Electromagnetic Field Focusing Research Articles

Enhancement of penetration of electromagnetic waves by field focusing applied to GPR detection

Ground penetrating radar (GPR) is limited by challenges such as signal attenuation and inadequate target detection in lossy dielectrics, prompting research on data processing algorithms to enhance detection capability. In this study, we propose a method for enhancing GPR detection capability based on electromagnetic field focusing (FF). The method involves calculating the phase difference attributable to the range difference between each antenna element and the focal point and compensating its feed phase accordingly. This approach effectively concentrates the energy of electromagnetic waves at the target area. Tapered slot antennas operating within the 2.5–8 GHz frequency band were employed for transmitting and receiving, thus facilitating algorithm verification and target detection. The synthetic aperture radar algorithm executed pulse compression and range migration on the received data, thereby intensifying the signal at the target object’s position and achieving double focusing. Notably, this study uniquely employs FF to enhance the penetrability of electromagnetic waves and augment the detection capability of GPR. Both simulation and experimental results demonstrated the effectiveness of the proposed method in improving the GPR imaging quality.

Novel Coil Transducer Induced Thermoacoustic Detection of Rail Internal Defects Towards Intelligent Processing

A novel resonant tri-coil transducer is proposed to induce thermoacoustic (TA) signals for detecting rail internal defects. It consists of a ferrite plate-backed tri-coil and its associated circuits, a shielding layer, and a three-dimensional printed enclosure for supporting and securing. General TA detection theory is illustrated to understand how to detect rail internal defects. For achieving electromagnetic (EM) field shaping and focusing, the physical structure of the proposed transducer is optimized. It reduces backward EM fields and interference. Then, an equivalent circuit model between the proposed transducer and the rail is constructed to analyze optimal power transfer efficiency as a function of distance and frequency. To validate the design concept, the proposed transducer is fabricated for inducing TA signals, and experiments are performed. Several engineered rail specimens (UIC-60E) with different types of defects are prepared. The induced TA waves are found to be compressional. With selected features, a support vector machine algorithm-based multinomial classifier model is trained and employed for intelligent processing. Then, the proposed transducer is integrated into the self-designed automatic rail monitoring system. Experimental results show that the self-designed system can achieve an accuracy rate of 96.4%, successfully identifying defects in defect classification. The proposed transducer has low cost in fabrication and maintenance, focused magnetic fields with a large lift-off distance and enhanced acoustic wave intensity. Compared to earlier version of the system, the spacing between the transmitter and the rail has been further increased.

A scale-critical trapped surface formation criterion for the Einstein-Maxwell system

In this study we show that, from arbitrarily dispersed initial data, both the focusing of electromagnetic fields and the concentration of gravitational waves could lead to the formation of trapped surfaces. We establish a scale–critical semi–global existence result from past null infinity for the Einstein–Maxwell system by assigning the signature for decay rates to both geometric quantities and Maxwell components. This result generalizes an approach of the first author in [4] on studying the Einstein vacuum equations to the physical Einstein-Maxwell system by employing additional elliptic estimates and geometric renormalizations and it also extends a result of Yu [18] and serves as the first scale-critical result for Einstein's equations coupled with matter.

ENZ-metamaterial–induced perfect transparency for the highly directive plano-concave lens

We propose an ENZ-metamaterial–based transparent sandwich design consisting of periodic slits in a metal screen integrated with ENZ metamaterials for the exploration of superior transmissions. An equivalent circuit is proposed to reveal the interactions between the slit array and ENZ metamaterials when electromagnetic fields are penetrating through, and indicates that the involvement of ENZ metamaterials with the frequency dispersion behaviors can create the perfect match for total transmissions. On this basis, we further propose the design of plano-concave lens with the non-uniform ENZ metamaterial interlayer and demonstrate the superior collimation and focusing of electromagnetic fields at specific frequency points with perfect transparency. These findings may initiate the quest for building up more advanced electromagnetic devices tailored to specific applications with extreme parameter metamaterials.

Local Asymptotics of Unfoldings of Edge and Corner Catastrophes

Using symbolic calculations, a method of local asymptotics is developed, which describes the diffraction focusing of electromagnetic and acoustic fields for edge and corner catastrophes. Explicit expressions are found for the unfolding coefficients, the functional module, and the phase of the traveling wave, when the family of primary (geometrical-optical) and secondary (edge) rays form focuses on the cuspoid $${\mathrm{\boldsymbol A}}_{\mathrm{2}}$$ type (simple edge catastrophe $${\mathrm{\boldsymbol F}}_{\mathrm{4}}$$ ), when the family of primary and secondary rays form focuses on the $${\mathrm{\boldsymbol A}}_{\mathrm{3}}$$ type (unimodal edge catastrophe $${\mathrm{\boldsymbol K}}_{\mathrm{4,2}}$$ ), as well as for a corner catastrophe $${\mathrm{\boldsymbol A}_{1}}^{4}$$ .

Features of the Use of Symbolic Calculations for Constructing Wave Field Local Asymptotics Using Catastrophe Theory

Base on symbol calculation a local asymptotic method is developed that describes the diffraction focusing of electromagnetic fields in the case when a family of primary (geometrooptical) and secondary (edge) rays form focusings of the cuspoid type A2 (wave catastrophe F4). Mathematical modeling of the unfolding coefficients and the traveling wave phase was performed. Explicit expressions for the parameters of unfolding are obtained.

Field Focusing for Implanted Medical Devices

In this paper, we present a novel method of electromagnetic field focusing applicable to 3D implantable devices. Focusing is achieved using two lines that guide the incident wave deeper into the body and concentrate it around their respective tips. The small gap between the tips of the lines provides constructive coupling and augments the focused field. Compared to the case where no lines are used, the focused power is 8 times and 16 times larger if one line and two lines are utilized, respectively. The proposed design can be modified to focus fields with arbitrary polarizations at different depths inside the body. We propose a method to create this focusing structure by extrusion inside the body using heat-activated polymer-based conductors.

Tight focusing of electromagnetic fields by large-aperture mirrors.

We derive nonparaxial input conditions for simulations of tightly focused electromagnetic fields by means of unidirectional nonparaxial vectorial propagation equations. The derivation is based on the geometrical optics transfer of the incident electric field from significantly curved reflecting surfaces such as parabolic and conical mirrors to the input plane, with consideration of the finite thickness of the focusing element and large convergence angles, making the propagation vectorial and nonparaxial. We have benchmarked numerical solutions of propagation equations initiated with the nonparaxial input conditions against the solutions of Maxwell equations obtained by vectorial diffraction integrals. Both transverse and longitudinal components of the electric field obtained by these methods are in excellent agreement.

Dipole pulse theory: Maximizing the field amplitude from4πfocused laser pulses

We present a class of exact nonstationary solutions of Maxwell equations in vacuum from dipole pulse theory: electric and magnetic dipole pulses. These solutions can provide for a very efficient focusing of electromagnetic field and can be generated by $4\ensuremath{\pi}$ focusing systems, such as parabolic mirrors, by using radially polarized laser pulses with a suitable amplitude profile. The particular cases of a monochromatic dipole wave and a short dipole pulse with either quasi-Gaussian or Gaussian envelopes in the far-field region are analyzed and compared in detail. As a result, we propose how to increase the maximum field amplitude in the focus by properly shaping the temporal profile of the input laser pulses with given main wavelength and peak power.

Electromagnetic field focusing by a plane multilayer structure with a Veselago medium

The focusing properties of a system of plane layers of a Veselago medium divided by vacuous intervals are investigated by the coordinate transformation method. The role of real and virtual foci in the mechanism of focusing by a multilayered lens is considered.

Application of the time reversal of electromagnetic fields to locate lightning discharges

In this paper, we propose a new method for locating lightning discharges. The proposed method is based on the time reversal technique introduced for acoustics in the early 1990s. By analogy to the derivations in acoustics, equations for the focusing of electromagnetic fields back to the source by time reversal are derived. We show that the wavefronts generated by back-propagating the time-reversed fields will add up in phase at the lightning strike location. Based on this observation, we present an algorithm to locate lightning discharges which requires at least three field sensors. The algorithm is illustrated and shown to be very efficient using numerically-generated fields for different cases and considering different numbers of sensors.

Subwavelength lateral confinement of microwave surface waves

Experimental verification of the “domino plasmon,” recently proposed by Cano et al. [Opt. Express 18(2), 754, (2010)] is presented. Using microwaves, it is demonstrated that this mode propagates along a periodic chain of metallic cuboids (“dominos”) and the dispersion of the mode is determined with results being compared to the predictions of analytical and numerical models. This mode is found to be surprisingly insensitive to the lateral width of the chain, even on a subwavelength scale. Having such tight confinement, “domino plasmons” show considerable promise for one-dimensional subwavelength guiding and focusing of electromagnetic fields.

Quasi-uniform excitation source for cascade enhancement of SERS via focusing of surface plasmons

A novel surface-enhanced Raman scattering (SERS) excitation source based on focusing of surface plasmons around the center hole of a metal disk for cascaded enhancement is put forward and studied theoretically. The device offers intense SERS excitation with quasi-uniformity and horizontal polarization over a comparatively large hole through the combination of electromagnetic field focusing and hole plasmon resonance. As revealed by finite-difference time-domain (FDTD) method, the intensity spectra and the characteristics of the near field for the wavelength range of 650-1000nm exhibit a number of enhancement modes. Electric field intensity of the optimal mode enhances the SERS signal inside the hole by over four orders. An analytical model was also developed to gain precise interpretation on FDTD results. Our model also reveals the possibility of achieving eight orders of enhancement by optimizing the scale of the disk. In addition to generation of highly optimized hot spots, the large active hole also offers potential applications in fluorescence enhancement and nonlinear spectroscopy.

Analytic study of electromagnetic-field focusing by a Veselago lens

Excitation of a 2D Veselago lens by a filamentary electric current is considered. Behavior of the features of the kernel of the integral representation of the lens field in the focusing region is analyzed. It is shown that, as the values of the lens’s constitutive parameters tend toward -1, degeneration of the forward and backward waves, which form the oscillation of the longitudinal resonance, is observed. Approximate analytic expressions for the components of the electric field in the focusing region are derived. Estimates of the dimensions of the spot near the lens focus are obtained.

Guiding and Focusing of Electromagnetic Fields with Wedge Plasmon Polaritons

We study theoretically electromagnetic modes guided by metallic wedges at telecom wavelengths. These modes are found to exhibit superior confinement while showing similar propagation loss as compared to other subwavelength guiding configurations. It is also shown that mode focusing can be realized by gradual modification of the wedge geometry along the mode propagation direction.

Electromagnetic field focusing instrument augments resection of meningiomas.

The electromagnetic field focusing (EFF) surgical instrument creates an oscillating electromagnetic field that induces eddy currents in the tissue, which converge at the point of contact. This energy creates a focal spark capable of vaporizing tissue. The EFF instrument was used to resect 17 meningiomas in 14 patients. The effectiveness of the EFF probe in resecting tumor tissue was compared with that of the Cavetron ultrasonic surgical aspirator (Model 100) in 11 patients. The EFF system was superior to the Cavetron ultrasonic surgical aspirator in tumor excision in all but two cases, in which the EFF grounding tip was poorly tuned. Surgical time and blood loss were reduced by subjective analysis in all but these two cases, especially in the rubbery or calcified meningiomas resistant to aspiration. No complications were directly attributable to use of the EFF. Drawbacks encountered with the EFF system include buildup of "char" on the tip, requiring scraping, and intense heat at the tip, which occasionally melted the insulating sheath, requiring replacement.

Endoluminal Thermal Occlusion of the Ureter with the Electromagnetic Field-Focusing Device

The authors attempted ureteral occlusion by means of heat application in nine ureters (24 sites) of New Zealand White rabbits with the electromagnetic field-focusing (EFF) device. The EFF device generates heat at the tip of a grounded probe by focusing eddy currents that have been induced within the tissues by an external radio-frequency field. The power settings were varied from 30 to 150 W. Heat was applied at multiple sites in each ureter. Immediate functional occlusion was seen in all nine ureters. Long-term complete occlusion was seen in six ureters at power settings ranging from 40 to 150 W, while long-term partial occlusion was seen in two ureters at 30-50 W. All sites at 30 W resulted in partial occlusions. Perforation of the ureter resulted in urinoma formation in one ureter at a site that was treated with 150 W. The EFF device can be used to endoluminally occlude the ureter by causing a fibrotic reaction to thermal injury. The effective power range for this application appears to be 40-100 W.

Bacteriophage ΦX-174 as an aerobiological marker for surgical plume generated by the electromagnetic field focusing system

The aerosol of surgical plume could be measured effectively with the use of bacteriophage ΦX-174 as a biological marker, in contrast to previous methodologies reported by others. Recovery of virus plaqueforming units was highest from hydrophobic polytetrafluoro-ethylene membranes compared to hydrophobic polycarbonate screen filters or polyvinylidene difluoride depth filters, indicating that the method of virus recovery strongly affects the utility of a virus as an aerobiological marker. With this new method, surgical plume was indeed found in significant amounts when cutting tissue phantoms made with agar containing virus. The Electromagnetic Field Focusing System was used, which is a new thermal surgical device. The nominal power setting did not appear to be a factor in the amount of virus recovered. However, when pulse modulating the power by adjusting the crest factor from 1·4 to 4·3, a measure of the duty cycle for power delivery which adjusted the device from its cutting to haemostatic mode, a nearly five-fold increase in surgical plume, as evidenced by the recovery of ΦX-174 plaque forming units, was seen. The data indicate that bacteriophage ΦX-174 can be used effectively as an aerobiological marker for aerosols generated during clinical procedures, and reinforce the need to use a safety vacuum during aerosol generating procedures. The availability of a safe and economical biological marker for aerosols from clinical procedures, which may lead to acquired infections in hospital personnel, makes evaluation of procedures and containment systems markedly easier. The data also indicates that surgical plume biohazard may be present in other techniques that employ pulse modulation including surgical lasers and electrocauteries.

Stereotactic microsurgical resection of intracranial tumors using the electromagnetic field focusing system.

The intense heat produced at the tip of the electromagnetic field focusing (EFF) probe at its point of contact with tissue can cut and vaporize tissue and coagulate blood vessels. As the probe is shaped like a bayonet and has a diameter of 0.3 mm at its tip, it can be used on deep structures through narrow openings, making it ideal for stereotactic craniotomy. Thirteen stereotactic craniotomy procedures using the EFF system were performed. Locations of the lesions were deep in the cerebrum, cerebellum and in the lateral ventricle. The system proved efficient with reduced blood loss and unobstructed view of deep structures. No complications resulted from the use of the system.

Intervascular Occlusion of Canine Renal, Splenic, and Vertebral Arteries Using Electromagnetic Field Focusing (EFF) Probe

Electromagnetic field-focusing (EFF) probe is a precision surgical and interventional tool. Use of the device produces maximum temperature in excess of 1800 degrees C by convergence of radio-frequency (RF) induced eddy currents in biological tissues. Applications of the EFF probe in angioplasty, aneurysm thrombosis, and neurosurgery have been previously reported. In the present work, the EFF probe was guided under fluoroscopic control and used to occlude renal, splenic, and vertebral arteries in dogs. The occlusion was typically accomplished with about one minute of RF power application. Histology of the treated vessel three to six weeks posttreatment showed total occlusion consisting of intimal and subintimal changes and organized thrombus in the lumen. This suggests that the EFF probe in comparison with other procedures is an inexpensive, relatively safe precision interventional tool for performing an occlusion for experimental and therapeutic purposes.