JPH0315801B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] This invention relates to an electric circuit using a shape memory alloy.

[Conventional technology]

Recently, shape memory alloy (Shape Memory Alloy)
SMA (hereinafter referred to as SMA) is an alloy that has the dual functions of a temperature sensor and acts as an actuator using the sensor, and its range of uses is expanding. For example, various applications were introduced in Asahi Shimbun (morning edition) ``Science of Life'' on Nov.
54, No. 5, pages 2 to 8, there is a description of its practical application to the wind direction adjustment mechanism of air conditioners.

When ordinary metals are deformed beyond their elastic limit, they become plastically deformed and never return to their original shape.
However, SMA recovers its shape even when subjected to plastic strain. This is done by reversible martensitic transformation, and the shape memorized at a high temperature is deformed at a low temperature below the temperature at which martensitic transformation occurs. Conversely, when the temperature is increased, a reverse transformation occurs from the martensitic phase to the original matrix phase, and the material deforms to the original shape memorized at the high temperature.

This alloy has Ti-Ni type and Cu type, and Cu type has
Cu-Zn alloy, Cu-Al alloy, Cu-Zn-Al alloy, etc. are used.

The temperature at which deformation occurs varies depending on the type of alloy, processing, heat treatment, etc., and various applications have been made to cause deformation at a predetermined temperature.

[Problem that the invention seeks to solve]

All conventional uses of SMA have been using temperature sensors and their mechanical operation, and an example of their use as an element in an electric circuit is a thermostat (which also uses mechanical operation). It was warm enough to be used.

The purpose of this invention is to realize an electric circuit using SMA as an electric circuit element.

[Means for solving problems]

The electric circuit of this invention is deformed into a coil shape.
An electric circuit is constructed using SMA as a variable impedance element.

[Effect]

In the electric circuit of the present invention, when the deformation temperature reaches or exceeds a predetermined deformation temperature, the SMA changes into a coil shape, the inductance of the electric circuit changes, and the circuit constant of the electric circuit changes.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. In Figures 1a and b, 1 is a shape memory alloy (SMA) wire. First, the coiled shape shown in FIG. 1b is memorized at a high temperature, and then deformed into the linear shape shown in FIG. 1a at a low temperature. When the ambient temperature or the temperature of the SMA wire 1 rises above a predetermined deformation temperature, it deforms to its original memorized shape and becomes the shape shown in FIG. 1b. If this SMA is used as an impedance element in an electric circuit, the impedance of the circuit can be changed at a predetermined deformation temperature.

An example thereof is shown in FIG. 2 is a capacitor, and 3 is an AC power source. At room temperature, the shape is as shown in FIG. 2a, but when the temperature reaches a predetermined deformation temperature or higher, the shape becomes as shown in FIG. 2b. At this time, the inductance (L) of the coil of SMA wire 1 and the capacitance of the capacitor
(C) to form a resonant circuit that resonates in series with the frequency of the AC power source 3, it is possible to know whether the temperature has exceeded a predetermined temperature by the presence or absence of a resonant state. Using this circuit, for example, a signal can be taken out from the resonant circuit and sent as a fire alarm, or radio waves can be generated from this circuit through an antenna and used for notification or monitoring.
That is, it can be used as a non-contact temperature sensor. In this example, a series resonant circuit is used, but a parallel resonant circuit may also be configured, or it may be used for amplifier gain adjustment, gain correction, phase correction, or in one arm of a bridge circuit to generate the signal. When the temperature of the SMA wire increases due to overcurrent flowing when the wire is taken out or used in series with an AC load,
The L portion of the coil automatically limits the current,
It is possible to detect the potential difference between both ends of L and disconnect the circuit using the detection signal. This is an IC
It can also be used to protect circuits from overheating. Also,
This coil can be used as an AC or DC electromagnet, that is, it can be used for various applications, such as by using the magnetic flux from the coil or by detecting the magnetic flux.

In this way, the effect of deforming the SMA wire into a coil shape can be widely used in electric circuits.

Furthermore, these circuits do not include contacts and can switch circuit constants, which has the great advantage of improving reliability.

FIG. 3 shows another embodiment of this invention,
4 is a resistor, and 1a and 1b are SMA wires that are deformed into coil shapes at different deformation temperatures, with 1b having a lower deformation temperature than 1a. 5a, 5
b and 5c are terminals. FIG. 3a shows the case where the temperature is low, and no signal is output between terminals 5a and 5b and between terminals 5b and 5c. Next, when the temperature exceeds the deformation temperature of the SMA wire 1b, the state shown in Fig. 3b occurs, and the terminals 5b and 5c
A potential difference is created between them and a signal appears. moreover,
When the temperature exceeds the deformation temperature of the SMA wire 1a, the terminals 5a,
A signal also appears between 5b. In this way,
This becomes an electric circuit that detects multiple temperature change points. For example, if a signal between terminals 5b and 5c is used to generate an alarm, terminal 5
The signal between a and 5b generates a treatment signal as an emergency situation. Alternatively, it may be inserted into one arm or into multiple arms of the bridge circuit.

Moreover, it can be widely applied to resonant circuits and other electric circuits.

Figure 3 shows an example of two SMA wires, but three or more SMA wires each with different deformation temperatures
A line may also be used.

Further, in the above embodiments, an example was shown in which the wire deforms into a coil shape when the temperature rises, but conversely, an SMA wire which becomes a coil shape at a low temperature and a straight shape at a high temperature may be used.
Incidentally, the inductance of the coil changes even if the shape is changed from a coarsely wound coil shape to a densely wound coil shape without deforming it to a straight line shape, and therefore, it can be used in the same way.

〔Effect of the invention〕

As described above, according to the present invention, since a shape memory alloy that deforms into a coil shape is used as a variable impedance element in an electric circuit, it is possible to provide an electric circuit that can change electric circuit constants in response to temperature changes. can.

[Brief explanation of drawings]

Figures 1a and b are principle diagrams of a variable inductance element according to an embodiment of the present invention, Figures 2a and b are electrical circuit diagrams using a variable inductance element according to an embodiment of the present invention, and Figure 3 is a diagram of the principle of a variable inductance element according to an embodiment of the present invention. FIG. 3 is an electrical circuit diagram showing another embodiment of the invention. In the figure, 1, 1a, and 1b are shape memory alloy wires, 2 is a capacitor, and 3 is an AC power source. In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Scope of Claims] 1. An electric circuit in which a shape memory alloy that deforms into a coil shape at a temperature above or below a predetermined temperature is used as a variable inductance element in the circuit. 2. The electric circuit according to claim 1, wherein when the variable inductance element is deformed into a coil shape, it forms a resonant circuit that resonates at a desired frequency. 3. The electric circuit according to claim 1 or 2, wherein the plurality of variable inductance elements are each deformed into a coil shape at different predetermined temperatures to change the circuit constant thereof.