FR4-Based Electromagnetic Scanning Micromirror Integrated with Angle Sensor

Abstract

This paper presents a flame retardant 4 (FR4)-based electromagnetic scanning micromirror, which aims to overcome the limitations of conventional microelectromechanical systems (MEMS) micromirrors for the large-aperture and low-frequency scanning applications. This micromirror is fabricated through a commercial printed circuit board (PCB) technology at a low cost and with a short process cycle, before an aluminum-coated silicon mirror plate with a large aperture is bonded on the FR4 platform to provide a high surface quality. In particular, an electromagnetic angle sensor is integrated to monitor the motion of the micromirror in real time. A prototype has been assembled and tested. The results show that the micromirror can reach the optical scan angle of 11.2° with a low driving voltage of only 425 mV at resonance (361.8 Hz). At the same time, the signal of the integrated angle sensor also shows good signal-to-noise ratio, linearity and sensitivity. Finally, the reliability of the FR4 based micro-mirror has been tested. The prototype successfully passes both shock and vibration tests. Furthermore, the results of the long-term mechanical cycling test (50 million cycles) suggest that the maximum variations of resonant frequency and scan angle are less than 0.3% and 6%, respectively. Therefore, this simple and robust micromirror has great potential in being useful in a number of optical microsystems, especially when large-aperture or low-frequency is required.

Investigation of Electromagnetic Angle Sensor Integrated in FR4-Based Scanning Micromirror

“…By comparing Equation (9) with (13), we can find that the parameter of torsional stiffness K is introduced in Equation (13) when considering the coupling voltage in the sensing coil coupled from the driving signal. Owing to the nonlinear spring effect of the torsion bars [15,24], K is not a constant, but varies with the change of the scan angle. Thus, a little nonlinear behavior of the test result is observed.…”

“…In general, the micromirror must scan the optical beam at a specific optical scan angle in practical applications. However, the current FR4 micromirror with a simple open-loop control cannot guarantee it, owing to the relatively poor stability of FR4 [12,15]. Therefore, an angle sensor is highly desired to monitor the scan angle in real time, and further form a feedback control.…”

“…Among these methods, electromagnetic angle sensing is more suitable to be integrated in the aforementioned FR4 micromirror, due to its excellent process compatibility. In our previous work [15], we presented a FR4-based electromagnetic scanning micromirror monolithically integrated with an electromagnetic angle sensor. However, it focused more on basic prototyping, driving performance, and reliability of the micromirror.…”

A Compound Control System for FR4-Based Electromagnetic Scanning Micrograting

“…In recent years, most of the scanning micrograting has been developed and fabricated using MEMS technology. The actuation mechanisms can be mainly divided into four categories: electrostatic [9], electrothermal [10,11], electromagnetic [12][13][14][15], and piezoelectric [16]. The electromagnetic actuation mechanism is widely used for its large driving torque, linear mechanical properties, and low driving voltage.…”

“…Electromagnetic coils are more suitable for integration into the flame-retardant 4 (FR4)-based electromagnetic scanning micrograting, due to its excellent process compatibility with printed circuit boards (PCBs). Because of the shortcomings of the silicon MEMS scanning micrograting, such as high manufacturing cost, fragility, and poor shock and vibration [17], we developed the FR4-based electromagnetic scanning micrograting [13][14][15].…”