Arlindo N. Montagnoli

Microlens array fabricated by a low-cost grayscale lithography maskless system

Abstract. This work presents the fabrication of a contiguous f/#=f/15 Fresnel microlens array (MLA) by employing a low-cost home-built maskless exposure lithographic system based on a digital light projector technology by using Texas Instruments’ digital micromirror device chip. A continuous diffractive phase relief structure was generated on a photoresist-coated silicon wafer, replicated in polydimethylsiloxane (PDMS) and electrostatically bonded to a glass substrate. The whole exposure time takes 10.8 min to expose a 2.4×2.4  mm MLA, with a resolution of 2.5 μm. This exposure time is relatively short, enabling high throughput or fast prototyping. Optical characterization was carried out using a He-Ne laser source (λ=633  nm), by evaluating the maximum intensity of each spot generated at the MLA focal plane, Imax, as well as its sharpness by measuring their full width at half maximum (FWHM) intensity values. The resulting FWHM and maximum intensity spot average values were FWHMAVG=20±8%  μm and ImaxAVG=0.71±7%  a.u., respectively. The quality of replication was evaluated by profile characterization of the resulting mold and replica based on step height measurement along 180 μm. The maximum obtained difference was 32 nm, corresponding to 2.5% of the total mold height or λ/20. AFM measurements were also carried out to quantify the roughness quality between mold and replica. The resulting RMS roughness was 4.73 nm (λ/130) and 6.66 nm (λ/95) for mold and replica, respectively. A comparison between theoretical and measured intensity profiles at the MLA focal plane was also carried out. A good correspondence between the results was found. Such an MLA can be applied as a Shack–Hartmann wavefront sensor in optical interconnects and to enhance the efficiency of detector arrays.

Improvement of Vocal Pathologies Diagnosis Using High-Speed Videolaryngoscopy

Introduction The study of the dynamic properties of vocal fold vibration is important for understanding the vocal production mechanism and the impact of organic and functional changes. The advent of high-speed videolaryngoscopy (HSV) has provided the possibility of seeing the real cycle of vocal fold vibration in detail through high sampling rate of successive frames and adequate spatial resolution. Objective To describe the technique, advantages, and limitations of using HSV and digital videokymography in the diagnosis of vocal pathologies. Methods We used HSV and digital videokymography to evaluate one normophonic individual and four patients with vocal fold pathologies (nodules, unilateral paralysis of the left vocal fold, intracordal cyst, and adductor spasmodic dysphonia). The vocal fold vibration parameters (glottic closure, vibrational symmetry, periodicity, mucosal wave, amplitude, and glottal cycle phases) were assessed. Results Differences in the vocal vibration parameters were observed and correlated with the pathophysiology. Conclusion HSV is the latest diagnostic tool in visual examination of vocal behavior and has considerable potential to refine our knowledge regarding the vocal fold vibration and voice production, as well as regarding the impact of pathologic conditions have on the mechanism of phonation.

Graphical Evaluation of Vocal Fold Vibratory Patterns by High-Speed Videolaryngoscopy

OBJECTIVE To characterize the voice and vocal fold function of an individual, it is essential to evaluate vocal fold vibration. The most widely used method for this purpose has been videolaryngoscopy. METHODS This article proposes a digital image processing algorithm to estimate the glottal area (ie, the space between the vocal folds) and produce graphs of the opening and closing phases of the glottal cycle. In eight subjects without voice disorders, vocal fold movements were recorded by high-speed videolaryngoscopy at 4000 frames per second. The video data were processed by a combination of image segmentation techniques that estimate the glottal area. The segmented area was used to construct the glottal waveform. RESULTS The graphs revealed important properties of vocal fold vibration, including amplitude, velocity, and other characteristics that have a major influence on voice quality. CONCLUSIONS The combination of the high-speed technology with the proposed method improves the vocal fold analysis given a numerical feedback through graphical representation of the real vibratory patterns of the folds.

Global Kalman filter approaches to estimate absolute angles of lower limb segments

BackgroundIn this paper we propose the use of global Kalman filters (KFs) to estimate absolute angles of lower limb segments. Standard approaches adopt KFs to improve the performance of inertial sensors based on individual link configurations. In consequence, for a multi-body system like a lower limb exoskeleton, the inertial measurements of one link (e.g., the shank) are not taken into account in other link angle estimations (e.g., foot). Global KF approaches, on the other hand, correlate the collective contribution of all signals from lower limb segments observed in the state-space model through the filtering process. We present a novel global KF (matricial global KF) relying only on inertial sensor data, and validate both this KF and a previously presented global KF (Markov Jump Linear Systems, MJLS-based KF), which fuses data from inertial sensors and encoders from an exoskeleton. We furthermore compare both methods to the commonly used local KF.ResultsThe results indicate that the global KFs performed significantly better than the local KF, with an average root mean square error (RMSE) of respectively 0.942° for the MJLS-based KF, 1.167° for the matrical global KF, and 1.202° for the local KFs. Including the data from the exoskeleton encoders also resulted in a significant increase in performance.ConclusionThe results indicate that the current practice of using KFs based on local models is suboptimal. Both the presented KF based on inertial sensor data, as well our previously presented global approach fusing inertial sensor data with data from exoskeleton encoders, were superior to local KFs. We therefore recommend to use global KFs for gait analysis and exoskeleton control.

High-speed Videolaryngoscopy: Quantitative Parameters of Glottal Area Waveforms and High-speed Kymography in Healthy Individuals

OBJECTIVES We conducted a study to obtain quantitative parameters of the vocal dynamic using high-speed videolaryngoscopy and to characterize the vocal fold vibration pattern of healthy individuals by analyzing glottal area waveforms and high-speed kymography. METHODS Laryngeal images of 45 healthy individuals were captured using high-speed videolaryngoscopy. The open and speed quotients of the glottal area waveforms and high-speed kymography were obtained and statistically analyzed according to the gender of each individual. RESULTS Glottal area waveforms revealed average values of 0.85 and 1.16 for open and speed quotients, respectively, for women, and 0.70 and 1.19 for men. Using high-speed kymography, quantitative parameters of open and speed quotients for women were 0.62 and 1.02, respectively, and for men were 0.57 and 1.12. By gender, a significant statistical difference emerged for open quotients obtained from both glottal area waveforms (P = 0.004) and high-speed kymography (P = 0.013). CONCLUSION Obtained by using computational tools specifically for analyzing laryngeal images from high-speed videolaryngoscopy, quantitative parameters of glottal area waveforms and high-speed kymography in healthy individuals provide reference data and normality for future studies.

Impact of Cricothyroid Muscle Contraction on Vocal Fold Vibration: Experimental Study with High-Speed Videoendoscopy

OBJECTIVES The aim of this study was to evaluate the effects of cricothyroid muscle contraction on vocal fold vibration, as evaluated with high-speed videoendoscopy, and to identify one or more aspects of vocal fold vibration that could be used as an irrefutable indicator of unilateral cricothyroid muscle paralysis. STUDY DESIGN This was an experimental study employing excised human larynges. METHODS Twenty freshly excised human larynges were evaluated during artificially produced vibration. Each larynx was assessed in three situations: bilateral cricothyroid muscle contraction, unilateral cricothyroid muscle contraction, and no contraction of either cricothyroid muscle. The following parameters were evaluated by high-speed videoendoscopy: fundamental frequency, periodicity, amplitude of vocal fold vibration, and phase symmetry between the vocal folds. RESULTS Although neither unilateral nor bilateral cricothyroid muscle contraction altered the periodicity of vibration or the occurrence of phase asymmetry, there was a significant decrease in fundamental frequency in parallel with decreasing longitudinal tension. We also found an increase in vibration amplitude of right and left vocal folds, which were similar in terms of their behavior for this parameter in the various situations studied. CONCLUSION Our results suggest that differences in vibration amplitude and phase symmetry between vocal folds are not reliable indicators of unilateral cricothyroid muscle paralysis.

Operational Modal Analysis with Photo Images from Low Speed Digital Camera

Structural vibration is commonly measured with single point sensors, thus requiring a number of sensors equal to the number of points to be measured in the structure. Depending on the structure, the number of sensors needed is large resulting in significant costs in the measurement procedure. For this reason, full field measurement systems have been developed, where one sensor is responsible for measuring the entire structure. However, such systems require expensive devices (fast cameras, stereographic cameras, laser scanners). In this work, one presents a more affordable approach for full field measurement based on photographic images obtained with a low speed camera (maximum of 3 fps). The method is suitable for structures under periodic excitations and 2D motion. Images of the vibrating structure are taken and post processing is used to calculate the displacements of points of interest in the structure. Gathering the information of all images, a sub-sampling technique is used to reconstruct the vibration signal. Experimental results show the effectiveness of performing an Operational Modal Analysis and retrieving normal modes and natural frequencies up to 20 Hz with an acquisition period of 1.5 s.

Low-cost Fresnel microlens array fabricated by a home-built maskless lithography system

This work presents the fabrication of a high fill factor Fresnel microlens array (MLA) by employing a low-cost homebuilt maskless exposure lithographic system. A phase relief structure was generated on a photoresist-coated silicon wafer, replicated in Polydimethylsiloxane (PDMS) and electrostatically bonded to a glass substrate. Optical characterization was based on the evaluation of the maximum intensity of each spot generated at the MLA focal plane as well as its full width at half maximum (FWHM) intensity values. The resulting FWHM and maximum intensity spot mean values were 50 ± 8% μm and 0.71 ± 7% a.u , respectively. Such a MLA can be applied as Shack-Hartmann wavefront sensors, in optical interconnects and to enhance the efficiency of detector arrays.

Low f-number microlens array fabricated in thick resist

In certain applications of MOEMS devices, it is often necessary to produce microlens array structures that concentrate optical power in semiconductor photodetectors. In this work, the design and fabrication of a low f-number cylindrical microlens array is presented. The lenses were fabricated in thick photo resist - 12 μm thick - using a contact printer exposure through a mask with a repetitive 6 μm line - 4 μm space pattern. The width of the resulting microlens array was determined to be 10 μm, with f-number of 0.5. Numerical calculations based on scalar diffraction theory were employed to model the light propagation inside the resist, determining the aerial image as a function of its thickness. Than the resist response characteristics, expressed by its contrast curve, and absorption rate were used to obtain a cross section profile. A good match between numerical and experimental results were found.

Low-cost polymer Fresnel Microlens Array Fabricated by Maskless Lithography

This work presents the fabrication of 8X8 PDMS Fresnel microlens array (MLA) by maskless lithographic system. The FWHM intensity values of each spot present a deviation of 8%. Such a MLA can be applied as Shack-Hartmann wavefront sensor and to enhance the efficiency of detector arrays.