Chenggen Quan

Piezoelectric MEMS Energy Harvester for Low-Frequency Vibrations With Wideband Operation Range and Steadily Increased Output Power

A piezoelectric MEMS energy harvester (EH) with low resonant frequency and wide operation bandwidth was designed, microfabricated, and characterized. The MEMS piezoelectric energy harvesting cantilever consists of a silicon beam integrated with piezoelectric thin film (PZT) elements parallel-arranged on top and a silicon proof mass resulting in a low resonant frequency of 36 Hz. The whole chip was assembled onto a metal carrier with a limited spacer such that the operation frequency bandwidth can be widened to 17 Hz at the input acceleration of 1.0 g during frequency up-sweep. Load voltage and power generation for different numbers of PZT elements in series and in parallel connections were compared and discussed based on experimental and simulation results. Moreover, the EH device has a wideband and steadily increased power generation from 19.4 nW to 51.3 nW within the operation frequency bandwidth ranging from 30 Hz to 47 Hz at 1.0 g. Based on theoretical estimation, a potential output power of 0.53 μW could be harvested from low and irregular frequency vibrations by adjusting the PZT pattern and spacer thickness to achieve an optimal design.

Investigation of a MEMS piezoelectric energy harvester system with a frequency-widened-bandwidth mechanism introduced by mechanical stoppers

This paper presents the design, microfabrication, modeling and characterization of a piezoelectric energy harvester (PEH) system with a wide operating bandwidth introduced by mechanical stoppers. The wideband frequency responses of the PEH system with stoppers on one side and two sides are investigated thoroughly. The experimental results show that the operating bandwidth is broadened to 18?Hz (30?48?Hz) and the corresponding optimal power ranges from 34 to 100?nW at the base acceleration of 0.6g and under top-?and bottom-stopper distances of 0.75?mm and 1.1?mm, respectively. By adjusting the mechanical stopper distance, the output power and frequency bandwidth can be optimized accordingly.

Shape measurement of small objects using LCD fringe projection with phase shifting

This paper describes the use of optical fringe projection method for three-dimensional shape measurement of small objects. In this method, sinusoidal linear fringes are projected on the object surface by a programmable liquid crystal display (LCD) projector and a long working distance microscope (LDM). The image of the fringe pattern is captured by another LDM and a CCD camera and processed by phase-shifting technique. A simple procedure is described which enables calibration of the optical setup for subsequent quantitative measurement of unknown object shapes. The method developed can also be applied to the measurement of the warp of a small component under thermal loading. This method is relatively simple and accurate, and is capable of conducting fully automated measurements.

Microscopic surface contouring by fringe projection method

Abstract This paper describes the use of optical fringe projection method for 3D surface profile and deformation measurement of micro-components. In this method, sinusoidal linear fringes are projected on a micro-component surface by a grating phase shifting projector and a long working distance microscope (LWDM). The image of the fringe pattern is captured by a high-resolution CCD camera and another LWDM and processed by phase-shifting technique. A simple procedure is described which enables calibration of the optical set-up for subsequent quantitative measurement of micro-components of unknown shapes. This method is relatively simple and accurate, and is capable of conducting fully automated measurements. In this paper, two micro-components, a micro-mirror ( 0.1 mm ×0.1 mm ) and a micro-electrode pad are used to demonstrate deformation measurement and microscopic surface contouring.

Fringe projection profilometry with nonparallel illumination: a least-squares approach

Under a nonparallel illumination condition, fringe patterns projected on an object have unequal fringe spacing that would introduce a nonlinear carrier phase component. This Letter describes a nonlinear carrier removal technique based on a least-squares approach. In contrast with conventional methods, the proposed algorithm would not magnify phase measurement uncertainty, nor does it require direct estimation of system geometrical parameters. The theoretical expression of the carrier phase function on the reference is derived and expanded in a power series. The unknown coefficients in the series are determined by a least-squares method. By subtracting the calculated carrier phase function from the unwrapped phase map, the phase distribution of the object profile is obtained.

Grating projection system for surface contour measurement

A grating projection system is a low-cost surface contour measurement technique that can be applied to a wide range of applications. There has been a resurgence of interest in the technique in recent years because of developments in computer hardware and image processing algorithms. We describe a method that projects a phase-shifted grating through a lens on an object surface. The deformed grating image on the object surface is captured by a CCD camera for subsequent analysis. Phase variation is achieved by a linear translation stage on which the grating is mounted. We compare the experimental results with the test results using a mechanical stylus method.

Feasibility study of a 3D vibration-driven electromagnetic MEMS energy harvester with multiple vibration modes

A novel electromagnetic energy harvester (EH) with multiple vibration modes has been developed and characterized using three-dimensional (3D) excitation at different frequencies. The device consists of a movable circular-mass patterned with three sets of double-layer aluminum (Al) coils, a circular-ring system incorporating a magnet and a supporting beam. The 3D dynamic behavior and performance analysis of the device shows that the first vibration mode of 1285 Hz is an out-of-plane motion, while the second and third modes of 1470 and 1550 Hz, respectively, are in-plane at angles of 60 ◦ (240 ◦ ) and 150 ◦ (330 ◦ ) to the horizontal (x-) axis. For an excitation acceleration of 1 g, the maximum power density achieved are 0.444, 0.242 and 0.125 μ Wc m −3 at vibration modes of I, II and III, respectively. The experimental results are in good agreement with the simulation and indicate a good potential in the development of a 3D EH device. (Some figures may appear in colour only in the online journal)

In situ surface roughness measurement using a laser scattering method

Abstract In this paper, the design and development of an optical probe for in situ measurement of surface roughness are discussed. Based on this light scattering principle, the probe which consists of a laser diode, measuring lens and a linear photodiode array, is designed to capture the scattered light from a test surface with a relatively large scattering angle ϕ (=28°). This capability increases the measuring range and enhances repeatability of the results. The coaxial arrangement that incorporates a dual-laser beam and a constant compressed air stream renders the proposed system insensitive to movement or vibration of the test surface as well as surface conditions. Tests were conducted on workpieces which were mounted on a turning machine that operates with different cutting speeds. Test specimens which underwent different machining processes and of different surface finish were also studied. The results obtained demonstrate the feasibility of surface roughness measurement using the proposed method.

Shape measurement by use of liquid-crystal display fringe projection with two-step phase shifting

The use of an optical fringe projection method with two-step phase shifting for three-dimensional (3-D) shape measurement of small objects is described. In this method, sinusoidal linear fringes are projected onto an objects surface by a programmable liquid-crystal display (LCD) projector and a long-working-distance microscope (LWDM). The image of the fringe pattern is captured by another LWDM and a CCD camera and processed by a phase-shifting technique. Usually a minimum of three phase-shifted fringe patterns is necessary for extraction of the object shape. In this method, a new algorithm based on a two-step phase-shifting technique produces the 3-D object shape. Unlike in the conventional method, phase unwrapping is performed directly by use of an arccosine function without the need for a wrapped phase map. Hence, shape measurement can be speeded up greatly with this approach. A small coin is evaluated to demonstrate the validity of the proposed measurement method, and the experimental results are compared with those of the four-step phase-shifting method and the conventional mechanical stylus method.

Multiple-image encryption by space multiplexing based on compressive sensing and the double-random phase-encoding technique

In this paper, a new multiple-image encryption and decryption technique that utilizes the compressive sensing (CS) concept along with a double-random phase encryption (DRPE) has been proposed. The space multiplexing method is employed for integrating multiple-image data. The method, which results in a nonlinear encryption system, is able to overcome the vulnerability of classical DRPE. The CS technique and space multiplexing are able to provide additional key space in the proposed method. A numerical experiment of the proposed method is implemented and the results show that the proposed method has good accuracy and is more robust than classical DRPE. The proposed system is also employed against chosen-plaintext attacks and it is found that the inclusion of compressive sensing enhances robustness against the attacks.