1,720,989 research outputs found
A Review on Guided Optical Feedback in Super-Luminescence Diodes for Metrological Purposes
No full textLow-coherence interferometry (LCI) is a widely used measurement technique. Typical applications of LCI range from optical low-coherence reflectometry (OLCR) to optical coherence tomography (OCT). The main advantages offered by LCI over coherent-interferometry (CI) are its usual greater capacity to spatially locating the region of the sample from where the interferometric signal came from (the volume under test VUT), and the greater robustness to stray-light. When the LCI technique is combined with the self-mixing (SM or optical-feedback, OF) technique, it is possible to obtain additional benefits in terms of compactness, and signal to noise ratio (SNR) of the interferometric signal. Optical layouts based on guided lightwaves generally allow to further improve the robustness and performances of the system. In this review, we focus on metrological applications of guided LCI-SM and, in particular, on the use of LCI-SM to measure positions and absolute distances, flow rates, fluid velocity profiles, and thicknesses
Optical feedback into a superluminescent diode cavity for absolute distance measurements
No full textThe development of accurate absolute distance interferometers is a long-term research goal. The key impact of this paper is the development of an absolute distance interferometer based on the optical feedback into a superluminescent diode cavity. The proposed approach employs a two arms interferometer feeds by a superluminescent diode. Thanks to the optical feedback, we obtained huge interference fringes even with diffusive targets. The proposed signal processing exploits a zero-crossing approach to determine the absolute target position. Preliminary results show a ratio between measurement uncertainty and range of about 50 ppm
A transimpedance preamplifier using a feedforward approach for robust rejection of DC photogenerated currents
Full text linkThe preamplifier proposed in this paper is designed to extract weak variable photogenerated signals from a high-level continuous background ensuring low noise and high transimpedance gain. An efficient cancellation of the DC component directly at the photodetector output, exploiting a feedforward approach, allows us to properly amplify the variable signal components of interest avoiding saturation of the preamplifier. Furthermore, the large transimpedance gain allows for minimizing the effects of the noise introduced by the following stages on the signal processing chain. In the paper, we present the proposed approach and a possible circuit realization with a signal AC/DC ratio as small as 1/1000 ensuring low noise, high gain, and a considerable bandwidth. The realized preamplifier offers a Noise Equivalent Power NEP ≃ 1.12 nW, an in-band transimpedance gain of 4.4 MΩ, and a wide bandwidth from about 1 Hz up to 100 kHz, making it suitable for use in several applications both in biomedical and industrial fields
Towards the development of a new model for the oculomotor system
Full text linkPupillary light reflex involves many sensory and motor functions of the eye. For this reason, it represents an important emergency diagnostic tool and provides information to assess brain stem function. The pupil system can be considered in terms of input-output black-box behavior: light stimuli can be easily applied to the eyes, and the pupil size can be measured effortlessly and non-invasively. In this paper, a model for short-light-flash-induced transient pupillary light reflex is presented and preliminary experiments designed to test the model features are described. Results confirm that the developed pupillary light reflex model is suitable to describe the pupil oculomotor system exposed to short-light-flashes
A simple multiparametric analysis to guide, compare and optimize the design of 'lensless' LED illuminators
No full textLED lighting is becoming increasingly pervasive in many areas ranging from ambient lighting, up to applications such as microscope illumination, UV-LED curing and, UV disinfection for air, surfaces, and water. Irradiance uniformity is often a fundamental parameter for guiding the design, comparison, and optimization of the illuminator. To this end, many methods and procedures have been proposed to guide the arrangement of the LED sources, as well as to guide the design of ad-hoc lenses. Nevertheless, there are many applications in which it is important to be able to consider other aspects as well as the uniformity of the irradiance. For this purpose, we propose both a method that allows calculating the irradiance generated by the used LED sources and, performance indicators for guiding the design and comparing different optical layouts
Towards a Temperature Compensated Model for a Blood-pH Sensor in Extracorporeal Circulation
No full textUnder physiological conditions, the body maintains blood pH within the very narrow range [7.36, 7.44] pH. Small deviations from this range can reveal the onset of pathological states. In this work the performances of a real-time, non-invasive pH measuring sysem for extracorporeal circulation (ECC) are analyzed. In particular, this study focuses on the analysis of the effects that temperature of the measurand may have on the error in estimating blood pH. Indeed, the sensor is based on the analysis of the fluorescence produced by HPTS, which is known to vary with temperature. The extent of such a variation, however, depends on various factors, including the chemical environment. Blood temperature in ECC is often thermostated at 37 °C. Nevertheless, there are treatments in which the blood temperature is varied by a few Celsius degrees, generally reduced, from the physiological temperature of 37 °C. Therefore, the first objective of this study was to evaluate whether a modest reduction in temperature, that is a few Celsius degrees, introduce an error such as the measuring system no longer conforms to the maximum permissible measurement error of ±0.04 pH. Once verified that the temperature-induced error could exceed the limit of ±0.04 pH, a correction factor for temperature compensation was investigated and its robustness to unevenness in the sensor production was explored. The results obtained from this preliminary study performed using Phosphate Buffer Saline (PBS) showed how the addition to the measuring system of a temperature sensor can effectively allow to maintain the measurement error within the ±0.04 pH range, even when the temperature of the measurand decreases by a few degrees from the physiological temperature of 37 °C
A Measuring Instrument for In-Line and Real-Time Measurement of Blood- pCO2in Extracorporeal-Circulation
No full textSince the late 1950s, blood CO2 can be measured by using electrodes and, more recently, also by using point-of-care instruments such as blood gas and chemistry analyzers. Nevertheless, nowadays no measurement method has succeeded in providing an economic, reliable, and accurate estimate of the blood- CO2 to be routinely used for the monitoring of extracorporeal (blood) circulation (ECC) treatments. Indeed, blood is a very complex biological matrix composed of several different constituents, thus apart from a limited maximum-admitted measurement error (about some mmHg) and a quite wide measuring interval (about [20, 100] mmHg), the measuring systems have to provide significant selectivity taking hemocompatibility and safety for the patient as a primary concern. In this article, we propose and demonstrate a measuring instrument consisting of a low-cost and disposable fluorescent pco-sensor that can be inserted in series with the bloodline, and a nondisposable optical head that contactless reads the sensor. The proposed measuring system is intrinsically safe for the patient, has adequate metrological performance, avoids blood sampling and the related issues, and may allow to comply with cost requirements. Preliminary tests, conducted simulating a 6-h ECC treatment by using bovine blood, revealed deviations from the reference measuring instrument of less than ±4 mmHg, while the blood- CO2 was varied in the range [20, 100] mmHg
Comparison of the VLP-16 LiDAR system with an absolute interferometer
No full textMany new technologies for ADAS are emerging in recent years. In this scenario, LiDARs are becoming one of the pillars for environmental sensing needed in ADAS.Driven by the automotive industry, nowadays many new manufacturers are continuously putting new LiDAR systems on the market, thus increasing LiDARs availability and concomitantly reducing prices. As a result, LiDARs are today finding many new applications in fields such as agriculture and industrial automation.In this paper, we describe and discuss a measurement procedure for the analysis of the performances of LiDARs and, we report the results obtained from the characterization of one the most widespread LiDAR systems -namely VLP 16 by Velodyne. In particular, we compare the estimates provided by the LiDAR with the estimates provided by an absolute interferometer. To the best of our knowledge, these are the first published data obtained comparing a LiDAR and an absolute interferometer.The proposed tests investigated both warm-up and stability and, errors in the measured coordinates.The obtained results indicate a warm-up times of about 42 min and errors of few millimeters over a measuring interval of about (2, 21) m
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