Dual-Color Antenna-Coupled LEKID for Next-Generation Multi-chroic CMB Focal Planes

We present an antenna-coupled Kinetic Inductance Detector for millimeter wave astronomy. Next-generation telescopes for observing the cosmic microwave background are demanding in terms of number of detectors and focal plane area filling efficiency. Moreover, foreground reduction in B-Mode polarimetry requires sky observation with multiple frequency bands. In this context, KIDs are a promising technology because of their large multiplexing rate, while antenna coupling can provide multi-band and dual-polarization solutions in compact design. We have developed polarization-sensitive dual-band pixel at 140 and 160 GHz with a bandwidth of almost 8% for each sub-band. The design involves a microstrip-excited slot antenna and two open-stub band-pass filters to direct the signal toward two resonators. These are lumped elements capacitively coupled to the antenna and include an aluminum strip as absorber. The architecture proposed is particularly simple to fabricate, via-less and only involves two metallization levels. The transition does not require any dielectric deposition above the resonator, thus preventing limitations from any source of noise due to a non-monocrystalline substrate. Furthermore, the same coupling technique can be applied to many types of microstrip-excited antennas, which allow to accommodate band-pass filters.     

Laboratory Calibration System for CMB Polarization Detectors

We present a novel system to calibrate millimeter-wave polarimeters for CMB polarization measurements. This technique is an extension of the conventional metal mirror rotation approach, however it employs cryogenically-cooled blackbody absorbers. The primary advantage of this system is that it can generate a slightly polarized signal?(～100?mK) in the laboratory; this is at a similar level to that measured by ground-based CMB polarization experiments observing a ～10?K sky. It is important to reproduce the observing condition in the laboratory for reliable characterization of polarimeters before deployment. In this paper, we present the design and principle of the system, and demonstrate its use with a coherent-type polarimeter used for QUIET. This technique can also be applied to incoherent-type polarimeters and it is very promising for the next-generation CMB polarization experiments.     

Novel Calibration System with Sparse Wires for CMB Polarization Receivers

A curl competent (also known as B-modes) in the cosmic microwave background (CMB) polarization is a smoking gun signature of the inflationary universe. To achieve better sensitivity to this faint signal, CMB polarization experiments aim to maximize the number of detector elements, resulting in a large focal plane receiver. Detector calibration of the polarization response becomes essential. It is extremely useful to be able to calibrate “simultaneously” all detectors on the large focal plane. We developed a novel calibration system that rotates a large “sparse” grid of metal wires, in front of and fully covering the field of view of the focal plane receiver. Polarized radiation is created via the reflection of ambient temperature photons from the wire surface. Since the detector has a finite beam size, the observed signal is convolved with the beam property. The intensity of the of the calibrator is reasonable (a few Kelvin or less) compared to sky temperature for typical observing conditions (～10?K). The system played a successful role for receiver calibration of QUIET, a CMB polarization experiment located in the Atacama desert in Chile. The successful performance revealed that this system is applicable to other experiments based on different technologies, e.g. TES bolometers.     

Multi-chroic Dual-Polarization Bolometric Focal Plane for Studies of the Cosmic Microwave Background

We are developing multi-chroic antenna-coupled Transition Edge Sensor (TES) focal planes for Cosmic Microwave Background (CMB) polarimetry. In each pixel, a dual polarized sinuous antenna collects light over a two-octave frequency band. Each antenna couples to the telescope with a contacting silicon lens. The antenna couples the broadband RF signal to microstrip transmission lines, and then filter banks split the broadband signal into several frequency bands. A TES bolometer detects the power in each band and polarization. We will describe the design of this device and demonstrate its performance with optical data measured using prototype pixels. Our measurements show low ellipticity beams, low cross-polarization, and properly partitioned bands in banks of 2, 3, and 7 filters. Finally, we will describe how we will upgrade the Polarbear CMB experiment using the focal planes of these detectors to increase the experiment’s mapping speed and its ability to discriminate between the CMB and polarized foregrounds.     

Development of Crystal Al MKIDs by Molecular Beam Epitaxy

We report here the effect of film qualities in superconductors on the properties of Microwave Kinetic Inductance Detectors (MKIDs). The sensitivity of MKIDs between crystal aluminum films and amorphous aluminum films is compared. The good quality and crystallized aluminum films have been prepared by using molecular beam epitaxy. We have confirmed that epitaxial Al(111) films were grown on Si(111) substrates with X-ray diffraction and in-situ reflection high-energy electron diffraction measurements. The amorphous aluminum films on the Si(111) wafers have been deposited by electron beam evaporation. We have measured transmission losses of MKIDs, noise spectrum and relaxation time against optical pulses, changing MKIDs’ bath temperature from 0.11?K to 0.55?K in a dilution refrigerator. Despite of the improvement in normal resistivity, the quasiparticle decay time of both films are equivalent and 450?μs at 0.11?K. The electrical noise equivalent power of the both MKIDs are also comparable and around $10^{-17}~\mbox{W}/\sqrt{\mbox{Hz}}$ . Fabrication details and performance data of both films are presented.     

Optimization of Geomagnetic Shielding for MKIDs Mounted on a Rotating Cryostat

Superconducting detectors, such as microwave kinetic inductance detectors (MKIDs), are sensitive to the effects of ambient magnetic fields. There are two effects magnetic fields have on the response of MKIDs; the trapping of magnetic fields inside the superconducting materials degrades the resonator quality, and the time variation of the magnetic fields results in a baseline fluctuation. In the case of radio astronomy, this means the detector must be protected from the geomagnetic field. Here, we construct a test system to evaluate the effects described. We also evaluate the impact of the magnetic shield. We find that a shielding power of 47 dB is necessary in the case of application with a noise equivalent power of \(2.4 \times 10^{-16}\,\text {W}/\sqrt{\text {Hz}}\). We also confirm that the measured shielding power obtained using permalloy films is consistent with simulations based on the finite element method to an accuracy of 1 dB. We have designed magnetic shields for the GroundBIRD CMB telescope using these results. We achieve a sufficient shielding power of 55 dB.     

GroundBIRD Experiment: Detecting CMB Polarization Power in a Large Angular Scale from the Ground

GroundBIRD is a ground-based experiment designed to detect large angular scale odd-parity patterns in the cosmic microwave background (CMB) polarization ( \(B\) -modes). We employ a high-speed rotation scan (20 rpm) instead of the usual left–right azimuthal scan; it allows a significant expansion of the scan range to \(60^{\circ }\) without any effect from the detector \(1/f\) noise. We use microwave kinetic inductance detectors (MKIDs) arrays with a small telescope; our target multipole ( \(\ell \) ) range is \(6\,\le \,\ell \,\le \,300\) . We plan to start the test observation in Japan in 2014; these will then be moved to the Atacama highland in Chile for scientific observations.     

压电陶瓷极化特性研究

使用DP-5型介电谱仪,测量由压电陶瓷材料制作的蜂鸣器的介电频率特性,验证理论猜测。实验测出压电陶瓷的极化方式与极化率与外场频率有关,随着频率的增加,压电陶瓷的离子位移极化率、电介质分子取向极化的极化率将减小,最终表现为相对介电常数减小。实验结果与理论猜测吻合。     

Chirality-Enriched Carbon Nanotubes for Next-Generation Computing

For the past half century, silicon has served as the primary material platform for integrated circuit technology. However, the recent proliferation of nontraditional electronics, such as wearables, embedded systems, and low-power portable devices, has led to increasingly complex mechanical and electrical performance requirements. Among emerging electronic materials, single-walled carbon nanotubes (SWCNTs) are promising candidates for next-generation computing as a result of their superlative electrical, optical, and mechanical properties. Moreover, their chirality-dependent properties enable a wide range of emerging electronic applications including sub-10 nm complementary field-effect transistors, optoelectronic integrated circuits, and enantiomer-recognition sensors. Here, recent progress in SWCNT-based computing devices is reviewed, with an emphasis on the relationship between chirality enrichment and electronic functionality. In particular, after highlighting chirality-dependent SWCNT properties and chirality enrichment methods, the range of computing applications that have been demonstrated using chirality-enriched SWCNTs are summarized. By identifying remaining challenges and opportunities, this work provides a roadmap for next-generation SWCNT-based computing.     

Organic Photodetectors for Next-Generation Wearable Electronics

Next-generation wearable electronics will need to be mechanically flexible and stretchable such that they can be conformally attached onto the human body. Photodetectors that are available in today's market are based on rigid inorganic crystalline materials and they have limited mechanical flexibility. In contrast, photodetectors based on organic polymers and molecules have emerged as promising alternatives due to their inherent mechanical softness, ease of processing, tunable optoelectronic properties, good light sensing performance, and biocompatibility. Here, the recent advances of organic photodetectors in terms of both optoelectronic and mechanical properties are outlined and discussed, and their application in wearable electronics including health monitoring sensors, artificial vision, and self-powering integrated devices are highlighted.     

Shear properties of CMB syntactic foam

In this research, a triaxial shear test is used as a means to provide yield surface data as well as other strength characteristics for carbon microballoon (CMB) syntactic foam. Additionally, pure shear tests and tensile tests are used to probe areas of this stress space not included in the triaxial shear tests. The data are used to characterize the material’s yield strength in stress space. The determined yield surface, the strain and other deformational behavior characteristics provide the necessary information for an accurate model and engineering design. The CMB foam specimens were divided into two sets: one with Thornel pitch-based carbon fibers and one without; both use Kerimid 601 as the binder. The CMB syntactic foam with fibers exhibited lower shear strength than the CMB syntactic foam without fibers. This is evident not only in the determined shear envelopes but also in the values obtained for the hydrostatic yield of both foams. Complementary analysis of the blending process of mixing fibers with CMB has been shown to destroy the microballoons and thus reduce the foams strength. The consequences of incorporating alternative materials can be verified with further testing.     

An 84 Pixel All-Silicon Corrugated Feedhorn for CMB Measurements

Silicon platelet corrugated feedhorn arrays for cosmic microwave background (CMB) measurements at millimeter wavelengths (130?GHz to 170?GHz) have been developed for deployment for the polarization-sensitive upgrade to both the Atacama Cosmology Telescope (ACTpol) and the South Pole Telescope (SPTpol). We present fabrication developments and the first results of a prototype monolithic feedhorn array consisting of 84?horns. Measurements at room temperature show good beam quality across the needed bandwidth, return loss of <?20?dB, an insertion loss of <?0.4?dB, and cross polarization of <?23?dB. The 32 platelets were aligned to a 1σ variation of 8?μm.     

Suppressing Beam Systematics in Antenna-Coupled TES Bolometers for CMB Polarimetry

We have deployed arrays of antenna-coupled TES bolometers for cosmic microwave background (CMB) polarimetry in the BICEP2 and Keck array experiments and will deploy similar detectors in SPIDER and Polar-1. Each pixel receives optical power centered at 146 GHz with a 20% bandwidth (?10 dB edges) through an integrated dual-polarized phased-array antenna. In past deployments, these detectors have shown offsets in the two polarizations’ beam centroids (differential ‘steering’), but we have redesigned the feed networks by strategically spacing lines and adding intentional phase delays to suppress this unwanted effect. We expect that the focal planes in this season’s deployment of Keck and in SPIDER will have detectors with less than 5′ steering, which is 0.5% of the 14.2° nominal antenna’s FWHM (i.e. without lenses). We have also redesigned the antenna-array’s illumination pattern to suppress side-lobe response in anticipation of the Polar-1 experiment, reducing spillover by a factor of 2.5.     

Optimizing Feedhorn-Coupled TES Polarimeters for Balloon and Space-Based CMB Observations

Maximizing the sensitivity of balloon-based and space-based observations of the cosmic microwave background (CMB) requires detectors with substantially lower saturation power and background noise than ground-based observations, because of reduced atmospheric loading and lower photon noise. We have fabricated and tested prototype transition-edge sensor (TES) bolometers that have architecture identical to that used in feedhorn-coupled TES polarimeter arrays developed for ground-based CMB observations, but have saturation power appropriate for balloon-based or space-based observations (0.5?pW–7?pW). The operating resistance of these bolometers (～3?mΩ) is appropriate for readout with time-division or gigahertz frequency-division SQUID multiplexers. Dark bolometer measurements show that the noise levels are near the expected thermal-fluctuation-noise background (<10^?17?W/Hz^1/2), that the thermal response times are faster than the observation requirements, and that low-frequency 1/f noise can be strongly suppressed to <10?mHz by pair differencing. We report on the performance of the prototype devices and progress towards optimizing them for balloon-based and spaced-based observations.