Showing papers by "Wen-Jong Wu published in 2019"

The fatigue behavior study of micro piezoelectric energy harvester under different working temperature

Abstract: The cantilever beam type of PEH (piezoelectric energy harvester) has been widely studied for years due to simple design and effectively generate high strain and high ouput power. In our previously researches, the PEH unit with area of 6 mm by 9 mm has output performance around 300 μW under base excitation of 0.5g acceleration level. Moreover, we have designed the tapered shape cantilever beam of PEH for optimizing the beam strain distribution and verified that the output performance and durability are not inferior to rectangular one we have fabricated before. In this study, the tapered shape cantilever beam PEHs are chosen for durability experiment to investigate the relevance among output performance, fatigability and mechanical properties of devices with a long-term working period under different working temperature. The result evidently shows the durability difference when the device is operated under high temperature (50°C) with significant natural frequency drop and the PEH could not maintain constant power output.

A high sensitivity piezoelectric MEMS accelerometer based on aerosol deposition method

Abstract: MEMS accelerometers are widely employed in the Internet of Things (IoT) era. Among them, capacitive types are commonly used due to their low cost and compatibility with the commercial CMOS fabrication lines. However, piezoelectric MEMS accelerometers have great research popularity attributed to their wide working range, self-generating property and removal of the need for vacuum sealing. This study designs, fabricates and analyzes a piezoelectriccantilever- beam-based accelerometer in meso scale, which is constructed by a tungsten proof mass and a composite beam comprising of PZT and stainless steel layers. Four structures with different geometries/dimensions are designed for comparison, including rectangular and trapezoid beam shapes. All the devices are fabricated by MEMS processes where aerosol deposition is utilized to make high-quality PZT sensing layer. And the implementation of stainless steel substrate makes the fabrication flow simple and cost-effective. Experiments show that the natural frequencies of the four structures range from 572.25 Hz to 769.01 Hz, corresponding to respective working frequency range from 110 Hz to 150 Hz. The low frequency limit of 10 Hz is determined by a tailor-designed charge amplifier, which is used to amplify the output charge signal of the developed sensor. At the working frequency of 95 Hz, charge sensitivities of 23.9 pC/g to 41.4 pC/g are measured for the four structures. Comparison with other studies, the designed devices have high sensitivities.

A Fast-Transient Switched-Capacitor DC-DC Converter with a Current Sensing Control Technique

Abstract: A low-power switched-capacitor step-down DC-DC converter using the proposed current sensing control technique to enhance the transient response is presented in this paper. By sensing the current outflow from the DC-DC converter and the load current simultaneously, the proposed technique scales the switching frequency (Fsw) accordingly from the very beginning of the load or the line transient. It leads to better transient response without depending on the output capacitance. It is suitable for sensor applications which usually use an LDO with a large output capacitor, resulting in lower efficiency. The converter is implemented in a 0.25-μm CMOS process with integrated flying capacitors and generates a fixed regulated output voltage of 1.8V from an input voltage ranging from 3.8V to 5.4V. From the measurement results, the transient response time is about 0.3μs after a step load current from 20μA to 2.5mA which is sufficient for low-power sensor applications. Its power efficiency (η) is higher than 70% over a wide range of the load current with a peak value of 72.8%.

Piezoelectric apparatus for motorization

Abstract: A piezoelectric motorization system for driving mechanical loads multi-dimensionally by an electronic circuitry is disclosed. The piezoelectric motorization system has a piezoelectric apparatus that is constructed by a mechanically flexible body that has multiple piezoelectric actuators attached its surfaces, where these actuators are controlled by an electronic circuitry. The mechanically flexible body has a finite structure with a sets of boundary conditions to determine its out-of-plane resonant modes. The electronic circuitry inject at least two sets of control signals into different groups of actuators at or near different resonant frequencies. Using these control signals, traveling waves can be generated on the piezoelectric apparatus to move mechanical loads placed on its surface. Or, the traveling waves are used to propel the piezoelectric apparatus for motorization. The moving direction and velocity are controlled and adjusted by amplitude ratio and phase difference among driving frequencies of control signals. The moving direction and velocity also is controlled by the size, shape and locations of piezoelectric actuators on the mechanically flexible body. Different combinations of bending and/or twisting modes are used to generate one-dimensional or two-dimensional movements. Finally, multiple piezoelectric apparatus can be placed on three orthogonal planes of a three-dimensional mass for three-dimensional motorization.