Fig. 5From: A vibration sensor approach to detect intra-articular needle tip placement in the knee joint: a proof-of-concept studyPower spectral density in decibel (dB) of the A. low (50–500 Hz) and B. high (500–1500 Hz) frequency bands for needle gauge of 18G, 21G and 24G, when the needle tips were either at the extra-articular (round markers) or intra-articular (star markers) locationsBack to article page