Non-Intrusive Liquid Level Measurement Using Lamb Waves
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Solution Overview
Problem
Existing non-intrusive liquid level measurement techniques face challenges such as the need for access to the bottom of the vessel, applicability only to vessels with vertical walls, and the use of potentially harmful and expensive X-ray or gamma-ray technologies, as well as the limitations of ultrasonic methods that require specific vessel geometries and sound speed calculations.
Innovation Solution
A system utilizing a frequency-tunable ultrasonic transmitter and receiver that emit and receive Lamb waves through the vessel wall, with the transmitter placed below the liquid surface to emit an inclined pressure wave that leaks into the liquid and is reflected back, allowing for continuous level measurement without direct contact, using the characteristic frequency-dependent radiation angle of leaky Lamb waves to determine the liquid level.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If X-ray or gamma-ray technology is used for non-intrusive level measurement, then measurement capability is achieved, but cost and safety risks increase
Solution Approach 1:
The patent replaces electromagnetic radiation (X-ray/gamma-ray) with acoustic waves (ultrasonic Lamb waves) for non-intrusive level measurement. This substitution eliminates radiation hazards and reduces cost while maintaining the non-intrusive measurement capability through the vessel wall
Solution Approach 2:
The patent uses Lamb waves propagating through the vessel wall as an intermediary medium to detect liquid level. The acoustic waves travel through the wall and interact with the liquid-gas interface, providing measurement information without direct contact with the liquid
2Measurement precision
If ultrasonic sensors are placed at the bottom of the vessel for level measurement, then measurement is possible, but access to the bottom is required
Solution Approach 1:
The patent transitions the sensor placement from the bottom (vertical dimension) to the side wall (horizontal dimension) of the vessel. Lamb waves propagate along the wall surface and can be directed at the liquid interface, enabling measurement without bottom access while maintaining measurement capability
Solution Approach 2:
The side wall-mounted sensor system serves multiple functions: it enables level measurement in vessels where bottom access is unavailable, works with various vessel geometries including non-vertical walls, and eliminates the need for separate bottom-mounted sensor installations
3Measurement precision
If ultrasonic signals are emitted horizontally through the liquid for speed of sound measurement, then speed measurement is achieved, but the method requires specific vessel geometries
Solution Approach 1:
The patent uses frequency-tunable Lamb wave excitation to dynamically adapt the wave propagation characteristics. By adjusting the excitation frequency, the radiation angle and penetration depth of the acoustic waves into the liquid can be optimized for different vessel geometries and liquid levels
Solution Approach 2:
The patent changes the physical parameters of the acoustic waves by varying the excitation frequency of the Lamb waves. This parameter change allows the system to adapt to different vessel configurations and maintain measurement capability across various geometries without requiring horizontal signal paths
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
Enables continuous and accurate non-intrusive liquid level measurement in various vessel geometries without the need for access to the bottom or expensive radiation technologies, providing reliable results by varying the frequency to optimize signal time of flight and amplitude for level determination.
Implementation Method 1
a first ultrasonic transmitter-receiver (5) for generating an ultrasound signal and for emitting it as a Lamb wave into a wall (51) of the vessel (1)
Implementation Method 2
the transmitter (38, 48) is able to emit the ultrasound wave as a primary Lamb wave (30) into the vessel wall so that a part of the primary Lamb wave leaks from the vessel wall into the liquid in form of a pressure wave (43)
Implementation Method 3
a second ultrasonic transmitter-receiver (5) for receiving the reflected acoustic wave through the vessel wall
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
A system and a method for non-intrusive and continuous level measurement of a liquid are described, where the liquid is enclosed by a solid wall of a vessel (41). The system comprises an ultrasonic transmitter (48) for generating an ultrasound wave and for emitting it into the vessel wall, an ultrasonic receiver (49) for receiving the ultrasound wave through the vessel wall, and at least one electronic control and data processing unit (6) for controlling operation of the transmitter (48) and of the receiver (49) and for determining the liquid level (H) from a time of flight of the ultrasound wave. The transmitter (48) is a frequency-tunable transmitter which is placed at a first position at the outside of the vessel wall and below the level of the liquid surface (44) in such a way that the transmitter (48) is able to emit the ultrasound wave as a primary Lamb wave into the vessel wall so that a part of the primary Lamb wave leaks from the vessel wall into the liquid in form of a pressure wave (43) in an inclined and upward direction towards the liquid surface (44). The receiver (49) is placed at a second position at the outside of the vessel wall and below the level of the liquid surface (44) in such a way that the receiver (49) is able to receive a secondary Lamb wave which is generated by the pressure wave (43, 45) hitting the vessel wall after having been reflected by the liquid surface (44). The at least one electronic control and data processing unit (6) is adapted to repeatedly determine the time of flight (t) of the pressure wave (43, 45), change the ultrasonic frequency (f) of the transmitter (48) until the determined time of flight reaches a minimum (tmin), and determine the liquid level (H) based on the relationship that the minimum time of flight (tmin) equals the length of the travel path of the pressure wave (43, 45) divided by the speed of the pressure wave in the liquid (cL).