Facial soft tissue segmentation

The importance of the face for socio-ecological interaction is the cause for a high demand on any surgical intervention on the facial musculo-skeletal system. Bones and soft-tissues are of major importance for any facial surgical treatment to guarantee an optimal, functional and aesthetical result. For this reason, surgeons want to pre-operatively plan, simulate and predict the outcome of the surgery allowing for shorter operation times and improved quality. Accurate simulation requires exact segmentation knowledge of the facial tissues. Thus semi-automatic segmentation techniques are required. This thesis proposes semi-automatic methods for segmentation of the facial soft-tissues, such as muscles, skin and fat, from CT and MRI datasets, using a Markov Random Fields (MRF) framework. Due to image noise, artifacts, weak edges and multiple objects of similar appearance in close proximity, it is difficult to segment the object of interest by using image information alone. Segmentations would leak at weak edges into neighboring structures that have a similar intensity profile. To overcome this problem, additional shape knowledge is incorporated in the energy function which can then be minimized using Graph-Cuts (GC). Incremental approaches by incorporating additional prior shape knowledge are presented. The proposed approaches are not object specific and can be applied to segment any class of objects be that anatomical or non-anatomical from medical or non-medical image datasets, whenever a statistical model is present. In the first approach a 3D mean shape template is used as shape prior, which is integrated into the MRF based energy function. Here, the shape knowledge is encoded into the data and the smoothness terms of the energy function that constrains the segmented parts to a reasonable shape. In the second approach, to improve handling of shape variations naturally found in the population, the fixed shape template is replaced by a more robust 3D statistical shape model based on Probabilistic Principal Component Analysis (PPCA). The advantages of using the Probabilistic PCA are that it allows reconstructing the optimal shape and computing the remaining variance of the statistical model from partial information. By using an iterative method, the statistical shape model is then refined using image based cues to get a better fitting of the statistical model to the patient's muscle anatomy. These image cues are based on the segmented muscle, edge information and intensity likelihood of the muscle. Here, a linear shape update mechanism is used to fit the statistical model to the image based cues. In the third approach, the shape refinement step is further improved by using a non-linear shape update mechanism where vertices of the 3D mesh of the statistical model incur the non-linear penalty depending on the remaining variability of the vertex. The non-linear shape update mechanism provides a more accurate shape update and helps in a finer shape fitting of the statistical model to the image based cues in areas where the shape variability is high. Finally, a unified approach is presented to segment the relevant facial muscles and the remaining facial soft-tissues (skin and fat). One soft-tissue layer is removed at a time such as the head and non-head regions followed by the skin. In the next step, bones are removed from the dataset, followed by the separation of the brain and non-brain regions as well as the removal of air cavities. Afterwards, facial fat is segmented using the standard Graph-Cuts approach. After separating the important anatomical structures, finally, a 3D fixed shape template mesh of the facial muscles is used to segment the relevant facial muscles. The proposed methods are tested on the challenging example of segmenting the masseter muscle. The datasets were noisy with almost all possessing mild to severe imaging artifacts such as high-density artifacts caused by e.g. dental fillings and dental implants. Qualitative and quantitative experimental results show that by incorporating prior shape knowledge leaking can be effectively constrained to obtain better segmentation results

Frequency Dependence of HEMT Under Optical Illumination

An analysis of the AC characteristics of Al-GaAs/GaAs HEMT under illumination with modulated light has been carried out for small signal condition. A new model for the photovoltage calculation is outlined. The effect of the signal frequency on the photoconduc-tive current is evaluated, the results show that photo-conductive current is very small and can be neglected in calculation. The frequency dependence of photovoltage along with 2-DEG charge density, drain-source current and transconductance of the device have been studied analytically for HEMT structure

Optical control on millimeter wave radiation in a semiconductor backed periodic structure

IEEE Antennas and Propagation Society, AP-S International Symposium (Digest)1154-157IAPS

Edge coupled microstrip resonators with periodical slot loading

Asia-Pacific Microwave Conference Proceedings, APMC19-1228

Leaky-wave radiation behavior from a double periodic composite right/left-handed substrate integrated waveguide

A double periodic composite right/left-handed ( DP-CRLH ) substrate integrated waveguide (SIW) is proposed based on the transmission line theory. A new leaky-wave radiation is observed at low frequency below the left-handed passband in addition to the composite right/left-handed property. First, the equivalent circuit of the proposed structure is analyzed, and dispersion characteristics are obtained including the expression for the cutoff frequencies. It is noted that transmission lines double periodically loaded with either alternate capacitances, or alternate inductances will contribute the new leaky-wave behavior. Next, SIW implementation of a DP-CRLH transmission line is designed and illustrated with simulated and experimentally demonstrated results. The electric field distribution plots are extracted from a full-wave simulation tool and exhibit the forward and backward wave propagation in the new leaky-wave region and the typical left-handed region, respectively. Finally, a compact leaky-wave antenna based on the DP-CRLH SIW is designed, and the radiation characteristics are tested and demonstrated to exhibit forward radiation at the new leaky-wave region from 5.2 to 5.8 GHz (covering IEEE 802.11a band) and frequency scanning from backward to forward directions in the left-handed and conventional right-handed region from 12.6 to 17.8 GHz

Efficiency enhancement for dynamic wireless power transfer system with segmented transmitter array

Achieving high efficiency with improved power transfer distance and misalignment tolerance is the major design challenge in realizing dynamic wireless power transfer (D-WPT) systems. This paper provides an analysis on designing D-WPT systems. Design parameters such as number of Tx coils, separation between Tx, operating frequency, and load characteristics are analyzed with respect to efficiency for the D-WPT system with segmented transmitter array. A double-spiral repeater (DSR) is proposed for improving efficiency, enhancing transfer distance, and misalignment tolerance. Experimental results of the proposed topology with DSRs show efficiencies of 81% and 60% at normalized transfer distances (normalized to geometric mean of Tx and Rx sizes) of 0.74 and 2.2, respectively. The proposed topology can be effectively used to alleviate efficiency deterioration against transfer distance and misalignment in D-WPT systems

Coil optimization against misalignment for wireless power transfer

The improvement of misalignment tolerance is a key challenge for the optimization of wireless power transfer (WPT) systems. WPT coil design plays an imperative role in improving the misalignment tolerance. However, misalignment tolerance needs to be considered along with the dynamics of the receiving coil. This paper presents a coil optimization method to improve misalignment tolerance according to the receiver positioning behavior. A novel figure-of-merit (FOM) is introduced by incorporating maximum efficiency and the probability of alignment (PA). A case study for parameter optimization of circular spiral coils is presented with the use of the proposed FOM

Wideband circularly polarized AMC reflector backed aperture antenna

A wideband, circularly polarized (CP), artificial magnetic conductor (AMC) reflector backed octagonal-shaped aperture (OSA) antenna is proposed for unidirectional radiation. The proposed antenna consists of an OSA fed by microstrip along with L-shaped stub and an AMC reflector. Bidirectional radiation of OSA antenna is changed to unidirectional radiation using an AMC reflector. The antenna height measured from the upper surface of the AMC reflector to OSA radiator is chosen to be small to realize a low-profile antenna: at the lowest analysis frequency of 4.5 GHz. Three different surfaces are studied and compared as back reflectors for OSA: perfect electric conductor (PEC), single layered AMC surface, and double layered AMC surface. The OSA with double-layered AMC surface demonstrates the largest measured 3-dB axial ratio bandwidth of 33.2% (5.20-7.19 GHz) with impedance bandwidth of 36.2% (5.04-7.21 GHz) for VSWR of 2. Almost constant gain of around 7 dBic is achieved over the band for the overall antenna volume of 0.72λo × 0.60λo × 0.19λo at the center frequency of 6.0 GHz