Multi-frequency Transmitter Research Articles

GaN-Based Dual-Mode Wireless Power Transfer Using Multifrequency Programmed Pulse Width Modulation

Multifrequency wireless power transfer (WPT) is advantageous in facilitating compatibility with different WPT standards. However, implementing a multifrequency transmitter often requires compromises in system size, complexity, power transfer capability, or output regulation. In this paper, a single-inverter-based dual-mode WPT system is proposed. The system employs a multifrequency programmed pulse width modulation scheme. This multifrequency modulated inverter can simultaneously generate and regulate 100-kHz and 6.78-MHz outputs, or multiple frequencies within ranges of 87–300 kHz, which facilitates the development of multistandard WPT technology for consumer electronics. The principle of the proposed modulation is illustrated, where two different frequencies are concurrently modulated using a programmed pulse train of square waveforms for power delivery, while eliminating certain harmonics. Design tradeoffs and constraints are examined through analytical circuit models. Finally, experimental results are provided to verify the method on a gallium-nitride-based WPT prototype.

Progressing from 1D to 2D and 3D near-surface airborne electromagnetic mapping with a multisensor, airborne sea-ice explorer

The polar ocean’s sea ice cover is an unconventional and challenging geophysical target. Helicopter electromagnetic (HEM) sea-ice thickness mapping is currently limited to 1D interpretation due to traditional procedures and systems. These systems are mainly sensitive to layered structures, ideally set for the widespread flat (level) ice type. Because deformed sea ice (e.g., pressure ridges) is 3D and usually also heterogeneous, ice thickness errors up to 50% can be observed for pressure ridges using 1D approximations for the interpretation of HEM data. We researched a new generation multisensor, airborne sea ice explorer (MAiSIE) to overcome these limitations. Three-dimensional finite-element modeling enabled us to determine that more than one frequency is needed, ideally in the range 1–8 kHz, to improve thickness estimates of grounded sea-ice pressure ridges that are typical of 3D sea ice structures. With the MAiSIE system, we found a new electromagnetic concept based on one multifrequency transmitter loop and a 3C receiver coil triplet with active digital bucking. The relatively small weight of the EM components freed enough payload to include additional scientific sensors, including a cross-track lidar scanner and high-accuracy inertial-navigation system combined with dual-antenna differential GPS. Integrating the 3D ice-surface topography obtained from the lidar with the EM data at frequencies from 500 Hz to 8 kHz in [Formula: see text]-, [Formula: see text]-, and [Formula: see text]-directions, significantly increased the accuracy of sea-ice pressure-ridge geometry derived from HEM data. Initial test flight results over open water showed the proof-of-concept with acceptable sensor drift and receiver sensitivity. Noise levels were relatively high (20–250 parts-per-million) due to unwanted interference, leaving room for optimization. The 20 ppm noise level at 4.1 kHz is sufficient to map level ice thickness with 10 cm precision for sensor altitudes below 13 m.

Nonlinear Multi-Frequency Transmitter for Seafloor Characterization

To gather with a single surveying tool the backscatter frequency response of the seafloor would be a large asset to characterize the nature of the bottom. One proposes to take advantage of the saturation effect occurring with a high powered source: numerous harmonic waves are created by non linear interactions along the propagation. The feasibility of a multi-frequency source that is adapted to seafloor characterization is investigated. In a preliminary approach, a pseudo-1D model is used to estimate the on-axis levels of the first multiple frequencies. Experimental measurements performed with two typical geometries of transducers are compared with simulations.

Nonlinear multifrequency transmitter for seafloor characterization

In the underwater context, it is known that the frequency diversity provides essential information to derive the nature of the seafloor. This presentation deals with a new concept based on a transmitter that generates simultaneously several harmonic frequencies. Our final objective is to assert the feasibility of a multi‐frequency tool whose desirable characteristics could be specified for applications such as detection of sunken oil slicks, sediment characterization, or surveys before cable or pipe laying. The acoustic beams are generated through the harmonic components of a shock wave radiated by an antenna driven at a high level. The source is unique in time and space so that the multi‐frequency responses are inherently perfectly matched. A numerical model based on a generalized KZK equation has been developed to estimate the saturated fields. Measurements of the first harmonic fields obtained in our outdoor tank facility are compared with simulations.

Closed-loop class E transcutaneous power and data link for microimplants.

Magnetic transcutaneous coupling is frequently used for power and data transfer to implanted electronic devices. The proposed development of MicroImplants, small enough to be injected through a hypodermic needle suggest the need for a high-efficiency magnetic transcutaneous link. This paper describes the use of a multifrequency transmitter coil driver based upon the Class E topology. The development of a "high-Q approximation" which simplifies the design procedure is presented. A closed-loop controller to compensate for transmitter and receiver variations, and a method of data modulation, using synchronous frequency shifting are described. The closed-loop Class E circuit shows great promise, especially for circuits with unusually low coefficients of coupling. Currents of several amperes, at radio frequencies, can easily and efficiently be obtained.

Multi-frequency transmitter for radio controlled models

In this article, the author, a former student at Luton Sixth Form College, describes how he designed and built a multifrequency transmitter for radiocontrolled models. This was a major project for his GCE A-level Technology examination, June 1989. The project was awarded first prize of £1000 in ‘Engineering Challenge 89’ for Bedfordshire Schools, and third prize in the South East of Britain regional final ‘Young Engineers for Britain 89’ competition.

Measurement of the radiation patterns of full-scale HF and VHF antennas

A system has been developed to measure the directivity patterns of full-scale antennas when located in their operational environments. The primary component of this system is an aircraft-towed multifrequency transmitter that is designed to approximate an elementary dipole antenna. An HF and a VHF version of this transmitter provide frequency coverage from 2 to 100 MHz. Techniques have been developed to measure the entire radiation pattern, from the horizon to the zenith, for several antennas simultaneously. Data derived from this system are processed to provide the radiation patterns as contour plots of the measured signal strength on azimuthal equal-area projections. The measurement hardware, data acquisition, and data processing techniques are described, and examples are given of measured and processed data derived from the system.

Intraoral occlusal telemetry part I. A multifrequency transmitter for registering tooth contacts in occlusion

An intraoral occlusal telemetry system has been developed utilizing a miniature multifrequency transmitter which broadcasts at three different frequencies, registers tooth contacts on three different surfaces of the same tooth, and coordinates tooth contacts with swallowing. The transmitter is small enough to fit into a pontic replacing a single mandibular molar.