Sensitivity of a fluidic oscillator to modifications of feedback channel and mixing chamber geometry

This experimental study investigates the effects of internal geometry modifications on the performance of a curved Sweeping Jet actuator. The modifications are applied to the geometry of the feedback channel and the mixing chamber Coanda surface, and the resulting actuator properties are evaluated using time-resolved static pressure measurements inside the actuator and hot-wire measurements of the external flow. The major result is that small, localized modifications of the curved sweeping jet actuator geometry can lead to a complete change in the external flow regime, making the jet velocity distribution homogeneous, similar to the angled variant of the actuator. The Coanda surface shape is identified as the primary cause of the external jet adopting the bifurcated or homogeneous flow regime. The relationships between the sweeping frequency, jet deflection angle, required supply pressure, and pressure fluctuations are analyzed and discussed in detail. External flow behavior and coherence are characterized by phase-averaged, phase-locked velocity profiles and auto-correlation of the velocity signals. Graphical abstract

Deep extended feedback codes

A new Deep Neural Network (DNN)-based error correction encoder architecture for channels with feedback, called Deep Extended Feedback (DEF), is presented in this paper. The encoder in the DEF architecture transmits an information message followed by a sequence of parity symbols which are generated based on the message as well as the observations of the past forward channel outputs sent to the transmitter through a feedback channel. DEF codes generalize Deepcode in several ways: parity symbols are generated based on forward channel output observations over longer time intervals in order to provide better error correction capability; and high-order modulation formats are deployed in the encoder so as to achieve increased spectral efficiency. Performance evaluations show that DEF codes have better performance compared to other DNN-based codes for channels with feedback.

On possible energy savings with transmission supported via feedback channel in CubeSat transceiver

Recently a transmission technique, which can save energy thanks to supportive transmission in the feedback channel, was presented for transmitted information with different probability distributions. The basic assumption for its practical exploitation is that a node collecting information has enough energy - much more than the supported node. So far, in the published theoretical analysis it was assumed that the node does not consume energy for receiving the supporting sequence or that the amount of this energy is negligible comparing to energy needed for transmission. This paper makes the analyses more exact and practically oriented. Particularly, it estimates possible energy savings by incorporating the energy expenditures for receiving the supporting sequence in scenarios with Poisson distributed payload messages. The data from a real transceiver for CubeSat are used for obtaining the numerical results in these estimations.

Fluidic Oscillators, Feedback Channel Effect under Compressible Flow Conditions

Fluidic oscillators are often used to modify the forces fluid generates on any given bluff body; they can also be used as flow, pressure or acoustic sensors, with each application requiring a particular oscillator configuration. Regarding the fluidic oscillators’ main performance, a problem which is not yet clarified is the understanding of the feedback channel effect on the oscillator outlet mass flow frequency and amplitude, especially under compressible flow conditions. In order to bring light to this point, a set of three-dimensional Direct Numerical Simulations under compressible flow conditions are introduced in the present paper; four different feedback channel lengths and two inlet Reynolds numbers Re = 12,410 and Re = 18,617 are considered. From the results obtained, it is observed that as the inlet velocity increases, the fluidic oscillator outlet mass flow frequency and amplitude increase. An increase of the feedback channel length decreases the outlet mass flow oscillating frequency. At large feedback channel lengths, the former main oscillation tends to disappear, the jet inside the mixing chamber simply fluctuates at high frequencies. Once the Feedback Channel (FC) length exceeds a certain threshold, the oscillation stops. Under all conditions studied, pressure waves are observed to be traveling along the feedback channels, their origin and interaction with the jet entering the mixing chamber are thoroughly evaluated. The paper proves that jet oscillations are pressure-driven.

Adaptive decision feedback equalization for multi-Gbps data links

Channel equalization combats the effects of the imperfection of wire channels. This dissertation deals with adaptive decision feedback channel equalization. The dissertation starts with an in depth study of the challenges encountered in the design of adaptive DFE and techniques that address these challenges. Various 2-dimensional eye-opening monitors (EOMs) based adaptive DFE are proposed and implemented. A novel 2-dimensional hexagon EOM is proposed and its effectiveness is validated using simulation. A simplified and power efficient 2-dimensional hexagon EOM is also introduced. Both EOMs are capable of differentiating the severity of the violation of the minimum eye-opening so as to allow the DFE to take different actions adaptively and achieve desired eye-opening more rapidly. A maximum-jitter EOM-based adaptive DFE is also introduced to greatly reduce system complexity. The adaptive DFE is taped out in a 130nm 1.2V CMOS technology and finally an improved adaptive engine that outperforms DFE utilizing sign-sign least-mean-square is proposed.

Adaptive decision feedback equalization for multi-Gbps data links

Channel equalization combats the effects of the imperfection of wire channels. This dissertation deals with adaptive decision feedback channel equalization. The dissertation starts with an in depth study of the challenges encountered in the design of adaptive DFE and techniques that address these challenges. Various 2-dimensional eye-opening monitors (EOMs) based adaptive DFE are proposed and implemented. A novel 2-dimensional hexagon EOM is proposed and its effectiveness is validated using simulation. A simplified and power efficient 2-dimensional hexagon EOM is also introduced. Both EOMs are capable of differentiating the severity of the violation of the minimum eye-opening so as to allow the DFE to take different actions adaptively and achieve desired eye-opening more rapidly. A maximum-jitter EOM-based adaptive DFE is also introduced to greatly reduce system complexity. The adaptive DFE is taped out in a 130nm 1.2V CMOS technology and finally an improved adaptive engine that outperforms DFE utilizing sign-sign least-mean-square is proposed.

Nozzle with a Feedback Channel for Agricultural Drones

In recent years, small drones have been used in agriculture, for spraying water and pesticides. Although spraying systems affect the efficiency of agricultural drones considerably, research on the spraying system of drones is insufficient. In this paper, a new nozzle with a feedback channel is proposed for agricultural drones. The proposed nozzle was manufactured through 3D printing, and its performance was compared with that of the nozzle used in commercial agricultural drones. Images taken with a high-speed camera were digitally processed, to track the area and location of spray particles, and the spraying characteristics were evaluated based on the size and uniformity of the droplets obtained from the images. The proposed nozzle provided a better performance, as it could spray smaller droplets more uniformly. Commercial nozzle droplets have an average diameter of 1.76 mm, and the proposed nozzle has been reduced to a maximum of 215 μm. In addition, the full width at half maximum (FWHM) of the commercial nozzle is 0.233, but the proposed nozzle is up to 1.519; the proposed nozzle provided better performance, as it could spray smaller droplets more uniformly. Under the condition of 30 kg, the best performance in the proposed nozzle, the minimum value of the average droplet diameter of the nozzle without feedback channel is 595 μm and the maximum value of FWHM is 1.329. Therefore, a comparison of the performance of the proposed nozzle with that of a nozzle with no feedback channel indicates that the feedback channel effectively reduces the droplet diameter and improves the spraying uniformity. It is expected that the proposed nozzle can be useful for designing the spraying systems of agricultural drones.