Arthroscopically implantable force probe Designed for medical research, this sensor can measure forces in living tissues. Micro-machined, heat treated stainless steel is used to create the tiny elliptical spring structure, which deforms elastically under load. A thermally matched strain gauge bonded to the steel probe provides a sensitive, linear output proportional to applied force. The elliptical cross section and ultra-flexible, flat tape cable keep the device anchored and oriented within fibrous materials. Specialized instruments have been developed to bury the transducer within tissue substance. A suture eyelet in the wall of the probe facilitates removal. The device is fully encapsulated with vacuum deposited, biocompatible parylene for protection against saline. Approximately the size of a No. 2 pencil Applications include orthopaedic research, tactile sensing, and feedback for electrical muscle stimulation. Electrical Specifications point, the patented AIFP is designed for placement in very tight areas. Mechanical Specifications Cross section Polyimide and copper tape cable, 20 cm long Approx. 1.5 N/micron Fatigue life Approx. 1 million cycles at 1/2 FS Transverse stiffness Temp. Coeff. - Offset - Span * Full scale range may be tailored for specific applications. section break U.S. Patent Nos. 4,993,428 & 5,083,573 and Patents Pending

AIFP's are factory calibrated by applying transverse forces. A calibrated load cell (accuracy +/- 0.12 N) is used as a reference. Non-linearity is defined as the % deviation from a best fit straight line, as determined by linear regression, over the calibrated range. AFP Nonlinearity: for direct transverse loading AFP Calibration: Probe output for direct transverse loading y = 1.7709e-2 + 0.20620x Load Cell Output (N) 4 Load Cell Output (N) Signal conditioning Measuring soft tissue forces Excitation and measurement is accomplished by classic Wheatstone bridge circuits and instrumentation amplifiers....