In this paper we report the electro-optic characterization of two homologous series of low molar mass bimesogenic siloxane-containing liquid crystals. The materials used have two alkoxycyanobiphenyl mesogenic units with variable alkyl chain joined by a two-or five-siloxane moiety and all exhibit stable smectic A mesophases over wide temperature ranges ͑up to 100°C wide͒. Due to their inherent ruggedness these materials have potential for use in polarizer-free, bistable, scattering display and storage devices. The bistable modes are at low and high frequencies. The low frequency mode ͑write͒ is a highly scattering focal conic texture resulting from electrohydrodynamic instabilities while the high frequency mode ͑erase͒ is a clear state due to dielectric reorientation of the material. Both modes are preserved upon removal of the applied electric field. We present threshold voltages as a function of temperature, frequency, and cell thickness and response times as a function of voltage for each of the bistable modes. We find reduced threshold voltages ͑5 ഛ V th ഛ 12 V / m͒ and response times that are strongly dependent on applied voltage ͑50 msഛ ഛ 10 s͒. These operating conditions would suggest that these materials are particularly suitable for slow update, large area, low power information panels and displays.
In-body medical devices can play an important role in clinical monitoring and diagnosis of diseases. Wireless devices implanted within a patient have to be physically small, and must overcome the challenges of having a little or no onboard electrical power and the highly attenuating electromagnetic propagation environment which is the human body. In this paper, we investigate the use of biodegradable implant to monitor the healing of soft-tissue trauma and to allow early stage diagnosis of infection. The implantable tag is designed to degrade in a predetermined and controlled method, the stage of which can be measured from outside the body without the need for further surgical intervention. The speed of degradation of the tag depends on the temperature and acidity of the subcutaneous tissue in which the tag is implanted. We show that as the electrical length of the tag pattern increases due to degradation, the resonant frequency changes significantly, and this change in resonant frequency can be detected from outside the patient. Results are presented showing the tag's performance at normal and oblique incidence, and techniques for miniaturizing and enhancing the tag's response sensitivity are given. As the entire tag is biodegradable, there is no need for further postoperative surgery to remove it from the patient at the end of its useful life.
A periodic comb reflection frequency selective surface (CR-FSS) is presented for reducing interference caused by the propagation of signals via corridors. The novel CR-FSS has been designed to reduce the power of the forward scattered signal and increase the backscatter. For a specified comb period and angle of incidence, the direct forward scatter of the CR-FSS can be reduced by 5-15 dB and the backscatter increased by 10-15 dB over a frequency range of 10.8-13.5 GHz for a vertically polarised signal and 10.8-17 GHz for the horizontal polarisation. The CR-FSS is thus shown to be effective for both vertically and horizontally polarised signals. Comb period and angle of incidence are chosen to satisfy the conditions of Bragg's Law to provide a maximum backscatter at 10.8 GHz. By installing this novel surface in corridors, interference between multiple neighbouring transmitters can be reduced.
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