Naohiro Ueno

Flexible piezoelectric pressure sensors using oriented aluminum nitride thin films prepared on polyethylene terephthalate films

We have investigated the high sensitive piezoelectric response of c-axis oriented aluminum nitride (AlN) thin films prepared on polyethylene terephthalate (PET) films. The AlN films were deposited using a radio frequency magnetron sputtering method at temperatures close to room temperature. The c axes of the AlN films were perpendicularly oriented to the PET film surfaces. The sensor consisting of the AlN and PET films is flexible like PET films and the electrical charge is linearly proportional to the stress within a wide range from 0to8.5MPa. The sensor can respond to the frequencies from 0.3 to over 100Hz and measures a clear human pulse wave form by holding the sensor between thumb and middle finger. The resolution of the pulse wave form is comparable to a sphygmomanometer at stress levels of 10kPa. We think that the origin of the high performance of the sensor is the deflection effect, the thin thickness and high elastic modulus of the AlN layer, and the thin thickness and low elastic modulus of the ...

Dynamic contact sensing by flexible beam

This paper discusses a new dynamic sensing system capable of detecting the contact point between a flexible beam and an object. The proposed sensing system, named dynamic antenna, is simply composed of an insensitive flexible beam, a torque sensor, a joint position sensor, an actuator, and a payload at the tip end of the beam. The contact point can be detected through estimation of the oscillation frequencies of the beam in contact with the object. First, a dynamic model of the sensor is derived. Next, it is shown that information of the fundamental and the second natural frequencies is sufficient for unique determining of the contact point if the beam has uniform mass and stiffness distribution. In practical realization, the fundamental and the second natural frequencies of the beam in contact with the object are extracted from the torque sensor measurements with the use of the maximum entropy method. Then, the frequencies are mapped into the contact-point coordinate. Extraction of the frequencies and mapping them into the contact point constitute a sensing strategy which is tested under experiment.

Monitoring of Respiration and Heartbeat during Sleep using a Flexible Piezoelectric Film Sensor and Empirical Mode Decomposition

Cardiorespiratory monitoring during sleep is one of the basic means for assessment of personal health, and has been widely used in diagnosis of sleep disorders. This paper proposes a novel method for non-invasive and unconstrained measurement of respiration and heartbeat during sleep. A flexible piezoelectric film sensor made of aluminum nitride (AlN) material is used in this study. This sensor measures pressure fluctuation due to respiration and heartbeat on the contact surface when a subject is lying on it. Since the AlN film sensor has good sensitivity, the pressure fluctuation measured can be further separated into signals corresponding to respiration and heartbeat, respectively. In the proposed method, the signal separation is achieved using an algorithm based on empirical mode decomposition (EMD). Experiments have been conducted with three subjects. The experimental results show that respiration and heartbeat signals can be successfully obtained with the proposed method.

Flexible pulse-wave sensors from oriented aluminum nitride nanocolumns

Flexible pulse-wave sensors were fabricated from density-packed oriented aluminum nitride nanocolumns prepared on aluminum foils. The nanocolumns were prepared by the rf magnetron sputtering method and were perpendicularly oriented to the aluminum foil surfaces. The sensor structure is laminated, and the structure contributes to avoiding unexpected leakage of an electric charge. The resulting sensor thickness is 50 μm. The sensor is flexible like aluminum foil and can respond to frequencies from 0.1 to over 100 Hz. The sensitivity of the sensor to pressure is proportional to the surface area. The sensor sensitively causes reversible charge signals that correlate with the pulse wave form, which contains significant information on arteriosclerosis and cardiopathy of a man sitting on it.

Influence of sputtering pressure on polarity distribution of aluminum nitride thin films

The authors have investigated the influence of sputtering pressure on the polarity distribution of aluminum nitride (AlN) films. They have found that sputtering pressure strongly influences the polarity distribution of AlN films prepared on molybdenum electrodes. The polarity distribution of the AlN films was observed by piezoresponse force microscopy. The polarity orientation is decided with respect to each fine grain constituting the AlN films, and polarity conversion from Al polarity to N polarity is observed with increasing sputtering pressure. The piezoelectric response of the films changes from +3.7to−4.4pC∕N with increasing sputtering pressure from 0.36to4.0Pa.

Local epitaxial growth of aluminum nitride and molybdenum thin films in fiber texture using aluminum nitride interlayer

The authors have found the local epitaxial growth of aluminum nitride (AlN) and molybdenum (Mo) films in fiber texture, although the interface between the AlN and Mo films has different crystal symmetries. The local heteroepitaxial relationship is (0001)AlN[21¯1¯0]‖(110)Mo[1¯11]‖(0001)AlN[21¯1¯0]. The AlN films changes from nonequiaxed microstructures to equiaxed columnar structures. The authors think that the AlN interlayer is effective in decreasing the crystallization energy of the Mo electrode due to the coherent heteroepitaxial nucleation. It is interesting that the local heteroepitaxial relationship does not satisfy the criteria for heteroepitaxial growth.

Polarity inversion in aluminum nitride thin films under high sputtering power

The authors have investigated the influence of sputtering power on the piezoelectric response of aluminum nitride (AlN) thin films prepared on titanium nitride bottom electrodes. The piezoelectric response strongly depends on the sputtering power. The polar inversion was found by piezoresponse force microscopy. The polarity gradually changes from the N polarity to Al polarity with increasing sputtering power. The piezoelectric response of the films changes from −2.7to+4.3pC∕N with increasing sputtering power from 100to500W. Furthermore, the polarity inversion from the N polarity to Al polarity is observed by increasing sputtering power during growth.

Theoretical and experimental investigation on dynamic active antenna

This paper discusses theoretical and experimental investigation, on dynamic active antenna which can detect the contact point between an insensitive flexible beam and an object through estimation of the oscillation frequency in contact with the object. We first prove that the contact position is uniquely determined if we consider every mode of natural frequencies of the beam in contact with the object, while the fundamental and the second order natural frequency, in most cases, satisfy the sufficient condition for providing the unique contact position. We also show a desirable mass distribution avoiding the estimation error for localizing the contact position. By utilising the maximum entropy method, we succeeded in experimental estimating the contact point from the fundamental and the second order natural frequencies.

On a new contact sensing strategy for dynamic active antenna

This paper discusses a new sensing strategy for the dynamic active antenna which can detect the contact point between an insensitive flexible beam and an object through the estimation of the oscillation frequency in contact with the object. The strategy is composed of two steps. In the first step, the fundamental and the second order natural frequencies of the beam in contact with the object are evaluated by utilizing an extended Kalman filter. Then by using the mapping diagram from those two frequencies into the contact point, we can uniquely obtain the contact point. We show that the use of the fundamental and the second order natural frequencies is sufficient for localizing the contact point.

Phosphorescence quenching by mechanical stimulus in CaZnOS:Cu

We have found that phosphorescence intensity of CaZnOS:Cu decreased visibly under an applied load. This mechanical quenching (MQ) of phosphorescence in CaZnOS:Cu corresponded to the mechanical stimuli. We have thus demonstrated that the MQ of CaZnOS:Cu could be used for visualizing stress distributions in practical applications. We propose that MQ arises from non-radiative recombination due to electron-transfer from trap levels to non-radiative centers as a result of the mechanical load.