Sensitive stress sensor using amorphous magnetostrictive wires on beam with both ends built in and diaphragm

Introductioq The authors have obtained giant straingauge factors of about 2W0 and 1200 using cold drawn and then tension annealed CoSiB amorphous wires (a-wire, for short) with 20 I UI and 30 p diameters respectively (made by UNlTlKA LID.). The wires are magnetized with a high frequency current or a sharp pulse current to generale the stress-impedance (SI, for short) effect [1][2]. We have also reported stress sensors using a pair of amorphous CoSiB wires fixed to a plastic cantilever beam combined with a CMOS IC multivibrator circuit (31. This type sensor has a high sensitivity and a high linearity in the range of -0.75-1.25 gr with a resolution of 2.5 mgr. However, the cantilever type sensor is not applicable lo detect distributed stresses as gas and liquid, because that two a-wires must be fixed on both sides of the plate. In this paper, new stress sensors with a beam with both ends built in and a diaphragm are presented in which a pair of a-wires are fixed on a single side of the substrates. A blood vessel pulsation is stably detected using the diaphragm type SI sensor with a CMOS IC multivibrator. Exoeriments and discuss ion Fig. 1 illustrates a beam with both ends built in type stress sensor head with induced stress distribution. When a weight (W) is loaded on the center of the beam, the a-wire@ (CoSiB with U) p diameter and 7 mm length) fixed on the central area of the plastic plate ( 45 X 15 X 0.4 mm) receives a compressive stress in longitudinal direction, while the a-wire @ fixed on a edge area receives a tensile stress in longitudinal direction. Fig. 2 shows measured results of SI characteristics of the a-wire @ and @set in a CMOS IC multivibrator sensor circuit as shown in Fig. 3. The rising time of the pulse current applied through @and @is 15 ns which corresponds to a sinusoidal current with about 30 MHz for the magnetization. Fig. 4 shows the output voltage Eout versus weight W characteristics of the SI sensor which shows a resolution of about 10 mgr in a linear range of -1-4 gr. Fig. 5 represents a detection of blood vessel pulsations of wrist artery in (a), and carotid artery in (b) using a flexible diaphragm.