microns. The step increment at which step motors 52a, 52b, 52c, and 52d move top tray 56 determines a calibration distance resolution of the material characterization system. This configuration of apparatus 50 allows measurement setups to obtain calibration data of a sample of a material having a thickness of at least between 50 microns and 40 mm.
In general, apparatus 50 mechanically attaches to a measuring module tray of the material characterization system to be calibrated, such that bottom tray 54 and top tray 56 are disposed substantially parallel to such measuring module tray. Accordingly, apparatus 50 may have one or more sensors to level bottom tray 54 and top tray 56 with respect to the measuring module tray. Moreover, apparatus 50 may be integrated with the material characterization system in a fixed or temporary configuration. Thus, apparatus 50 may be portable and used to calibrate the material characterization system only once or as needed. Alternatively, apparatus 50 may be attached to and become an integral part of the material characterization system.
Preferably, in an alternative configuration, apparatus 50 further comprises hardware, software, and firmware to enable apparatus 50 to perform automated, electronic calibration of a material characterization system as a self-contained E-Cal Tray Kit. In a preferred configuration as an E-Cal Tray Kit, apparatus 50 comprises a motor controller to drive step motors 52a, 52b, 52c, and 52d and is connected to a computer by means of a Universal Serial Bus (USB) connector. More preferably, an E-Cal Tray software installed in the computer may be used to perform automated measurements of the scattering parameters required for the calibration process.
The use of apparatus 50 as an E-Cal Tray Kit helps also to reduce inaccuracies of the characterization measurements by calibrating out any inconsistencies resulting from the manufacturing and assembly phases of the material characterization system. More specifically, an E-Cal Tray Kit may be programmed to automatically position top tray 56, by means of a motorized unit, and measure the scattering parameters of a reference material at every 10 microns over a range of up to 40 mm or in accordance with the specifications of the material characterization system to be calibrated. Most preferably, such reference material comprises a material highly reflective of electromagnetic waves at the frequencies of interest, including a conductive material, such as a metal plate or a layer of a metal compound.
Those skilled in the art will recognize other ways of integrating apparatus 50 with a material characterization system, including by means of a straight, L-shaped or U-shaped arm; a flange; fasteners; hooks; clamps; adhesive, and straps, depending on the temporary or permanent nature of the attachment. Preferably, the integration of apparatus 50 incorporates existing trays to compensate for manufacturing and material inconsistencies of the material characterization system. Accordingly, in an alternative configuration, apparatus 50 may not require two trays. However, replacement of a component of the material characterization to install apparatus 50 may be advisable in certain situations.
A preferred mechanism to attach apparatus 50 to a material characterization system includes a manner to have an adjustable set up, including by means of a gear mechanism, calibrated screws, and knobs. More preferably, the attachment mechanism is also reconfigurable to adapt to different settings of spacing and positioning of a material. Those skilled in the art will also realize that other operational modes of using apparatus 50 may be implemented, such as manual or semi-automated. In particular, the movement of apparatus 50 to set up a position may be controlled by a hand-operated dial system.
Those skilled in the art will also realize that in certain instances a sample of a material having an edge treatment, such as a radio frequency absorber material, may need to be measured. In these instances, the absorber material may be configured to easily integrate into the material characterization system. Alternatively, apparatus 50 may comprise an absorber material, configured as a mold and cast into top tray 56, wherein a sample of a material to be measured fits. Thus, casting the absorber material allows to more easily obtain a desired shape, such as a wedge, as compared to casting the reference material.
In accordance with another embodiment,
Preferably, each top mounting plate 69b, 69d, and 69f attaches to top tray 64 by means of two thumb screws 65a and 65b, 65c and 65d, and 65e and 65f. Likewise, each bottom mounting plate 69a, 69c, and 69e attaches to bottom tray 62 by means of two thumb screws (not shown). In this configuration, the thumb screws are preferred for easy mounting and dismounting of mounting plates 69a, 69b, 69c, 69d, 69e, and 69f to and from bottom tray 62 and top tray 64. However, those skilled in the art will recognize other means of attaching mounting plates 69a, 69b, 69c, 69d, 69e, and 69f to bottom tray 62 and top tray 64.
More preferably, mounting plates 69a, 69b, 69c, 69d, 69e, and 69f are attached to bottom tray 62 and top tray 64, such that step motors 66a, 66b, and 66c are disposed equidistant one another around the perimeters of bottom tray 62 and top tray 64, forming an equilateral triangle. Most preferably, step motors 66a, 66b, and 66c are wired in series or daisy-chained together to a motor driver and controller connected to a computer via a USB cable, as well known in the prior art. Most preferably, an E-Cal Tray software is installed in the computer and may be used to perform automated measurements at different setups during the calibration process.
The method and various embodiments of the apparatus for setting up the data collection configurations to perform the calibration of a material characterization system have been described herein in an illustrative manner, and it is to be understood that the terminology used is intended to be in the nature of words of description rather than of limitation. Any embodiment herein disclosed may include one or more aspects of the other embodiments. The exemplary embodiments were described to explain some of the principles of the present invention so that others skilled in the art may practice the invention. Obviously, many modifications and variations of the invention are possible in light of the above teachings. The present invention may be practiced otherwise than as specifically described within the scope of the appended claims and their legal equivalents.
This application is based upon and claims priority from co-pending U.S. Provisional Patent Application Ser. No. 62/097,898 entitled “Method and Apparatus for Calibration of a Material Characterization System” filed with the U.S. Patent and Trademark Office on Dec. 30, 2014, by the inventors herein, the specification of which is incorporated herein by reference.
This invention was made with Government support under contract number SB1341-13-CN-0035, awarded by National Institute of Standards and Technology (NIST). The Government may have certain rights in the invention.
Number | Date | Country | |
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62097898 | Dec 2014 | US |