This is a home page on the research and educational activities of Dr. Arata Masuda at Smart Structural System Research Group in Department of Mechanical and System Engineering, Kyoto Institute of Technology.
We pursue fundamental principle, design, and integration methodology of smart structural systems that exploit the nonlinearity, passivity, and energy exchangeability of matrials, structures, and their interaction with surroundings.
Structural health monitoring (SHM)
The concept of structural health monitoring (SHM) aims to realize continuous, in-service monitoring and diagnosis of the healthiness of target structures by detecting and evaluating structural damages from their early stages using permanently deployed sensors.
Nonlinear piezoelectric impedanace modulation
When the structure involving contact-type damages is subjected to a low-frequency vibrational load, an electro-mechanical coupled admittance of the piezoelectric patch in high-frequency range is perturbed in synchronization with the low-frequency pump excitation, so that the current response to the high-frequency harmonic probe voltage source is modulated both in amplitude and phase.
This phenomenon, referred to as nonlinear piezoelectric impedance modulation (NPIM), has been modeled by a single-mode representation of the structure coupled with the piezoelectric active sensor whose modal stiffness is perturbed by the pump load. Based on this model, a damage index that relates the magnitude of the stiffness perturbation to the current modulation observed has been derived and a damage detection procedure has been presented.
Vibration energy harvesting
An energy harvester is a micropower generator that is designed to collect unused or wasted energy from the environment and convert it to electric energy. It has attracted increasing attention in the last decade as a local and decentralized power source for embedded systems such as mobile information devices, and wireless sensor nodes for environment monitoring, structural health monitoring, machine condition monitoring, and human health monitoring.
Among the environmental energy source available for the energy harvester, vibration is one of the most ubiquitous and commonly recognized mechanical energy sources that has attracted considerable interest from the industry.
In our research, a resonance-type vibration energy harvester with Duffing-type nonlinearity is adopted to make the harvester perform effectively in a wide frequency range. Such a nonlinear oscillator, however, can have multiple stable steady-state responses in the resonance band with different levels of regeneration energy. In this study, the principle of self-excitation is utilized to destabilize the solutions, except for the highest-energy solution. A load circuit with a switch between the conventional load circuit and a negative resistance circuit and the switching control law, which depends on the amplitude of the oscillator's response, are introduced to impart the self-excitation capability in order to entrain the oscillator with the excitation only in the highest-energy solution.
Ocean wave energy harvesting
One of the most effective ways to protect the coastal region from tsunami disasters is to detect tsunami before its arrival and raise an early alert promptly. A GPS buoy network installed offshore is one of the core equipments in such an early-warning system. To improve the accuracy and reliability of the system, dense deployment of GPS buoys is expected. The Existing designs of GPS buoys are, however, not suitable of the dense deployment because of their heavy, bulky, and expensive design. Application of smart structures and materials technologies, such as smart composites, smart sensors and actuators, deployable structures, and energy harvesting technologies, would have potential advantages to realize miniaturized and affordable design of the GPS buoys.
We try to utilize the smart structures technologies to design a power generation device for a GPS buoy miniaturized in several tens of centimeters. Because the offshore GPS buoy should equip a GPS receiver and other motion and environmental sensors, data processing system, and satellite communication system to send the observation to the processing center on land, the power generation device is demanded to produce electric power of at least several tens of watts from the vibratory motion of ocean wave, which has quite low but wide range of frequencies from 0.05 Hz to 0.5 Hz.
In this study, we first discuss the required specification of the power generation device, and discuss the possible solutions to realize such a device. A design of high-efficiency, direct push-pull type energy harvesting device is presented, and a preliminary design using cantilevers with piezoelectric ceramic patches is presented with some experimental studies.
Assistance of human motion by "semi-active" wearable robotics
A concept of semi-active power assistance of human motion, called "nonpositive power assistance" is proposed, mainly targeting the prevention of injuries in nursing-care activities. In this concept, only the human motions accompanied by isometric and eccentric muscle contractions, which are the main cause of the muscle fatigue and muscle fibre damages, are assisted, whereas the motions with concentric contraction, which require positive power input, are not supported. Since the nonpositive power assistance is feasible by using ON/OFF-controlled passive breaks installed in parallel with the muscles, this concept allows a design of an energy-saving power assist apparatus which may effectively prevent the user from muscle fatigue and muscle injury.
A single-axis poof-of-concept test apparatus for the cubital joint assistance has been designed, and the experiments of cyclic loading-unloading-holding tasks using eight subjects have been carried out to evaluate the effectiveness of the proposed concept in terms of the surface electromyographic signals from the biceps brachii. It has been concluded that the progress of the muscle fatigue has been significantly reduced (p<0.05) by using the proposed nonpositive power assist apparatus.
Characterization and monitoring of human walking