Artificial Metal-Based Muscle

BioMetal Fiber
BMF Series

BioMetal Butterfly Robot Kit, sensitive at various sound, vibration and various shock.  The above BioMetal Butterfly Robot Kit sensing the sound of finger snap sound.

Features of the BMF Series

The BioMetal Fiber is a fiber-like actuator (drive unit) designed to contract (tense) and extend(relax) like muscles.

The key feature of this product is its flexible, smooth movements like those of real life. Although soft and pliable like a nylon thread under normal conditions, it becomes stiff like a piano wire and sharply contracts, when a current is fed through it.

If the passage of a current is stopped, it will soften and extend to its original length.

The BMF can also be moved by changing its temperature. It begins to contract when heated to about 70˚C.

If it is cooled to below the temperature, it will return to its original length.

Because of its stable internal structure, the BMF has very high durability and exhibits stable operating characteristics.

Being thin but capable of producing a powerful force, this product is ideally suited for milli and micro actuators.

  • Current-driven type fiber-like solid-state actuator.

  • Ultra lightweight, spacing saving design (one-several thousandths lighter and smaller than solenoids).

  • Maximum displacement (contraction or elongation) of over 4% of its total length and kinetic distortion.

  • Strong shrinkage force and starting force.

  • Capable of high-resolution micro movements.

  • Vibration and noise-free, highly-dumped, flexible operation.

  • High size and operating stability, and long service life.

  • Can be driven at low voltage.

  • Involves no rush current, counter-electromotive force, or electromagnetic noise.

  • Usable as a temperature-activated device.

  • Chemically and structurally stable, allowing boiling.

  • Low cost.

Applications of the BMF Series

  • Uses as an analog actuator, relays, electrically-driven valves, electric locks,  shutters, dynamo-electric brakes, clutches, etc.

  • Uses as a bimetal-like device,  servo actuators, servo valves, micro robots, etc.

  • Uses as a bimetal-like device,  circuit breakers, intermittent switches, temperature  operated actuators, etc.

  • Uses as an electronic part  electric switches, electric volume controls, etc.

  • Uses as a general-purpose small-size actuator, ultra-thin actuators, small-size actuators for toys,  silent alarms, etc.

  • Special applications  Simplified electric discharge machines, simplified welding machines, etc

  • Since the BMF is an area force actuator, it exhibits best performance as a micro actuator.

  • BioMetal (a trademark of TOKI CORPORATION) is a fiber-like actuator which is anisotropic ally structured by our own fabrication method from a Ti-Ni shape-memory alloy so as to deliver its superb performance characteristics in a specific direction.

  • Since it is made of a metal and looks like a living thing because of its smooth movement, it is designated as BioMetal.

  • The BMF differs from general shape-memory alloys in terms of basic characteristics in that it exhibits stable movement and high elasticity because it is rigidly structured in the fiber direction.

  • It is not intended as a material for shape-memory alloys, and it is therefore used in a different manner.

  • It is impossible to make BioMetal remember shapes, with its performance characteristics maintained, as in the case of general shape-memory alloys.

  • If it is subject to ordinary memorization processing (machining, heat treatment), its original performance characteristics will be impaired.

Characteristics and Specifications of the BMF Series

The BMF is not made of a homogeneous substance of the same quality. It has highly structured construction. The thinner the BMF, the greater tend to be its durability, elasticity, and other performance characteristics. For use as an actuator to be repeatedly operated, it is recommended to select a BMF thinner than the BMFl50 except when a powerful force needs to be can be produced by a single fiber.


The maximum kinetic strain of the BMF may reach 6%. When the BFM is to be operated repeatedly, it should be used within an appropriate range, referring to the diagrams shown above. For instance, the SA-01 Silence Arm, a micro robot of our company, which is designed to allow no more than 100,000 repetitive operations, utilizes 5.0 % of kinetic distortion from the BMF 100 under the stress of 80 MPa. Refer to the black bar In the above diagram.


The service Iife of the BMF is closely associated with the magnitude of the load and the kinetic distortion. It has a track record of having made more than 300 million reciprocation motions under appropriate load and movement conditions.

(Example: BMF100. 330,000 motions completed at the load of 80 gf and at the kinetic distortion of 2.5%. The test is still under way. The testing condition is indicated by the gray bar In the above diagram.)


The BMF makes non-linear, asymmetric motions (contractions and expansions). It can be quickly contracted if it is heated in an adiabatic manner by feeding a large current through it.

However, it cannot be quickly elongated without forced cooling because the rate of elongation depends on cooling speed.

In the case of self-cooling the BMF is affected by the ambient temperature and the wind.

The data shown in the table below are these obtained at the room temperature of 20˚C under the windless condition.


The upper limit of operating temperature is between 65˚C and 70˚C. It varies with the load condition. This limit can be increased to some extent by increasing the bias. In that case, however, the service life of the BMF may be shortened.

There is no lower limit of operating temperature.

The current required for driving by heat increases with decreasing ambient temperature.

  • The number following BMF in the product name is the value d its diameter expressed in  micrometers. For example, the BMF100 has a diameter of 0.1mm.

  • The BMF is uniform in the longitudinal direction. For this reason, most of the numerical data in the table are determined with reference to the unit length (1 m) of the BMF.

  • The kinetic distortion is represented by the ratio in percentage of the displacement (contraction or expansion) of the BMF to its total length.

  • The numerical data in the table are standard values used as a guide for device design. The actual performance characteristics may differ from them, depending on the operating conditions .

  • The numerical data in the table are not guaranteed values but reference values. The actual numerical data may be varied improvement of the BMF.

  • There are also slight variations between lots.