Self-Powered Galvanic Vibration Sensor

Abstract

The development of the IoT demands small, durable, remote sensing systems that have energy harvesters and storage. Various energy harvesters are developed, including piezoelectric, triboelectric, electromagnetic, and reverse-electrowetting-on-dielectric. However, integrating energy storage and sensing functionality receives little attention. This paper presents an electrochemical vibration sensor with a galvanic cell (Zn-Cu cell) as energy storage and a vibration transducer. The frequency response, scale factor, long-term response, impedance study, and discharge characteristics are given. This study proved the possibility of integrating energy storage and vibration sensing functionality with promising performance. The performance of the sensor halved within 74 min. The longevity of the sensor is short due to the spontaneous reactions and ions drained. The sensitivity can be restored after refilling the electrolyte. The sensor could be rechargeable by changing to a reversible electrochemical system such as a lead-acid cell in the future.

Keywords: battery; electrochemical vibration sensor; self-powered vibration sensor; vibration.

Figure 1

Illustration of the galvanic vibration sensor mechanism. (a) Schematic illustration of the sensor under acceleration. Bulk electrolyte moves opposite to acceleration and stops by the elastic membranes. The current from the Zn and copper electrodes passing through an external varies with the flow generated. (b) Drawing of the diffusion layer formed due to spontaneous displacement reaction and the ion diffusion without acceleration. (c) Drawing of the diffusion layer with acceleration.

Figure 2

The fabrication procedure of the Ecoflex membranes (step 1–3) and the galvanic vibration sensor (4–8).

Figure 3

(a) The exploded view of the sensor; (b) the illustration of the copper and zinc wires in the semi-cylindrical grooves inside the rectangular channel; (c) the illustration of glue surrounding the metal wires at the inserting holes; (d) the illustration of glue underfilling the metal wires inside the rectangular channel.

Figure 4

(a) A photograph of the fabricated sensor. (b) Showing the experimental setup of the vibration sensor characterization. A vibration exciter moves the sensor and the ADXL 335 reference accelerometer sinusoidally according to the signal generator output. The output from the sensors is recorded using a voltage acquisition card.

Figure 5

(a) The readout circuit of the galvanic vibration sensor. The zinc and copper wires connect to two RC high-pass filters with a cut-off frequency of 1.59 Hz. The filtered outputs then amplify using an instrumentation amplifier AD620 with a differential gain of 413. The voltage input v(t) and current input i(t) from the vibration sensor have different output behaviors. (b) The output behavior of v(t) with no offset voltage in the output; (c) the i(t) output behavior with an offset voltage, and always positive.

Figure 6

(a) The frequency response of the galvanic vibration sensor, plotting the scale factor as a function of frequency in linear scale from 20 Hz to 90 Hz. It peaks at the mechanical resonance frequency of the sensor (68 Hz). (b) The signal magnitude of the vibration sensor against acceleration from ±0.044 g to ±0.580 g and the regression line. The regression agrees from ±0.044 g to ±0.378 g with a slope of 0.748 V/g.

Figure 7

The output waveform of the galvanic vibration sensor. (a) The output waveform of the galvanic vibration sensor is at $\pm$0.485 g, is sinusoidal and stable. It indicates it is within the measurement range of the sensor. (b–d) Output waveform under $\pm$0.580 g at 70 Hz, (b) t = 0 s to 0.1 s; (c) t = 6.5 s to 6.6 s; (d) t = 8 s to 8.1 s. The waveform is unstable when the acceleration is outside the sensor’s measurement range.

Figure 8

(a) The DC component of the waveform against acceleration; (b) The output magnitude over time under $\pm$0.179 g at 70 Hz for 74 min.

Figure 9

Electrochemical impedance spectroscopy of a Cu/CuI/Zn cell with 10 mV AC voltage and open circuit potential as DC voltage from 0.05 Hz to 100k Hz. The data obtained when: 1. Electrodes just immersed in the electrolyte; 2. After 50 min; 3. After two hours; 4. After being immersed for two hours and finished stirring. (a) Nyquist plot. (b) Magnitude part of Bode plot; (c) Phase part of Bode plot.

Figure 10

Discharge characteristics of the Cu/CuI/Zn cell with a large amount of saturated CuI solution. (a) At a discharge rate from 0.1–2$\mathsf{\mu }$A; (b) Discharge under 0.9 $\mathsf{\mu }$A for one hour without significant degradation.