The odor of different fresh shrimp

The odor of different fresh shrimp was detected using electronic nose, the output of voltage of each sensor increased with acquisition time in the beginning, then got stable 2min later. The mean of the stable stage was indicated as output voltage of each gas sensor and used to analyze the odor change of shrimp.
Acknowledgments This work was supported by the Key Project of Science and Technology Foundations of Tianjin Province of China (Grant No. 11JCZDJC17800) and Projects in the National Science & Technology Pillar Program during the Eleventh Five-year Plan Period (Grant No.2012BAD38B01).
Introduction Previous work has demonstrated the idea of using a fully-compliant bistable mechanism as a threshold accelerometer [1,2]. Such a device is especially interesting as a sensor requiring zero power which can be left in place over long periods. Potential applications would include package shipping in which these types of sensors could indicate harmful shocks or drops. Sensors could also be placed on vehicles, buildings, or bridges [3–5] to monitor impacts or seismic activity. Reports have been made on a variety of low power or zero power accelerometer designs, often involving MEMS structures and monitoring circuitry built on VLSI chips [6–9]. While a macroscopic bistable design cannot be readily fabricated on a silicon substrate, it can be integrated with RFID sensors for remote, zero power sensing of acceleration events [10]. While a number of zero power mechanical structures exist and are commercially available [11,12] there remains a desire to pursue lower cost alternatives which can be easily adapted to automated readout systems. The previous and present bistable mechanism designs use four compliant flexible members with two stable positions. The mechanism\'s central shuttle is meant to attach to an object and measure its acceleration. In these types of mechanisms, as the flexible members are acted upon by an external force, elastic Homoharringtonine manufacturer can be stored and then released as kinetic motion. The device\'s outer frame serves as a proof mass which causes a force on the compliant members when under acceleration. If acceleration goes beyond a threshold, the proof mass moves between two possible stable positions, in effect recording a “threshold” event. The basic design and a force–displacement diagram are shown in Fig. 1. Compliant mechanism threshold accelerometers have been made from sheets of Delrin and ABS plastic and formed through laser cutting [1]. While plastic offers low manufacturing costs and these devices did display bistable switching behavior, they were susceptible to changes in switching threshold over time due to stress relaxation of their flexor elements [13]. In fact, an average increase of 54% in the threshold acceleration was measured after leaving the devices in the stressed state for 72h [13]. This kind of drift is very undesirable for a zero power sensor meant to be used over long periods. To address the problem of plastic relaxation, metal threshold accelerometers have been made from sheets of spring steel with designs cut using wire Electrical Discharge Machining (EDM) [14]. Flexor elements were formed by bending thin strips of the spring steel perpendicular to the outer frame. These devices exhibited long term stability with regard to threshold acceleration, but were susceptible to “out of plane” movement during switching. Bracketing elements had to be added to the frames, which induced friction and made thresholds unpredictable from device to device.
Fabrication
Testing The acceleration threshold for switching between two stable states was measured using a centrifuge and a tachometer. Between tests, the switches were left in their stable, stressed-state position. The testing procedure consisted of placing switches in the centrifuge and increasing its rotation speed until an audible snap was heard — indicating a switch had changed bistable positions. The tachometer was used to measure rotations per minute (RPM) at the switching threshold. Seven trials were made for each switch during each day of testing. Switch velocity was calculated using the equationwhere v is the velocity (in m/s), R is the distance from the center of rotation (in meters) to the center of the shuttle, and ω was the measured RPM for the trial. The radial distance of the sensor from the centrifuge\'s center was R=0.276m. Switching acceleration was determined using the equationand average acceleration for each set of tests is reported in Figs. 6 and 7.