Receiving Loop Antenna Research Articles

Enhanced RF Energy Harvesting System Utilizing Piezoelectric Transformer.

RF energy harvesting converts ambient signals into electrical power, providing a sustainable energy source. This study demonstrates the use of a piezoelectric transformer for efficient RF energy harvesting. In this work, a piezoelectric transformer (PT) is employed as a high-gain, efficient inverting amplifier to enhance RF wireless energy harvesting. The PT, composed of lead zirconate titanate (PZT), is placed after the receiving loop antenna, with its output connected to an AC-to-DC converter circuit. Maximum harvested power was observed at the PT's resonance frequency of 50 kHz, with an optimal load of 40 kΩ. The system, comprising the antenna, transformer, and rectifier circuit, continues to resonate at 50 kHz, as confirmed by input impedance measurements, demonstrating stable and effective performance. The overall system efficiency was characterized to be 88%.

Measurement of induced currents in radio frequency magnetic fields based on near field antenna perturbations

A measurement system is developed utilizing electromagnetic compatibility test equipment for the study of induced current in conductive materials subjected to radio frequency (RF) magnetic field strengths similar to the 1.5 T magnetic resonance imaging (MRI) B1 magnetic field at ∼65 MHz. The intent of developing such a system was to produce μT range RF magnetic fields in the laboratory to facilitate characterization of induction in conductive materials with modified surface electromagnetic properties to address unintended eddy current issues like Joule heating caused by implanted devices during MRI. A Helmholtz coil (HHC) is used as the RF magnetic field source, and the radiated field is monitored using a receiving loop antenna positioned coaxially outside the HHC. The measurement system operates in continuous wave and pulsed wave modes. Analytical models of the system were derived, which calculate the spatial distribution of RF magnetic flux and the induced current within a coaxially located sample in the transmission path between the HHC and receiving (R/C) loop from output voltage measurements at a single coaxial position. Induced currents were evaluated at multiple flux densities and at different frequencies, showing direct proportionality over the flux densities tested. Induced current results recorded in samples of different sizes and electrical conductivities (ranging from 0.1 to 5.8 × 107 (Ω m)−1 produced changes, matching trends predicted by conductive, closed-loop antenna theory. Induced currents were also used with simultaneous temperature rise measurements to characterize the effective surface conductivity for wire with non-uniform properties at 65 MHz.

Control of whistler radiation efficiency of a loop antenna by generation of ambient magnetic field irregularities

Electrodynamic means for the control of loop antenna radiation efficiency in plasma is proposed, which can be used in the whistler frequency band. The method is based on the generation, without perturbing the plasma density, of localized ambient magnetic field irregularities in the vicinity of the antenna. In order to produce such irregularities, it is suggested to feed the antenna with additional dc current along with the rf current. Experiments performed in a large laboratory magnetoplasma showed that the generation of localized magnetic field enhancements provides the possibility of increasing the amplitude of the whistlers emitted by the loop antenna. Moreover, experiments have shown that the amplification of the whistlers’ signals from the receiving loop antenna fed with additional dc current is observed when a static magnetic field enhancement is generated in the vicinity of the receiver. The experimental data are in good agreement with the theoretical results obtained for comparatively weak ambient magnetic field perturbations.

Measurement of propagation velocity of bound electromagnetic fields in near zone

We start with the general approach based on conventional solutions to Maxwell’s equations and show that in the near zone of macroscopic electromagnetic sources the electromotive force produced in receiving loop antenna is intimately linked to the fundamental structure as well as to causal properties of the classical electromagnetic field as a superposition of bound and radiation components. As a consequence, we propose and implement a direct experimental procedure for the correct identification of retarded positions of bound field contributions on the oscilloscope time scale as a function of a distance from the emitting loop antenna. It provides unambiguous empirical information on causal characteristics of bound electromagnetic fields. According to the observation of no retardation inside the near zone of the emitting loop antenna, the experimental evidence for nonlocal properties of bound electromagnetic fields is reported.

A Receiving Loop Antenna for Super-Broadband Pulsed Signals

A Receiving Loop Antenna for Super-Broadband Pulsed Signals

Numerical modeling of an enhanced very early time electromagnetic (VETEM) prototype system

In this paper, two numerical models are presented to simulate an enhanced very early time electromagnetic (VETEM) prototype system, which is used for buried-object detection and environmental problems. Usually, the VETEM system contains a transmitting loop antenna and a receiving loop antenna, which run on lossy ground to detect buried objects. In the first numerical model, the loop antennas are accurately analyzed using the method of moments (MoM) for wire antennas above or buried in lossy ground. Then, the conjugate gradient (CG) methods, with the use of the fast Fourier transform (FFT) or MoM, are applied to investigate the scattering from buried objects. Reflected and scattered magnetic fields are evaluated at the receiving loop to calculate the output electric current. However, the working frequency for the VETEM system is usually low and, hence, two magnetic dipoles are used to replace the transmitter and receiver in the second numerical model. Comparing these two models, the second one is simple, but only valid for low frequency or small loops, while the first modeling is more general. In this paper, all computations are performed in the frequency domain, and the FFT is used to obtain the time-domain responses. Numerical examples show that simulation results from these two models fit very well when the frequency ranges from 10 kHz to 10 MHz, and both results are close to the measured data.

Computation of electromagnetic field scattered by three-dimensional permeable objects

A surface integral equation is derived for electromagnetic scattering by highly conducting permeable objects of irregular shapes and solved, numerically, using the method of moments. The analysis make uses of the impedance boundary condition to simplify the formulation and reduce the computation time and memory requirements associated with the method of moments. Results for the induced voltage across a receiving loop antenna are presented. The computed and exact theoretical results for spherical objects are in good agreement. >

General formulas for calculating magnetic field at a receiving loop placed at an arbitrary position from a radiating loop in a shielded room

The standard magnetic field radiated by a small loop antenna is used for sensitivity testing of radio receivers. To avoid interference from external sources, the test is often carried out in a shielded room. A formula to obtain the intensity of the magnetic field at the receiving loop, when a small radiating loop antenna and the receiving loop antenna are placed at random locations in a shielded room, is derived. The convergence of the formula is analyzed. Using the formula, an equation is derived which expresses the shielded room error or the effect of the room on the standard magnetic field. The correlations between the calculated values of the error and the measured results are reported. >

Studies of magnetic field for transmitting and receiving loop antenna placed in a copiane

A near-zone magnetic field generated by a small transmitting loop antenna has been used for the calibration of a radio receiver and a field intensity meter. In the calibration, the transmitting and receiving loops are sometimes located in a coplane with each other. In such a case, a theory to obtain magnetic-field strength is derived by using an infinite series. The errors due to treating the infinite series as a finite series and due to simplifying frequency terms are estimated. The applicable regions of the theory are shown as functions of loop spacing, loop radii, and wavelength. The differences between theoretical values and measured values were within ±0.1 dB at loop spacings of 25 to 60 cm for frequencies from 10 to 30 MHz.

Theory of Loop Antenna with Leakage between Turns

The theory of the receiving loop antenna of two turns with distributed leakage, conductive and reactive, is developed. Equations are derived for currents and voltages along the loop and at the terminals. For terminal currents and voltages the effect of leakage may be expressed by means of a single function H, and the loop may be represented by an equivalent two-mesh circuit of lumped constants. The effect of leakage upon the Q of a loop is discussed, and methods are described for the precise measurement of Q in the presence of leakage. Experimental applications are described.