Hydraulic Control of a Buck Converter

This paper investigates a concept for the pure hydraulic control of a buck converter using a hydraulically piloted 2-2 way on-off valve. The pilot system is controlled by the desired output pressure of the buck converter in form of a pressure signal and the RC filtered feedback of the actual pressure. These pressures act via small plunger cylinders in opposite direction on the on-off valve. An additional pilot cylinder features a jumping active hydraulic area for a robust feedback. The valve performs close to rectangular oscillations, the frequency of which is mainly determined by the characteristic time of the RC filter. The concept is studied by a simple analytical model to obtain its basic operating characteristics and by a detailed numerical model to analyze the role of parasitic effects on system performance. The paper shows that this concept works and can robustly follow the commanded output pressure. The converter has a moderate response dynamics; in certain operation conditions it shows an aperiodic behavior by alternating between phases of periodic switching and pause.

Imperfect symmetry of real annular combustors: beating thermoacoustic modes and heteroclinic orbits

In jet engines and gas turbines, the annular shape of the combustion chamber allows the appearance of self-oscillating azimuthal thermoacoustic modes. We report experimental evidence of a new type of modal dynamics characterised by periodic switching of the spinning direction and develop a theoretical model that fully reproduces this phenomenon and explains the underlying mechanisms. It is shown that tiny asymmetries of the geometry, the mean temperature field, the thermoacoustic response of the flames or the acoustic impedance of the walls, present in any real systems, can induce these heteroclinic orbits. The model also explains experimental observations showing a statistically dominant spinning direction despite the absence of swirling flow, or pairs of preferred nodal line directions.

Technique and Circuit for Contactless Readout of Piezoelectric MEMS Resonator Sensors

A technique and electronic circuit for contactless electromagnetic interrogation of piezoelectric micro-electromechanical system (MEMS) resonator sensors are proposed. The adopted resonator is an aluminum-nitride (AlN) thin-film piezoelectric-on-silicon (TPoS) disk vibrating in radial contour mode at about 6.3 MHz. The MEMS resonator is operated in one-port configuration and it is connected to a spiral coil, forming the sensor unit. A proximate electronic interrogation unit is electromagnetically coupled through a readout coil to the sensor unit. The proposed technique exploits interleaved excitation and detection phases of the MEMS resonator. A tailored electronic circuit manages the periodic switching between the excitation phase, where it generates the excitation signal driving the readout coil, and the detection phase, where it senses the transient decaying response of the resonator by measuring through a high-impedance amplifier the voltage induced back across the readout coil. This approach advantageously ensures that the readout frequency of the MEMS resonator is first order independent of the interrogation distance between the readout and sensor coils. The reported experimental results show successful contactless readout of the MEMS resonator independently from the interrogation distance over a range of 12 mm, and the application as a resonant sensor for ambient temperature and as a resonant acoustic-load sensor to detect and track the deposition and evaporation processes of water microdroplets on the MEMS resonator surface.