Passive Wireless Strain Sensor with Micro-Cavity
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Solution Overview
Problem
Existing strain sensors lack sensitivity for pico-strain measurements and are not battery-free or capable of wireless communication, making them inadequate for precise and remote deformation detection.
Innovation Solution
A planar-structure capacitive strain sensor with a micro-scale sealed cavity and a passive LC circuit, utilizing interdigitalized capacitors and a planar inductor on a three-layer dielectric substrate, which allows for enhanced sensitivity and wireless communication without a battery, using a Kapton polyimide film with copper-clad sheets for fabrication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional capacitance strain sensors are used, then the device structure is simple, but the sensitivity for pico-strain measurements is insufficient
Solution Approach 1:
The patent implements a nested structure by placing a micro-scale sealed cavity inside the sensor device, which contains a vacuum or gas environment. This nested cavity structure amplifies the capacitance change signal in response to strain, enabling pico-strain measurement sensitivity without requiring overly complex external systems
Solution Approach 2:
The patent transitions from traditional planar electrode configurations to a three-dimensional structure by introducing a sealed cavity with vacuum or gas environment. This dimensional change creates a fringing electric field that extends into the cavity, significantly enhancing the capacitance response to strain while maintaining a compact sensor footprint
2Measurement precision
If environmental pressure changes are accounted for, then measurement accuracy improves, but device complexity increases
Solution Approach 1:
The patent extracts the pressure-sensitive measurement function by creating a sealed cavity isolated from the external environment. By sealing the cavity with a flexible substrate, external pressure changes are prevented from directly affecting the internal measurement environment, thereby eliminating the need for complex pressure compensation mechanisms while maintaining measurement accuracy
Solution Approach 2:
The patent applies different quality requirements to different regions: the sealed cavity maintains a controlled internal environment (vacuum or gas) isolated from external pressure changes, while the flexible substrate transmits strain locally to the electrodes. This local differentiation allows the sensor to be sensitive to strain while being insensitive to external pressure variations
3Measurement precision
If active strain sensors with power supply are used, then measurement capability is enhanced, but device portability and wireless application are limited
Solution Approach 1:
The patent implements a passive sensor design that harvests energy from the electromagnetic field of the reader coil through electromagnetic induction. The sensor self-generates the necessary power for measurement and wireless communication without requiring an internal battery or power supply, enabling truly portable and wireless applications
Solution Approach 2:
The patent replaces the traditional active electronic measurement system with a passive electromagnetic measurement system. By using electromagnetic induction to both power the sensor and transmit data wirelessly, the design eliminates mechanical power sources and complex wireless communication hardware, achieving portable strain measurement through field-based energy transfer and signal transmission
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 high sensitivity for pico-strain measurements and remote strain detection, with the micro-scale cavity improving sensitivity and holes in the substrate minimizing environmental pressure influence, enabling accurate and battery-free wireless communication.
Implementation Method 1
The electrodes of the interdigitalized capacitor generate a fringing field that penetrates into the micro-scale cavity and also into the third dielectric substrate. This micro-scale sealed cavity offers an enhanced sensitivity to the interdigital capacitive strain sensor when pico-strain measurements are required.
Implementation Method 2
The electrodes of the interdigitalized capacitor generate a fringing field that penetrates into the micro-scale cavity and also into the third dielectric substrate.
Implementation Method 3
An planar coil inductor is built on the first dielectric around the interdigitalized capacitor and connected across it to form a simple LC circuit. The resonant frequency of this LC circuit changes with changes to the capacitance.
Implementation Method 4
When, for example, the sensor is attached to a bending beam, the third substrate is bent following the bending beam. This deformation of substrate causes the sealed cavity to vary in thickness, which measurably changes the capacitance.
Data Source
AI summary
A high sensitivity strain sensor that utilizes a micro-scale cavity built in a multi-layer structure, with a pair of interdigitalized capacitor incorporated on one of the layers, is described in this document. The device's capacitance changes produced by unattended deformations of the cavity can be used to measure the associated strain without using any movable electrodes. The sensor can be remotely energized from a radio frequency wave sent by a reader antenna to construct a battery-free wireless instrument. Changes on the sensor's resonant frequency are remotely detected so that a strain level is measured from fluctuations in the received signal. This detection method provides a simple, reliable and sensitive technique to measure small strain changes down to the pico-scale. Materials with a highly strain-dependant permittivity are integrated in the sensor to enhance its sensitivity. The proposed sensor consists of a simple planar structure. It can be used as the main component on low-cost, accurate and highly stable strain measuring instruments capable of monitoring very small strain levels. Furthermore, the sensor is passive, may be operated wirelessly, and can, thus, be used for remote long-term embedded strain detection.