A Flexible and Highly Sensitive Inductive Pressure Sensor Array Based on Ferrite Films

There is a rapid growing demand for highly sensitive, easy adaptive and low-cost pressure sensing solutions in the fields of health monitoring, wearable electronics and home care. Here, we report a novel flexible inductive pressure sensor array with ultrahigh sensitivity and a simple construction, for large-area contact pressure measurements. In general, the device consists of three layers: a planar spiral inductor layer and ferrite film units attached on a polyethylene terephthalate (PET) membrane, which are separated by an array of elastic pillars. Importantly, by introducing the ferrite film with an excellent magnetic permeability, the effective permeability around the inductor is greatly influenced by the separation distance between the inductor and the ferrite film. As a result, the value of the inductance changes largely as the separation distance varies as an external load applies. Our device has achieved an ultrahigh sensitivity of 1.60 kPa−1 with a resolution of 13.61 Pa in the pressure range of 0–0.18 kPa, which is comparable to the current state-of-the-art flexible pressure sensors. More remarkably, our device shows an outstanding stability when exposed to environmental interferences, e.g., electrical noises from skin surfaces (within 0.08% variations) and a constant pressure load for more than 32 h (within 0.3% variations). In addition, the device exhibits a fast response time of 111 ms and a good repeatability under cyclic pressures varying from 38.45 to 177.82 Pa. To demonstrate its practical usage, we have successfully developed a 4 × 4 inductive pressure sensor array into a wearable keyboard for a smart electronic calendar application.

Alveolar pressure measurement in open-chest rats

In open-chest rats, alveolar pressure was measured with alveolar capsules connected via pliable tubing to inductive pressure transducers. By means of the interrupter technique during constant-flow inflation, it was possible to determine pulmonary static elastance (Est,L) and tissue and airway resistances (Rdiff,L and Rinit,L, respectively). In eight anesthetized paralyzed mechanically ventilated rats, 118 measurements of Rdiff,L and Est,L were performed over a wide range of flows and tidal volumes. There was excellent agreement between the data calculated using transpulmonary pressures and those computed using capsule pressures, the latter being measured at different points of the lung. In another group of rats studied under the same experimental conditions, two capsules were simultaneously placed on different pulmonary lobes. No regional differences in pulmonary mechanics could be detected in either experiment. In addition, alveolar pressure could also be measured accurately by a catheter inserted into lung parenchyma.

Investigations of Pulsating Turbulent Pipe Flow

Measurements of velocities and pressure gradients in pulsating turbulent pipe flow are performed by means of a directionally sensitive Laser-Doppler Velocimeter and inductive pressure transducers. The desired accuracy of the instrumentation was confirmed by preliminary tests in turbulent pipe flow without pulsations and in laminar oscillating flow. The temporal and spatial velocity field in the pulsating turbulent pipe flow could be satisfactorily determined for the entire flow field with the exception of the region extremely close to the wall (y < 0.0065, where y expresses the ratio of wall distance to pipe radius). The results are discussed and compared with results of theoretical calculations.