Measuring and testing – Vibration – Resonance – frequency – or amplitude study
Patent
1999-05-05
2000-07-18
Moller, Richard A.
Measuring and testing
Vibration
Resonance, frequency, or amplitude study
73159, G01N 2918
Patent
active
060890940
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention measures the thickness distribution of the protective barrier membrane used in personal protective equipment such a surgical latex or other gloves, protective clothing or condoms, in order to provide information on the thickness and the correspondent relative area of the protective barrier membrane.
BACKGROUND ART
Thickness is one of the quality control data of the protective barrier membrane which is required by the U.S. Government and American Society for Testing and Materials (ASTM). The minimum thickness requirement is 0.1 mm for rubber surgical gloves [2], and 0.08 mm for rubber examination gloves [3].
The thickness of rubber barrier can be tested using the following methods:
Micrometer method. A dial micrometer with an anvil and a pressure foot is used to exert a certain force on the membrane, which is placed between the anvil and the pressure foot. The dial is graduated to read the thickness of the membrane [4], [5].
Optical method. A microscope equipped with a mechanical stage, and a ruled glass disk or ocular micrometer is used to directly read the scale of the thickness of a barrier membrane, which stands edgewise on the stage [6].
Acoustic echo method. An acoustic system measures the thickness of a barrier by propagating an acoustic wave through the barrier membrane such that echo waves are generated and received by a transducer. The thickness value is obtained from the time lapse between the propagated wave and receipt of the echo wave [7].
Two U.S. patents deal with the acoustic echo method using a sweeping acoustic frequency and the echo waves from the interfaces either to measure the thickness of a coating layer on a substrate, or to control the depth of removal of a selected material on a polishing pad [8], [9]. The transmission pattern of the acoustic waves is provides a basis for determining the thickness of the coating or the depth of the removal.
Glossary of Symbols
wave.
DISCLOSURE OF THE INVENTION
The present invention relates a method and a system for membrane thickness and the correspondent area distribution measurement based on the dependence of the acoustic intensity transmission coefficient upon the thickness of the insertion membrane and the proportion of the power of the transmitted acoustic plane waves to the area of the insertion membrane. The principle of this invention is that when the acoustic wave travels in the acoustic medium and encounter an insertion membrane with different acoustic impedance, the intensity transmission coefficient T is related to the thickness of the insertion membrane d, and the frequency of the transmitting acoustic wave f. As f sweeps, maximum T (T.sub.max =1) occurs at a set of frequency points corresponding to a certain thickness of the insertion membrane. By confining the sweeping frequency within a certain range, T.sub.max can only occur at one frequency point corresponding to a certain thickness of the insertion membrane. This frequency can be converted into the correspondent membrane thickness. The power of the maximum transmission of a plane wave is proportional to the area of the correspondent thickness of the membrane. The transmitted power of the acoustic wave at the frequency of T.sub.max can be converted into the area of the insertion membrane with the correspondent thickness. If the insertion membrane has different thicknesses, T.sub.max occurs at different frequency points with different maximum transmission power values corresponding to different thicknesses of the insertion membrane with different correspondent areas. The derived method to measure the thickness of the barrier membrane is to observe maximum power of a plane acoustic wave reflected from the insertion barrier membrane. This derived method is actually equivalent to the former method, since the intensity reflection coefficient R is equal to 1-T for normal incidence acoustic wave.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 shows the system for measuring the thickness distribution of barrier membranes using the maximum transmis
REFERENCES:
patent: 3844166 (1974-10-01), Carossi et al.
patent: 4539847 (1985-09-01), Paap
patent: 5222329 (1993-06-01), Yu
patent: 5271274 (1993-12-01), Khuri-Yakub et al.
patent: 5672828 (1997-09-01), Allan
Kinsler, LE, Frey Art, Coppens AB, Sanders JV [1982]. Fundamentals of acoustics. 3.sup.rd ed., New York, NY; W.J., pp. 126-131.
American Society for Testing and Materials [1990]. Standard specification for rubber surgical gloves. In: ASTM Standards on protective clothing. Philadelphia, PA, American Society for Testing and Materials, pp. 133-135.
American Society for Testing Materials [1990]. Standard specification for rubber examination gloves. In: ASTM standards on protective clothing. Philadelphia, PA, American Society for Testing and Materials, pp. 136-138.
Method 2011: Thickness micrometer, flat foot [1955]. Fed. Test method std., No. 601.
Method 2031: Thickness, optical [1955]. Fed. Test method std. No.
Berardinelli Stephen P.
Zeng Shengke
Moller Richard A.
The United States of America as represented by the Department of
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