Multi-responsive 3D Structured PVDF Cube Switch for Security System Using Piezoelectric Anisotropy

Advancements in �exible electronics using piezoelectric materials have paved the way for their numerous applications. In this study, we suggest a 3D structured polyvinylidene �uoride (PVDF) �lm cube switch to maximize piezoelectric anisotropy and �exibility. Unlike piezoelectric material-based �exible electronics, PVDF cube switches have a simple design and easy fabrication process. Each side of the cube switch demonstrates independent voltage signals with pressing displacements and corresponding directions. With cutting angle variation and planar �gure designs, derived cube switches respond with various combination of voltage waveforms. PVDF switches can endure more than 1000 cycles of 70% vertical strain in terms of both electrically and mechanically. As an application, we establish security system with multi-responsibility of a cube switch. This security system can protect users from potential threats owing to its multi-responsibility and user-dependent operability.


Introduction
Flexible electronics and strain sensors have attracted considerable attention over the past few decades.[1] Owing to the rapid growth in the sensor and electronic elds, researchers and scientists are discovering smart materials that meet the demands of the industry and our daily lives.[1] Among the various smart materials, piezoelectric materials have attracted a great attention because of their advantages.[2][3][4][5] Piezoelectric materials such as lead zirconate titanate (PZT), barium titanate (BaTiO 3 ), and piezoelectric polymer polyvinylidene uoride (PVDF) have been frequently used by scientists and researchers.[6,7] Piezoelectric materials convert mechanical energy into electrical energy and vice versa.
Owing to their distinct ability, piezoelectric materials are used in applications such as pressure sensors [8,9], strain sensors [10,11], actuators [12,13], and energy harvesters [14,15].Among these materials, PVDF has attracted the attention of scientists in the eld of exible electronics and sensors because of its high durability, chemical stability, and exibility compared with PZT-based piezoelectric materials [16][17][18][19][20]. Anisotropy, which is a property of piezoelectric materials, is a drawback because it deteriorates the piezoelectric material-based devices, generating voltage in terms of uniformity.In this study, we employ this property to develop a device that operates with a single input to provide multiple output responses in accordance with the force and piezo element directions derived from the polarization direction.Previous studies on PVDF lms have generally focused on advancing fabrication methods, such as patterning processes [21,22] or modifying the molecular phase [23,24].However, applications of PVDF lms with anisotropic [25] and three-dimensional (3D) structures have rarely been introduced.[26,27] In addition, piezoelectric material-based electronics, such as sensors, operate within a single voltage waveform.[28][29][30] Herein, we propose a cube-type switch with a PVDF lm to diversify its responses from a single stimulus.The cube switch has ve sides: front, rear, left, right, and top.Each side generates a voltage depending on its piezo element de nition, which in turn triggers other sides.Using the cube planar gure designs and cutting angle variations, we expanded and variegated the possible cases of voltage waveforms from the device.The durability and reproducibility of the switch were veri ed through a cyclic test.The cube-type switch for the security systems can compensate for the current problems of conventional security systems, such as ngerprint marks and a limited combination of security patterns, which may lead to fatal outcomes for the users.[31] A multi-responsive security system is highly userdependent and inimitable by a third party.Users can easily de ne their own passcode by diversifying the voltage waveforms with pressing depth, cube design selection, and adjusting the number of cubes involved in the system.

Results
Design and basic mechanism of PVDF cube switch Figure 1a demonstrates three different cube planar gure designs.The PVDF cube switch was fabricated using a PVDF lm with planar cube designs and cutting angles.These two methods are paramount to adjusting the response of the cube in the design stage.Figure 1b illustrates the planar gure being assembled and when it is pressed by a human index nger.When the top side of the cube is pressed (perpendicular to the surface), the remaining sides (left, right, front, and rear) begin to de ect.This eventually causes an output voltage, owing to the piezoelectric effect of the PVDF lm.The top surface also de ects in the vertical direction due to the pressing force.Figure 1c shows the schematic illustrations of three different cube planar gure designs and their responses.The ve sides of the cube are wired to conductive lms, which can be further connected to the voltage-measuring device to receive its responses.The responses from the PVDF cube can be varied with different planar gure designs and cutting-angle variations.The cube planar gure design and cutting angle are closely related to the piezoelectric anisotropy of the PVDF, which eventually increases the number of voltage response waveforms from the independent cube and the sides of a single cube.This behavior of the PVDF lm and the derived cube switch will be discussed in the section "Basic model of a PVDF cube switch and its anisotropy."Fig. 1d is a photograph image of cube planar design and its assembled features.With its ability to produce numerous responses with a simple fabrication method, this cube switch is applied to a security system wherein input multiplicity is extremely crucial (Fig. 1e).

Basic Model Of Pvdf Cube Switch And Its Anisotropy
Figure 2a, b, and c are schematic illustrations of a PVDF lm.PVDF is a piezoelectric material, which generates a voltage when it de ects.Silver layers deposited on the top and bottom surfaces of the PVDF act as electrodes.Electrode layers with a thickness of 200 nm are deposited through the E-beam process.
The PVDF lm has three directions as illustrated in Fig. 2a.The polarized direction is perpendicular to the silver electrode layer which is denoted as a thickness direction in the cartesian coordinate.For fabrication and to control the behavior of voltage waveform from the PVDF lm, we de ne the #1 and #2 direction as the direction that is parallel to the transverse and drawn direction, respectively (Fig. 2b).Let the dimensions of a PVDF lm in the initial state be w × d × l (Fig. 2c).As shown in Fig. 2d, the PVDF lm has anisotropic material behavior in terms of the piezoelectric effect.It generates an independent voltage in accordance with the direction of the force applied to it, which are called d 31 (Fig. 2d ( )), d 32 (Fig. 2d ( )), and d 33 mode (Fig. 2d ( )). Figure 2e shows the behavior of PVDF lm when it is under two different directions of forces: #1 direction and #2 direction.A transverse compressive force leads to de ection along the width and is denoted as #1 direction (Fig. 2e ( )).This directional force eventually causes #1 direction bending of PVDF lm, where d 31 mode contributes dominantly in terms of voltage response.
Similarly, #2 direction bending occurs when the compressive force is applied to the PVDF lm in the drawn direction (Fig. 2e ( )).In this de ection, d 32 mode is dominant when PVDF lm generates voltage signal.As this anisotropy of the PVDF lm determines the amount of electrical potential value, different voltage waveform sets can be obtained using various combinations of force direction.We developed a three-dimensionally constructed PVDF lm cube switch to simultaneously receive an individual response from each side caused by a single force.Figure 2f delineates a cube-shaped PVDF lm, demonstrating its response to a vertical pressing force.The pressing displacement of the cube structure is categorized as 1 mm, 3 mm, 5 mm, and 7 mm for the experiment.The front and rear sides of the cube are along the #1 direction force, while the left and right sides are along the #2 direction force.The output voltage is measured from the front and right side.The corresponding electrical potential values with pressing displacement and force direction on each side, when this model is vertically pressed continuously accompanied by categorized displacement six times, are shown in Fig. 2f ( ).This trend becomes more distinct when its responses are plotted with the pressing displacements.The average voltage values and the standard deviations along with the pressing displacements are plotted in Fig. 2f ( ).When the cube is pressed by 1 mm, an output voltage of 0.96 V and 0.04 V is measured at the front and right side, respectively.These values indicate the response from two sides are not identical.The front side manifests the greater output voltage.The PVDF lm has piezoelectric constant, which is d 31 , d 32 and d 33 of 22 pC/N, 2 pC/N, and 35 pC/N, respectively.[21] The output voltage of the piezoelectric materials strongly depends on their coe cients and the stress applied.The slope of the voltage line along #2 direction becomes steeper between displacements of 5 mm and 7 mm (Fig. 2f ( )).When the cube is slightly pressed, d 32 is a governing factor to generate the voltage on the left and right sides (#2 direction).
However, as the pressing displacement increases, d 31 and d 33 contribute to the voltage generated along those two sides.This is closely related to the stress behavior of the structure, and relevant analysis will be discussed in "FEA of PVDF cube switch" section.When the cube is pressed up to 7 mm, the output voltage difference from those sides becomes more apparent.An output voltage of 19.42 V is measured at the front, while 7.90 V is measured on the right side.

Multifariousness Cube Planar Designs
The PVDF cube switch has utility for various combinations of voltage waveforms by adjusting the planar cube designs.A cube structure with different #1 directions on its sides can be derived from six possible planar gure designs.In Fig. 3a, the possible cube planar gure designs are schematically illustrated with #1 direction (arrows) and assigned numbers to correlate with the table in Fig. 3b.In the section "Basic model of a PVDF cube switch and its anisotropy," we showed that the force direction of a cube switch is closely related to the voltage output due to the anisotropy of the PVDF lm.In the cutting design, the force direction of the individual sides in a 3D structure varies.In line with the characteristic property of anisotropy, the cube planar gure design is directly related to the voltage waveforms.Here, the #1 directions are indicated by arrows (Fig. 3a and 3b).In the 2D plane, the #1 direction patterns on each side are identical, regardless of the cube planar gure designs (Fig. 3a).However, when this cube planar gure is folded and assembled into a 3D structured cube, each side of the cube is assigned individual coordinates in terms of the piezo axis.This dimensional change causes each side of the cube to respond differently to a single stimulus.We assigned separate colors to compare the respective sides (A, B, C, and D) of the individual cubes.The table in Fig. 3b denotes #1 direction patterns in accordance with the cube planar gure design.As shown in Fig. 3b, each planar gure design has its pattern of direction #1.This eventually generates a cube response with different output voltage combinations from each side.In the 2D plane, the #1 direction indicators (arrow) that are opposed to one another demonstrate the same trait in generating the voltage (Fig. 3b).In other words, the paired direction, namely right/left, and upwards/downwards are identical.The voltage generated from the sides and indicators with left/right arrows are activated primarily by the d 31 mode, while the upright/downwards arrows are activated by the d 32 mode.The basic model has #1 direction patterns that include right, up, left, and up on sides A, B, C, and D, respectively.This pattern creates a cube response with sides A and C in #1 direction, while responses with sides B and D are obtained along the #2 direction when it is pressed.The response from the basic model is discussed in the previous section (see Fig. 2f).Recalling the results from the basic model, each side of the cube demonstrates two different voltage responses generated along the #1 and #2 directions at the front and right sides, respectively.Figure 3c demonstrates responses obtained from the sides of the individual cubes.In this experiment, cube #1 (the basic model), #3, and #6 were selected for comparison.Three different cubes were pressed six times (with a displacement variation) each to obtain different datasets.As shown in the graph, the cube from each planar gure design shows a nonidentical combination of voltage waveforms from the sides.
In the basic model (cube #1), voltages of 11.52 V, 2.26 V, 10.28 V, 2.23 V, and 2.56 V from sides A, B, C, D, and top, respectively, were obtained for a pressing displacement of 5 mm.As per the obtained results, the parallel sides of the cube generated similar voltages because the dominant factors causing the output voltage were the same.This result also indicates that the output voltage combination obtained from the basic cube exactly follows the initial design purpose.Sides A and C generated voltages primarily in the d 31 mode, while sides B and D generated voltages along the d 32 mode.Additionally, the top surface generated voltage along the d 33 mode.
From the planar gure design of cube #3, the four sides of the cube (A, B, C, and D) generated voltages along the #2 direction.This pattern causes all the sides to respond to the same electrical potential value.The voltage reading from sides A, B, C, D, and top of cube #3 were 3.99 V, 3.25 V, 3.46 V, 3.43 V, and 3.21 V, respectively.The experimental results showed that the sides of the cube generated a similar output voltage.All sides of the cube, except the top, generated a voltage in the #2 direction.
The electrical potential values from cube #6 were 10.80 V, 10.26 V, 9.13 V, 9.13 V, and 2.59 V for sides A, B, C, D, and top, respectively, when it was pressed up to 5 mm.The sides A, B, C, and D of cube #6 exhibited electrical signals in the #1 direction.Thus, four sides of cube #6 responded with a voltage of approximately 10 V and a standard deviation of 0.72 V.
A voltage of approximately 3 V was measured at the top side of the three cubes, regardless of the planar gure design.This indicates that the voltage response from the top side is independent of the structural factors.Cyclic tests were conducted to investigate the long-term durability and structural stability of the cube switch (Figure S1, S2, and S3).The voltage was measured from ve sides of the cube (A, B, C, D, and top).No signi cant voltage drop was recorded when the cube was pressed more than 1000 times (Figure S1, S2, and S3) with a pressing displacement of 3 mm.In addition, the voltage waveforms in the last ve cycles demonstrated a homogeneous trend without distortion, just as in the rst ve cycles.This implies that the cube switch has excellent mechanical durability and electronic reproducibility.When this planar design is expanded to an n-side polyhedron, a greater voltage response from the device with a single stimulus (Figure S4, S5, and S6) can be achieved.

Basic Pvdf Cube Switch With Cutting Angle Variation
The anisotropy of the PVDF lm leads to individual responses from each side of the cube.This feature helps in designing different cube sides by varying the cutting angles.Figure 4a shows a PVDF lm with various cutting angles.The modi ed #1 direction is denoted by the angle deviation from the original #1 direction.Each illustration depicts the modi ed #1 direction deviation from the original by 30°, 45°, and 60°. Figure 4b shows the images of the basic cube planar gure designs with angle variations.When the PVDF lm is cut with the speci ed angles to modify #1 direction, the cutting line starts to deviate from the origin.Consequently, the cutting line and #1 direction axis create intersection points, which are indicators of the modi cation.Here, an acute angle is considered between the cutting line and #1 direction.Figure 4b ( ), ( ), ( ), and ( ) shows the magni ed section of the PVDF cutting line from its origin.As the angle varies by 0°, 30°, 45°, 60° and 90°, ve different waveforms are obtained.However, the waveforms from 0°/90° and 30°/60° are identical (Figure S7).This is because of the geometrical relationship between the paired cubes (cutting angle of 0° and 90° / 30° and 60°).The basic cube model has a geometrical relationship between the adjacent sides in terms of direction (Figure S8).When one of the cutting angle deviations from #1 direction among the four sides (left, right, front, or rear) is de ned, the remaining deviations are determined from its geometry.Here, we de ne as the angle between #1 direction and the cutting line.Because the #1 direction and #2 direction of the adjacent side in the basic cube is perpendicular to each other, xing one of the angles on the sides automatically de nes the rest of the angles (Figure S8).For the top side, the d 33 effect is dominant, which is not affected by the cutting angle in terms of the voltage output.For the laser-cutting process, an adequate output selection for each step is crucial.High laser power in the electrode removal process results in cutting.In addition, excessive laser output damages the PVDF lm and triggers a pyroelectric effect, which mutates the dipole direction of the piezoelectric materials.Here, a parametric study on the power of the laser cutter was conducted to determine the laser output required to cut the PVDF lm.The power-speed condition of the laser cutter is divided into three sections: no damage, electrode removal, and cutting zone (Figure S9).We selected laser θ outputs of 127 W for electrode removal and 576 W for cutting.Photographs of the magni ed section for each process showed that the selected laser output for each step was adequate (Fig. 4b ( )). Figure 4c ( ) shows the voltage responses of the two cubes with front-side cutting at 30° and 60°.Two sides, having geometric relations with each other, generate identical voltages when pressed with the same amount of displacement (Figure S8).With this geometric relation and voltage response, we measured the output voltage from one side, and the results are plotted in Fig. 4c ( ).As the cutting angle deviates more from #1 direction, the output voltage starts to decrease.The obtained voltage trend is attributed to the piezoelectric coe cient of the PVDF lm.As the cutting angle deviates more from #1 direction, the cube side (where the d 31 mode is dominant) changes its voltage output behavior compared to the side where the d 32 mode is dominant.As d 31 coe cient is greater than that of d 32 , this geometrical shift eventually decreases the electrical potential.This phenomenon can be explained using the piezoelectric equation and vector component of the axial stress direction.The piezoelectric materials conform to the following equation: [32] 1 where P 1 , P 2, and P 3 are the electric displacements in the transverse, drawn, and thickness directions, respectively (Fig. 2a).T 1 , T 2 , and T 3 are the normal stresses in three directions; T 4 , T 5 , and T 6 are the shear stresses in three directions; d 15 and d 24 are the shearing strain coe cients.Due to negligible shear stress in a cube structure, the associated components can thus be eliminated.The output charge of the PVDF lm can be expressed as follows: 2 where Q, A, and are the electric charge, electrode area, and normal stress, respectively.The subscripts 1, 2, and 3 indicate the axial stress directions in the x-, y-, and z-directions, respectively.Because the cube structure is symmetrical, the normal stress applied on the four sides (front, rear, left, and right) will be the same (e.g., ).As we can see from the results of the pressed cube sides (Fig. 2f geometrical de ection.The geometrical attributes are discussed in the stress analysis section.With the electric charge equation and the given conditions, the experimental data when the cutting angle is at its origin are calculated.By combining the geometrical relation between the modi ed cutting angle and the #1 direction with the electric charge equation, we obtain: where is the cutting angle.To estimate the electrical charge on each side of the cube when the cutting angle rotates from its origin, the axial stress that triggers the voltage with the piezoelectric coe cient must be considered.By aligning the axial stress with the piezoelectric component (#1 and #2 directions), the electric charge that occurs during pressing can be explained.Figure 4c ( ) demonstrates the voltage change slope along with the displacement range ( ).We de ne the response rate in accordance with the displacement as the sensitivity of the cube switch.With the increase in the deviation of the cutting angle from its origin, the sensitivity decreases.When the cutting angle is parallel to #1 direction, the sensitivity is calculated as 2.77 V/mm, while the sensitivity is 1.13 V/mm when it deviates from its origin to 90°.
In the previous sections, we discussed two dominant parameters for the response of the cube switch: cube design (planar gure design and cutting angle) and pressing depth.Using these two parameters, we can determine the possible electrical signals from the device.Using the cumulative experimental data and polynomial regression analysis, we de ned a tting equation as follows: 4 where V side denotes the estimated voltage from the cube side.θ and d are the cutting angle and pressing depth, respectively.Here, the range of θ is 0° ≤ θ ≤ 90° and d ≤ 7 mm.For the direction pattern, θ = 0° and θ = 90° in #1 and #2 directions, respectively.Figure S10 shows the experimental values of the cube switch and the tting results.In this tting model, the R 2 value is 0.979, which indicates that the response of the device is predictable with the given information (cube design and pressing depth).In addition, using this tting result, the user can design customized cubes based on their demands, such as the target peak value of the voltage signal.

FEA of PVDF cube switch
The PVDF cube switch generates a voltage signal when pressed.To understand the behavior of the cube switch and the stress applied on the sides of the cube, we conducted nite element analysis (FEA).The computational simulation results (Fig. 5) show the overall stress of the cube (Fig. 5a) and the axial stresses on one of the cube sides (Figs.5b, c, and d)) when it is pressed to a displacement of 3 mm.As demonstrated in Fig. 5a, the four sides of the cube develop identical stresses when pressed and de ected symmetrically.In the previous section, we mentioned how the piezoelectric coe cient and the stress applied to the materials contribute to the voltage signal.In Fig. 4c, the measured data shows identical voltages.The same coe cient is obtained when the cube planar gure is designed on all sides (except the top) and operates in the same mode.The second condition for an identical voltage to be measured on four sides when pressed is the distribution of stress within the structure.The FEA results verify that the stress is equally distributed on cube sides and it eventually makes four sides of the cube generate identical voltages when operated in the same mode.Along with the identical behavior of the sides, we conducted axial stress analysis of one side in three directions: the rst one being normal to the surface, while the second and third are parallel and perpendicular to the force direction, respectively.This result veri es the mathematical analysis of the output voltage presented in the previous section.Regardless of the cutting angle or the force direction, the stress normal to the side contributes to the d 33 effect.
Although this is the smallest stress (Fig. 5b), the d 33 coe cient allows this stress to generate an output voltage.For stresses that are parallel and perpendicular to the force direction, the maximum formal value is 34.2 MPa and the latter is 12.1 MPa.The parallel stress is twice that of the perpendicular stress, indicating that the meaningful stress for the electrical response has an identical action direction.

Security System With Pvdf Film Cube Switch
As an application, we constructed a security system using a PVDF lm cube switch.Owing to the anisotropy of the PVDF lm, this cube switch responded to the diverse voltage combinations.In addition, the obtained response could be varied through the planar gure designs and cutting-angle variations.In this security system, the cube response characteristics dependent on the cube planar gure design, cutting angle, and pressing depth were utilized.Figure 6a, b, and c depict the security system with a PVDF lm cube switch.Each side was connected to a 30 kΩ resistor for measuring the voltage response from the cube switch.For user convenience, while using the system, readings with a gap of 1 mm were marked inside the switch cover (Fig. 6a). Figure 6c shows the display monitor for visualization.Software processing was used to visualize the overall system during operation.Each user interface (UI) shows the status of the system during operation.The designated RGB signs of the cube sides were turned on when the voltage responses were measured from the corresponding sides.For setting the passcode, the user had to click the UI "Setting" and press the cube for 3 s with the target pressing depth.Subsequently, the combination of the voltage response from the cube triggered by the user was recorded as a "Passcode."This recorded voltage information decides the authorization of the person accessing the system.Initially, the message on the display was shown as "Enter your passcode" when the system was locked.When the user pressed the cube to unlock the system, the voltage information between the passenger and the realtime voltage signal was compared.When the recorded voltage from an authorized person and real-time voltage signal matched, the message changed to "Welcome back!", and the system was unlocked.
Figure 6d ( ), ( ), and ( ) demonstrate the response of a cube when it is pressed by User A with a displacement of 3 mm, 5 mm, and 7 mm, respectively.By comparing three different responses of a cube in Fig. 6d ( ), ( ), and ( ), it can be observed that the pressing depth is an important parameter of the voltage response behavior.The voltage trend of the cube switch in the security system is similar to that of the previous experiment in terms of the pressing depth.The voltage waveform of the cube in Figs.6d ( ) and 6e ( ) shows that the voltage responses triggered by the same user (User A) are not identical.This result veri es that the combination of the voltage waveform in the security system can be adjusted using the cube planar design and cutting angle variation.
Moreover, nger-skin resistance is perceived as an interesting parameter that makes the system more user-dependent.Figures 6e ( ), ( ), and ( ) show the real-time voltage response when the switch is pressed up to 5 mm by three different personnel.The nger skin resistance values of users A, B, and C are 8.9 MΩ, 15.5 MΩ, and 13.1 MΩ, respectively.In this experiment, cube #6, with a cutting angle of 0°, was used.The response of the device, when pressed by three different individuals, is proportional to the skin resistance (V ∝ R skin ).However, a minor difference was found in the theoretical voltage value and the value derived from the user's nger-skin resistance.This difference helped determine the accuracy of the pressing motion of the participants.Through this experiment, we found that the skin resistance of the human index nger can function as a parameter to strengthen this user-dependent security system.
A owchart of the security system is presented in Figure S11.The supplementary video demonstrates a case in which a non-authorized person tries to unlock the system.The third party presses the cube switch to access the security system with possible pressing patterns but cannot unlock the system.In this video, cube #1, with a cutting angle of 60°, was used.As demonstrated in this section, the PVDF cube switch can be applied to a customized, highly user-dependent security system with a cube planar design, cutting angle variation, pressing depth, and skin resistance of the users.The user can increase the security level of the system by increasing the number of cubes.

Conclusion
In this study, we suggest a multi-responsive 3D structured PVDF cube switch.Each side of the 3D structured PVDF cube switch responded differently in accordance with the direction, owing to its anisotropy.As the 2D cube planar design is assembled into a 3D structure, each side of the cube acquires an individual piezo de nition.Thus each side of the structural response has individual electrical potential value.By changing the cube planar gure design and cutting angle, a variety of responses can be obtained from a 3D structured cube switch with a single stimulus.When this 3D structured switch is transformed into an n-side polyhedron, enhanced characteristics are obtained by increasing the number of voltage responses from the sides.Further, a multi-responsive cube switch was installed in a security system.The security system thus provided user dependency and inimitability.Owing to its simple fabrication process and cost-effectiveness, this multi-responsive device has great potential for applications in diverse elds.The 3D structured cube switch showed excellent performance within a strain range of 3-7 mm in terms of sensitivity.We believe that the sensitivity of this device can be enhanced under small strains with advanced circuit designs.

Fabrication process of PVDF cube switch
Figure S12 shows the schematic illustration of PVDF cube switch fabrication process.The polarized PVDF lm was subjected to a low-power laser cutter to remove the electrode from the area to be folded for assembly.In the electrode removal process, the ultraviolet (UV) laser wavelength was 355 nm, the pulse duration was 30 kHz, and the scan speed was 160 mm/s.The edge-electrode-eliminated PVDF lm was subjected to a high-power laser cutter to form the nal planar gure.In the cutting process, the wavelength was 355 nm, the pulse duration was 50 kHz, and the scan speed was 100 mm/s.After the PVDF lm was cut into a designed cube planar gure, each side of the cube was wired with an anisotropic conductive lm to measure the electrical potential from individual sides.The vertices of the cube were xed with UV resin (UV-8800, Skycares, South Korea) to maintain the nal structure.For the resin curing process, the cube was exposed to UV light at a power of 36 W for 1 min.

Characterization Of Piezoelectric Property
To characterize the performance of the PVDF cube switch, it was pressed by a jig-mounted motorized stage (OSMS26-100, Opto-Sigma, USA).The motorized stage was controlled by software offered by Opto-Sigma.The pressing speed of the stage was 30 mm/s.The electrical signal from the sensor was measured using an electrometer (Keithley 6514, Tektronix, USA) at a sampling rate of 60 Hz.

Finite Element Analysis
Finite element analysis was conducted using the commercial software, ANSYS, to analyze the stress distribution in the overall structure and its behavior when pressed.The following material properties were considered: Young's modulus = 2.54 GPa, Poisson's ratio = 0.35, Shear modulus = 0.93 GPa, and Bulk modulus = 3.0 GPa.The mesh size was uniform throughout the structure, with a size of 0.1 mm.A total of 12,467 elements were used for the FEA.

Data Availability
Data are available on request from the authors Declarations Figures The ( )), the output voltage values approximately follow the tendency of the piezoelectric constant proportions.The observed trend can be supported by analyzing the effect of d 33 on the sides when it operates.On both the front and right sides, the d 33 effect occurs simultaneously when pressed.This is because of a greater d 33 coe cient affects response of those two sides, where d 31 and d 32 mode is dominant, due to multiaxial PVDF cube switch.Schematic illustration of a) three possible cube planar designs, b) a planar gure being assembled and a PVDF cube pressed by a human index nger, c) various responses from cubes derived by planar gure designs, d) a photograph of the PVDF cube switch and cube planar gures, and e) a security system with the PVDF cube switch.