This article presents the design of a dielectric lens antenna that utilizes the concept of a stepped Fresnel lens for focusing electromagnetic millimeter waves. Based on the quasi-optical properties of these waves, a Cartesian Oval is optimized and employed as a focusing lens. Multiple such lenses are combined to two different Fresnel-based lens antennas. We survey these newly designed lens antennas and compare them with a focusing lens antenna based on a Cartesian oval and a far-field lens antenna. Simulations and measurements with a frequency-modulated continuous-wave (FMCW) radar validate the effectiveness of the new design, demonstrating an even improved focus size while significantly reducing the size and weight of the lens antenna by up to 53% and by nearly 48 %, respectively. Additionally, the Fresnel-based lens antennas reveal a frequency dependency, enabling frequency-based steering of the focal length over a wide relative tuning range of 177%, which we thoroughly investigate for various bandwidths and center frequencies.

Current methods for fabricating lenses rely on mechanical processing of the lens or mould, such as grinding, machining and polishing. The complexity of these fabrication processes and the required specialized equipment prohibit rapid prototyping of optical components. This work presents a simple method, based on free-energy minimization of liquid volumes, which allows us to quickly shape curable liquids into a wide range of spherical and aspherical optical components, without the need for any mechanical processing. After the desired shape is obtained, the liquid can be cured to produce a solid object with nanometric surface quality. We provide a theoretical model that accurately predicts the shape of the optical components, and demonstrate rapid fabrication of all types of spherical lenses (convex, concave, meniscus), cylindrical lenses, bifocal lenses, toroidal lenses, doublet lenses and aspheric lenses. The method is inexpensive and can be implemented using a variety of curable liquids with different optical and mechanical properties. In addition, the method is scale invariant and can be used to produce even very large optical components, without a significant increase in fabrication time. We believe that the ability to easily and rapidly create optical components, without the need for complex and expensive infrastructure, will provide researchers with new affordable tools for fabricating and testing optical designs.

Accurate identification is the first step in weed control. Weed photography is important because a good picture, plus a descriptive botanical key, more accurately identifies plants. Also, quality pictures provide an important learning tool for students, agribusiness personnel, and producers. This paper includes recommendations for selecting photographic equipment and film as well as practical techniques for controlling backgrounds, light, plant movement, and depth of field in photographing plants.

Patients with bilateral corneal blindness in whom corneal transplantation has either been unsuccessful or inappropriate may be considered for osteo–odontokeratoprosthesis surgery. During a two–stage procedure the surface of the cornea is removed and covered with a graft of buccal mucosa. An optical cylinder, supported by an osteo–odonto lamina planed from a tooth is then inserted into the mucosa to act as a lens. The anaesthetic implications of this operation include care of patients from a wide age range, often with underlying medical problems undergoing two operations of prolonged duration. The eye can be ‘open’ during both stages of the operation and anaesthetic techniques directed towards prevention of rises in vitreal pressure are essential. This article outlines the surgical process of osteo-odonto-keratoprosthesis surgery with reference to our anaesthetic experiences from nine cases.