Design of non-autonomous pH oscillators and the existence of chemical beat phenomenon in a neutralization reaction

The beat in physical systems is a transparent and well-understood phenomenon. It may occur in forced oscillatory systems and as a result of the interference of two waves of slightly different frequencies. However, in chemical systems, the realization of the latter type of the beat phenomenon has been lacking. Here we show that a periodic titration of acid and alkaline solutions with each other using programmable syringe pumps in a continuous stirred-tank reactor exhibits the beat phenomenon in the temporal pH oscillation pattern if the time periods of sinusoidal inflow rates of the reagents are slightly different. Interestingly, the frequency of the chemical beat pattern follows the well-known relationship from physics, namely the frequency of the beat is equal to the absolute value of the difference of the two wave frequencies. Based on our strategy, we can design and engineer non-autonomous pH oscillatory systems, in which the characteristics of the temporal oscillations (amplitude, time period) can easily and precisely be controlled by the experimental conditions such as the inflow rates and feed concentrations. The demonstrated phenomena can be exploited in practical applications, we use the non-autonomous pH oscillators to drive the reversible assembly and disassembly of pH-sensitive building blocks (oleic acid and gold nanoparticles), both highly relevant in nanotechnology and biomedical applications.

The Effect of the Beat Phenomenon on the Oscillating Water Column Device

The oscillating water column is the most natural type of wave energy converter because of its simple mechanical structure. To achieve maximum energy conversion efficiency, the incident waves and the natural frequency of the device’s construction have to be in resonance. This paper discusses the beat phenomenon as a form of resonance and several factors that allow the beating to occur, namely the relative depth of the wave (h/L) and the ratio of the submerged front wall length to the water depth (a/h), and their effect on oscillating water column efficiency. The test results show that the beat phenomenon occurs in the wave period T = 1.7 s, with a maximum efficiency of 22.12% achieved at conditions h/L = 0.114 and a/h = 0.4.

Transparent Film-Type Vibrotactile Actuator Array and Its Haptic Rendering Using Beat Phenomenon

The most important thing in a thin and soft haptic module with an electroactive polymer actuator array is to increase its vibrotactile amplitude and to create a variety of vibrotactile sensations. In this paper, we introduce a thin film-type electroactive polymer actuator array capable of stimulating two types of human mechanoreceptors simultaneously, and we present a haptic rendering method that maximizes the actuators’ vibrational force without improving the array’s haptic performance. The increase in vibrational amplitude of the soft electroactive polymer actuator array is achieved by creating a beat vibration, which is an interference pattern of two vibrations with slightly different frequencies. The textures of a target object are translated into haptic stimuli using the proposed method. We conducted qualitative and quantitative experiments to evaluate the performance of the proposed rendering method. The results showed that this method not only amplifies the vibration’s amplitude but also haptically simulates various objects’ surfaces.