Spatially Resolved Measurement Using DDS Digital Filtering
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Solution Overview
Problem
Existing spatially resolved measurement systems face limitations in speed and noise levels due to reliance on analog filters, which are prone to component tolerances and require long settling times, affecting amplitude and phase measurements.
Innovation Solution
The method involves generating three electrical signals with specific frequencies, using direct digital synthesis to produce a digitized signal that allows for digital filtering, eliminating the need for analog filters and enabling faster and less noisy measurements by precise digital sampling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If analog filters are used in the measurement system, then the system can process signals, but the measurement speed is reduced due to long settling times and noise levels increase due to component tolerances and drift
Solution Approach 1:
The patent replaces the mechanical/analog filtering system with a digital signal processing system. Specifically, analog filters are substituted by digital filters implemented in a microprocessor or DSP, which eliminates the settling time issues and component drift problems inherent in analog systems while maintaining signal processing capability. The digital system processes the mixed signal through ADC conversion followed by digital filtering and Fourier transformation, achieving both fast response and high measurement accuracy.
2Loss of time
If the difference frequency is increased to improve time resolution, then measurement speed improves, but the bandwidth requirements increase making the system more complex
Solution Approach 1:
The patent employs dynamic frequency modulation where the optical carrier frequency is modulated by a sinusoidal signal at frequency f1, and the local oscillator operates at frequency f2 = f1 - f_diff. This dynamic modulation scheme allows the system to achieve high time resolution through appropriate choice of difference frequency while the digital signal processing adapts to process the resulting mixed signal. The system dynamically adjusts the modulation parameters to optimize both time resolution and bandwidth utilization.
3Object-affected harmful factors
If narrow bandwidth detection is used to improve frequency selectivity, then signal-to-noise ratio improves, but the measurement of amplitude and phase becomes less accurate
Solution Approach 1:
The patent implements continuous signal processing where the mixed signal is continuously digitized and processed through digital filtering followed by Fourier transformation. The digital filter operates continuously to suppress noise while preserving the signal components, and the subsequent Fourier transformation continuously extracts amplitude and phase information. This continuous processing chain ensures that noise suppression and measurement precision are both maintained without the trade-off present in discrete analog filtering approaches.
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 approach enables faster and more accurate amplitude and phase measurements by using digital filters, reducing noise and eliminating settling times, allowing for higher difference frequencies and narrower bandwidth detection.
Implementation Method 1
an optical radiation source, more particularly a laser, for generating an optical signal, that can be actuated, or the output signal thereof can be modulated, such that an optical signal modulated by the first frequency can be generated
Implementation Method 2
transducer means, which can convert the modified optical signal into at least one electrical signal
Implementation Method 3
a D/A converter for digitizing the at least one mixed signal
Data Source
AI summary
A device for spatially resolved measuring of a physical variable has a device for generating a first electrical signal with a first frequency and a device for generating a second electrical signal with a second frequency. The second frequency differs from the first frequency by a difference frequency. An optical radiation source generates an optical signal modulated by the first frequency. The optical signal can interact with a test object and be modified in the process. A mixer can mix an electrical signal emerging from the optical signal with the second signal. A device, particularly embodied as a DDS system, generates a third electrical signal with a third frequency that corresponds to the difference frequency or a multiple of the difference frequency. A digital/analog converter digitizes the at least one mixed signal by sampling the mixed signal at the third frequency in order to digitize it.