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ABSTRAKLampu sinyal memiliki peranan yang penting dalam persinyalan kereta api. Pemeliharaan lampu sinyal perlu diperhatikan agar kondisi lampu sinyal tetap sesuai standar. Penelitian ini merancang Wireless Sensor Network (WSN) untuk mengakuisisi parameter lampu sinyal agar dapat dipantau, dianalisis, dan disimpan. Parameter yang diakuisisi berdasarkan dari standar peraturan Menteri Perhubungan Indonesia mengenai lampu sinyal kereta api antara lain intensitas cahaya, tegangan, suhu, dan kelembapan lingkungan lampu sinyal. Sistem tersusun dari tiga subsistem, yaitu sensor node, gateway, dan server. Sistem dapat melakukan pemantauan intensitas lampu sinyal, suhu dan kelembapan lingkungan lampu sinyal, serta tegangan lampu sinyal yang dikirim secara nirkabel yang dapat mencapai jarak hingga 200 m memanfaatkan spektrum radio frekuensi 433 Mhz. Pada saat ada gangguan terhadap lampu sinyal, sistem telah mampu melakukan predictive maintenance berdasarkan standarisasi lampu sinyal.Kata kunci: lampu sinyal, sensor node, gateway, server, wireless sensor network ABSTRACTSignal lights has an important role in railway signaling. Proper maintenance must be taken to maintain signal lights so that signal lights condition remain in accordance with the standard. This study designed the Wireless Sensor Network (WSN) to acquire signal lights parameter information so that it can be monitored, analyzed and stored. The parameters acquired are based on the Indonesian Minister of Transportation's regulatory standards regarding railway signal lights such as light intensity, voltage, temperature, and humidity of signal lights. System consists of three subsystems, namely sensor node, gateway, and server. System can monitor signal lights intensity, ambient temperature, ambient humidity, and voltage of signal lights then send those parameters which can reach distances of up to 200 m utilizing the radio frequency spectrum 433 Mhz. When there are interferences with signal lights, system has been able to perform predictive maintenance based on the signal lights standardization.Keywords: signal lights, sensor node, gateway, server, wireless sensor network

This work reports the acoustic evaluation of a tungsten-epoxy composite which is functioned as a backing material of an ultrasonic transducer. The composite is prepared by mixing tungsten powder in epoxy at a weight ratio of 4:1 using a shaker milling and curing the mixture under a vacuum condition. The sound velocity and acoustic attenuation in the prepared composite is measured by propagating a 200-kHz ultrasonic wave with a through transmission mode. The prepared composite is subsequently assembled with a 1-MHz piezoelectric disk (PZT-8) and an epoxy layer as the active element and the matching layer, respectively, into a fabricated ultrasonic transducer. A square-wave burst pulse is used as an excitation signal for the evaluation of the fabricated transducer. The generated ultrasonic wave shows a higher damping in the presence the backing layer. In addition, the measured sound velocity and acoustic attenuation of prepared composite showed that the ratio of 4:1 is sufficient composition in order to apply as a backing material. In conclusion, control the transducer characteristics is determined by the acoustic properties of tungsten-epoxy composite.