Speed of Sound Gas Sensor with Time-Division Multiplexing
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Solution Overview
Problem
Existing methods for determining gas composition, temperature, and humidity using sound measurements face challenges when the sender and receiver are mounted on a common structure, as structure-borne sound interference complicates the separation of gas-borne and structure-borne sound signals, especially at close transducer arrangements.
Innovation Solution
The method involves arranging the sender and receiver on a common structure with a higher sound speed than the gas, operating them in alternating 'on' and 'off' statuses to separate sound contributions in time, and using a signal processing unit to calculate the speed of sound and determine gas properties based on phase angle differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the sender and receiver are mounted close together on a common structure, then the device compactness is improved, but the structure-borne sound interference increases making signal separation difficult
Solution Approach 1:
The patent applies periodic action by operating the sender and receiver in alternating time intervals. The sender transmits ultrasonic signals during specific time windows, and the receiver measures signals during different time windows. This time-division multiplexing creates periodic measurement cycles that separate the detection of gas-borne sound from structure-borne sound interference, enabling compact mounting while maintaining measurement accuracy.
Solution Approach 2:
The patent extracts the gas-borne sound signal from the total received signal by using time-gating techniques. The receiver isolates specific time intervals where only gas-borne sound is present, separating it from structure-borne sound that occurs at different times. This extraction method allows the system to reject structure-borne interference while maintaining compact transducer placement.
2Object-affected harmful factors
If mechanical damping structures are added to reduce structure-borne sound, then the sound interference is reduced, but the device complexity and manufacturing cost increase
Solution Approach 1:
The patent replaces mechanical damping structures with an electronic/time-based solution. Instead of using complex mechanical elements to physically isolate or dampen structure-borne sound, the system uses temporal separation techniques where the sender and receiver operate in alternating intervals. This substitution of mechanical complexity with electronic control achieves the same interference rejection goal with simpler device architecture.
Solution Approach 2:
The patent changes the operational parameters of the transducers by implementing time-varying operation modes. The sender and receiver are switched between active and inactive states in a periodic manner, changing the temporal parameters of signal transmission and reception. This parameter change approach controls structure-borne sound interference through timing rather than mechanical means, reducing device complexity.
3Speed
If the sender and receiver are mounted face by face, then the sound transmission path is shortened improving measurement speed, but the structure-borne sound amplitude at the receiver increases
Solution Approach 1:
The patent uses periodic action with face-by-face mounted transducers by implementing alternating operational intervals. The sender transmits during specific periods and the receiver measures during different periods, creating time-separated measurement cycles. This allows the transducers to be mounted close together for fast response while the periodic operation prevents structure-borne sound from overwhelming the measurement signal.
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 effectively suppresses structure-borne sound influence, allowing for accurate and cost-effective measurement of gas composition, temperature, and humidity, even in applications with high temperature and pressure conditions, such as in internal combustion engine scavenge air measurement.
Implementation Method 1
the speed of sound is only influenced by its temperature and its composition. Measuring the speed of sound can therefore yield the temperature for a gas with known composition, or the composition of a gas at the known temperature. The measurement can be performed with ultrasonic sound or non-ultrasonic sound.
Implementation Method 2
arranged on that common structure side by side in parallel within a distance of less than 10 mm such that the sound emitted by the sender reaches the receiver via an acoustical reflector
Data Source
Figure 1~3
Figure 4
AI summary
Detection of gas characteristics, especially the detection of the gas composition, the temperature and/or humidity of a gas, by measuring the speed of sound with a sound sender (1) and a sound receiver (2) both mounted on common structure (3). The invention further concerns a method for determining the humidity of the scavenge air of an internal combustion engine. The invention further concerns a speed of sound based gas sensor arrangement adapted to measure gas characteristics, especially the gas composition, the temperature and/or the humidity of a gas, comprising a sender (1), a receiver (2) and a signal processing unit. The speed of sound is determined by driving the sender (1) and receiver (2) at different operation cycles in order to differentiate between the different travel times of the sound through the gas and the common structure (3) of solid material.