Fluxflowtype Josephson oscillator for millimeter and submillimeter wave region. III. Oscillation stability J. Appl. Phys. 58, 441 (1985); 10.1063/1.335643 Fluxflowtype Josephson oscillator for millimeter and submillimeter wave region. II. Modeling An oscillator which utilizes the effect of the vortex motion in long Josephson tunnel junctions, i.e., flux flow, has been presented in millimeter and submillimeter wave region. An electromagnetic wave generated by the oscillator is detected with a small tunnel junction as a detector with a refined coupling configuration. Quantitative evaluation of the detected power showed that the detected power attained the value of 10-6 W in the frequency range between 100 and 400 GHz, which is far superior to previous results. Frequency and magnetic field dependences of the present system were also measured, which showed that the output power was able to be controlled by the dc magnetic field. The present oscillator will be promising as the local oscillator in the integrated Josephson receiver systems.PACS numbers: 74.50. + r, 85.25. + k A) counter-electrode of the detector is evaporated after formation of the tunneling barrier. Upon this electrode an SiO 3302

The nonlinear Brownian rotational relaxation of magnetic fluids for the case of large excitation field was studied in relation to its biomedical applications. The Fokker-Planck equation, which describes the nonlinear behavior of magnetic fluids, was solved by numerical simulation when a large step or a sinusoidal field was applied. Deviations from the Debye theory were quantitatively clarified. First, it was shown that the response time of the magnetic fluids became shorter than the Brownian relaxation time for a larger excitation field, which can be expressed in terms of the field-dependent Brownian relaxation time. Next, the amplitude of the ac susceptibility became lower for larger excitation fields, and the frequency characteristic of the ac susceptibility moved to a higher frequency compared with that predicted by the Debye theory. Finally, higher harmonics occurred with increasing excitation fields. Approximate equations, that describe such nonlinear behaviors reasonably well, were also obtained. These equations are expected to be useful for developing biosensors based on Brownian relaxation.

A system is developed to magnetically measure biological antigen-antibody reactions with a superconducting quantum interference device (SQUID) magnetometer. In this system, antibodies are labeled with magnetic nanoparticles of γ-Fe2O3, and the antigen-antibody reactions are measured by detecting the magnetic field from the magnetic nanoparticles. A setup of the system is described, and the sensitivity of the system is studied in terms of detectable weight of nanoparticles. Magnetic particles as small as 600 pg can be detected at present. An experiment is also conducted to measure antigen-antibody reaction with the present system. It is shown that the sensitivity of the present system is better than that of the conventional optical method. A one order of magnitude improvement of sensitivity will be realized by the sophistication of the present system.

The magnetite nanoparticles were synthesized in an ethanol-water solution under ultrasonic irradiation from a Fe(OH)(2) precipitate. XRD, TEM, TG, IR, VSM and UV/vis absorption spectrum were used to characterize the magnetite nanoparticles. It was found that the formation of magnetite was accelerated in ethanol-water solution in the presence of ultrasonic irradiation, whereas, it was limited in ethanol-water solution under mechanical stirring. The monodispersibility of magnetite particles was improved significantly through the sonochemical synthesis in ethanol-water solution. The magnetic properties were improved for the samples synthesized under ultrasonic irradiation. This would be attributed to high Fe(2+) concentration in the magnetite cubic structure.

We have characterized fractionated magnetic nanoparticles (MNPs) for magnetic particle imaging. Original Ferucarbotran particles were magnetically divided into three fractionated MNPs called MS1, MS2, and MS3. Harmonic spectra from the three fractionated MNPs were measured at excitation fields of 2.8 and 28 mT with a frequency of 10 kHz. MS1 showed a 2.5-fold increase in the harmonic spectrum over that of the original MNPs. To understand the origin of the enhancement in the harmonic spectrum from MS1, we explored the magnetic properties of the MS series, such as distributions of effective core size and anisotropy energy barrier, and the correlation between them. Using these results, we performed numerical simulations of the harmonic spectra based on the Langevin equation. The simulation results quantitatively explained the experimental results of the fractionated MS series. It was also clarified that MS1 includes a large portion of the MNPs that are responsible for the harmonic spectrum. V C 2013 AIP Publishing LLC.

Globally, the demand for improved health care delivery while managing escalating costs is a major challenge. Measuring the biomagnetic fields that emanate from the human brain already impacts the treatment of epilepsy, brain tumours and other brain disorders. This roadmap explores how superconducting technologies are poised to impact health care. Biomagnetism is the study of magnetic fields of biological origin. Biomagnetic fields are typically very weak, often in the femtotesla range, making their measurement challenging. The earliest in vivo human measurements were made with room-temperature coils. In 1963, Baule and McFee (1963 Am. Heart J. 55 95−6) reported the magnetic field produced by electric currents in the heart (‘magnetocardiography’), and in 1968, Cohen (1968 Science 161 784−6) described the magnetic field generated by alpha-rhythm currents in the brain (‘magnetoencephalography’). Subsequently, in 1970, Cohen et al (1970 Appl. Phys. Lett. 16 278–80) reported the recording of a magnetocardiogram using a Superconducting QUantum Interference Device (SQUID). Just two years later, in 1972, Cohen (1972 Science 175 664–6) described the use of a SQUID in magnetoencephalography. These last two papers set the scene for applications of SQUIDs in biomagnetism, the subject of this roadmap. The SQUID is a combination of two fundamental properties of superconductors. The first is flux quantization—the fact that the magnetic flux Φ in a closed superconducting loop is quantized in units of the magnetic flux quantum, Φ0 ≡ h/2e, ≈ 2.07 × 10−15 Tm2 (Deaver and Fairbank 1961 Phys. Rev. Lett. 7 43–6, Doll R and Näbauer M 1961 Phys. Rev. Lett. 7 51–2). Here, h is the Planck constant and e the elementary charge. The second property is the Josephson effect, predicted in 1962 by Josephson (1962 Phys. Lett. 1 251–3) and observed by Anderson and Rowell (1963 Phys. Rev. Lett. 10 230–2) in 1963. The Josephson junction consists of two weakly coupled superconductors separated by a tunnel barrier or other weak link. A tiny electric current is able to flow between the superconductors as a supercurrent, without developing a voltage across them. At currents above the ‘critical current’ (maximum supercurrent), however, a voltage is developed. In 1964, Jaklevic et al (1964 Phys. Rev. Lett. 12 159–60) observed quantum interference between two Josephson junctions connected in series on a superconducting loop, giving birth to the dc SQUID. The essential property of the SQUID is that a steady increase in the magnetic flux threading the loop causes the critical current to oscillate with a period of one flux quantum. In today’s SQUIDs, using conventional semiconductor readout electronics, one can typically detect a change in Φ corresponding to 10−6 Φ0 in one second. Although early practical SQUIDs were usually made from bulk superconductors, for example, niobium or Pb-Sn solder blobs, today’s devices are invariably made from thin superconducting films patterned with photolithography or even electron lithography. An extensive descriptio...

Inductance dependence of noise properties of a highT c dc superconducting quantum interference deviceEffects of thermal noise on the characteristics of the dc superconducting quantum interference device (SQUID) have been studied. Numerical simulation on the SQUID characteristics operating at T=77 K has been performed by taking into account the thermal noise. It is shown that the voltage versus flux relation of the dc SQUID is degraded considerably with the thermal noise. The degradation becomes significant when the inductance of the SQUID increases. Due to this degradation, there exists significant limitation for the range of the inductance available at T=77 K, unlike the case at T=4.2 K. The maximum inductance should be around 200 pH in order to avoid significant degradation of the transfer function. This limited value of the inductance must be taken into account when we realize the SQUID coupled to an input coil. The analytical expression for the degradation of the transfer function due to the thermal noise is also obtained. The theoretical result explains experimental results reported recently.

The dynamics of a magnetic fluid in a rotating magnetic field in the presence of thermal noise were studied by performing numerical simulations based on the Fokker-Planck equation. We first clarified the dynamic properties by numerical simulation such as the frequency dependence of the fluid magnetization, the field-dependent relaxation time, and the M-H curve in a rotating magnetic field. Using the simulation results, we modified an existing analytical model and obtained an empirical expression to quantitatively describe the particle dynamics. The simulation results were compared with experimental results in a rotating magnetic field. The frequency dependence of the magnetization of the magnetic fluid was measured over the linear and nonlinear regions. In order to make a quantitative comparison, the hydrodynamic and effective core size distributions were independently estimated from measurements of the ac susceptibility and the M-H curve. The phase lag and amplitude in a rotating magnetic field obtained from our simulation agreed well with the experimental results.