Patent Description:
Various micro-transducers incorporating piezoelectric materials for converting energy in one form to useful energy in another form are disclosed in <CIT>. In one embodiment, a piezoelectric micro-transducer can be operated either as a micro-heat engine, converting thermal energy into electrical energy, or as a micro-heat pump, consuming electrical energy to transfer thermal energy from a low-temperature heat source to a high-temperature heat sink. In another embodiment, a piezoelectric micro-transducer is used to convert the kinetic energy of an oscillating or vibrating body on which the micro-transducer is placed into useful electrical energy. A piezoelectric micro-transducer also is used to extract work from a pressurized stream of fluid. Also disclosed are a microinternal combustion engine and a micro-heat engine based on the Rankine cycle in which a single fluid serves as a working fluid and fuel.

<CIT> discloses a manufacturing method of a capacitive ultrasonic transducer by which mechanical characteristics of a membrane and yield are enhanced, and increase in parasitic capacity is suppressed. The manufacturing method of the capacitive ultrasonic transducer comprises processes of: preparing an Silicon On Insulator (SOI) substrate having an active layer on a support substrate via an insulation layer; forming a through-hole on the active layer or support substrate; forming a cavity by introducing fluid for etching the insulation layer from the through-hole formed on the active layer or support substrate and etching the insulation layer; forming an insulation film inside the cavity formed by etching the insulation layer; and sealing the through-hole after forming the insulation film inside the cavity.

Numerous, piezoelectric materials and constructions as well as suitable harvesting methods were disclosed in <NPL>. It is stressed that ambient energy can usually be found in the form of solar energy, thermal energy, electromagnetic waves, and vibration energy. Amongst these energy sources, vibration energy presents a persistent presence in nature and manmade structures. Various materials and transduction mechanisms have the ability to convert vibratory energy to useful electrical energy, such as piezoelectric, electromagnetic, and electrostatic generators. Recovering vibrational energy in piezoelectric transducer has been widely explored owing to their inherent simplicity, significant power densities and simple construction comparing with electrostatic and/or electromagnetic transducers.

Possibility of harvesting energy form atmospheric variations has been discussed in <NPL>. Approach was based on the daily temperature variations. A change of <NUM> was assumed. Variations that high are not always available. Atmospheric pressure expresses certain daily variations which depend on the geographical region - <NPL>.

Patent document <CIT>, describes harvesting energy from pressure changes using electromagnetic means. Patent document <CIT> discloses a system for generating electric energy comprising a bellows system configured to expand or contract a bellows based on temperature changes and/or atmospheric pressure changes and a piezoelectric generator configured to generate electric energy by a piezoelectric element elastically deformable by forces of the expanding or contracting bellows.

It has been observed that most commonly recognized kinds of ambient energy specifically energy of vibrations, solar energy or wind energy are not always and not everywhere available. Energy of daily pressure variations is a kind of energy that is universally available. Unfortunately, it is relatively low and difficult to harvest and to use. Energy generation module using this kind of energy needs to be suited for manufacturing in large number of items.

Posed problem is solved with an energy generation module, comprising pressure transducer with at least one pressure-to-displacement converter having a cavity confined with a membrane susceptible to deformation under pressure difference between fluid inside and outside the cavity. At least piezoelectric element mechanically coupled with the at least one pressure-to-displacement converter for converting energy resulting from a move caused by deformation of membrane to electrical energy, which has electrical energy storage means connected to piezoelectric element. The cavity closed with the membrane is airtight and membrane is selected so that the pressure difference causing deformation corresponds to range of daily atmospheric pressure changes i.e. approximately <NUM> - <NUM> hPa over <NUM> - <NUM> hours. The module has plurality of spatially distributed piezoelectric elongated members engageable with at the least one pressure-to-displacement converter so that energy is released when pressure changes since previous energy release exceeds predetermined value. The module consists of energy storage elements which are coupled with at least one of the pressure-to-displacement converter. Stored energy is released when reaching predetermined value. Daily pressure change causes movement of the membrane which engages piezoelectric elongated members. During the day, as change of pressure goes on, the energy is gradually stored in the energy storage means. When pressure change exceeds certain value falling within a range (<NUM> Pa, <NUM> Pa) energy storage means release energy and due to coupling with piezoelectric element mechanical energy is converted to electrical energy and stored. Use of plurality of piezoelectric elongated members enable re-engaging if pressure change is higher and further use of long-term changes.

Advantageously the cavity is realized in SOI technology. Application of this technology is convenient in a mass production.

Advantageously the membrane has a size of at least <NUM> and advantageously its cavity is axially symmetrical. Small elements are less effective as they deliver less energy. However, they are easier to manufacture and less prone to damage. Membrane having diameter of <NUM> and more were tested to be reasonable in terms of energy and still represent sufficient mechanical strength.

Advantageously the piezoelectric elongated members are adapted to store mechanical energy, while being bent by pressure-to-displacement converter and releasing it when being disengaged. Daily pressure changes are slow. It is difficult to convert them to electrical energy. Solution to this problem is storing the mechanical energy while bending the elongated members and then releasing the energy when resilient elongated members are disengaged and move in a manner fast enough to easily use piezoelectric effect. Additionally resilient elements tend to oscillate after disengaging and therefore produce more energy.

Advantageously plurality of spatially distributed piezoelectric elongated members comprises plurality of substantially parallel scuts of Lead zirconate titanate - PZT. This configuration proved to deliver high voltages.

Alternatively plurality of spatially distributed piezoelectric elongated members comprises a structure of Zinc Oxide- ZnO nanorods, which are convenient to use in mass production.

Advantageously plurality of spatially distributed piezoelectric elongated members comprises a silicon comb with ZnO layer.

Advantageously the energy generation module has a first electrode and a second electrode. The electrodes are parallel to each other. The plurality of spatially distributed piezoelectric elongated members comprise nano-rods forming a forest like structure encompassed between the first electrode and the second electrode. The first electrode is fixed and the second electrode is coupled with pressure-to-displacement converter for engaging nano-rods. Use of forest like structure trapped between electrodes allows applying the same displacement to a large number of piezoelectric elongated members simultaneously. All piezoelectric members are connected to the same electrodes and deform in the same way. Accordingly they discharge electrical energy at the same time and discharges combine constructively providing sufficient amount of electrical energy to be stored.

Advantageously the cavity is filed with a fluid with comprising a substance subjected to phase transition during operation of the module. Use of such substance allows generating more energy in the same conditions.

An energy generation module according to claim <NUM>, wherein the substance is a substance selected from a group including chloroethane, acetone, isopropanol and ethanol or a mixture thereof.

Advantageously the electrical energy storage means comprise low leak capacitor. Use of such capacitor enables lightweight and durable electrical energy storage. The amount of energy to be stored is rather low and the time of harvesting rather long, this unusual circumstances make low leak capacitors advantageous.

An energy generation module advantageously comprises plurality pressure to displacement converter stacked one on another.

Pressure to displacement converters advantageously have cavities filed with fluid under different pressures.

A method of ambient energy harvesting comprising conversation of mechanical energy to electrical energy with piezoelectric element in which energy is harvested in a daily doses of atmospheric pressure variations with at least one module according to the invention.

Although energy delivered by the module according to the invention is not sufficient for may traditional applications it occurred that it is enough for numerous Internet of Things (IoT) applications that require small doses of energy in peaks concentrated in narrow time slots as observed in <NPL>.

Although mean value of daily pressure is quite unpredictable as shown in [<FIG>] one can relay that everyday a variation of pressure of at least few tens of Pa is going to be observed. <FIG> represents only data of Warsaw which are even more promising, however the inventors have examined multiple locations all over the world to get reasonable grasp of daily pressure variation amplitude. Energy generation module according to the invention takes benefit of this observation.

An energy generation module according to embodiment of the invention, comprises a pressure transducer with at least one pressure to displacement converter <NUM> having a cavity <NUM> confined with a membrane <NUM> susceptible to deformation under pressure difference between fluid inside and outside the cavity as shown in <FIG>.

If pressure inside cavity <NUM> is higher than ambient pressure, then the membrane <NUM> is pressed outwards forming convex part 303a. If the pressure inside cavity <NUM> is lower than ambient pressure, then membrane <NUM> is pressed inwards the cavity forming concave shape 303b. Accordingly daily variations of pressure translate to movement of the membrane <NUM>. Energy of movement can be estimated with formula: <MAT>.

Where V<NUM> represents volume of the cavity <NUM>, ΔP represents change of pressure, P<NUM> represent value of pressure before change. Depending on the size the pressure to displacement converter <NUM> can provide from a few to few hundreds of µJ per day. This can be significantly improved when cavity is filed with a substance susceptible to phase change during daily pressure/temperature variations, such as e.g. chloroethane.

The pressure to displacement converter <NUM> can be manufactured in well-known and optimized measurement process, from layered wafer comprising substrate layer <NUM>, box layer <NUM> and SOI layer forming membrane <NUM>. The substrate layer <NUM> and box layer <NUM> are subjected to etching to form cavity <NUM> which is thereafter closed with cap <NUM>. It is a very convenient technology applicable for mass production. Especially for smaller units thanks to the proposed technology being compatible with the CMOS Silicon technology, we can consider a huge number of small modules having cylindrical shape and membrane greater than <NUM> working in parallel. The formula given above shows that if the cumulative volume V<NUM> of the cavities is in the order of <NUM><NUM> , the daily production provides sufficient amount of energy for the most efficient IoT application devices.

Prior to closing with cap <NUM> the cavity is filed with fluid under pressure corresponding to expected daily average. Additionally, the fluid may comprise substance susceptible to phase change in expected variations of pressure and/or air temperature. An example of such fluid is chloroethane (C<NUM>H<NUM>Cl). It is also possible to use other substances that evaporate in conditions close to normal - good results were obtained acetone, isopropanol, ethanol.

Although membrane made of SOI makes the device very convenient for mass production other materials for membranes can also be used. A silicon rubber (Granta Design Limited. Properties of Silicone Rubber, AZo Materials; Granta Design: Cambridge, UK, <NUM>. ) is a material that shows very advantageous properties.

Mechanical energy from the pressure to displacement converter <NUM> can be converted to electrical energy thanks to piezoelectric effect by piezoelectric element <NUM> mechanically coupled with pressure to displacement converter with coupling element <NUM>. Changes of daily pressure are very slow therefore it is necessary to provide energy storage means. Sole displacement caused by membrane is too slow. Therefore, mechanical energy needs to be stored in energy storage means and then discharged in faster manner.

Energy storage means can be embedded in the piezoelectric element. A use of elongated and resilient piezoelectric element <NUM> engaging with coupling element <NUM> causes gradual bending of the resilient element during motion of coupling element displaced by pressure to displacement converter 300n. Once displacement exceeds certain value coupling element <NUM> disengages piezoelectric element <NUM> and energy principles in structural mechanics is discharged in oscillation movement thereof causing transformation of said energy to electrical energy due to piezoelectric properties of the piezoelectric element, as shown schematically in [<FIG>].

Electrical energy can be delivered to energy storage means such as capacitor (not shown in figures).

The membrane closing cavity <NUM> is selected so that the pressure difference corresponds to range of daily atmospheric pressure changes, piezoelectric element is coupled with a mechanical energy storage means being elastic and therefore being adapted to store mechanical energy - accumulating mechanical energy of move of the membrane resulting from daily pressure changes. Value of pressure inside the cavity <NUM> determines reference level for pressure changes. Daily operation can be guaranteed if module is configured so that energy is released when pressure change since previous release exceeds predetermined value falling within a range (<NUM> Pa, <NUM> Pa).

Although the invention can be implemented with just one pressure-to-displacement converter it is more convenient with <NUM>-<NUM> pressure to displacement converters 300a, 300b, 300c, 300n stacked one on another as shown schematically in [<FIG>], [<FIG>] it is easier to provide sufficient displacement. Alternatively filing the cavities of converters with different pressures and/or using different membranes for different sensitivity to pressure change enable covering larger variety of conditions. It is also possible to connect the pressure to displacement converters in parallel.

It is a further improvement to use a piezoelectric element <NUM> that comprises a plurality of spatially distributed piezoelectric elongated members adapted to store mechanical energy engageable with at the least one pressure to displacement converter as shown schematically in <FIG>, <FIG>.

There are multiple methods of implementing piezoelectric element and plurality of piezoelectric elongated members adapted to store mechanical energy. Successful tests were made with a plurality of piezoelectric elongated members realized as scuts of PZT or structures of ZnO nanorods. Use of PZT allows obtaining highest voltages while keeping ability to store mechanical energy. ZnO nanorods on the other hand are very convenient for mass production and still have reasonable mechanical and electrical properties. Person skilled in the art would be able to suggest a number of possible realization of elongated piezoelectric structures being resilient enough to provide mechanical energy storage sufficient for this application.

It is also possible to use piezoelectric elongated members devoid of resilient properties. It requires engagement by pressing instead of bending. This approach allows forest-like structures which are convenient to grow. Example of such structure is shown in [<FIG>] which illustrates schematically a structure, having two horizontal electrodes <NUM>, <NUM> interconnected with plurality of nano-rods <NUM> forming a forest like structure between the horizontal electrodes <NUM>, <NUM>. Nanorodes <NUM> are made of a piezoelectric material, e.g. ZnO. The bottom metallic plate rests on a plurality of pressure-to-displacement converters 300a, 300b, 300c, 300n discussed above. Using plurality of pressure-to-displacement converter make it easier to obtain sufficient displacement, but in principle it is possible to use even one. The bottom of the pressure-to-displacement converter is fixed to an immobile base <NUM>. The upper metallic plate is fixed to apposite immobile base <NUM>.

When the pressure-to-displacement converters 300a, 300b, 300c, 300n react to a change in ambient pressure with vertical displacement, nonorods <NUM> are compressed (when the pressure-to-displacement converters expand), or stretched (when the pressure-to-displacement converters shrink). Thanks to the piezoelectric properties of the rods, there appears an uncompensated electrical field in the rods that attracts or repulses electrons, thus producing electrical pulses in the circuit relaying the electrodes <NUM>1nd <NUM>. The voltage pulses occuring in-between the electrodes <NUM>, <NUM>, are rectified, and the electrical energy is stored in a capacitor (not shown in figure). As the nanorods <NUM> are substantially identical they tend to discharge the pulses in the same time. Thanks to the synchronized action of a multitude of nanorods <NUM>, the portions of energy produced by nanorods <NUM> are adding cumulatively.

To reduce power consumption, it is possible to turn IoT device powered with module only when sufficient amount of energy is accumulated in electrical energy storage means. It requires only additional analog triggering device. This provides a synergistic effect as pace of gathering energy is synchronized with daily fluctuations of pressor and hence parameters of the energy generation module or a number of modules can be adapted to generate specific amount of energy in predictable time. It is significant advantage over energy generation devices based on solar or wind energy.

Claim 1:
An energy generation module, comprising
a pressure transducer with at least one pressure-to-displacement converter (<NUM>) having a cavity (<NUM>) confined with a membrane (<NUM>) susceptible to deformation under a pressure difference between fluid inside and outside the cavity (<NUM>), and at least one piezoelectric element mechanically coupled with the
at least one pressure-to-displacement converter (<NUM>) for converting energy resulting from a movement caused by deformation of the membrane (<NUM>) to electrical energy,
characterized in that
the cavity (<NUM>) closed with the membrane (<NUM>) is airtight, and
the membrane (<NUM>) is selected so that the pressure difference corresponds to a range of daily atmospheric pressure changes,
the at least one piezoelectric element comprises a plurality of spatially distributed piezoelectric elongated members (<NUM>, <NUM>) engageable with the at least one pressure-to-displacement converter (<NUM>, 300a, 300b, 300c, 300n) so that an energy is released when pressure change since a previous release exceeds a predetermined value falling within a range of <NUM> Pa to <NUM> Pa.