Pocketable and Smart Electrohydrodynamic Pump for Clothes

Seamlessly fusing fashion and functionality can redefine wearable technology and enhance the quality of life. We propose a pocketable and smart electrohydrodynamic pump (PSEP) with self-sensing capability for wearable thermal controls. Overcoming the constraints of traditional liquid-cooled wearables, PSEP with dimensions of 10 × 2 × 1.05 cm and a weight of 10 g is sufficiently compact to fit into a shirt pocket, providing stylish and unobtrusive thermal control. Silent operation coupled with the unique self-sensing ability to monitor the flow rate ensures system reliability without cumbersome additional components. The significant contribution of our study is the formulation and validation of a theoretical model for self-sensing in EHD pumps, thereby introducing an innovative functionality to EHD pump technology. PSEP can deliver temperature changes of up to 3 °C, considerably improving personal comfort. Additionally, the PSEP system features an intuitive, smartphone-compatible interface for seamless wireless control and monitoring, enhancing user interaction and convenience. Furthermore, the ability to detect and notify users of flow blockages, achieved by self-sensing, ensures an efficient and long-term operation. Through its blend of compact design, intelligent functionality, and stylish integration into daily wear, PSEP reshapes the landscape of wearable thermal control technology and offers a promising avenue for enhancing personal comfort in daily life.


Design of electrode layers for PSEP
Figure S1 shows the interdigitated PSEP electrode design.We set the electrode width and gap to 0.5 mm, electrode pair gap to 1.7 mm, and the number of electrode pairs to 10.The optimal values of the relationship between the electrode and the electrode pair gaps identified in previous studies were adopted.The electrode tips were chamfered to prevent unnecessary electric field concentrations.The substrate size was 10 × 2 cm, and the electrodes were placed 8 mm outward for wiring.We used copper tape as the electrode material and PMMA as the substrate for easy fabrication and costeffectiveness.The copper tape and PMMA thicknesses were 0.035 and 5 mm, respectively.

Fabrication of PSEP
Figure S2 shows the digital fabrication method for PSEP.First, interdigitated shapes were cut from the copper tape using a cutting plotter (CE6000-40 plus, GRAPHTEC).
Next, the interdigitated electrodes were attached to the PMMA for the electrode layer, which was cut using a laser-cutting machine (Speedy 100, Trotech).A double-sided adhesive acrylic elastomer for the channel layer was cut using a laser-cutting machine (Speedy 100, Trotech).Finally, the PSEP was fabricated by laminating two electrode layers and one channel layer.This digital fabrication process allows a high degree of design freedom and speed for mass production.

Experimental Setup
Figure S3 shows a schematic of the experimental evaluation system used in this study.
The channel was filled with a working liquid before the experiment to prevent insulation breakdown owing to bubbles.HVPS (HEOPT-20B10, MATSUSADA Precision) was used to power the PSEP and induce EHD flow in the tube.The liquid was circulated through a tube with outer and inner diameters of 4 and 2 mm, respectively.The flow rate was measured using a noncontact flow rate sensor (FD-XS8, KEYENCE).Two circuit protection resistors of 100 kΩ and a shunt resistor of 5.1 kΩ were placed in series on the GND side of the PSEP, and the current was detected from the voltage across the shunt resistor.The flow rate was varied by deforming the tube and squeezing the cross-sectional area of the flow path using a linear stage developed in previous studies to evaluate soft materials.

Compression test of soft tube
Figure S4 shows the compression test results of a tube filled with the working fluid and 3 kV applied to the PSEP.The force during compression was measured using a load cell attached to a linear stage, and each deformation force was plotted, revealing a linear relationship.Moreover, the results of Figure S4 and 2A revealed that the tube closed when a force of approximately 25 N was applied.

FFT analysis and Noise filtering
From the experimental results of the cyclic tests (Figure 4A, B, and C), FFT analysis was performed.Figure S5 shows the results of the FFT analysis for each input frequency (0.25, 0.05, and 0.025 Hz) of the tube deformation.The peaks with the highest flow rates and current amplitudes were plotted.The frequencies at which the flow rate and current peaked were 0.234, 0.050, and 0.025 Hz, confirming the selfsensing response.As the raw values of the current through the PSEP contain noise, the current data with amplitude < 0.08 µA and frequency > 0.5 Hz were filtered for evaluation.

Circuit for power/control
Figure 5C shows the developed circuit for power and control in wearable applications.
The size of this circuit is 70 × 35 × 15 mm, close to that of wearable and mobile devices and can be stored in a pocket.Figure S6 shows the circuit design.This circuit comprises a high-voltage output to the PSEP, voltage output to the Peltier element, current measurement of the PSEP, alert to the wearer in case of flow blockage, and a wireless control/monitoring function.The high-voltage output function for the EHD pump drive uses a DC/DC converter (A30P-5, XP Power).A maximum voltage output of 3kV is possible using microcontroller voltage control.A motor driver (BD6211F-E2, ROHM) applies the voltage output function to the Peltier element.The voltage applied to the Peltier element can be controlled in the range of -3.7 to 3.7 V using a PWM signal from the microcontroller, thus achieving cooling and heating functions.The voltage across the shunt resistor was read by the microcontroller to calculate the current flowing in the PSEP.A circuit protection resistor with a maximum voltage of 10 kV protects the microcontroller in case of an EHD pump breakdown.A red LED is turned on to alert the wearer.In this circuit, the microcontroller TinyPico (Unexpected Maker) was used to control the system.The microcontroller processor was an ESP32 PICO-D4 (ESP32 PICO-D4, Espressif) controlled in a general-purpose Arduino environment.The system was powered using a 1-cell lithium polymer battery.The entire system is powered by connecting a 3.7 V battery to the VBAT Pin of the TinyPico.The wireless control/monitoring function uses 2.4 GHz Wi-Fi in the ESP32 PICO-D4.Wireless communication over Wi-Fi allows users to use the device while storing it in a pocket.
Furthermore, the measured data can be stored in the cloud and operated and monitored remotely.

Figure S3 .
Figure S3.Digital and rapid fabrication process of (A) electrode, (B) substrate, and

Figure S5 .
Figure S5.Compression test to clarify the relationship of tube deformation to the load

Figure S6 .
Figure S6.FFT analysis of currents and flow rates for cycling tests with left) 0.025

Figure S7 .
Figure S7.The response time (t2-t1) as the difference between the time of the lower

Figure S8 .
Figure S8.Electrical schematic of the power/control circuit.

Figure S9 .
Figure S9.Temperature versus time in heating (left) and cooling (right) demonstrations.