Search

Retinal prosthesis system is currently being developed in various places around the world. This system involved data transfer between an implanted antenna inside an eyeball and an external camera that is located just in front of the eyeball. While there are plenty of publications about the stimulating electrodes or the processing unit of the system itself, very limited amount has been published regarding the wireless communication link between the two antennas despite the fact that the electromagnetic wave will propagate through a complex medium in the form of Vitreous Humor. This paper will discuss about the constraints associated with implanting an antenna into an eyeball. An antenna design and simulation was performed with the aid of High Frequency Structure Simulator (HFSS) and its Finite Element Method (FEM) mathematical solver in the operating frequency of 402 - 405 MHz. The antenna, which was a 4 layer microstrip antenna, was positioned at the centre of a spherical model filled with homogeneous Vitreous Humor material. Antenna performances that include return loss, bandwidth, gain, radiation pattern, and SAR value are analysed and compared against those of other implantable antennas operating in Medical Implant Communication Service (MICS) band. Free space and simulating fluid measurements were also conducted on the fabricated antenna to validate the simulation results. It was concluded that the fabricated antenna was able to produce the similar performance to the simulation results and hence at the same level as the other antennas operating in material with lower dielectric constants and conductivities. [ABSTRACT FROM AUTHOR]

A novel 3D Frequency Selective Surface (FSS) architecture based on a circular ring unit element is presented. The circular ring was made 3D by creating a cylindrical element of a certain length, adding an extra degree of freedom into the structure. The length of the cylinder is shown through electromagnetic simulation to have a significant effect on the frequency characteristics of the FSS. Increasing the length of the cylinder can change the FSS from a band-stop to a band-pass filter response. The center frequency of both band pass and band stop responses can also be tuned with adjustment to the length. Dielectric materials are introduced in the center of the cylindrical unit cell elements to simultaneously obtain a stop and pass band with a sharp transition. For high dielectric filling materials, the 3D periodic structure exhibits negative refractive index metamaterial properties. A parametric analysis was conducted on these new cylindrical unit elements, and a prototype 3D FSS structure has been constructed and experimentally validated. [ABSTRACT FROM AUTHOR]

An array of conformal antenna structures mounted on a bending surface exhibits a substantial shift in main beam direction. This paper demonstrates a method to compensate for the induced beam shift by using the change in length of the surface produced by the bend. This change in length modifies the capacitance in a composite right/left-handed transmission (CRLHTL) line, causing a phase shift in the line. A potential implementation is proposed that can correct an 18° beam shift with only an induced change in length of 0.144%. The paper establishes that this passive compensation concept is feasible and provides significant benefits over active compensation systems in terms of weight reduction, cost, simplification and the ability to operate in radio silence. [ABSTRACT FROM AUTHOR]

RF radiation due to corona and dry-band arc discharges have been observed using an antenna. Variations in radiated energy were observed due to change in the distance between two water droplets, the contact angle and the volume of the droplets, and the condition of the insulator surface. Changes in the frequency spectrum within the 800 MHz-900MHz and 1.25 GHz-1.4 GHz frequency bands have been used to identify the transition from corona discharge to dry- band arc discharge. The 800 MHz-900MHz emission band has also been used to monitor the condition of the insulator. These findings highlight the potential for RF sensing in the identification of partial discharges and insulator condition monitoring. [ABSTRACT FROM AUTHOR]

Unidirectional carbon/epoxy composite laminates are highly orthotropic, with their conductivity and permittivity being strongly dependent on the incident angle relative to the fibre orientation. This paper presents a novel frequency selective polarizing subreflector manufactured from unidirectional carbon fibre reinforced polymer (CFRP), placed a certain distance from a conducting ground also made from CFRP laminate. Theoretical analysis, computational simulation, and experimental measurements are conducted to investigate the effects of separation offset, laminate thickness and incident angle on the performance of a reflector manufactured from a unidirectional IM7/977-3 CFRP. The results show that this new reflector reduces the cross polarization at S-band by 13 dB while remaining a good reflector at X-band and the incident angle has minimal effect on the frequency response of the polarizer. The single reflector can support two orthogonal polarized frequencies, unlike traditional wire grid polarizer screens. [ABSTRACT FROM AUTHOR]

In this paper, the anisotropic conductivity effect of quasi-isotropic carbon fiber laminates on conformal load-bearing antenna structures (CLAS) is presented. The conductivity of a quasi-isotropic IM7/977-3 CFRP laminate is measured using waveguide techniques. The results show that orientation of the surface ply relative to the polarization of the incident E-field has a major influence on the reflectivity. This difference is attributed to the fact that carbon fibres oriented parallel to the E-field plies behave as good conductors, while off-axis plies present as lossy dielectric layers with a finite conductivity. This anisotropic behavior of the ply layers is shown to have a distinctive influence on the operation of both microstrip patch and slot antennas. [ABSTRACT FROM AUTHOR]

In this paper, an attempt is made to extend the deformation model of a communication device embedded in a viscoelastic thermoset composite polymer such as Sheet Moulding Compound (SMC). The original model takes into account time dependent heat transfer from the mould surface into the SMC charge and the consequent time dependent viscosity propagation during the initial stage of mould closing and subsequent filling. The required model parameters for viscosity and elasticity have been determined from rheological testing. The extended model will examine the effects of a number of process parameters such as mould closing speed, mould temperature and initial charge temperature. The effect of these parameters on the deformation of the communication device is discussed and compared to experimental findings. In addition the signal quality due to antenna deformation as a result of its embedding process is investigated by comparing simulation and experimental results. [ABSTRACT FROM AUTHOR]

A new edge-fed patch antenna that mitigates spurious radiation issues when thick substrates are used to create the antenna is presented. The radiator can be classified as an edge-fed cavity backed patch. Here, a thin substrate is used to develop the microstrip feed line, thereby ensuring the track widths are small and subsequently decreasing spurious feed radiation. The patch radiator utilises the thick substrate employed in the cavity ensuring reasonable return loss bandwidth can be achieved. A single element and a 2×2 array have been designed, fabricated and tested using the proposed technique and it has been shown that significant reduction in pattern distortion and increase in gain can be achieved compared to conventional edge-fed microstrip patch configurations. Because of the thin tracks used to feed the radiators, the new technique is very applicable to large arrays of microstrip patches where the area consumed by the distribution network must be minimised to ensure good radiation performance. [ABSTRACT FROM AUTHOR]

An innovative approach to the design of a centre-fed omnidirectional collinear array for use in the 900 MHz band is presented. The coplanar printed circuit realisation using a combination of the CPW and coplanar strips is shown to be very effective in eliminating beam tilt with change in frequency. Both measured and simulated results confirm less than 1.5° of beam tilt in the omnidirectional pattern with an azimuth ripple of approximately +/-0.7 dB, over an impedance bandwidth of greater than 10%. [ABSTRACT FROM AUTHOR]

A printed antenna realised on an indium phosphide wafer is presented. The antenna provides an efficient, broadband antenna solution for MMIC/OEIC systems and subsystems. The antenna is based on an aperture coupled patch architecture with the substrates layers in a hi-lo configuration. Measured results exhibit an impedance bandwidth of around 12% for VSWR<2, and a gain of 8 dBi. [ABSTRACT FROM AUTHOR]