Wideband dual-polarized linear-circular and linear-cross angular stable THz reflective polarizer based on a modified square loop FSS.

A simple wideband reflective type linear-cross and linear-circular polarization converter for terahertz (THz) applications is proposed in this paper. The top frequency selective surface (FSS) consists of a thin gold coated figure of eight square loop with the connected strip line corners on a thin grounded polyamide dielectric substrate. For the y/x-polarized incidence, the design exhibits linear-circular conversion with an axial ratio (≤3dB) from 0.49-0.50, 0.60-0.83, 1.16-1.62, and 1.81-1.85 THz with 2.02%, 32.17%, 33.09%, and 2.19% fractional bandwidth (FBW), respectively. In addition, it also performs the linear-cross conversion with a minimum 90% polarization conversion ratio (PCR) from 0.53-0.56, 0.92-1.07, and 1.69-1.75 THz having 5.50%, 15.08%, and 3.49% FBW, respectively. Multiple plasmonic resonances are the reason behind different polarization conversions and are confirmed with surface current distribution profiles of the FSS and ground. The metasurface's performance is stable up to 45° for both transverse electric (TE) and transverse magnetic (TM) oblique incidences. The polarizer's unit cell architecture is compact with structural dimensions of 0.121×0.121×0.041λL3, where λL is the lowest operating frequency's free-space wavelength. The authors believe this design is compact, with angular stable multi-band multi-conversion ability that will significantly impact the THz applications in real time.

A palmar pressure sensor for measurement of upper limb weight bearing by the hands during transfers by paraplegics.

Paraplegic patients have to effect transfer from one seat to another by using their upper limbs. In this process the hands bear almost the entire weight of the body in at least some phases of the transfer. It is desirable to train patients, especially those who are elderly and otherwise weak, to distribute their weight so as to avoid large forces being sustained on any one hand for an extended period. It is also desirable to evaluate the effectiveness of assistive devices like lower limb FES in sharing the load on the hand. This study presents a simple and versatile method of measuring palmar hand force during transfers by paraplegic patients. It is important that this force sensor should not interfere with the grasping and stabilizing properties of the hands and should permit normal transferring. The force sensor comprises an air-filled pouch or pillow that can be placed on any surface. This pneumatic sensor feels like upholstery padding on the surface on which it is placed. The sensor integrates the total pressure applied to the surface of the pouch, thereby obtaining the total force exerted by the palm/hand. The fabrication of the sensor is described, as well as the associated measurement circuit. The static calibration shows that the sensor is linear up to 350 N and the dynamic calibration shows that it has a bandwidth of 13 Hz. The sensor was fabricated using an inflated inelastic airbag attached to a pressure transducer. An automatic offset correction circuit in the preamplifier module ensures that any offset due to initial pressure or sensor drift is removed and the output is zero under no load condition. The key to this sensor arrangement is the ease of fitting it into the intended location without disturbing the existing arrangement for the subject's activities of daily living (ADL).