Technical Evaluation of Engineering Model of Ultra-Small Transmitter Mounted on Sweetpotato Hornworm

Abstract

The authors are making a prototype flexible board of a radio-frequency transmitter for measuring an electromyogram (EMG) of a flying moth and plan to apply for an experimental station license from the Ministry of Internal Affairs and Communications of Japan in the summer of 2022. The goal is to create a continuous low-dose exposure standard that incorporates scientific and physiological functional assessments to replace the current standard based on lethal dose 50. This paper describes the technical evaluation of the hardware. The signal of a bipolar EMG electrode is amplified by an operational amplifier. This potential is added to a voltage-controlled crystal oscillator (27 MHz, bandwidth: 4 kHz), frequency-converted, and transmitted from an antenna about 10 cm long (diameter: 0.03 mm). The power source is a 1.55-V wristwatch battery that has a total weight of about 0.3 g (one dry battery and analog circuit) and an expected operating time of 20 minutes. The output power is −7 dBm and the effective isotropic radiated power is −40 dBm. The signal is received by a dual-whip antenna (2.15 dBi) at a distance of about 100 m from the moth. The link margin of the communication circuit is above 30 dB within 100 m. The concepts of this hardware and the measurement data are presented in this paper. This will be the first biological data transmission from a moth with an official license. In future, this telemetry system will improve the detection of physiological abnormalities of moths.

Autocorrelation Coefficient for Detecting the Frequency of Bio-Telemetry

“…Because the autocorrelation Rff (τ) of the sine wave is the product of the sine wave separated by time τ, it is expressed as equation ( 14), which is transformed to obtain equations ( 15), (16), and (17). Because the ratio of integration against τ=0 is the correlation coefficient R, finally equation ( 19) is obtained.…”

“…For small subjects, such as moths, butterflies, and small birds, our proposed digital processing (autocorrelation function) enables efficient use of frequencies and reproduction even when the S/N ratio is low [15][16][17][18].…”