Confocal Laser Particle Sensor for Soot Detection

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Solution Overview

Problem

The detection of soot particles in the exhaust section of motor vehicles is hindered by extraneous thermal radiation from the hot environment, causing strong detector signals that can be mistaken for smaller particle signals due to lower power density at the edge of the focus, leading to incorrect particle size distribution analysis.

Innovation Solution

A confocal detection method is employed using a beam splitter and focusing optical elements to direct thermal radiation only from the sharply defined first spot onto the detector, filtering out unwanted thermal interference and enhancing the signal-to-noise ratio by ensuring only signals from the immediate focus area are detected.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a laser beam is focused to detect thermal radiation from particles, then the detection sensitivity is improved, but extraneous thermal radiation from the hot environment enters the detector causing false signals

Engineering Contradiction:

Improvedetection sensitivityVSAvoidextraneous thermal radiation

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The detection system is divided into two separate optical paths: one for delivering laser light to the focus region and another for collecting thermal radiation from the focus region only. This segmentation allows independent optimization of each path to minimize interference while maximizing signal collection.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A beam splitter is introduced as an intermediary optical element that separates the laser light path from the thermal radiation detection path. The beam splitter directs laser light toward the focus while allowing thermal radiation from the focus to pass through to the detector, effectively filtering out extraneous thermal radiation from other regions.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Temperature

If the laser power density at the focus is reduced to avoid overheating, then the environmental thermal radiation decreases, but the LII signal from particles becomes weaker

Engineering Contradiction:

Improveenvironmental thermal radiationVSAvoidLII signal strength

Core Design Contradiction:

TemperatureVSMeasurement precision

Solution Approach 1:

The detection system extracts only the thermal radiation originating from the immediate focus region where particles are heated, while excluding thermal radiation from the broader hot environment. This is achieved through the confocal arrangement that collects radiation only from the specific focal volume, thereby maintaining high laser power density without being overwhelmed by environmental thermal radiation.

Inventive Principle:

Principle #2Taking out (Extraction)

3Area of stationary object

If particles at the edge of the focus are detected, then the detection area is increased, but the power density is lower causing weaker signals that are mistaken for smaller particles

Engineering Contradiction:

Improvedetection areaVSAvoidparticle size measurement accuracy

Core Design Contradiction:

Area of stationary objectVSMeasurement precision

Solution Approach 1:

The optical system is designed with different properties at different locations: the center of the focus receives high power density laser light for heating particles, while the detection optics are configured to collect thermal radiation primarily from the central high-power-density region. This local quality differentiation ensures that particles at the edge, which receive lower power density, do not produce detectable signals that could be misinterpreted.

Inventive Principle:

Principle #3Local quality

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 significantly reduces false signals and improves measurement accuracy by isolating thermal radiation from the first spot, allowing for more precise detection of low-power LII signals and accurate particle size distribution analysis.

Implementation Method 1

the soot particles produced upon combustion are heated to several thousand degrees Celsius with a nanosecond pulse of a high-powered laser

Methodology Applied

Scientific EffectLaser-induced incandescence: Laser

Implementation Method 2

the thermal light emission of the particle is measured with a light detector

Methodology Applied

Scientific EffectThermal radiation: Thermal Radiation

Implementation Method 3

an optical apparatus that is configured to focus laser light proceeding from a laser module into a first spot and is configured to focus thermal radiation proceeding from the first spot into a second spot

Methodology Applied

Scientific EffectOptical focusing: Focusing

Data Source

PatentUS11467078B2Laser-induced incandescent particle sensor comprising a confocal arrangement of a laser spot and of a thermal radiation spot

Publication Date: 2022.10.11 ROBERT BOSCH GMBH

AI summary

A particle sensor is described. The particle sensor includes a laser module having a laser, and a detector configured to detect thermal radiation. The particle sensor has an optical apparatus that is configured to focus laser light proceeding from the laser module into a first spot and is configured to focus thermal radiation proceeding from the first spot into a second spot, a radiation-sensitive surface of the detector being located in the second spot, or behind the second spot in the beam path of the thermal radiation focused onto the second spot.