Sensors and Actuators A 255 (2017) 21–27 Contents lists available at ScienceDirect Sensors and Actuators A: Physical j ourna l h o mepage: www.elsevier.com/locate/sna Optimization of piezo-fiber scanning architecture for low voltage/high displacement operation R. Khayatzadeh, F. C ¸ ivitci, O. Ferhano˘ glu ∗ Department of Electronics and Communication Eng., Istanbul Technical University, Istanbul, 34469, Turkey a r t i c l e i n f o Article history: Received 1 August 2016 Received in revised form 30 November 2016 Accepted 28 December 2016 Available online 3 January 2017 Keywords: Confocal microscopy Endoscopic device Fiber optics Piezo-fiber scanning a b s t r a c t Piezo-based fiber scanning probes have emerged as low-cost and compact tools for various optical imag- ing modalities, allowing access to tissue sites that are hard to reach. These instruments exploit scanning of a fiber optic cable via a piezoelectric element, which is driven at the mechanical resonance of the extended fiber piece. However, the dynamics of the piezo-scanning structure is often neglected, resulting in an inefficient electromechanical conversion. This work presents a methodology, together with exper- imental evidence, to collectively optimize the geometries of the piezo-scanner and the extended fiber optic cable to achieve maximum displacement for a given drive voltage. Our findings suggest that match- ing the individual resonances of the fiber optics cable and the piezo-scanner alone, leads to optimum electromechanical conversion efficiency. Simulations, circuit model, and experimental results reveal more than x2 improvement in the achieved fiber displacement when piezo and fiber resonances are matched, as opposed to the unmatched (i.e., when piezo element length is varied approximately by ±20% from its optimal value) case. Besides offering lower power consumption for the actuation of the piezo-element, our findings paves the way for safer (electric shock-free) minimally-invasive procedures using the piezo-based fiber scanning probes, which is crucial for patient safety. © 2017 Elsevier B.V. All rights reserved. 1. Introduction Thanks to their compact geometry and simple architecture, piezo-scanning based fiber probes have been exploited in confo- cal imaging [1], optical coherence tomography [2], multiphoton imaging [3], and imaging of Raman scattering [4]. Their size advan- tage enables accessing tissue sites that are difficult to reach, while providing high-resolution images that reveal pathological informa- tion. In this regard, piezo-scanning fiber probes have been widely utilized in biological studies such as calcium imaging of the rat cere- bellum [5], epithelial imaging [6], monitoring collagen morphology in the cervix [7], minimally invasive imaging of the mouse lung and colon tissues [8], brain imaging in freely moving animals [9]. With their superior form factor, piezo-scanning fiber probes have also been involved in commercial applications, such as compact display systems [10,11]. In a piezo-scanning fiber probe, light is mapped onto the tissue that is exiting the extended optical fiber, which is encircled and actuated by a cylindrical piezoelectric tube. The piezo-tube, which converts applied voltage to mechanical movement, is driven at the ∗ Corresponding author. E-mail address: ferhanoglu@itu.edu.tr (O. Ferhano˘ glu). mechanical resonance of the extended fiber to create the desired scan pattern. Owing to its four quadrant electrodes surrounding the piezo-tube, various 2D tissue scan patterns (spiral or lissajous patterns) can be achieved for imaging and microsurgery [12,13]. Furthermore, combination of orthogonally placed piezo-sheet can- tilevers has been exploited to establish a raster scanning pattern, which cannot be achieved with conventional piezo-tube based fiber scanning [14]. Actuating the piezo-element (tube or cantilever) at the mechan- ical resonance frequency of the extended fiber optic cable, results in a high fiber tip displacement, for a much lower displacement of the piezo-element free-end. Yet, the dynamics of the piezo- scanning structure is often neglected, i.e. the relationship between the geometry and resonant frequencies of the piezo-element and the extended fiber for optimized electromechanical coupling has not been treated. A high degree of electromechanical coupling not only ensures achieving high Field-of-View (FOV), but also acts as a safeguard towards electric shock-free interventions (for worst-case scenarios, where electrical connections to the endoscopic device gets detached from the piezo-element, or get stripped off, result- ing in an electrical contact with the tissue) with the piezo-scanning fiber probe. Besides safety and power consumption issues, lowering http://dx.doi.org/10.1016/j.sna.2016.12.025 0924-4247/© 2017 Elsevier B.V. All rights reserved.