Patent Publication Number: US-11654613-B2

Title: Printed multifunctional skin for aerodynamic structures, and associated systems and methods

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. application Ser. No. 16/168,726, filed Oct. 23, 2018, which is a continuation of U.S. application Ser. No. 15/295,702, filed Oct. 17, 2016, which claims the benefit of U.S. Provisional Application No. 62/242,492, filed Oct. 16, 2015, the disclosures of which are hereby incorporated in their entirety. 
    
    
     STATEMENT OF GOVERNMENT LICENSE RIGHTS 
     This invention was made with Government support under contract No. FA9550-15-C-0007 awarded by the U.S. Air Force Research Laboratory—Office of Scientific Research. The Government has certain rights in the invention. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to sensors and actuators attached to the structures, including aircraft. 
     BACKGROUND 
     Conventional aircrafts may carry large numbers of sensors and actuators. For example, the aircrafts are typically equipped with instruments that can measure outside temperature, speed of the aircraft, outside/inside pressure, humidity, weight of the aircraft, etc. Some measurement sensors (e.g., inside humidity and temperature) and most of the supporting electronics are typically installed inside the aircraft. On the other hand, other measurement sensors typically protrude outside of the aircraft (e.g., pitot tube for the pressure/speed measurements). Additionally, the aircrafts also carry actuators (e.g., for landing gear deployment and retraction, for wing flaps, ice protection systems, etc.). These actuators are generally bulky and, when not exercised, are typically concealed within the aircraft. Some other sensing/actuation aerospace systems perform monitoring for the structures, ice protection, thermal management, vibration damping, etc. 
     However, the available space for the instruments and their supporting electronics is generally reduced in the newer, smaller aircraft. For example, small drones may not have enough space to carry all the actuators and sensors, and the supporting electronics. Similar problems exist with the newer manned aircraft, because those are also smaller at least in part due to stronger materials used for these aircraft that, in turn, enable smaller aircraft. 
     Furthermore, additional instruments/sensors may measure, for example, loading of the aircraft structure, especially during the development of the aircraft (Testing and Evaluation or T&amp;E). For example, strain sensors may be mounted on the load bearing parts of the aircraft structure during the testing of the aircraft, but the production aircraft would not include these strain sensors. Existing methods for assessment/management of the structural health, certification of flight readiness and fleet management are largely based on statistical data about the history of the aircraft, and depend heavily on the expertise of mechanics and engineers. Accordingly, there remains a need for the sensors and actuators that are compact, light, and inexpensive, and that can be used for the manned and unmanned aircraft. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: 
         FIG.  1    is a schematic view of an aircraft equipped with sensors in accordance with an embodiment of the presently disclosed technology. 
         FIG.  2    is an isometric view of an aircraft structure equipped with sensors and actuators in accordance with an embodiment of the presently disclosed technology. 
         FIG.  3    is a top plan view of a printed multifunctional skin (pSKIN) equipped with sensors and actuators in accordance with an embodiment of the presently disclosed technology. 
         FIGS.  4 A- 4 C  are isometric views of a pSKIN mounted on an aircraft structure in accordance with an embodiment of the presently disclosed technology. 
         FIG.  5    is an exploded view of a pSKIN assembly in accordance with an embodiment of the presently disclosed technology. 
         FIGS.  6 A and  6 B  are plan and isometric views of an aircraft with sensors and actuators in accordance with an embodiment of the presently disclosed technology. 
         FIGS.  7 A- 7 F  are schematic views of equipping an aircraft structure with sensors and actuators in accordance with an embodiment of the presently disclosed technology. 
         FIG.  8    is an isometric view of printing sensors and actuators over an aircraft in accordance with an embodiment of the presently disclosed technology. 
         FIG.  9    is an isometric view of a wind tunnel testing of sensors and actuators in accordance with an embodiment of the presently disclosed technology. 
         FIGS.  10 A and  10 B  are graphs of load measurements in accordance with an embodiment of the presently disclosed technology. 
     
    
    
     DETAILED DESCRIPTION 
     Specific details of several embodiments of representative sensors and actuators carried by aircraft, and associated methods of manufacturing and use are described below. The system and methods can be used for equipping the aircraft or an aerodynamic structure with the sensors, actuators, and the supporting electronics (also referred to as printed multifunctional skin (pSKIN) or instrumentation), and for using the instrumentation for developing, testing and using the aircraft or the aerodynamic structure. 
     In at least some embodiments, the sensors (pressure sensors, temperature sensors, strain sensors, ice sensors, strain transducers, RF antennas, etc.) and actuators (e.g., heaters, ionic actuators, plasma actuators, miniature air blowers, etc.) may be built using 3D printing (also referred to as 3D manufacturing, additive printing, additive manufacturing, or direct write). The sensors and actuators may be printed directly over the aircraft structures or inside relatively shallow cavities of the aircraft structures. In some embodiments, the host aircraft structures can also be made by 3D printing. 
     Furthermore, in at least some embodiments, the electronics may also be printed using specialized 3D printing equipment, methods and materials or “inks” (e.g., conductors, semiconductors, and dielectrics). Some examples of 3D-printed electronic elements or components are interconnects, electrodes, resistors, capacitors, and active electronics. As a result, a multifunctional, smart and lightweight device can be created. 
     In many embodiments, a relatively high density of sensors/actuators at a reduced unit cost/weight is advantageous over the bulky legacy systems. For example, many sensors/actuators and their supporting electronics (e.g., microcontrollers, op-amps, analog to digital (A/D) converters, resistors, power supplies, etc.) can be 3D manufactured at the outer surface of the aircraft structure in conjunction with the manufacturing of the aircraft structure itself (as opposed to placing the conventional sensors/actuators/electronics deeper inside the aircraft structure with the conventional technology). In some embodiments, one or more relatively shallow openings (e.g., 2-10 millimeter deep) in the aircraft structure may house power supplies, electronics, connectors, etc., for the sensors/actuators. Because of their relatively low height, the sensors/actuators closely approximate the surface of the aircraft structure, therefore not impeding or disturbing the airflow around the aircraft structure. In some embodiments, the sensors/actuators may be 3D printed directly over the outer surface of the aircraft structure in conjunction with manufacturing of the aircraft structure itself, or after the aircraft structure has been already manufactured. 
     In some embodiments of the inventive technology, the sensors/actuators, and the electronics may be printable onto a conforming foil (e.g., a decal, also referred to as pSKIN) that is subsequently transferred to an existing aircraft structure. In some embodiments, the conforming foils may have thickness of several micrometers (e.g., less than 100 μm, or 5 μm-100 μm) to several millimeters (e.g., 2-10 mm). 
     Data from the 3D-printed sensors may provide an assessment of the state of the aircraft and/or an improved modeling (e.g., numerical simulation) of performance over time, therefore resulting in improved monitoring of the structure and better prediction of maintenance needs. In some embodiments, the inventive technology can enable a “Digital Twin,” which is a mirror computer model of the aircraft that integrates numerical simulation with data from aircraft sensors (e.g., 3D printed sensors), the aircraft maintenance history, and historical statistical data across aircraft of the same type to enable improved safety and reliability. In some embodiments, the Digital Twin may be used to improve the models of the aircraft. 
     In some embodiments, the above-described methods and systems may be applied to other structures, e.g., pumps, wind turbines, submarines, ships, engines, blades, prosthetics, pipelines, etc. For example, a vane of an air fan may be equipped with 3D-manufactured sensors/actuators (a pSKIN) at an outer surface of the vane for monitoring or optimization of the air fan&#39;s performance. 
       FIG.  1    is a schematic view of an aircraft  1000  equipped with sensors in accordance with an embodiment of the presently disclosed technology. The aircraft  1000  can carry 3D-printed pressure sensors  105 , temperature sensors  110 , and/or strain sensors  115 . These sensors may send their measurement data to a local or a central processing/display unit (e.g., a display in the airplane cockpit, computer carried by an unmanned vehicle, etc.). Other numbers and types of sensors are also possible. In some embodiments, the aircraft  1000  may also carry 3D-printed actuators. 
       FIG.  2    is an isometric view of an aircraft structure  200  equipped with sensors and actuators in accordance with an embodiment of the presently disclosed technology. The illustrated aircraft structure  200  may be, for example, a segment of an aircraft wing. In some embodiments, the aircraft structure  200  can include openings  255  for connecting with the adjacent aircraft structures. The aircraft structure  200  carries a decal (pSKIN)  280 . The combination of the pSKIN  280  and the aircraft structure  200  may be referred to as a smart structure or a smart device  2000 . The illustrated pSKIN  280  includes sensors  215  (e.g., strain sensors or strain gauges) and actuators  220  (e.g., heaters), but other sensors/actuators are also possible. The sensors  215  and actuators  220  are connected with conductive traces  230  to the connectors  225  (e.g., metal pads or plugs). In at least some embodiments, the supporting electronics (not shown) may be connected through the connectors  225  to the sensors/actuators  215 / 220 . In some embodiments, the supporting electronics may be at least partially embodied in the pSKIN  280 . Generally, the pSKIN  280  remains flexible because of its relatively small thickness (e.g., less than 10 μm to few mm). As a result, the pSKIN  280  may follow the shape of the aircraft structure  200 , and may be folded over the edges of the aircraft structure  200 . The pSKIN  280  can also be directly printed over the aircraft structure  200 . 
       FIG.  3    is a top plan view of a pSKIN  380  with sensors and actuators in accordance with an embodiment of the presently disclosed technology. In the illustrated embodiment, the pSKIN  380  includes sensors  215  (e.g., for temperature measurements), and an actuator  310  (e.g., a heater). In other embodiments, the pSKIN  380  may include different type and number of sensors/actuators and supporting electronics, only sensors, or only actuators. The sensors  215  and the actuator  310  are connected with conductive traces (e.g., metal traces) with the connectors  225 . 
       FIGS.  4 A- 4 C  are isometric views of the pSKIN  380  mounted on an aircraft structure in accordance with an embodiment of the presently disclosed technology.  FIG.  4 A  shows the pSKIN  380  applied over the aircraft structure (e.g., an airfoil or a segment of the aircraft wing)  200  (collectively, a smart structure or a smart device). The illustrated pSKIN includes two sensors  215  and the actuator  310 , but other combinations of sensors/actuators are also possible. In some embodiments, the pSKIN  380  may be folded over an edge  360  of the aircraft structure  200 . An integrated circuit (IC) chip  410  may be connected to the connectors  225 . In some embodiments, the IC chip  410  may be bonded or soldered to the connectors  225 . In some embodiments, the IC chip  410  is on the side of the aircraft structure  200 . As a result, the IC chip  410  and the connectors  225  may be better protected against the environment, as explained with reference to  FIGS.  4 B- 4 C  below. 
       FIG.  4 B  shows an aircraft structure  200   a  connected to another aircraft structure  200   b . In some embodiments the aircraft structures  200   a ,  200   b  may be segments of the aircraft wing or fuselage. In other embodiments, the aircraft structures  200   a ,  200   b  may be segments of a rotorcraft, e.g., segments of a helicopter propeller. Since the illustrated aircraft structures  200   a ,  200   b  butt against each other, the IC chip  410  and the connectors  225  are protected against the environment, e.g., rain or air drag. In some embodiments, conductive traces  230  or other wiring can electrically connect the pSKIN  380  with electronics (e.g., power supplies, controllers, etc.) away from the aircraft structure  200   a . For example, the power supplies, controllers, etc. may reside on the aircraft itself, but away from the structure  200   a . In some embodiments, the pSKIN  380  may be wirelessly connected (e.g., Bluetooth, WiFI, etc.) with external electronics. 
       FIG.  4 C  shows aircraft structures  200   a ,  200   b ,  200   c  that are mutually connected, and mounted on a stand  420  inside a wind tunnel  400 . In some embodiments, the aircraft structure  200   a  has its leading edge  350  oriented to face an incoming airflow at velocity U. In some embodiments, the actuator  310  (e.g., a heater) may manipulate (e.g., heat up) the incoming air to change its physical properties. The downstream sensors  215  (e.g., thermocouples or strain gauges) may measure some physical properties (e.g., temperature of air or drag force) that are influenced by the upstream actuator  310 . In some embodiments, the pSKIN  380  may be used for, e.g., deicing or flow control. As explained with reference to  FIGS.  4 A and  4 B , the IC chip  410  and/or the connectors  225  are less exposed to the environmental force and degradation since they are not in the path of the flow. In some embodiments, the conductive traces  230  (or other wired or wireless connections) may connect the pSKIN  380  with electronics outside of the wind tunnel  400 . 
       FIG.  5    is an exploded view of a pSKIN assembly  5800  in accordance with an embodiment of the presently disclosed technology. In some embodiments, the pSKIN assembly  5800  includes a pSKIN  580  having a foil  580   a  (e.g., a polymer, wax paper, thin PCB, etc.) with the 3D-printed electronics and a layer of adhesive  580   b  (e.g., an epoxy). The illustrated pSKIN  580  is covered with a protective cover  510  having a protective foil  510   a  (e.g., a polymer) and a layer of adhesive  510   b . In some embodiments, the protective cover  510  and/or the pSKIN  580  can be made by casting one-part epoxy resins onto a wax paper or olefin based foils. In some embodiments, the foils  580   a / 510   a  may be rigid enough to handle, yet remain pliable enough to conform to many curved surfaces. The sensors/actuators (e.g., a heater  310 ), conductive traces  230 , and connectors  225  can be 3D-printed over the foil  580   a . In some embodiments, the sensors, actuators and/or electronics of the pSKIN  580  may be made by lithography or screen printing. The combination of the pSKIN  580  and the protective cover  510  can be applied over the aircraft structure  200 . In some embodiments, in-situ curing can be used to cure the pSKIN assembly  5800  without affecting the aircraft/host structure substrate using, for example, photonic based curing, UV based curing, electromagnetic systems such as induction heating and microwaves, and/or thermal blankets. In at least some embodiments, the cured pSKIN assembly  5800  retains good adhesion and functionality in presence of a hole  290  (e.g., a rivet hole). 
       FIGS.  6 A and  6 B  are plan and isometric views of an aircraft  6000  that carries sensors and actuators in accordance with an embodiment of the presently disclosed technology.  FIG.  6 A  is a plan view of the aircraft  6000  that includes several sensors, actuators and power supplies (e.g., batteries). Collectively, the aircraft  6000  and the sensors/actuators/electronics may be referred to as a smart structure or a smart device  6100 . The aircraft  6000  may be, for example, an unmanned airplane, but other types of aircraft are also possible. 
       FIG.  6 A  shows an embodiment of the aircraft  6000  that carries several sensors and actuators: thermocouples  610 , ice sensors  620 , sensors  215  (e.g., strain sensors), and pressure sensors  105  (collectively, pSKIN or printed multifunctional skin). Other numbers and arrangement of the sensors and actuators are also possible. In some embodiments, the sensors/actuators may be at least in part powered by batteries  630 . In some embodiments, the aircraft  6000  may include electronics (not shown) for digital or analog processing, wireless data transmission to ground or to another aircraft, etc. For example, the aircraft  6000  may include heaters that are turned on and off based on the signal from the ice sensors  620  that is processed by the on-board electronics. In other embodiments, high-bandwidth pressure sensors can be coupled with ionic wind generators for boundary layer control. Furthermore, distributed sensors can be used to determine the position of streamwise vortices, and then surface electrodes for ionic wind may nudge or force the vortices back to their optimal location using a closed-loop control system. As a result, more efficient aerodynamic vehicles with low skin friction can be developed to, for example, reduce fuel consumption. 
       FIG.  6 B  shows the aircraft  6000  that has openings in the aircraft for housing the sensors, actuators and power supplies. For example, in some embodiments, openings  105   h  may be shaped and configured to receive the pressure sensors  105 , and openings  630   h  may be shaped and configured to receive the batteries  630 . Manufacturing of the openings  105   h ,  630   h  is discussed with reference to  FIGS.  7 A- 7 F  below. 
       FIGS.  7 A- 7 F  are schematic views of equipping an aircraft structure with sensors and actuators in accordance with an embodiment of the presently disclosed technology.  FIG.  7 A  schematically illustrates a step  7100  for manufacturing the aircraft structure  200 . In some embodiments, a 3D printer  710  may eject a 3D material  720  (e.g., aerosols, powdered metals, melted materials, polymer ceramic composites, etc.) that form the aircraft structure  200 . The 3D printer  710  may be controlled by a controller or a computer (not shown). 
       FIG.  7 B  schematically illustrates a step  7200  for manufacturing the aircraft structure  200 . In the step  7200 , an opening  730  (e.g., a pocket or a housing, also referred to as a first opening) is created for housing the electronics for sensors/actuators. 
       FIG.  7 C  schematically illustrates a step  7300  for manufacturing the aircraft structure  200 . In the step  7300 , an electronics printer  740  (also referred to as “3D electronics printer” or “additive electronics printer” or “direct write electronics printer”) prints electronics  750   a  for supporting the sensors/actuators. The electronics printer  740  places a functional material  745  on the surface the electronics  750   a . Active and passive elements may be placed directly on the surface or inside the pockets of the aircraft structure  200 . In some embodiments, the electronics printer  740  can directly deposit a range of commercial and custom electronic materials such as resistors, conductors (copper, silver, gold, etc.), dielectrics, piezoelectrics, carbon nanotubes, adhesives, polymers, and other materials. Using these materials, different sensors, resistors, capacitors, transducers, interconnects, coils, active circuit elements, and/or antennas may be fabricated over the aircraft structure  200 . In some embodiments, electronics  750   b  may also be printed in-situ or may be pre-made using a 3D printer or conventional methods (e.g., surface mount technologies). 
       FIG.  7 D  schematically illustrates a step  7400  for manufacturing the aircraft structure  200 . In the step  7400 , a buildup of the aircraft structure  200  continues using the 3D printer  710 . In some embodiments, the electronics  750   a / 750   b  may become encapsulated in the 3D material  720 , leaving openings  760  for accessing the electronics  750   a / 750   b.    
       FIG.  7 E  schematically illustrates a step  7500  for manufacturing the aircraft structure  200 . In the step  7500 , a wiring  770  may be added by the electronics printer  740 . In some embodiments, the 3D printer  710  may print conductive materials, e.g., the wiring  770  inside the openings  760  (also referred to as second openings). In some embodiments, the wiring  770  may connect the electronics  750   a / 750   b  to the surface of the aircraft structure  200 . 
       FIG.  7 F  schematically illustrates a step  7600  for manufacturing the aircraft structure  200 . In the step  7600 , the electronics printer  740  may add, for example, the pressure sensor  105 , the temperature sensor  110  and the strain sensor  115  to the surface of the aircraft structure  200 . In other embodiments, different combinations of the sensors/actuators may be added by the electronics printer  740 , for example, the pSKIN  580  may combine thermistor-based temperature sensors, strain gauges, and pressure sensors. Generally, the sensors/actuators are relatively thin in comparison to the aircraft structure  200 . For example, in some embodiments, the sensors/actuators may be less than 10 μm, less than 100 μm, or less than 2 mm thick. In some embodiments, the wiring  770  connect the electronics  750   a / 750   b  with the sensors/actuators of the pSKIN  580 . 
       FIG.  8    is an isometric view of printing sensors and actuators over the aircraft  6000  with in accordance with an embodiment of the presently disclosed technology. In some embodiments, the electronics printer  740  may be positioned above the aircraft  6000 , and may be driven by a computer controlled positioning system (not shown). In some embodiments, the electronics printer  740  may use different functional material for printing different components of the pSKIN (e.g., the functional material for the conductive traces  230  and dielectric-based ink for the insulation of the ice sensor  620 ). Some embodiments of the sensors that are manufacturable by the electronics printer  740  are temperature sensors, strain sensors, static or low frequency pressure sensors, force sensitive resistors, dynamic or high frequency pressure sensors, heat flux sensors, negative pressure or vacuum sensors, piezoelectric sensors, vibration sensors, impact sensors, airflow sensors, acoustic sensors, electric field sensors, antennas, magnetic field sensors, crack detection sensors, ice sensors, sensors detecting other characteristics relating to flight, sensors detecting other characteristics of the environment, sensors detecting other characteristics relating to aircraft structural health, and a metamaterial with an ordered one-dimensional, two-dimensional or three-dimensional structure. Some embodiments of the actuators that are manufacturable by the electronics printer  740  are: ice remediation heaters, ion actuators, plasma actuators, piezoelectric transducers, aircraft controls, and other planar functional devices printed or adhered to the surface of the aerodynamic structure. 
     Electronics Printer 
     In some embodiments, an OPTOMEC Aerosol Jet (AJ) system can be used as the electronics printer  740 . The pSKIN sensors/actuators may be printed directly on metallic structures, other 3D printed structures, and other suitable substrates such as composites. Some examples of functional material  745  are: carbon nanotube inks, conductors (e.g., metals), insulators, semiconductors, semimetals, resistors, dielectrics, adhesives, epoxies, filled epoxies, polymers, filled polymers, elastomers, filled elastomers, ceramic particulates, piezoelectric materials, magnetic materials, functional materials, graphene inks, biological materials, and composites of these material. 
     Printed Strain Gauge Sensors 
     In some embodiments, the strain sensor (strain gauge)  115  can be printed over different substrates (e.g., aircraft structure  200 ): glass, polyimide, composite materials, ceramics, and anodized aluminum 2024 T3. The functional materials  745  may include metals, elastomers, piezolectrics, PARU silver nano ink, Heraeus PEDOT:PSS 1000 and Brewer Science Carbon Nano Tube (CNT) inks. In some embodiments, the electrical resistance for the functional material  745  is between 100Ω and 350Ω for Paru silver, around 200 kΩ for CNTs and between 0.4MΩ and 0.6MΩ for PEDOT:PSS. Since aluminum is conductive, several layers of Sigma Aldrich polyimide may be printed onto the aluminum aircraft structure  200  prior to the conductive ink application. In some embodiments, the strain sensors (strain gauges) can be printed in about 10 layers with a total print time of about 60 minutes at 4 mm/s translations. 
     Printed Temperature Sensors 
     In some embodiments, the temperature sensors  110  are thermocouples or thermistors. Conventional manufacturing of the thermocouples requires an oxygen free atmosphere and high curing temperatures. In some embodiments of the present technology, a low-temperature curing process for the thermocouples can be used by having the functional material that requires low processing temperature conditions. 
     In some embodiments, the thermistors can be made of semiconducting mixtures of oxides of transition metals with low processing temperature conditions (e.g., silicon based silistors, switching type materials, or graphite). In some embodiments, these materials may be solvable in a solvent to produce the functional material  745 . In one embodiment, the functional material  745  may include Molybdenum Disulphide (MoS2) and Molybdenum Disulphide (MoS2) diluted 1:1 with Toluene (polar solvent), to lower viscosity and to facilitate printing. In other embodiments, the functional material  745  may include Molybdenum Disulphide (MoS2), Magnetite, and poly polystyrene sulfonate (PEDOT:PSS). 
     Printed Pressure Sensors 
     In some embodiments, the sensors may include printed pressure sensors  105 , for example, Force Sensitive Capacitors (FSCs), Force Sensitive Resistors (FSRs), and/or Lead Zirconate Titanate (PZT) sensors. In an embodiment, the FSC can operate by continuously evaluating a capacitance of a printed capacitor having two parallel conductive plates separated by a dielectric material. The capacitance of the capacitor may by modeled by the equation C=kεA/D, where k is the permittivity of the dielectric between the plates, ε is the permittivity of space, A is the area of the capacitor, and D is the thickness of the dielectric. By printing these sensors using appropriate functional materials  745 , the conductor plates and dielectric material can be made relatively thin, increasing the static capacitance of the sensor. In some embodiments, the printed conductor plates/dielectric material may have the thickness of about 100 nm to 30 μm. In some embodiments, PARU silver nano ink can be used as the conductive material, and Sigma Aldrich polyimide as the dielectric layer. 
     In some embodiments, the sensors (e.g., pressure sensors) may be manufactured by sintering micro-scale lead zirconate titanate (PZT) films with relatively low substrate temperature increases. In other embodiments, the functional material  745  may include ink formulated from PZT nanoparticles, solvent, dispersant and adhesion promoter. In some embodiments, the inks may dry for a few hours (e.g., two hours) in a vacuum at about 200° C. In some embodiments, the functional material  745  may be photonically sintered using sub-millisecond pulses of broad spectrum light. In some embodiments, the remanent polarization and coercive field for thermally sintered PZT film were 16.1 μC/cm2 and 4.3 kV/cm, respectively. For the photonically sintered materials, the remanent polarization can be 27.7 μC/cm2 and coercive field can be 3.1 kV/cm. The piezoelectric voltage constants (g31) for the two film groups can be −5.0×10−3 V-m/N (for thermally sintered functional material) and −5.5×10−3 Vm/N (for photonically sintered functional material). For at least some embodiments, the foregoing values indicate that the PZT films were successfully sintered. In some embodiments, to avoid the relatively high temperature of sintering the conventional PZT material, a colloidal based functional material  745  may be used. As a result, instead of conventional sintering at about 600° C., the curing and sintering of the PZT particles in the functional material  745  may occur in a temperature range of 150-200° C., therefore being suitable for direct printing over many metallic and non-metallic aircraft structures  200 . 
       FIG.  9    is an isometric view of a wind tunnel testing of sensors and actuators in accordance with an embodiment of the presently disclosed technology. In the illustrated embodiments, the aircraft  100  carries the sensor  310  (e.g., a heater) and the sensor  215  (collectively, pSKIN). The aircraft  100  is mounted on the stand  420 , and oriented to face the incoming airflow at velocity U. In some embodiments, the sensors/actuators of the pSKIN may make measurements and/or manipulate the fluid flow to, for example, improve flight characteristics of the aircraft  100 . 
       FIGS.  10 A and  10 B  are graphs of load measurements in accordance with an embodiment of the presently disclosed technology. In particular,  FIG.  10 A  is a graph of the load over time, and  FIG.  10 B  is a graph of the measured load over time. The horizontal axes for both graphs are time in seconds. 
     The vertical axis of the graph in  FIG.  10 A  corresponds to applied load in lbF. In the illustrated embodiment, the applied load increases over the time, reaches a peak of about 250 lbF after about 19 seconds, and then decreases to about 25 lbF after 25 seconds. In some embodiments, the load may be applied over an aircraft structure (e.g., a wing of an aircraft). 
     The vertical axis of the graph in  FIG.  10 B  corresponds to the resistance in Ω of a strain sensor (e.g., the strain sensor  115  placed over an aircraft wing). The behavior of the measured resistance in Ω in  FIG.  10 B  generally corresponds to the loading shown in  FIG.  10 A , i.e., the shape, maximum, and minimum of the graph in  FIG.  10 B  generally follows the shape of graph in  FIG.  10 A , therefore indicating a generally linear response of the strain sensor. In at least some embodiments, a linear response of a sensor is a preferred response. 
     From the foregoing, it will be appreciated that specific embodiments of the technology have been described herein for purposes of illustration, but that various modifications may be made without deviating from the disclosure. Moreover, while various advantages and features associated with certain embodiments have been described above in the context of those embodiments, other embodiments may also exhibit such advantages and/or features, and not all embodiments need necessarily exhibit such advantages and/or features to fall within the scope of the technology. For example, ice protection systems can be printed next to temperature sensor arrays for de-icing/anti-icing. In some embodiments, the pSKIN-based control of the aerodynamics/hydrodynamics of the vehicles may result in improved performance of the vehicles. Accordingly, the disclosure can encompass other embodiments not expressly shown or described herein.