Nasa Tech Briefs

This probe can measure tissue inside living bodies non-invasively using a thin-film piezoelectric pressure sensor.

This ultrasonic echo apparatus can measure tissue inside living bodies, non-invasively. The developed probe has a film-like piezoelectric sensor installed on the contact surface of an ordinary medical ultrasonic probe, and it can measure the contact pressure distribution between the probe and living bodies. Since it can measure, with an ultrasonic echo image, the deformation of living bodies when a probe is pressed against them dynamically, it can calculate the distribution of mechanical impedance within living bodies by using information on contact pressure at the contact surface.

A schematic of the Ultrasonic Echo Probe.
The piezoelectric sensor uses an aluminum nitride piezoelectric film on the contact surface of the ultrasonic probe. Its thickness is 40 micrometers, and it can measure the contact pressure directly, with little affecting ultrasonic transmissions/receptions.

Mainstream pressure sensors are adapted to measure deformation of a diaphragm under pressure using a strain gauge or a laser. The applied pressure on the diaphragm is detected from a correlation between the degree of deformation and the pressure. However, in this type of pressure sensor, the diaphragm requires a supporting mechanism and the structure is complex. Accordingly, the thickness of the pressure sensor can only be reduced to several millimeters.

Another type of pressure sensor uses a pressure-sensitive material to measure an electric resistance shift that is generated when pressure is applied. A value of the applied pressure is computed from a correlation between the electric resistance and the pressure. This type of pressure sensor does not tolerate a thickness of 100 mm or less because such a thickness impairs durability and mechanical strength.

The pressure sensor used in this technology has a simple and thin structure with sufficient durability and sufficient mechanical strength. This is achieved by placing a single internal electrode between a pair of thin-film external electrodes that have piezoelectric layers on the inner sides, and by completely shielding the internal electrode from outside between the pair of external electrodes.

The pressure sensor includes a pair of external electrodes, which are made of conductive thin films that are provided with piezoelectric layers on the inner sides; and a single internal electrode, made of a conductive thin film, which is sealed between the pair of external electrodes. The thin pressure sensor can be brought into direct contact with a conductor such as the living body. Further, the sensitivity of the thin pressure sensor can be increased by increasing the pressure face area. These characteristics enable the thin pressure sensor to capture a pressure change on a skin surface of the living body.

This technology is offered by the Japan Industrial Technology Association. For more information, view the TechPak at

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