Passive Lens Research Articles

Proposals for the type tests criteria and calibration conditions of passive eye lens dosemeters to be used in interventional cardiology and radiology workplaces

Abstract The paper is aimed at making a proposal for the type test and calibration of eye lens passive dosemeters especially used in the interventional cardiology/radiology (IC/IR). Starting from the only existing standard dealing with eye lens dosimetry using TLDs ( ISO 12794 ), parameters such as, detection threshold, energy and angle dependence of response criteria have been reviewed and it has been tried to harmonise them as much as possible with the IEC 62387 requirements, taking into account the particular use at IC/IR workplaces. Conversion coefficients from air kerma to dose equivalent at 3 mm depth for RQR and ISO radiation qualities, employed for type test and calibration purposes, have been calculated in a new phantom introduced within the ORAMED (Optimization of RAdiation protection for MEDical staff) project. This phantom is more representative of the head so that the estimation of H lens by H p (3) is more accurate.

Lenses for Circular Polarization Using Planar Arrays of Rotated Passive Elements

A planar array of passive lens elements can be phased to approximate the effect of a curved dielectric lens. The rotational orientation of each element can provide the required phase shift for circular polarization. The array elements must be designed so that the hand of circular polarization changes as the electromagnetic wave passes through the lens. An element is presented that is based on an aperture-coupled microstrip patch antenna, and two lenses are designed. Each lens has a diameter of 254 mm and contains 349 elements. The elements have identical dimensions but the rotational orientation of each element is selected to provide a specific lens function. The first lens is designed to collimate radiation from a feed horn into a beam pointing 20° from broadside. At 12.9 GHz the aperture efficiency is 48%. The second lens acts as a Wollaston-type prism. It splits an incident wave according to its circular polarization components.

A novel method for the collimation of ions at atmospheric pressure

Measured gains in source-to-target ion transmission of well over two orders of magnitude are reported from the application of a robust and versatile electrostatic lens that requires no voltage supply and consumes negligible power. When exposed to an ion flux across a potential gradient, a series of electrically-floating circular conductors automatically attain a profile of convergent potentials. This passive ion lens is used to collimate atmospheric ion source currents that range from 30 pA to 7 nA, increasing the ion signal strength at the target by factors of 20–130 times that of the unaided signal.

LP‐1: Late‐News Poster: High Efficiency Reconfigurable 2D/3D Autostereoscopic Display

AbstractA novel architecture to enable flat panel displays to be electrically reconfigured between a full resolution 2D mode and a half resolution, low cross talk, autostereoscopic 3D mode is described. A Polarisation Activated Microlens comprising a high precision passive birefringent lens array and a commodity switchable polariser element is added to existing LCD panels with a low cost premium. The architecture enables high optical efficiency in 2D and 3D modes and is suitable for transmissive, reflective and transflective LCD devices. The implementation of the component on a transmissive TFT‐LCD is described and measured performance presented.

Observation of Return Current Effects in a Passive Plasma Lens

Observations of relativistic beam focusing by a passive plasma lens have demonstrated a reduction in focusing strength due to plasma return current. A 50 MeV beam was propagated through a 1--3 cm long plasma with density around ${10}^{14}{\mathrm{cm}}^{\ensuremath{-}3}$. Beam size was measured as a function of propagation distance. For a ratio of collisionless plasma skin depth to beam spot size ${k}_{p}{\ensuremath{\sigma}}_{r}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.33$, no significant reduction in focusing was observed. Reduced focusing was measured for ${k}_{p}{\ensuremath{\sigma}}_{r}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1.1$, where a significant fraction of the inductively driven return current in the plasma flows within the beam. The observations are in good agreement with an envelope equation model and with particle-in-cell simulations.

A space-fed phased array for surveillance from space

A space-fed radar antenna called a venetian blind is proposed for all-weather wide-area surveillance from space. Radar requirements for tasked and untasked operation are discussed, and the process of selecting the venetian blind concept, which can support both, is described. In its untasked form (essentially a space-fed passive lens), it achieves off-axis squint angles of many beamwidths with negligible performance degradation. It is inherently insensitive to mechanical distortion and is a first step in the evolution to the more complex tasked system antenna. The antenna lens consists of easily manufactured slats with microstrip dipole radiating elements and matching networks on a dielectric substrate. Phase control is achieved with low-loss delay lines in the passive lens or active transmit/receive modules if electronic scan is desired.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Optical technique for broadbanding phased arrays

An optical method for broadbanding a phased array is considered. A narrow band feed-through aperture lens comprised of pick-up elements, radiating elements, and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">360\deg</tex> type phase shifters is fed by a small feed array with an intervening passive lens. The lens has fixed frequency-sensitive properties. The feed array has variable time delay compensators which are selected in accordance with the desired scan angle in the far field. Using geometrical optics, design formulas are derived that relate bandwidth and scan angle to the minimum number of variable time delayers. To demonstrate performance, diffraction theory is used to calculate patterns, sidelobe levels, and efficiencies as a function of bandwidth and scan angle out to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">50\deg</tex> scan for several aperture sizes. In the worst cases, the optical system provides somewhat less gain than the comparable constrained subarray antenna; however, it always provides much better sidelobe levels.

Conjugate-Concentric Laser Resonator

A laser resonator is described in which both reflective and refractive surfaces are used as parts of the “resonating circuit.” The basic geometry of the resonator, termed conjugate-concentric resonator, is that of a simple imaging system in which the passive lens is replaced by an active one while the external concentric mirrors occupy an object and an image surface. The eigenvalue problem for this resonator is formulated in both Cartesian and polar coordinates and the corresponding eigenvalues and eigenfunctions are computed numerically. It is then shown that the basic property of this resonator is its high angular degeneracy. This property makes it well suited for the application of internal spatial filtering techniques. The practically interesting case of a cosine-shaped spatial filter is considered in some detail.