Fluid disc pump with square-wave driver
View Patent ↗A pump having a substantially cylindrical shape and defining a cavity formed by a side wall closed at both ends by end walls wherein the cavity contains a fluid is disclosed. The pump further comprises an actuator operatively associated with at least one of the end walls to cause an oscillatory motion of the driven end wall to generate displacement oscillations of the driven end wall within the cavity. The pump further comprises a valve for controlling the flow of fluid through the valve.
1. A pump comprising:
a pump body having a substantially cylindrical shaped cavity having a side wall closed by two end surfaces for containing a fluid, the cavity having a height (h) and a radius (r), wherein a ratio of the radius (r) to the height (h) is greater than about 1.2;
a piezoelectric device operatively associated with a central portion of one end surface and adapted to cause an oscillatory motion of the end surface at a frequency (f) having bending modes and breathing modes of resonance, thereby generating radial pressure oscillations of the fluid within the cavity including at least one annular pressure node in response to a drive signal being applied to the piezoelectric device;
a drive circuit having an output electrically connected to the piezoelectric device for providing the drive signal to the piezoelectric device at the frequency (f), wherein the drive signal is a square-wave signal having a duty cycle that attenuates a harmonic component of the square-wave signal coinciding with a frequency of a mode of the piezoelectric device other than the fundamental bending mode of the piezoelectric device;
a first aperture disposed at any location in the cavity other than at the location of the annular pressure node and extending through the pump body;
a second aperture disposed at any location in the pump body other than the location of the first aperture and extending through the pump body; and,
a valve disposed in at least one of the first aperture and second aperture to enable the fluid to flow through the cavity when in use.
2. The pump of claim 1 , wherein the frequency (f) is set at a value about equal to a fundamental bending mode of the piezoelectric device.
3. The pump of claim 1 , wherein the height (h) of the cavity and the radius (r) of the cavity are further related by the following equation: h 2 /r>4×10 −10 meters.
4. The pump of claim 1 , wherein the piezoelectric device has a radius (a) greater than or equal to 0.63(r).
5. The pump of claim 4 , wherein the radius (a) of said the piezoelectric device is less than or equal to the radius of the cavity (r).
6. The pump of claim 1 , wherein said second valve aperture is disposed in one of the end surfaces at a distance of about 0.63(r)±0.2(r) from the centre of the end surface.
7. The pump of claim 1 , wherein said valve permits the fluid to flow through the cavity in substantially one direction.
8. The pump of claim 1 , wherein the ratio is within the range between about 10 and about 50 when the fluid in use within the cavity is a gas.
9. The pump of claim 1 , wherein the ratio of h 2 /r is between about 10 −3 meters and about 10 −6 meters when the fluid in use within the cavity is a gas.
10. The pump of claim 1 , wherein the volume of the cavity is less than about 10 ml.
11. The pump of claim 1 , wherein the drive circuit includes a low-pass filter for attenuating the harmonic component of the square-wave signal.
12. The pump of claim 1 , wherein the drive circuit includes a notch filter for attenuating the harmonic component of the square-wave signal.
13. The pump of claim 1 , wherein the duty cycle is equal to a value wherein the harmonic component of the square-wave signal coinciding with the frequency of a mode of the piezoelectric device is set to zero.
14. The pump of claim 13 , wherein the duty cycle is about 42.9% to attenuate the seventh harmonic component of the square-wave signal coinciding with the frequency of a fundamental breathing mode of the piezoelectric device.