A. Ashrif A. Bakar

Surface Electromyography Signal Processing and Classification Techniques

Electromyography (EMG) signals are becoming increasingly important in many applications, including clinical/biomedical, prosthesis or rehabilitation devices, human machine interactions, and more. However, noisy EMG signals are the major hurdles to be overcome in order to achieve improved performance in the above applications. Detection, processing and classification analysis in electromyography (EMG) is very desirable because it allows a more standardized and precise evaluation of the neurophysiological, rehabitational and assistive technological findings. This paper reviews two prominent areas; first: the pre-processing method for eliminating possible artifacts via appropriate preparation at the time of recording EMG signals, and second: a brief explanation of the different methods for processing and classifying EMG signals. This study then compares the numerous methods of analyzing EMG signals, in terms of their performance. The crux of this paper is to review the most recent developments and research studies related to the issues mentioned above.

Advances in Bio-Tactile Sensors for Minimally Invasive Surgery Using the Fibre Bragg Grating Force Sensor Technique: A Survey

The large interest in utilising fibre Bragg grating (FBG) strain sensors for minimally invasive surgery (MIS) applications to replace conventional electrical tactile sensors has grown in the past few years. FBG strain sensors offer the advantages of optical fibre sensors, such as high sensitivity, immunity to electromagnetic noise, electrical passivity and chemical inertness, but are not limited by phase discontinuity or intensity fluctuations. FBG sensors feature a wavelength-encoding sensing signal that enables distributed sensing that utilises fewer connections. In addition, their flexibility and lightness allow easy insertion into needles and catheters, thus enabling localised measurements inside tissues and blood. Two types of FBG tactile sensors have been emphasised in the literature: single-point and array FBG tactile sensors. This paper describes the current design, development and research of the optical fibre tactile techniques that are based on FBGs to enhance the performance of MIS procedures in general. Providing MIS or microsurgery surgeons with accurate and precise measurements and control of the contact forces during tissues manipulation will benefit both surgeons and patients.

Analysis of independent strain-temperature fiber Bragg grating sensing technique using OptiSystem and OptiGrating

In this paper, a combination of two simulation tools provided by Optiwave Systems Inc. is used to perform a remote fiber Bragg grating (FBG) based strain-temperature sensor setup. Two Gaussian apodized FBG sensors were designed and characterized by OptiGrating. The customized FBGs were incorporated into OptiSystem tool to perform the analysis. Full ability to utilize the combination to perform remote strain-independent temperature FBG setup was demonstrated. 1.2 pm/μstrain and 14.4 pm/°C sensitivities obtained for strain and temperature respectively.

Self-mixing displacement sensing using the junction voltage variation in a GaN laser

The self-mixing (SM) laser sensing technique allows a simple, self-aligned and robust system for measuring displacement. Low-cost blue emitting GaN laser diodes have recently become available due to the high volume requirements for Blu-ray disc devices such as high-definition video players and gaming consoles. These GaN lasers have a significantly shorter wavelength (around 405 nm) compared to other semiconductor lasers (generally around 800 nm for SM sensors). Therefore, if used in SM displacement sensors, they provide significantly higher resolution. Further to that, the measurement resolution is affected by the ability of the system to properly interpret the movement corresponding to the fraction of the half wavelength of the laser resulting in an incomplete fringe. Doubling the number of fringes will reduce the global error when a fringe is not properly detected. In this paper we report the worlds first SM displacement measurement system based on junction voltage variation in blue emitting semiconductor lasers. Instead of monitoring the SM signals using a photo-diode, the signal is obtained via direct sensing of the laser junction voltage variation. This removes the need for a photo-diode, providing a cost reduction and increasing the reliability of the system. The sensitivity and precision of this system is evaluated and compared against the performance of systems using red (650 nm) and near IR (780 nm) laser based sensors with all three sensors sharing the same optical and electronic hardware.

Performance evaluation of 8 channel CWDM system with cascaded SOAs

Cascaded amplifiers would enhance the network functionality in the transmission of multi-wavelength signals for longer reach. In this paper, the proposed system is amplified with cascaded SOAs which individually operate in the S band and C band to support the transmission of eight CWDM channels ranging from 1471 nm to 1611 nm. The proposed amplified system produced maximum gain peak of 26 dB for the gain bandwidth of 80 nm.

Centralized monitoring and fault localization for passive optical network

A real-time, centralized and cost efficient monitoring and fault localization system is presented. In this system, a superluminescent diode (SLED) is used as the monitoring signal and the signal is reflected by using different types of fiber Bragg gratings (FBGs); uniform and phase-shifted FBGs as branch identifiers. We demonstrate the enhancement of monitoring wavelength whereas for a distinct center wavelength, it represents the reflection spectrum of two types of FBG or two branches in the network. Thus, more optical network units (ONUs) can be monitored for the specific monitoring source with limited bandwidth. The system is capable to monitor up to 64 ONUs with BER of 10-15.

Temperature and current dependence of doppler SNR in a VCSEL based self-mixing sensor

This paper proposes a method for maintaining the maximum signal-to-noise ratio (SNR) of the signal obtained from the self-mixing sensor based on a Vertical-Cavity Surface-Emitting Laser (VCSEL). The SNR of the Doppler self-mixing signal was investigated experimentally as a function of laser driving current and ambient temperature. It was found that the locus of the maximum SNR in the current-temperature space can be well approximated by the simple analytical model based on the temperature behaviour of the VCSELs threshold current. A self-mixing Doppler signal was acquired from the variation in VCSEL junction voltage rather than from a conventional variation in laser optical power to reduce the complexity of the system. It was found that the optimum sensor performance over a wide range of ambient temperatures can be achieved by tuning the laser current according to the proposed model. This enables the sensor to operate without temperature stabilisation making it attractive for mobile applications and applications with limited power supply.

Comprehensive Numerical Analysis of Finite Difference Time Domain Methods for Improving Optical Waveguide Sensor Accuracy

This paper discusses numerical analysis methods for different geometrical features that have limited interval values for typically used sensor wavelengths. Compared with existing Finite Difference Time Domain (FDTD) methods, the alternating direction implicit (ADI)-FDTD method reduces the number of sub-steps by a factor of two to three, which represents a 33% time savings in each single run. The local one-dimensional (LOD)-FDTD method has similar numerical equation properties, which should be calculated as in the previous method. Generally, a small number of arithmetic processes, which result in a shorter simulation time, are desired. The alternating direction implicit technique can be considered a significant step forward for improving the efficiency of unconditionally stable FDTD schemes. This comparative study shows that the local one-dimensional method had minimum relative error ranges of less than 40% for analytical frequencies above 42.85 GHz, and the same accuracy was generated by both methods.

Link Power Level Improvements in an Amplified 8-Channel CWDM System with Hybrid EDFA-SOA Pre-Amplifier

The link power improvement in a coarse wavelength division multiplexing (CWDM) system which is transmitted using a hybrid erbium-doped fiber amplifier (EDFA) and semiconductor optical amplifier (SOA) scheme as a pre-amplifier, is discussed. The network is designed for amplifying 8 CWDM channels ranging from 1471 nm to 1611 nm. The hybrid amplifiers’ gain measurement is obtained from experimental work with gain peak at 22 dB which is observed at 1531 nm. The amplifiers also caused power increment of 5.06 dB in the transmission link before the signal is split individually at the receiving end. Based on the higher gain peaks and power spectrum at 1531 nm and 1551 nm wavelengths, the proposed amplified link would be useful for the transmission of video applications.

Characterisation of a polymeric electro-optic phase modulator for sensing applications

Electro-optic (EO) modulator is a device used primarily in optical communication systems to provide an external optical high-speed bandwidth modulation. Instead, the EO modulator can also be employed as sensing instrument with some modification. In this paper, we demonstrate the performance study of a polymer EO phase modulator compared with the commonly used waveguide material LiNbO3 to obtain better low insertion loss and length extension. Both parameters are substantial for biosensing applications such as biomedical equipment to detect human body response.