Wireless communication is ineffective for communicating through a solid steel wall due to the shielding effect of the metal. In some cases, holes can be made in the wall to allow wires to pass through, enabling the transport of electronic data. However, holes are often undesirable because they can reduce the integrity of the wall. This paper describes several approaches for using ultrasound to communicate low-rate digital data through a steel wall. The techniques minimize the complexity and power consumption of the communications hardware on the side of the wall from which the data is being sent, supporting applications in which a sensor may be either permanently embedded in a structure or is difficult to reach for servicing. Both pulsed and continuous-wave ultrasound techniques are described. Experimental data is presented showing the performance of the techniques when implemented using 1 MHz transducers mounted on a 15.24 cm (6 inch) thick steel wall. The results show that data rates on the order of 500 bits per second are readily available using simple communications techniques. Higher rates are possible if equalization is used to mitigate the effects of the multipath propagation within the steel block

Electromagnetic "wireless" techniques are ineffective for communicating through a solid steel barrier due to the shielding effect of the metal. Although holes can be made in the barrier to allow wires to pass through, they are often undesirable because they can reduce the integrity of the barrier. In contrast, ultrasound propagates readily through steel and can be used to convey information without degrading the barrier. Since it may be inconvenient to periodically access the sensor side of the barrier, it is also desirable to make the sensor/communication system operate for an indefinite period without servicing. Power harvesting can be used to derive electric power for the circuits from the ultrasonic power applied at the other side of the barrier, making batteries unnecessary. This paper describes an ultrasonic communication system with power harvesting using two ultrasonic transducers and continuous-wave ultrasound techniques. Experimental results are presented, which were obtained using a 5.7 cm thick steel block with 2.54 cm piezoelectric transducers at 1 MHz. The data shows reliable communication at rates of up to 55 kbps and power delivery of over 0.25 W.

In many commercial, industrial, and military applications, supplying power to electronics through a thick metallic barrier without compromising its structural integrity would provide tremendous advantages over many existing barrier-penetrating techniques. The Faraday shielding presented by thick metallic barriers prevents the use of electromagnetic power-transmission techniques. This work describes the electrical optimization of continuouswave power delivery through thick steel barriers using ultrasound. Ultrasonic channels are formed by attaching pairs of coaxially-aligned piezoelectric transducers to opposite sides of thick steel blocks. The thickness of the steel considered is on the order of, or greater than, one quarter wavelength of the acoustic power signal inside of steel, requiring the use of wave propagation theory to properly analyze the system. A characterization and optimization methodology is presented which measures the linear two-port electrical scattering parameters of the transducersteel- transducer channel. Using these measurements, the simultaneous conjugate impedance-matching conditions at both transducers are calculated, and electrical matching-networks are designed to optimize the power transfer from a 50Ω power amplifier on one side of the steel block to a 50Ω load on the opposite side. In addition, the impacts of, and interactions between, transducer and steel geometries are discussed, and some general guidelines for selecting their relationships are presented. Measurements of optimized systems using transducers designed to resonate at 1 MHz with diameters from 12.7 mm to 66.7 mm, and steel block thicknesses from 9.5 mm to 63.5 mm, reveal power transfer efficiencies as high as 55%, and linear delivery of 81 watts through an optimized channel.

Ultrasonic waves at 1 MHz are used to send information across solid walls without the needs for through wall penetrations. A communication channel is established by attaching a set of three ultrasonic transducers to the wall. The first transducer transmits a continuous ultrasonic wave into the wall. The second transducer is mounted on the opposite side of the wall (inside) and operates as a receiver and signal modulator. The third transducer, the outside receiving transducer, is installed on the same side as the first transducer where it is exposed to the signal reflected from the blended interface of the inside wall and inside transducer. Inside sensor data is digitized and the bit state is used to vary in time the electrical load connected to the inside transducer, changing its acoustic impedance in accordance with each data bit. These impedance changes modulate the amplitude of the reflected ultrasonic signal. The modulated signal is detected at the outside receiving transducer, where it is then demodulated to recover the data. Additionally, some of the ultrasonic power received at the inside transducer is harvested to provide energy for the communication and sensor system on the inside. The entire system (ultrasonic, solid wall, and electronic) is modeled in the electrical domain by means of electro-mechanical analogies. This approach enables the concurrent simulation of the ultrasonic and electronic components. A model of the communication system is implemented in an electronic circuit simulation package, which assisted in the analysis and optimization of the communication channel. Good agreement was found between the modeled and experimental results.

Sustainable development throughout the world depends on several factors such as the economy, quality education, agriculture, industry, among others, but the environment is one of the most important. Industrialization and new land use plans have caused the proliferation of pollutants in water resources, which poses a serious public challenge. As outlined in the sustainable development goals (SDGs), innovative water quality monitoring methods are needed to ensure access to water, sustainable management and sanitation. In this sense, technologies are sought that contribute to the development and implementation of groundwater and surface water quality monitoring systems in real time, so that their parameters can be evaluated through descriptive analysis, in rural populations and areas of difficult access. Nowadays, the internet of things (IoT) and the development of modern sensors are more used, so this research reviews the latest technologies to monitor and evaluate water quality using the potential and possibilities of the IoT. The main contribution of this article is to present an overview of the state of the art of IoT applications and instrumentation for water quality monitoring, focusing on the latest innovations, in order to identify interesting and challenging areas that can be explored in future research.