Whisker Sensor Calibration and Replication

Animal whiskers play a vital role in their navigation and sensing; almost all mammals have them (humans are an exception) [1]. Rats use their whiskers to measure distance and feel out their surroundings, and seals are able to hunt fish without sight and hearing, relying solely on their whiskers for information [2]. Hence, a whisker sensor would allow an underwater vehicle to determine when it is close to the shore, an obstacle, or marine wildlife and detect changes in currents, allowing it to plot optimal navigation paths and not disrupt marine life. These sensors have the potential to be low cost, power efficient, and with high sensitivity, making them versatile for underwater projects where space and power limitations are greater compared to those on land. Building off of the work done by Professor Pablo Valdivia y Alvarado of the Singapore University of Technology and Design, we began a testing regiment using a collection of sensors fabricated by Prof. Alvarado’s team. The sensor is essentially a resistor - when the whisker is bent, the resistance of the device changes, which can be measured as a voltage change. However, the relationship between force, displacement, and voltage in the supplied whiskers was unknown, and there is no set procedure for whisker replication. Our goals for this stage of the project were to calibrate the supplied sensors to determine a relationship between the force applied, displacement of the whisker, and measured voltage so that we could predict the forces that cause the measured readings as well as the voltages we expect from currents of certain strengths. Furthermore, we plan to investigate a way to replicate the sensors consistently while improving the current design. This will allow us to eventually equip an AUV, such as a robot fish, with a group of sensors to gather data. For the calibration experiment, we designed wheatstone bridge circuits that are compatible with the variety of supplied sensors to measure the voltage changes. The whisker’s resistance was matched with a potentiometer so that the circuit started with a balanced 0V, which made it easy to measure voltage changes. The whiskers were held horizontally by a custom mount while a vertical force was applied and measured. For replication, various application techniques and lengths of conductive carbon grease were tested.. Additionally, casts with materials of different flexibilities were tested to determine the optimal stretch of the sensor base and stiffness of the whisker element. Based on the results, we have determined that the optimal application of the whisker sensors in their current design is for detecting relative changes in force. The sensors should not be used to relate voltage measurements to exact forces and displacements. In addition, we gathered observations to help improve the design of the sensor, such as noting the base sensitivity in changing voltage readings. We decided that Ecoflex-30 and carbon conductive grease will be used as the base polymer and the resistive material, respectively. Furthermore, we developed a mold for casting the sensor as well as two methods to explore for base replication: one with a flared bottom whose upwards motion causes change and another which aims to displace the grease by the whisker’s sideways bending. Preliminary experiments with these methods were explored with more to do in the future.