Research Papers

Battery-Less Wireless Instrumented Knee Implant

[+] Author and Article Information
R. Rajamani

Department of Mechanical Engineering,
University of Minnesota,
Minneapolis, MN 55455

J. E. Bechtold

Department of Orthopaedic Surgery,
University of Minnesota,
Minneapolis, MN 55455

Manuscript received April 28, 2012; final manuscript received January 2, 2013; published online February 11, 2013. Assoc. Editor: Vijay Goel.

J. Med. Devices 7(1), 011006 (Feb 11, 2013) (11 pages) Paper No: MED-12-1057; doi: 10.1115/1.4023412 History: Received April 28, 2012; Revised January 02, 2013

Over 400,000 total knee replacement procedures (TKR) are performed annually in the United States. This paper focuses on the development of a battery-less wireless instrumented tibial tray for performance feedback in TKR implants. The proposed instrumented tibial tray is powered internally by an integrated piezoelectric energy harvesting system. Energy is harvested during the walking of the patient when forces are exerted on the tibial component. The sensors and wireless electronics are entirely powered from the harvested energy. This tibial tray is also instrumented with capacitive force sensors and an ultra low-power method to measure the capacitive force sensors. A bench top test rig is developed for testing the battery-less wireless knee replacement implant. For a person with a body weight of 55 kg, the energy harvesting system can fully charge the storage capacitors in 11 steps and can harvest an average of 1051 μJ per step. To power the force measurement system for ten seconds and to transmit the data, the piezoelectric energy harvesting system must be charged before the force measurement process is initiated by a minimum of 11 steps and a minimum of two steps must be taken during the force measurement process. During the force measurement process, each force sensor is sampled at a frequency of 10 Hz for ten seconds; thereafter, all of the data is transmitted to the RF base station. The resulting capacitive force sensors adequately represented cyclic loads; however, the sensors demonstrated some issues with repeatability.

Copyright © 2013 by ASME
Your Session has timed out. Please sign back in to continue.



Grahic Jump Location
Fig. 2

Total knee replacement implant

Grahic Jump Location
Fig. 3

Layout of instrumented tibial tray

Grahic Jump Location
Fig. 4

Schematic of typical PEHS circuit

Grahic Jump Location
Fig. 5

State diagram of energy harvesting system

Grahic Jump Location
Fig. 6

Schematic for RC time constant measurement circuit

Grahic Jump Location
Fig. 7

Diagram of concept for a capacitive sensor

Grahic Jump Location
Fig. 8

Graph showing nonlinear relation between dielectric thickness and sensor sensitivity

Grahic Jump Location
Fig. 9

Final design of capacitive force sensor

Grahic Jump Location
Fig. 10

Arrangement of force sensors in tibial component

Grahic Jump Location
Fig. 11

Cross-section of prototype knee implant showing layout of various components

Grahic Jump Location
Fig. 12

Pictures of tibial component showing circuit board, ground plate, and compliant material for sensors

Grahic Jump Location
Fig. 13

Picture of knee load application device

Grahic Jump Location
Fig. 14

Typical loading cycle with knee load application device at 276 kPa air pressure

Grahic Jump Location
Fig. 15

Typical charging cycle for 836 N nominal peak force

Grahic Jump Location
Fig. 16

Relationship between harvested energy of PEHS and applied force

Grahic Jump Location
Fig. 17

The top graph shows the force linearly increasing on the piezo transducer. The middle graph shows the voltage on the input capacitor which is coupled to the piezo transducer by a full-wave rectifier. The bottom graph shows the voltage on the storage capacitor.

Grahic Jump Location
Fig. 18

State diagram for capacitive sensor measurements

Grahic Jump Location
Fig. 19

Relationship between discharge time and capacitance

Grahic Jump Location
Fig. 20

Charge/discharge cycle for capacitance measurement

Grahic Jump Location
Fig. 21

Relationship between measured sensor capacitance and force

Grahic Jump Location
Fig. 22

Force measurements for sensor #1, after calibration completed

Grahic Jump Location
Fig. 23

Storage capacitor voltage while measuring sensors at 10 Hz

Grahic Jump Location
Fig. 24

Storage capacitor voltage while transmitting data




Some tools below are only available to our subscribers or users with an online account.

Related Content

Customize your page view by dragging and repositioning the boxes below.

Related Journal Articles
Related eBook Content
Topic Collections

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In