Use of EMFi as a blood pressure pulse transducer

This paper describes and tests two prototype series of pressure transducer arrays based on electromechanical film (EMFi). By offering high (∼TΩ) resistance, EMFi is an excellent material for low-current long-term measurement applications. About 50 transducer arrays were designed and tested using different configurations and electrode materials to sense low-frequency pressure pulsations on the radial artery in the wrist. Essential requirements included an adequate linear response in the desired temperature range and uniform quality. Transducer sensitivity was tested as a function of temperature in the range of 25°C-45°C at varying dc and ac pressures. The average sensitivity of the EMFi used in the transducers proved adequate (∼2.2mV/mmHg and ∼7 mV/mmHg for normal and high-sensitive films) for the intended purpose. Moreover, EMFi´s spectral response covered the required range for biomedical applications, but it was unable to measure static pressure (f_{3 dB}≈38 μHz). The sensitivity of the EMFi material was sufficiently constant for measuring blood pressure pulses in the desired range (0-300 mmHg), and the best achieved deviation in sensitivity was ±5.1%. It was also established that in addition to sensitivity and its standard deviation, crosstalk between electrode elements also depends strongly on electrode thickness.