Proof of concept New Configurable Chip free RFID Strain Sensor

Tech 2023-07-06 10:13:18 Source: Network

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History of the Universe

Editor | History of the Universe

Review existing and proposed sensor designs

The developed strain sensor is based on the electric LC (ELC) resonator used in various Metamaterial related publications, which is considered as a base resonator, through which strain sensing can be realized.

Due to its small size and large central capacitance, other works have used this capacitor in successful sensor designs.

From the existing literature on the design of chipless RFID strain sensors, it can be seen that the developed resonator utilizes various deformation mechanisms to change its resonant response.

These include elastic deformation, bending, and to some extent rigid body motion, which occurs when the substrate expands between conductive regions to cause capacitance changes or capacitance/inductance coupling changes.

Another observation of current literature in this field is the use of elastic deformation or bending as the main sensing method, which greatly emphasizes the mechanical properties of deposited conductors.

Min et al. created a successful design in which AgNP/MWCNT based deposition was utilized to support strain levels exceeding 20%.

Other works, such as those in Teng et al., heavily rely on the bending of MLA antennas and support strain levels up to 50%.

The latter work utilizes liquid metal Galenstein to support these strain levels, while other designs focus on detecting strains belowThe strain level, such as the cited strain level.

Notable works include the use of Thai et alCantilever mechanismDevelop works for designing high sensitivity strain sensors.

Although these projects have achieved impressive strain sensitivity, they require the manufacturing of suspended cantilevers, which brings significant manufacturing complexity to implementing these designs using direct writing technology.

However, the design and analysis proposed in this work focus on graphic design, so that in-situ deposition can be easily achieved using techniques such as inkjet or aerosol deposition.

For this discussion, it is important to note that many of the sensor designs mentioned above use different resonator types and substrate materials, and operate at different frequencies.

Some work attempts to use indicators such as strain coefficient, maximum range and many other indicators to compare these different Strain gauge designs to compare various chip free RFID Strain gauge designs.

However, such comparisons do not seem to reveal the optimal design of chipless RFID strain sensors.

The reason why this article proposes this viewpoint is that it seems impossible to compare strain sensors operating in various different strain ranges, as not every resonator design (SRR, ELC, MLA) can achieve arbitrary strain sensitivity and range.

Generally speaking, the selection of substrate materials and their height seem to determine the overall performance of strain sensors, while the relative mechanical properties of the conductor and substrate will determine the main deformation mechanism within the resonator. An observation of existing RFID sensor literature is that.

Compared to other sensors, sensors that exhibit multiple deformation mechanisms seem to exhibit more impressive performance and may be more easily able to support significant changes in stimulus range, which can be customized by changing the substrate material.

This observation is based on the fact that a high strain level (> 20%) requires a highly customized substrate to convert this strain into a level suitable for strain resonators operating solely through elastic deformation (< 0, 5%).

Use of dedicated substrate materials

The next point of this section is to emphasize the advantages of using specialized substrate materials located between MUTs and resonators.

To a large extent, many dielectric strain sensing applications can avoid the need for such additions, but known dielectric materials, including the application of resonators, have advantages. Detecting strain in metals or general conductive materials will require the use of intermediate materials between MUTs and resonators.

Having a consistent resonant response position in the RCS response would be advantageous, and the use of a dedicated substrate would facilitate implementation, as dielectric MUTs may have significantly different dielectric constants.

Some dielectric materials have significant loss tangent angles, and the use of intermediate dielectrics can help alleviate their adverse effects on the resonant response of sensors.

The strain performance (sensitivity and range) of sensors can be adjusted by using specific substrate materials and heights.

The surface roughness and curvature level of MUT are very high, which may make it difficult to successfully/accurately deposit the resonator in place. The substrate material can help provide a smooth and flat surface for conductor deposition.

This material may have a negative impact on the function of the strain sensor, and examples of how this occurs include the effect of substrate expansion, if the expansion coefficient of this material is different from that of MUT.

This will become a particularly interesting issue, which is likely to occur, as certain materials may easily absorb the strain caused by MUT in their substrate.

And this deformation cannot be successfully transmitted to the resonator on its top surface, which is likely only a problem with flexible substrates such as soft rubber when the MUT is at a low strain level.

Although the height of the substrate can be changed, the thickness resolution of films that are prone to deposition is limited.

The selection of substrate materials may not be within the free choice range of sensor designers, as the usage environment of the sensor may determine the use of unfavorable materials.

Overall, a dedicated substrate is required to detect metal, and since the proof strain of the metal is about 0.2%, it is likely that the substrate needs sufficient stiffness to transmit these strains to the resonator.

Similarly, other applications will require a larger strain range and require more flexible substrates.

Therefore, the best way to support all these possible scenarios is to develop sensor designs that can operate under all these conditions.

Sensor modeling

The FEM software based on Ansys Park is used to simulate the relevant sensors in this work, while Ansys HFSS is used to simulate the electromagnetic behavior of the device.

AnsysMechanical is used to perform related steady-state structural and thermal/humidity analysis. The previous simulation environment includes all relevant material properties for electromagnetic simulation, and other parameters required for mechanical modeling are taken from relevant published literature.

The HFSS environment utilizes a built-in grid partitioning system that iteratively improves grid resolution, allowing the results at specific (grid partitioning) frequencies to converge within a certain deviation between continuous grid iterations.

A plane wave excitation was used at a distance of 10cm from the sensor, and bistatic RCS results were used to explore the directional dependence of the zero position. In order to simulate the influence of the upper metal layer, perfect electric conductor (PEC) boundary conditions were used.

This sensor design is designed to support different substrate types so that the sensitivity and range of the sensor can be customized.

For this purpose, AnsysMechanicalFEA modeling is used to evaluate the degree to which different deformation mechanisms (expansion, bending, rigid body motion) occur during different types of loading processes.

The physical test results clearly demonstrate the strain sensing ability of the resonator when used with soft substrate materials.

Since polyimide is much harder than rubber, the degree of rigid body motion will undoubtedly decrease during sensor operation. Therefore, it is very important to evaluate the contribution of each deformation mechanism to sensor operation.

Harder substrates may benefit from additional new substrate modifications, such as slots, to allow for more specific customization of device sensitivity.

The performance of polyimide in aerospace environment has been well characterized, and their cross sensitivity has been extensively discussed in the literature.

Electromagnetic simulation results

As can be seen from the polyimide substrate for sensor design outlined, the response includes the response of the design with and without a metal upper layer.

These simulations and physical tests indicate that the resonator appears to exhibit a separate resonance mode on the metal superlattice, which is believed to be caused by monopole based coupling resonance between the resonator sides.

The results mentioned here show two resonance positions, one from a finite size metal superlayer, and the other due to the presence of sensors.

Although promising strain sensitive results were collected in both simulation and testing, the "on metal" resonance response appears to exhibit some strong dependencies related to the tangent of the substrate loss, as well as other dependencies related to the upper layer size.

Further research is needed on the 'metal' performance of the device, similar to the performance found in, but preliminary results indicate that it can operate as a viable sensor for these materials.

Overall conclusion

This work involves the development of a new type of chip free RFID strain sensor, which has been successfully implemented. The strain sensor developed in this work exhibits impressive strain coefficients exceeding units, and there is sufficient evidence to suggest that it should operate successfully in various combinations of conductor substrate materials.

More generally, this article attempts to dismantle the current strategy for developing chipless RFID strain sensors, which largely leads to a comparison of substrate materials.

The general issue of cross sensitivity seems inevitably to be a larger issue than described in this small work organization.

Future Work

This work proposes an improved ELC resonator, mainly because it is suitable for supporting large deformations and high sensitivity, and there are other designs with other advantages, such as polarization insensitivity and/or strong operation on conduction overshoots.

The main reason for advancing a single design is that it will allow for subsequent focused exploration of other challenges surrounding strain sensing, such as various cross sensitivity, directional limitations, and complete in situ manufacturing. The future goals of this overall work are as follows:

(1) Proof of concept Strain SenseShould be less than 0.2%Using an enhanced resonator design on a rigid substrate, the sensor should utilize other deformation mechanisms that are largely avoided by this work.

(2) Sensor manufacturing uses mature in-situ manufacturing methods that will support consistent electrical, thermal, and mechanical sensor characteristics. Then, reliable physical testing should be conducted under different environmental conditions such as humidity and temperature,

(3) Fully characterize the performance of the sensor at dielectric and conductive overspeed below 0.2% strain.

(4) Explore design methods to mitigate/compensate for the potential lateral strain sensitivity of the current sensor design.

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