Piezo switch
Encyclopedia
A piezo switch is an electrical switch
based on the piezoelectric effect
.
The folcharge
generated
by the piezoelectric element in the switch is typically used to turn on an integrated semiconductor
device such as a field effect transistor (FET), causing the switch assembly's output to be active, or "on". When the FET is on, current can flow through it as with a conventional metal contact-based switch
. After the voltage pulse is dissipated in the gate resistor
, the FET turns back "off", its normal high impedance state. The piezoelectric effect
uses the fact that force
applied to certain materials causes stresses
that generate
this electric charge
. In the case of piezo switches
, the force
could be compressive pressure
that causes the (typically disc-shaped) piezo element to bend very slightly like a drumhead
.
Thus piezo switches produce a single, brief "on" pulse
. This pulse can vary with the amount of pressure which is applied, since higher pressures generate higher voltages which take longer to dissipate. A capacitor may be used to store the charge in order to lengthen the time constant
of the gate circuit and therefore the width of the pulse. With additional circuitry this pulse can be extended further or used to change the state of an output from steady "Off" to steady "On" by toggling a flip-flop
.
Piezo switches have some interesting advantages over their conventional mechanical counterparts. One is that there are no moving parts
necessary for them to do their job. This means the lifetime of such a switch can be ensured to be tens of millions of operations, since there is no wear involved.
Another advantage is that they may easily be completely sealed from the environment and thus made weatherproof. They are often constructed with stainless steel
housings such that they are resistant to damage by vandals or heavy use.
Switch
In electronics, a switch is an electrical component that can break an electrical circuit, interrupting the current or diverting it from one conductor to another....
based on the piezoelectric effect
Piezoelectricity
Piezoelectricity is the charge which accumulates in certain solid materials in response to applied mechanical stress. The word piezoelectricity means electricity resulting from pressure...
.
The folcharge
Charge (physics)
In physics, a charge may refer to one of many different quantities, such as the electric charge in electromagnetism or the color charge in quantum chromodynamics. Charges are associated with conserved quantum numbers.-Formal definition:...
generated
Generate
Generate may refer to:* CreateScience and math* Generate and test * Generating function, in math and physics* Generating primes* Generating set* Generating trigonometric tablesOther* Generate ministry, young adult event...
by the piezoelectric element in the switch is typically used to turn on an integrated semiconductor
Semiconductor
A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...
device such as a field effect transistor (FET), causing the switch assembly's output to be active, or "on". When the FET is on, current can flow through it as with a conventional metal contact-based switch
Switch
In electronics, a switch is an electrical component that can break an electrical circuit, interrupting the current or diverting it from one conductor to another....
. After the voltage pulse is dissipated in the gate resistor
Resistor
A linear resistor is a linear, passive two-terminal electrical component that implements electrical resistance as a circuit element.The current through a resistor is in direct proportion to the voltage across the resistor's terminals. Thus, the ratio of the voltage applied across a resistor's...
, the FET turns back "off", its normal high impedance state. The piezoelectric effect
Piezoelectricity
Piezoelectricity is the charge which accumulates in certain solid materials in response to applied mechanical stress. The word piezoelectricity means electricity resulting from pressure...
uses the fact that force
Force
In physics, a force is any influence that causes an object to undergo a change in speed, a change in direction, or a change in shape. In other words, a force is that which can cause an object with mass to change its velocity , i.e., to accelerate, or which can cause a flexible object to deform...
applied to certain materials causes stresses
Stress (physics)
In continuum mechanics, stress is a measure of the internal forces acting within a deformable body. Quantitatively, it is a measure of the average force per unit area of a surface within the body on which internal forces act. These internal forces are a reaction to external forces applied on the body...
that generate
Generate
Generate may refer to:* CreateScience and math* Generate and test * Generating function, in math and physics* Generating primes* Generating set* Generating trigonometric tablesOther* Generate ministry, young adult event...
this electric charge
Charge (physics)
In physics, a charge may refer to one of many different quantities, such as the electric charge in electromagnetism or the color charge in quantum chromodynamics. Charges are associated with conserved quantum numbers.-Formal definition:...
. In the case of piezo switches
Switch
In electronics, a switch is an electrical component that can break an electrical circuit, interrupting the current or diverting it from one conductor to another....
, the force
Force
In physics, a force is any influence that causes an object to undergo a change in speed, a change in direction, or a change in shape. In other words, a force is that which can cause an object with mass to change its velocity , i.e., to accelerate, or which can cause a flexible object to deform...
could be compressive pressure
Pressure
Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...
that causes the (typically disc-shaped) piezo element to bend very slightly like a drumhead
Drumhead
A drumhead is a membrane stretched over one or both of the open ends of a drum. The drumhead is struck with sticks, mallets, or hands so that it vibrates and the sound resonates through the drum.-History:...
.
Thus piezo switches produce a single, brief "on" pulse
Pulse wave
A pulse wave or pulse train is a kind of non-sinusoidal waveform that is similar to a square wave, but does not have the symmetrical shape associated with a perfect square wave. It is a term common to synthesizer programming, and is a typical waveform available on many synths. The exact shape of...
. This pulse can vary with the amount of pressure which is applied, since higher pressures generate higher voltages which take longer to dissipate. A capacitor may be used to store the charge in order to lengthen the time constant
Time constant
In physics and engineering, the time constant, usually denoted by the Greek letter \tau , is the risetime characterizing the response to a time-varying input of a first-order, linear time-invariant system.Concretely, a first-order LTI system is a system that can be modeled by a single first order...
of the gate circuit and therefore the width of the pulse. With additional circuitry this pulse can be extended further or used to change the state of an output from steady "Off" to steady "On" by toggling a flip-flop
Flip-flop (electronics)
In electronics, a flip-flop or latch is a circuit that has two stable states and can be used to store state information. The circuit can be made to change state by signals applied to one or more control inputs and will have one or two outputs. It is the basic storage element in sequential logic...
.
Piezo switches have some interesting advantages over their conventional mechanical counterparts. One is that there are no moving parts
Moving parts
The moving parts of a machine are those parts of it that move. Machines comprise both moving and fixed parts. The moving parts have controlled and constrained motions....
necessary for them to do their job. This means the lifetime of such a switch can be ensured to be tens of millions of operations, since there is no wear involved.
Another advantage is that they may easily be completely sealed from the environment and thus made weatherproof. They are often constructed with stainless steel
Stainless steel
In metallurgy, stainless steel, also known as inox steel or inox from French "inoxydable", is defined as a steel alloy with a minimum of 10.5 or 11% chromium content by mass....
housings such that they are resistant to damage by vandals or heavy use.