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Receivers
Published in Mike Golio, Commercial Wireless Circuits and Components Handbook, 2018
Vibrations and mechanical shocks will result in physical relative movement of hardware. Printed circuit boards (PCBs), walls, and lids may bow or flutter. Cables and wire can vibrate. Connectors can move. Solder joints can fracture. PCBs, walls, and lids capacitively load the receiver circuitry, interconnects, and cabling. Movement, even very small deflections, will change this parasitic loading, resulting in small changes in circuit performance. In sensitive areas, such as near oscillators and filters, this movement will induce modulation onto the signals present. In phase-dependent systems, the minute changes in physical makeup and hence phase length of coaxial cable will appear as phase modulation. Connector pins sliding around during vibration can introduce both phase and amplitude noise. These problems are generally addressed by proper mechanical design methods, investigating and eliminating mechanical resonance, and minimizing shock susceptibility. Don’t forget that temperature changes will cause expansion and contraction, with similar but slower effects.
Abnormal Frequency Protection
Published in Donald Reimert, Protective Relaying for Power Generation Systems, 2017
Steam turbines are more adversely effected by off-frequency operation than are the generators they drive. A key feature of turbine blade design is assuring that the blades are not damaged by mechanical resonance. Mechanical resonance produces high vibratory stress that can cause fatigue cracking and eventual blade failure. Resonance occurs when a natural frequency of a blade coincides with vibratory stimuli. The steam flow path is not homogeneous. Physical irregularities in the flow path produce turbulence that appears as a cyclic force to the blades. As an example, a single strut would produce excitation once per revolution, whereas a joint would excite twice per revolution. The strut would represent fundamental frequency excitation while the joint would produce second-harmonic excitation.
Physical sensors based on photonic crystals
Published in Guangya Zhou, Chengkuo Lee, Optical MEMS, Nanophotonics, and Their Applications, 2017
Cantilever is one of the most commonly used MEMS structure. It has wide freedom to design the proper mechanical characteristics, such as the mechanical resonance frequency and mode, stress and strain distributions and mechanical tunabilities. Hence, integration of the PhC structure together with the MEMS cantilever can easily transfer the mechanical variation of the surroundings to the PhC optical mode region and generate high sensitivity signals. Moreover, since the cantilever usually contains a bigger active area, two-dimensional PhC slab is usually implied to obtain better optical confinement and higher mechanical variation to the PhC structure.
Comparative Analysis of Torque Ripple for Direct Torque Control based Induction Motor Drive with different strategies
Published in Australian Journal of Electrical and Electronics Engineering, 2022
Pravinkumar D. Patel, Saurabh N. Pandya
The high-frequency pulsating torque component is induced due to PWM control of inverter that produces a ripple current in the phases. Actually, this pulsating torque effect is negligible due to enough high inertia of the motor. At low-frequency operation, mechanical resonance may occur, causing severe shaft vibration, fatigue, wearing of gear teeth, instability of the feedback control system (Bimal 2002).
Energy efficient piezoelectrically actuated transducer for direct-contact ultrasonic drying of fabrics
Published in Drying Technology, 2020
Drying is one of the most energy-intensive processes that consumes approximately 10–15% of the total energy generated in the United States.[1] In 2014, nearly 80% of U.S. households owned clothes dryers, which constituted 6% of all residential electricity usage and costed consumers nearly $9 billion.[2,3] To reduce energy consumption, increase cost savings and improve efficiency, a variety of technologies such as heat pump dryers,[4–6] air-vented dryers,[4,7,8] and condensing dryers[4,7,8] have been introduced to the market. Recently, high-frequency, direct-contact vibrational drying of fabrics using ultrasonic transducers have been introduced by us in the very first[9–12] as a promising technology to reduce both the drying time and energy consumption of the drying process. In this technique, pieces of fabric are put in direct-contact with an ultrasonic transducer made by piezoelectric ceramic (lead zirconate titanate, PZT). According to the reverse piezoelectric effect, the ultrasonic transducer can be mechanically vibrated when a high frequency electric field is applied. If the oscillation frequency is high enough (usually larger than 20 kHz), the transducer can generate ultrasonic waves that propagate through its surrounding media. At the appropriate frequency, the vibration causes mechanical resonance and large strain. The transducer applies mechanical vibrations to the fabric, in which water leaves as a cold mist of water droplets, bypassing the latent heat of evaporation. Since this dewatering process lacks thermal evaporation, it is highly energy efficient. In our previous studies, direct-contact ultrasonic fabric drying has been successfully applied in small-scale and mid-scale prototype.[9] For the small-scale prototype, a single 24-piezoelectric transducer module to dry a 142 cm2 sized fabric was achieved; when the prototype was scaled up to mid-scale, five such modules were utilized (totally 120 transducers) and drying fabric with a size of 750 cm2 was achieved. Our performance evaluation results have illustrated that this direct-contact ultrasonic drying technology shows energy efficiency an order of magnitude higher than a typical electrical resistance dryer, and five times higher than the latent heat of evaporation at water content greater than 20%. Compared with the most energy efficient existing drying technique, heat-pump dryer, it consumes 80% less energy. Therefore, the development of direct-contact ultrasonic drying technology using ultrasonic transducer will allow for global reduction in electricity consumption related to clothes drying.