Clutter Suppression for Indoor Self-Localization Systems by Iteratively Reweighted Low-Rank Plus Sparse Recovery.

Self-localization based on passive RFID-based has many potential applications. One of the main challenges it faces is the suppression of the reflected signals from unwanted objects (i.e., clutter). Typically, the clutter echoes are much stronger than the backscattered signals of the passive tag landmarks used in such scenarios. Therefore, successful tag detection can be very challenging. We consider two types of tags, namely low-Q and high-Q tags. The high-Q tag features a sparse frequency response, whereas the low-Q tag presents a broad frequency response. Further, the clutter usually showcases a short-lived response. In this work, we propose an iterative algorithm based on a low-rank plus sparse recovery approach (RPCA) to mitigate clutter and retrieve the landmark response. In addition to that, we compare the proposed approach with the well-known time-gating technique. It turns out that RPCA outperforms significantly time-gating for low-Q tags, achieving clutter suppression and tag identification when clutter encroaches on the time-gating window span, whereas it also increases the backscattered power at resonance by approximately 12 dB at 80 cm for high-Q tags. Altogether, RPCA seems a promising approach to improve the identification of passive indoor self-localization tag landmarks.

Planar Microwave Sensor for Theranostic Therapy of Organic Tissue Based on Oval Split Ring Resonators.

Microwave sensors in medical environments play a significant role due to the contact-less and non-invasive sensing mechanism to determine dielectric properties of tissue. In this work, a theranostic sensor based on Split Ring Resonators (SRRs) is presented that provides two operation modes to detect and treat tumor cells, exemplary in the liver. For the detection mode, resonance frequency changes due to abnormalities are evaluated, and in the treatment mode, microwave ablation is performed. The planar sensor structure can be integrated into a needle like a surgery tool that evokes challenges concerning size limitations and biocompatibility. To meet the size requirements and provide a reasonable operating frequency, properties of oval shaped SRRs are investigated. By elongating the radius of the SRR in one direction, the resonance frequency can be decreased significantly compared to circular SRR by a factor of two below 12 GHz. In order to validate the detection and treatment characteristics of the sensor, full wave simulations and measurements are examined. Clear resonance shifts are detected for loading the sensor structures with phantoms mimicking healthy and malignant tissue. For treatment mode evaluation, ex vivo beef liver tissue was ablated leading to a lesion zone 1.2 cm × 1 cm × 0.3 cm with a three minute exposure of maximum 2.1 W.

Network-Structured BST/MBO Composites Made from Core-Shell-Structured Granulates.

A finite element method (FEM)-based simulation approach to predict the tunability in composite materials was developed and tested with analytical data. These tests showed good prediction capabilities of the simulation for the test data. The simulation model was then used to predict the tunability of a network-structured composite, where the dielectric phase formed clusters in a paraelectric network. This was achieved by simulating a reciprocal core-shell unit cell of said network. The simulation showed a high tunability for this network model, exceeding the tunability of the analytically evaluated layered, columnar, and particulate model. The simulation results were experimentally verified with a Ba0.6Sr0.4TiO3/Mg3B2O6 (BST/MBO) composite, where core-shell granulates were made with a two-step granulation process. These structured samples showed higher tunability and dielectric loss than the unstructured samples made for comparison. Overall, the structured samples showed higher tunability to loss ratios, indicating their potential for use in tunable radio frequency applications, since they may combine high performance with little energy loss.

Broadband Microwave Electroporation Device for the Analysis of the Influence of Frequency, Temperature and Electrical Field Strength.

In this paper, a broadband microwave device for cell poration is presented, that enables the analysis of the relation between frequency, electrical field strengths and temperature for a successful cell poration. Electromagnetic-thermal coupled simulations in the frequency range from 1 GHz to 10 GHz show that the device reaches electrical field strengths of 100 V/cm and temperatures lower then 40°C. Electroporation experiments with adherent C2C12 mouse myoblast cells show successful uptake of an anti-histone γ -H2A.X nanobody at a frequency of 10 GHz. This MWP device allows the fast electro-poration of adherent cells. After 15 min, the cells show uptake of γ -H2A.X-specific nanobody while most of them survived.

Numerical Optimization of an Open-Ended Coaxial Slot Applicator for the Detection and Microwave Ablation of Tumors.

A multiobjective optimization method for a dual-mode microwave applicator is proposed. Dual-modality means that microwaves are used apart from the treatment, and also for the monitoring of the microwave ablation intervention. (1) The use of computational models to develop and improve microwave ablation applicator geometries is essential for further advances in this field. (2) Numerical electromagnetic-thermal coupled simulation models are used to analyze the performance of the dual-mode applicator in liver tissue; the sensitivity evaluation of the dual-mode applicator's sensing mode constrains the set of optimal solutions. (3) Three Pareto-optimal design parameter sets are derived that are optimal in terms of applicator efficiency as well as volume and sphericity of the ablation zone. The resulting designs of the dual-mode applicator provide a suitable sensitivity to distinguish between healthy and tumorous liver tissue. (4) The optimized designs are presented and numerically characterized. An improvement on the performance of previously proposed dual-mode applicator designs is achieved. The multiphysical simulation model of electromagnetic and thermal properties of the applicator is applicable for future comprehensive design procedures.

All-Oxide Varactor Electromechanical Properties Extracted by Highly Accurate Modeling Over a Broad Frequency and Electric Bias Range.

Since the dielectric permittivity of ferroelectric materials depends on the electric field, they allow designing switchable and continuously tunable devices for adaptive microwave front ends. Part of the ongoing research is the field of all-oxide devices, where epitaxial oxide conductors are used instead of polycrystalline metal electrodes, leading to epitaxial ferroelectric layers and resulting in high device performance. In particular, they allow engineering the acoustic properties separated from the electric ones due to the structural similarity between the dielectric and conducting oxide films. Two major results are reported in this work. First, a highly accurate model for the microwave impedance of ferroelectric varactors is derived that tracks the superposition of induced piezoelectricity and field extrusion into the substrate caused by thin electrodes. In difference to previous works, this model covers both a wide frequency and biasing range up to 12 GHz and 100 V/ [Formula: see text]. Second, the high model accuracy enables the determination of all relevant electric and mechanic properties based on a mere microwave characterization. This approach will be especially valuable when independent measurements of mechanical properties of the thin-film materials are impeded by a high integration of the devices. Though derived for all-oxide varactors, the presented model can as well be adapted for thin-film bulk acoustic wave resonators (FBARs) and varactors with conventional metal electrodes when eventual dead layers at the interface are modeled correctly.

Ex vivo validation of microwave thermal ablation simulation using different flow coefficients in the porcine liver.

The purpose of the study was to validate the simulation model for a microwave thermal ablation in ex vivo liver tissue. The study aims to show that heat transfer due to the flow of tissue water during ablation in ex vivo tissue is not negligible. Ablation experiments were performed in ex vivo porcine liver with microwave powers of 60 W to 100 W. During the procedure, the temperature was recorded in the liver sample at different distances to the applicator using a fiber-optic thermometer. The position of the probes was identified by CT imaging and transferred to the simulation. The simulation of the heat distribution in the liver tissue was carried out with the software CST Studio Suite. The results of the simulation with different flow coefficients were compared with the results of the ablation experiments using the Bland-Altman analysis. The analysis showed that the flow coefficient of 90,000 W/(K*m3) can be considered as the most suitable value for clinically used powers. The presented simulation model can be used to calculate the temperature distribution for microwave ablation in ex vivo liver tissue.

Theranostic microwave applicator suitable for minimal invasive therapy of malignant tissue.

A microwave applicator is presented that realizes the theranostic approach by providing two operation modes to detect and treat tumor cells, exemplary in the liver. The tool is based on a planar sensor structure with Split Ring Resonators (SRR) as key elements. For the detection, changes in dielectric properties caused by tissue abnormalities are evaluated by analyzing shifts in the resonance frequency of the SRR. For the treatment mode, the input power is amplified to the specific resonance frequency and microwave ablation is performed. The device is designed to fit into a needle like operation tool for minimal invasive therapies. From this requirement, challenges concerning size limitation, packaging, and bio compatibility can be derived. Therefore, novel shapes of the SRR and substrate materials are investigated by full wave simulations and measurements. Material models and phantoms mimicking dielectric properties of healthy and malignant tissue are introduced. Clear resonance shifts of 100 MHz are detected for loading the sensor with corresponding phantoms. In order to examine the treatment mode characteristics, thermal simulations and measurements exhibit a significant temperature increase up to 62 °C for an input power of 500 mW.

Dual mode microwave tool for dielectric analysis and thermal ablation treatment of organic tissue.

A dual mode tool design to analyze organic tissue and locally perform thermal ablation treatment is presented. The tool is made of an array of split-ring resonators. It can operate on a sensing mode to track the relative dielectric changes from the organic tissue and on a treatment mode to perform thermal ablation at different input powers. The measurements were done with phantoms of human tissue. The tool is able to focus a hot spot of approximately 0.2mm with a temperature of 109 °C at an input power of 10W.