source:© 2013 IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control
The characterization of the spatial and frequency response of acoustic detectors is important for enabling accurate optoacoustic imaging. In this work, we developed a hybrid method for the characterization of the spatially dependent response of ultrasound detectors. The method is based on the experimental determination of the receive-mode electrical impulse response (EIR) of the sensor, which is subsequently convolved with the corresponding spatial impulse response (SIR), computed numerically. The hybrid method is shown to have superior performance over purely experimental techniques in terms of accurate determination of the spatial and temporal responses of ultrasonic detectors, in high as well as low sensitivity regions of the sensor.
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Fig. 1 Effect of the spatial impulse response (SIR) on an optoacoustic signal. (a) Optoacoustic waves emanating from the source at r ′ reach the different points of the transducer, r d1 and r d2 , at different times t1 and t2(c represents the speed of sound). (b) Geometry for the numerical example: the sensor is 1.8 mm along the y direction, 15 mm along the z direction (here the sensor is shown from the side) and it is cylindrically focused to 40 mm. The source is located at 33 mm from the sensor along its median axis x . The relative dimensions have been exaggerated for ease of representation. (c) Simulated optoacoustic signal (solid blue curve) and the distorted signal (dashed red curve) that results after convolution with the SIR at a point out of focus. Inset: SIR used for convolution. (d) Frequency spectra of the simulated signal (solid blue curve) and the signal convolved with the SIR (dashed red curve). Inset: spectrum of the SIR.