This paper studied the effect of curvature on the charge sensitivity of a curved PVDF sensor. The sensor was fabricated by attaching a PVDF film along the X-axis on a group of cylindrical silicon rods to form an outline with several bumps. The open output voltage of a curved sensor was simulated by using ANSYS with a rod curvature of 333 m-1, 400 m-1 and 500 m-1. It was found that the sensitivity was the highest when the curvature was 500 m-1, and the lowest when the curvature was 333 m-1. Curved PVDF sensors were fabricated and tested with a PVDF patch of 30 mm long and 28 μm thick and a radius of silicon rod of 3 mm, 2.5 mm and 2 mm, respectively. A shaker and mass block were used to apply the same dynamic force to the curved sensors and an oscilloscope was used to observe the output charge. The experiment results are not ideal but do show the same tendency as the simulation. The charge sensitivity increased as the curvature of substrate increased.
Offshore platform, which is the base of the production and living in the sea, is the most important infrastructure for developing oil and gas resources. At present, there are almost 6500 offshore platforms servicing in the 53 countries' sea areas around the world, creating great wealth for the world. In general, offshore platforms may work for 20 years, however, offshore platforms are expensive, complex, bulky, and so many of them are on extended active duty. Because of offshore platforms servicing in the harsh marine environment for a long time, the marine environment have a great impact on the offshore platforms. Besides, with the impact and erosion of seawater, and material aging, the offshore platform is possible to be in unexpected situations when a badly sudden situation happens. Therefore, it is of great significance to monitor the marine environment and offshore platforms. The self-contained sensor for deep-sea offshore platform with its unique design, can not only effectively extend the working time of the sensor with the capability of converting vibration energy to electrical energy, but also simultaneously collect the data of acceleration, inclination, temperature and humidity of the deep sea, so that we can achieve the purpose of monitoring offshore platforms through analyzing the collected data.
The self-contained sensor for monitoring of deep-sea offshore platform includes sensing unit, data collecting and storage unit, the energy supply unit. The sensing unit with multi-variables, consists of an accelerometer LIS344ALH, an inclinometer SCA103T and a temperature and humidity sensor SHT11; the data collecting and storage unit includes the MSP430 low-power MCU, large capacity memory, clock circuit and the communication interface, the communication interface includes USB interface, serial ports and wireless interface; in addition, the energy supply unit, converting vibration to electrical energy to power the overall system, includes the electromagnetic generator, voltage multiplier circuit and a super capacitor which can withstand virtually unlimited number of charge-discharge cycles. When the seawater impacts on offshore platforms to produce vibration, electromagnetic generator converts vibration to electrical energy, its output(~ 1 V 50 Hz AC) is stepped up and rectified by a voltage multiplier circuit, and the energy is stored in a super capacitor. It is controlled by the MSP430 that monitors the voltage level on the super capacitor. The super capacitor charges the Li-ion battery when the voltage on the super capacitor reaches a threshold, then the whole process of energy supply is completed. The self-contained sensor for deep-sea offshore platform has good application prospects and practical value with small size, low power, being easy to install, converting vibration energy to supply power and high detection accuracy.
Piezoelectric actuators often work in a close-loop feedback position control system due to hysteresis. Our objective is to make an actuator self-sense its output force and displacement without using extra sensor, which is termed self-sensing actuator/actuation (SSA). A compound circuit was proposed to voltage-drive the piezoelectric actuator and get the resulting charge concurrently. Based on the circuit, the unstressed actuator can self-sense its free strain. If the actuator is externally stressed, an observer was constructed to estimate the actuator's stress and strain state. The observer-based self-sensing approach is akin to state estimation techniques, depending on the fact that the electric field is controllable and the electric displacement is measurable. In order to compensate hysteresis, voltage versus charge relation was modeled sign GMS model, and the observer was improved to a nonlinear one. The observer-based SSA approach successfully bypasses the impedance mismatching problem bothering the bridge-based SSA approach. Experiments validated the approach.