KEYWORDS: Modulation, Data transmission, Transmitters, Transceivers, Receivers, Demodulation, Electrodes, Signal attenuation, Analog to digital converters
Conductive intracardiac communication (CIC) can be utilized for the synchronization of multi-chamber leadless pacemakers (LLPMs) to overcome complications arising from traditional pacemaker lead connections. Current CIC methods are mainly based on pulse modulation (PM) and On-Off Keying (OOK), which suffer from high power consumption and poor interference resilience, with transmitter output bit energy (Ebit) exceeding 5 pJ. Addressing these concerns, we proposed a method of conductive intracardiac communication based on Gaussian Minimum Shift Keying (GMSK). In the transmitter, a power-optimized GMSK modulation method is employed for signal transmission. In the receiver, a variable gain amplifier is utilized for CIC signal reception, and signal recovery is achieved through low-power demodulation and bit synchronization methods. A prototype transceiver was designed for measuring the bit error ratio (BER) and transmitter output Ebit of GMSK and OOK methods in in-vitro experiments using porcine hearts as channels. The transceiver was connected to the right atrium and right ventricle via stainless steel needle electrodes. At data rates of 75-500 kbps and a BER of 1e-4, the average Ebit for OOK ranged from 0.06-0.61 pJ, whereas for GMSK, it was lower, ranging from 0.02-0.35 pJ. This study demonstrates that LLPM achieving reliable CIC using GMSK at transmission powers below 35 pW is feasible in practical channel conditions. The proposed GMSK-based CIC method is more preferable to PM and OOK due to its higher reliability and lower transmission power requirements.
A method for generating a high-order (≥2 ) polarized vortex beam by using achromatic meniscus axicon doublets (MADs) is described. The MAD has a rotationally symmetric structure and consists of a pair of identical meniscus axicons with the same apex angle. It exploits four total internal reflections when collimated rays pass through it to produce a half-wave retardation, but with azimuth-variant polarization orientations. The characteristics of high achromatism of retardance, reasonable acceptance angular aperture for MAD, are numerically demonstrated. The effect of the remaining stress birefringence of optical materials on retardation is also discussed.
We present a new method for converting circularly polarized light into radially or azimuthally polarized light by using an achromatic meniscus axicon and two additional halfwave retarders. The rotationally symmetric meniscus axicon, consisting of a pair of convex and concave conical surfaces with the same apex angle, exploits the double total internal reflections when light passes through it to produce π/2 phase retardation with an azimuth-variant polarization orientation. The properties of highly achromatic retardation, which provide excellent stability of retardation against temperature variation for the meniscus axicon, is numerically demonstrated.
A new four-step phase-shifting method for birefringence measurement based on the plane polariscope is proposed. The plane polariscope to carry this phase-shifting method is characterized by triple polarizers. One fixed polarizer is used as a linearly polarized state generator; the other two rotatable linear polarizers act as phase shifters. The measurement ranges are (0, π ) for phase retardation and (−π/4 , +π/4 ) for azimuth angle. Numerical simulation is carried out, and two mica wave plates are tested and evaluated. Compared with other commonly used methods on Senarmont or circular polariscopes, this method has the simplest optical setup and also is free from the errors of quarter wave plates. It has less wavelength dependence and temperature dependence and is expected to be more cost-effective and environmentally robust.
The theoretical and experimental analysis on the effects of extinction ratios of linear polarizer and analyzer in the measurement of birefringent retardance by a five-step phase-shifting method based on the plane polariscope is presented. Stokes vector and Mueller matrix are the tools used to perform this theoretical analysis. The theoretical analysis show that the coefficients of extinction ratios of linear polarizer and analyzer in plane polariscopic configuration can be eliminated by phase shifting and will not introduce errors with our proposed five-step method. A mica quarter waveplate with previously given phase retardation is tested and evaluated. The experimental comparison has been made between the calcite Glan-Thompson based system with extremely high extinction ratios and plastic Polaroid film based system with relatively lower extinction ratios. The experimental results show that there is no significant difference between the measured values from these two systems, which agrees well with the conclusion of theoretical analysis. Also, good experimental accuracy and repeatability are achieved as well by the proposed five-step phase-shifting method.
Segmentation of optical coherence tomography (OCT) cross-sectional structural images is important for assisting ophthalmologists in clinical decision making in terms of both diagnosis and treatment. We present an automatic approach for segmenting intramacular layers in Fourier domain optical coherence tomography (FD-OCT) images using a searching strategy based on locally weighted gradient extrema, coupled with an error-removing technique based on statistical error estimation. A two-step denoising preprocess in different directions is also employed to suppress random speckle noise while preserving the layer boundary as intact as possible. The algorithms are tested on the FD-OCT volume images obtained from four normal subjects, which successfully identify the boundaries of seven physiological layers, consistent with the results based on manual determination of macular OCT images.
A new six-step phase shifting method is presented in this paper to determine the phase retardation for whole-field
photoelastic stress analysis in optical glass based on the plane polariscope setup. This new phase stepping strategy is of no
quarter wave plate errors and with less intensity variations of emerging light. By this method, it's not necessary to
determine the isoclinic angles in advance when measuring the phase retardations, so the data processing will be simplified
and the isoclinic angle errors will cause no influnces on the measurement. A plane polariscope is setup including a LED
array light source, rotatable dichroic polymer film polarizer and analyser, a digital CCD camera and image grab system.
Two mica waveplates with known phase retardances are measured, and the experimental results agree well with the those
values. This method is expected to be used for the stress induced birefringence test in optical glass.
Due to the phasing effects, the measurements of Minimum Resolvable Temperature Difference (MRTD) for Staring
array thermal imagers often get abnormal results when the targets approaching system Nyquist frequency (fn). To
simulate the relations between MRTD values and four-bar targets' frequencies, this paper introduces the concept of best
contrast. Clearly, the MRTD results are inversely proportional to the best contrasts under optimum phases, higher
contrast corresponding to a lower MRTD. On the other hand, with the spatial frequencies increasing, the target's
opening area shrinking and leads the effective infrared eradiation decreasing, this means the MRTD results are inversely
proportional to the opening area of the target. Based on these two assumptions, and through numerical simulations, this
paper depicts the tendency chart of MRTD under optimum phases to the four-bar targets' spatial frequencies. The
tendency chart adequately explains the hump curve happens at frequencies between 0.6fn and fn. From the simulations,
the maximum of MRTD values can be predicted at the frequency of 0.89fn. The tendency chart illustrated by numerical
simulation is consistent with the MRTD results get in laboratory. While in Dynamic Minimum Resolvable Temperature
Difference (DMRTD) testing, moving the four-bar targets introduces temporal effects not present in static MRTD test.
Simulation reveals that DMRTD test can get more realistic shape of the curve between 0.6fn and fn, the characteristic
hump in the static MRTD curve between 0.6fn and fn is not seen.
In order to overcome the sampling-scene phase effect in the modulation transfer function (MTF) measurement of sampled imaging systems, a method using a pseudorandom number generating algorithm to generate several random targets displayed on a liquid-crystal-display (LCD) graph generator to evaluate the MTF of charge-coupled device (CCD) in visible region is discussed. The major advantages of this technique are that it has been demonstrated as a shift-invariant method without requiring mechanical scanning, and it is easy to generate a large number of random targets on LCD by computer program to get the average result and reduce measurement noise. By experiments, this technique has got a reliable MTF result and agrees with the usual methods. This method is expected to be used to develop a real-time video MTF testing software system.
A novel means to measure optical multi-parameter is overviewed in this paper and an integrated measurement system consisting of CCD camera, LCD graph generator, testing software and computer is described. Based on this system, novel methods of measuring focal length of lens and visual magnification of infinite conjugate system are given. In addition, the measurement of other parameters such as MTF, parallax, distortion, etc. is also discussed. Three automatic focusing criteria are proposed and selectively used to locate CCD target accurately in the image plane.
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