Small Signal Loss Research Articles

A 3D coaxial transition with continuous ground wall fabricated by a 12-inch wafer-level packaging method for radio frequency applications

Purpose This paper aims to realize the vertical interconnection in 3D radio frequency (RF) circuit by coaxial transitions with broad working bandwidth and small signal loss. Design/methodology/approach An advanced packaging method, 12-inch wafer-level through-mold-via (TMV) additive manufacturing, is used to fabricate a 3D resin-based coaxial transition with a continuous ground wall (named resin-coaxial transition). Designation and simulation are implemented to ensure the application universality and fabrication feasibility. The outer radius R of coaxial transition is optimized by designing and fabricating three samples. Findings The fabricated coaxial transition possesses an inner radius of 40 µm and a length of 200 µm. The optimized sample with an outer radius R of 155 µm exhibits S11 < –10 dB and S21 > –1.3 dB at 10–110 GHz and the smallest insertion loss (S21 = 0.83 dB at 77 GHz) among the samples. Moreover, the S21 of the samples increases at 58.4–90.1 GHz, indicating a broad and suitable working bandwidth. Originality/value The wafer-level TMV additive manufacturing method is applied to fabricate coaxial transitions for the first time. The fabricated resin-coaxial transitions show good performance up to the W-band. It may provide new strategies for novel designing and fabricating methods of RF transitions.

MRI of radiation chemistry: First images and investigation of potential mechanisms.

Paramagnetic species such as O2 and free radicals can enhance T1 and T2 relaxation times. If the change in relaxation time is sufficiently large, the contrast will be generated in magnetic resonance images. Since radiation is known to be capable of altering the concentration of O2 and free radicals during water radiolysis, it may be possible for radiation to induce MR signal change. We present the first reported instance of x-ray-induced MR signal changes in water phantoms and investigate potential paramagnetic relaxation enhancement mechanisms associated with radiation chemistry changes in oxygen and free radical concentrations. Images of water and 10 mM coumarin phantoms were acquired on a 0.35 T MR-linac before, during, and after a dose delivery of 80Gy using an inversion-recovery dual-echo sequence with water nullified. Radiation chemistry simulations of these conditions were performed to calculate changes in oxygen and free radical concentrations. Published relaxivity values were then applied to calculate the resulting T1 change, and analytical MR signal equations were used to calculate the associated signal change. Compared to pre-irradiation reference images, water phantom images taken during and after irradiation showed little to no change, while coumarin phantom images showed a small signal loss in the irradiated region with a contrast-to-noise ratio (CNR) of 1.0-2.5. Radiation chemistry simulations found oxygen depletion of -11µM in water and -31µM in coumarin, resulting in a T1 lengthening of 24ms and 68ms respectively, and a simulated CNR of 1.0 and 2.8 respectively. This change was consistent with observations in both direction and magnitude. Steady-state superoxide, hydroxyl, hydroperoxyl, and hydrogen radical concentrations were found to contribute less than 1ms of T1 change. Observed radiation-induced MR signal changes were dominated by an oxygen depletion mechanism. Free radicals were concluded to play a minor secondary role under steady-state conditions. Future applications may include in vivo FLASH treatment verification but would require an MR sequence with a better signal-to-noise ratio and higher temporal resolution than the one used in this study.

Ultrashort low-loss \u03a8 gates for linear optical logic on Si photonics platform

Nonlinear optical gates are usually considered as fundamental building blocks for universal optical computation. However, the performance is severely limited by small optical nonlinearity, thereby bounding their operation speed, consumption energy, and device size. In this paper, we propose and experimentally demonstrate linear optical logic operations with ~3 μm-long Si wire “Ψ” gates consist of 3 × 1 optical combiners including auxiliary bias port, which maximizes the binary contrast of the output in telecom wavelength. We have demonstrated 20 Gbps Boolean “AND” operation with experimentally measured small signal loss (1.6 dB experimentally). A single Ψ gate can perform representative Boolean operations by changing the bias power and relative phases. We have also demonstrated wavelength-independent operation by seven wavelengths, which leads to wavelength-division multiplexed parallel computation. This ultrashort, highly-integrable, low-loss, and energy-efficient optical logic gates pave the way for ultralow latency optical pattern matching, recognition, and conversion.

RF power limiter using capacitively-coupled contacts III-nitride varactor

Reported is a low-loss RF power limiter built using a voltage-controlled capacitor formed by two planar Schottky contacts deposited over an AlGaN/GaN heterostructure. The symmetrical structure of the varactor enables dual-polarity voltage clamping. Small electrode size and electrode spacing of 2 μm ensures a low impedance and low loss. Varying the varactor width in the range 0.25 - 1 mm allows tuning of the limiting powers in the range 17 - 40 dBm, also dependent on the operating frequency. The small-signal loss at 10 GHz is 0.2 - 0.67 dB. The varactor structure fabrication does not require gate alignment or annealing; the device is robust and fully compatible with MMICs; it also provides the DC block with around 95 V breakdown. The PL operation in the temperature range 25 - 200°C without significant parameter degradation was demonstrated. Power limiter CW stress during 100 hat 24 dBm revealed no performance degradation.

Mixing oxygen with hyperpolarized (3)He for small-animal lung studies.

Hyperpolarized helium (HP (3)He) is useful for direct MR imaging of the gas spaces of small animal lungs. Previously, breaths of 100% HP (3)He were alternated with breaths of air to maximize helium signal in the lungs and to minimize the depolarizing effects of O(2). However, for high-resolution imaging requiring many HP (3)He breaths (hundreds) and for pulmonary disease studies, a method was needed to simultaneously deliver O(2) and HP (3)He with each breath without significant loss of polarization. We modified our existing computer-controlled ventilator by adding a plastic valve, additional relays and a controller. O(2) and HP (3)He are mixed at the beginning of each breath within the body of a breathing valve, which is attached directly to the endotracheal tube. With this mixing method, we found that T(1) relaxation of HP (3)He in the guinea pig lung was about 20 s compared to 30 s with alternate air/HP (3)He breathing. Because imaging times during each breath are short (about 500 ms), the HP (3)He signal loss from O(2) contact is calculated to be less than 5%. We concluded that the advantages of mixing HP (3)He with O(2), such as shorter imaging times (reduced T(1) losses in reservoir) and improved physiologic stability, outweigh the small signal loss from the depolarizing effects of oxygen on HP (3)He.

Relationship between losses under a large flux excitation and small signal loss factors tanδ in magnetic cores for high frequency use

AbstractFor the evaulation of magnetic core losses in a high‐frequency region, the small‐signal parameter tan δ or the relative loss coefficient tan δ/μs, which are a small‐signal parameter in the region of an initial permeability, has been used. The magnetic cores for transformers or reactors have recently been used at a frequency greater than 100 kHz, and with a magnetic flux density far greater than the initial permeability, due to the demands of miniaturizing switching power supplies. This paper examines the relationship between the large‐signal loss of magnetic cores and their tan δ in a frequency range of 1 kHz to 1 MHz. It was found that the large‐signal loss has poor correlations with a small‐signal parameter, such as tan δ or tan δ/μs. ‘A loss‐evaluation parameter’ ζ = tanδ/μs (1 + tan2δ) was newly introduced. It is shown that the large‐signal eddy‐current losses of most magnetic cores at a frequency greater than 100 kHz can be estimated with a high accuracy by using this parameter; ζ is expected to be a useful parameter for evaluating the losses of cores for power applications at a frequency greater than 100 kHz.