Coaxial Fill Level Sensor for Low-Permittivity Media Detection
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Solution Overview
Problem
Existing fill level sensors are sensitive only to media with higher permittivity and face challenges in detecting fill levels in containers with lower permittivity media, due to parasitic resonances and difficulty in implementing high sensitivity, especially in small containers.
Innovation Solution
A fill level sensor design featuring a resonant circuit and antenna with a resonant input impedance that transforms to a real impedance, allowing detection of changes in the near field by shifts in resonant frequency, and incorporating a terminating circuit to prevent reflections, with a coaxial supply and antenna for direct contact, enhancing sensitivity and reducing size and thermal load.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If prior art fill level sensors with planar patch antennas are used, then the structure is simple, but the sensitivity is insufficient for media with lower permittivity and parasitic resonances occur in small containers
Solution Approach 1:
The patent changes the fundamental parameter of the antenna structure from planar patch to coaxial waveguide configuration. This structural parameter change enables direct contact with the fill medium and eliminates parasitic resonances, thereby achieving high sensitivity for detecting fill levels in media with lower permittivity values while maintaining structural simplicity
Solution Approach 2:
The patent extracts the antenna element from the traditional planar configuration and implements it as a coaxial waveguide structure that extends into the fill medium. This extraction allows the sensing element to be in direct contact with the medium, improving the detection of near field changes while avoiding the parasitic resonance issues associated with planar patch antennas in small containers
2Measurement precision
If the antenna resonant frequency is close to the supply resonant frequency, then the near field is affected by the fill medium for detection, but this causes difficulty in distinguishing the fill medium effect from the supply resonance
Solution Approach 1:
The patent segments the resonant frequencies into two distinct ranges: the supply resonant frequency is kept below the antenna resonant frequency. This frequency segmentation creates a clear separation between the supply resonance and the antenna resonance, allowing the near field changes caused by fill medium to be detected without interference or confusion from supply resonance effects
Solution Approach 2:
The patent introduces a mode filter as an intermediary component between the antenna and the container environment. This mode filter suppresses higher order modes and parasitic resonances, acting as a mediator that allows only the fundamental resonance mode to be excited. This ensures that detected signals are purely from the fill medium interaction with the antenna, not from parasitic resonances
3Measurement precision
If the sensor is designed for high sensitivity with direct contact, then detection capability improves, but the thermal load on the antenna increases
Solution Approach 1:
The patent segments the sensor into two distinct parts with different functions: the antenna element that requires direct contact with the fill medium for high sensitivity detection, and the feed line and supply components that are kept thermally isolated. This spatial segmentation allows the antenna to experience the fill medium environment while protecting the sensitive electronic components from thermal stress
Solution Approach 2:
The patent introduces a process window as an intermediary component that separates the antenna from the container wall and the external environment. This process window allows the antenna to be in direct contact with the fill medium for sensing while providing thermal isolation and mechanical support, acting as a mediator that enables direct contact sensing without transmitting excessive thermal load to the antenna structure
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
The sensor achieves increased sensitivity for detecting fill levels in media with lower permittivity, is suitable for smaller containers, and effectively reduces thermal stress and size constraints, enabling accurate detection across a range of permittivity values.
Implementation Method 1
The resonant circuit transforms the resonant input impedance at the resonant frequency to a real impedance having a predetermined resonant impedance value
Implementation Method 2
The antenna is designed to radiate the electromagnetic waves into a container with a fill medium
Implementation Method 3
The near field is formed by the electromagnetic waves emitted by the antenna and the change in the near field is caused by the fill level change of the fill medium in the container
Implementation Method 4
A fill level change of the fill medium in the vicinity of the antenna changes the near field of the antenna if the fill medium and the other medium have different permittivities from one another
Implementation Method 5
A change in the near field around the antenna due to a change in the fill level of a fill medium, for example in the direction of the antenna, causes a decrease in the resonant frequency
Data Source
AI summary
A fill level sensor for detecting a level of a fill medium in a container includes a generator having a feed line, an antenna, a supply and a controller. The generator generates electromagnetic waves having a resonant frequency and outputs the electromagnetic waves via the feed line having a line impedance with a line impedance value. The supply is arranged between the feed line and the antenna and transmits the electromagnetic waves from the feed line to the antenna. The supply has a resonant circuit. The resonant circuit and the antenna together have a resonant input impedance in the transmission direction. The resonant circuit transforms the resonant input impedance at the resonant frequency into a real impedance having a predetermined resonant impedance value. The antenna has an antenna resonant frequency different from the resonant frequency.