Design of Electrolarynx to Increase Energy Efficiency by Varying the Driving Source

The larynx is an organ in the human respiratory system that forms the basis of the speech production system. An electrolarynx is a device used by most laryngectomees to regain their verbal communication. Our objective was to design an electrolarynx with increased energy efficiency by modifying the driving source. Initially, we designed the electrolarynx to accommodate various driving signals. We then compared the voice output obtained by different input signals for quality and measured energy consumption using a digital multimeter. When compared to existing methods, the proposed driving source was found to be 11.1% more energy efficient. Voice quality was also better than the traditional driving source by 31.6%.

Driving signal; Electrolarynx; Energy efficiency; Laryngectomee; Larynx; Speech

Voice is a powerful mechanism to express ourselves. Voice production is an organized control of sensory and motor nervous systems (Simonyan and Horwitz, 2011). The cortical and subcortical areas of the brain control the speech production system. The lungs, larynx, vocal tract, and oral cavity are the main motor organs for speech production in human beings (Ackermann et al., 2014). The energy for producing speech originates from the lungs through the exhalation of breath. This vibrates the larynx and produces regular movement, resulting in laryngeal vibrations known as glottal waves (Bouchard et al., 2016). These periodic movements resonate, and intelligible speech is produced by the articulators in the oral cavity, such as the tongue, teeth, and lips (Visser, 2006).

    A person loses his ability to speak when the larynx is removed surgically due to unavoidable circumstances, such as laryngeal cancer. The electrolarynx is an electro-mechanical device that acts as a larynx substitute. This device has an oscillator and a vibrator, which is held against the neck when the laryngectomee intends to speak. The vibrational energy passes through the neck surface, and speech is produced by proper articulator movement (Gironda and Fabus, 2011). Apart from laryngectomees, this device can also help patients who are critically ill and rely on artificial ventilation (Tuinman et al., 2015; Sato et al., 2016; Rose et al., 2018). The electrolarynx being a handheld device, one of the hands must be engaged in operating the device. This could prove awkward for laryngectomees as they socialize. Many researchers are working toward reducing the device’s size to ease consumers’ lives.

A wearable device has been designed that uses a thin vibrator on a plastic support attached to the neck region (Hashiba et al., 2007). This vibrator is controlled by a wireless controller kept in the user’s pocket. Due to the required 9 v energy supply, this entire system is still substantial. The vibrator size reduction method was also employed in Madden et al. (2011), where the researchers designed an actuator for handsfree operation using a pager motor. However, pager motors’ current handling capacity is very low at about 100 ma, meaning there is insufficient vibration at the neck region to produce audible speech, as sound level affects speech intelligibility (Knox and Anneberg, 1973; Weiss et al., 1979).

The recent work on electrolarynxes suggests a variation of fundamental frequencies to produce different tones for tonal languages (Guo et al., 2016; Ifukube, 2017; Wang et al., 2017a; Wang et al., 2017b). However, extensive training is required to produce pitch variations.

Control electronics designed using the electromyography activity of the neck muscles (Arifin et al., 2014; Fuchs et al., 2015; Oe et al., 2017) and video cameras to capture lip movement (Wu et al., 2013) provide an automatic control over the electrolarynx. A statistical method for varying fundamental frequencies suggests that, this allows for more natural speech (Tanaka et al., 2016; Tanaka et al., 2017). Based on the electrolarynx speech signals’ feedback, the excitation signal is varied to accommodate differences in fundamental frequency. To decrease the electrolarynx’s self-radiated noise, an interpolation of ultrasonic waves (Mills and Zara, 2014; Massey and Yilmaz, 2016) and time domain enhancement methods (Xiao et al., 2018) are used. The findings from Sardjono et al. (2009) and Coetzee et al. (2018) suggested that voices change due to advancing age after examining the mel-frequency cepstral coefficients, implying the possible changes in voice excitation sources. A simulated modified excitation source design revealed improved voice quality over conventional vibration methods (Madhushankara et al., 2017).

Being a battery-driven device, an electrolarynx’s size should be as small as possible. However, battery technology is not advanced enough for new technology, so alternative energy-saving methods must also be accommodated (Madhushankara et al., 2015; Fuchs et al., 2016; Sofyan et al., 2016; Ejidokun et al., 2018). In our research, we designed an energy-efficient electrolarynx by modifying the driving source, thereby reducing battery size, which is proportional to battery capacity. We also employed li-ion batteries, which are commonly found in mobile phones due to their light weight and high energy capacity.

We have shown how an alternative electrolarynx driving signal leads to less power consumption and hence more energy efficiency with either improved or analogous performance in terms of formant distance, amplitude, quality factor, and leakage noise.

     In addition, the present work was carried out using an Arduino Uno development platform, which consists of as many as 20 pin chips, along with other peripherals that are not required for the proposed electrolarynx. The design of an application-specific integrated circuit with fewer pins and constituents will lower the inactive current and further improve battery performance.

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