MEMS Mirror Design for Forward-Looking OCT Probe
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Solution Overview
Problem
Current forward-looking optical coherence tomography (OCT) endoscopic probes face challenges in achieving a large lateral scanning angle with small dimensions, which limits their ability to image irregularly shaped hollow organs effectively, such as the bladder, uterus, stomach, and lungs, due to limitations in MEMS mirror technology, particularly with electrostatic and electrothermal actuation methods.
Innovation Solution
A MEMS mirror design with a stator, rotor, and actuator featuring interdigitated comb elements and torsion beams allows for a large mirror surface area with a narrow cross-sectional size, enabling a high fill factor and low resonance frequency, facilitating low-power operation and high lateral resolution imaging. This design includes a rotor body with peripheral portions extending beyond the stator, allowing for increased mirror surface area without increasing footprint, and uses through-silicon-via technology for electrical connection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If conventional MEMS mirror designs are used, then the device can be manufactured with standard processes, but the lateral scanning angle is limited and the mirror surface area is small relative to the footprint
Solution Approach 1:
The patent extends the mirror surface area in the transverse direction (perpendicular to rotation axis) beyond the stator boundaries, utilizing third-dimensional space above and below the stator plane. This allows the rotor body with mirror to achieve larger surface area without proportionally increasing the footprint, as the mirror extends into the vertical dimension relative to the stator support structure.
Solution Approach 2:
The rotor body with extended peripheral portions is nested within the overall device housing, allowing the mirror surface to extend beyond the stator footprint while remaining contained within the total device envelope. This nesting arrangement enables high fill factor without proportionally increasing the external dimensions of the probe.
2Use of energy by moving object
If electrostatic or electrothermal actuation methods are used, then the MEMS mirror can be actuated, but the resonance frequency is high and power consumption is high
Solution Approach 1:
The patent utilizes torsion beams as mechanical springs to create a compliant suspension system for the rotor. This mechanical vibration approach with optimized beam geometry (width, thickness, length) enables lower resonance frequency operation compared to electrostatic or electrothermal actuation, reducing power consumption while maintaining effective mirror actuation through electromagnetic or other low-power means.
3Adaptability or versatility
If the mirror surface area is increased to improve imaging coverage, then the lateral scanning angle increases, but the probe dimensions increase
Solution Approach 1:
The mirror surface extends in the transverse direction (y-axis, perpendicular to rotation axis) beyond the stator boundaries, utilizing the vertical dimension relative to the support structure. This allows increased imaging coverage through larger mirror area without proportionally increasing the probe length or width, as the extension is in the transverse dimension within the existing probe envelope.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The MEMS mirror enables a forward-looking OCT probe with a large scanning angle and high lateral resolution, suitable for imaging hollow organs, while maintaining compact dimensions and reducing power consumption, thus improving diagnostic capabilities in urology and other medical applications.
Implementation Method 1
The actuator has at least one pair of mutually interdigitated comb elements including at least a first comb element and a second comb element. The first comb element is fixed to the stator and the second comb element is fixed to the rotor. When voltage is applied to the comb elements, electrostatic force is generated between the interdigitated teeth, causing the rotor to rotate relative to the stator.
Implementation Method 2
The rotor is further coupled at mutually opposite sides via a respective torsion beam to the stator. These torsion beams, one at each end extend along a rotation axis in the reference plane to allow the actuator to rotate the rotor within a rotation range relative to the stator along the rotation axis.
Data Source
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Figure 3A
AI summary
A forward looking MEMS based OCT probe (50) is provided that comprises an elongate probe housing (51) having at a first end a probe interface (54) for an optic fibre (56), and at a second opposite end a viewing window (58). The probe housing accommodates a MEMS mirror (10) for sweeping a hght beam (60) through the viewing window and for reflecting light received through the viewing window towards the probe interface, wherein a rotation axis (18) of the MEMS mirror extends transverse to a longitudinal axis (62) defined by the probe housing. The MEMS mirror (10) has a stator (12), a rotor (14), and an actuator (16) with at least one pair of mutually interdigitated comb elements including at least a first comb element fixed to the stator defining a reference plane and at least a second comb element fixed to the rotor and that is further coupled at mutually opposite sides via a respective torsion beam (20A, 20B) to the stator. The rotor has a rotor body (14RB) and a rotor support (14RS), fixed at a first face of the rotor body, that keeps the rotor body at a distance from the stator within said rotation range, the rotor body having a mirror surface (14MS) at a second face opposite the first face, the MEMS mirror comprising the stator (12) and the rotor support (14RS) at mutually opposite sides of the reference plane (RP).