Abstract
In this paper, two remote sensors for noncontact surface hardness evaluation are proposed, which are based on acoustics of air in the space between sensor and object surface. In the first method the acoustic impedance of the air is measured with the sensor set in front of object surface. The impedance is sensitive to surface hardness near the resonant frequency in the room surrounded by the sensor and the object. In the second one, hardness is evaluated using the compound sound composed of a high tone and a low tone. The lower frequency tone is used for driving surface and the higher one for measuring the induced vibration of surface, from which hardness is evaluated. These two sensors have their own merits. Using them we can estimate dryness of wet painted surface, or state of components fixed on circuit board without any mechanical contact, and they do not suffer from any problems caused by mechanical contact which is, the inherent difficulty with any other tactile sensor.
