Ami Tanaka

A wireless self-powered urinary incontinence sensor system

A self-powered urinary incontinence sensor system consisting of a disposable urine-activated coin battery and a wireless transmitter has been developed as an application for wireless sensor networks. The urine-activated battery makes possible both the sensing of urine leakage and self-powered operation. An intermittent power-supply circuit that uses an electrical double-layer capacitor (EDLC) with a small internal resistance suppresses the supply voltage drop due to the large internal resistance of the battery. This circuit and a 1-V SAW oscillator reduce the power dissipation of a wireless transmitter. The SAW oscillator quickly responds to the on-off control of the power supply, which makes it suitable for intermittent operation. To verify the effectiveness of the circuit scheme, we fabricated a prototype sensor system. When the volume of urine is 0.2 ml, the battery outputs a voltage of over 1.3 V; and the sensor system can transmit signals over a distance of 50 cm.

Self-powered wireless urinary incontinence sensor for disposable diapers

A self-powered urinary incontinence sensor with a flexible wire-type urine-activated battery that is embedded in a diaper has been developed as an application for wireless biosensor networks. Since the battery is flexible, it conforms to the shape of the diaper when the diaper is worn. The stress produce by the curvature presses the electrodes firmly against the diaper material, providing greater contact with any urine present. Thus, due to the curvature, the battery generates more power than when it is flat, as in an unworn diaper. The battery also acts as a wide ground plane for the antenna of a wireless transmitter, providing a large radiated power. To verify the effectiveness of the battery, we fabricated a battery and a prototype sensor and embedded the battery in a diaper. When 80 cc of urine is poured onto the diaper, the battery outputs a voltage of 1 V, which allows the sensor to transmit an ID signal over a distance of 5 m.

Wireless self-powered plant health-monitoring sensor system

A self-powered plant-health-monitoring sensor powered by a battery that is activated by the sap of a vascular plant has been developed as an application for wireless biosensor networks. The battery consists of a galvanized iron nail inserted into a tree trunk and a stainless-steel electrode planted in the soil nearby. It outputs on the order of 1 μW of power. An intermittent power supply circuit with a divided-power-line structure, which separates the power line of a storage capacitor while it is discharging, makes it possible to charge the capacitor with an input power of around 1 μW and to supply power to a wireless transmitter. To verify the effectiveness of the circuit scheme, a prototype sensor was fabricated and tested on a potted pachira tree. The sap-activated battery acted as a current source (3 μA) with an open voltage of 1 V, and the sensor had a 10-mF storage capacitor. This setup enabled the sensor to transmit a signal about every 40 minutes over a distance of 5 m.

Attofarad-level capacitance variation detector uses RF-sensor with 98/100 MHz oscillator/local superheterodyne scheme for wireless pest sensor

An ultrasmall-capacitance-variation detector was developed that consists of a VHF-band LC oscillator, sensing pads, and a superheterodyne scheme that magnifies the resonant-frequency shift. An oscillator frequency (~100 MHz) in the VHF band allows a small base capacitance to be used for resonance, which provides a high sensitivity to small changes in capacitance. An RF sensor with a superheterodyne scheme magnifies the frequency shift and enhances the sensor sensitivity up to the attofarad level. The sensitive sensor must be isolated from human movement and other environmental influences to ensure accurate measurements. A simple shield consisting of a small ground loop with a perimeter of 17 cm was added to the sensor assembly. As an application of the sensing system, a wireless sensor for the non-invasive detection of pests inside wood was constructed. It was able to detect the movement of insects inside a wooden post.

Wearable self-powered diaper-shaped urinary-incontinence sensor suppressing response-time variation with 0.3-V start-up converter

A wearable, wireless self-powered urinary-incontinence sensor has been developed that consists of a diaper-shaped urine-activated battery, an intermittent-power-supply circuit with a 0.3 V start-up converter, and a wireless transmitter. The battery is embedded in a diaper and consists of absorbent material sandwiched between an aluminum electrode and a spongiform carbon electrode, which are safe to wear. The intermittent-power-supply circuit with the start-up converter makes it possible to boost the 0.6 V output of the battery to 2 V. The boosting operation reduces the variation in the charging time of the storage capacitor among batteries, thereby reducing the variation in the delay time of the intermittent-power-supply circuit, which contains the storage capacitor. A design method for determining both the optimum input-voltage range, in which the variation in charging time is small, and also the capacitance of the storage capacitor is also described. A prototype urinary-incontinence sensor was fabricated to verify the effectiveness of our sensor. When 80 cm3 of urine is poured onto a diaper, the sensor transmits an ID signal over a distance of 5 m. The response time of the sensor is 17 s, and the period of intermittent operation is 12-s long.

Self-powered wireless digital tachometer scheme without sensors for measuring spin of Yo-yo

A wireless yo-yo system with a digital tachometer function has been developed. The system consists of a self-powered wireless yo-yo and a receiver. The yo-yo contains a micropower generator and a wireless transmitter. Ultralow-power wireless on-off-keying modulation synchronized to the AC output of the generator makes it possible to determine the maximum rotational frequency of the yo-yo from the minimum period of the pulses detected by a receiver without sensors. Another advantage of the antenna of the transmitter of the yo-yo is that the receiver can detect transmitted pulses at any location around the yo-yo, even though the antenna is directional. The antenna acts as a rotational polarization antenna as it rotates along with the yo-yo. This type of antenna makes it possible for the receiver to detect transmitted pulses once every rotation of the antenna. To verify the effectiveness of our self-powered wireless yo-yo with digital tachometer scheme, we made a wireless yo-yo system consisting of a wireless yo-yo with a micropower generator and a receiver with a PC. When the yo-yo is thrown, the PC calculates the maximum rotational frequency and displays the result on the screen at a distance of up to 3 meters.

Wearable Self-Powered Diaper-Shaped Urinary-Incontinence Sensor Suppressing Response-Time Variation With 0.3 V Start-Up Converter

A wearable, wireless self-powered urinary-incontinence sensor has been developed that consists of a diaper-shaped urine-activated battery, an intermittent-power-supply circuit with an ultralow-voltage start-up converter, and a wireless transmitter. The battery is embedded in a diaper and consists of absorbent material sandwiched between an aluminum electrode and a spongiform carbon electrode, which are safe to wear. The intermittent-power-supply circuit has a start-up converter that boosts the 0.5-V output of the battery to 2 V and drives a DC-DC converter. The two-stage boosting operation from 0.5 V suppresses the variation among batteries in the charging time of a storage capacitor, thereby reducing the variation among diapers in the response time of the sensor. A prototype urinary-incontinence sensor was fabricated to verify the concept. When 80 cc of urine are poured onto a diaper, the sensor transmits an ID signal over a distance of 5 m.

Self-powered wireless disposable sensor for welfare application

A self-powered urinary incontinence sensor consisting of a flexible urine-activated battery and a wireless transmitter has been developed as an application for wireless biosensor networks. The flexible urine-activated battery is embedded in a disposal diaper and makes possible both the sensing of urine leakage and self-powered operation. An intermittent power-supply circuit that uses an electric double-layer capacitor (EDLC) with a small internal resistance suppresses the supply voltage drop due to the large internal resistance of the battery. This circuit supplies the power to a wireless transmitter. A 315-MHz-band wireless transmitter performs low-power operation. To verify the effectiveness of the circuit scheme, we fabricated a prototype sensor system. When 80 cc of urine is poured onto the diaper, the battery outputs a voltage of 1 V; and the sensor can transmit an ID signal over a distance of 5 m.

A self-powered photosensor switch detects only rising edge of infrared-light pulse for wireless zero-standby-power wake-up receiver

A self-powered photosensor switch that detects only the rising edge of an infrared (IR) pulse has been developed to reduce the standby current of battery-operated wireless devices with an IR remote controller and to enable removal of the external on/off switch. It consists of a VDD-rising-edge detector, an external-noise current canceller, and an IR LED energy harvester. The detector is powered by the energy harvester and detects a steep rising edge in the supply voltage. The power dissipation of the detector is kept at the picowatt level so that the detector operates only when the supply voltage passes through the sub-Vth region. The external-noise current canceller subtracts the offset current due to environmental noise. It uses a diode-connected low-Vth MOSFET to reduce the supply voltage to less than the operating voltage of the detector, and it keeps the supply voltage constant at a value determined by the constant current source of a low-Vth MOSFET in which the gate is replaced with a hold capacitor,. The photosensor switch makes possible the self-powered detection of IR light signals from a remote controller, even in the presence of environmental noise. To verify its effectiveness, a wake-up receiver containing the photosensor switch was fabricated and tested on a battery-operated wireless device. A commercial IR remote controller was able to wake the device up at a distance of 6 meters, and the standby current of the power-on controller was found to be 0.5 nA. The power dissipation of the photosensor switch was 40 pW.

Contactless direct heart-motion sensor using femtofarad-level capacitance-variation detector with VHF-band LC-oscillator

As the heart expands and contracts, the distance between the walls of the heart and the surface of the body changes continuously. This structural change causes the dielectric constant of the body to vary. To detect that variation, a capacitance-variation detector with a high sensitivity on the order of 100 aF has been developed. It employs an LC-oscillator architecture with 98 MHz, and the change in capacitance is determined from the oscillation frequency shift. Experiments demonstrated that it detected the movement of the heart of an actual person from the frequency shift. The system detects not only heart-beat count but also the real movement of heart itself.