Ultrasound power measurement system design using PVDF sensor and FPGA technology

Abstract

Ultrasound machine is widely used in industrial and medical institutions. With the purpose of avoiding the unwanted power exposed on human, ultrasound power meter is employed to measure output power of ultrasound machine for diagnostic, therapeutic and non-destructive testing purposes. The existing ultrasound power meter, however, is high-cost, low-resolution and only for specific machine. Radiation balance method consists of calculation and calibration complexity while the calorimetric produces inaccurate result compared to the standard. On the other hand, application of piezoelectric sensor in hydrophone-based measurement requires advancement on processing device and technique. This work deals with the development of ultrasound power measurement system on Field Programmable Gate Array (FPGA) platform. Polyvinylidene Fluoride (PVDF) was employed to sense medical ultrasonic signal. PVDF film’s behavior and its electro-acoustic model were observed. Signal conditioner circuit was then described. Next, a robust low-cost casing for PVDF sensor was built, followed by the proposal of the use of digital-system ultrasound processing algorithm. The simulated sensor provided 2.5 MHz to 8.5 MHz response with output amplitude of around 4 Vpp. Ultrasound analog circuits, after filtering and amplifying, provided frequency range from 1 MHz until 10 MHz with -5 V to +5 V voltage head-rooms to offer a wideband medical ultrasonic acceptance. Frequency from 500 kHz to 10 MHz with temperature span from 10 oC to 50 oC and power range from 1 mW/cm2 up to 10 W/cm2 (with resolution 0.05 mW/cm2) had been expected by using the established hardware. The test result shows that the platform is able to process 10 us ultrasound data with 20 ns time-domain resolution and 0.4884 mVpp magnitude resolutions. This waveform was then displayed in the personal computer’s (PCs) graphical user interface (GUI) and the calculation result was displayed on liquid crystal display (LCD) via microcontroller. The whole system represents a novel design of low-cost ultrasound power measurement system with high-precision capability for medical application. This may improve the existing power meters which have intensity resolution limitation (at best combination, of all products, utilize: 0.25 MHz - 10 MHz frequency coverage; 10 oC to 30 oC working temperature; 0 W/cm2 - 30 W/cm2 power range; 20 mW/cm2 resolution), neither having mechanism to handle the temperature disturbance nor possibility for further data analysis.