Non-mechanical Steering Research Articles

A Wireless Drive and Control Method for Robots: Multifrequency Microwaves

Microwave (MW)‐driven strategies could potentially offer transmissivity through obstacles, selective energization, wave‐focusing, and nonmechanical steering via phased‐array technologies, which have unique application prospects in confined environments. Implementing multidegree of freedom (MDOF) control is the key to developing motion strategies for advanced MW‐driven robots. However, the use of MWs for MDOF control of robots has so far remained a challenge. This article first presents examples of wireless driving and controlling millimeter‐scale peristaltic pipeline robots (diameter, 4 mm; length, 30 mm; weight, 0.39 g) utilizing multifrequency MWs in complex nonmetal channel environments. Herein, shape memory alloy springs combined with passive wires, whose length depends on the frequencies of MWs, are adopted to form selectively controlled robot components, and silicon rubber replica technology is utilized to achieve miniaturization of the robot. The monopole antenna model is developed for the actuator, and its structure is refined using antenna theory. This allows the successfully achievement of MDOF control of the robot at several MW frequencies (2.4, 4, and 5.9 GHz). Powered by MWs from outside the pipe, the pipeline robot achieves horizontal, vertical, and curved motions in a pipe with a diameter of 5 mm.

Non-mechanical steering of the optical beam in spectral-domain optical coherence tomography

We demonstrate in a proof-of-concept experiment spectral-domain optical coherence tomography where steering of the optical beam that probes the sample in a transverse scan does not make use of any mechanical element. Steering is done with the help of a phase-only spatial light modulator, that introduces a spatially-dependent phase between the two orthogonal polarization components of an optical beam, and some optical elements that control the polarization of light. We demonstrate that making use of the non-mechanical beam steering system considered here, we can reproduce the main traits of imaging with standard OCT that makes use of mechanical-assisted optical beam steering.

A wireless radiofrequency-powered insect-scale flapping-wing aerial vehicle

Insect-scale aerial vehicles are useful tools for communication, environmental sensing and surveying confined spaces. However, the lack of lightweight high-power-density batteries has limited the untethered flight durations of these micro aerial vehicles. Wireless power transmission using radiofrequency electromagnetic waves could potentially offer transmissivity through obstacles, wave-targeting/focusing capabilities and non-mechanical steering of the vehicles via phased-array antennas. But the use of radiofrequency power transmission has so far been limited to larger vehicles. Here we show that a wireless radiofrequency power supply can be used to drive an insect-scale flapping-wing aerial vehicle. We use a sub-gram radiofrequency power receiver with a power-to-weight density of 4,900 W kg–1, which is five times higher than that of off-the-shelf lithium polymer batteries of similar mass. With this system, we demonstrate the untethered take off of the flapping-wing micro aerial vehicle. Our RF-powered aircraft has a mass of 1.8 g and is more than 25 times lighter than previous radiofrequency-powered micro aerial vehicles.

Non-Mechanical Beam Steering with Polarization Gratings: A Review

Polarization gratings (PGs) enable a novel architecture for dynamic non-mechanical steering of light over large angles and with large clear apertures. This beam steering approach has many applications in active sensing and optical communications. In this review, we describe some of the defining characteristics of this beam steering architecture and highlight several applications of the technology.

Progress and opportunities in the development of nonmechanical beam steering for electro-optical systems

We discuss over three decades of progress in nonmechanical beam steering, provide a comparison of approaches being developed, and comment on promising approaches not yet fully developed. Most of the work in nonmechanical beam steering has been for narrowband optical systems, but a brief discussion is provided of broadband. The majority of the nonmechanical approaches to beam steering create a tilted optical path delay (OPD) to change the wavefront, but some directly create a phase delay. OPD-based approaches may be true time delay, with no resets or modulo 2π n optical phased arrays that have resets. Most of the nonmechanical optical beam steering approaches tilt an existing wavefront and are called space fed approaches, because the beam is already formed when the wavefront is tilted. For the majority of radar nonmechanical beam steering, the tilted wavefront is formed by individual transmit/receive modules. Periodic structures (gratings) spread different wavelengths of light in angle, thus steering light, and are also used for nonmechanical steering. Our paper is derived from a conference paper presented at Photonics West in February 2019.

Theoretical analysis on power stability and switch time of the non-mechanical beam steering using liquid crystal optical phased array

ABSTRACTFocusing on the coherent optics of phased array, a dynamic theoretical model is built to analyse the process of laser beam steering using the device of liquid crystal optical phased array. Based on the dynamics of electrical field induced liquid crystal molecule rotation and the mechanism of phased control non-mechanical steering, switching time is redefined according to two curves representing receiving power on the current direction and targeting direction. Meanwhile, including the far field distribution, power stability and pointing direction, two cases with large steering step and tiny steering step are evaluated. The steering time between two angles is minished to be less than the switch-off decay time. In addition, the instability on the process of beam steering is obvious although the steering step is only half of beam width. To overcome this instability, tinier steering step is suggested although it is also limited by the driving algorithm and driving circuits.

Reflective Inverse Diffusion

Phase front modulation was previously used to refocus light after transmission through scattering media. This process has been adapted here to work in reflection. A liquid crystal spatial light modulator is used to conjugate the phase scattering properties of diffuse reflectors to produce a converging phase front just after reflection. The resultant focused spot had intensity enhancement values between 13 and 122 depending on the type of reflector. The intensity enhancement of more specular materials was greater in the specular region, while diffuse reflector materials achieved a greater enhancement in non-specular regions, facilitating non-mechanical steering of the focused spot. Scalar wave optics modeling corroborates the experimental results.

A Review of Phased Array Steering for Narrow-Band Electrooptical Systems

Nonmechanical steering of optical beams will enable revolutionary systems with random access pointing, similar to microwave radar phased arrays. An early approach was birefringent liquid crystals writing a sawtooth phase profile in one polarization, using 2pi resets. Liquid crystals were used because of high birefringence. Fringing fields associated with voltage control required to implement the 2pi resets have limited the efficiency and steering angle of this beam steering approach. Because of steering angle limitations, this conventional liquid crystal steering approach is usually combined with a large angle step-steering approach. Volume holograms, birefringent prisms or sawtooth-profile birefringent phase gratings, and circular-type polarization gratings are the large angle step steering approaches that will be reviewed in this paper. Alternate steering approaches to the combined liquid crystal and step-steering approach exist. Microelectromechanical system mirrors, lenslet arrays, electrowetting, and a variable birefringent grating approach will be reviewed and compared against the conventional liquid crystal and step-steering approaches. Step-steering approaches can also be combined with these approaches. Multiple nonmechanical steering approaches are developing that will allow high-efficiency steering, excellent steering accuracy, and wide fields of view.