The hair is public as everyone could see it, personal as it is a body part, and malleable as it suits cultural and personal preferences . This work proposes the use of (modified) artificial hair extensions as a novel electronic device to be used in wearable computing. We used a chemical platting technique that makes the l hair extensions to be conductive but, at the same time, looks like human hair. Then, they could be connected to a microcontroller to be used as sensors or actuators. We use hair clips for attaching the circuit to the hair extensions in order to be easily removable and replaceable. Also this makes it possible to put the circuit in different accessory such as a hairclip, headband, brooch and the top of the hair extensions.
This section describes the materials and the prototyping process used. It also shows the feasibility of this technology as an input and output device.
3.1 Chemical Process for Creating Hairware
Artificial hair extensions are chemically metalized for acquiring electrical conductivity and also keeping a natural coloration. We used 6 strands of hair extensions of approximate 1.5 by 25 cm each. Before passing by the chemical process, they are cleaned and weighted. Tests are performed at DC voltages of 5 V, with a multimeter and a balance.
The chemical process is carried out in two phases: Activation and Electrolysis. During the first phase, artificial hair extensions, being plastic non-conducting surfaces, require some kind of activation to enable them to be submitted to an electrochemical process. For the first activation, hydrogen and tin (II) chloride are used. Then, a silver nitrate solution is added for the second activation, where the extensions are set up to catalyze electron transfer reactions, making them ready for metalizing. Next, electrolysis is used for platting them. Copper is electrochemically deposited for making them electrically conductive while “black nickel” gives the natural black effect. A copper plaque is needed for the electrolysis process. Table 1 shows the formulations and times needed for creating Hairware.
After the chemical process, the hair extensions are weighted. Table 2 shows each of the hair extensions initial weight, the final one and the percentage of weight variation. The hair extensions got an average of 21 % more of their original weight. Also electrical resistances of each hairpiece were measured with a multimeter. It is highly conductive with a surface resistivity of less than 5 ohm/sq.
3.2 Hairware as an Output Device
Figure 2 shows our first application for showing the feasibility of Hairware as an output device. Different kinds of actuators such as buzzers and LEDs could be attached to the conductive hair extensions to be triggered by a microcontroller. We connected 2 Hairware strands to LEDs using hairclips. Its positive pin connected to the sender pin in the Arduino and the negative one connected to ground. Artificial hair extensions with no conductivity are placed between the conductive hair extensions for isolating them. This wearable turns on the LEDs attached to the hair and changes their intensity and the lighting effects could also repeat the rhythm of music. Other actuators such as buzzers and vibration motors could replace LEDs.
3.3 Hairware as an Input Device
In order to show the feasibility of using Hairware as an input device, we used it as a capacitance sensor that detects the touch on the extensions. We used an Arduino microcontroller, LEDs, resistors and 2 Hairware strands. Each of the Hairware strands is connected to a send and receive pin of the microcontroller and 2 LEDs are also connected. Figure 3 shows Hairware’s capacitance sensors functionality. When the receive pin’s state change by making a low touch on a strand, the corresponding LED is turned on. Thus, each LED is ON when this sensor detects when someone touches Hairware. This circuit creates a delay in the pulse that is the time the capacitor takes to charge and discharge. In this way, Hairware is used as a conductive surface that detects when another conductive surface approximates to it. Therefore, as the human body is conductive, the average internal resistance of a human trunk is ~ 100 Ω , touching Hairware will affect capacitance and result in a different charging time.
Other approach of the use of Hairware as an input device is to use hair extensions as layers on the conductive hair extension. Three layers of non- conductive hair extensions are added for isolating the hair from the skin. Also, these layers improved the capacitor sensor values. Each time the user touch the top, middle or tip, the capacitor sensor differentiates these values. The circuit compares an output that transmits the pulse and an input, which receives the pulse. When a finger touches Hairware, it creates a delay in the pulse, and this delay is recalculated by the Arduino microcontroller. The circuit diagram is also composed with four 1 MΩ resistors and one 100pF capacitor. The resistors selects the sensitivity, bigger the resistor, the farther away it detects a human. With 4 MΩ resistors between the output and input pins the circuit is tuned to start to respond one inch away, just the sufficient to overcome the non-conductive hair layer. The small capacitor (100 pF) placed from sensor pin to ground improves stability and repeatability. Some LEDs were added to the system to give feedback to the user whenever a touch is detected.