Simple, effective and high sensitivity transducer for force measurement of myofibrils Kien Nguyen Phan and Takakazu Kobayashi Abstract—In previous research, T-shape transducer was used for force measurement of myofibrils but there are some disadvantage with sensitivity and natural frequency. After improved transducer and set up new apparatus for force measurement of myofibrils, the transducer was proved that it is useful for force measurement of myofibrils with 1μN in resolution and 100Hz in frequency. Especially, the optimization T-shape transducer is simple and effective to manufacture and high sensitivity in comparison with others type of transducer. Ca 2+ activated force and recovery force during quick release of myofibrils have successfully measured. Keywords—force transducer, ring magnet, high sensitivity, T-shape, myofibrils. I. INTRODUCTION HERE are many researches on force measurement of myofibrils and/or myocytes to get more information about mechanical parameters of muscle contraction. It is used different types of transducer such as commercial capacitive force transducer [8, 12], optical fibers [13, 17], suction pipettes [9, 19, 11], glass needle [18], microfabricated polysilicon beam [15, 16] and current carrying wires in magnetic field [1, 14]. Each type of transducer has their own parameters that useful for force measurement of myofibrils with high precision measurement. It is also used strain gauges [18], video analysis [15, 16], optoelectronics [14], laser beam reflection measurement that projected the image of a slit or the blackened glass needle onto a different photodiode [9, 10, and 11]. Each method has its own advantage and disadvantage but most transducers are difficult to manufacture and set up and/or even attach to myofibrils. In this research, a novel transducer is designed for force measurement with the requirements of our transducer is: 1) easy to manufacture, 2) easy to attach, 3) high sensitive, 4) sufficient bandwidth and 5) inexpensive production. We have created a novel transducer called T-shape transducer that is mentioned in [2], operational principle is same as the compass. In previous research, T-shape transducer is horizontally placed and the results received from force measurement of myofibrils are rather noisy and sensitivity is insufficient (4µN in resolution and ~80Hz in frequency [2]). The optimistic transducer is vertical style, making the advantages to reduce the noise and increases the sensitivity of the system (up to 1µN in resolution and 100Hz in frequency). In addition, T-shape transducer is simpler than other types. For example, in Iwazumi’s transducer type [14], current wire moving in magnetic field, the sensitivity of transducer not only depend on sensitivity of current measurement circuits but also in stiffness, length, curl of wire, and current controlled through Manuscript received Sep 17, 2007. K. NP. Author is with Shibaura Institute of Technology, 135-8548 Tokyo (phone: +81-3-5520-6743; fax: +81-3-5859-8321; e-mail: phankien-fet@mail.hut.edu.vn). T. K Author, is with Shibaura Institute of Technology, 135-8548 Tokyo (phone: +81-3-5859-8321; fax: +81-3-5859-8321; e-mail: kobataka@sic.shibaura-it.ac.jp). Figure 1. T-shape transducer from version 1 to 6. The principle of transducer is the same as the compass. Cubodial permanent magnet is replaced by rare earth ring magnet in version 4 with the aim of reducing the unwanted attracted force that exerts on the tip of T-shape. Version 5 and 6 use rare earth ring magnet for controlling the transducer. All attached parts of transducer are made from standard stainless steel with 3 mm long and 50 µm in diameter. Myofibrils are attached to this part by using silicon glue (Down Corning 5431 RTV). Pivot is parallel with T-header and created by contacting points between T-header and the surface of permanent magnets because of magnetic force exerted on T-header. T