# Ultrasonic Power and Data Transfer through Multiple Curved Layers Applied to Pipe Instrumentation
## 4 System Implementation
### Multilayer Curved Wall Full System Experiment  
Figure 8 shows the experimental setup. The inside and outside blocks, as well as the other components, are highlighted. In the inside block, a pressure and temperature sensor from Openfield replaces the digital pulser of the diagram in Figure 6 and a low-power microcontroller, MSP430F2619 from Texas Instruments(r), Thief River Falls, MN, USA, acquires the data of the sensor and generates asynchronous information based on Manchester coding [25]. The sensor, located in the inside block, is interrogated once per second, characterizing a low-power mode. The energy storage circuit guarantees the necessary power for the inside block when the transistor is in the on-state. The outside  
Figure 6: Overall LTSpice schematic system. Figure 7: Results of the electrical model. block has an envelope detector circuit and a digital signal processing code implemented inside the MCU to conclude the demodulation of the sensor data. The carrier frequency of the system is generated using a signal generator NI-VirtualBench model 8012, and amplified by a power amplifier before driving the outside piezoelectric transducer. After rebuilding the digital information of the sensor, the data is sent to a computer via a serial port. The voltage signals shown in Figure 9 were measured using a digital oscilloscope model MDO3024 from Tektronix(r). A typical voltage signal produced on the inside block by the inside transducer is presented in Figure 9b. Such as what occurred in the simulation analysis, the voltage has two levels depending on the state of conduction of the MOSFET. These two levels correspond to the sensor data rate of 1200 bit/s. The high level baseline is approximately 10 V; sufficient to power the electronic components even when the energy supply is almost null due to the MOSFET short-circuited state. The outside signal in purple in Figure 9b is the voltage after the envelope detector circuit. This is the first stage of demodulation, and typical values of the difference in voltage amplitude range from 150 mV to 500 mV, approximately, depending on the input voltage. The transmission of the sensor data between the inside and the outside is implemented using amplitude shift keying (ASK) modulation [25], varying the impedance of the internal transducer. The data flows in only one direction, from the inside to the outside. However, the reverse direction would also be possible, working as a half-duplex, by varying the amplitude of the carrier in such a way to identify which side is transmuting, either inside or outside. Figure 8: Experimental setup. In the reception, the demodulation is implemented using a non-coherent circuit, which means that the modulated signal passes through an envelope detector and a low-pass filter. In most common circuit demodulations, a comparator with a threshold level reconstructs the digital signal; however, in our system, the amplitude variation of the demodulated signal is often low, approximately 300 mV. Other characteristics of the system that affect detection capability, other than the low signal, include the dynamic DC level of the signal in the reception. In the idle mode, when no bits are being transmitted, the DC level is constant; however, when the inside block starts streaming the data, the direct current (DC) level decreases to balance the signal and therefore would require different threshold levels for a proper demodulation. The system is also affected by the amount of power that reaches the inside block, which is directly related to the power capacity to activate the MOSFET. These characteristics make it difficult to have a static threshold level on the comparator, increasing the error detection. The solution, therefore, was to use Manchester coding, which is less susceptible to noise and variations in DC level data. Thus, after passing through the envelope detector and low pass filter, the signal is inserted into the analog-digital converter (ADC) microcontroller to complete the second stage of demodulation using a digital processing unit.