Photo-acoustic Sensor Head Interference Suppression
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Solution Overview
Problem
Photo-acoustic measuring apparatuses face interference from reflected measuring light signals that are not effectively suppressed by existing methods, leading to noise contamination in detected acoustic signals.
Innovation Solution
A photo-acoustic sensor head design with a contact prism and a material layer containing a measuring-light-absorbing material between the detection surface and the detection device, directing reflected measuring light to the detection surface or light entry surface to absorb and separate interference signals from useful signals, and a data recording system that captures signals in non-overlapping time intervals to isolate interference from useful signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional photo-acoustic sensor head is used with direct detection, then the detection sensitivity is high, but interference signals from reflected measuring light contaminate the acoustic signals
Solution Approach 1:
The patent divides the detection process into two separate temporal segments: interference signal detection and useful acoustic signal detection. By using time-gated detection, the system separates these signals in the time domain, allowing high-sensitivity detection without contamination from reflected light interference
Solution Approach 2:
The patent applies preliminary action by detecting and characterizing the interference signal first (before the useful acoustic signal arrives), then using this information to gate the detection window. This preliminary detection of the interference pattern enables subsequent rejection of these signals during the acoustic measurement phase
2Measurement precision
If signal filtering methods are applied to remove interference, then the signal-to-noise ratio improves, but part of the useful acoustic signal may be filtered out
Solution Approach 1:
The patent employs dynamic time-gating where the detection window is dynamically adjusted based on the known arrival times of interference versus useful signals. This dynamic approach allows maximum signal-to-noise ratio improvement while preserving the full useful acoustic signal by precisely opening the detection window only when useful signals are present
3Area of stationary object
If the detection device covers the entire detection surface, then the acoustic signal detection coverage is maximized, but reflected light interference is also maximized
Solution Approach 1:
The patent segments the detection process spatially and temporally: while the detection device covers the entire detection surface for maximum acoustic signal collection, the time-gated detection selectively accepts signals only during time windows when useful acoustic signals are present, excluding periods when reflected light interference occurs
Solution Approach 2:
The system uses feedback from the known characteristics of interference signal timing to control the detection gating. By monitoring the temporal pattern of reflected light and using this feedback to gate the detector, the system maintains full surface coverage while rejecting interference through intelligent temporal filtering
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
Effectively suppresses interference signals by temporally separating them from useful signals, improving signal-to-noise ratio and allowing for accurate detection of acoustic signals from samples.
Implementation Method 1
acoustic signals, which are triggered in a sample through absorption of a pulsed measuring light
Implementation Method 2
The energy imported through the light absorption causes the sample to heat up and thermo-mechanically expand
Implementation Method 3
Commonly used sound converters are manufactured from a piezo-electric material and convert pressure fluctuations directly into electric signals
Implementation Method 4
a material layer containing a measuring-light-absorbing material is arranged between the detection surface and the detection device
Data Source
AI summary
The disclosure relates to a photoacoustic sensor head for detecting acoustic signals which are excited in a sample by absorption of pulsed measuring light, comprising a contact prism which is transparent for the measuring light and has a sample contact surface, a detection surface arranged opposite the sample contact surface and a light entrance surface arranged adjacent to the detection surface, as well as means for radiating the measuring light through the light entrance surface in the direction of the sample contact surface, wherein a detection device comprising at least one sound transducer is arranged in a manner covering the detection surface, characterized in that those portions of the measuring light which are reflected at the sample contact surface are directed to the detection surface or to the light entrance surface, wherein a material layer containing a material which absorbs the measuring light is arranged between the detection surface and the detection device.