1,721,011 research outputs found
Propagation of error analysis in a total least squares estimator in absolute gravimetry
No full textHigh-precision measurements often resort to least-squares estimation via observation models in which the quantity of interest is one of the unknowns. The case when both the dependent and independent variables of the model are stochastic is of particular interest. An example is absolute gravimetry, where the orbit of a test mass is tracked by a laser interferometer and is reconstructed by the least-squares method. In orbit reconstruction, space and time enter symmetrically and both time and position are stochastic. We present orbit reconstruction as a total least-squares problem to establish an error model for the propagation of tracking errors. We also give an asymptotic formula expressing the relevant contribution to the uncertainty of gravity determination
Propagation of error analysis in least-squares procedures with second-order autoregressive measurement errors
No full textAccuracy evaluation is an integral part of parameter estimation by least-squares analysis. We present an analysis of error propagation when the measurement error is a second-order autoregressive process. When the measurement correlation is neglected, least-squares procedures underestimate the uncertainty. In order to scale up the uncertainty, we investigated autoregressive measurement errors, calculated their correlation, and assessed the estimate uncertainty in terms of the sampling frequency. Our results, which are amenable to approximations and numerical computations, show clearly how correlation influences error propagation and are useful in devising strategies for optimal measurement design
Procedimento per la misura della conduttanza ultrasonora e relativo sistema di misura
No full textIl brevetto proposto è relativo ad un apparato per la misura della forza di radiazione prodotta da un fascio ultrasonoro in acqua su bersaglio, che può essere sia assorbente, sia riflettente.
L'uso di una cella di carico immergibile consente di avere una risposta nel tempo assai più rapida rispetto ad una bilancia a forza di radiazione tradizionale e consente quindi l'uso di tecniche di elaborazione delle serie temporali per migliorare il rapporto segnale rumore della misura
A comparative evaluation of three hydrophones and a numerical model in high intensity focused ultrasound fields
No full textThe pressure fields of two different high intensity focused ultrasound (HIFU) transducers operated in burst mode were measured at acoustical power levels of 25 and 50 W (continuous wave equiva- lent) with three different hydrophones: A fiber-optic displacement sensor, a commercial HIFU nee- dle hydrophone, and a prototype of a membrane hydrophone with a protective coating against cavitation effects. Additionally, the fields were modeled using a freely available simulations soft- ware package. The measured waveforms, the peak pressure profiles, as well as the spatial-peak tem- poral-average intensities from the different devices and from the modeling are compared and possible reasons for differences are discussed. The results clearly show that reliable pressure meas- urements in HIFU fields remain a difficult task concerning both the reliability of the measured val- ues and the robustness of the sensors used: Only the fiber-optic hydrophone survived all four exposure regimes and the measured spatial-peak temporal-average intensities varied by a factor of up to 1.5 between the measurements and the modeling and between the measurements among them-
selves
Misura della potenza ultrasonora utilizzando una cella di carico immergibile
No full textUno dei principali indici che caratterizzano un trasduttore ultrasonoro è la Potenza emessa, P. Le applicazioni principali degli ultrasuoni, in ambito biomedico, si possono distinguere in tre categorie caratterizzate da diversi valori di potenza:
- Diagnostica (esami ecografici), potenze di lavoro inferiori ai 500 mW;
- Terapia (terapie fisioterapiche),potenze comprese tra 800 mW e 4 W;
- HIFU (High Intensity Focused Ultrasound, tecnica utilizzata per cura di tumori) potenze comprese tra da 40 W fino a 500 W.
Presso i laboratori dell’Istituto Nazionale di Ricerca Metrologica, I.N.RI.M., è da tempo attivo il sistema di misura per ultrasuoni che consente la determinazione della potenza ultrasonora emessa da un trasduttore ultrasonoro sia esso di tipo metrologico o sia commerciale. Viene proposto un apparato di misura innovativo che consente di estendere la misura della potenza a valori molto elevati senza danneggiare i bersagli dell’apparato di misura. Il sistema è stato proposto per un brevetto
HIFU Ultrasound Power Measurement at INRiM
No full textThe new measurement apparatus, based on a submersible load cell is presented. Result of measuremetn on plane wave and HIFU transuders are shown in comparison with conventional Radiation Force Balance
PROGETTO EURAMET: HLT03 DUTY - DOSIMETRIA PER TERAPIE ULTRASONORE. CONFRONTO TRA METODI DI MISURA EURAMET PROJECT: HLT03 DUTY - DOSIMETRY FOR ULTRASOUND THERAPY. INTERCOMPARISON OF METHODS
No full textStandardized and traceable dose has not yet been developed for medical ultrasound applications. This means that the ‘amount’ of ultrasound required for a particular therapy cannot be calculated and that the ‘amount’ actually delivered quantified. The aim of EURAMET EMRP project “Dosimetry for Ultrasound Therapy - DUTy” project was developing the metrological infrastructure (definitions, validated measurement and modelling methods) which underpins the specification of dose for therapeutic ultrasound applications allowing appropriate treatment planning and risk assessment
Accuracy assessment of data analysis in absolute gravimetry
No full textThis paper presents an accurate assessment of fringe processing in absolute gravimetry. The use of a computer-based digitizer and digital data processing proved effective in the validation of gravity measurements
- …
