Disposable blood sensor
Invasive blood pressure transducers must accurately reproduce the heart's blood pressure waveform as electrical signals; the manufacturing process must be repeatable and biocompatible; and cost must be low enough to discard after use, reducing contamination risk.
One solution: A single-use pressure sensor well suited to low-cost batch production. Semiconductor manufacturing techniques create four piezoresistive strain gauges arranged as a Wheatstone Bridge within a silicon wafer. Etching away the wafer's underside beneath the resistors leaves a 15-micron diaphragm.
| Blood flow through the sensor deforms the silicon diaphragm, creating tensile and compressive stress zones. |
 |
During use, blood pressure imposes stress zones within the diaphragm; two strain gauges come under tensile stress, two suffer compression. Changes in resistance unbalance the Wheatstone Bridge producing an output signal directly proportional to applied pressure.
Available for license, the design accommodates a -100 to 300 mm Hg pressure range and an overpressure of [email protected] maximum pressure. Another application: washing machines.
Javier Gracia,
Centro de Estudios Investigaciones Tecnicas (CEIT) (E),
Paseo de Manuel Lardizabal 15
PO Box 1555, 20009 San Sebastian
Spain
Tel: +34 943 213076.
Fluid-powered stepper
The main piston chamber, formed within the housing, contains two arcuate (curved) pistons. Piston chambers, within each housing half, use a clutch piston affixed to the outer diameters of two mounting rings (one left hand, one right hand), that are concentric to the output shaft.
 |
| A pneumatic or hydraulic single-direction rotary device for automation, the AVS rotary stepper's output shaft rotates the same direction when either port is pressurized, yet it operates as a double-acting cylinder without a return stroke or air accumulation. |
To work, pressurized fluid enters either port and flows into the clutch piston chamber. One clutch piston locks onto the shaft as it moves axially onto a dowel pin. The other clutch piston locks on another pin attached to the housing as it moves to the end of its stroke.
Fluid drives both the clutch pistons along the output shaft, and the main pistons as they are alternately engaged with the output shaft to translate rotational energy to the output shaft. Available configurations provide up to eight steps per revolution, and additional flexibility is possible using a belt drive or pulley arrangement.
Daniel Hughes, Holmes Automation Components (F), 10513 Two Notch Rd., Elgin, SC 29045; (803) 699-4996.