Wireless Sensor Reader Using Fixed Frequency Excitation
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Solution Overview
Problem
Current passive wireless sensor readers face inefficiencies due to large size, high power consumption, inaccuracy, and interference issues, particularly with swept-frequency and digital tracking methods, which limit their use in battery-powered devices and compliance with electromagnetic spectrum regulations.
Innovation Solution
A reader device that transmits a short pulse of energy at a fixed frequency to excite the sensor, allowing it to ring at its resonant frequency, and uses a phase-locked loop to lock onto and measure this frequency, reducing power consumption and interference while complying with spectrum regulations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If swept-frequency or digital tracking methods are used to measure sensor resonant frequency, then measurement capability is achieved, but device size and power consumption increase
Solution Approach 1:
The reader device transmits periodic excitation pulses at a fixed frequency to the sensor, causing the sensor to ring at its resonant frequency. This periodic excitation allows the sensor to naturally oscillate, and the reader measures the resonant frequency by detecting the sensor's response to these periodic pulses, avoiding the need for continuous frequency sweeping or complex digital tracking circuits.
2Measurement precision
If swept-frequency or digital tracking methods are used to measure sensor resonant frequency, then measurement capability is achieved, but device size increases
Solution Approach 1:
The system changes the operational parameters by using a fixed excitation frequency rather than sweeping through multiple frequencies. The sensor's resonant frequency is determined by measuring its natural oscillation response to the fixed-frequency excitation pulses, eliminating the need for large swept-frequency synthesizers or digital tracking circuits in the reader device.
3Measurement precision
If continuous transmission or swept-frequency methods are used, then frequency measurement is achieved, but electromagnetic interference increases
Solution Approach 1:
The reader transmits periodic excitation pulses rather than continuous signals, allowing the sensor to ring down naturally between pulses. This periodic transmission minimizes the duty cycle and reduces electromagnetic interference, while the sensor's resonant frequency is measured during its natural oscillation period after each pulse.
4Reliability
If traditional reader designs are used, then measurement function is provided, but accuracy and power efficiency are compromised
Solution Approach 1:
The sensor serves itself by naturally oscillating at its resonant frequency when excited by the reader's pulses. The sensor's own physical resonance provides the measurement signal, eliminating the need for active frequency generation or complex signal processing in the reader, thereby improving both accuracy and power efficiency.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enables a compact, low-power, and accurate measurement system that minimizes electromagnetic interference and complies with frequency allocation regulations, suitable for battery-powered applications and biomedical telemetry.
Implementation Method 1
The reader 10 transmits an excitation pulse 14 to the sensor 12. The excitation pulse 14 may be a fixed or rapidly varying frequency burst at or near the resonant frequency of the sensor 12.
Implementation Method 2
Passive wireless sensor systems that employ resonant circuit technology are known. These systems utilize a passive wireless sensor in remote communication with excitation and reader circuitry.
Implementation Method 3
Some readers utilize phased-locked-loop ('PLL') circuitry to lock onto the sensor's resonant frequency. U.S. Pat. No. 7,245,117 by Joy, et al. discloses an active PLL circuit and signal processing circuit that adjusts a transmitting PLL frequency until the received signal phase and the transmitting PLL signal phase match.
Implementation Method 4
The PLL 30 includes a voltage controlled oscillator ('VCO') 32 that may lock a frequency within the range of sensor resonance frequencies when no signal is present, or may be chosen to prefer a frequency above or below the range of sensor resonant frequencies when no signal is present to enhance lock time when a sensor resonant frequency is received.
Data Source
AI summary
A wireless sensor reader is provided to interface with a wireless sensor. The wireless sensor reader transmits a narrowband, fixed frequency excitation pulse to cause the wireless sensor to generate a ring signal. The ring signal corresponds to the value of the physical parameter being sensed. The wireless sensor reader receives and amplifies the ring signal and sends the signal to a phase-locked loop. A voltage-controlled oscillator in the phase-locked loop locks onto the ring signal frequency and generates a count signal at a frequency related to the ring signal frequency. The voltage-controlled oscillator is placed into a hold mode where the control voltage is maintained constant to allow the count signal frequency to be determined. The low power, simple circuitry required to generate the excitation pulse allows the reader to be a small, battery operated unit. Alternative methods of frequency determination are also disclosed.