Robert Kamberger

Optical characterization of adaptive fluidic silicone-membrane lenses

We present an extended optical characterization of an adaptive microfluidic silicone-membrane lens at a wavelength of 633 nm, respectively 660 nm. Two different membrane variations; one with a homogeneous membrane thickness, and one with a shaped cross section, have been realized. This paper includes the theoretical predictions of the optical performance via FEM simulation and ray tracing, and a subsequent orientation dependent experimental analysis of the lens quality which is measured with an MTF setup and a Mach-Zehnder interferometer. The influence of the fabrication process on the optical performance is also characterized by the membrane deformation in the non-deflected state. The lens with the homogeneous membrane of 5 mm in diameter and an aperture of 2.5 mm indicates an almost orientation independent image quality of 117 linepairs/mm at a contrast of 50%. The shaped membrane lenses show a minimum wave front error of WFE(RMS) = 24 nm, and the lenses with a planar membrane of WFE(RMS) = 31 nm at an aperture of 2.125 mm.

Fabrication of a fluidic membrane lens system

We present the fabrication process of a fluidic membrane lens system with an integrated piezoelectric pumping actuator. The optical unit and the pumping unit are fabricated through casting using a hot embossing machine. Two different systems, one with a homogeneous membrane thickness, and one with an inhomogeneous membrane thickness distribution, are manufactured. The influence of the volume shrinkage of the silicone during curing on the membrane shape and on the focal length is analyzed. The assembled system achieves a focal length between +52.4 mm and −70.9 mm at a piezovoltage of ±40 V. The full-scale response time of the system is below 24 ms.

Articulation and vocal tract acoustics at soprano subject's high fundamental frequencies

The role of the vocal tract for phonation at very high soprano fundamental frequencies (F0s) is not yet understood in detail. In this investigation, two experiments were carried out with a single professional high soprano subject. First, using two dimensional (2D) dynamic real-time magnetic resonance imaging (MRI) (24 fps) midsagittal and coronal vocal tract shapes were analyzed while the subject sang a scale from Bb5 (932 Hz) to G6 (1568 Hz). In a second experiment, volumetric vocal tract MRI data were recorded from sustained phonations (13 s) for the pitches C6 (1047 Hz) and G6 (1568 Hz). Formant frequencies were measured in physical models created by 3D printing, and calculated from area functions obtained from the 3D vocal tract shapes. The data showed that there were only minor modifications of the vocal tract shape. These changes involved a decrease of the piriform sinus as well as small changes of tongue position. Formant frequencies did not exhibit major differences between C6 and G6 for F1 and F3, respectively. Only F2 was slightly raised for G6. For G6, however, F2 is not excited by any voice source partial. Therefore, this investigation was not able to confirm that the analyzed professional soprano subject adjusted formants to voice source partials for the analyzed F0s.

Single chamber adaptive membrane lens with integrated actuation

In this work we introduce an extremely thin single chamber adaptive fluidic membrane lens with an integrated piezoelectric bending actuator. The height of the system is 1.76 mm and the membrane diameter 10 mm. The lens consists of a ring shaped piezo bending actuator with an optical clear silicone membrane in the center. A refractive power range of 11.3 dpt is achieved at a piezo voltage between ±40 V. The system shows a maximum resolution of 189 lp/mm measured at 50 % contrast and a focal length of 200 mm.

Hollow microcoils made possible with external support structures manufactured with a two-solvent process

We present a process to manufacture solenoidal microcoils with external support structures, which leaves the space within the coil windings free. The manufacturing procedure is based on a two solvent approach (water and acetone), for selectively etching polyvinyl alcohol and polymethyl methacrylate. Two sets of microcoils were manufactured with an inner diameter of 1.5 mm, an interwinding pitch of 100 μm and five or eight coil windings respectively. The coils were designed for application in magnetic resonance imaging and spectroscopy, and characterised in a 9.4 T MR scanner. An NMR spectrum of water and MR images in receive only and transceive mode were acquired as proof of concept.

A comparison of different methods to generate tooth surface models without applying ionizing radiation for digital 3-dimensional image fusion with magnetic resonance imaging-based data of the head and neck region

Objective The 3-dimensional display of the vocal tract and teeth is necessary in numerous clinical and scientific contexts. Due to the different tissue properties this can only be achieved by combining different imaging techniques. A comparison of methods to record the tooth surface to create combined models of the vocal tract and teeth without applying ionizing radiation is displayed in this study. Methods Four methods to record the tooth surface were compared concerning their clinical accuracy after combination with magnetic resonance imaging (MRI)–based vocal tract models. With 2 of the presented methods the information of the tooth surface was obtained from MRI data. With the other 2 methods, the tooth surface was captured using a digital and a conventional impression technique. Results Impression techniques received the best rating results. Conclusions The digital 3-dimensional image fusion of dental impression and MRI resulted in a virtual model of the vocal tract and teeth with a high clinical accuracy without applying ionizing radiation.

Closed-loop pressure control of an adaptive single chamber membrane lens with integrated actuation

We introduce a closed-loop pressure control of a single chamber adaptive fluidic membrane lens with an integrated piezoelectric bending actuator. For this purpose a pressure sensor is integrated into the lens and allows for a measurement of the chamber pressure as a function of the refractive power. The linear relation between pressure and refractive power allows to eliminate the typical hysteresis effects of piezo actuators.

Relevance of the Implementation of Teeth in Three-Dimensional Vocal Tract Models

Purpose Recently, efforts have been made to investigate the vocal tract using magnetic resonance imaging (MRI). Due to technical limitations, teeth were omitted in many previous studies on vocal tract acoustics. However, the knowledge of how teeth influence vocal tract acoustics might be important in order to estimate the necessity of implementing teeth in vocal tract models. The aim of this study was therefore to estimate the effect of teeth on vocal tract acoustics. Method The acoustic properties of 18 solid (3-dimensional printed) vocal tract models without teeth were compared to the same 18 models including teeth in terms of resonance frequencies (fRn). The fRn were obtained from the transfer functions of these models excited by white noise at the glottis level. The models were derived from MRI data of 2 trained singers performing 3 different vowel conditions (/i/, /a/, and /u/) in speech and low-pitched and high-pitched singing. Results Depending on the oral configuration, models exhibiting side cavities or side branches were characterized by major changes in the transfer function when teeth were implemented via the introduction of pole-zero pairs. Conclusions To avoid errors in modeling, teeth should be included in 3-dimensional vocal tract models for acoustic evaluation. Supplemental Material https://doi.org/10.23641/asha.5386771.

A comparison of Lenz lenses and LC resonators for NMR signal enhancement

Abstract High signal‐to‐noise ratio (SNR) of the NMR signal has always been a key target that drives massive research effort in many fields. Among several parameters, a high filling factor of the MR coil has proven to boost the SNR. In case of small‐volume samples, a high filling factor and thus a high SNR can be achieved through miniaturizing the MR coil. However, under certain circumstances, this can be impractical. In this paper, we present an extensive theoretical and experimental investigation of the inductively coupled LC resonator and the magnetic Lenz lens as two candidate approaches that can enhance the SNR in such circumstances. The results demonstrate that the narrow‐band LC resonator is superior in terms of SNR, while the non‐tuned nature of the Lenz lens makes it preferable in broadband applications.