Position Sensitive Diode Research Articles

Parametric study of sensor placement for vision-based relative navigation system of multiple spacecraft

In order to overcome the limited range of GPS-based techniques, vision-based relative navigation methods have recently emerged as alternative approaches for a high Earth orbit (HEO) or deep space missions. Therefore, various vision-based relative navigation systems use for proximity operations between two spacecraft. For the implementation of these systems, a sensor placement problem can occur on the exterior of spacecraft due to its limited space. To deal with the sensor placement, this paper proposes a novel methodology for a vision-based relative navigation based on multiple position sensitive diode (PSD) sensors and multiple infrared beacon modules. For the proposed method, an iterated parametric study is used based on the farthest point optimization (FPO) and a constrained extended Kalman filter (CEKF). Each algorithm is applied to set the location of the sensors and to estimate relative positions and attitudes according to each combination by the PSDs and beacons. After that, scores for the sensor placement are calculated with respect to parameters: the number of the PSDs, number of the beacons, and accuracy of relative estimates. Then, the best scoring candidate is determined for the sensor placement. Moreover, the results of the iterated estimation show that the accuracy improves dramatically, as the number of the PSDs increases from one to three.

Laser-Based Sensing, Measurement, and Misalignment Control of Coupled Linear and Angular Motion for Ultrahigh Precision Movement

This paper presents a novel methodology for position and orientation (pose) measurement of stages used for micro/nano positioning which produce coupled motions with three planar degrees of freedom (DOF). In the proposed methodology, counter-rotation of the entire mechanism prevents the misalignment of the measurement beams within a laser-interferometry-based sensing and measurement technique. To detect such a misalignment, a sensing strategy constructed around a position sensitive diode has been developed. A feedforward-feedback compound controller has been established to provide the necessary counter-rotation input to reduce the misalignment error. Experimental validation has been conducted through the measurement of the workspace of a three-DOF planar micro/nano positioning stage. Experimental results demonstrate the capability of the technique to provide combined linear/angular measurement.

Analysis and experimental investigation of the temperature property of sensors based on symmetrical metal-cladding optical waveguide

Symmetrical metal-cladding waveguide (SMCW) is a kind of new waveguide construction, and it consists of a planar glass slab sandwiched in two metal films with different thicknesses. The metal in this structure is usually a noble metal, such as Au, Ag and Cu etc. One of the characteristics of the glass is the sub-millimeter thickness, which is useful for exciting the ultrahigh order mode. Since the SMCW structure was proposed, it has received much attention from the researchers for its excellent characteristics of free-space coupling technique and ultrahigh order mode excitation. This free-space coupling technology has a higher sensitivity compared with the end-face coupling, prism coupling and grating coupling techniques. The ultrahigh order mode is very sensitive to the incident light wavelength, the thickness of guiding layer and the refractive index, but not sensitive to polarization. Based on the thermal-optical effect and thermal expansion effect of metal film and guiding layer materials, we research the temperature property of the SMCW structure. Researching methods include simulation analysis and experimental demonstration. First, we calculate the relation of the thickness and dielectric property of metal films, and the thickness and refractive index of the guiding layer with the temperature. Results show that these four factors are nearly proportional to the temperature difference. Then, we simulate the relationship of the reflectivity of the SMCW structure with those four factors by means of single-factor investigation under spectral and angular interrogation mode of operation, and find that the temperature-dependence of thickness of the guiding layer makes the chief contribution to the waveguide function of SMCW. Meanwhile, we analyze the sensitivity of the sensors based on SMCW structure, and the result shows that the sensitivity of this kind of sensor can be up to 21.89 pm/K (spectral mode) and 1.449×10-3 rad/K (angular mode). Finally, we demonstrate the simulation results by experiment. In our experiment, a series of reflectivity is measured at temperatures varying from 320 to 380 K, and the value is expressed in the form of voltage output of PSD (position sensitive diode). The sensor shows a good linearity and a high average resolution of 0.517×10-3 rad/K; furthermore, we fit the experimental data and get the linear function between angle shifts and temperature difference of Δθ = 0.02965×ΔT. So, once the temperature has any minute variation, it will easily give a change in the resonance incident angle and show the effect of sensor. Owing to the advantages of high sensitivity, low cast and easy fabrication, the temperature sensor based on SMCW will be a promising sensor in many fields.

Relative position and attitude estimation for satellite formation with coupled translational and rotational dynamics

This paper develops a relative position and attitude estimation approach for satellite formation. A coupled relative translational dynamics is derived to represent orbital motion of arbitrary feature points on deputy, and the relative attitude motion is formulated by a rotational dynamics for no-gyro satellite. A position sensitive diode (PSD) sensor is used to provide multiple line-of-sight (LOS) vectors from a feature point to beacons fixed on the chief. The LOS measurements are coupled with dynamical models in an extended Kalman filter (EKF) to estimate relative attitude of the deputy and relative position of the feature point. Four different scenarios are simulated to validate that the estimation accuracy is affected by the beacons configuration and measurement distance. Through comparisons, the proposed approach is approved to provide high accurate relative attitude and position estimation for the no-gyro satellite.

Small field measurements with a novel silicon position sensitive diode array

DOSI, a novel dosimeter based on position sensitive detectors for particle physics experiments, was used for relative clinical dosimetry measurements in small radiotherapy fields. The device is capable of dynamic measurements in real time and provides sub-millimetre spatial resolution. The basic beam data for a stereotactic radiotherapy collimator system (BrainLAB) using 6 MV photons were measured and compared with the corresponding data acquired with a small diamond detector and a PinPoint ionization chamber. All measurements showed an excellent agreement between DOSI and the diamond detector. There was an increasing discrepancy between the relative output factors (ROF) measured with DOSI and those measured with the ionization chamber with decreasing field size, specifically for collimators with a diameter smaller than 15 mm. The percentage depth doses (PDD) were in agreement to better than 1% for all depths. The agreement on off-axis ratios (OAR) was better than 3% for all collimators, whereas the agreement on relative output factors (ROF) was at the 1% level. DOSI's fast read-out electronics made it possible for all measurements to be recorded within 45 min including time to change collimators. This should reduce the overall time for commissioning and QA measurements, an important factor especially for busy radiotherapy departments.

High speed photon-counting imager using a position sensitive diode

A new use for a 2-dimensional position sensitive diode (PSD) is described. A duolateral PSD was used with a microchannel plate image intensifier as a proof-of-concept photon counting (event driven) imager for astronomical imaging and photometry. This produced an imager capable of counting 25–30 kcps over the astronomical bands B, V & R, with an overall efficiency of ∼19%.

A silicon continuous position sensitive diode and associated electronics: modelling and simulation

In contrast to the segmented detectors (micro-strips and pixels) widely used in high energy physics experiments, continuous detectors such as position sensitive diodes (whose localisation principle is based on charge division) remain of interest when count rate and multiplicity are not critical. That is the case with several imaging applications in nuclear medicine and biology. In that context, our group has developed a γ camera dedicated to the detection of body tumour tissue during operative cancer surgery. This per-operative compact imager consists of an image intensifier tube viewed by a PSD of 25×25 mm 2. In order to improve detection performances of this camera we have developed a simulation model of the PSD (schematic form) and associated electronics (behaviour form) using CAO AWB/Cadence. This allows an accurate estimate of both spatial resolution and linearity. These simulations provide an exhaustive study of the performance of various types of PSD and readout electronics configurations. In our application which requires high resolution imaging, we have demonstrated that a classical detector filtered by a trapezoidal shape offers the best compromise between linearity and spatial resolution.

Performance characterization and first clinical evaluation of a intra-operative compact gamma imager

The growing interest of cancer surgeons in intra-operative probes has led to the development of several prototypes of high resolution mini gamma cameras. The aim of this paper is to present a global characterization of the one that we developed and the corresponding first evaluation in a clinical context. The current prototype of POCI (per-operative compact imager) is a 24 mm diameter intensified position sensitive diode optically coupled to a scintillation crystal plate and a novel parallel hole tungsten collimator. In order to face the various clinical situations, two sets of collimator/scintillator imaging heads have been developed either for high spatial resolution or high efficiency purposes. Both of them have first been optimized for /sup 99m/Tc labeled tumor detection. Performances of POCI for these two head modules are presented using phantom studies. The results show spatial resolution values ranging between 1 and 1.9 mm (without significant distortion) and a corresponding detection efficiency ranging from 6/spl middot/10/sup -3/ up to 0.2 events/kBq/sec. Finally, first clinical evaluation of this new high-resolution compact camera concerned sentinel lymph node imaging which is included in melanoma and breast cancer staging protocols. Preliminary results already demonstrate that the performance characteristics of POCI are compatible with intra-operative imaging purposes and suggest how such mini-cameras can improve the success rate of tumor removal surgeries.

POCI: a compact high resolution /spl gamma/ camera for intra-operative surgical use

The development of a hand-held /spl gamma/ imaging probe for inside body localization of small tumors is of first interest for radio-guided operative cancer surgery. In that context, we have developed a sub-millimeter spatial resolution, small field of view, /spl gamma/ per-operative compact imager (POCI). It consists of a head module composed of a high resolution tungsten collimator and a YAP:Ce crystal plate, optically coupled to an intensified position sensitive diode (HSD). We report here the essential imaging performance characteristics of the POCI camera (spatial resolution, position linearity, efficiency and energy response). These were obtained by studying the influence of the collimator and the crystal design to evaluate the optimal configuration. The present version of POCI has a 24 mm diameter usable field of view and an intrinsic spatial resolution of 0.9 mm to 1.2 mm FWHM at 120 keV. These good detection performance characteristics combined with the small size of the camera make the device well suited to provide intra-operative monitoring in several medical procedures, such as thyroid and breast tumor removal.

RITM: a mini /spl gamma/ camera for pre and per-operative radio guided cancer surgery evaluation for bone tumor localization in theater blocks

The authors have developed a multi-functional portable /spl gamma/-radio-imager (RITM) based on a position sensitive photo-multiplier tube (PSPMT) in order to evaluate the potential of such a mini /spl gamma/-camera concept in radio-pharmacology and nuclear medicine. The authors report here an evaluation of their RITM device for bone surgery. It concerns localization of the Osteoid Osteoma (benign bone tumor) performed in the theater block before skin incision and during the surgical lesion extraction. In the over 13 cases the authors studied, the diagnosis furnished by RITM was always confirmed by post-operation anatomopathological analysis. This shows how RITM can be used as an additional indicator to monitor the operation. Following RITM experience, the authors are developing a new small field of view /spl gamma/-per-operative compact imager (POCI) with submillimeter spatial resolution performance. It consists of a high resolution collimator and a YAP:Ce crystal assembly coupled to an intensified position sensitive diode (IPSD). This hand-held imaging probe is first dedicated to intra-operative monitoring for thyroid tumor and neuroblastoma removal. Characteristics of the POCI device and preliminary results are briefly presented.

An optical device to measure the dynamics of apex rotation of the left ventricle.

Systolic counterclockwise rotation of the left ventricular apex with respect to the base has been defined as left ventricular (LV) twist or torsion. If rotation of the base during systole is small, we hypothesized that the dynamics of twist can be well characterized through the measurement of apical rotation alone. A device was designed to measure apical rotation in a simpler, more direct fashion, providing continuous high-fidelity dynamic measurements. The device consists of a light source, a position-sensitive diode, and a small rotating mirror that is coupled to the apex of the heart by a wire. As the wire rotates, apical rotation (measured in degrees) can be calculated from the position of the deflected light beam. The timing of apical rotation was compared with simultaneous recordings of electrocardiogram, LV pressure, and LV diameter measurements. An initial clockwise rotation (untwist) of 4 +/- 2 degrees (SD) occurred during isovolumic contraction followed by counterclockwise rotation (twisting) through ejection, reaching maximum apical rotation of -15 degrees just before the end of systole. Rapid untwisting during isovolumic relaxation was shown with near-complete dissipation of twist by the first one-third of the diastolic filling period. Caval occlusion caused a downward and leftward shift of the pressure-apical rotation loops, and more twist/untwist was seen to occur during the respective isovolumic contraction and relaxation periods. We conclude that this device provides precise timing and definition of rapid changes during isovolumic contraction and relaxation, confirms results obtained by more laborious methods, and provides an easy method to measure the dynamics of apical rotation continuously during interventions such as load changes.