4,936 research outputs found
Wisent: Robust Downstream Communication and Storage for Computational RFIDs
Computational RFID (CRFID) devices are emerging platforms that can enable
perennial computation and sensing by eliminating the need for batteries.
Although much research has been devoted to improving upstream (CRFID to RFID
reader) communication rates, the opposite direction has so far been neglected,
presumably due to the difficulty of guaranteeing fast and error-free transfer
amidst frequent power interruptions of CRFID. With growing interest in the
market where CRFIDs are forever-embedded in many structures, it is necessary
for this void to be filled. Therefore, we propose Wisent-a robust downstream
communication protocol for CRFIDs that operates on top of the legacy UHF RFID
communication protocol: EPC C1G2. The novelty of Wisent is its ability to
adaptively change the frame length sent by the reader, based on the length
throttling mechanism, to minimize the transfer times at varying channel
conditions. We present an implementation of Wisent for the WISP 5 and an
off-the-shelf RFID reader. Our experiments show that Wisent allows transfer up
to 16 times faster than a baseline, non-adaptive shortest frame case, i.e.
single word length, at sub-meter distance. As a case study, we show how Wisent
enables wireless CRFID reprogramming, demonstrating the world's first
wirelessly reprogrammable (software defined) CRFID.Comment: Accepted for Publication to IEEE INFOCOM 201
Low scatter and ultra-low reflectivity measured in a fused silica window
We investigate the reflectivity and optical scattering characteristics at
1064\,nm of an antireflection coated fused silica window of the type being used
in the Advanced LIGO gravitational-wave detectors. Reflectivity is measured in
the ultra-low range of 5-10\,ppm (by vendor) and 14-30\,ppm (by us). Using an
angle-resolved scatterometer we measure the sample's Bidirectional Scattering
Distribution Function (BSDF) and use this to estimate its transmitted and
reflected scatter at roughly 20-40\,ppm and 1\,ppm, respectively, over the
range of angles measured. We further inspect the sample's low backscatter using
an imaging scatterometer, measuring an angle resolved BSDF below
sr for large angles (10--80 from incidence in the plane
of the beam). We use the associated images to (partially) isolate scatter from
different regions of the sample and find that scattering from the bulk fused
silica is on par with backscatter from the antireflection coated optical
surfaces. To confirm that the bulk scattering is caused by Rayleigh scattering,
we perform a separate experiment, measuring the scattering intensity versus
input polarization angle. We estimate that 0.9--1.3\,ppm of the backscatter can
be accounted for by Rayleigh scattering of the bulk fused silica. These results
indicate that modern antireflection coatings have low enough scatter to not
limit the total backscattering of thick fused silica optics.Comment: 9 pages, 10 figure
Optical scatter of quantum noise filter cavity optics
Optical cavities to filter squeezed light for quantum noise reduction require
optics with very low scattering losses. We report on measured light scattering
from two super-polished fused silica optics before and after applying
highly-reflective ion-beam sputtered dielectric coatings. We used an imaging
scatterometer that illuminates the sample with a linearly polarized 1064 nm
wavelength laser at a fixed angle of incidence and records images of back
scatter for azimuthal angles in the plane of the laser beam. We extract from
these images the bidirectional reflectance distribution function (BRDF) of the
optics with and without coating and estimate their integrated scatter. We find
that application of these coatings led to a more than 50% increase of the
integrated wide-angle scatter, to 5.00+/-0.30 and 3.38+/-0.20 ppm for the two
coated samples. In addition, the BRDF function of the coated optics takes on a
pattern of maxima versus azimuthal angle. We compare with a scattering model to
show that this is qualitatively consistent with roughness scattering from the
coating layer interfaces. These results are part of a broader study to
understand and minimize optical loss in quantum noise filter cavities for
interferometric gravitational-wave detectors. The scattering measured for these
samples is acceptable for the 16 m long filter cavities envisioned for the
Laser Interferometer Gravitational-wave Observatory (LIGO), though reducing the
loss further would improve LIGO's quantum-noise limited performance.Comment: 10 pages, 3 figure
Interactive singulation of objects from a pile
Abstract—Interaction with unstructured groups of objects allows a robot to discover and manipulate novel items in cluttered environments. We present a framework for interactive singulation of individual items from a pile. The proposed framework provides an overall approach for tasks involving operation on multiple objects, such as counting, arranging, or sorting items in a pile. A perception module combined with pushing actions accumulates evidence of singulated items over multiple pile interactions. A decision module scores the likelihood of a single-item pile to a multiple-item pile based on the magnitude of motion and matching determined from the perception module. Three variations of the singulation framework were evaluated on a physical robot for an arrangement task. The proposed interactive singulation method with adaptive pushing reduces the grasp errors on non-singulated piles compared to alternative methods without the perception and decision modules. This work contributes the general pile interaction framework, a specific method for integrating perception and action plans with grasp decisions, and an experimental evaluation of the cost trade-offs for different singulation methods. I
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