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We describe a sensor for measuring budburst and blossom in plants and trees. A pair of plastic optical fibers is placed behind a bud. One fiber carries modulated light to the bud and the other fiber carries reflected light to detector electronics. When the plant's bud opens, the amount of reflected light changes. The sensor uses lock-in detection to suppress ambient and other light noise. A microcontroller manages the sensor operation and saves data on a secure digital memory card. The sensor incorporates calibration, and the user can set the integrated real-time clock, and the data collection interval through with a simple menu via an RS-232 serial connection. The sensor is power efficient and can operate for an entire growing season without having to replace its batteries. We have conducted initial field testing of the sensor. [ABSTRACT FROM PUBLISHER]

We propose and demonstrate a technique for phase change measurement of continuous terahertz (THz) wave using two 1550 nm laser diodes and optical frequency shifter. Generation of the THz wave is based on photomixing using a uni-traveling-carrier photodiode. Detection of the THz wave is based on heterodyne mixing of the THz wave using a low-temperature-grown GaAs photoconductor with frequency-shifted optical LO beat signal. Measurement of phase shift induced by a single sheet of paper with 85-μm thickness has been demonstrated at 300 GHz. [ABSTRACT FROM PUBLISHER]

This paper introduces a custom digital lock-in amplifier for detecting the imbalance signal of a precision audio frequency bridge. The lock-in amplifier is designed with a PXI measurement system which is equipped with a signal generator and simultaneous data acquisition adapters. The advantage of this design is that the demodulation algorithm can be flexibly reconfigured when the imbalance signal changes in the AC bridge system. The resolution and linearity of the lock-in amplifier can also be improved by using higher resolution A/D adapters. Simulations and experiments have verified the basic concept of the designed lock-in amplifier. [ABSTRACT FROM PUBLISHER]