Air-Coupled Ultrasonic Interferometry for Submicron Surface Measurement
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Solution Overview
Problem
Current high-precision measurement methods for free-form surfaces, such as three-axis coordinate machines and optical probes, face challenges in achieving submicron accuracy due to material-specific issues, light absorption, and interference, limiting their applicability and accuracy in nano-machining.
Innovation Solution
An air-coupled ultrasonic interferometric method that uses a probe emitting ultrasonic waves with varying frequencies to measure distance based on phase changes, allowing for high accuracy and reduced interference, with the measurement error proportional to the frequency bandwidth and distance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If optical probes are used for high-precision measurement, then measurement sensitivity can reach 30 mV/μm, but the measurement is greatly affected by material type, color, and light absorption properties
Solution Approach 1:
The patent replaces optical measurement systems with air-coupled ultrasonic interference systems. Instead of using light to measure surface profiles, the invention uses ultrasonic waves propagating through air to interact with the workpiece surface, converting optical measurement problems into acoustic measurement problems that are insensitive to material optical properties.
Solution Approach 2:
The patent changes the measurement parameter from optical properties (light reflection, absorption) to acoustic properties (ultrasonic wave reflection, interference patterns). By measuring the interference pattern of ultrasonic waves rather than light, the system achieves universal applicability across different materials while maintaining high measurement precision.
2Measurement precision
If laser interferometric probes are used, then small relative changes can be detected, but absolute measurement accuracy is limited by three-dimensional coordinate aiming and requires specific laser reflection characteristics
Solution Approach 1:
The patent replaces the laser interferometric system with an air-coupled ultrasonic interference system. Instead of using laser beams and optical interferometry, the invention uses ultrasonic waves in air to create interference patterns that can be detected by a single probe, eliminating the need for complex three-dimensional coordinate aiming while improving both relative and absolute measurement accuracy.
Solution Approach 2:
The ultrasonic interference probe can measure both relative changes and absolute positions with high accuracy, unlike laser interferometric probes that are primarily sensitive to small relative changes. The ultrasonic system provides universal measurement capability across different measurement scenarios without requiring specific surface reflection characteristics.
3Measurement precision
If high-frequency ultrasonic waves are used for air-coupled ultrasonic ranging, then ranging accuracy improves, but attenuation in air becomes too high for practical use
Solution Approach 1:
The patent uses continuous sinusoidal ultrasonic waves instead of short pulses, allowing the ultrasonic wave to maintain stable amplitude over time. This periodic continuous action enables the use of higher frequencies for improved accuracy while the continuous wave nature compensates for atmospheric attenuation through sustained energy presence.
Solution Approach 2:
The patent employs continuous ultrasonic wave emission rather than pulsed transmission, maintaining constant useful action throughout the measurement process. This continuity allows the system to achieve high ranging accuracy by utilizing the steady-state interference pattern of continuous waves, which are less affected by attenuation than pulsed signals.
4Ease of manufacture
If the time difference method is used for air ultrasonic ranging, then implementation is simple, but ranging accuracy is greatly disturbed by external factors and limited to one wavelength accuracy
Solution Approach 1:
The patent replaces the time difference measurement method with an interference pattern measurement method. Instead of measuring the time delay of ultrasonic wave propagation, the invention measures the spatial interference pattern created by reflected ultrasonic waves, converting a time-based measurement into a spatial frequency-based measurement that is much less sensitive to external disturbances.
Solution Approach 2:
The patent changes the measurement parameter from time delay to spatial interference pattern frequency. By measuring the frequency and pattern of ultrasonic interference rather than time differences, the system achieves dramatically improved ranging accuracy (sub-wavelength precision) while maintaining relative implementation simplicity through the use of standard interference detection techniques.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method achieves submicron accuracy for short distances and up to 1% wavelength accuracy for long distances, offering superior precision and robustness against interference, suitable for both free-form surface contouring and automotive ultrasonic radar applications.
Implementation Method 1
the ultrasonic waves emitted by an ultrasonic transducer will be reflected back and forth between the ultrasonic transducer and the surface of the workpiece
Implementation Method 2
the ultrasonic waves emitted by an ultrasonic transducer will be reflected back and forth between the ultrasonic transducer and the surface of the workpiece
Implementation Method 3
air-coupled ultrasonic interferometric method that uses a probe emitting ultrasonic waves with varying frequencies to measure distance based on phase changes
Implementation Method 4
an air-coupled ultrasonic probe is placed directly facing the surface of a workpiece, the ultrasonic waves emitted by an ultrasonic transducer
Data Source
AI summary
An air-coupled ultrasonic interferometric method is disclosed. An air-coupled ultrasonic transducer, as a probe, is placed directly facing the surface of a workpiece, and an ultrasonic wave is reflected back and forth between the ultrasonic transducer and the surface of the workpiece; the phase difference of the first echo reflected from the surface of the workpiece and reaching the air-coupled ultrasonic transducer is measured; based on the change of the ultrasonic frequency and wavelength, the measured distance is transformed into the rate of change of the acoustic phase with respect to the acoustic angular frequency, wherein the change in the acoustic angular frequency is a product obtained by multiplying 2π by the difference between the highest frequency F2 and the lowest frequency F1 within the bandwidth fB of the air-coupled ultrasonic transducer.