Low MHz Range Research Articles

Effects of low-level RF fields reveal complex pattern of magnetic input to the avian magnetic compass

The avian magnetic compass can be disrupted by weak narrow-band and broadband radio-frequency (RF) fields in the lower MHz range. However, it is unclear whether disruption of the magnetic compass results from the elimination of the perception pattern produced by the magnetic field or from qualitative changes that make the pattern unrecognizable. We show that zebra finches trained in a 4-arm maze to orient relative to the magnetic field are disoriented when tested in the presence of low-level (~ 10 nT) Larmor-frequency RF fields. However, they are able to orient when tested in such RF fields if trained under this condition, indicating that the RF field alters, but does not eliminate, the magnetic input. Larmor-frequency RF fields of higher intensities, with or without harmonics, dramatically alter the magnetic compass response. In contrast, exposure to broadband RF fields in training, in testing, or in both training and testing eliminates magnetic compass information. These findings demonstrate that low-level RF fields at intensities found in many laboratory and field experiments may have very different effects on the perception of the magnetic field in birds, depending on the type and intensity of the RF field, and the birds’ familiarity with the RF-generated pattern.

Demonstration of MHz frequency domain multiplexing readout of 37 transition edge sensors for high-resolution x-ray imaging spectrometers

We report on the development and demonstration of MHz frequency domain multiplexing (FDM) technology to readout arrays of cryogenic transition edge sensor (TES) x-ray microcalorimeters. In our FDM scheme, TESs are AC biased at different resonant frequencies in the low MHz range through an array of high-Q LC resonators. The current signals of all TESs are summed at superconducting quantum interference devices (SQUIDs). We have demonstrated multiplexing for a readout of 31 pixels using room temperature electronics, high-Q LC filters, and TES arrays developed at SRON, and SQUID arrays from VTT. We repeated this on a second setup with 37 pixels. The summed x-ray spectral resolutions @ 5.9 keV are ΔE31pix MUX=2.14 ± 0.03 eV and ΔE37pix MUX=2.23 ± 0.03 eV. The demonstrated results are comparable with other multiplexing approaches. There is potential to further improve the spectral resolution, to increase the number of multiplexed TESs, and to open up applications for TES x-ray microcalorimeters.

Expansion of alternatively extracted ion–ion beam in a low pressure collisional medium

The aim of this paper is to investigate, through particle-in-cell with Monte Carlo collisions (PIC-MCC) simulations, the effects of collisions on the expansion of an ion–ion beam formed by the alternate extraction of oppositely charged ions. This beam is extracted from an ion–ion plasma, formed in the downstream of a radiofrequency magnetically filtered iodine electronegative plasma, by the mean of two extraction grids. In this grid system, the screen grid is biased with a square voltage waveform, in the low MHz range, while the acceleration grid is grounded. The collisionless interaction between the extracted ion packets involves and enhances electrostatic waves propagating at beam velocity. Our results show that in addition to these electrostatic waves, the presence of significant fraction of low energy ions, produced by charge exchange, beside extracted fast ions gives rise to two-stream instability. Furthermore, space and time dependent electric field might accelerate the slow ions, produced by charge exchange collision. This acceleration, involving Landau damping and its inverse mechanism, is mainly due to the interaction between ions and potential patterns inherent to two-stream instability.

The absolute frequency reference unit for the spaceborne methane-sensing lidar mission MERLIN

Lidar systems have become an important technology in a variety of industrial and scientific applications. For terrestrial applications, such systems have been developed over the last decade and are commercially available. In space, this technology does not have a comparable maturity level and is still far from being a standard technology. In this paper, we present the operating principle, the design, and performance of the spaceborne absolute frequency reference used in the instrument of the French–German methane remote-sensing lidar mission, MERLIN. The MERLIN instrument operates on a methane absorption feature at 1645.55 nm. To achieve the accuracy goal for the column-integrated methane concentration of 3 ppb, absolute frequency accuracy levels in the low MHz range are required. The absolute frequency reference unit provides the stabilized seed lasers for the high-power laser sources at the required wavelengths and measures the absolute frequency of the outgoing laser pulses by means of a wavemeter. The focus of this paper is on the implementation of the absolute frequency referencing and the obtained frequency stability and accuracy.

International Electrotechnical Commission (IEC) and Food and Drug Administration (FDA) efforts to develop standards for ultrasound physiotherapy

Ultrasound physiotherapy devices produce acoustic energy, typically in the low MHz range, to generate deep heat for relief of pain and spasms, and have been used since the 1940’s. The IEC and the FDA have an interrelated history of developing standards for these devices. The IEC produced the first such standard “Testing and calibration of ultrasound therapeutic equipment”(1963). The FDA, with the IEC document as guide, developed its own “Ultrasonic Therapy and Surgery Products Performance Standard”(1978, 2012). Then the IEC, with FDA involvement and using many of the FDA’s concepts, produced “Medical electrical equipment—Part 2-5: Particular requirements for the basic safety and essential performance of ultrasonic physiotherapy equipment (1984, 2000, 2009) and “Ultrasonics—Physiotherapy systems—Field Specifications and methods of measurement in the frequency range 0.5 MHz to 5 MHz” (1996, 2007, 2013). FDA personnel are also currently leading an IEC effort to write a standard dealing with new, lower frequency physiotherapy. The FDA is also committed to harmonizing FDA regulations with IEC standards whenever possible. This presentation recounts the history of these efforts and examines some similarities and differences among the documents.

Submillimeter coils for stimulated-echo spectroscopy of a solid sodium ion conductor by nonselective excitation of MHz broad 23Na quadrupolar satellite spectra

In solids the detection of ionic motion covering the time range of milliseconds and longer is often accomplished using stimulated-echo spectroscopy. For spectral line widths much below or much above 1MHz nonselective or fully selective radio-frequency pulse excitation, respectively, is typically applied in such experiments. To enable the study of samples with quadrupolarly broadened satellite spectra featuring intermediate widths (in the lower MHz range) the present work exploits microcoils. Using such coils, stimulated-echo spectroscopy can be performed under conditions of nonselective excitation for instance with 23Na as a nuclear probe. Nutation experiments carried out used to assess the coil performance. The impact of second-order quadrupolar interactions is studied using explicit density-matrix calculations. The applicability of the present approach is successfully tested for a sodium orthophosphate based solid ion conductor.

Near-field plume properties of an ion beam formed by alternating extraction and acceleration of oppositely charged ions

This paper is devoted to study the expansion of a beam composed of packets of positively and negatively charged ions generated by alternating extraction and acceleration. This beam is extracted from an ion–ion plasma, i.e. the electron density is negligible compared to the negative ion density. The alternating acceleration of ions is ensured by two grids placed in the ion–ion plasma region. The screen grid in contact with the plasma is biased with a square voltage waveform while the acceleration grid is grounded. A two-dimensional particle-in-cell (2D-PIC) code and an analytical model are used to study the properties of the near-field plume downstream of the acceleration grid. It is shown that the possible operating bias frequency is delimited by an upper limit and a lower one that are in the low MHz range. The simulations show that alternating acceleration with bias frequencies close to the upper frequency limit for the system can achieve high ion exhaust velocities, similar to traditional gridded ion thrusters, and with lower beam divergence than in classical systems. Indeed, ion–ion beam envelope might be reduced to 15° with 70% of ion flux contained within an angle of 3°. Thus, this alternating acceleration method is promising for electric space propulsion.

Design, fabrication, and testing of surface acoustic wave devices for semiconductor cleaning applications

Numerous cleaning steps are utilized in the production of IC's in semiconductor facilities, involving the consumption of considerable amounts of energy and chemical cleaning agents. Sonication of surfaces containing particulate defects is one of the cleaning methods used to enhance particulate removal and increase device yield. The mechanisms of action achieving this particle removal are generally considered to involve contributions from two physical phenomena: 1) acoustic cavitation and 2) acoustic streaming. In efforts to reduce damaging effects of sonication, while enhancing the ability to remove particles of decreasing sizes, semiconductor tool manufactures have historically increased the operating frequencies moving from ultrasonics, characterized by frequencies in the kHz range, to megasonics, with frequencies in the low MHz range. This work focuses on the development of various MEMS acoustic transducers designed for efficient operation at frequencies in the hundreds of MHz. Design, fabrication, and results of testing exploring the ability of these devices to remove nano-scale particles is presented and discussed.

Design, fabrication and characterization of thin power inductors with multilayered ferromagnetic-polymer composite structures

This paper presents the design, fabrication and characterization of ultra-thin inductors using a new class of multilayered ferromagnetic-polymer composite structures as magnetic cores. The multilayered composite structures comprise of high-permeability, high saturation magnetization (Ms>0.5T), low-coercivity magnetic layers stacked with ultrathin polymer adhesives. The adhesive acts as an insulating layer to reduce eddy current losses while also preventing degradation in permeabilities at higher operating frequencies. Toroid-based integrated inductors were designed with the composite structures to operate in the low MHz range for power conversion applications. The magnetic composite film synthesis and patterning was successfully combined with toroid coils in order to fabricate the inductors. The process of micro-patterning the composite structure and forming 3D coils around them to demonstrate ultra-thin inductors is described in detail. The fabricated inductors with the multilayered magnetic composite films showed stable inductance beyond 10MHz and 10× enhancement in inductance density over air-core inductors with the same designs.

Propagation of pulsed ultrasonic fields in a band gap of a two dimensional phononic crystal

A band gap in the transmission spectrum of a finite two dimensional phononic crystal is examined in the time domain using pulsed ultrasonic fields. The phononic crystal consists of a hexagonal array of copper cylinders (r = 1.19 mm) in an aqueous matrix with a lattice constant of 2.9 mm. Measurements of the transmission properties of the sample are performed using ultrasonic wave groups of various center frequencies and bandwidths. Among the band gaps in the low-MHz range, we concentrate on the gap from 1.48 MHz—1.70 MHz. The phase velocity, group velocity, and attenuation coefficient spectra are determined and compared with expectations.

Speed of Sound in (Carbon Dioxide + Propane) and Derived Sound Speed of Pure Carbon Dioxide at Temperatures between (248 and 373) K and at Pressures up to 200 MPa

The speed of sound in (carbon dioxide + propane) mixtures, with mole fractions of carbon dioxide between 0.938 and 0.998, has been measured at temperatures from (248 to 373) K and at pressures between (8 and 200) MPa. We find that the addition of propane to carbon dioxide is highly effective in catalyzing vibration-translation energy transfer and reduces the sound absorption coefficient sufficiently to permit sensitive measurements of the speed of sound at frequencies in the low-MHz range. In this work, a 2 MHz ultrasonic cell based on the double-path pulse-echo method was used. The cell was calibrated with degassed ultrapure water at T = 298.15 K and p = 1 MPa, making use of the speed of sound computed from the International Association for Properties of Water and Steam equation of state (IAPWS-95). The estimated overall standard relative uncertainty of the speeds of sound measured in this study are 0.035 %. The speed of sound in pure carbon dioxide was obtained by extrapolation of the sound-speed data w...

Cellular-foam polypropylene ferroelectrets with increased film thickness and reduced resonance frequency

Ferroelectrets are piezoelectric materials suitable for acoustic applications such as airborne ultrasonic transducers. Typical ferroelectrets exhibit resonance frequencies in the high kHz to low MHz range. In order to decrease the transducer resonance frequencies to the low kHz range, processes such as gas-diffusion expansion and electric charging were adjusted to cellular films which are initially twice as thick as in earlier studies. The demonstrated film expansion and electric charging lead to mechanically soft cellular structures which show high piezoelectric activities with coefficients up to 130 pC/N. Due to the simultaneously increased film thicknesses, the resonance frequencies are lowered down to about 233 kHz.

A Refined Modeling for the Liquid Loading Effect in Microacoustic Sensors

The liquid loading effect on microacoustic sensors can be modeled using an acoustic impedance boundary con- dition. A rigorous expression for the acoustic impedance tensor is derived for isotropic linear elastic layers backed by a defined impedance. This formulation is generalized to enclose viscous liquids. Furthermore, the impedance tensor is also applied to the half-space, free surface and rigid backing boundary conditions and is compared to the one dimensional expressions of bulk impedance for the half-space and the transmission line equations for layers of finite thickness. In contrast to these 1D expressions, the coupling of pressure- and shear-wave propagation is considered which results in interesting phenomena for viscous liquid layers. For example, it is found that also for liquid layers much thicker than the decay length of the shear waves (e.g., hundreds of nanometers for a QCR in the lower MHz range), the boundary affects the shear impedance, due to pressure and shear wave coupling.

Strategies for single particle manipulation using acoustic radiation forces and external tools

The use of primary acoustic radiation forces has been shown to be a valid technique for the handling of micron sized suspended particles, such as beads or biological cells. These forces arise as a nonlinear effect when an acoustic wave or vibration, which is set up in the fluid by exciting to resonance the system containing the suspension, interacts with the particles. The typical frequencies (upper kHz - lower MHz range) and the periodicity (in the range of hundreds of micrometers) of the acoustic field make this technique particularly suited for the handling of particles within microfluidic systems.A variety of devices for separation, fractionation, trapping and positioning of beads or biological cells, working both in batch or fluid flow mode, have been proposed. With the exception of the ports used to inject or remove the sample or the carrier medium, these systems can be considered as closed systems. Nevertheless, access to the particles with external tools is sometimes needed after acoustic manipulation has been performed. For instance, particles or cells pre-positioned in a sequence along the centerline of a channel using acoustic radiation forces need to be removed from it using a microgripper for further handling. Furthermore, in the field of crystallography research protein crystals have to be placed one by one onto a nylon loop prior to X-ray analysis with synchrotron radiation. This is usually done using the loop to pick up the crystal from the solution where it has been growing with other ones. As this process is sometimes repeated for a large number of crystals there are efforts to automate it. To this purpose it would be advantageous to bring the crystals spatially separated into a known position where they than can be sequentially collected with the loop.Here strategies for single particle manipulation are presented combining the effects of acoustic fields, fluid flow, surface tension and external tools. They are discussed by means of numerical results from FE-simulations of both two and three dimensional models as well as corresponding experiments.

Evaluation of Tissue Mimicking Quality of Tofu for Biomedical Ultrasound

The tissue mimicking quality of tofu has been evaluated in terms of acoustic properties and acousto/thermal conversion as functions of frequency and diffraction corrected intensity over the 2 MHz to 18 MHz range using three unfocussed transducers with center frequencies of 5 MHz, 10 MHz and 15 MHz. The density and acoustic velocity were close to the American Institute of Ultrasound in Medicine (AIUM) recommended values for the soft tissue, however, the attenuation increases nonlinearly with frequency as α = 0.56 × f 1.3. As a result, the temperature rise in tofu due to ultrasound absorption is expressed by the product of the acousto/thermal conversion factor and the attenuation/diffraction corrected acoustic intensity. The decrease of temperature rise with depth measured by embedded thermocouples agrees with the theoretical exponential decrease of the attenuation/diffraction corrected acoustic intensity. The heat capacity per unit mass of tofu is 0.76 cal/g°C (equivalent to 3.18 J/g°C) of which about 76% is water. The nonlinear frequency dependence of attenuation in tofu as f 1.3 correctly describes the frequency dependence of temperature rise. The present results suggest that tofu may only be used in a limited low MHz range in view of the estimation of temperature rise and penetration depth due to nonlinear frequency dependence of attenuation. (E-mail: ytkim@kriss.re.kr)

Flat coil-based tunnel diode oscillator enabling to detect the real shape of the superconductive transition curve and capable of imaging the properties of HTSC films with high spatial resolution

Owing to a pick-up coil's flat design, relatively low MHz-range operation frequency, and six orders relative resolution a flat coil-based tunnel diode oscillator has advantages, compared to all other methods. They become crucial in studies with thin high-Tc superconductivity (HTSC) materials (with small signals), especially at the start of the Cooper pairs’ formation. Due to this the superconductivity precursor ‘paramagnetic’ effect was detected recently in YBaCuO films at N/S transition. It precedes Meissner ejection and specifies details of the shape of the transition curve. We discuss the influence of the currents on this effect, and the relationship between the quality of the material and the shape of the effect. A new imaging device has also been created based on this test method (using a focused He–Ne laser beam as a probing signal), capable of imaging the properties of HTSC films with ∼3μm spatial resolution. The method is based on detection of the inductance and Q-factor value changes of a single-layer flat coil, placed at the face of the sample. This leads to frequency and/or amplitude changes of the stable oscillator. The test device enabled 2D-mapping of the grain structure of a bridge-shaped YBaCuO film. Basically, the method is capable of imaging 2D-current distribution in thin HTS with sub-μm spatial-resolution, using non-bolometric response. However, the achieved resolution ∼3μm of a bolometric nature (in a given device with 3.5mm-size coil) by no means is limited by the abilities of the method, but mainly, it depends on how narrowly it is possible to focus the probing beam, while the own resolution of a present flat coil-based technique is better than 0.1μm, and can be improved essentially by reducing the coil size.

Application of time delay spectrometry for rough surface characterization

This paper describes the design and performance of an ultrasound measurement system, utilizing a swept frequency excitation signal, for analyzing the backscattered signal from planar rough surfaces. The implementation is in the form of a time delay spectrometry (TDS) system operating in reflection mode whose advantages are improved signal-to-noise ratio even with low peak power relative to conventional pulse-echo methods. Because of simultaneous transmission and reception, the TDS system requires two transducers. The TDS measurement system uses a swept frequency spectrum analyzer as the central analog processing unit. Both planar piston and focused transducers in the low MHz range were used for the measurements. Due to the statistical nature of rough surface backscatter, the mean of several statistically uncorrelated measurements is required to characterize the scattering behavior of a given rough surface. Backscatter data are obtained for a series of planar rough surfaces, in the form of scattering magnitude vs. frequency and vs. incident (=backscattered) angle. Analysis of the results reveals a good correlation between the root-mean-square (RMS) height and mean backscatter magnitude at 0° incident angle, and between the ratio of RMS height to correlation length and the difference in mean backscatter magnitude between 0° and 5°.

Recovery effect in radiowave propagation

The recovery effect in inhomogeneous propagation, often referred to as sea gain, is analysed by means of the Compensation Theorem. The resulting solution takes the form of an integral equation, but in the particular case when the second medium is a perfect conductor a solution in simple integral form is possible. Numerical results applied to sea water, considered as a perfect conductor in the low MHz range, agree well with those obtained by experiment.

Small-Signal Dynamic Analysis of Regulated Class E DC/DC Converters

Class E dc/dc converters can operate at high switching frequencies with very low switching power losses. Using commercially available power transistors and diodes, Class E converters can operate at switching frequencies in the low-MHz range, with efficiencies of about 85 percent. Previous papers dealt with the circuit parameter values needed to obtain high-efficiency operation and output-voltage regulation, and with the static control characteristics of the Class E dc/dc converter cell. The analysis is extended to include the dynamic control characteristics and further information about the static characteristics. The theoretical predictions are verified by experimental measurements on a 40-W 1.5-MHz converter.

Speech processing for a multiple-electrode cochlear implant hearing prosthesis.

The basic problem of measuring the angular dependence ofreflection coefficient in solids is the d•culty of steering around the acoustic tmun. Although pure dectronic scanning is posablc too, only some kind of mechanical solution seems to be practicable. As for mechanical scanning, we may choose to movc the transduce• along a curved surface, •$., a cylindrical one, a;ming the beam at the same point in the center and hitting the interface plane on the axis of the cylinder at different angles of incidence. On the other hand, we may choose to move the transducer along a plane surface using some device to convert his motion into rotation around the given interface point. Former experiments • howed that mechanical scanners based on the first method are inevitably very sensitive to mechanical misalignments and acceptable reproducibility can be achieved only by rather expensive and highly sophisticated quipment. We found it simpler to move the transducer along a plane surface and to convert this movement into rotation by a diffraction grating (geometrical means, such as a paraboloid reflector, are much more difficult to machine). The geometrical arrangement of the diffraction scanner is shown in Fig. 1. The aluminum scanner was designed so that it could measure reflection coelficients in a relatively large angular range between 30 and 60 deg. The two similar broadband contact transducers are moved symmetrically to the center. Their perpendicular alignment with respect o the grating is ensured by two simple rails. The angle of incidence of the through-transmitted signal is uniquely determined by the positions of the transducers and easily calculated from the measured distance between them. The output Sj_enal iS ira/ted to the •l•t burst arriving before many stray pulses due to multiple reflections. Only certain frequency components diffracted into the right direction reach the receiver in th• first burst, therefore, in spite of using broadband transducers, the measurement iS limited to a rather narrow bandwidth which changes with the angle of incidence. Although the elastic parameters are usually frequency independent inthe low MHz range, the interface between the two media is of•n some kind of thin layer with different acoustical properties from both neighboring media, which may result in frequencydependent behavior. To determine the reflection coefficient in aluminum for a particular acoustic load (including the second medium and the separating interface), we compare the level of the output signal with that of one received from an unloaded, i.e., free surface. The calcnlated reflection coefficient and the measured output signal for free surface are shown in Fig. 2. The difference between the two curves is due to such factors as the frequency response of the transducers, changing diffraction efficiency of the grating at different frequencies, and for different orders ofdiffruction, frequencyand distancedependent attenuation due to beam divergence and absorption. All of these factors are constant parameters of the scanner and can be taken into consideration by calibrating the system in the case of free surface (using the calculated, but probably fairly accurate data for aluminum ).