Design and Electronic Interfacing of FR4 and Polyimide PCB-based Electromagnetic Resonating Micro-mirrors
, Russell Farrugia, Owen Casha, Barnaby Portelli, Joseph Micallef
Adv. Sci. Technol. Eng. Syst. J. 11(1), 1–10 (2026);
DOI: 10.25046/aj110101
This paper presents the design and fabrication of an electromagnetically actuated PCB-based resonating scanning micro-mirror for LiDAR applications, with optimization targeted towards low-cost fabrication and a high scanning angle. Traditional silicon MEMS-based micro-mirrors, while offering high precision and compatibility with CMOS processing, are limited by fragility at low scanning frequencies and costly fabrication processes. To overcome these challenges, novel alternative polymer-based substrates, namely FR4 and polyimide (PI), were employed to implement PCB-compatible mirror prototypes. Electromagnetic actuation was chosen because it achieves a high scanning angle at low driving voltages and is therefore compatible with modern electronic drive circuitry. The resonant frequency and von Mises stresses were assessed via COMSOL finite element simulations. Various scanning mirror prototypes, each featuring an optical mirror aperture of 10 mm by 10 mm, were fabricated using two different materials: 0.3 mm-thick FR4 and polyimide substrates. Different electromagnetic coil structures, embedded on the mirror plate, were evaluated with the aim of optimizing the scanning performance. The magnetic field was generated using neodymium permanent magnets. The performance attained by each prototype is compared and discussed. The scanning mirrors were designed to have a low resonant frequency in the range of 250 Hz to 550 Hz. The maximum optical scanning angle achieved for the FR4 and polyimide substrates are 31.3° and 52.1°, respectively. The paper also delves into the design of a microcontroller-based electromagnetic actuation and sensing circuitry of the mirror. Custom electronic circuitry comprising a low-power STM32L432KC microcontroller, H-bridge motor drivers for mirror actuation, and INA241-based coil voltage and current sensing was designed for this purpose. The coil voltage and current sensing circuitry enable the eventual real-time sensor less angular position feedback of the micro-mirror.
Introduction
This paper presents an extended version of the preliminary work describing PCB-based micro-mirrors originally presented in the IEEE 31st International Conference on Electronics, Circuits, and Systems [1]. Scanning micro-mirrors are used in various applications, including miniature projection displays, LiDAR, micro-spectrometers, and biomedical imaging [2]. Previous work in this area includes an FR4-based micro-mirror featuring a 12 mm by 12 mm platform with a rectangular spring structure, achieving an optical scanning angle of 11.2° at 361.8 Hz and requiring only 425 mV of driving voltage. This design also integrated an angle sensor for real-time feedback, demonstrating strong durability through long-term vibration and shock testing [3]. Another study, involving FR4-based scanning mirrors, evaluated three different configurations, with the most optimal one achieving a 140˚ scan angle at 417.4 Hz using serpentine springs, which were chosen for their lower spring constant [4]. Two other rectangular spring-based variants were also investigated: these achieved a scanning angle of 16.9˚ and 30˚ at an operating frequency of 1.787 kHz and 807 Hz, respectively, under similar conditions [4]. Another micro-mirror design was intended for a near infrared (NIR) spectrometer application and incorporated a 12 by 12 mm FR4-based diffraction grating with serpentine springs and reached a scanning angle of 13˚ at an operating frequency of 190 Hz [5].
In this work, polyimide (PI) is also considered and compared with FR4 as an alternative substrate material for its potential use in low-frequency resonating high scanning angle micro-mirrors due to its inherently low value of Young’s modulus and mechanical robustness.
Table 1: Comparison of typical material properties: FR4, flexible PI, and Silicon.
| Property | FR4 | Flexible Polyimide | Silicon (single-crystal 100) |
|---|---|---|---|
| Material Type | Rigid laminate | Flexible laminate | Crystalline semiconductor |
| Glass Transition Temp (Tg) | 130°C–180°C | 200°C–250°C | N/A |
| Thermal Conductivity | 0.3–0.4 W/m·K | 0.12–0.22 W/m·K | ∼149 W/m·K |
| Decomposition Temp (Td) | ∼300°C | >400°C | >1,414°C (melting point) |
| Moisture Absorption | 0.10–0.20% | 0.8–1.0% | 0% |
| Ductility | Medium | High | Low |
| Cost | Lower | Medium | High |
| Mechanical Strength | High | Moderate | Very high (but brittle) |
| Ultimate Tensile Stress | ∼375 MPa | ∼230 MPa | ∼2 GPa |
$$
T_{\mathrm{mag}} = 2 \sum_{j=1}^{N} B \, i \, l_j \, r_j
\tag{2}
$$
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