title: Frequency response in bone joint acoustic sensor development.
abstract: BACKGROUND
  Elderly people are often affected by age-related knee osteoarthritis (KOA). The development of sensors for measuring and diagnostic devices used in preventive healthcare of that illness therefore constitutes an urgent issue.
  
  
  OBJECTIVE
  After developing a bone joint acoustic sensor (BJAS) that receives signals of mechanical vibrations in the knee joints during bending and stretching motions, we tested it and compared responses with those of an acceleration sensor used as a reference.
  
  
  METHODS
  For six examinees in their 20 s, using an acceleration sensor as a reference for comparison with BJAS, we conducted two frequency-response tests of impact excitation and knee bending and stretching. For impact excitation tests, two transmission systems of hard materials and soft materials were applied. We examined the cross spectral density, coherence function, Fourier transform and quantified signal.
  
  
  RESULTS
  Although BJAS detected signals of 0.5-15.0 kHz in impact excitation tests, considerably strong damping was found for soft specimens at higher frequencies. Therefore, acceleration sensors showed superiority over BJAS for impact excitation. However, for knee bending and stretching, BJAS detected signal frequencies of 0.5-8.0 kHz for all six examinees. BJAS demonstrated marked superiority over the acceleration sensor. Furthermore, we were able to quantify the signal intensity for each frequency for comparison.
  
  
  CONCLUSIONS
  The BJAS frequency response was superior to that of the acceleration sensor for capturing signals from knee bending and stretching. This superiority suggests its promise for application to clarify mechanical signals from knees.
authors.affiliation: College of Engineering, Nihon University, Koriyama, Japan.
authors.forename: Mitsuo
authors.initials: M
authors.lastname: Nagao
authors.affiliation: Department of Orthopedic Surgery, Fukushima Medical University, Fukushima, Japan.
authors.forename: Shin-ichi
authors.initials: S
authors.lastname: Konno
authors.affiliation: Department of Biomedical Engineering, Yonsei University, Wonju, Korea.
authors.forename: Young Ho
authors.initials: YH
authors.lastname: Kim
authors.affiliation: College of Engineering, Nihon University, Koriyama, Japan.
authors.forename: Osamu
authors.initials: O
authors.lastname: Yokota
mesh_terms: D061725:Accelerometry; D000162:Acoustics / Q000295:instrumentation*; D005583:Fourier Analysis; D064368:Healthy Volunteers; D006801:Humans; D007719:Knee Joint; D020370:Osteoarthritis, Knee / Q000175:diagnosis* / Q000503:physiopathology*; D058998:Remote Sensing Technology / Q000295:instrumentation*; D055815:Young Adult
keywords: Bone joint; acoustic sensor; coherence; frequency response; impact excitation method; knee joint; pig skin; short time Fourier transform (STFT)