Characterization of objects by means of ultrasonic waves
First Claim
1. A method for characterizing an object with boundary surfaces by means of ultrasound, comprising the steps ofa) determining a time dependent base impulse from reference signals, b) creating at least one ultrasonic wave in said object, c) detecting echo waves reflected by said boundary surfaces, thus determining a time dependent measuring signal, d) digitalizing said time dependent measuring signal, e) creating a time dependent calculated signal as the sum of temporally shifted and weighed modifications of said base impulse, f) evaluating the sum of the squares of the differences between said measuring signal and said calculated signal, g) repeating evolution steps e) and f) until one optimal calculated signal is found, for which said sum of the squares of the differences between the measuring signal and the calculated signal is minimized, and h) determining a measurement result from the temporal shifts and weightings of this one calculated signal.
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Abstract
To characterize an object (3) to be measured, for example to gauge the thickness (d7) of a layer (7) borne by a substrate (4), an ultrasonic wave (8.1) is transmitted by a measuring device (1). Echo impulses (8.2, 8.5) reflected by boundary surfaces (5, 10) of the object (3) to be measured are detected by the measuring device (1); the measuring signal is digitalised and subjected to an evolution analysis in the time domain. The evolution analysis uses an algorithm which is computation-efficient by orthogonalisation and implemented search strategy. The characteristics of the object to be measured, for example the thicknesses, are determined from the delay time differences of the echo waves (8.2, 3.5).
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Citations
24 Claims
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1. A method for characterizing an object with boundary surfaces by means of ultrasound, comprising the steps of
a) determining a time dependent base impulse from reference signals, b) creating at least one ultrasonic wave in said object, c) detecting echo waves reflected by said boundary surfaces, thus determining a time dependent measuring signal, d) digitalizing said time dependent measuring signal, e) creating a time dependent calculated signal as the sum of temporally shifted and weighed modifications of said base impulse, f) evaluating the sum of the squares of the differences between said measuring signal and said calculated signal, g) repeating evolution steps e) and f) until one optimal calculated signal is found, for which said sum of the squares of the differences between the measuring signal and the calculated signal is minimized, and h) determining a measurement result from the temporal shifts and weightings of this one calculated signal.
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13. A method for characterizing, an object with boundary surfaces by means of ultrasound, comprising the steps of
a) determining a time dependent base impulse from reference signals, b) creating, at least one ultrasonic wave in said object, c) detecting echo waves reflected by said boundary surfaces, thus determining in a time dependent measuring signal, d) digitalizing said time dependent measuring signal, e) creating a time dependent calculated signal as the sum of temporally shifted and weighed modifications of said base impulse, f) evaluating a measure for the difference between said calculated signal and said measuring signal, g) repeating evolution steps e) and f) until one optimal calculated signal is found, for which said measure for the difference between said calculated signal and said measuring signal is minimized, and h) determining a measurement result from the temporal shifts and weightings of this one calculated signal, wherein orthogonalization is used for creating the time dependent calculated signal.
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14. A measuring device characterizing an object with boundary surfaces by means of ultrasound, comprising a transducer unit or a plurality of transducer units with ultrasound transducer means for converting electrical energy to ultrasound energy, an ultrasound transmitter unit to supply said transducer unit with electrical signals, an ultrasound receiver unit for receiving echo waves reflected by said boundary surfaces, and means for convicting, ultrasound energy contained in said echo waves to electric energy thus determining a time dependent measuring signal, a storage means for storing a digital representation of a time dependent base impulse from reference signals, an analogue-digital transducer unit for digitalizing said time dependent measuring signal, a microprocessor system possessing a code for control and evaluation, such code configured to make the microprocessor system carry out the following evaluation steps:
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a) creating a time dependent calculated signal as the sum of temporally shifted and weighed modifications of said base impulse, b) evaluating the sum of the squares of the differences between said measuring signal and said calculated signal, c) repeating evolution steps e) and f0 until one optimal calculated signal is found, for which said sum of the squares of the differences between the measuring signal and the calculated signal is minimized, and d) determining a measurement result from the temporal shifts and weightings of this one calculated signal. - View Dependent Claims (15, 16, 17, 18, 19, 20, 21, 22, 23, 24)
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Specification