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Radulescu E.G.♦, Lewin P.A.♦, Wójcik J., Nowicki A., Berger W.A.♦, The influence of finite aperture and frequency response of ultrasonic hydrophone probes On the determination of acoustic output,
Ultrasonics, ISSN: 0041-624X, DOI: 10.1016/j.ultras.2003.11.019, Vol.42, No.1-9, pp.367-372, 2004Streszczenie: The influence of finite aperture and frequency response of piezoelectric ultrasonic hydrophone probes on the Thermal and Mechanical Indices was investigated using a comprehensive acoustic wave propagation model. The experimental verification of the model was obtained using a commercially available, 8 MHz, dynamically focused linear array and a single element, 5 MHz, focused rectangular source. The pressure–time waveforms were recorded using piezoelectric polymer hydrophone probes of different active element diameters and bandwidths. The nominal diameters of the probes ranged from 50 to 500 μm and their usable bandwidths varied between 55 and 100 MHz. The Pulse Intensity Integral (PII), used to calculate the Thermal Index (TI), was found to increase with increasing bandwidth and decreasing effective aperture of the probes. The Mechanical Index (MI), another safety indicator, was also affected, but to a lesser extent. The corrections needed were predicted using the model and successfully reduced the discrepancy as large as 30% in the determination of PII. The results of this work indicate that by accounting for hydrophones' finite aperture and correcting the value of PII, all intensities derived from the PII can be corrected for spatial averaging error. The results also point out that a caution should be exercised when comparing acoustic output data. In particular, hydrophone's frequency characteristics of the effective diameter and sensitivity are needed to correctly determine the MI, TI, and the total acoustic output power produced by an imaging transducer. Słowa kluczowe: Ultrasound imaging, Nonlinear propagation, Spatial averaging, Safety indices Afiliacje autorów:
Radulescu E.G. | - | inna afiliacja | Lewin P.A. | - | Drexel University (US) | Wójcik J. | - | IPPT PAN | Nowicki A. | - | IPPT PAN | Berger W.A. | - | inna afiliacja |
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Radulescu E.♦, Wójcik J., Lewin P.A.♦, Nowicki A., Nonlinear Propagation Model for Ultrasound Hydrophones Calibration in Frequency Range up to 100 MHz,
Ultrasonics, ISSN: 0041-624X, DOI: 10.1016/S0041-624X(03)00124-0, Vol.41, No.4, pp.239-245, 2003Streszczenie: To facilitate the implementation and verification of the new ultrasound hydrophone calibration techniques described in the companion paper (somewhere in this issue) a nonlinear propagation model was developed. A brief outline of the theoretical considerations is presented and the model’s advantages and disadvantages are discussed. The results of simulations yielding spatial and temporal acoustic pressure amplitude are also presented and compared with those obtained using KZK and Field II models. Excellent agreement between all models is evidenced. The applicability of the model in discrete wideband calibration of hydrophones is documented in the companion paper somewhere in this volume. Słowa kluczowe: Nonlinear propagation modeling, Nonlinear propagation, JW model Afiliacje autorów:
Radulescu E. | - | inna afiliacja | Wójcik J. | - | IPPT PAN | Lewin P.A. | - | Drexel University (US) | Nowicki A. | - | IPPT PAN |
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Radulescu E.♦, Lewin P.A.♦, Wójcik J., Nowicki A., Calibration of Ultrasonic Hydrophone Probes up to 100 MHz using Time Gating Frequency Analysis and Finite Amplitude Wave,
Ultrasonics, ISSN: 0041-624X, DOI: 10.1016/S0041-624X(03)00123-9, Vol.41, No.4, pp.247-254, 2003Streszczenie: A number of ultrasound imaging systems employs harmonic imaging to optimize the trade off between resolution and penetration depth and center frequencies as high as 15 MHz are now used in clinical practice. However, currently available measurement tools are not fully adequate to characterize the acoustic output of such nonlinear systems primarily due to the limited knowledge of the frequency responses beyond 20 MHz of the available piezoelectric hydrophone probes. In addition, ultrasound hydrophone probes need to be calibrated to eight times the center frequency of the imaging transducer. Time delay spectrometry (TDS) is capable of providing transduction factor of the probes beyond 20 MHz, however its use is in practice limited to 40 MHz. This paper describes a novel approach termed time gating frequency analysis (TGFA) that provides the transduction factor of the hydrophone probes in the frequency domain and significantly extends the quasi-continuous calibration of the probes up to 60 MHz. The verification of the TGFA data was performed using TDS calibration technique (up to 40 MHz) and a nonlinear calibration method (up to 100 MHz). The nonlinear technique was based on a novel wave propagation model capable of predicting the true pressure–time waveforms at virtually any point in the field. The spatial averaging effects introduced by the finite aperture hydrophones were also accounted for. TGFA calibration results were obtained for different PVDF probes, including needle and membrane designs with nominal diameters from 50 to 500 μm. The results were compared with discrete calibration data obtained from an independent national laboratory and the overall uncertainty was determined to be ±1.5 dB in the frequency range 40–60 MHz and less than ±1 dB below 40 MHz. Słowa kluczowe: Time gating frequency analysis (TGFA), Time delay spectrometry (TDS), High frequency hydrophone calibration, Nonlinear hydrophone calibration, High frequency ultrasound, Ultrasonic metrology Afiliacje autorów:
Radulescu E. | - | inna afiliacja | Lewin P.A. | - | Drexel University (US) | Wójcik J. | - | IPPT PAN | Nowicki A. | - | IPPT PAN |
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