PIER Letters | PIER Journals

2021-01-21

PIER Letters

Vol. 95, 163-169, 2021

doi:10.2528/PIERL20110406

download: 752

New Theoretical Floquet Modal Analysis to Study 3-D Finite Almost Periodic Structures with Coupled Cells

Bilel Hamdi and Taoufik Aguili

This research letter offers a generalization character to our previous work [4, 5] to examine a 3-D almost periodic phased array antenna excited by arbitrarily located sources. An original modal formulation based on the Floquet analysis procedure is proposed utilizing the periodic walls along x, y, and z-axes, where the analysis region in the spectral domain is reduced to the Brillouin zone. Here, a good idea is provided to enforce the given boundary conditions for obtaining an integral equation formalism developed through Galerkin's method for solving periodic volumic structure (e.g. 3-D regular structure in the cubic grid). The interaction between cells in 3-D geometry (lattice) could be deduced using a novel expression of mutual coupling. However, it is possible to obtain it explicitly by the mean of Fourier transform and its inverse. Then, it is proven how Floquet analysis can be employed to study a 3D-finite array configuration with arbitrary amplitude and linear phase distribution along x, y, and z directions, including mutual interaction effects. To deal with the real hole 3D array configuration, a superposition theorem is suggested to describe the electromagnetic behavior in the spatial domain. For modeling the given 3D antenna array, one numerical method is adopted: The moment method combined with an equivalent circuit (MoM-GEC). An important gain in the running time and memory used would be achieved using Floquet analysis in comparison with other spatial conventional methods (especially, when the number of cells increases by adding the second and third directions).

NEW THEORETICAL FLOQUET MODAL ANALYSIS TO STUDY 3-D FINITE ALMOST PERIODIC STRUCTURES WITH COUPLED CELLS

2021-01-19

PIER Letters

Vol. 95, 155-162, 2021

doi:10.2528/PIERL20090406

download: 772

Conductivity Estimation by Characterization of the Anomalous Dispersion Region

Omar F. Siddiqui

Anomalous dispersion region is a resonance signature in the frequency response of resonators known as Lorentz resonators. It is identified by two consecutive slope reversals of the transmission phase response and a dip in the amplitude response. In this letter, we propose to exploit this unique resonant phase signature in characterization of the conductivity of solid and liquid material samples. The microwave resonator sensor consists of an open microstrip stub whose conductivity is designed to vary in response to an intruding sample. The transmission response of the resonator containing the material sample is measured using a vector network analyzer. The change of conductivity affects the Q-factor which can be detected by either the slope changes of the anomalous dispersive phase or the 3dB bandwidth of the amplitude spectrum. The hypothesis is practically demonstrated by detecting resistive changes of a saline solution whose conductivity depends on the amounts of additive salt.

CONDUCTIVITY ESTIMATION BY CHARACTERIZATION OF THE ANOMALOUS DISPERSION REGION

2021-01-13

PIER Letters

Vol. 95, 147-153, 2021

doi:10.2528/PIERL20102102

download: 1020

Dual-Band Bandpass Filter Design Using Stub-Loaded Hairpin Resonator and Meandering Uniform Impedance Resonator

Yun Xiu Wang, Yuan Li Chen, Wen Hui Zhou, Wei Chao Yang and Jin Zen

A novel microstrip dual-band bandpass filter (BPF) by coupling a stub-loaded hairpin resonator and two stub-loaded uniform impedance resonators (UIRs) is proposed. First, a open-ended stub is tap-connected to a meandering UIR at its centre, and these two stub-loaded meandering UIRs are further placed at symmetrical locations with respect to a stub-loaded hairpin resonator. Secondly, by introducing two parallel coupled lines at the two sides of the stub-loaded hairpin resonator, a dual-band BPF with two passbands at 2.4 GHz and 5.2 GHz is constructed. Finally, a prototype filter is designed and fabricated, and its measured results are provided to verify the predicted dual-band filter design.

DUAL-BAND BANDPASS FILTER DESIGN USING STUB-LOADED HAIRPIN RESONATOR AND MEANDERING UNIFORM IMPEDANCE RESONATOR

2021-01-12

PIER Letters

Vol. 95, 143-146, 2021

doi:10.2528/PIERL20102712

download: 575

A Novel Asymetric Structure for Photonic Crystal Based All Optical Silicon Logic or Gate

Shahram Hosseinzadeh, Mohammad Ali Tavakoli and Nastaran Saeedi

In this paper, a novel simple structure for all optical photonic crystal based logic gate is presented. The structure is based on coupling the input signals to a combiner and thresholding the output signal of the combiner. The unit cell of the structure is designed to achieve band gap around the communication wavelength (i.e. 1.5 μm). The presented structure reveals low cross couple between gate inputs. The structure has no symmetry between inputs, which enables realization of the gate on small footprint photonic crystal. The structure offers 0.1 μ bandwidth around the communication wavelength. The footprint of the structure is 25.59 μm × 25.31 μm.

A NOVEL ASYMETRIC STRUCTURE FOR PHOTONIC CRYSTAL BASED ALL OPTICAL SILICON LOGIC OR GATE

2021-01-05

PIER Letters

Vol. 95, 135-141, 2021

doi:10.2528/PIERL20110103

download: 731

A Slotted Patch Antenna with Enhanced Gain Pattern for Automotive Applications

Stefano Maddio, Giuseppe Pelosi, Monica Righini and Stefano Selleri

A single-layer via-less rectangular patch antenna for automotive applications in C-band is proposed. To match the needs of a vehicular dedicated short range communication protocol, the resonant edge of the antenna is enlarged to narrow the beam-width in the H-plane, while at the same time a pair of thin slots serve as inhibitors for the higher modes, permitting adequate matching and polarization purity. The proposed single patch antenna presents a realized gain about 6.85 dB, H-plane beam-width narrower than ±32˚, E-plane beam-width larger than ±45.5˚, and return loss exceeding 20 dB with a 3 dB bandwidth of 500 MHz, with a minimum at 5810 MHz, hence suitable for coexistence of different communication standard in the C-band. Furthermore, its compact dimension permits the direct integration within a radio front-end.

A SLOTTED PATCH ANTENNA WITH ENHANCED GAIN PATTERN FOR AUTOMOTIVE APPLICATIONS

2020-12-28

PIER Letters

Vol. 95, 125-134, 2021

doi:10.2528/PIERL20102101

download: 1039

A Simple Matrix Approach for Computing the Equivalent Resistance and Unknown Components in Resistor Networks

Aris Alexopoulos

A method is presented for computing the equivalent resistance and the unknown components of simple series and parallel resistor networks. The approach consists in taking the product of a simple 2×2 matrix (N-1) times, where N is the total number of components in the network. The matrix approach originates from the study of continued fractions. Numerical computations only require an algorithm that handles matrix multiplication.

A SIMPLE MATRIX APPROACH FOR COMPUTING THE EQUIVALENT RESISTANCE AND UNKNOWN COMPONENTS IN RESISTOR NETWORKS

2020-12-28

PIER Letters

Vol. 95, 115-123, 2021

doi:10.2528/PIERL20092303

download: 782

Design and Simulation of CMOS Circuit Structure for CTL-CTM Crosstalk Cancellation Method in High-Speed Interconnects

Huifang Sun, Yafei Wang, Yanxiao Zhao and Xuehua Li

A circuit module for coupled transmission line channel transmission matrix (CTL-CTM) crosstalk cancellation is designed and simulated by using CMOS technology in a high-speed interconnection system. The module consists of an adder and a subtractor to realize analog addition and subtraction of digital signals. The adder is composed of CMOS transistor pair connected to an inverter at the next stage. The subtractor is composed of a current mirror as the load of CMOS differential pair. The crosstalk cancellation circuit module is simulated and verified by advanced design system (ADS) software. The designed adder and subtractor work well and have no significant difference with the ideal output, and the signal eye diagram recovered by the crosstalk cancellation circuit is of good quality, which solves the circuit implementation problem in the CTL-CTM crosstalk cancellation method.

DESIGN AND SIMULATION OF CMOS CIRCUIT STRUCTURE FOR CTL-CTM CROSSTALK CANCELLATION METHOD IN HIGH-SPEED INTERCONNECTS

2020-12-27

PIER Letters

Vol. 95, 107-114, 2021

doi:10.2528/PIERL20083102

download: 699

Design of Independently Tunable Dual-Band Filter with High Selectivity and Compact Size Using Multipath Propagation Concept

Yue-Peng Zhong, Yang Xiong and Jian Huang

A novel tunable dual-band bandpass filter (DBPF) with high selectivity and independently tunable passbands is proposed in this paper. Electric and magnetic coupling is employed in this design to create transmission zeros. The proposed tunable DBPF has the advantage of fully independent and controllable passbands due to the multipath propagation mechanism. The measured results of tunable DBPF show that the center frequency of the first passband can be shifted from 2.34 to 2.45 GHz when the bias voltage VL increases from 3 V to 15 V, and the second passband can be tuned from 4.73 to 5.04 GHz when the bias voltage VH varies from 6 V to 15 V. Moreover, the core circuit-size of the tunable DBPF is about 0.293 λ_g x 0.067 λ_g, where λ_g is the guided wavelength at 2.4 GHz. The proposed filter exhibits the merits of fully independent and tunable passbands, high selectivity, and compact size.

DESIGN OF INDEPENDENTLY TUNABLE DUAL-BAND FILTER WITH HIGH SELECTIVITY AND COMPACT SIZE USING MULTIPATH PROPAGATION CONCEPT

2020-12-23

PIER Letters

Vol. 95, 99-105, 2021

doi:10.2528/PIERL20102703

download: 643

An Efficient Technique for Wide Band RCS Reduction of Patch Antenna Array Using Rectangular Cavity Walls and Phase Cancellation Principle

Xiaoyuan Zhang, Xiaoxiang He, Yang Yang and Chenyue Xu

The rectangular cavity is investigated and applied in the field of the radar cross section reduction (RCSR) of patch antennas for the first time. An integrated and efficient design technique is presented which uses both a slotted rectangular cavity and reflective phase cancellation by a simple artificial magnetic conductor (AMC) element. On condition that ensuring the radiation performance of the patch antenna does not deteriorate, the in-band radar cross section (RCS) of the antenna can be reduced by 12.2 dB at 7.6 GHz just relying on a type of phase-regulated AMC elements. On this basis, the rectangular cavity walls were first loaded surrounding the above-mentioned low-RCS patch antenna. The relative bandwidth (in which RCS was reduced by more than 8 dB) went from 3.33% to 50% in the RCSR ohttps://www.baidu.com/?tn=62095104_43_oem_dgf the antenna. Meanwhile, the RCS could be reduced by an additional 5 dB at its working frequency (7.6 GHz).

AN EFFICIENT TECHNIQUE FOR WIDE BAND RCS REDUCTION OF PATCH ANTENNA ARRAY USING RECTANGULAR CAVITY WALLS AND PHASE CANCELLATION PRINCIPLE

2020-12-22

PIER Letters

Vol. 95, 91-97, 2021

doi:10.2528/PIERL20102901

download: 807

Average BER Analysis of Free-Space Optical Communications with Adaptive Threshold Technique Over Exponentiated Weibull Distribution

Li Zhang, Jingyuan Wang, Liu Huang, Han Zhang and Ning Xu

Average bit error rate (BER) performance of on-off keying (OOK) modulation in a free space optical (FSO) system, which is based on adaptive threshold technique under atmospheric turbulence described by exponentiated Weibull (EW) distribution, is studied and compared with that of using fixed threshold technique. In order to solve the adaptive threshold, the equation is simplified by using the generalized Gauss-Laguerre polynomial function, which significantly improves the operational efficiency. The simulation results show that the adaptive threshold varies with the average transmitted power under different noise variances, receiving aperture sizes and turbulence conditions. Compared with the fixed threshold technique, the adaptive threshold technique can greatly improve the BER performance of FSO communication system.

AVERAGE BER ANALYSIS OF FREE-SPACE OPTICAL COMMUNICATIONS WITH ADAPTIVE THRESHOLD TECHNIQUE OVER EXPONENTIATED WEIBULL DISTRIBUTION

2020-12-19

PIER Letters

Vol. 95, 83-90, 2021

doi:10.2528/PIERL20091702

download: 1083

A Broadband UHF RFID Tag Antenna Design for Metallic Surface Using Module Matching

Fei You and Zhi Jiang

In this paper, a broadband RFID tag antenna based on module matching is proposed, which is suitable for metallic surface. The antenna's 10-dB effective bandwidth covers 820-980 MHz. In order to achieve a more appropriate impedance matching in a wideband, a new technique of module matching to reach a wide frequency band is studied, the consistent change of the tag antenna impedance and the chip impedance is fulfilled, and the frequency band is effectively widened. The feasibility of module matching to achieve maximum power transmission is analyzed. Further results demonstrate that the proposed tag antenna provides a stable gain when mounted on metal plates of various sizes. In addition, the proposed design is cost-effective since it does not require metallic vias and has a compact size. The maximum reading distance at 910 MHz on the metallic surface is 4.5 m.

A BROADBAND UHF RFID TAG ANTENNA DESIGN FOR METALLIC SURFACE USING MODULE MATCHING

2020-12-19

PIER Letters

Vol. 95, 73-81, 2021

doi:10.2528/PIERL20102004

download: 761

Design of a Dual-Band 12-Element MIMO Antenna Array for 5G Mobile Applications

Vishakha Thakur, Naveen Jaglan and Samir Dev Gupta

This article presents a dual-band 12-designed to operate at LTE 42 and LTE 43 bands ranging from 3400-3600 MHz and 3600-3800 MHz respectively. The impact on the antenna parameters due to the user's hand is also explored. The isolation between antenna elements is better than 14.8 dB with a total efficiency of more than 74%. A small envelope correlation coefficient less than 0.05 and the channel capacity of 61.9 bps/Hz make the proposed array a viable solution for 5G smartphones.

DESIGN OF A DUAL-BAND 12-ELEMENT MIMO ANTENNA ARRAY FOR 5G MOBILE APPLICATIONS

2020-12-18

PIER Letters

Vol. 95, 63-71, 2021

doi:10.2528/PIERL20103003

download: 885

Novel Monopole Microstrip Filtenna for UWB Applications

Md. Maqubool Hosain, Sumana Kumari and Anjini Kumar Tiwary

This manuscript proposes an Ultra-Wide band (UWB) Filtering Antenna (Filtenna) with application-based notches at Wi-MAX (3.3-3.7 GHz), WLAN (5.15-5.875 GHz) and ITU (7.725-8.275 GHz) bands. Initially, a monopole antenna is designed. To enhance bandwidth and bring about impedance matching, its ground plane is modified by introducing a triangular shaped defected ground structure (DGS) under the feedline, smoothening of upper edges of the ground plane and a rectangular DGS. Later, the triple notched band is created at 3.5 GHz, 5.5 GHz and 8 GHz by utilizing the notches generated by Inverted-U shaped defected microstrip structure (DMS) on the patch, U-type DMS on feedline, and C shaped resonator adjacent to the feedline respectively. The filtenna is an omnidirectional radiation pattern antenna which works within the proposed frequency band of operation having low insertion loss and good selectivity. Also, the VSWR is found to be <2, and peak gain is found to be 4 dBi. While studying the proposed filtenna, the simulated and measured frequency responses were observed to be in almost unison as if following each other.

NOVEL MONOPOLE MICROSTRIP FILTENNA FOR UWB APPLICATIONS

2020-12-15

PIER Letters

Vol. 95, 55-61, 2021

doi:10.2528/PIERL20062805

download: 710

Accurate Vortex Beam Mode Measurement Based on Rotational Antenna Method

Yuming Nie, Gaohua Ju, Jiarun Chen, Lu Ma and Yufei Zhao

For the application of electro-magnetic (EM) wave with orbital angular momentum (OAM), which is also called the vortex beam, it is essential to determine the real OAM mode of the transmit antenna, i.e., accurately measure the OAM mode of the manufactured antenna with systematic error. The traditional methods measure the OAM mode based on the OAM far-field approximation or the phase gradient in the transverse plane. The corresponding performance degrades when alignment error is not negligible or OAM modes increases. In this paper, an accurate OAM measurement of EM wave based on rotational antenna is proposed. Specifically, the EM beam with helical phase fronts can be well measured via frequency shift detection by rotating the OAM wave at the transmitter. The accuracy can be greatly improved compared with the traditional ways.

ACCURATE VORTEX BEAM MODE MEASUREMENT BASED ON ROTATIONAL ANTENNA METHOD

2020-12-14

PIER Letters

Vol. 95, 43-53, 2021

doi:10.2528/PIERL20100704

download: 998

SRR Loaded Compact Tri-Band MIMO Antenna for WLAN/WiMAX Applications

Venkatesan Rajeshkumar and Rengasamy Rajkumar

A multiband four-element multiple-input-multiple-output (MIMO) antenna configuration is proposed. The antenna consists of split ring resonators (SRRs) along with inverted L-shaped monopole antenna (ILA) structure on the top of the substrate and a slotted ground plane. The antenna without the SRRs exhibits resonances at 2.4 GHz, 3.66 GHz, and 5.5 GHz with with the impedance bandwidth (IBW) of 14.5%, 35.1%, and 9.6%, respectively. With the addition of SRRs the antenna exhibits additional resonance at 5.1 GHz with improved bandwidth and minimizes the reflections. Consequently, the impedance bandwidth at 5 GHz frequency band gets improved to 17.2%. Overall, the proposed antenna will cover the 2.4 GHz wireless local area network (WLAN) & industrial, scientific, medical (ISM) band, 3.5 GHz worldwide interoperability for microwave access (WiMAX), and 5 GHz WLAN 4G/5G applications. In spite of very compact area (0.094 λ₀², for the highest operating wavelength) and presence of common ground, the antenna exhibits high inter-element isolation of ≥ −14 dB and S₁₁ ≥ −10 dB. The proposed antenna design is fabricated, tested, and analyzed.

SRR LOADED COMPACT TRI-BAND MIMO ANTENNA FOR WLAN/WIMAX APPLICATIONS

2020-12-09

PIER Letters

Vol. 95, 33-42, 2021

doi:10.2528/PIERL20093003

download: 862

A New Equivalent Circuit Scheme for Grounded Back-to-Back GCPW-MS-GCPW Transitions Fabricated on a Thin Low-k Substrate

Pierre-Vincent Dugue, Mohammed El-Gibari, Mathieu Halbwax, Stephane Ginestar, Vanessa Avramovic, Jean-Pierre Vilcot and Hongwu Li

We hereby present a new equivalent circuit model including both lumped and distributed elements for GCPW-MS transitions (GCPW for Grounded Coplanar Waveguide and MS for Microstrip). In order validating the modelling results, such transitions have been fabricated on a 20 µm-thick BCB (Benzocyclobutene resin) substrate using grounding pads including via-holes of different diameters. The study focuses on the impact of the via-hole design on the performance of the transition and more specifically on its bandwidth. The transitions were made using a simple technological process based on photosensitive polymer. ADS simulation data of the new equivalent circuit model were in very good agreement with measured S-parameters. Both theoretical and experimental results show that the bandwidth of such a transition can reach up to 100 GHz bandwidth using via-holes of 900 µm diameter.

A NEW EQUIVALENT CIRCUIT SCHEME FOR GROUNDED BACK-TO-BACK GCPW-MS-GCPW TRANSITIONS FABRICATED ON A THIN LOW-K SUBSTRATE

2020-12-09

PIER Letters

Vol. 95, 25-32, 2021

doi:10.2528/PIERL20102303

download: 752

Augmented Quaternion MUSIC Method for a Uniform/Sparse COLD Array

Zhiwei Jiang, Zehao Zhang, Tianyi Zhao, Hua Chen and Weifeng Wang

The quaternion multiple signal classification (Q-MUSIC) algorithm reduces the dimension of covariance matrix, which would result in performance degrading of DOA estimation. An augmented quaternion MUSIC algorithm (AQ-MUSIC) based on concentered orthogonal loop and dipole (COLD) array is presented in this paper. The proposed algorithm uses an augmented quaternion formalism to model the completely polarized signals, which allows a concise and novel way to an augmented covariance matrix. The fact reveals that more accurate DOA parameters could be extracted from an augmented covariance matrix. Even compared with the long vector MUSIC (LV-MUSIC) algorithm whose dimension of covariance matrix is the same as AQ-MUSIC, the accuracy of DOA parameter estimation is also improved. Simulation results verify the performance promotion of the proposed approach.

AUGMENTED QUATERNION MUSIC METHOD FOR A UNIFORM/SPARSE COLD ARRAY

2020-11-27

PIER Letters

Vol. 95, 17-24, 2021

doi:10.2528/PIERL20090601

download: 1398

Double-Layer TM110 Mode of Substrate Integrated Waveguide Circular Cavity (SIWCC) for Wireless Communication Applications

Siti Aminah Nordin, Zuhani Ismail Khan, Muhammad Asraf Hairuddin, Norfishah Ab Wahab and Nur Dalila Khirul Ashar

A substrate integrated waveguide circular cavity (SIWCC) bandpass filter is developed using printed circuit board technology. A circular cavity structure using TM₁₁₀ mode was employed in the design of the filter to operate at the frequency of 4.75 GHz, which is in the C-band frequency range. The filter was designed based on double-layer elements comprising a substrate integrated circular cavity (SICC) and a transmission line (TL) that produce single-mode resonance. In the proposed structure, circular resonators consisting of vias and a rectangular patch at the top layer are combined into a circular substrate integrated waveguide (SIW) structure. To achieve the desired resonance frequency, a triangle probe is etched at both sides of the microstrip line feeding section. The proposed structure is put in a conducting box to prevent radiation to the outside and eliminate radiation loss. Furthermore, the desired centre frequency and bandwidths of the passbands can be obtained by adjusting the dimension of the filter. To prove the concept, the filter structure is fabricated using Rogers RO₄₃₅₀B^TM circuit materials with a dielectric constant of ε_r = 3.48 and height of the substrate of 1.52 mm. The design was simulated using Ansoft HFSS simulator and measured using a vector network analyser. Simulation and fabrication results are compared for verification. The proposed SIWCC bandpass filter has potential applications in satellites and wireless communication systems.

DOUBLE-LAYER TM110 MODE OF SUBSTRATE INTEGRATED WAVEGUIDE CIRCULAR CAVITY (SIWCC) FOR WIRELESS COMMUNICATION APPLICATIONS

2020-11-26

PIER Letters

Vol. 95, 9-16, 2021

doi:10.2528/PIERL20101501

download: 801

An Octaband Temperature Tunable Terahertz Metamaterial Absorber Using Tapered Triangular Structures

Bhargav Appasani

The recent growth of terahertz (THz) applications has sparked interest in the design of novel electromagnetic structures for this frequency regime. One of the structures is the THz absorber, used in sensing and imaging applications. Metamaterial based designs are commonly used to achieve the desired absorption characteristics. Absorbers whose spectra can be tuned by changing the temperature are a subclass in the broad family of THz absorbers that are used for temperature sensing. In the beginning years, single band temperature tunable absorbers were designed, and at present the focus has shifted to the design of multi-band temperature tunable absorbers. Absorbers with six tunable bands have already been proposed. In this paper an octa-band temperature tunable terahertz metamaterial absorber is proposed, whose unit cell consists of four orthogonally placed tapered triangular structures connected by a ring resonator on top of an InSb dielectric substrate. At 210K it is observed that the structure's absorption spectra are: 98.7% at 1.026 THz, 79.5% at 1.245 THz, 90.4% at 1.301 THz, 95.2% at 1.442 THz, 97.44% at 1.585 THz, 96.4% at 1.644 THz, 97.1% at 1.756 THz, and 90.4% at 2.071 THz. The temperature sensitivities of the proposed structure in eight of its absorption bands are 10.3 GHz/K, 8.22 GHz/K, 7.96 GHz/K, 7.02 GHz/K, 6.44 GHz/K, 6.17 GHz/K, 5.5 GHz/K, and 3.2 GHz/K, respectively. Thus, the proposed design can have practical applications in terahertz temperature sensing applications.

AN OCTABAND TEMPERATURE TUNABLE TERAHERTZ METAMATERIAL ABSORBER USING TAPERED TRIANGULAR STRUCTURES

2020-11-27

PIER Letters

Vol. 95, 1-8, 2021

doi:10.2528/PIERL20092701

download: 683

A Model Assisted Probability of Detection Approach for ECNDT of Hidden Defect in Aircraft Structures

Mohammed Chebout, Hakim Azizi and Mohammed Rachid Mekideche

In a probabilistic approach, the performance of the control is characterized by statistical indi-cators such as the Probability of Detection (PoD) which describes the probability of detecting a defect of a given size knowing that it is present in the inspected structure. In this paper, an experimental analysis and simulation using FEM of the eddy current testing on three-dimensional riveted structure is performed on small fatigue cracks to identify and quantify probability of detec-tion curves. The PoD curves are plotted in terms of characteristic dimensions of the defect (depth, length, orientation, etc.) and are dependent on a number of factors including material, geometry, defect type, operator, and environmental effects.