Abstract

This thesis investigates the design and experimental validation of a bio-inspired whisker sensor system with distributed piezoresistive sensing and enhanced robustness against drift. The whisker shaft is fabricated from a flexible elastomer (e.g., Ecoflex) with optional elastic modulus tuning via internal structural modification (adding a flexible core). As this project aims to investigate the whisker sensor concept, the size of the final fabricated version of the sensor can be scaled up to the cm range rather than mm. The sensing mechanism is realized through conductive composite (CC) elements embedded in a soft PDMS-based follicle side (coupler), mimicking biological whisker follicles. The CC sensing elements are designed as segmented 3d arc structures arranged circumferentially around the whisker base (0°, 90°, 180°, 270°), enabling directional bending detection through a half-Wheatstone bridge configuration. Additional multi-layer and multi-electrode configurations are explored to enhance sensitivity, repeatability, and drift observability. The readout circuit for the sensor is built in another project and will be provided with the ability to read 8 different sensing elements. The thesis includes fabrication of 0–3 and 1–3 CC using polymer matrices and conductive fillers, followed by microstructural characterization (e.g., SEM, optical microscopy) and electromechanical testing (linearity, hysteresis, repeatability, temperature sensitivity). Advanced experiments investigate distributed vs point loading, contact-location sensitivity, and dynamic response for the final complete whisker sensor instead of sensing element itself. A key contribution is the implementation of a multi-electrode sensing architecture to enable drift detection and partial compensation, addressing instability caused by microstructural evolution in conductive composites. The final integrated whisker–follicle system is evaluated under realistic loading conditions to assess sensing performance and robustness.

Tasks and Duties

1. Mold Design & Fabrication (3d printing) – Mechanical design

• Redesign of the current version of the whisker mold

• 3D model design of the mold for casting segmented CC sensing elements (arc shape)

• 3D model design of the assembly mold for casting the final assembled whisker sensor

• Mold design and fabrication (3D printing)

2. Preparation of conductive composites (CC) – Material design

• Mixing a PDMS with conductive fillers (e.g., Ag, carbon-based powder or carbon fiber) and casting mixture into molds. 

·        Investigate the effect of filler fraction, dispersion quality, and structure (0–3 vs 1–3 composite) on the resistivity of the cured CC element.

3. Microstructural Characterization

·       Stress-strain test on PDMS based CC

·        Optical microscopy

·        SEM analysis, evaluation of dispersion, agglomeration, percolation network, fiber alignment (for 1–3 composite)

4. Electrical & Electromechanical Testing (of the sensing element)

• Resistivity and I–V characterization

• Temperature coefficient of resistance

• ΔR/R vs strain (gauge factor)

• Linearity, hysteresis, repeatability for dynamic loading

5. Drift Evaluation & Compensation (of the sensing element)

• Characterization of drift sources such as particle rearrangement or fiber breakage after cyclic load

• Implementation of multi-electrode sensing and resistance mapping across CC volume for performing a simple drift-aware compensation strategy

6. Sensor Functional Testing (of the assembled final version of the whisker sensor)

• Multi-electrode measurement configurations for both static and dynamic load (readout circuit will be provided)

• Crack initiation and propagation monitoring

• Drift test under cyclic loading scenarios

Project Start: As soon as possible

Project Duration: 6 months

Contact Person ----- Supervisor: emin.istif@tuhh.de, Co-Supervisor: Mohammad.sadeghi@tuhh.de