Ernst Dalhoff

Bio: Ernst Dalhoff is an academic researcher from University of Tübingen. The author has contributed to research in topics: Interferometry & Astronomical interferometer. The author has an hindex of 6, co-authored 28 publications receiving 128 citations. Previous affiliations of Ernst Dalhoff include University of Würzburg & University of Stuttgart.

Absolute interferometric distance measurement using a FM-demodulation technique.

Abstract: When applying interferometric techniques to measure the distance between two points separated by an amount larger than half the laser wavelength used the measurement become ambigous. To overcome this disadvantage, among others, two wavelength interferometry1–4 was developed. By applying two wavelengths \(\lambda _{1}\) and \(\lambda _{2}\) simultaneously to the object under test, the sensitivity is reduced to an effective wavelength \(\Lambda =\lambda _{1}\ \lambda _{2}/|\lambda _{1}-\lambda _{2}|\). Since the laser diode wavelength can easily be tuned via the laser injection current, the concept of two-wavelength interferometry can be extended to multiple-wavelength interferometry5–8. In this paper, we present a novel approach to derive the absolute distance information from the phase modulated detector signal by using a PLL (phase locked loop) based FM-demodulator. In this case, there is no need to generate a reference signal in the interferometer for the purpose of demodulation. By using a FM-demodulator, no unambiguity jump occurs if the phase deviation exceeds 2π. In this case, we are able to determine absolute distances with a noise limited resolution of about 1 μm, even if the distance is much larger than the synthetic wavelength.

Upper Bounds for Energy Harvesting in the Region of the Human Head

Abstract: This paper investigates different approaches for supplying power to implantable hearing systems via energy harvesting. Because of the specific nature of the problem, only energy harvesting in the region of the human head is considered. Upper bounds as well as more conservative estimations for harvesting mechanical, thermal, and electromagnetic energy are presented and discussed.

Low-coherence fibre heterodyne interferometer for both dc and high-frequency vibration measurements in the inner ear

Abstract: A coherence encoded heterodyne interferometer with a fibre-optic sensor head of 1.8mm diameter designed to detect both high-frequency vibrations as well as low-frequency non-harmonic phase shifts in the inner ear is presented. The light source was a laser diode with a multimode spectrum of width 4.6nm. In order to achieve low sensitivity to spurious phase drifts, a coherence selective configuration was used, comprising an entrance Mach–Zehnder interferometer, so that object and reference light travel the same path in the fibre. Phase measurements yielded a square root of the Allan variance of [sgrave] z = 0.26 A for an integration time of 0.1 s and [sgrave] z = 3.6 A for an integration time of 3.2s. A phase measurement, at an object of 1.18 × 10−4 reflectivity, showed a rms resolution of 0.46° over a measurement duration of 10s, corresponding to a distance resolution of 5.2 A.

Vibro-EAS: a proposal for electroacoustic stimulation.

Abstract: Hypothesis In situ evaluation of the vibration performance of a hybrid system for intracochlear fluid stimulation, constructed from a floating mass transducer (FMT) coupled to an electric acoustic stimulation (EAS) cochlea implant (CI) electrode. Background EAS uses both CI technology to restore severe-to-profound hearing loss at high frequencies and acoustic amplification for mild-to-moderate hearing loss in the low-to-mid frequency range. More patients with residual hearing are becoming candidates for EAS surgery because of the improved techniques for hearing preservation. Most patients with partial deafness fulfill the audiological criteria at low and mid-frequencies for the active middle-ear implant with FMT (VSB). The FMT of the VSB is a potential device for acoustical stimulation in EAS. Methods In seven fresh human temporal bones, stapes amplitude responses for fixation of a FMT to the long incus process (standard coupling) was compared with those for FMT fixation to a 20-mm inserted standard cochlea electrode array (31.5 mm) via the round window (Vibro-EAS). Vibration of the stapes footplate was measured by laser Doppler vibrometry. Results For 0.316 Vrms drive voltage, stimulation of the intracochlear fluid using a FMT-driven CI electrode (Vibro-EAS) yielded stapes amplitude responses comparable to those for acoustic stimulation with 84 dB SPL. These amplitude responses are 30 to 42 dB lower at frequencies up to 4 kHz than those for VSB standard coupling. Conclusion Intracochlear combined electrical and mechanical stimulation may be a viable technique for electroacoustic stimulation. A reliable technique for attachment or integration of the FMT to the cochlea electrode array has yet to be developed.

Double heterodyne interferometry for high-precision distance measurements

Abstract: We present a double-heterodyne interferometer for absolute distance measurements at rough surfaces up to 100 meters. The two wavelengths are generated by frequency shifting the light of a monomode laser diode using a 500 MHz acousto-optic modulator. The synthetic wavelength obtained is (Lambda) equals 60 cm. In order to yield unambiguity up to 100 meter distance two measurements have to be taken using slightly different frequency shifts of 500 resp. 501.5 MHz. Measurements showing a resolution of 0.1 mm are presented.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Overview of three-dimensional shape measurement using optical methods

Abstract: We first provide an overview of 3-D shape measurement us- ing various optical methods. Then we focus on structured light tech- niques where various optical configurations, image acquisition tech- niques, data postprocessing and analysis methods and advantages and limitations are presented. Several industrial application examples are presented. Important areas requiring further R&D are discussed. Finally, a comprehensive bibliography on 3-D shape measurement is included, although it is not intended to be exhaustive. © 2000 Society of Photo-Optical Instrumentation Engineers. (S0091-3286(00)00101-X)

Review of 20 years of range sensor development

Abstract: We review 20 years of development in the field of 3-D laser imaging. An overview of 3-D digitizing techniques is presented with an emphasis on commercial techniques and systems currently available. It covers some of the most important methods that have been developed, both at the National Research Council of Canada (NRC) and elsewhere, with a focus on commercial systems that are considered good representations of the key technologies that have survived the test of years. © 2004 SPIE and IS&T.

Apparatus and methods for optical stimulation of the auditory nerve

Abstract: A cochlear implant placed in a cochlea of a living subject for stimulating the auditory system of the living subject, where the auditory system comprises auditory neurons. In one embodiment, the cochlear implant includes a plurality of light sources, {Li}, placeable distal to the cochlea, each light source, Li, being operable independently and adapted for generating an optical energy, Ei, wherein i=1, ..., N, and N is the number of the light sources, and delivering means placeable in the cochlea and optically coupled to the plurality of light sources, {Li}, such that in operation, the optical energies {Ei} generated by the plurality of light sources {Li} are delivered to target sites, {Gi}, of auditory neurons, respectively, wherein the target sites Gl and GN of auditory neurons are substantially proximate to the apical end and the basal end of the cochlea, respectively.

Review of 20 years of range sensor development

Abstract: We review 20 years of development in the field of 3-D laser imaging. An overview of 3-D digitizing techniques is presented with an emphasis on commercial techniques and systems currently available. It covers some of the most important methods that have been developed, both at the National Research Council of Canada (NRC) and elsewhere, with a focus on commercial systems that are considered good representations of the key technologies that have survived the test of years. © 2004 SPIE and IS&T.

Flexible piezoelectric energy harvesting from jaw movements

Abstract: Piezoelectric fiber composites (PFC) represent an interesting subset of smart materials that can function as sensor, actuator and energy converter. Despite their excellent potential for energy harvesting, very few PFC mechanisms have been developed to capture the human body power and convert it into an electric current to power wearable electronic devices. This paper provides a proof of concept for a head-mounted device with a PFC chin strap capable of harvesting energy from jaw movements. An electromechanical model based on the bond graph method is developed to predict the power output of the energy harvesting system. The optimum resistance value of the load and the best stretch ratio in the strap are also determined. A prototype was developed and tested and its performances were compared to the analytical model predictions. The proposed piezoelectric strap mechanism can be added to all types of head-mounted devices to power small-scale electronic devices such as hearing aids, electronic hearing protectors and communication earpieces.