Antennas and other electromagnetic applicators in biology andmedicine

Medical and biological applications of antennas can be classified into two broad groups: (1) therapeutic and (2) informational (including diagnostics and measurement of material electromagnetic (EM) properties). Most of these applications involve EM coupling into or out of the body which requires a device such as an antenna or other applicator. A common characteristic of many applications is the difficulty of coupling EM energy into the interior of the body without damaging the surface. Rapidly increasing computing power and new developments in numerical EM techniques are expected to have a great impact on the use of EM devices in medicine and biology     

A Coaxial Microwave Applicator for Direct Heating of Liquids Filling Chemical Reactors

A coaxial microwave applicator radiating in a liquid medium contained inside a chemical reactor is described. The applicator consists of an insulated asymmetrical dipole antenna that radiates almost isotropically. Hence, it appears well suited to directly heat the medium that fills the vessel, making it unnecessary to use a microwave oven as currently done in microwave assisted chemistry. The electromagnetic (EM) properties of the insulated dipole antenna emitting in high permittivity lossy media are first reviewed to define the applicator design criteria. A 3-D numerical EM solver is then employed to analyze the radiation of the applicator in the surrounding medium taking into account the whole structure of the reactor. Safe operations are always assured by the proper design of the applicator-vessel mechanical connection that drastically reduces unwanted stray radiation. The agreement between the theoretical analysis and the experiments performed is good, thus confirming that the coaxial applicator compares favorably with the traditional methods of activation, which use a single or multimode resonant EM cavity.     

A Direct-Contact Microwave Lens Applicator with a Microcomputer-Controlled Heating System for Local Hyperthermia

A direct-contact lens applicator for local microwave hyperthermia is proposed and developed with a computer-controlled microwave heating system. The applicator is a practical one that can converge the radiated electromagnetic field to deposit its energy deep in human tissues. The experimental results, which agree well with the theoretical ones, show that the applicator which operated at 2450 MHz could heat at twice the depth at which a simple and conventional waveguide applicator could heat. The experimental results using a developed computer system that supplies microwave energy and circulated cooling water to the developed applicator show that the fluctuations of temperature at the heating location in the human tissue model were maintained within +-0.3° C of the set temperature. The results of the phantom model and the animal experiment using the system with the applicator show that the maximum depth of noninvasive heating was more than 30 mm below the surface. These results are available for the clinical hyperthermia treatment of cancer.     

Numerical computation of fat layer effects on microwave near-fieldradiation to the abdomen of a full-scale human body model

Numerical computation results of fat layer effects on the microwave near field radiation to the abdomen of a three-dimensional (3-D) full-scale human body model are presented. The human body is modeled as a 3-D homogeneous muscle phantom with a fat layer covering the abdomen part. The dipole wire-antenna located proximate to the abdomen is used as the microwave radiation source at 915 MHz. This is to study the effects on hyperthermia heating by using the microwave applicator (at 915 MHz) or the near-field exposure from the proximate handset antenna to the human body at ISM band wireless communication band (902-928 MHz). Coupled integral equations (CIE) and the method of moments (MoM) are employed to numerically compute electromagnetic (EM) energy deposition specific absorption rate (SAR) from the radio frequency (RF) antenna applicator into the proximate fat layer covered abdomen. The antenna input impedance (proximate to the body), return loss (RL), and the resonant antenna length (proximate to the body) will also be numerically determined to increase the microwave power delivered into the body. The study of fat layer effects is important for microwave hyperthermia applications. It is also important for the investigation of the potential health hazard from the near-field radiation of a wireless communication antenna     

Contact flexible microstrip applicators (CFMA) in a range from microwaves up to short waves

Contact flexible microstrip applicator (CFMA) is a new light-weight microstrip applicator type for superficial and deep local hyperthermia. Typical specimens are developed for operation at frequencies of 434, 70, 40, and 27 MHz. The main common features of CFMA, namely, their flexibility and light weight, as well as their aperture dimensions slightly depend on the operating frequency. Two antenna types are used in CFMAs: inductive antennas with a radiating plane electrical dipole at microwaves, and coplanar capacitive antennas, providing depression of the normal component of the electrical field in the very high-frequency (VHF) and high-frequency (HF) range. The flexibility of the applicators enables one to conform them with curved surfaces. In a bent state of the applicators there arises a focusing effect of energy deposition in deeper located tissues due to linear polarization of the irradiated electromagnetic (EM) field, inherent in CFMA. All CFMA are integrated with silicon water boluses which serve as a matching element, so as a skin cooling agent. Due to this and to the predominance of the tangential electrical component in the radiated EM field, no fat overheating effects are noticed, as a rule. The aperture of the developed applicators overlap the range 160-630 cm2 providing effective heating field sizes (EFSs) 64-400 cm2, respectively. The most bulky CFMAs with an aperture of (21 x 29) cm2 operating at the frequency of 434 MHz weigh 0.8 kg and 2.5 kg at 27 MHz. Phenomenological analysis of the radiating systems, as well as experimental evaluation of the applicators are presented. CFMAs operating at frequencies of 434 and 40 MHz are used in clinical practice. CFMA at 70 and 27 MHz are subjected to laboratory clinical investigations.     

Design of a UHF applicator for rewarming of cryopreservedbiomaterials

The dielectric properties of cryopreserved biological tissue are discussed in relation to the problems which arise when EM fields are used for rapid rewarming. The UHF band is favored from two aspects: the avoidance of thermal runaway and the uniformity of heating inhomogeneous material. Various resonant cavity applicators are considered for efficient and uniform rewarming. The square-aspect TE 111 cylindrical applicator is favored principally because it allows variation of the E-field orientation as required during the warming profile. An appropriate kidney phantom organ is described. It is used to obtain measured values of the overall efficiency of a TE 111 applicator. The efficiency values are found to fall steadily with increasing temperature from 85% at -40 degrees C to 45% at the phase change, mainly due to the decreasing tan delta value of the phantom material.     

Initial results for automated computational modeling ofpatient-specific electromagnetic hyperthermia

Developments in finite-difference time-domain (FD-TD) computational modeling of Maxwell's equations, super-computer technology, and computed tomography (CT) imagery open the possibility of accurate numerical simulation of electromagnetic (EM) wave interactions with specific, complex, biological tissue structures. One application of this technology is in the area of treatment planning for EM hyperthermia. In this paper, we report the first highly automated CT image segmentation and interpolation scheme applied to model patient-specific EM hyperthermia. This novel system is based on sophisticated tools from the artificial intelligence, computer vision, and computer graphics disciplines. It permits CT-based patient-specific hyperthermia models to be constructed without tedious manual contouring on digitizing pads or CRT screens. The system permits in principle near real-time assistance in hyperthermia treatment planning. We apply this system to interpret actual patient CT data, reconstructing a 3-D model of the human thigh from a collection of 29 serial CT images at 10 mm intervals. Then, using FD-TD, we obtain 2-D and 3-D models of EM hyperthermia of this thigh due to a waveguide applicator. We find that different results are obtained from the 2-D and 3-D models, and conclude that full 3-D tissue models are required for future clinical usage.     

Molecular Patching Engineering to Drive Energy Conversion as Efficient and Environment‐Friendly Cell toward Wireless Power Transmission

Spatial electromagnetic (EM) radiation, big data, is both an opportunity and a challenge. Harvesting and converting waste EM energy for high‐efficient recycling has a huge significance in the energy field. Herein, a new and effective patching engineering method using conductive polymers to repair magnetic graphene (NF‐P) is proposed, tailoring the microstructure network controllably, including conductive network and relaxation genes. It realizes the precise tuning of EM property, and the EM response shows a significant increase of 52%. The energy transformation inside materials is surveyed, and a revolutionary mode of energy conversion is constructed, ingeniously utilizing the stored electrical energy and the converted heat energy inside the material with the theoretical utilization of absorbed EM energy up to 100%. The NF‐P patching network serves as a prototype for a potential cell device with the EM energy conversion improved by ≈10 times and effective bandwidth increased by 13 GHz that covers the entire research frequency band (2–18 GHz). This research opens up a new idea for energy utilization inside materials, providing a novel and effective path for harvesting, converting and delivering spatial EM energy.     

Microwave disinfestation of bulk timber.

In this paper a complete microwave system for bulk timber disinfestation is developed and tested. A commercial FEM simulator has been used to design the applicator, looking for structures providing uniform field distributions, which is a factor of capital relevance for a successful treatment. Special attention has also been given to the reduction of electromagnetic energy leakage. A dual polarized cylindrical applicator with a corrugated flange has been designed. The applicator has also been numerically tested emulating some real-life operating conditions. A prototype has been built using two low-cost magnetrons of 900 W and high power coaxial cables and it has been tested inside a shielded semianechoic chamber. The tests have been carried out in three stages: validation of the applicator design, determination of the lethal dosage as a function of the insect position and the maximum wood temperature allowed and statement of safe operation procedures.     

Radiation-Type Metasurfaces for Advanced Electromagnetic Manipulation

Manipulating the phase, polarization, and energy distribution of electromagnetic (EM) waves has facilitated numerous applications. Nowadays, metasurface provides an innovational scenario to carry out more promising and advanced control of EM waves. However, it is a great challenge to manipulate polarization, phase, and energy distribution simultaneously with a low profile. Herein, a class of single-layer radiation-type metasurfaces to achieve advanced EM manipulation is proposed. Desired EM functions can be achieved based on the geometric phase and resonant phase. Such metasurfaces enable the capability to manipulate arbitrary phases and linear polarization states simultaneously. Moreover, arbitrary energy distributions can be controlled. As examples of potential applications, three advanced EM functional devices are presented: a novel multiple-input multiple-output antenna with efficient crosstalk suppression and information encryption, an energy-controllable router, and a metasurface holographic imaging based on power transmission algorithm, respectively. The proposed strategy may open up an alternative way of controlling EM waves with advanced performance and minimalist complexity. Moreover, it may lead to advances in information encoding and cryptography.     

A Diathermy Applicator for the Irradiation of Rat Brain

A direct contact microwave applicator, constructed of dielectric-loaded J-band waveguide, was designed for local irradiation of the rat head with 2450 MHz CW microwaves. A stereotaxic method was used to achieve precise and reproducible orientation of the Applicator with the animal's head. Calorimetric measurements of specific bsorption rate, watts/kg, for the whole head indicated that approximately 62 percent of the net power applied to the applicator is absorbed in the head, and that a reproducible exposure condition could be achieved from one animal to the next. Thermographic pictures were taken of the bisected rat head immediately after exposure, and showed that the maximum rate of energy absorption took place within the brain, in the thalamus and mesencephalon.     

Latch Applicator for Efficient Delivery of Dissolving Microneedles Based on Rapid Release of Elastic Strain Energy by Thumb Force (Adv. Funct. Mater. 11/2023)

Dissolving microneedle (DMN) is an attractive alternative to parenteral and enteral drug administration owing to its painless self-administration and safety due to non-generation of medical waste. For reproducible and efficient DMN administration, various DMN application methods, such as weights, springs, and electromagnetic devices, have been studied. However, these applicators have complex structures that are complicated to use and high production costs. In this study, a latch applicator that consists of only simple plastic parts and operates via thumb force without any external complex device is developed. Protrusion-shaped latches and impact distances are designed to accumulate thumb force energy through elastic deformation and to control impact velocity. The optimized latch applicator with a pressing force of 25 N and an impact velocity of 5.9 m s⁻¹ fully inserts the drug-loaded tip of the two-layered DMN into the skin. In an ovalbumin immunization test, DMN with the latch applicator shows a significantly higher IgG antibody production rate than that of intramuscular injection. The latch applicator, which provides effective DMN insertion and a competitive price compared with conventional syringes, has great potential to improve delivery of drugs, including vaccines.     

Atomic-Molecular Engineering Tailoring Graphene Microlaminates to Tune Multifunctional Antennas

Atomic-molecular engineering is an effective way to accurately tailor the microstructures and components of materials at the micro-nano scale, which can be applied to flexibly manipulate their electromagnetic (EM) response. Herein, graphene microlaminates with multi-layer structure are fabricated by atomic cluster engineering and oxidative molecular layer deposition for the first time. The microlaminates enable a tunable EM loss (from 0.93 to 3.94 for imaginary permittivity and from 0.17 to 0.25 for imaginary permeability) by changing poly(3,4-ethylenedioxythiophene) cycles, and the attenuation constant reaches 160. On this basis, multifunctional antennas are conceived, achieving frequency-selective response that enables steady harvest of > 90% of EM energy from signal source, and tactfully recycling waste heat energy and mechanical energy. This study will furnish a new horizon for information transmission and artificial intelligence in the future.     

Use of the impedance method to calculate 3-D power depositionpatterns for hyperthermia with capacitive plate electrodes

We have used the three-dimensional impedance method to calculate the power deposition in the human pelvic region due to a radio frequency current at 13.56 MHz applied through round or oval capacitive-plate applicators. We compare the energy deposited in several tumor sites when energy is applied using a variety of applicator sizes, locations, and boluses of various conductivities. We show detailed maps of the power deposition in these cases for selected regions of the body and suggest useful configurations of applicators for heating tumors in several locations in the body.     

Development and Testing of a 2450-MHz Lens Applicator for Localized Microwave Hyperthermia (Short Paper)

A new type of applicator with a convergent lens for localized microwave hyperthermia is developed. A lens applicator of direct contact type was designed to conduct actual and progressive experiments with phantoms of simulated fat and muscle tissues heated at 2450 MHz. The experimental results showed that the heating power penetration depth increased 40 percent with this applicator as compared to a simple rectangular waveguide applicator with the same size aperture that had generally been used for microwave hyperthermia. Our applicator had a concave-shaped aperture and was designed to contact well with the heating medium whose shape was cylindrical like a human body.     

Em Local Heating with HF Electric Fields (Comments)

The above paper recently described a synthesis procedure that is intended for use in designing multisection capacitor-plate applicators for treatment by hyperthermia. The distribution of potentials on the subelectrodes is determined in order to obtain a specified pattern of energy deposition. While the derivation in that paper appears to be sound, considerable care must be used if the procedure is to be applied for the design of a practical applicator for use in patient treatment.     

Electromagnetic Response and Energy Conversion for Functions and Devices in Low‐Dimensional Materials

Low‐dimensional materials have been long sought after for their particular electromagnetic (EM) functions, with promising applications in EM wave absorbing and shielding, communicating and imaging, sensing and detecting, driving and actuating, etc. Herein, across the whole EM spectrum, low‐dimensional EM functional materials and devices are highly focused on. The crystal engineering and function‐guiding features addressed relate to crystal and electronic structures, EM responses and properties, energy conversion, as well as EM wave absorbing and shielding. Moreover, insight is given into this rapidly broadening field, the main challenges are proposed and future directions are predicted.     

Electromigration in sputtered copper film on plasma-treated hydrogen silsesquioxane dielectric

Electromigration (EM) damage is one of the major causes for the failure of interconnects. Plasma treatment, such as dry etching, is frequently employed in the fabrication of multilevel interconnection patterns. This work investigates the hydrogen silsesquioxane (HSQ) and copper integrated systems and the effect of H₂ plasma treatment on the EM of Cu. Hydrogen plasma bombardment induces a rough HSQ surface and results in a coarse morphology of the Cu film deposited on HSQ. The crystallographic texture of Cu is also affected by the plasma treatment. A decrease in the Cu I(111)/I(200) peak ratio is observed for a specimen treated with H₂ plasma. The activation energy for EM in Cu and the EM lifetime of the Cu interconnect decreases with an increased degree of plasma treatment. The activation energies obtained, ranging from 0.76 eV to 0.94 eV, suggest that the electromigration in copper proceeds via an interfacial diffusion path. Possible mechanisms for the effects of plasma treatment are explored. The rough surface and the retarded Cu (111) orientation induced by H₂ plasma bombardment are the major causes for the decrease of activation energy and EM lifetime.     

人体吸收电磁能量与入射方向和极化的关系

本文讨论了用时域有限差分法计算在平面电磁波照射下人体对电磁能量的吸收问题。计算了各种入射方向和极化条件下非均匀块状人体模型中的局部比吸收率(SAR)分布。计算结果表明,人体并不总是在正面入射时吸收能量最多;同时还表明,局部比吸收率比平均比吸收率更值得重视,因为局部吸收率的最大值往往比全身平均值大几倍到十几倍。本文的计算结果丰富了人们在人体电磁剂量学方面的知识。     

THE RELATIONSHIP BETWEEN THE EM ENERGY ABSORPTION OF HUMAN BODY AND THE INCIDENT DIRECTION AND POLARIZATION OF PLANE WAVE

The problems of EM energy absorption of human body irradiated by plane wave arediscussed by the Finite-Difference Time-Domain(FD-TD)method.The local Specific AbsorptionRates(SARs),the whole-body average SARs and the layer average SARs for the inhomogeneousblock model of human body with different incident direction and different polarization of theincident waves are calculated.The results show that the appearance of maximum EM energyabsorption is not always at the situation of the front incidence and the local SARs are moreimportant for the interaction of the EM fields with human body.All results provide more infor-mation about the electromagnetic dosimetry for human body.