Piezoelectric Rheometer Flexure for High-Frequency Torque
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Solution Overview
Problem
Commercial rotational shear rheometers are limited to a maximum frequency range of 20-50 Hz due to inertia, making it difficult to analyze complex materials that require higher frequency measurements, such as colloids and polymers, with existing setups exhibiting resonance issues, complexity, and sub-optimal accuracy.
Innovation Solution
A rotational shear rheometer design featuring a first plate pivotable about a pivot axis with a piezoelectric element extending tangentially, using a flexure configuration that allows for high-frequency operation by minimizing translational movements and maximizing rotational stiffness, enabling both actuation and sensing with a single piezoelectric element, and allowing for combination with existing devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a rotational shear rheometer uses traditional multi-element piezoelectric actuation, then actuation capability is achieved, but device complexity increases and measurement precision decreases due to alignment requirements and bending moments
Solution Approach 1:
The patent merges the actuator and sensor functions into a single piezoelectric element. This element serves both to actuate the plate through radial expansion/contraction and to sense the torque applied by the sample, eliminating the need for separate actuator and sensor assemblies and their complex alignment requirements
Solution Approach 2:
The single piezoelectric element performs multiple functions: it acts as both the actuator (through radial dimension changes) and the sensor (through tangential stress measurement). This multi-functionality reduces device complexity while maintaining measurement precision
2Speed
If a rotational shear rheometer uses bendable metal foil with piezoelectric elements, then flexibility is achieved, but resonance effects occur and upper frequency is limited
Solution Approach 1:
The patent employs a thin flexible plate that can be radially expanded and contracted by the piezoelectric element without significant bending. This flexible yet stable design allows high-frequency operation (up to kHz range) while maintaining dimensional stability and avoiding resonance effects
Solution Approach 2:
The patent eliminates harmful resonance vibrations by using a rigid support structure for the piezoelectric element and a flexible yet stable plate design. The system operates at high frequencies without experiencing resonant oscillations that would compromise measurement accuracy
3Measurement precision
If a rotational shear rheometer uses separate actuator and sensor elements, then actuation and sensing functions are fulfilled, but alignment complexity increases and accuracy decreases
Solution Approach 1:
The patent combines the actuator and sensor into a single integrated piezoelectric element, eliminating the alignment complexity between separate elements. The element is bonded to the plate such that its radial dimension changes drive the plate while its tangential face directly measures the applied torque
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 design enables robust high-frequency rheological measurements up to 20 Hz or more, improving dimensional stability and accuracy while reducing complexity and cost by using a single piezoelectric element for both actuation and sensing, and allowing for analysis of polymers above their glass transition temperature.
Implementation Method 1
a piezoelectric element extending between a first end of the piezoelectric element and a second end of the piezoelectric element along a longitudinal axis
Implementation Method 2
the piezoelectric element is configured as an actuator capable of introducing a torque to the first plate about the pivot axis, such that the first plate is pivoted about the pivot axis... The piezoelectric element is further configured as a sensor capable of detecting a torque or a force acting on the first plate
Data Source
AI summary
The invention relates to a rotational shear rheometer (1) comprising a first plate (10), a first flexure (11) pivotally connecting the first plate (10) to a support (60), a piezoelectric element (40) extending along a longitudinal axis (L) arranged tangentially in respect of the first plate (10), wherein said piezoelectric element (40) is configured to elongate and/or undergo compression along said longitudinal axis (L), and wherein said first end (41) is mechanically coupled to said first plate (10), wherein said first flexure (11) comprises a first flexural element (12) and a second flexural element (13) non-parallel to the first flexural element (12), wherein the first flexural element (12) and the second flexural element (13) connect said first plate (10) to said support (60), extend radially in respect of the pivot axis (P) and intersect with the pivot axis (P), wherein said piezoelectric element (40) is further configured as a sensor capable of detecting a torque acting on said first plate (10). Furthermore, the invention relates to a method for determining mechanical properties of a sample using the rotational shear rheometer.