Haruki Okano

Picogram Mass Sensor Using Piezoresistive Cantilever for Biosensor

A harmonic vibrator using a piezoresistive cantilever has been developed for a picogram mass biosensor. We constructed a prototype vibrator sensor using the cantilever, Wheatstone bridge circuits, positive feedback controller, a piezoactuator and a phase-locked loop (PLL) demodulator. As experimental results, a mass sensitivity of 2.2 pg/Hz was obtained from water molecular adsorption on the cantilever. We confirmed that the mechanism of water molecular growth has 2 modes, island growth and layer growth. The critical point of the mechanism change was a humidity of about 42%. At the critical point, the adsorbed mass corresponds to the water layer of about 13 monolayers.

Femtogram Mass Biosensor Using Self-Sensing Cantilever for Allergy Check

A self-sensing mass biosensor with a femtogram mass sensitivity has been developed using a piezoresistive microcantilever. The mass change due to antigen and antibody adsorption on the cantilever in water was detected by the resonance frequency shift of the cantilever. We constructed a prototype harmonic vibration sensor using a commercial piezoresistive cantilever, Wheatstone bridge circuits, a positive feedback controller, an exciting piezoactuator and a phase-locked loop (PLL) demodulator. As experimental results, a mass sensitivity of about 190 fg/Hz, and a mass resolution of about 500 fg were obtained in water. The mass sensitivity is 100 times higher than that of a quartz crystal oscillation method. We demonstrated that the sensor can detect the reaction between an antibody of immunoglobulin (IgG) and an antigen of egg albumen (OVA). We confirmed that the binding ratio between the antibody and the antigen was about 1 : 2. The detection method is available for allergy check because the measured reaction ratio occurring on the cantilever concurs with the theoretical method.

Piezoresistive Acceleration Sensor with High Sensitivity and High Responsiveness

In this work, a new-type piezo-resistive acceleration sensor with a slit in the beams is proposed to improve sensitivity by reducing the twisting of the beams. Experimental results demonstrated that the new-type acceleration sensor has about 3.5 times higher than that of the conventional acceleration sensor without the slit. Furthermore, resonant frequency of the new-type sensor increases to about 5 kHz by a factor of 25, compared with commercial acceleration sensor.

Prototype of Frame-Type Cantilever for Biosensor and Femtogram Detection

The possibility of realizing femtogram mass detection using a frame-type microcantilever has been studied in bioscience. To realize highly sensitive mass detection by reducing the viscose resistance in liquids, we designed frame-type cantilevers using finite element modeling (FEM). We fabricated prototypes of mesh-type, hole-type and conventional-type cantilevers using a semiconductor process. The properties of the cantilevers were measured by a conventional atomic force microscope (AFM) system. The measured resonance frequencies of the cantilevers were almost consistent with the calculated results of the FEM simulation in air. The resonance frequency and quality (Q) factor of the mesh-type cantilever were larger than those of the conventional-type cantilever in water. We measured the frequency change due to gold film deposition on the mesh-type cantilever. Then, we estimated the mass sensitivity of the cantilever at about 16.6 fg/Hz. This value is more than 10 times smaller than that of the conventional-type cantilever. These results indicate that the mesh-type cantilever has the advantage of reducing the viscous resistance and achieving high sensitivity in liquids.

Impact Response Evaluation of Force Transducer for Use in Falling Weight Deflectometer System

The impact response of a force transducer in a falling weight deflectometer system is evaluated by an optical method. In the method, a mass is made to collide with a force transducer and the impact force is measured highly accurately as the inertial force acting on the mass. A pneumatic linear bearing is used to realize linear motion with a sufficiently small friction acting on the mass, i.e., the moving part of the bearing. The method is an improved variation of the Levitation Mass Method, which has been proposed and developed by the first author. The impact force, which has a maximum value of approximately 1.66 kN and a full width at half maximum of approximately 5.0 ms, has been applied and measured using the Levitation Mass Method with the standard uncertainty of approximately 3.3x10 N. This corresponds to 2x10-2 (2%) of the maximum applied force in the experiments. The present status of the method and the points to be considered for the future improvements are discussed.

Impact Response Measurements of Force Transducers

The impact response of force transducers was measured. An object encountering negligible friction, because it was levitated with a pneumatic linear bearing, was made to collide with a force transducer under test. The force acting on the object is calculated as the product of mass and acceleration. The acceleration was accurately measured using an optical interferometer. The output signal of the force transducer and the accurately measured force acting on the levitated object were compared. Approximately 91 sets of experiments have been conducted using five force transducers. The maximum values of the impact forces varied between 30-240 N, with the full width at half maximum (FWHM) varying between 6-10 ms. Force transducers of beam type-A1, A2 and S-shaped type-B1, B2, and B3 were tested. The impact response of force transducers of different type and capacity are discussed in this paper