Reflective Lens Research Articles

Ultrasonic gas analyzer and method to analyze trace gases

An ultrasonic gas analyzer includes an acoustic cavity through which an air sample is drawn by a low speed air pump or other mechanism. The cavity has a pair of ultrasonic wave transmitters/receivers on opposite sides of the acoustic cavity. An electronic circuit controls the transmitters/receivers so that a high frequency ultrasonic wave is propagated across the cavity and thereby through the gas flowing through the cavity. This ultrasonic wave reflects back and forward across the acoustic cavity and the transmitters/receivers receive this wave and supply a signal indicative of the wave to an electronic circuit. Based on the time of flight data for the ultrasonic wave being reflected in a gas/air mixture and in air and the amplitude of those reflected ultrasonic waves, a determination is made as to the gases within the gas/air mixture. This determination then can be displayed and an audio signal can be generated depending on the amount of detected gases. In one embodiment of the gas analyzer, a switch valve is used to selectively provide the gas/air mixture or air through the acoustic cavity. In another embodiment of the gas analyzer, two acoustic cavities are provided with a double concave reflector lens separating the cavities and each with a transducer at an opposite end from the lens. Air is drawn through one of the acoustic cavities and the gas/air mixture is drawn through the other of the acoustic cavities

Million frames per second infrared imaging system

An infrared imaging system has been developed for measuring the temperature increase during the dynamic deformation of materials. The system consists of an 8×8 HgCdTe focal plane array, each with its own preamplifier. Outputs from the 64 detector/preamplifiers are digitized using a row-parallel scheme. In this approach, all 64 signals are simultaneously acquired and held using a bank of track and hold amplifiers. An array of eight 8:1 multiplexers then routes the signals to eight 10 MHz digitizers, acquiring data from each row of detectors in parallel. The maximum rate is one million frames per second. A fully reflective lens system was developed, consisting of two Schwarszchild objectives operating at infinite conjugation ratio. The ratio of the focal lengths of the objectives determines the lens magnification. The system has been used to image the distribution of temperature rise near the tip of a notch in a high strength steel sample (C-300) subjected to impact loading by a drop weight testing machine. The results show temperature rises at the crack tip up to around 70 K. Localization of temperature, and hence, of deformation into “U” shaped zones emanating from the notch tip is clearly seen, as is the onset of crack propagation.

Seismic images of Caledonian, lithosphere-scale collision structures in the southeastern North Sea along Mona Lisa Profile 2

The unexposed suture between Baltica and Eastern Avalonia is imaged by coincident normal-incidence reflection and wide-angle reflection/refraction seismic data of the MONA LISA project. We present new results of the upper lithospheric, seismic structure from the N–S-striking profile 2 across the Caledonian Deformation Front, which represents the crustal collision suture between Baltica and Eastern Avalonia that formed after closure of the Tornquist Sea during the Caledonian orogeny in Late Ordovician times. Three different crustal types are identified with great similarities to the nearby profile 1: (1) a three-layered crust typical of shields to the north; (2) a transitional crust (suture zone) in the central part; and (3) a two-layered crust of Caledonian origin to the south characterized by very low velocities throughout the crust. The crustal thickness varies from 38–35 km under the northern margin of the Ringkøbing-Fyn High (Baltica crust) to 28–27 km beneath the North German Basin in the Caledonian crust to the south. The suture zone is imaged by S-dipping crustal reflections from 1.9 to 10.6 s two-way travel time (twt) over a horizontal distance of ∼70 km within the transitional crust. The reflection suture zone terminates in a ∼60 km wide reflective lens with velocities of 6.6–6.8 km/s in the lowermost crust. The reflective lens may be interpreted as a remnant of oceanic or island-arc crust that was accreted to the leading edge of Baltica during closure of the Tornquist Sea. Alternatively, the reflective lens may represent an indentor of Baltica crust into the Avalonian terrane. The change in lower crustal reflectivity and the abrupt transition from a three- to a two-layered crust further south suggest that the Trans-European Fault and the Elbe Lineament continue into the North Sea. The upper mantle reflectivity is dominated by bands of strong-amplitude, S-dipping reflections from 13.5 to 21.8 s twt, and a weaker band of N-dipping reflections from 12 to 16 s twt. Reversed wide-angle refractions and reflections indicate the presence of a S-dipping high-velocity layer (8.65–8.8 km/s) in the uppermost mantle. The sub-Moho high-velocity layer partially coincides with the strong S-dipping normal-incidence mantle reflections. We propose that the S-dipping mantle structure may represent a late-Caledonian or Late Carboniferous to Early Permian mantle shear zone.

Compact mechanically scanned antennas for real-time passive-millimetre-wave imaging

The paper describes a novel reflective lens for use at millimetre and microwave frequencies. This lens uses twist-polarisation techniques and consists of two wire grid polarisers and a Faraday rotator. The authors also discuss how a high-speed rotary scanning mechanism can be used to produce a linear scan pattern, again using twist-polarisation techniques. This linear scanner employs a wire grid polariser in the form of a roof prism, a rotating disc inclined with respect to its axis of rotation and a Faraday rotator or quarter-wave plate. This scanner may be used with the novel reflective lens to form the basis of a real-time imager. A more compact design uses just the lens and rotating disc and has been demonstrated in a real-time passive-millimetre-wave imager.

A reflector lens antenna consisting of an artificial dielectric

Reflector lens antennas consisting of an artificial dielectric are proposed. The design equations of the lens surface using geometrical optics under the thin/near-axis approximation are introduced. The focusing characteristics of the lenses developed by the proposed equations are estimated by the ray tracing method. From the results, the developed surface of the lens for normal incidence converges 100% of the incident ray in a circle with a diameter of a quarter wavelength, and another lens for an offset angle of 30° converges about 90% of the rays in a diameter of a half wavelength. A reflector lens antenna with an offset angle of 30° having a diameter of 12.5 wavelength yields a gain of 28.6 dBi and an aperture efficiency of 47%. A three-beam antenna with the same size having a zenith beam and beam tilted toward the north and east at 15° for use in a wind profile radar shows a gain of 27.5 dBi. © 1999 Scripta Technica, Electron Comm Jpn Pt 1, 82(7): 44–52, 1999

A reflector lens antenna consisting of an artificial dielectric

A reflector lens antenna consisting of an artificial dielectric

Flux leakage effect on subsidiary resonance of optical disk drives

An asymmetric actuator can be used to reduce the distance between the reflective mirror and objective lens of a small optical disk drive for use in the notebook-sized personal computer data storage devices. However, this asymmetric actuator is very sensitive to the subsidiary resonance. A main factor causing the subsidiary resonance is found and verified by experimental results.

Electromagnetic scattering by the Luneberg lens with reflecting cap

The near-field distribution in the case of the normal incidence to the Luneberg lens reflector is numerically obtained by using the modal expansion technique and point-matching method. As a model of the Luneberg lens, six different homogeneous media is used. A microwave experiment was also performed.

Zone characteristics of planar kinoform lenses of any specific order for stigmatic imaging between extra-axial conjugate points

An analytical approach is presented for determining the characteristics of the zones of a planar kinoform lens of any specific order for stigmatic imaging between extra-axial conjugate points. It is shown that, by use of a suitable normalization, the zone characteristics are obtained in terms of dimensionless variables. This facilitates ready estimation or comparison of pertinent zone parameters in given applications. The convenient amenability of the approach to the case of reflective kinoform lenses is also indicated.

Reflective block optics for packaging of optical computing systems

A new optical packaging technique, which we call reflective block optics, for optical computing systems is proposed and demonstrated experimentally. This technique is based on solid optics, which is advantageous with respect to stability, reliability, and alignability. Reflective lenses are used to attain high lens power, compactness, and a large space-bandwidth product. Glass blocks, cube beam splitters, and reflective optical elements are combined to form optical blocks. We can construct several optical systems by assembling the optical blocks.

Photorefractive holographic lenses and applications for dynamic focusing and dynamic image shifting

Wavelength-multiplexed reflective holographic lenses were recorded in a 1-mm-thick Fe-doped LiNbO3 crystal. A simple theoretical model based on Kogelnik’s coupled-wave theory and Kuktarev’s photorefractive-material equations was used to characterize the photorefractive lenses in terms of Bragg-limited field of view, optimum space-bandwidth-product, and wavelength selectivity. Experimental measurement verified the theoretical calculations. An f/3 lens was recorded, and nearly aperture-limited diffraction performance was observed. Applications of wavelength-multiplexed photorefractive lenses were shown by demonstration of dynamic focusing and lateral image shifting.

Fabrication of high-resolution multilayer reflection zone plate microlense for the soft x-ray range

The fabrication of linear, circular, and elliptical reflective zone plate lenses by a multistep process using microfabrication technologies is reported. The diffractive elements were generated by electron-beam lithography on a Mo/C multilayer mirror obtained by means of the triode sputtering technique. The patterns were transferred anisotropically into the multilayer mirror by reactive ion etching in a fluorinated plasma. An intermediate metallic mask made by the lift-off process was used for the transfer process. The groove depth could be monitored by following the reflectivity ofthe structure with a helium-neon laser during etching. Linear, circular (with 0.4-μm outer zones), and elliptical Fresnel zone plates (with 0.8-μ.m outer zones) were produced. Test patterns with a 50-nm top and 90-nm bottom resolution were produced. The groove profile and dimensional control were also investigated.

Radiation pattern of a test reflector antenna from near-field measurements over focal region of a coupled lens or offset reflector

A novel scheme has been investigated by which the radiation pattern of a test reflector antenna is determined by rescaling a plot of the electric field distribution in the focal plane of a large lens or in the offset focal plane of a large offset reflector placed in front of the transmitting antenna under test. The major advantage of the technique is that it permits a direct plot of the desired radiation pattern from near-field amplitude data without requiring any phase measurements. The test method is simpler and the test data more accurate than for pervious test methods. >

Thin dielectric lens reflector

The ray trace equations for a dielectric lens reflector with a tilted linear front surface are derived, and the reflecting profile obtained. A thin lens results when the angle of tilt is such that the lens reflector has zero thickness at the apex. It is found that, for fixed radius and maximum subtended angle at the focus, the reflecting profile is approximately constant with angle of tilt and can, to the same approximation, be constructed from circular arcs.

Single-longitudinal-mode stabilized graded-index-rod external coupled-cavity laser

An active-passive coupled-cavity semiconductor laser using a slightly shorter than 1/4 pitch graded-index-rod lens reflector as the external cavity has been demonstrated. The graded-index lens is prepared from an optical fiber waveguide. We report (1) stable single-longitudinal-mode operation of the graded-index-rod external coupled-cavity (GRECC) lasers with 2-Gbits/s modulation and (2) digital transmission at 1 Gbits/s over 99 km of fiber using a 1.55-μm GRECC laser.

Compact optical data processor employing holographic reflective lenses

A compact optical data processor is described that employs holographic reflective lenses. The processor is inexpensive and requires one-half of the length of the optical bench as that required for using glass lenses. The fabrication of the holographic lenses is described, and the results of optical processing reported. The results show that an inexpensive data processor employing holographic lenses is a feasible project. The processor may find use for onboard optical processing on spacecrafts and satellites. The most distinguishing characteristic of such a processor is its extreme light weight. The angular alignment tolerances for holographic lenses are very low. The processor must, therefore, be made rugged, designed, and mounted to withstand vibrations, shocks, and other environmental problems associated with spacecrafts and satellites.

風圧による船舶の横偏流について-I(日本航海学会第31回講演会)

The causes of ship's side-drifting are the force of wind on the upper structure of the ship, drift current increasing with the wind, rolling caused by wind wave and swell, and the ocean current and the tidal current. To search for the effect by wind action on the side-drifting, one of the above causes, it is necessary to make an experiment which is possible when removing the effects by the other causes. The authors planned to measure the side-drifting way with parameter V (speed of ship) when the ship's course took a right angle to the direction of the wind. The method 1. This experiment was carried out in Oshoro maru, a fishing training ship of Hokkaido University, when her speed was 3.5, 6, 9, 12kt, in the Bering Sea. 2. The Luneberg lens reflector (diameter 8 inch) which was connected to the salmon-gill net was selected as the datum point of experiment. In this case, the reflector was allowed to drift equally with the ship by current and wave, but felt no effect from the wind in spite of the movement of the ship. 3. As shown in Fig.1 the observers on the ship measured the distance and bearing of the reflector by radar at observation points 1 & 2, and calculated the side-drifting by those elements and the course and distance of the ship. The result 1. The relation between the wind velocity and side-drifting are expressed by equations (1)〜(4). 2. The relation between the proportional coefficient (K) in the equations (1)〜(4) and the ship's speed (V) is shown K=0.132e^<-0.143V>. 3. By 1, 2, they searched the relation between the side-drifting and the ship's speed and wind velocity, and got the experimental equation as follows U(kt)=0.132e^<-0.143V>W(m/sec). 4. The calculated value in the above-mentioned equation against any combination of wind velocity and ship's speed are indicated in Table 2. 5. The correction angle of the course is indicated in Table 3 when the ship's course took a right angle to the direction of the wind.