Masayoshi Tsubai

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 ...

Visualization of active crack on bridge in use by mechanoluminescent sensor

Innovative mechanoluminescent (ML) particles emit light repeatedly in response to small stresses applied, such as deformation, friction, or impact. When dispersedly coated on a structure, each particle acts as a sensitive mechanical sensor, while the 2-dimentional emission pattern of the whole assembly reflects well the dynamical stress distribution inside the structure and mechanical information around crack and defect. Thus, we have applied the remarkable strong points of ML sensing technique to a bridge in use as a real social structure for the first time. For the first ML monitoring test at bridge, we selected a relatively old bridge (established in 1954, 3-span continuous T-type RC bridge, length 24.4 m, width: 7.89 m). The ML sheet type sensors were put around the central area (700×400 mm) of the main girder, and ML images originated from dynamic load application via general traffic vehicles had recorded by using lab-made CCD camera under roughly dark condition. As the result, we successfully detected intense ML patterns not only along visible crack but also at round soundless part on the girder at a glance with responding ML intensity reflecting the crack mouth opening displacement (CMOD) of visible crack and invisible progressing microcrack.

Development of an ultrasound system for measuring tissue strain of lymphedema

This paper develops a portable measurement system for tissue strain distribution using ultrasonic pulse echo method. A single element ultrasonic transducer attached to a force sensor compresses biological tissue and observes the deformation process of the tissue. The center frequency of the ultrasound pulse is 3 MHz. The force applied to the tissue is kept at 10 N by an internal coil spring. Received echo signals are transferred to a personal computer via Universal Serial Bus. The developed measurement system was applied to measuring strain of subcutaneous fat for lymphedema patients and healthy subjects. The results quantified the fact that affected tissue becomes harder than unaffected tissue. Our experiment demonstrated that the system can be used for evaluating the condition of lymphedema with measurement of strain in subcutaneous tissue.

Impedance Estimation of Soft Tissue Using Ultrasound Signal

This paper proposes a new impedance estimation method for soft tissue using ultrasound. This method estimates the impedance distribution inside an object. An ultrasound probe, which is attached to a force sensor, compresses soft tissue and observes the deformation process of tissue while measuring reaction force. The impedance parameters are then estimated based on this information. Experiments were conducted under two conditions, a static analysis and a dynamic analysis. In the static analysis, the ultrasound probe compressed the soft tissue slowly while keeping a balance of the power. In the dynamic analysis, the probe compressed tissue dynamically, and the deformation process of the soft tissue was observed. Experimental results demonstrated that our method can estimate the impedance of a soft object.

Development of a Flexible System for Measuring Muscle Area Using Ultrasonography

Muscular strength can be estimated by quantification of muscle area. For this purpose, we developed a flexible measuring system for muscle area using ultrasonography. This method is completely safe and is particularly suitable for elderly people because the subjects are not required to perform any muscular contraction during measurement. The ultrasound probe is installed on a mechanical arm, and continuously scans fragmental images along the body surface. A wide-area cross-sectional image is then constructed using the measured images. The link mechanism is very flexible, enabling the operator to measure images for any body posture and body site. Use of the spatial compounding method reduces speckle and artifact noise in the resultant cross-sectional images. The operator can observe individual muscles (extensor, flexor muscle, etc.) in detail. We conducted experiments to evaluate the performance of the system. In the experiments, the position of the ultrasound probe was calculated with high accuracy according to the link posture. In addition, a high degree of correlation was verified between MR images and those of the developed system. We observed a reduction in noise due to use of the spatial compounding method, and propose a new calibration method for correcting the measured muscle area, which were slightly deformed by the contact pressure of the ultrasound probe. Finally, we examined the relation between muscular area and muscular strength in young and middle-aged subjects. The results of these experiments confirm that the developed system can estimate muscular strength based on muscular area.

Automated discrimination method for measuring the thickness of muscular and subcutaneous fat layers based on tissue elasticity

The balance between human body composition, e.g. bones, muscles, and fat, is a major and basic indicator of personal health. This paper proposes a new discrimination method for measuring the thickness of subcutaneous fat and muscular layers based on tissue elasticity. The validity of the proposed method was evaluated in twenty-one subjects (twelve women, ten men; aged 20-70 yr) at three anatomical sites. Experimental results show that the proposed method can achieve considerably high discrimination performance.

A cross-sectional ultrasound imaging for measuring body composition

We have developed a measuring system to visualize a complete cross-sectional image of the human extremity using ultrasonography. This system uses several ultrasound probes, and these probes measure fragmentary graphical images of one cross-sectional plane which are then transformed into a complete cross-sectional image. The developed system is superior to other imaging devices in many respects because it is portable, safe, and inexpensive. These advantages can be available in the field survey. This paper discusses the system components and the experiments to verify the proposed method.

An implementation of image sharpening based on morphological operations for ubiquitous echo.

Ubiquitous echo is a portable ultrasound imaging equipment. We discuss an image sharpening method based on geometrical information by mathematical morphology with double structuring element (DSE) for on-line processing on ubiquitous echo. The sharpening method improves the contrast of tissue boundaries without speckle emphasis. The computational complexity of the morphological operations is reduced by chain rule of the operations and decomposition of the DSE not to delay refreshing the ultrasound moving image

A Portable Measuring System for Cross-Sectional Ultrasound Images Using Spatial Compounding and Edge Sharpening

This paper proposes a compensation for a blurred image caused by misregistration in spatial compounding. The edge sharpening based on morphological operations is applied to the compounded image. A portable measuring system of a cross-sectional ultrasound image is designed for measuring body composition. The system is developed for non-medical applications, for example, measurement of the volume of muscle and subcutaneous fat in lower extremities, upper extremities and abdomen for health care and sports science. A number of partially overlapping images that have been obtained from multiple angles are combined into a single compounded image. In experiment on human abdomen, the image quality was improved in speckle suppression and edge enhancement by using ensemble averaging and morphological edge sharpening. Resulting wide field-of-view image was sufficiently deblurred without emphasizing noise.

Development of an Ultrasonic Probe with Measurement of Contact Pressure Distribution

We have developed an ultrasonic probe with a film-type pressure sensor installed on its contact surface. The film-type pressure sensor, which uses aluminum nitride (AlN) as a piezoelectric material, is thin, flexible, durable and heat-resistant. The AlN is deposited on a polyimide film in high orientation using the sputtering method. The sensor can measure contact pressure directly, with little effect on ultrasonic transmission. We have demonstrated the simultaneous acquisition of tissue images and contact pressure distribution for the human carotid artery. Internal tissue was successfully visualized and the pulsating arterial wall was observed. At the same time, a pulse wave of blood pressure is observed with characteristic waveshapes. The results indicate the possibility of estimating the viscoelasticity of biological tissue