Thermal injuries are important complications of magnetic resonance imaging (MRI) and are mediated by electric fields within the body. Although several mechanisms at the molecular and cellular level have been implicated in the specific interaction of electric fields with tissues, the relative contributions of these mechanisms have not been elucidated at the frequencies most often used in MRI, and there is controversy in the literature regarding which mechanisms contribute. These mechanisms include ionic conduction, water dipole rotation, ion channel and cell surface polarization, and the Maxwell–Wagner effect. Using a commonly employed tissue dielectric model together with available experimental data, the relative contributions of different terms of the model to the real effective conductivity are estimated for seventeen different tissue types. The conductivity is one of the factors controlling the specific absorption rate (SAR) and radiofrequency (RF) heating during MRI under fixed electric field and thermal assumptions. This model-based approach suggests that the contribution of effective conductivity to heating in MRI at the molecular and cellular level under these assumptions is more complex than previously indicated in the MRI literature. The differences in polarization and, hence, heating mechanisms between tissue types are interpreted in terms of tissue structure and function.

Soft tissue artefacts (STA) are widely considered the most critical source of error in skin-mounted marker-based biomechanics, negatively impacting the clinical usability of skin-mounted marker-based data. Amongst the numerous solutions proposed to ameliorate STA, incorporating true bone movement—acquired using adaptive constraints, projection of markers, or various imaging modalities—has been reported to improve kinematic accuracy. However, efficacy of these proposed solutions reduces for different investigated motions and participants. In this study, we propose two novel marker projection schemes, wherein a cluster of markers are projected onto the bone surface during motion. Additionally, we investigate the feasibility of applying a novel, safe and cost-effective imaging modality—microwave imaging—to detect the location of the bone from the skin surface. Our results indicate that the novel marker projection schemes reduce kinematic errors significantly (by 50%) and improve the quality of computed kinematics (95% correlation to true bone movement). In addition, our results show that microwave imaging was able to detect the bone from the skin surface in both male and female anatomical models of varying body mass index scores and poses. We believe our findings underscore the generalisability and applicability of our proposed solution to reduce STA.

In this paper, a method of estimating the probability of susceptibility of a component on a circuit board to electromagnetic interference (EMI) is presented. The integrated circuit electromagnetic compatibility (IC EMC) standard IEC 62132-4 enables the assessment of the susceptibility of an IC by determining the forward power incident on each pin required to induce a malfunction. Although we focus on IC susceptibility, the method might be applied to other components and sub-circuits where the same information is known. Building upon a previously established numerical model capable of estimating the average coupled forward power at the end of a trace of a lossless PCB trace for a known load in a reverberant environment, this paper updates the model by incorporating PCB losses and utilizes the updated model to estimate the distribution of coupled forward power at the package pin over a number of boundary conditions in a reverberant field. Thus, the probability of failure can be predicted from the known component susceptibility level, the length, transmission line parameters, and the loading of the track to which it is attached. To validate this numerical model, the paper includes measurements obtained with a custom-designed RF IC detector, created for the purpose of measuring RF power coupled into the package pin via test PCB tracks.

Understanding the shielding effectiveness (SE) of enclosures across different frequency ranges is crucial for electromagnetic compatibility (EMC) applications. While well-established methods exist for evaluating SE in the reverberant frequency range, the transition between reverberant and resonant behavior remains less explored. This paper investigates the shielding performance of a brass enclosure containing Transmission Line Representative Contents (TL ReCos) across the reverberant, transition, and resonant frequency regions. The study employs a mechanically stirred reverberation chamber (RC) to analyze the SE response using a combination of wall-mounted and internal monopole antennas. Results confirm the existence of a transition frequency region with change in field distribution and SE behavior. The findings highlight how variations in frequency, internal contents, and measurement positions influence SE, providing valuable insights for enclosure design and EMC testing.

This paper presents a novel technique for the measurement of complex permittivity of dielectric materials using samples of arbitrary shape and size. Traditional methods for the use of measuring dielectrics have historically required either large, flat samples of a material, or the material to be in powder form. This is limiting when it comes to modern applications, or in the study of archeological objects. Our approach, based on Resonant Cavity Perturbation theory (RCP), allows for the measurement of small, irregularly shaped samples by combining perturbations from three orthogonal modes in a cuboid cavity. We validate this technique by measuring various materials such as polymers and woods, the results of which demonstrate the effectiveness of the technique in providing reliable dielectric readings at microwave frequencies. This method may be particularly useful in the nondestructive characterization of archeological objects, or in the characterization of new materials.

This article describes the development and testing of a suite of high-voltage pulse antennas for IEMI susceptibility testing. The antennas are designed to operate with pulses up to 33 kV from a common solid state double exponential pulse generator, and to be light enough to operate on a standard EMC test mast. A broadband (hyperband) antenna intended to transmit the full pulse spectrum and two resonant (mesoband) antennas to produce damped sinusoidal pulses are presented. The antennas were prototyped using full wave numerical modelling and tested in an anechoic chamber in the frequency domain and with a high voltage pulse generator.

Incorporating actual bone movement in kinematic pipelines has shown to reduce the influence of soft tissue artefacts (STA), a critical source of error, in clinical biomechanical analysis. Ultrasound imaging, a non-ionising and cost-effective imaging modality, has been extensively integrated in biomechanics to locate the underlying bone. However, limitations of needing a probe to be held at the location to be imaged and the need for coupling liquid, impedes their widespread applicability. In this study we explore the feasibility of applying another non-ionising and cost-effective imaging modality, microwave imaging, in biomechanics. By collecting data, from both simulated and experimental tissue-mimicking phantoms, under conditions aimed to emulate a wearable system, our results indicate that the underlying bone can be detected from the skin surface using microwave imaging. We believe our findings support the fidelity of microwave imaging as an alternative imaging modality to ultrasound imaging and underscore the need for further research in integrating microwave imaging in biomechanics.

This paper investigates the shielding effectiveness (SE) of reverberant enclosures containing electronic systems susceptible to electromagnetic interference (EMI). The approach is based on the Power Balance technique that requires values for transmission cross sections (TCS) of enclosure apertures and absorption cross sections (ACS) of enclosure internal walls and enclosure contents. Previous work has demonstrated this technique in principle for enclosures with low SE and a single simple aperture. The new approach extends the applicability of SE measurements to enclosures with various aperture shapes and sizes. Values of TCS and ACS are extracted in each case. Experimental results, conducted in a mechanically stirred reverberation chamber, show improved SE predictions, reaching up to 50 dB for enclosures with multiple complex apertures. The technique demonstrates enhanced accuracy and flexibility, crucial for designing robustly shielded electronic equipment.

In this paper, we discuss the design of an RF IC detector with eight channels connected to the package pins, designed to determine the incident RF power on each pin. Some of these channels possess different sensitivity levels based on the amplification circuit block they use. A PCB test bench with test tracks has been designed to allow the measurement of RF power coupled to the detector IC pins when illuminated by a RF source. Our discussion will also encompass the applications of the RF IC detector in detecting stochastic EM fields in reverberant or equivalent real-world environments. The key contribution in this paper is the design of RF IC detector which has these applications.

Imaging of the bone is an important clinical tool in detecting fractures, determining loss of bone density and in improving movement and gait analysis, with visualisation predominantly performed using ionising imaging. Microwave imaging, an alternative non-ionising imaging modality, has shown promising results in analysing bone density variation and in determining the presence of tears in joint tissues. In this study, we aimed to detect the location of the bone in the leg using radar-based microwave imaging. Confocal imaging algorithms were applied to scattering data acquired from simulated wearable antennas on a male human model without the use of a coupling liquid. We successfully detected both thigh and shin bones, with a localisation error of 2.5 cm, 0.91 cm and 1.34 cm for the femur, tibia and fibula centres respectively. Notably, these errors are in line with tumour detection errors. Our methodology and results illustrate a safe, easy-to-implement and simple pipeline using off-the-shelf antennas and algorithms to determine bone position using wearable sensors. We believe this technique has wide ranging applications, particularly in improving the accuracy of clinical movement analysis systems.

Interference analysis and prediction in integrated circuits (ICs) is of significant interest to the Electromagnetic Compatibility (EMC) community. In this paper, an easy method is introduced to estimate the level of RF interference coupled into ICs through the package. Although IC packages are in different forms with large number of pins, the presented analysis method provides a general solution and greatly shortens the computation time by creating a simplified model with consideration of the cross coupling between pins. The expected voltage range at the outer ends and inner ends of the pins are also investigated for resistive loads. The levels of energy coupled into PCB traces and packages are also compared for immunity analysis.

This paper shows that the Shielding Effectiveness of a printed circuit board shield (PCBS) varies depending on the shield’s external environment when the circuit board level shield is installed within a larger external enclosure. A reverberation chamber based technique is demonstrated that allows the underlying Shielding Effectiveness of the circuit board level shield to be evaluated along with an estimate of its expected variability due to the external enclosure.

The human body absorption cross section (ACS) is important in nonionizing radiation dosimetry, but it is always hard to accurately evaluate the ACS of an individual from his or her morphological parameters, such as height and weight. To obtain an empirical formula that can evaluate the ACS from morphological parameters, 48 subjects with different morphological parameters were measured from 1 to 16 GHz in a reverberation chamber. The ACS was extracted from the power delay profile. This has the advantage of not requiring antenna radiation efficiency, and it has not been previously used in a wideband group study like this. The accuracy of the ACS measurement is demonstrated by comparison with the ACS of a spherical model with known structure and material, and the mean absolute percentage error of the sphere measurement is just 3.4%. Statistical analysis shows that the body surface area (BSA) has the strongest correlation with the ACS among all the morphological parameters; therefore, we present a new empirical ACS formula as a function of BSA and frequency. This will be of interest to those considering dosimetry, and in computing the effect of human body absorption on radio propagation in vehicles and other structures.

Predicting the probability of susceptibility to electromagnetic interference for a system would be of significant interest to the EMC community. In this paper, we consider the coupling of electromagnetic energy into printed circuit board (PCB) traces and how it relates to the power balance model of shielding effectiveness. We show results of some measurements of the absorption cross-section of a load on a PCB trace and compare them with previously published results.

Stochastic electromagnetic fields coupling to printed circuit board (PCB) traces are important to the understanding of electromagnetic compatibility at high frequencies when the circuits or systems are electrically large. In this article, it is studied both numerically and analytically, and the factors affecting the absorbed power are investigated. We present new methods to determine the level of coupling on PCB traces or other transmission lines on a dielectric substrate. A Monte Carlo method is applied to generate random uniform fields, and the quasi-TEM transmission line model is employed to compute the response of the trace for each plane wave numerically. In the analytical method, the closed-form expressions of the zero-order and the first-order approximations are established for the PCB trace. Based on the first-order approximation method and the numerical results, a computationally efficient empirical method is developed to estimate the power received. The absorbed power increases with frequency in the electrically short case after which multiple resonances can be seen. The absorbed power in the matched case is neither the largest nor the smallest among all the cases. It increases with the square of the substrate height but decreases with the permittivity of the substrate.

PurposeProvide a proof of concept for the potential of using a novel RF resonant cavity device for accurately and repeatedly measuring fat and fat‐free masses in phantom infants.Materials & MethodsDesign, construct, and characterize an RF resonant cavity with dimensions compatible to holding an infant. The cavity was characterized using spherical phantoms of 0%fat, 50% fat, and 100% fat to empirically calibrate shifts in resonant frequency. The phantoms were constructed using emulsions of bovine lard, water, and dish soap inside spherical containers which do not interact with the electric field. The calibration phantoms were compared with a phantom of a test sample to assess the ability of the resonant cavity perturbation technique for measuring body composition.ResultsPhantoms of distinct %fat (0%, 50%, and 100%) were used to calibrate the resonant cavity for measuring body composition. The calibration phantoms were used to create calibration lines of unique %fat and were compared to a 475‐mL sample of unknown %fat as a measure of how accurate the resonant cavity technique is for measuring body composition.ConclusionA 475 mL test sample was used to examine the robustness of the RCP technique. The sample was 25% fat and had a fat mass of () g. The measured fat mass from the RCP technique was g, or a 2% difference. The resonant cavity perturbation technique provides an accurate and repeatable measurement of fat mass in spherical phantoms and suggests the technology might be an effective obesity research tool for infants. Future studies will focus on extending the work to more complex anthropomorphic shapes.

t The power balance technique for the prediction of shielding effectiveness of reverberant enclosures is fast and simple to use. However, it assumes a uniform field in the enclosure, which has been shown to be incorrect in the presence of dissipative contents. The diffusion model is a generalization of the power balance method that can account for the field inhomogeneity due to the presence of losses with much lower computational effort than a full-wave solver. Evaluation of a two-dimensional diffusion model produced promising results compared to physical measurements. Here, we present a three-dimensional (3-D) diffusion model applied to an enclosure with an aperture and dissipative contents. Comparisons between the 3-D diffusion model, measurements, and a full-wave solver suggest that it is able to account for the variation of the electromagnetic field due to dissipative contents with far less computational effort than full-wave solvers. The diffusion model allows rapid solution of the shielding effectiveness of enclosures with dissipative contents and arbitrary geometries and reduces the time to model equipment enclosures from hours to minutes, while still determining the variation of field strength due to contents. In addition, the method may help predict field inhomogeneity in reverberation chambers.

This paper presents calculated and measured Shielding Effectiveness data for shielded enclosures operated in the frequency range where the enclosure is reverberant. The calculated data are obtained from component measurements and are calculated using the Power Balance technique. The Shielding Effectiveness of the different cavities of an enclosure partitioned by stacked circuit cards is obtained.

Dielectric measurements provide valuable information about the properties of materials, and could be used to classify and identify the source of objects in fields such as archaeology. Current methods of identification are all partly destructive, so an innovative electromagnetic method developed by the authors, based on resonant cavity perturbation (RCP), provides an attractive, non-destructive alternative. A problem with traditional RCP is that the changes in frequency and Q-factor vary with the object's shape; however, we overcome this by creating a replica of the object, from a material whose dielectric properties are known. Then, by combining three separate perturbations with orthogonal field directions, due firstly to the object and then to its replica, we eliminate the shape dependency, and thus determine the object's dielectric constant and loss factor. After developing the theory of this novel DRM technique, we demonstrate the principle using a set of geometric shapes made in both polytetrafluoroethylene and a 3D printed material. Further measurements then enable second-order terms to be included in the model, improving its accuracy. Finally, DRM is shown to be capable of distinguishing two irregularly shaped objects of different materials. Potential applications of DRM include determining the provenance of pottery, glasses and flints, and distinguishing ivory from bone. These would be of interest to customs and environmental agencies, as well as museum curators and archaeologists.