Desiccant HVAC system driven by a micro-CHP: Experimental analysis

In the Mediterranean area, there is increase in demand for summer cooling satisfied by electrically driven units in domestic and small commercial sectors; this involves electric peak loads and black-outs. Consequently, there is an increasing interest in small scale polygeneration systems fuelled by natural gas.In this paper, attention is paid to a test facility, located in Southern Italy, to carry out experimental analysis on a small scale polygeneration system based on a natural gas-fired Micro-CHP and a desiccant HVAC system. The MCHP provides thermal power, recovered from engine cooling and exhaust gas, for the regeneration of the desiccant wheel and electric power for the chiller, the auxiliaries and the external units (computers, lights, etc.). The HVAC system can also operate in traditional way, by interacting with electric grid and gas-fired boiler. An overview of the main experimental results is shown, considering both the desiccant wheel and the global polygeneration system.The experimental results confirm that the performances of the desiccant wheel are strongly influenced by outdoor thermal-hygrometric air properties and regeneration temperature. The polygeneration system guarantees primary energy savings up to 21.2% and greenhouse-gas emissions reductions up to 38.6% with respect to conventional HVAC systems based on separate energy “production”.     

Error vector-based measurement method for radiofrequency digital transmitter troubleshooting

The rapid growth of modern telecommunications systems has created the need to get new test equipment and measurement techniques operational in a very short time. Performance assessment of radiofrequency digital transmitters, with special regard to the troubleshooting of their I/Q modulation section, calls for new, reliable, and time-effective measurement methods because those based on the analysis of constellation diagrams, currently supported by major manufacturers, show some intrinsic limitations. To overcome these limitations, a new measurement method based on the use of the error vector is proposed in the paper. It works properly when only one or two I/Q impairments are significant, and assures comparable accuracy and reduced measurement time with respect to other solutions already presented in the literature. Besides describing the fundamental steps and basic relations characterizing the proposed method, the paper gives details of the extended experimental activity carried out on actual telecommunication signals in order to assess the performance.     

Estimating ultrasonic time-of-flight through quadrature demodulation

A new digital signal-processing (DSP) method for ultrasonic time-of-flight (TOF) estimation is presented hereinafter. The method applies a traditional quadrature-demodulation scheme to the acquired ultrasonic signal in order to suitably extract the envelope of the main echo and locate its onset (i.e., the starting time of the echo). It is also possible to assure reduced bias and uncertainty in critical TOF measurements, such as those involving low signal-to-noise ratio (SNR) as well as severe distortion of echo shape. A number of numerical tests are conducted on simulated signals with the aim of highlighting the good performance of the method when operating in critical conditions; to reduce the computational burden without losing significance in the analysis, a statistical experimental design-based technique is enlisted. Results attained in TOF-based distance measurements finally assess the method's reliability and efficacy even in the presence of actual ultrasonic signals.     

Evaluating phase noise power spectrum with variable frequency resolution

Measurement of phase noise affecting sinusoidal carriers is dealt with here. A new method is proposed, mainly intended to overcome the limits of two digital signal-processing solutions, already presented by the authors and devoted, respectively, to far-from-the-carrier and close-to-the-carrier phase noise analysis. Thanks to an original measurement procedure, the method optimizes the frequency resolution in the evaluation of phase noise power spectral density; in particular, the closer to the carrier the analysis, the finer the frequency resolution granted. It is possible to obtain accurate and reliable results in a wide range of frequency offsets with no need for heavy computational burden and expensive hardware resources of the adopted data acquisition system. The results of a number of experiments, conducted on actual sinusoidal carriers through a measurement prototype implementing the method, confirm the efficacy and reliability of the proposal.     

A measurement method based on Kalman filtering for ultrasonic time-of-flight estimation

A new digital signal-processing method for ultrasonic time-of-flight (TOF) estimation is presented. The method applies the discrete extended Kalman filter (DEKF) to the acquired ultrasonic signal in order to accurately estimate the shape factors of the echo envelope as well as locate its onset. It is also possible to assure reduced bias and uncertainty in critical TOF measurements, such as those involving low signal-to-noise ratio (SNR) as well as severe distortion of echo shape. A number of numerical tests are conducted on simulated signals with the aim of highlighting the good performance of the method when operating in critical conditions. Results attained in TOF-based distance measurements finally assess the reliability and efficacy of the method in the presence of actual ultrasonic signals.     

A digital signal-processing instrument for impedance measurement

A digital signal processing (DSP)-based instrument for impedance measurement is proposed. It implements two measurement techniques: the first technique allows the tracking of a time varying impedance to be carried out, and the second assures that good accuracy is obtained in reasonable measurement times. Both the software and the hardware of a prototype model are described in detail. The measurement rates and accuracy are evaluated and compared with those obtained using a reference Digibridge for a wide range of impedance values     

Design and implementation of a reconfigurable test-bed for real-time security measurements in VoIP systems

Voice over Internet Protocol (VoIP) systems have to face a great number of security threats, which are basically connected to the underlying Internet Protocol (IP) infrastructure. Along with relevant economic losses and malfunction for the VoIP system itself, external attacks exploiting a security hole could also bring to a major security failure for the interconnected Public-Switched Telephone Network (PSTN), usually regarded as a reliable and secure domain. This is the reason why before connecting a private VoIP network to the carrier infrastructure, a great number of tests have to be carried out, to verify the security robustness of the VoIP network to common attacks.     

Scaling of Hc2⊥(T) in Nb/CuMn Multilayers

Measurements of the perpendicular upper critical magnetic field H _c2(T) are reported for several Nb/CuMn multilayers. It is found that, despite the magnetic nature of the samples, the data for samples with low Mn percentage in the CuMn layers are simply described by the Werthamer–Helfand–Honenberg theory for conventional type-II superconductors, neglecting both Pauli spin paramagnetism and spin orbit impurity scattering. For high Mn concentration a different theoretical approach is needed.     

Thin thickness measurements by means of a wavelet transform-based method

A non-invasive method for thin thickness measurements of multilayer structures is presented herein. This measurement method uses the wavelet transform for the analysis and processing of the ultrasonic signal received from the structure under test. The wavelet transform also shows itself to be a powerful tool for the detection of partially overlapping echoes in a noisy environment. This paper first describes the basic idea underlying the measurement method and then a procedure, set up by the authors, and suitable for the validation of the method when a standard multilayer structure to be used as a reference is not available, is presented and discussed. Finally, measurements of the thicknesses of actual multilayer structures and, in particular, of structures in the ophthalmic and microelectronic technology field, are carried out.