Highly Sensitive Pressure Transducer for Measuring Arterial Pulse Wave Velocity Based on Giant Magneto-Impedance Sensors

Figures

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  Figure 1. Configuration of the pressure transducer using a GMI sensor and an incompressible chamber [18].

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  Figure 2. The main methods for assessing the carotid-radial distance in PWV evaluation: “direct” measurement of the carotid-radial distance, using distance (da); “subtractive” method for measuring the carotid-radial distance, using lengths (db) and (dc) [2].

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  Figure 3. Helmholtz coil with a GMI sample positioned at its centre.

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  Figure 4. Average curves of (a) magnitude and (b) phase of the GMI sample with a length of 3 cm, excited by iC = [40 + 30sin(2π(700 × 103)t)] mA. (c) Linear Region of the average phase curve of the GMI sample (0.3 Oe ≤ H ≤ 0.7 Oe).

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  Figure 5. (a) Block diagram of the magnetic field-to-voltage electronic transduction circuit and (b) Final version of the magnetic field-to-voltage electronic transduction circuit.

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  Figure 6. Experimental measurement results of the circuit output voltages for different H values expressed in Oe.

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  Figure 7. Dependence of the magnetometer sensitivity on the frequency of the excitation magnetic field.

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  Figure 8. Noise spectral density of the output voltage of the developed magnetometer, expressed in nT/√Hz, using an average of (a) 10 and (b) 30 samples.

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  Figure 9. Experimental setup implemented for the direct measurement of the pulse wave, without mechanical amplification, using the magnetometer and magnetic marker positioned at the pulse wave measurement points: (a) carotid, (b) brachial, and (c) radial.

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  Figure 10. Result of experimental measurements of pulse waves: (a) carotid, (b) brachial, and (c) radial acquired with the magnetometer and magnetic marker adhered to the research participant’s skin.

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  Figure 11. (a) Filtered signal, (b) first derivative, and (c) second derivative of a carotid pulse wave signal acquired with the magnetometer and a magnetic marker adhered to the research participant’s skin.

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  Figure 12. Recordings of the carotid pulse wave in (a) and the radial pulse wave in (b), acquired synchronously using two GMI magnetometers. The red squares correspond to the starting point of each cycle in the carotid and radial records. The delay time (dT) corresponds to the time interval between the pink and green lines.