Postdoc Researcher, Stanford University
Design and implement systems that can compute and operate with microwatts of power budget.
The wide deployment of Internet-of-Thing (IoT) devices is limited by two fundamental factors: battery energy density and wireless radio power consumption. The first limiting factor, battery energy density, has only improved by three times over the past twenty-two years. As a result, an IoT device can only continuously operate for several days on a coin cell battery. One example of this is Fitbit where you have to charge the wristband once every several days. The second limiting factor is the wireless radio power consumption. When we turn on a wireless radio for data transmission, the radio itself consumes tens to hundreds of miliwatts power and becomes the power bottleneck of an IoT device.
To address this problem, we propose a fundamental shift on how an IoT device should communicates its data. Instead of generating the wireless signal and transmitting it out, we propose using backscatter communication for connecting IoT devices. In backscatter communication, a device takes an ambient wireless signal as its excitation signal and reflects it back to a receiver. During the signal reflection, the device modifies the backscattered signal to embed its own information. Since signal reflection only consumes microwatts of power, backscatter communication is very efficient. Despite its efficiency, we actually do not see the wide deployment of backscatter-based IoT devices mainly because we do not have backscatter readers, such as RFID readers, around us to communicate with backscatter-based devices. The overhead of deploying such RFID reader-based infrastructure is so high such that we do not see the wide deployment of backscatter-based IoT systems.
To address this challenge, we propose a system that can leverage commodity radios, such as WiFi and Bluetooth, for backscatter communication. In this system, a backscatter radio can talk to commodity WiFi and Bluetooth radios without any hardware modification on these radios. The key observation here is that a signal transmitted by a commodity radio, either WiFi or Bluetooth, is generated using a codeword from a codebook. If a backscatter radio can transform a codeword in the excitation signal into another codeword in the backscattered signal, then we have the opportunity of using commodity radios for receiving the backscattered signal and decoding the IoT device information. Such transformation can work because both the excitation codeword and the backscattered codeword stay within the same codebook.
Abstract: Lidars are active optical remote sensing instruments with unique capabilities for atmospheric sounding. A manifold of atmospheric variables can be profiled using different types of lidar: concentration of species, wind speed, temperature, etc. Among them, measurement of the properties of aerosol particles, whose influence in many atmospheric processes is important but is still poorly stated, stands as one of the main fields of application of current lidar systems. This paper presents a review on fundamentals, technology, methodologies and state-of-the art of the lidar systems used to obtain aerosol information. Retrieval of structural (aerosol layers profiling), optical (backscatter and extinction coefficients) and microphysical (size, shape and type) properties requires however different levels of instrumental complexity; this general outlook is structured following a classification that attends these criteria. Thus, elastic systems (detection only of emitted frequencies), Raman systems (detection also of Raman frequency-shifted spectral lines), high spectral resolution lidars, systems with depolarization measurement capabilities and multi-wavelength instruments are described, and the fundamentals in which the retrieval of aerosol parameters is based is in each case detailed.
Pub.: 21 Jun '17, Pinned: 28 Jun '17
Abstract: Although it has previously been shown that the spectral analysis of ultrasound backscatter data is sensitive to the cellular changes caused by apoptosis, the sensitivity of spectral analysis to oncosis or ischemic cell death had not previously been studied. Whereas many anticancer treatments induce apoptosis, others induce cell starvation, or oncosis. HT-29 colon adenocarcinoma cells were formed into pellets and covered in phosphate-buffered saline at room temperature for 56 h. The pellets were imaged every 8 h with high-frequency (55 MHz) ultrasound and the raw radio-frequency data processed. The lack of nutrients available to the cells induced cell death due to oncosis. The attenuation slope, speed of sound, spectral slope, and midband fit were estimated at each of the eight time points to identify changes as the cells died due to starvation. The spectral slope decreased monotonically over the 56 h, whereas the attenuation slope showed an increase between 1 and 48 h, followed by a slight decrease between 48 and 56 h. The midband fit did not vary over time. The speed of sound increased from 1514 to 1532 m/s over the first 24 h, after which time it plateaued. These in vitro results indicate different trends in ultrasound parameter changes from those of in vitro apoptotic cells, suggesting that these different methods of cell death can be identified not only by morphological markers, but also by specific ultrasound signatures.
Pub.: 22 Jun '17, Pinned: 28 Jun '17
Abstract: We tested the hypothesis that left atrial (LA) mechanics and myocardial calibrated integrated backscatter (cIB) are altered in anthracycline-treated long-term survivors of childhood cancers. Forty-nine survivors and 25 controls were studied. Survivors had significantly smaller maximal (p = 0.009) and minimal (p = 0.017) LA volumes and lower peak negative LA strains (p = 0.011). For left ventricular (LV) indices, survivors had significantly lower shortening fraction (p < 0.001), ejection fraction (p < 0.001) and mitral annular late diastolic velocity (p = 0.003). Myocardial cIB of the LA posterior wall, ventricular septum and LV posterior wall was significantly greater in survivors than controls (all p values <0.05). Peak negative LA strain was related to late diastolic mitral annular velocity (r = 0.27, p = 0.018), whereas LA cIB was related to the average of septal and LV posterior wall cIB (r = 0.54, p < 0.001). In conclusion, LA remodeling as characterized by contractile dysfunction and increased cIB suggestive of fibrosis occurs in adult survivors of childhood cancers.
Pub.: 25 Jun '17, Pinned: 28 Jun '17