RESEARCH
Study on Plant
Estimation of water stress of plant by vibration analysis of leaf
In order to perform optimum irrigation control at a plant factory or greenhouse, it is necessary to know the crop needs for water (i.e. water stress of plant) non-invasively in real-time. But, plants do not speak language. Therefore we need to "hear" the message from the plant observing appearance or various responses. Such a method is called "SPA" (Speaking Plant Approach). In our laboratory, we proposes a method to estimate the water stress of plants from the change of natural frequency of plants, which reflects wilting of plant, and verifies effectiveness of this method. At present, in order to push a leaf to vibrate, we employ ultrasonic acoustic radiation pressure. And the damped vibrations of leaf is measured by using a laser displacement sensor or a high speed camera. The obtained vibration displacement is subjected to Fourier transformation to obtain a power spectrum, and the natural frequency of the leaf is obtained from the peak frequency. As a ultrasonic wave, we use a 40 kHz carrier radiated from a "parametric speaker" known as a directional speaker.
Study on Clinical Engineering
Estimation of vascular age by sphygmogram vibration during upper arm compression.
Arteries of Everyone lose its elasticity gradually with age. That is, the arteries become stiff according to age. The degree of hardening of this artery is expressed by the corresponding age, which is called "blood vessel age".
It has been reported that the blood vessel age can be estimated by acceleration plethysmogram (APG) which is obtained by second derivative of the sphygmogram wave (Plethysmographic) at the fingertip. And in general, a large vibration is observed in the case of young supple blood vessels. On the other hand, the vibration become obscure according with the curing progresses.
We consider that sphygmogram vibration or Korotkoff sound which is observed by pressing an upper arm also contain such information of elasticity of blood vessel. Thus we have been investigating such waves in our laboratory. We are investigating not only Korotkoff sound but also the sphygmogram vibration of cuff pressure, because recent automatic sphygmomanometers measure the maximum and minimum blood pressures directly from sphygmogram vibration at the time of blood pressure measurement.
Study on Noncontact Respiratory Rate Monitor to Check Sleep Apnea Syndrome
There are several ways to monitor respiration rate, and the method of measuring breath sound is one of them. However, it is necessary to adhere a microphone near the nose for acquiring the breath sound, and there are some problems such as being disconnected during sleeping and cable tangling. Therefore, we are studying whether it is possible to monitor the respiratory rate by selectively collecting the sound near the face with a sound collecting microphone. Estimation by this method alone is difficult, but we believe that more reliable diagnosis will be possible by using it complementarily with other methods.
Study on internal power generation for pacemaker power supply
Because pacemakers are driven by primary batteries, periodic battery replacement surgery is necessary, which has a problem of a heavy burden on wearers. Also, when charging from outside the body using a secondary battery,Long time constraint is necessary for charging. Therefore, we are considering a method for obtaining semi-permanently supplying power by storing the energy of vibration of beating or the energy of daily activities to a large capacity of electric double layer capacitor little by little.